Sustainable Irrigated Agriculture Through Command Area Development
Sustainable Irrigated Agriculture Through Command Area Development
Editors
S. K. Ambast S. K. Gupta Gurbachan Singh
Sponsored by:
Organised by:
Command Area Development & Water Management Ministry of Water Resources, New Delhi (India)
Central Soil Salinity Research Institute Karnal (India)
Contents Preface Water Management - Vision for Sustainable Agriculture
1
Gurbachan Singh
Indian Perspective of Water Resources Development and Issues Relating to Water Management
7
S. K. Gupta
Concept of Efficiencies in Irrigation System Management and Options for System Improvement
16
S. K. Ambast
Analysis of Soil and Water for Diagnosing Salinity/Sodicity Problems
26
Khajanchi Lal
Reclamation and Management of Alkali Soils
35
R. Chhabra
On- Farm Water Management
50
M. J. Kaledhonkar
Land Levelling, Shaping, Planning and Design in Irrigation Command Areas
60
S. K. Ambast
Design of Surface Drainage Systems
71
S. K. Gupta
Subsurface Drainage for Reclamation of Waterlogged Saline Soils
82
S.K. Kamra
Control of Canal Seepage through Conventional and Bio-Interceptor Drains
93
Chhedi Lal
Crop Tolerance to Waterlogging and Salinity Stress and Strategies for Conjunctive Water Use
106
D. P. Sharma
Drip Irrigation with Marginal Quality Land and Waters R. S. Pandey and C. K. Saxena
118
An Overview of Ground Water Recharge Studies by CGWB in India
133
S. Marwaha
Concept of Virtual Water and Its Relation with Agricultural Trade
145
Ashok K. Keshari
Resource Conservation Technologies in Rice-Wheat System and Need for Conservation Agriculture
153
R. K. Sharma
Application of SURFER in Command Area Development Activities
168
C. K. Saxena
Participatory Watershed Management Programme in Sirsa Nadi Micro-Watershed (Panchkula - Haryana)
183
T. S. Puri
Cost-Benefit Analysis of Command Area Development Projects
190
R.S. Tripathi
Subsurface Drainage Project in Kalayat (Haryana) P. S. Kumbhare
200
Sustainable Irrigated Agriculture Through Command Area Development
National Level Training Course Command Area Development with Emphasis on Land Levelling, Shaping, Planning and Design
6-12 February, 2006
Editors
S. K. Ambast S. K. Gupta Gurbachan Singh
Central Soil Salinity Research Institute Karnal 132001 (India)
Ambast, S.K., Gupta, S.K. and Singh, Gurbachan (2006). Sustainable Irrigated Agriculture Through Command Area Development, Central Soil Salinity Research Institute, Karnal, India, p 202
Sponsored by:
Command Area Development & Water Management, Ministry of Water Resources, New Delhi (India)
Organised & Published by:
Central Soil Salinity Research Institute, Karnal-132001 (India) Telephone: 0184-2290501 Fax : 0184-2290480 E-mail:
[email protected] website: http://www.cssri.org
The views expressed in this book are authors view. CSSRI, Karnal and CAD&WM, New Delhi assume no liability for any losses resulting from the use of this book.
Printed by:
Intech Graphics, #5, Ankush Chambers, Opp. Dyal Singh College, Karnal-132001 Ph. : 0184-2271451, 3092951
PREFACE India has to support 16% of world's population with 2.4% of world's land and roughly 4% of world's fresh water resources. The burgeoning population, urbanization, industrialization and improved living standards together is exerting tremendous pressure on India's land and water resources and has given rise to competing demands for water. The water resource that once appeared to be inexhaustible has now become a scarce commodity. Thus, the most pliable sector to face the crunch would be the agriculture sector, as it has the least capacity to pay. Lest the scarcity of water hampers the economic growth of the country, it is essential to conserve the limited available water resource through scientific management strategies. Against this background, water resource development and management in agriculture have assumed greater importance. During the post Independence period, high priority was given to the development of irrigation for increasing the agricultural production. The irrigation potential, which stood at 22.6 M ha in 1950-51, increased to 33.6 M ha by mid sixties and stands at 94 M ha in 2002. On realization that potential utilized is not keeping pace with the created irrigation potential, Irrigation Commission in 1972 recommended systematic development of canal command areas. The centrally sponsored Command Area Development (CAD) programme was launched in 1974-75 with the objective of bridging the gap between the irrigation potential created and utilized for ensuring efficient utilization of created irrigation potential and to increase the agricultural productivity from irrigated lands on a sustainable basis. The programme envisaged interdisciplinary approach to integrate various activities relating to irrigated agriculture. As on March 2001, there were 233 projects covered under the programme with a culturable command area of 22.72 M ha spread over 28 States and 2 Union Territories. In 2004 the programme has been restructured to focus on water management and has been renamed as Command Area Development and Water Management (CAD & WM). Central Soil Salinity Research Institute, Karnal is conducting research and development work relating to reclamation of salt affected lands, irrigation system management, command area development, prevention and management of waterlogging and salinity in irrigated commands, use of advanced techniques i.e. remote sensing and geographical information system for dealing with these problems in a systematic manner. The capacity building is another dimension of CSSRI activities. The current programme supported and funded by CAD&WM, Division of the Ministry of Water Resources strengthens our efforts and helps to upgrade the interaction between the two organizations in tackling the problems of irrigated agriculture. Publication of this book on sustainable irrigated agriculture has become possible through the joint efforts of Indian Council of Agricultural Research (ICAR) and Command Area
Development and Water Management (CADW&M, MoWR). The editors gratefully acknowledge the support and encouragement received from Dr. J. S. Samra, DDG (NRM), ICAR, New Delhi and Er. A. S. Dhingra, Commissioner, CADW&M, MoWR, New Delhi. The editors place on record their special thanks to all the contributors for providing manuscripts well in time and their eagerness for knowledge sharing with the participants of the training programme. Financial support extended by the CADW&M, MoWR that made the publication of this document is thankfully acknowledged. The overwhelming support extended by the staff of the CSSRI, Karnal, particularly the Division of Irrigation and Drainage Engineering, has been our strength during the publication of this document. We believe that this publication would serve as a useful document to all the participants in their day-to-day official activities related to land and water management in irrigation commands. We hope that this publication will be extensively used at CSSRI in their future training programmes and would pave the way for other extended publications on this subject. S. K. Ambast S. K. Gupta Gurbachan Singh
Water Management - Vision for Sustainable Agriculture Gurbachan Singh Central Soil Salinity Research Institute, Karnal-132001 Climate, soil and availability of water mainly determine the distribution of plants in a given geographical area. The Planning Commission has divided India into 15 agro-climate zones for sustainable agriculture planning. More recently, National Bureau of Soil Survey and Land Use Planning has divided the country into 20 agroecological zones depending upon rainfall, soil and length of growing period etc. Promising and eco-friendly crops and cropping systems, which can yield optimum sustainable production, have been identified for each agro-eco-region. However, the new science based knowledge developed in last about three decades has made it possible to grow crops even in areas which are agro-ecologically unsuitable for such crops. The notable example is that of rice. Rice was generally considered a plant of marshy areas about 30 years back. The crop was almost unknown in Punjab and parts of Haryana. At present, these are one of the dominating states as far as rice production in the country is concerned. The rice cultivation in these states has been extended to even areas used to support sand dunes. This kind of new innovations no doubt increased food production significantly but at the same time threatened the natural resource base particularly soil, water and bio-diversity. Inefficient and indiscriminate uses of fertilizers, irrigation water, pesticides and energy have deteriorated soil physico-chemical properties and ground water resources. Other negative environmental impacts of green house gases (GHG) due to large scale burning of rice and wheat residues are creating alarming condition. The concentration of CO2 in the atmosphere during last 100 years has exceeded the record of increase even during last 1000 years. Further, the indiscriminate and over use of inputs has increased cost of production over the years and deteriorated economic conditions of the farmers. This calls for some paradigm shift from the less efficient and environmental degrading farming practices towards the efficient and environment conserving precision farming system targeted at optimizing productivity and profitability. Concerted efforts are required to increase input use efficiency of water, soil and energy. Appraisal of Natural Resource Base-Total Factor Productivity Analysis The modeling experiments have predicted a climatic potential of 15-20 t/ha/annum for the Indo-Gangetic alluvial plains. This potential has to be realized by judicious deployment of natural resources. The potential achieved so far is nearly 10/t/ha/annum. As far as climatic potential is concerned there is gap of 5 to 10 t/ha/annum and there is a long way to go. However, even at 10 t/ha/annum production level, growth rate of factor productivity worked out by National Centre for Agriculture Economics and Policy Research, New Delhi is quite alarming. The growth rates in total factor productivity of wheat in different agro-eco-regions of Indo-
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Gangetic plains were positive for the period during 1966 to 1976 (Table 1). For example total factor productivity of wheat in northwestern plain was 1.43% per annum during 1966-76 which declined to –8.26% per annum between 1987-1996. This calls for self-introspection and development of cost effective technologies and proper management of resource base and inputs in particular the scarce and dwindling resource of water. The data in Table 1 clearly indicated that marked jump in food production in last three decades has been at the cost of over exploitation and wrong use of natural resources particularly the soil and water and high use of chemical based inputs. Table 1.Growth rate in total factor productivity of wheat in different Agro-Eco-regions (percent/annum) Wheat Agro-eco-region 1966-76 1977-86 1987-96 Trans-Gangetic Plains Foothills of Shivalik 5.12 0.30 0.28 Plains 2.41 -3.23 -3.77 Arid 3.52 0.29 -0.57 Upper-Gangetic Plains North-western plain 1.43 -0.51 -8.26 South western plain 1.59 -1.03 -8.72 Central plain 3.23 -0.63 -8.90 Lower-Gangetic Plain Central alluvial plain 19.87 -2.26 -10.46 Rorh plain 15.32 -0.26 -9.16 Alluvial coastal saline plain 26.25 -1.99 -12.93 (Source: Nation Centre for Agricultural Economics and Policy Research)
Target Ahead-Projections of Demand and Supply The human population is predicted to be increased from present about 1047 million to 1310 million by 2025 and 1460 million by 2050. Accordingly, the corresponding food requirement would be 315 and 464 M tones during 2025 and 2050 respectively. The scope for increase in gross irrigated area and gross cropped area as per projections are from 71 and 178 M ha at present to 95 and 204 M ha by 2025 and 130 and 226 M ha by 2050, respectively. However, major share of future requirements is expected to be met by reclamation or improvement of degraded resources and increase in productivity per unit area. Increase in future productivity will largely depend upon how best our natural resources particularly water and soil are managed. Water Related Issued and Strategies Water will be a major constraint in food production-both in quantity and quality. The total dynamic water available through rainfall plus upcountry flows will remain constant i.e. 4400 km3/year. As per observations of Randhawa and Sarma
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(1997), the total utilizable natural water will also remain constant at 1086 km3/year till 2050. However, utilizable return flow to ground water is expected to increase marginally by 2025 and 2050. The per capita availability of water is predicted to decrease from present level of 2100 m3 to about 1700 m3 in the next 2-3 decades. At present only about 29% of the total water available through rainfall is effectively utilized. In-situ and ex-situ conservation of rainwater and recycling to provide supplementary irrigation in rainfall areas should get high priority is the near future. Large scale pumping of ground water to meet irrigation requirement of predominant rice-whet system in the Indo-Gangetic plain has resulted in depletion of ground water. The problem of ground water depletion is serious in the states of Punjab, Haryana, Gujarat, Rajasthan and Tamil Nadu. For example between the period from 1989 to 1995, the number of blocks having dark and over-exploited ground water increased from 3% to 14% in case of Gujarat, from 33 to 47% in Haryana (Table 2). The present scenario is much worse. Table 2. Status of groundwater exploitation Status Blocks, 1989 Dark (%) Gujarat 3 Haryana 33 Punjab 54 Rajasthan 9 Tamil Nadu 16
Blocks, 1995 Dark & over exploited (%) 14 47 59 24 25
In states, like Punjab the ground water level is decreasing @ 30 to 50 cm/year in about 70% of the area. This increases pumping cost as in many situations the farmers are compelled to replace their centrifugal pumps with submersible pumps. Replacement cost varies from Rs. 0.6 to 1.2 lac. Substitution of centrifugal tube well by submersible pumps mainly by progressive and economically sound farmers is affecting adversely the efficiency of centrifugal pumps in the vicinity of these deep tube wells and in many cases such bores have become non-functional. This is bound to result in social conflicts in the society. The options available to balance falling ground water level include: recharging of the ground water through conservation of precious rainwater during monsoon season; diversification from high water demanding crops like rice with crops which consume less water per unit dry matter production; increasing efficiency of water use following precision irrigation schedules; matching the critical growth stage concept and agronomic manipulations such as adopting zero tillage, bed-furrow and micro-irrigation practices and direct seeding of rice. Some kind of policy decision is also required to stop paddy transplanting before June 10. Experiments conducted on ground water recharge in Kandi area of Punjab and Madhya Ganga Canal area in UP clearly indicate that ground water recharge is possible provided proper soil and water conversation measures are adopted. In
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Kandi area it has been achieved through (i) forest rehabilitation in 45,000 ha in upper catchments (ii) construction of 19 water harvesting dams and 7 medium capacity irrigation dams and (iii) on-farm development. The results obtained by Khepar and his team showed that all these practices resulted in revising the water balance from (-) 97, 867 ha-m to (+) 52,075 ha-m during 1979-98. Thus reversing the falling trend with the rising trend of the water table. Similarly, in UP Madhya Ganga Canal ((234 m3/sec) was constructed to divert surplus monsoon flow for development of irrigation in dry pockets. Seepage losses from 115 km long unlined canal (Lakhooti Branch System, 193000 ha) and from paddy fields (49,500 ha) recharged the rapidly declining aquifers from 11 m bgl (meter below ground level) to 6-5 m bgl. This stored water could then be used to irrigate a rabi crop. Without this canal water input, the water table would have dropped to an average depth of 18.4 m by 1999 from 11 m with very high cost of pumping. Adoption of micro-irrigation practices such as drip and sprinkler as replacement for traditional flooding and furrow irrigation methods have the potential to yield higher with almost less than half the water used. The comparison of different methods of irrigation to cotton is given in Table 3. It clearly indicates that cotton yield of 1890 kg/ha can be obtained with 81 cm of water in drip system compared to 1257 kg/ha with 203 cm of water in flood method of irrigation. Similarly, the yield per unit water applied was almost double in sprinkler and four times in drip irrigation compared to flooding method of irrigation. There is an urgent need to promote the use of micro-irrigation practices in declining ground water areas. Table 3. Average cotton yield under different methods of irrigation Irrigation methods Particulars Flooding Furrow Sprinkler Lint yield (Kg/ha) 1257 1350 1300 Water applied (cm) 203 165 106 Yield to water use 6.19 8.18 11.3 ratio (Kg/cm)
Drip 1890 81 23.3
The rising trend of water table in irrigation commands is another serious concern. Depending upon situations, the water table is rising @ 0.29 m to 1.20 m/annum (Table 4) in major canal commands due to inefficient water conveyance system. Table 4. Rate of rise in water table for some irrigation commands Irrigation command Rise of water table (m/annum) IGNP, Rajasthan Western Yamuna & Bhakra Canal Sharda Sahayak, U.P. Nagarjuna Sagar, A.P. Malprabha canal command, Karnataka
0.29 – 0.88 0.30 – 1.00 0.68 0.32 0.60 – 1.20
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In many situations, rising water table is also associated with development of salinity and thus making otherwise productive lands unsuitable for crop production. The strategies for balancing this hydrological imbalance should involve: (i) lining of the water conveyance system, (ii) planting of trees like Eucalyptus and Populus which act as bio-pumps to consume seepage flow, (iii) inclusion of trees such as Eucalyptus and Populus as a component of cropping in all areas having rising water table trends and (iv) installation of effective drainage system for release of excess water. It has been proved that by lining of all the components of canals irrigation system, canal water supply could increase by 66%. The contribution of lining canal system components is: main canal 15%, distributaries 8%, channels 28% and field channels 15%. Issues of Poor Quality Waters and their use Strategy Studies on groundwater resources indicate that 25 to 84% of the poor quality waters are used for irrigation particularly in arid and semi-arid regions (Table 5). Table 5. Percentage use of poor quality water in different states State Estimated values (%) Andhra Pradesh 32 Gujarat 30 Haryana 62 Karnataka 38 Madhya Pradesh 25 Rajasthan 84 Uttar Pradesh 47 (Source: CSSRI, Karnal)
Based upon climate, soil, water and crop factors the Central Soil Salinity Research Institute, Karnal has standardized water quality guidelines for successful use of poor quality waters for agricultural production. These guidelines may be kept in mind while irrigating the crops using poor quality waters. It has also been proved that detrimental effect of such waters can be moderated through mixing or alternate use of limited good quality water. Data in Table 6 on 6 years average yield of rice and wheat showed that almost similar yields of these crops could be obtained with alternate use of sodic and canal water as with canal water. Table 6. Management of sodic waters for irrigation of rice and wheat Average yield of 6 years (t/ha) Water quality Rice Wheat Canal water (CW) 6.8 5.4 Sodic water (SW) 4.2 3.1 2 CW-SW 6.7 5.2 CW-SW 6.3 5.1 CW-2SW 5.7 4.8 (Source: CSSRI, Karnal)
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As stated above, currently only 29% of the total precipitation is conserved, that too not optimally utilized. With the existing practices, water use efficiency seldom exceeds 40%. Further, inefficient use of water also leads to inefficiency of all other resources/inputs. Thus, the strategy would be to follow an integrated approach emphasizing greater conservation and enhanced efficiency through following approaches: • • • • • • • • •
System approach on multiple water uses in crop, livestock, fish and horticulture production Simultaneous and multiple uses of water for integrated farming and wetland systems Conservation of rainwater Recycling of wastewater Efficiency improvement through modern methods of irrigation (drips, sprinklers, etc.) Evolving innovative methods for efficient crops/varieties Water use efficiency in conjunction with other inputs (energy, nutrients, etc.) Reviving degraded lands and polluted environment Extending watershed based planning in rainfed areas of the country
Bibliography Randhawa, N.S. and Sarma, P.B.S. (1997). National Water Policy - Agricultural Scientists’ Perceptions, National Academy of Agricultural Sciences, New Delhi.
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Indian Perspective of Water Resources Development and Issues Relating to Water Management S. K. Gupta Central Soil Salinity Research Institute, Karnal - 132 001 Water is essential to all the living matter on the earth, be it humans, animals or plants. The importance of water could be gauged from the fact that while looking for life on other planets, presence of water on the planet is first examined as an indicator of presence of life on the planet. Civilizations have developed along the rivers. Yet, it would not be the exaggeration of facts that civilizations doomed not because the water was not available but because of its improper applications resulting in unsustainable use of the resources impacting adversely the quality of other resources as well as the life. Current example is the Aral Sea Basin where large-scale mismanagement of water has played havoc on agriculture, environment and the life. Historical Water has always been scarce and people by habit have been mismanaging the resource resulting in wastage and severe pollution of the water bodies. If it had not been so then - Rahim ji would not have said "Rahiman pani rakhiye, bin pani sab soon, Pani gaye na ubre, moti, manush chun". Lord Krishna as revealed through the Episode on 'Kaliya Mardan' tried to sensitize the people on pollution of surface water bodies. Our elders, even today, ask their children to throw some coins in the river. Although, this practice has become a ritual today since people throw any coin that is available in their pockets. Earlier, invariably a copper coin was thrown, which is considered to be the water purifying metal. Surface Water Resources of India From the point of view of surface water resources, India has been divided into 20 river basins. These comprise of 12 major basins each having a catchment area exceeding 20,000 sq km and 8 composite river basins combining suitably together all the other remaining medium and small river systems. The total water potential of these basins is estimated at 187.9 M ha m. A break up of this resource reveals that 105 M ha m is the runoff from rainfall that flows into rivers and streams including reservoir and tanks. Additional water is received from snow melt (10 M ha m), flow from outside India (20 M ha m), from groundwater (37 M ha m) and from irrigated areas (11 M ha m) making a total of about 183 M ha m. The largest potential of water is available in Ganga/ Brahmaputra/Barak and others making a total of 117 M ha m followed by Godavari and by west flowing rivers from Tapi to Tadri each having an average annual potential of more than 10 M ha m.
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Due to extreme variability in precipitation, which disallows assured storage of all the water, due to non-availability of storage space in hills and plains, evaporation losses and water going to the sea and outside India, it is anticipated that utilizable surface water resources would be 69 M ha m which will be utilized by the year 2025. It is assessed that on full development 76 M ha area would be irrigated through surface water resources. Groundwater Resources of India Replenishable groundwater resource is mostly derived from the precipitation. Out of 400 M ha m, 215 M ha m of rain water percolates into the ground out of which only 50 M ha m joins the groundwater or is available for exploitation. While a part of this water would regenerate into streams, there would be net addition of water through streams and irrigation which is presently estimated at 26 M ha m. Deep percolation adds another 11 M ha m. The state wise groundwater potential as recently estimated by Central Ground Water Board (now Authority) is 43.2 M ha m. Basin wise estimates reveal that Ganga basin has the maximum groundwater potential and account for more than 38% of the total groundwater potential. It is followed by Brahmani and Baitarni at 5.9 M ha m. After deducting the provision for domestic and industrial purposes, the potential available for irrigation is 36.03 M ha m. The utilizable groundwater for irrigation is thus assessed at 32.47 M ha m. It is likely to increase to 35 M ha m in 2025. About 5-6 M ha m of water goes into storage, which results in rising water table and is lost through evaporation. Amongst the states, Uttar Pradesh, which mostly lies in the Ganga basin, has the highest potential. Himachal Pradesh on the other hand has the least potential amongst the states. In terms of area, the irrigation potential of the groundwater has been revised and placed at 64.05 M ha. Problems of Water Resources in India Spatial and temporal distribution: On an average over space and time, average annual rainfall over the Indian sub-continent has been estimated at 1200 mm. On this basis, the annual precipitation including snowfall is estimated at 400 M ha m (4000 km3). Distribution of this resource with respect to different rainfall zones reveal that more than 50 % of the resource is generated in the zone with rainfall ranging from 1000-2500 mm (Table 1). The area receiving less than 1000 mm of rainfall constituting about 48 % of the geographical area contributes only 24.6 of the water resource. About 300 M ha m of this resource is generated during June to September while another 100 M ha m is during the rest of the year. Another characteristic of the rainfall is that in many areas of the country, it is only a few heavy storms, which account for most of the annual rainfall. Absence of heavy storms would generally mean reduced rainfall. The consequence of the spatial and temporal distribution is reflected in the per capita availability of water in different basins. For example, per capita availability of water is 13636 cubic m in Brahmaputra-Barak basin while it is only 298 cubic m in Sabarmati basin.
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Table 1. Distribution of geographical area in different rainfall zones in India Rainfall zone (mm) Geographical area (M ha) Rainwater availability (M ha m) 100-500 500-750 750-1000 1000-2500 > 2500 Total
52.07 40.26 65.86 137.24 32.57 328.00
15.62 25.16 57.63 205.86 95.73 400.00
Conflicting objectives of water resources development: Major and medium projects are multipurpose projects with hydropower generation, flood control and irrigation. For example, irrigation requirement could be quite different over the seasons/years while hydropower generation may require steady release of water to meet any eventuality. Similarly storage for irrigation and hydropower may overweigh concerns for the flood control. Therefore, operational aspects of multi-purpose projects need to be optimized to meet most objectives. Concern to maintain water quality, river regime, maintenance of river ecosystem or other public necessities is given the least importance. Increasing sectoral competition between for water: Increasing population, change in eating habits, life style changes and increasing emphasis on travel/tourism and environment, the demand scenario of water is for a big change. Agriculture, which is currently consuming 83% of the developed water resource, would be the looser and would require to release fresh water for other sectors of economy. Although, overall quantity of water allocated to agriculture would increase yet it would be less than the demand. Therefore, agriculture needs to look at other sources particularly the socalled wastewaters released after first use by other sectors. Researches on the use of such water have already begun with right earnest. Pollution of surface and groundwater resources: We are all witness to extreme pollution of surface water bodies and more so of the rivers that turn into drains during non-monsoon season since effluents from large number of municipal and industrial establishments is being discharged untreated into the rivers. The groundwater pollution is even more serious which goes unnoticed and remains hidden from the public view. Non-point source (agriculture use of excessive fertilizers, insecticides and pesticides) and land disposal of industrial and domestic sewage (point sources) have resulted in contaminant concentrations exceeding the limits prescribed by WHO. Direct disposal of effluents in the bore wells in unorganized colonies and industries is even more serious matter. It may be mentioned that it should be possible to take remedial measures to remove pollution of surface water bodies but it would be difficult almost bordering on the impossible to reverse the process once the groundwater aquifers gets contaminated.
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Irrigation and crop productivity: Rainfall is the most significant climate factor that affects the crop growth and production from the rainfed areas in the country. A good example is the annual food grain production in India and the summer monsoon rainfall, which reveals the fall in production during deficit and rise during years of excess rainfall. The difference in total annual food grain production of the country was about 20% between the poor monsoon of 1974 and the succeeding good monsoon of 1975. The annual rainfall in the rain fed region is quite erratic with large spatial and temporal variations. The coefficient of variation increases with decreasing rainfall. While it is about 20% in dry sub-humid region it is as high as 61% in the arid rain fed region. Besides water, other bio-physical and socio-economic constraints limit the productivity of crops and livestock. Progress has been quite slow in rain fed agriculture, which constitutes bulk of our agricultural land. The productivity of rain fed agriculture is less than half of the productivity of irrigated lands (Table 2). It may be seen that irrigation can lead to substantial improvements in the productivity of rain fed crops. A major concern however stems from the fact that even the productivity of irrigated agriculture is not as high as anticipated in the project proposals or as spectacular as in other countries. There is no national level assessment of the overall irrigation efficiencies. The irrigation efficiency in surface irrigation systems might be in the range of 35-40% while it could be 65-70% for groundwater. Overall low productivity of Indian irrigated agriculture could be attributed to system inefficiencies. Lag in utilization of irrigation potential is also a cause of concern. The irrigation potential utilized is around 90% of the developed irrigation potential. It has locked in huge investment made in developing the irrigation potential. A modest estimate revealed locking up of Rs. 12500 billion due to non-utilization of the potential alone. Table 2. Yields of principal crops under irrigated and unirrigated conditions Crop Irrigated Unirrigated % increase expected over unirrigated Rice 1880.3 1220.4 54.1 Sorghum 1242.6 606.9 104.7 Pearl millet 1170.2 596.2 96.2 Maize 2040.5 1339.2 52.4 Ragi 1966.8 995.9 97.5 Wheat 2068.1 1100.1 88.0 Barley 1836.6 1127.2 62.9 Gram 830.0 548.5 51.3 Groundnut 1244.2 844.4 47.3 Sugarcane 70687.5 43161.2 63.8 Rapeseed & mustard 893.6 573.2 55.9 Cotton 440.3 195.1 125.7 Jute 1952.6 1502.8 29.9 Average of 1985-86 to 1991-92 over different states; (Source: Central Water Commission, 1995)
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Paradox of rising and falling water table: Most irrigation projects in India are operating at low efficiencies. Clearly, 60-65% of the irrigation water is lost either during conveyance or in the fields. This has led to rising water table in irrigation commands, particularly in areas underlain with poor quality ground waters. This has also given rise to problem of soil salinization since these are considered to be twins. It is estimated that around 8.5 M ha of agriculturally productive lands have turned barren because of the twin problems of waterlogging and soil salinity. Large areas might be producing below the potential productivity. The estimate for such areas has not been made so far. Because of the inadequacy and unreliability of canal waters, farmers have gone for intensive irrigation through the development of groundwater. Overexploitation of groundwater is causing water table to decline by 0.2-1.0 m per annum in Punjab, Haryana and Western Uttar Pradesh. Besides one third of the total geographic area or about 108 m ha area inhabited by 263 million people is drought prone. This 26 % of the population has a marked tendency of intensive exploitation of groundwater particularly during drought years. Some of the coastal areas are now facing the problems of seawater intrusion. Even in the state of Haryana, the reversal of gradient might lead to mixing of poor quality and good quality aquifers, causing a severe set-back to the farming community and the state. Water - the cause of the conflicts: War or no war, yet danger of large conflicts arising over water cannot be ruled out. There are at least 300 conflicts zones where water could be the cause of the conflict. Nile River has catchments spread over 10 countries. Nearer home, India has several such conflict zones with Pakistan, Bangladesh and Nepal. World war over water foreseen by policy planners might or might not occur but fierce fight for water with in states in India has already begun with no end in sight. Conflicts between Tamil Nadu - Karnatka - Andhra Pradesh and Punjab - Haryana - Rajasthan are too well known. Statistics and the water resources: When one looks at the statistics that is being fed through the media one becomes quite skeptical to the future scenario. Doubts have been raised on the socio-economic development, sustainability of irrigated agriculture and environmental quality. But let us face the facts. Water has been as scarce in the past as it was when our population was a fraction of what we are today. Our forefathers were equally worried about the scarcity and pollution of surface water bodies. Yet we could survive so far. There are still many opportunities to tap our water resources. Let us look at some of these opportunities so that we can make a better choice in exploiting these resources. It is estimated that a 10% improvement in agriculture sector could compensate the 40% increased demand of domestic and industrial sectors. Irrigation Improvement: Suggestion on modernization of existing Irrigation systems with better operation and maintenance, rationalization of water rates, techniques for equitable water distribution, night irrigation, dynamic regulation through decision support system, computer use, information technology and advanced methods of
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communication have been emerging at various forums. Inadequacy and uncertainty is being tackled through inter-basin transfer of water. It is slowly becoming a reality. It has been estimated that in due course of time inter-basin transfer of water would add to 35 M ha of irrigated lands. Participatory Irrigation Management (PIM) could play a very effective role in irrigation management. Many people think it to be the panacea for all the ills that plague the irrigation system. Such a overemphasis on this issue has already burdened the concept of PIM and voices are now heard to go for privatization of the irrigation system in participatory mode. What it really means is yet to emerge? Dew: Dew is the water vapour in the atmosphere, condensed on surface of objects exposed to nocturnal radiation. Observations of dew in India were started on a regular basis from 1968 and have since then expanded greatly. Although, dew may not add much to our water resource compared to the magnitude of other sources, yet dew accumulation is 15-30 mm in north and north east India during a period of 6 months i.e. October-March. The largest value is over Assam. About 25 to 50% of water deficiency in the month of January in South Punjab to Assam could be met with dew. The total water stress in this month is assessed at about 40 mm. The importance of dew in relatively drier areas is not much promising. Green-Blue water integration: Green water constitutes about 50 % of the total water resource. While too much emphasis is placed on the development and use of blue water, not much attention has been paid to green water. If efficiency of green water is increased, it alone would be able to generate about 230 M ha m water at the global scale. The syndrome of green and blue water could be broken. The increased efficiency of green water in itself can raise the productivity of irrigated lands. Reuse of drainage water: Not long back drainage waters were treated as wastewaters. Analysis of water Samples from surface drains showed that water in these drains during monsoon season is of good quality and it can be used in agriculture without affecting the land resource or the crop yields. Fortunately for the nation, farmers are quite conscious of this fact and this source is being exploited to the hilt. It is very encouraging scene to see the farmers pumping water from the drains, borrow pits and depressions to irrigate their fields. Water so pumped is being transported for more than a kilometer. If low weight Chinese kind of pump is made available, there would be a spurt in the reuse of drainage water. Exploitation of saline/sodic waters: This issue would be discussed in a number of lectures. Therefore, discussion on this issue is not being included in this lecture. However, it may be appropriate to add that head-end to tail-end transport of water and skimming of fresh water floating on the poor quality groundwater is catching up fast in western Haryana and southwest Punjab. Multiple use of water: We have discussed the issue where water released from one sector after first use would be used in agriculture. However, multiple use of water within agriculture sector should also be implemented to enhance water productivity.
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For this purpose non-consumptive and consumption activities needs to be identified. Aquaculture with agriculture could be one major activity where value added water from aquaculture would be used to irrigate crops. Reuse of drainage water discussed before in this lecture could also be cited as an example of multiple use. Separation of Grey/Black Waters: Freshwater withdrawals by urban areas will rise from an estimated minimum of about 15 BCM to a projected maximum of 60 BCM. More than 80 % of this water would be released back. It would be released in the form of grey and black water (Table 3). Grey water in the water released from washbasins, kitchens and bathrooms etc. This water is relatively of good quality and could be used to irrigate lawns and to irrigate and kitchen gardens. On the other hand sewage water is black water. The quantity of black water is more because currently gray and dark waters are being mixed up creating problems of disposal. In many countries it is now mandatory to separate grey and black waters. The day is not far off when we would need to adopt this kind of regulations to reutilize grey waters as well as to minimize the disposal related problems. Table 3. Categorization of waters and their role in agriculture Type of Source Potential for use in agricultural or remarks water Blue Sea, lakes, rivers, Extensively used for irrigation. Its availability is likely water canals to decrease with increasing competition from other sectors. Green Soil moisture & Mostly used by plants and agricultural crops water water in plants particularly forest, grass lands and rain fed agriculture. Fossil Groundwater Use for domestic and agricultural uses. Its water availability to agriculture would decrease with time as a result of competitive demand from other sectors. Grey Domestic Potential for use in crop production. Suitable for water wastewater kitchen gardening and irrigating lawns. Black Domestic Potential for use in crop production. 21st century water sewage and water resource for agriculture. Cleaner technologies Industrial waste required to avoid heavy metals/pathogens entering human chain. Virtual Water used in Export-import of food grains/animal product indirectly water producing results in export-import of water. A kg of rice or grains/animal wheat export means export of at least 2000 liters of product water for rice and 800 liters of water for wheat. For 1 liter of milk it could be 2500-3000 liters of water. It is estimated that Mehsana and Banaskantha export 1.8 billion cubic meters of water annually due to milk export. It is going to assume importance in exportimport during next few decades.
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Technology upgradation in agriculture: Researches in water management have shown many areas where water could be saved without detrimental effect on crop yields. It could be achieved through deficit irrigation as well as by crop diversification. Switchover from high water requiring crops to low water requiring crop could save a major fraction of water in agriculture. Application of resource conservation technologies such as land leveling, zero tillage, bed and furrow planting of wheat, dry or semi-dry seeding of rice could save water. Improved irrigation techniques such as drip and sprinkler can save water as well as result in higher productivity. As such there would be a sharp increase in water productivity. Controversy of big and small: In the Indian context, sustainable management of water resources with due respect to ecological, economic and ethical blended with technical feasibility requires a holistic and integrated approach involving engineering, socio-economic and environmental aspects. Water resources development requires a judicious mix of large, medium and small reservoirs based on the integration of techno-economic feasibility and environmental capability along with regional demand. There seems to be no scope of any controversy in this respect since India lags far behind in meeting its demand for water. Therefore, any addition to its resource through any means big or small would contribute to the socio-economic uplift of the people of India. It also seems that no single strategy such as reduction of losses and water saving alone (Table 4) would work unless it is fully supported by development of additional sources of water (including additional run-off capture) for its multiple use. Therefore, the focus must lie both on development and management (Table 5). Table 4. Water saving strategies in agriculture Sr. No. Items 1
2 3 4 5 6
7
On farm land and water management that would include, land leveling, zero tillage, bed and furrow farming, precision farming, improved surface irrigation techniques and land drainage Improved pressurized irrigation techniques Improved agronomic practices that would include time of sowing, crop varieties, cropping systems and mulching Crop diversification Rainwater management in agriculture including three tier system developed at CSSRI, Karnal Irrigation regime in rice crop including shallow submergence, irrigation scheduling at hair cracking and dry seeding or irrigations at critical stages in other crops Deficit irrigation particularly under high water table conditions
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Table 5. Strategies to increase the water resource Sr. No. Items 1 2 3 4 5 6 7
Use of Fog and dew Green and Blue water Syndrome Increase in storage capacity Interlinking of rivers Minimization of waste Reuse or use of non-conventional naturally occurring saline or domestic and industrial waste water Desalination of sea water
Bibliography Anonymous (1993). Proposal for Technology Research in Irrigation and Drainage. International Program for Technology Research in Irrigation and Drainage. IPTRID. World Bank. Anonymous (1990). Rainwater harvesting. Govt. of India, Deptt. Rural Devp., Ministry of Agril., New Delhi. Bhatia, P.C. (1998). Crops and Weather Resources. In :50 years of natural resource management research, (Singh, G.B, and Sharma, B.R.,eds.). ICAR, New Delhi: 49-62. Central Ground Water Board (1995). Ministry of Water Resources, GOI, Ground Water Resources of India, CGWB, Faridabad. Central Water Commission (1995). Water Statistics. Central Water Commission, Ministry of Water Resources, GoI, New Delhi. Prihar, S.S., and Sandhu, B.S. (1997). Irrigation of field crops: principles and practices. ICAR.,New Delhi: 142 pp Rao, N.H. (1991). Irrigation scheduling with limited water supplies. Pub. No.218. C.B.I.P., New Delhi: 108 pp Report of the Working Group on Problem Identification in Irrigated Areas with Suggested Remedial Measures, 1991. Ministry of Water Resources, Government of India, New Delhi.
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Concept of Efficiencies in Irrigation System Management and Options for System Improvement S. K. Ambast Central Soil Salinity Research Institute, Karnal - 132 001 Water is a limited and crucial resource for agricultural crop production. However, water demand is globally increasing while the availability and quality of water resources are decreasing, mainly because of population growth, wider ownership of domestic water-using goods, ongoing urbanization, industrialization and the intensification of agriculture. Recognising the fact that water is an increasingly scarce resource in future, substantial increase in output of water used particularly in agriculture, which is the largest freshwater consuming sector, is essential to meet the goals of food and environmental security. India is diverse in nature both climatically as well as geo-morphologically. It has highly productive part of Indo-Gangetic plain as well as very low productive part of the Thar Desert. Although, there is no specific and systematic information available on water productivity at field or system level in these states, it is generally considered as quite low (varying from 0.25 to 1.5 kg/m3). In such situation, where systematic information on water productivity is lacking, a concerted effort is needed to establish a database to use it as a benchmark. This will help to suggest need, means and ways of improving water productivity apart from generating the current state of water productivity at field, system, basin and possibly at state levels. This necessitates for reviewing the issues relating to agricultural water productivity in India and their analysis at regional, irrigation system and even further down to micro level for developing policy framework for improving water productivity in the region as a whole. Irrigation System Management A system is defined as a set of objects, which act in a regular and interdependent manner. Inputs that may be controllable or uncontrollable, environmental factors and the outputs that may be desirable, undesirable or neutral are the essential components of the system. Irrigation system as such defies a rational description, because it means different things to different people. Early (1983) has described irrigation system as an entire set of physical, biological, geographical, social, political and economic entities and objects, from the source of water through the conveyance to the farm and the land that is irrigated including drainage network. Functionally, delivery, application and disposal are the three components of an irrigation system. As management systems, they transform the general policy goals into specific objectives defined as desired inputs such as reliable and adequate supply of water, priorities and programme schedules to produce output as agricultural production.
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Irrigation system framework: The irrigation sector may be represented as a set of nested systems. Each system in the framework has its own particular set of objectives (Small and Svendsen, 1990). They incorporated five systems into their model: (i) (ii) (iii) (iv) (v)
the irrigation system, which has its function as the conveyance of water from the source to the farmers field. The output from this system, water delivery at the farm gate, then becomes an input to the irrigated agriculture system where farmers use water and other inputs to produce crop; these crops become the inputs to the agricultural economic system that includes rainfed agriculture as well as irrigation; the value of the crops produced then forms part of the rural economic system that deals with the entire set of economic activities in rural areas that in turn form part of the highest level, the national political–economic system.
Performance diagnosis framework: Irrigation management is manipulation and use of water resources, canal system, command areas, plant, soil and knowledge of technical disciplines to provide water to the root zone at proper rate, time and place to produce food and fiber (Clyma et al., 1977). Some of the key elements of irrigation water management are: (i)
(ii) (iii) (iv)
Performance monitoring and evaluation: Monitoring and evaluation are the activities to estimate the performance of the irrigation system. In the present context, monitoring may be defined as continuous or periodical surveillance over the implementation of necessary irrigated agricultural activities, including their various components. Whereas evaluation may be defined as a process that determines systematically and objectively to the extent possible, effectiveness and the impact of project activities in terms of their objectives. Diagnostic appraisal: It includes activities involved in identifying the interventions/ alternatives in the system and the consequences of such interventions in improving irrigation performance. Action research: Action research involves validation of interventions meant for improvement on experimental basis in a project and its monitoring for purposeful evaluation. People’s participation: Farmers are the ultimate water managers in the real sense and their active participation will increase system performance by inculcating a sense of participation in decision making.
Irrigation Efficiencies It is important to review the concepts of efficiencies used in irrigation. Initially, the concept of irrigation duty, the amount of water needs to be diverted from source to crop root zone for its harvest, was used to design irrigation systems. However, the term irrigation duty was not good enough to indicate relative availability of water. Moreover, it was more a rule of thumb without clear rationale. Subsequently, with the
17
introduction of actual evapotranspiration, the concept of irrigation efficiency, as ratio of crop water requirement to amount of water diverted both expressed in meter, was used. Further, project efficiency (also called as classical irrigation efficiency) was typically subdivided in to field application efficiency (ratio of water delivered to the root zone to water delivered to the field) and conveyance efficiency (ratio of water delivered to the field to water diverted from source). Irrigation efficiency decreases as one moves from the field towards the reservoir. Although, the concept of irrigation efficiency is used for design and evaluation of irrigation system, it was later realized that its concept is erroneous and misleading. This is for the fact that not all the water that is accounted as loss is lost to the system as a whole. The real losses to the hydrological systems are evaporation and flows to the sinks. But much of the so-called losses may be captured and recycled for use elsewhere in the basin. Thus irrigation efficiency tend to underestimate the true efficiency of surface water and ignore the role of surface water in recharging the groundwater and providing the downstream sources of water for agriculture and other eco-system services (Kijne et al., 2003). This issue was addressed by introducing percentage losses that is potentially available for recovery within the system. Subsequently, the concept of effective irrigation efficiency (also termed as neoclassical irrigation efficiency) incorporating the percentage reusable part of the outflow was developed. Also, the concept of fractions to use in irrigation was also advocated. However, these concepts of irrigation efficiencies ignore economic values. Water use efficiency has been used in the past as an indicator of the water worth in irrigated agriculture. It may be defined in a number of ways; it is basically the amount of organic matter produced by a plant divided by the amount of water used by the plant in producing it. In practice, water use efficiency is the ratio of crop output to water input. However, the term efficiency is not considered quite appropriate as output is expressed in terms of agricultural produce per unit area (Kg/ha) and input as per unit of water (m3) against the conventional wisdom of output and input expressed in the same unit in efficiency term. Interestingly, both numerator and denominator in water use efficiency are also expressed in the same unit, though rarely, as ratio of the water required in evapotranspiration and percolation losses to irrigation water supply and rainfall. More recently, water use efficiency is better termed as water productivity and referred hereafter. Status of Land and Water Productivity in India India has remarkably increased its food grain production from 50.82 M tones in 1950-51 to 212.05 M tones in 2003-04. The crop wise increase in food production is given in Table 1. However, over the last few years the yield has more or less stabilized, which calls for renewing attempt to further increase the productivity. The scope of further improvement in crop productivity may be adjudged by the gap in the average yield of the major crops in the country and the achievable yield of the frontline demonstrations. It is to add here that there is even much higher scope of
18
yield improvement while comparing it with the experimentally obtained yield (Table 2). Although, the scope of improvement on land productivity is visible, there is much more concern on availability of water resources to agriculture that may limit the crop productivity in future. Therefore, it is important to generate information on crop water productivity so as to optimize land and water productivity. The state wise information on water productivity for major crops is estimated based on reported experimental results. It is interesting to note here that WP for rice is estimated accounting losses as lost part, which may be true at field level but not at system/basin scale unless this water is going to sink (say saline groundwater). Such issues need to be addressed. Further, the information on state wise land productivity is available but there is hardly Table 1. Scenario of food grain production in India Crop Production (M t) Average Yield 1950-51 2003-04 (t/ha) 2.09 87.00 20.58 Rice 2.77 72.06 6.46 Wheat 2.02 14.72 1.73 Maize 0.88* 23.04 13.65 Millet 15.23 8.41 Pulses 0.85** *
for Pearl millet; **for Chickpea, #Frontline demonstration yields
FLD# Yield (t/ha) 3.53 3.79 3.99 1.99 1.57
Table 2. Crop water productivity for some major crops in India Region/ Avg. Land# Exp. Productivity crops Productivity Land Water Reference (Kg/m2) (Kg/m3) Rice Hira et al. (2004) 0.66 0.34 0.35 Punjab Tyagi et al. (2000) * 0.64 0.44 0.27 Haryana 0.63 0.33 0.21 Uttaranchal Mishra et al. (1990) 0.46 0.38 0.21 Uttar Pradesh CSSRI (2005) 0.70 0.46 0.14 Chhattisgarh Mukherjee et al. (1990) 0.17 0.21 0.16 Orissa Kar et al. (2004) 0.42 0.36 0.25 West Bengal Ambast et al. (1998) 0.61 0.22 Karnataka Manjunatha et al. (2004) Wheat Punjab Haryana Uttaranchal Uttar Pradesh Rajasthan West Bengal
0.45 0.41 0.19 0.28 0.28 0.22
0.54 0.49 0.50 0.43 0.30
1.40 1.44 1.00 1.11 1.15
Hira et al. (2004) Tyagi et al. (2000) Mishra et al. (1995) CSSRI (2005) Ambast et al. (1998)
Crop water productivity (Kg/m3) = Yield (Kg/ha)/Water consumed in ET+ Losses (m3/ha) # Based on Statistical Abstract of India, 2003 * Authors reported water use efficiency as 1.08 on the basis of actual ET
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any information available on crop water productivity in the farmers field. Moreover, there is no information available on system or basin water productivity that includes crop, orchards, forest, livestock, fishery, domestic uses etc. This calls for generating benchmark information on water productivity for different sectors using water. The water productivity information may help to assess a scheme by cross comparing it other schemes and over the time. A comprehensive framework for water productivity depicting the processes involved at different scales, unit of measuring water use and role of different professions at different scales is shown in Fig.1 (Ambast, 2005). Water productivity in irrigated lands: Over the past decades, increase in food production has been mainly attributed to the expansion of irrigated area. It is estimated that even though only about 20% of the world’s agricultural land is irrigated at present, it accounts for 40% of the global agricultural production. Worldwide, a huge investment has been made in the irrigation sector in the past. It is estimated that in India alone, 16 billion rupees (0.34 billion $US) per annum is being invested in this sector after independence. While enormous irrigation potential has been created at huge cost, the gap between created potential and utilization is significantly large. Therefore, along with the thrust towards creation of higher irrigation potential, efforts should also be directed towards better utilization of already created potential. In spite of the fact that a considerable amount of work has been done in the past, the question "How is irrigated agriculture performing with limited water and or land resources?" has still not been answered satisfactorily (Sakthivadivel et al., 1999). This is mainly due to the inherent limitation in collection and measurement of data required for evaluating the irrigation system performance. Further, in future, decisions on water availability to irrigated agriculture will depend on competition between enterprises, returns from irrigation and environmental factors, apart from the impact of climate change. These are all likely to decrease the amount of water available per hectare land and put more pressure on farming community to improve efficiency. Some of the important issues related to water productivity in irrigated agriculture, which needed to be addressed are: (a) defining water productivity for irrigated agriculture (b) benchmark information on water productivity of current irrigation schemes (c) trade-off between water productivity and groundwater recharge (d) hydraulic means of improving water productivity vis-à-vis water worth (d) system approach for value-added irrigated cropping system (e) water productivity and participatory irrigation management. Water productivity in rainfed areas: Statistics indicate that about 67% of the total cultivated area in India depends on rainfed agriculture. It produces about 44% of total food grain and supports nearly 40% of the population. Rainfall in these areas, being semi-arid in character, is limited and occurs in a small part of the year. This leads to an average production of about 0.7 to 0.8 t ha-1. Many poor people live in marginal areas dependent on rainfed agriculture. Increasing productivity of rainfed areas could increase food security, improve livelihoods of poor, and lessen the need for more irrigation. A focus on this question will explore (a) the potential contribution to food and environmental security from rainfed agriculture, and (b) promising approaches to sustainable improvements in rainfed productivity considering soil-water conservation,
20
agronomic aspects, supplemental irrigation of rainfed crops, water harvesting to supplement rain, conjunctive use of rainwater and other water sources, germplasm, drought alleviation land use changes and cross cutting issues such as socioeconomic, institutional and policy issues. Hydrologist and Economists
Surface & subsurface inflows and precipitation
At basin level
Rs/m 3 Reservoir
Inter-sectoral allocation
Storage losses
Irri. Engineers and Social scientist
Sinks
At system level
Water released Conveyanc losses
Water delivered at farm gate
Total water available at farm
Water applied to field
Kg/m 3 , Rs/m 3
Rainfall
Ag. Engineers and Ag. Economist
Return flow, Watertable, Groundwater
At farm level
Application losses
Sinks Water retained in soil
Crop scientist and Soil scientist
Kg/m 3
Water consumed by crop
At field level
Breeders and Physiologist
Crop production
Figure 1. A comprehensive framework for water productivity at different scales
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Estimation of Water Productivity in the SLLC System In irrigated systems, where water is a constraining resource, output per unit of water consumed may provide the basis for comparison of irrigation systems. Sakthivadivel et al. (1999) presented some indicators for cross system comparison as: Production Output per unit water consumed = Volume of water consumed in ET Production Output per unit water supply = Diverted irrigation water supply
3.00
3.00
Evp fract (-) Yield (Ton/ha) WUE (Kg/m3)
2.50
Evp fract (-) Yield (Kg/ha) WUE (Kg/m3)
Evp fract / Yield / WUE-S
Evp fract / Yield / WUE-C
Remote sensing in conjunction with geographical information system may be used to estimate water productivity at system or basin level. Here, an application of remote sensing based procedure is illustrated in the Sone Low Level Canal system, India. The region is climatically sub-humid (annual rainfall-1100 mm). Three Landsat5 TM data (31 Jan, 16 Feb and 4 Mar 2000; path/row-141/042; lat/long-25.1077N/ 84.5899E; scene centre time-04.29.32 GMT) covering wheat crop growth in winter season were analysed. In this study, the output per unit water consumed is computed for the SLLC system. However, it has been scaled up to output per unit water supply as it has an advantage of comparing the values with conventional water use efficiency. The crop production is estimated using relationship between remotely derived normalized difference vegetation index and crop productivity data for limited ground observations. An operational method on regional evapotranspiration through surface energy partitioning (RESEP; Ambast et al., 2002) was applied on all images to estimate actual evapotranspiration (ETa). Further, weather data for November 1999-April 2000 were used to calculate potential evapotranspiration (ETp) using Penman-Monteith method. The ETa/ETp ratios for three dates have been used to calculate ETa for three equally divided crop growth periods for estimation of seasonal ETa. The water productivity consumed and supply are presented in Fig.2.
2.50 2.00
2.00
1.50
1.50
1.00
1.00
0.50
0.50 0.00
0.00
P
A
B
D
X
C
G
W1
W2
P
Canal ID
A
B
D
X
C
G
W1
W2
Canal ID
(a)
(b)
Figure 2. Water productivity (a) consumed and (b) supply in the SLLC system, India
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It is observed that the WP-consumed for branch canals is in the range of 1.41.6 Kg/m3. WP-consumed when scaled down to WP-supply, the range is observed between 0.60-1.0 Kg/m3. It can be seen that WP is low in the Arrah and the Behea branch canal than other branch canals. The WP is high in W1 and W2, which are the distributaries directly fed by main canals. Although, the average evaporative fraction for W1 is nearly equal to all irrigating branch canals, the high mean yield in this distributary command has increased its WP, whereas the WP is even higher in W2 due to lower average water availability in spite of low mean yield. This indicates a better WP in distributaries directly fed by main canal than the branch canals. One of the reasons for this is the smaller command area having less conveyance losses and thereby high irrigation efficiency. Among the irrigating branch canals, all branches are having nearly equal water productivity. It is seen that the mean yield in the Chausa branch nearly equals to other branches but it received more water and thus has poor water productivity. Irrigation System Improvement Options In order to improve irrigation system performance, a policy guideline for LLC system has been prepared. In this, the impact of various possible rotational schedules is analysed and a suitable rotation schedule is suggested. The alternative cropping patterns have been evaluated for their water use efficiency and economic returns. After the modernisation of the SLLC system and release of Government of Bihar (GoB) share of water from Bansagar project, it is expected that an additional parallel canal will run during kharif season, whereas the existing canals will run with designed capacity of water throughout the rabi season. The proposed cropping pattern after modernization (which is quite close to the existing cropping pattern) and the alternative cropping patterns during rabi season are given in Table 3. Cropping patterns, CP1-CP2-CP5 have increased cropping intensity, however, CP3-CP5 have the maximum intensity (100%) with increased area for the wheat crop (Table 4). Therefore, cropping patterns CP3-CP5 can be adopted depending on the farmer’s choice. However, economic analysis indicated CP5 as the best cropping pattern. Table 3. Proposed and alternative cropping patterns Area (%) Cropping pattern Wheat I
Pulses
Oilseeds
Vegetables
Perennial
II
CP1 (proposed)
35.0 20.0
15.0
5.0
3.0
2.0
CP2
40.0 25.0
15.0
5.0
3.0
2.0
CP3
45.0 30.0
15.0
5.0
3.0
2.0
CP4
50.0 35.0
5.0
5.0
3.0
2.0
CP5
60.0 40.0
0.0
0.0
0.0
0.0
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Table 4. A summary of irrigation scheduling for different cropping patterns Crop ETc Net Irrig. Lost Irrig Prod Loss Prodn. WUE (mm) (mm) (mm) (%) (kg) (Kg/m3) CP1 Wheat-I
401.9
460.0
96.3
0.0
1575
0.98
Wheat-II
446.6
460.0
87.5
1.5
887
0.96
Pulses
230.5
208.0
0.0
2.8
194
0.47
Vegetable
357.5
391.0
50.5
2.5
585
5.11
Sugarcane
88.4
90.0
0.0
0.0
1000
-
Wheat-I
385.7
340.0
48.9
4.3
2153
1.27
Wheat-II
401.2
340.0
45.1
12.0
1386
1.17
Pulses
100.5
78.0
0.0
7.2
93
1.28
Vegetable
357.5
391.0
50.5
2.5
585
5.11
Sugarcane
88.4
90.0
0.0
0.0
1000
-
Wheat-I
385.7
340.0
48.9
4.3
2584
1.27
Wheat-II
401.2
340.0
45.1
12.0
1584
1.17
CP4
CP5
Conclusions In the growing scarce water conditions, it is important to understand the concept and utility of water productivity at field, system and basin level. There is a need to develop consensus to standardize the estimation methods of water productivity at different levels. There is very little information available on crop water productivity for actual field conditions, whereas hardly any information available on total water productivity at system or basin level. The synthesis of information on water productivity may be useful to assess the scope of water productivity improvement and to estimate the possible enhancement by different improvement interventions. The possibility of enhancing water productivity exists through promotion of hybrid varieties, integrated nutrient and pest management, promotion of in-situ moisture conservation, improved irrigation scheduling, precision farming and farming system approach through multiple uses of water. The basis for such improvement may be micro zoning of the crop wise potential regions. However, a number of research issues, listed in the paper, are to be examined carefully before recommending suitable action.
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Bibliography Ambast, S.K., Sen, H.S. and Tyagi, N.K. (1998). Rainwater management for multiple cropping in Sundarbans delta (W.B.). Bulletin No 2/98, Regional Research Station, Central Soil Salinity Research Institute, Canning Town, India, 69 pp. Ambast, S.K., Keshari, A.K. and Gosain, A.K. (2002). An operational model for estimating evapotranspiration through surface energy partitioning (RESEP). International Journal of Remote Sensing, 23(22): 4917-4930. Ambast, S.K. (2005). Benchmarking water productivity in India-Policy issues and action plans. XII World Water Congress, New Delhi (India), Nov. 22-25, 2005. Keller, A. and Keller, J. (1995). Effective Efficiency: a Water Use Concept for Allocating Freshwater Resources. Water Resources and Irrigation Division discussion paper 22. Winrock International, Arlington, Virginia, USA. Kijne, J.W., Barker, R. and Molden, D. (2003). Water Productivity in Agriculture: Limits and Opportunity for Improvement, CABI Publishing, Wallingford, UK. Sakthivadivel, R., Fraiture, C.D, Molden, D.J., Perry, C. and Kloezen, W. (1999). Indicators of land and water productivity in irrigated agriculture. International Journal of Water Resources Development, 15(1/2): 161-179. Tyagi N.K., Agrawal, A., Sakthivadivel, R., Ambast, S.K. and Sharma, D.K. (2004). Productivity of rice-wheat cropping system in a part of Indo-Gengetic plain: A spatial analysis. Irrigation and Drainage Systems, 18(1): 73-88.
25
Analysis of Soil and Water for Diagnosing Salinity/Sodicity Problems Khajanchi Lal Central Soil Salinity Research Institute, Karnal –132 001 Salt affected soils contain excessive concentration of either soluble salts or exchangeable sodium, which impair plant growth. Such soils occur in about 7% of total land area of the earth. The major ionic composition of salts is Ca+2, Mg+2, Na+, K+, Cl-, SO4-2, HCO3- and CO3-2. Based upon pH of saturated paste (pHs), electrical conductivity (ECe) and exchangeable sodium percentage (ESP), these soils can be classified as: The USDA System Type of soil
ESP
PHs
Saline
ECe (dS/m) >4.0
4.0
>15
4 dS/m
Variable, mostly5000 35000 >350000
Residual sodium concentration (RSC): It is one of the methods to evaluate the sodicity hazards of carbonate and bicarbonate rich waters. Carbonates and bicarbonates affects the soil permeability thus water availability to the crops. The residual sodium carbonate may be calculated by subtracting the quantity of Ca+++Mg++ from total of carbonate and bicarbonate determined separately in a given sample and expressed in me L-1. Thus, RSC = (CO3 + HCO3) – (Ca + Mg) Presence of such anions in irrigation waters results in precipitation of calcium and magnesium of the soil and thus increase sodicity hazard.
30
Based upon the concept of Eaton (1950) waters with more than 2.5 RSC are not suitable for irrigation. Waters containing 1.25 to 2.50 meq L-1 are marginal, and those containing less than 1.25 meq L-1 RSC are probably safe. Good management practices and proper use of amendments might make it possible to use successfully some of the marginal or even unfit waters. Sodium adsorption ratio (SAR): The SAR procedure encompasses the infiltration problems due to an excess of sodium in relation to calcium and magnesium. High SAR waters can cause severe permeability problems. Meeting the crop water under these conditions may become extremely difficult. SAR can be calculated by the following equation:
SAR =
Na (C a + M g ) 2
Where Na, Ca and Mg are in me/l For SAR values greater than 6 to 9, the irrigation water is expected to cause permeability problem on the shrinking swelling types of soil. Permeability refers to the ease with which water enters and percolates down through the soil and is usually measured and reported as infiltration rate. An infiltration rate as low as 3mm/hour is considered low while a rate above 12 mm/hour is relatively high. At a given SAR, infiltration rate increases as water salinity increases. Based on EC, SAR and RSC ground waters are grouped for irrigation as follows: Water Quality A. Good B. Saline -Marginally saline -Saline -High SAR saline C. Alkali waters -Marginally alkali -Alkali -Highly alkali
ECiw (dS/m) 1.5
79km2 For A 52km2 C= 0.3 for discharge of 1012 cusecs
Q = discharge in cumecs, A = catchment area in km2 and C is a coefficient, which depends upon rainfall. Values vary from 3.5 for 500 mm rainfall to 35 for rainfall in the range of 7502. 1000mm. # The values vary from 0.22 to 0.44 for areas in between 13 to 79 km
More elaborate calculations are made in designing permanent structures for which frequency analysis procedures are used. The design frequencies for various structures are given in Table 5. Table 5. Design frequencies for minor structures Type of minor structure (%) Highway cross road drainage Air fields Storm drainage Levees Drainage ditches
10-2 20 50-10 50-2 20-2
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Probability/return period Years 10-50 5 2-10 2-50 5-50
EXAMPLE Table 4. A typical design of a field drain 1 Salient Information Catchment area Land Slope Soil type Average annual rainfall 2 Assumed Parameters Slide slope Channel bed slope S=0.10% Run off coefficient 3 Design run off
4
100 ha 0.10% Clay loam 1220 mm H: V = 1.1 (Depending upon soil type) 0.001 (As per survey) C = 0.30 Q = C x A 5/6 A = Catchment area in Sq. Km Q = 0.30 x (1.0)5/6 = 0.30 cumec or 9.96 cusec
Design of section For efficient channel section
Velocity of flow For clay loam soil value of
Since Solving With 20% free board total depth of flow
Where Therefore the design section is Top width Bottom Width Depth
B = 2d R = 0.6213 d Where R = hydraulic radius d = depth of flow A = 3d2 V = 1/nxR2/3 x S½ n = 0.035 V = 1/0.035 x (0.6213d)2/3 x (0.001)½ = 0.6578 d Q=AxV = 3d2 x 0.65782/3 = 1.9736 x d8/3 Q=AxV 0.30 = 1.9736 xd8/3 d = 0.0.49 say 0.50 m d = 1.20 x 0.50 = 0.60 m b = 2d = 1.20m T = b+2 x z x d Z = side slope = 1 T = 2.40m 2.4 m 1.20 m 0.6 m
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DRAIANGE CHANNEL (EARTHEN) (10 CUSEC) 2.40
0.60
0.9
1.2 4.00
All dimensions in m Figure 1. Section of a field channel under reclamation of waterlogged area programme in Orissa Benefits of Surface Drainage There is land loss in implementing surface drainage has been a common argument against surface drainage. However evidences generated at research stations (Table 6) and in irrigation commands (Table 7) amply prove that benefits outweigh the loss due to drainage in terms of land loss. The data in Table 6 reveal a loss in the crop yield to the extent of 2-50% depending upon the crop and the duration of water stagnation. Clearly, these losses would be benefits upon implementation of land drainage. The data in Table 7 highlights the real benefits in the range of 20-50% in the Ukai-Kakrapar project in Gujarat (Table 7). Table 6. Yield in drained plots and percent yield reduction due to water stagnation of various duration for tested crops Yield Crop Yield reduction# over drained (%) for water -1 (t ha ) stagnation (days) Drained 1 2 4 6 Sorghum 4.13 3 11 16 20 Pearl millet 2.22 6 15 22 27 Pigeon pea 1.52 4 14 18 21 Wheat 4.20 8 17 27 39 Barley 3.65 4 7 13 25 Mustard 1.43 8 16 22 29 Berseem (seed) 0.48 2 21 35 48 Sunflower 1.86 13 19 26 30 #
Yield reduction due to water stagnation is relative to drained plots
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Table 7. Increase in yield of various crops after improvement in surface drainage Crop Yield improvement (% over poorly drained) Sugarcane 19.1-27.7 Paddy
19.7-24.7
Gram
32.1
Indian bean
49.8
Command Area Guidelines on On-Farm Water Management/Drainage Ministry of Water Resources, GOI restructured the CAD programme as CAD&WM during the year 2004. The revised ceiling as well as funding pattern has also been revised as shown in Table 8. Table 8. Revised guidelines on expenditure and its share by various stakeholders Sl Items Cost norms per ha Central State Farmers No share share share 1 Construction of Field Rs. 10,000/50% 40% 10% Channel 2 Construction of Field Rs. 4,000/50% 50% Drains 3 Reclamation of Water Rs. 15,000/50% 40% 10% Logged Area 4 Adaptive Trials, Action As per location research and specific need (Rs. Demonstration 5,000/ha) 5 Farmer Training As per location specific need (Rs. 10,800/per training) New Items 6 Correction of system Rs. 4,000/50% 50% deficiencies above out let up to Distributaries of 150 Cusec capacity 7 Renovation and Rs. 15,000/50% 40% 10% desilting of existing Irrigation tanks within the irrigated command
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Improved Drainage - the Long-term Solution Lack of drainage or inadequacy of it is rapidly becoming a major constraint to limit agricultural production. Productivity of agricultural lands can only be sustained if drainage improvements are undertaken on cropland currently affected by submergence or high water table. Very often, the natural drainage in an area along with good water management is sufficient to eliminate excess water and to preclude the need for drainage systems. However, there would be many situations where surface drainage would be essentially required. The degree of drainage needed in an area could be assessed through a drainage index proposed by Gupta and his coworkers. It may be noted that if the problem is low, drainage may not be a serious issue and good crops can be grown with land and crop management that would avoid the adverse effect of drainage (Table 9). As the value of the drainage index increases, the degree of drainage to be provided also increases and management alone would not be sufficient if the index is more than 50. Table 9. Drainage index and the degree of the problem Index
Degree of problem
< 25
Low
25-50
Moderate
50-75
High
75-100
Acute
With low to moderate degree of the problems, a group of farmers can join hands to provide reasonably good drainage to the crops. Following activities can be initiated at the farmer’s land: •
•
•
Land levelling is an essential component of a drainage programme. Deviations in land levels within the field can affect production and productivity. Such variations can be minimized through levelling. Farmers with heavy textured soils, soils with plow sole as develops in lowland ricewheat system, alkali lands with poor water absorption characteristics or those who rely mainly on surface irrigation should have adequate surface drainage facilities to remove excess water. A uniform slope of about 1:1500 is desirable to drain irrigation water or rainfall off a field. Many times, drainage problem stems from inadequate maintenance of an existing drainage system. In this era of fund crunch, farmers should maintain the system falling in their territory. If a group of farmer’s joins hand, a good portion of the system could be maintained. Depressions around farm/village or village ponds could be deepened or multi-purpose farm ponds could be constructed to drain the surplus surface drainage water.
80
•
At the individual level, cavity wells commonly used to develop groundwater in this part of the country (Haryana, Punjab and Western U. P.) can be used to drain excess water resulting from the occasional heavy rainfall events to minimize damage. As a short-term measure, this practice has been successfully tried and adopted by many farmers. Bibliography Gupta, S.K., Dinkar, V.S. and Tyagi, N.K. (Eds.) (1995). Reclamation and Management of Salt Affected Lands in Irrigation Commands. Published by CSSRI on Behalf of Ministry of Water Resources (GoI),New Delhi. pp 144. Gupta, S.K. and Tyagi, N.K. (Eds.) (1996). Waterlogging and Soil Salinity in UkaiKakrapar Command-Causes and Remedial Measures. CSSRI, Karnal and Department of Science and Technology, New Delhi. pp 89. Murthy, V.V.N. (1985). Land and Water management Engineering. Kalyani Publishers, Delhi. National Institute of Hydrology (1995-96). Drainage Manual. NIH, Jal Vigyan Bhawan, Roorkee. 216 pp. Suresh, R. (2000). Soil and water Conservation Engineering. Standard Publishers and Distributors, Delhi. WAPCOS (1987). Handbook for Drainage of Irrigated Areas in India. Schwab, G., Maheswari, K.M., Gupta, S.K. and Johri, G.B. (Eds.) Tech. Report No. 5. IMTP (LBII and WAPCO), New Delhi.
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Subsurface Drainage for Reclamation of Waterlogged Saline Soils S.K. Kamra Central Soil Salinity Research Institute, Karnal- 132001, Haryana The sustainability of irrigated agriculture in arid and semi- arid regions is frequently impaired due to waterlogging and soil salinity problems. The recent CSSRI estimates indicate that nearly 8.5 M ha area is affected with soil salinity and alkalinity problems in different states, out of which about 5.5 M ha waterlogged saline soil is distributed in the irrigation commands, especially those in the states of Haryana, Rajasthan, Gujarat, Maharashtra, Andhra Pradesh and Karnataka. In about 0.7 to 1.0 M ha semi- arid part of Indo- Gangetic plains in north- west India, comprising the states of Punjab, Haryana, north-western Rajasthan and western Uttar Pradesh, the waterlogging and soil salinity problems are very severe and the area with impaired agricultural production is increasing alarmingly. The waterlogging and soil salinity/ sodicity problems in deep black vertisols, distributed primarily in the states of Maharshtra, Gujarat, Madhya Pradesh, Andhra Pradesh and Karnataka, are more difficult to handle than relatively coarse textured soils of North west India. Irrigation induced waterlogging and soil salinity problems are caused due to a complex web of technical, economic, political and social factors. Technically most of these problems arise due to non- incorporation of adequate drainage measures at the design and planning phases of irrigation projects. Most irrigation projects in India lack well defined drainage measures. The other technical factors contributing to irrigation induced salinity include poor on-farm water use efficiency and poor construction, operation and maintenance of irrigation canals leading to excessive seepage. Further, drainage measures are also generally not provided when the problem starts to emerge or, even if provided, are not properly designed, constructed, operated or maintained. The productivity of irrigated agriculture in arid and semi- arid regions can be sustained for a long time if proper leaching techniques are employed and adequate drainage is provided to remove the salts accumulated in the root zone and to keep the water table sufficiently deep to prevent capillary rise of salt laden groundwater into the root zone. Since early 1980's, CSSRI has shifted emphasis in establishing guidelines for management of saline soils. The research efforts at CSSRI since 1984 have been strengthened by an Indo-Netherlands Collaborative Project on Land Drainage for finding solutions to waterlogging and soil salinity problems in Haryana State. These research efforts have resulted in the development of a package of practices, consisting of providing appropriate subsurface drainage, leaching of salts, and management of saline drainage effluents for reclamation and management of waterlogged saline soils. Under an Indo-Dutch Network Project on Drainage and Water Management in Irrigation Commands (1996-2002), the subsurface drainage
82
technology was transferred on a pilot basis in four states of Andhra Pradesh, Karnataka, Rajasthan and Gujarat in collaboration with agricultural universities of these states. Small scale projects involving manual installation of subsurface drains are slowly giving way to large mechanically installed drainage projects. Under a Haryana operational pilot project with Dutch collaboration, mechanical installation of subsurface drains has been completed in 1000 ha area in Gohana and 1000 ha in Kalayat block of Kaithal. Similarly under the Rajasthan Agricultural Drainage Project (RAJAD) with Canadian collaboration, about 5000 ha area in Chambal Command has been provided with subsurface drainage to ameliorate it from waterlogging and soil salinity. More large-scale drainage projects are envisaged in near future in other states like Punjab, Maharashtra, Andhra Pradesh, Gujarat and Karnataka. Subsurface Drainage Technology Two types of man made systems of subsurface drainage i.e., (i) horizontal and (ii) vertical are in vogue. Both systems aim at lowering the water table in response to recharge caused by rainfall, irrigation, leaching- water and seepage. Vertical drainage is mainly achieved by pumping out groundwater through the tube wells and the horizontal drainage involves open or pipe drains laid at some depth below soil surface parallel to ground which work like tube wells laid horizontally. The success of vertical drainage system depends on the presence of a favourable aquifer within 12 to 20 m and of favourable water quality, which could be utilised for irrigation. In this paper, aspects dealing with horizontal drainage only will be dealt with. A horizontal drainage system, consisting of open ditches or covered pipe drains, involves three categories of drains: the laterals, the collectors and the main drains. Lateral drains, laid parallel to each other at small gradients, cover the entire field, accept excess ground water whenever it rises above drain level and serve to control the water table. Water entering the laterals flows into the collectors, which carry it to the main drain. The main drains carry the water to the outlet from where it is disposed out of the area either by gravity or by pumping from a sump. In areas with low soil permeability or high rainfall intensities or where surface water is the main problem, open ditches are preferred. Subsurface drains are preferred in high permeability areas where excessive water in the soil is the main problem. The most common materials used in the manufacture of lateral drainpipes are clay, concrete and plastic. Clay and concrete pipes (often referred to as tiles) are usually made in lengths of 30 cm with 10 cm internal diameter. The water enters the pipeline through the gaps between the tiles. These have now been totally replaced by PVC pipes which come in smooth and corrugated varieties. The length of PVC pipes varies from about 5 m in case of smooth rigid pipes to 200 m in case of corrugated, flexible pipes available in coils, which can be joined by sockets. Water entry into smooth pipes is via slits cut or punched in the walls while corrugated pipes have small openings in the valley of the corrugations. Perforations of 1 to 2 mm dia. are to be provided at a rate of 2 to 3% of the surface area of the pipe. The advantage of plastic pipes over clay
83
and concrete is their considerably lighter weight and their productions in larger lengths, thus involving lower transport cost and cheaper installation. The collector and main drains are either of pipes or open ditches. Bigger diameter RCC or PVC pipes (of convenient length) with no end gap but joined together with sockets are generally used for collector drains. The joining of laterals to collector through manholes helps in maintenance of drain lines. The lateral drains are laid at a slope of 0.05 to 0.1%, while collectors are generally laid at a slope of 0.1%. The sump must have some storage capacity below the level of entry of the collector drain to avoid continuous operation of the pump. Two design variables of subsurface drainage system are drain spacing and drain depth, which control water table depth. Other factors influencing the height of water table include various recharge components, evaporation and other discharge sources, hydraulic properties of soil and aquifer and cross sectional area of the drains. Several equations relating these factors with drain spacing are available. The depth of the lateral drains is influenced by the required water table levels (for optimum crop production and for preventing soil resalinization, texture of different soil layers, and the depth within the reach of available drainage machinery. In general, the depth of drains may be limited between 1.5 and 2.0 m. The length of lateral drains varies from 200 to 600 m depending on available natural slope and layout of the area. Envelope (filter) materials are provided around the pipe drains to facilitate water flow into the drain and to prevent the entry of soil particles into the drain. The most common envelope materials are graded gravel and synthetic filters, the later having lot of advantage over gravel in terms of transportation and installation. CSSRI’s Experience on Subsurface Drainage CSSRI has undertaken a number of subsurface drainage pilot studies directly or in collaboration with different state departments for amelioration of waterlogged saline soils in the country. Most of these manually installed subsurface drainage projects were conducted in the states of Haryana, Rajasthan, Gujarat while a few studies were also conducted in the states of Andhra Pradesh and Karnataka. The total area of these drainage studies, conducted at about 20 project sites ranging in size from 30 ha to 120 ha, in different parts of country is about one thousand hectare. Of these, the subsurface drainage project at Sampla (distt. Rohtak) has been most intensively monitored. At most of these sites, the water table fluctuated between about 1.5 m from ground level during summer to near the surface during monsoon. The initial salinity of groundwater at most sites was more than 10 dS/m, being as high as 40 dS/m in extreme cases. In the earlier installations, cement clay tiles were used for laterals and cement concrete pipes for the collectors. However, after 1986, PVC rigid and corrugated pipes are being increasingly used as sub- surface drains. Either graded natural gravel or PVC (synthetic) netting (60-75 mesh size) have been used as
84
envelope at these sites. The saline drainage effluent is being pumped into surface drains or canal distributaries. At most sites, drains were installed at about 1.5m depth; the maximum adopted drain depth being 1.75m. The average salinity of root zone at all the sites has been considerably reduced resulting in good production of a number of crops in hitherto barren highly saline lands. At Sampla a continuous reduction in soil salinity has been observed and the seepage from outside areas, which may range from 20 to 60% of drain discharge during different seasons at Sampla, has not seriously affected the salinity situation in the root zone; it, however, has pronounced effect on the quality of drainage effluent. After about 12 years, the salinity of drainage effluent is still about 7dS/m from an initial value of 30 dS/m. It may also be observed that the yields of crops are good at all sites. At Sampla, the installation of drainage system in initially barren soils enabled cultivation and production of about 2 t/ha of coarse cereal grains or seed cotton in kharif and more than 4 t/ha of wheat or barley and 2.0 t/her of mustard in rabi season. For these sandy loam soils and the existing climatic conditions, drain spacing of 65 to 80m with drain depths ranging from 1.5 to 2.0m can be safely adopted. For heavy textured soils narrow spacing is advised. In areas having no natural outlet, the evaporation pond technology has been experimented by CSSRI in collaboration with Central Institute for Research on Buffaloes (CIRB), Hisar for reclaiming land for fodder production (Kamra et. al, 1996). The project aimed to evaluate the efficacy of a pond of 1 ha surface area for storage, evaporation or possible reuse of subsurface drainage effluent from 52 ha waterlogged saline area having no suitable outlet. Drain spacing of 75 and 100m and drain depth of 1.75 m were adopted in the system. The soils in the area are generally silty loam and the salinity in the surface layer was ranging from 10 to 30 dS/m, with sodium chlorides being the dominant salts. The water table depth in the area ranged from 100 to 150 cm below ground surface and groundwater had salinity of 10 to 15 dS/m. The hydraulic conductivity is about 0.5 m/day, while average annual rainfall is about 500 mm. Lateral drains were installed also on the sides of the farm pond to intercept seepage losses from the pond. Drainage measures over the years have resulted in gradual reduction in salinity of soil and drainage water and consequent increase in cropping area as well as yields of fodder crops in CIRB farm. Weekly and seasonal water and salt balance analysis of evaporation pond indicated that about 75% of water and 60% of salt inputs to the pond were lost due to seepage. Though peripheral drains on the sides restricted the effect of pond water storage on surrounding groundwater quality to within 60 m radial distance from pond, more stringent measures like provision of drain lines below pond bed or use of some sort of lining are recommended for evaporation bed constructed in sandy substratum.
85
Mechanical Installation of Subsurface Drainage System Small scale manually constructed pilot schemes for subsurface drainage highlighted the necessity of undertaking pipe drainage schemes by machinery in larger areas and assessing its acceptance within socio- economic framework. Under a Haryana Operational Pilot Project on Land Drainage, subsurface drains have been mechanically installed since 1994 in two blocks of 1000 ha each with the support of the Netherlands govt. Total budget of the project was about Rs. 230 million, out of which 22 million was to be the contribution of the Haryana Government. A central feature of the HOPP activities has been the integration of farmers in the management of project through farmer drainage societies for its operation and maintenance. CSSRI was entrusted with the responsibility of monitoring and evaluation of the project in Gohana block of Rohtak district. A drain spacing of 60- 67 m, drain depth of 1,7 m and disposal of subsurface drainage effluent in surface drains and canal distributaries have been adopted. Achthoven and Lohan (1998) reported an average cost of Rs. 37000 for providing subsurface drainage per ha gross area (Table 1) based on model calculations for a block of 47 ha in HOPP area. Similarly about 5000 ha area in Chambal Command has been provided with subsurface drainage to ameliorate it from waterlogging and soil salinity. Table 1. Estimate of costs for a drainage block in HOPP* Items
Cost (Rs./ha)
% of total cost
10,505 6,656 2,630
28 18 7
8,770 6,601 264 1,771 37,199
24 18 1 5 100
Pipes & Fittings Filter Structures Machinery -Fixed -Variable Labour Miscellaneous Total (Source: Achthoven and Lohan, 1998)
The operational cost of the drainage system is mainly due to pumping of the drainage effluent. After one or two years of operation of the drainage system, the quality of drainage effluent improves to a level where it can be reused for irrigation. Disposal of Drainage Effluent Drainage waters generally contain high concentrations of soluble salts and plant nutrients, and sometimes potentially toxic trace elements and pesticides. The disposal and storage of such waters can have remarkable impacts on the degradation of surface and ground water quality, threat to aquatic organisms, wildlife and plants and potential risk to public health. The aspects relating to disposal, reuse and management of saline drainage water for cropping or agro- forestry in arid and
86
semi-arid regions are priority research areas for CSSRI. Besides, work on selection and breeding of salt tolerant varieties has been going on and a number of salt resistant varieties of rice, wheat and mustard have been released and few others are in advanced stage of development. Some important option for disposal of saline drainage effluent are discussed below: River discharge with and without dilution: Disposal of the drainage water into rivers or canal can deal with large volumes and may be a practical medium term solution for the inland sites. Discharge to the river system is inexpensive but the disposal of large volumes of saline drainage effluent through this mode is likely to become increasingly difficult due to environmental restrictions imposed by downstream users. The maximum drain discharge generally occurs during the rainy season when the irrigation demands are relatively less and consequently large volumes of saline drainage water can be discharged into the river system. However, there is a strong need to establish numeric water quality standards for various points along the river, monitoring and modelling of spatial and temporal water quality trends and provisions for diverting saline drainage waters away from the river. In a case study on the disposal of drain discharge into the Yamuna river during June to October, UNDP (1985) assumed the electrical conductivity (EC) of river and surface drainage water as 0.2 dS/m and 1.2 dS/m respectively, of subsurface drainage water (ECd) as 6 and 10 dS/m and restricted the salinity of river water after mixing at 0.75 dS/m. Based on 80% frequency discharges of the river at Wazirabad (Delhi) and of drain No. 2 and 8 of Haryana, additional allowable discharge of subsurface drainage water was calculated. Assuming a subsurface drainage surplus of 1.5m/ha/day during the monsoon period, the area that could evacuate its drain discharge into the river was calculated (Table 2). It is seen that about 0.1 M ha critical area in the command can evacuate even 10 dS/m drainage water in river Yamuna during July and August. Table 2. Allowable subsurface drain discharge and drainable area into Yamuna river Months Drainable area (ha) Drain discharge (m3/s) ECd(dS/m) = 6 10 6 10 June July August September October
0.9 25.4 47.6 6.5 3.0
0.5 14.4 27.0 3.7 1.7
5,000 46,000 274,000 37,000 17,000
3,000 83,000 156,000 21,000 10,000
Evaporation ponds: One means of drainage water disposal in inland basins with no outlet is its storage and possible evaporation in natural or artificially constructed ponds. This can be a convenient and economic option in areas which have high evaporative demand and abundance of natural depressions and salt lakes far from the cultivated lands. Accumulated salts and minerals may ultimately require disposal
87
at some other facility or location. Many areas in Rajasthan can be ideal sites for construction of evaporation ponds. Based upon the case study of an evaporation pond in Haryana (Kamra et al., 1996) and similar studies in Rajasthan, it can be stated that evaporation ponds may require about 3-10% of the drainage area in arid and semi-arid conditions. Environmental concerns related to evaporation ponds include potential contamination of groundwater in the vicinity of the pond. Installation of drain lines under the pond facilitates interception and recycling of seepage water back to the pond. Experiences of other countries indicate that the long-term problems of evaporation ponds may exist and the solution should be seen only as a temporary and partial remedy. Reuse of drainage water for agriculture, agro- forestry, aquaculture: A promising solution for the disposal of saline drainage water is its reuse reclamation leaching and for irrigation of crops and trees of moderate to high salt tolerance. Minhas and Gupta (1992) presented the guidelines for using saline waters for crop production in different agro- climatic regions of India. Salient conclusions on reuse aspects of drainage waters include that (i) drainage waters of up to 10 dS/m salinity can be used for irrigating wheat and mustard crops during non- rainy seasons, (ii) drainage waters of salinity up to 12 dS/m can be safely used in rotation with good quality canal water for irrigating wheat, barley and mustard and (iii) reuse Of saline waters will require pre- sowing irrigation with good quality water. Reuse is an accepted solution during the initial stages of drainage development when the volumes of saline drainage water are small. However, there is uncertainty about the long-term effects of this practice on soil crusting, reduced water infiltration capacity, and accumulation of toxic elements. The saline drainage waters also have good potential for raising salt tolerant tree and grass species (Singh, 1993) and perhaps also for promoting composite fish culture (Garg, 1993) in saline water stored in ponds. For command areas, Singh (1993) suggests planting of 100 m or more wide belt along the canals on both sides with high water demanding trees such as Eucalyptus, Populus, Laucaena and grasses such as Spartina, Panicum, Leptochloa, Brichairia for the interspaces. Disposal to the sea: For sustainable irrigated agriculture in inland saline soils, drainage water needs to be disposed of in the ocean or in terminal lakes. The most intensively irrigated part of India, encompassing western portions of the states of Punjab, Haryana and Rajasthan, needs drainage but faces a serious long- term problem of effluent disposal. Barber (1985) estimated that about 1 M ha area in these states had water table less than 3 m from the surface and 0.25 M ha had water table at less than 1 m depth for long periods in the year. The ground water in most part of the region is saline and not suitable for irrigation. Among other engineering and management alternatives suggested by Barber (1985), the proposal of an outfall drain through Indian territory of 900 km, including 600 km in the irrigated area (in the states of Punjab, Haryana, Uttar Pradesh, Rajasthan and Gujarat), and requiring a lift of 80 m needs serious consideration and should not be dismissed only on the plea of 88
huge investments involved. A similar 250 km long Left Bank Outfall Drain (LBOD), aligned along the left side of Indus river to dispose drainage effluent from sizeable areas of Punjab and Sind provinces into the Arabian sea, has already been commissioned in Pakistan. Based upon the experience of subsurface drainage in North western states, following salient observations can be made: •
•
• •
Subsurface drainage (SSD) is considered for control of waterlogging and soil salinity once the problem becomes aggravated. Without obvious problems, the scarce financial resources are allocated by state governments to more pressing problems. Since the drains are installed underground and are not visible, the technology does not appeal easily to the imagination of farmers and local political leadership. The farmers are not easily convinced about its cost effectiveness. In N-W India, SSD has resulted in reclamation of saline soils in 2-4 years ensuing a significant increase in cropping intensity, yield and land value. Following guidelines may be followed to assess the need of an envelop which contributes significantly to the overall cost of technology (Table 3) Table 3. Guideline to assess the need of an envelop Clay Need (%) > 40 Not Required
• • •
30-40%, SAR > 16
Required
< 30
Required
Farmers tend to stop pumping after the land has been apparently (initially) improved. For sustained success of the technology, pumping should be continued to drain salts added through irrigation water. Irrigation Induced salinity must bee managed at a regional level; master plans must be formulated to devise environmentally safe management strategies of saline drainage effluent. For regional management of irrigation and drainage systems, improved methodologies like EM 38, GIS and remote sensing and mathematical models must be used for integrating on-farm water management with regional stream-aquifer system.
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Lessons for Narmada Command Area Sardar Sarovar Project is an interstate multipurpose project of Gujarat, Madhya Pradesh, Maharastra and Rajasthan in India. Provision of irrigation through this project is resulting in a major change in cropping pattern in Narmada command area with a shift to more water intensive crops like rice, irrigated cotton, sugarcane, wheat and vegetables. Since the hydrology of the command is likely to undergo a sea change with the introduction of irrigation, earnest care and precautions must be undertaken to prevent or slow the development of waterlogging and soil salinity. A major part of Narmada command area belongs to deep black vertisols having more than 35% clay through out the profile and having swelling and cracking characteristics. Vertisols occupy about 27.7 M ha area, which form about 38% of the total black soil area (72.9 M ha) of the country. Vertisols occurring in Maharashtra, Madhya Pradesh, Gujarat, Andhra Pradesh, Karnataka and Tamil Nadu cover about 95% of the vertisols in the country (Table 3); about 8.6% geographical area of Gujarat is occupied with deep black vertisols. Table 3. Geographical area of deep black vertisols in different states State % geographical area under deep black soils Maharashtra M. P. Gujarat A. P. Karnataka
14.1 10.2 8.6 3.3 17.6
Vertisols are associated with the following soil and irrigation related constraints which limit productivity of crops: • • • • •
Much reduced permeability during swollen state resulting in low infiltration and internal drainage Development of perched water table and consequent high moisture (poor aeration) Narrow moisture range for tillage and seeding operations Salinity hazards associated both with rising groundwater and the use of poor quality irrigation water Development of sodic conditions leads to severe structural degradation due to high degree of clay dispersion
These conditions result in excessive soil moisture content in the root zone unless appropriate drainage measures are adopted. The surface drainage seems a better option since subsurface drainage may be economically acceptable under saline groundwater conditions and will require narrow spacing. A number of surface drainage systems like raised and sunken bed system, moderately sloping furrow system, ridge and furrow system and parallel open ditch system have been found to
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be reasonably effective to improve the soil physical conditions during rainy season in moderately sodic black vertisols. It is strongly recommended to study the effectiveness of mole drains, subsoiling and special drainage systems like chimney drains for control of waterlogging and soil salinity in Narmada command area. Adequate care and efforts may be made on the following aspects: • • • • • • •
Reassessment and improvement in regional surface drainage system and maintenance Prioritise area needing or likely to need drainage. In low spots with high WT and on both sides of canals, trees of high transpiration rates may be planted. Rationalize water allowance (delta); introduce automated control system for water distribution Conduct pilot project and test plot studies on drainage and irrigation water management; strengthen monitoring network and analysis Encourage participatory irrigation management through water users / drainage associations through NGOs, mass awareness programmes, training and consultancy. Amend water pricing, subsidiary policies and enforce changes in cropping pattern and groundwater extraction through legislation and incentives. Allocate funds for drainage in irrigation projects
References Achthoven, A.J.van and Lohan, H.S. (1998). The Haryana Operational Pilot Project for the reclamation of waterlogged saline lands of Haryana. In Salinity Management in Agriculture (Ed. S.K. Gupta, S.K. Sharma, N.K. Tyagi), Central Soil Salinity Research Institute, Karnal, 57- 68 pp. Barber, W. (1985). The rising water table and development of waterlogging in Northwestern India. A Drainage Sub-Sector Report, World Bank, Washington, D.C. Garg, S.K. (1993). Fish Culture. In: Salinity Research In H.A.U. (Ed. H.R.Manchanda, S.P.S. Karwasra, H.C. Sharma), C.C.S. Haryana Agricultural University, Hisar- 125004, India, 103- 109. Kamra, S.K., Rao, K.V.G.K., Sharma, D.P. and Kaledhonkar, M.J. (1996). Management of saline drainage water in evaporation ponds. Proceedings of the 6th Drainage Workshop, ICID, Ljubljana (Slovenia), April 21- 29, 1996, 55- 63. Minhas, P.S. and Gupta, R.K. (1992). Quality of Irrigation Water- Assessment and Management. Indian Council of Agricultural Research, New Delhi, 123pp. Singh, Gurbachan (1993). Agroforestry systems for optimal water use in salt affected soils. In: Sustainable Irrigation in Saline Environment (Ed. N.K. Tyagi, S.K. Kamra, P.S. Minhas and N.T.Singh), CSSRI, Karnal, India, 125- 136. United Nations Development Programme (1985). Studies on the use of saline water in command areas of irrigation projects, Haryana, India: Interim technical report (draft) by Haryana Minor Irrigation and Tube well Corporation.
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Manual installation
Mechanical installation Plate 1: Subsurface drainage for amelioration of waterlogged saline soils
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Control of Canal Seepage through Conventional and BioInterceptor Drains Chhedi Lal CSSRI-Regional Research Station, Lucknow-226016 Seepage problem from the water storing structures, canals and other water conveyance systems could be tackled either by restricting the seepage flow through the water bodies or by arresting the seepage water before it joins the ground water in the adjoining areas. Checking or Impeding the Seepage A wide variety of canal lining materials are used throughout the world to reduce seepage losses and making the water distribution more efficient. This provides benefits of an increased potential for cultivated land by increasing the available water resources and recovering areas, which hitherto have suffered due to waterlogging. Linings are used in water containing structures for one or more of the following reasons: • • • • • •
Conserve water Lower maintenance costs, reclaim waterlogged areas Improve water quality Prevent weed growth Stabilize channels and Increased hydraulic capacity of the channel
Types of Lining Lining materials can be grouped into following main categories. • • •
Exposed rigid lining Exposed non-rigid lining Buried membrane lining
Exposed rigid linings: These linings are used extensively in countries where mechanical means of laying have been developed and where the necessary materials are readily available. In most of the cases these linings provide a hard working surface, which can be very smooth. As a result roughness coefficient tends to be low making them efficient in transporting water. Exposed lining includes those, which are subject to wear, erosion and deterioration effect of the flowing water, operation and maintenance equipment and
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other hazards. Such linings are made of concrete and mortar, asphaltic materials, soil cement linings, plaster linings and tile linings etc. Cement concrete lining: There are two main types of concrete linings according to method of construction. • •
Reinforced or un-reinforced cast in-situ Pre-cast concrete slabs
The in-situ concrete lining is one of the most conventional types of lining, which has been used successfully in India. Cement concrete lining is most preferred lining where the channel has to carry water at high velocity (up to 2.5 m/s velocity is considered permissible with adequate water depth). A marked disadvantage of the cement concrete lining is its lack of extensibility, which results in frequent cracks due to contraction. It is also likely to get damaged by the highly alkaline or saline water. Proper sub-grade preparation is essential for all types of concrete lining and a wellcompacted base on to which concrete is laid. Improper sub-grade preparation can lead to settlement and cracks appearing in the lining very quickly. Asphaltic concretes lining: Asphaltic concrete is made by mixing aggregate with an asphaltic cement at elevated temperature. It has two main advantages over cement concrete, • •
An inferior quality aggregate can be used Lining may be placed in cold weather at a time when there is no irrigation demand.
The seepage rate through asphaltic lining depends mainly on the grade of aggregates used and the degree of compaction at the time of laying. The main disadvantages of asphaltic linings are. • • •
Velocity in these lining are limited to 1.5 m/s. There is a danger of sliding during the hot season. Resistance to external hydrostatic pressure is low.
Soil cement lining: This type of lining is made from a mixture of cement and natural sandy soil. The use of soil cement lining is sometimes hampered by the nonavailability of suitable soil. Plaster lining: The lining consists of locally produced plaster materials that may be provided with a protective cover of soil or brick tiles. These lining appears ineffective in reducing seepage. Tile lining: Tile lining is common in Indian subcontinent including Pakistan where labour is relatively inexpensive. Canal lining of this type usually have a cement plaster layer which acts as an impervious barrier and this is either sandwitched
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between two layers of brick tiles or covered by single layer of brick. The exposed brick surface plays little part in preventing seepage because of it’s porous nature but instead acts as a wearing surface and a protective cover for cement layer. Both single and double tile linings have been used extensively for canal linings in India. Single tile lining is generally favoured. A significant amount of data regarding seepage rates from such canals have been published by Indian Irrigation Research Institute which show average seepage rates of 0.03 m/day for double tile lining and 0.05 m/day for single tile types. Experience has shown that the addition of surkhi or kankar lime to the plaster mix can significantly reduce both permeability of the layer and its tendency to crack as result of temperature changes. This has advantage of low initial as well as maintenance costs, quicker construction and natural safeguard against cracking due to closely spaced joints. Exposed non-rigid linings: Asphalt membrane lining: Exposed asphalt membrane for canal lining usually takes the form of prefabricated sheets of up to 15 mm thick with various reinforcing materials. This type of lining may not be economical under normal circumstances due to their short service life. Main causes of failure are of their low resistance to puncture and therefore problem of weed growth, burrowing arrivals and mechanical damage are recorded. Plastic membrane lining: Many types of plastic and synthetic rubber membranes have been successfully adapted for use as lining material. In general they have low resistance to puncture and may be sensitive to sunlight and for these reasons the US Bureau of Reclamation regards them as more suitable for buried lining. In recent years however, various composite lining materials have been produced which have typically a nylon reinforced plastic outer layer, which is combined with membranes such as butyl rubber of polyethylene. The exposed outer mat provides protection for the membrane beneath which acts as the impervious barrier. Plastic membrane is extremely impervious provided they remain intact. Exposed PVC and polyethylene membrane linings have been used experimentally by US Bureau of Reclamation but were found to be generally unsustainable. Compacted earthen lining: Compacted earthen linings are of two types, thick or thin which describes the depth of impervious layer. Thick earth lining has 300 mm of compacted material whilst thin earth lining have 150-300 mm thick compacted earth layer on the bed and side of the canals. Thick earth lining in general is preferred. Thin earth lining has got certain constraints for its use such as low canal velocity to avoid scour and continuous operation of the canal for avoiding frequent drying cycles. The soil type and degree of compaction play an important role in the seepage rates possible from the earth lining. Clay and chemical sealants: Clay particularly bentonite has been used for canal lining successfully. Bentonite has got peculiar characteristic of becoming impervious on
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wetting due to swelling and imbibing of water. As such it is a very useful material for lining if locally available at low cost. It has been used by spreading 2-30 mm or more in thickness over the canal sub-grade and sides and by sedimentation process pores of subgrade is sealed which reduces seepage. Chemical sealants also when added to canal water, it enters into the soil pores and choke them and reduces seepage. Buried membrane linings: Buried membrane lining utilize an impervious and relatively thin material covered by a protective. The protective layer saves the membrane from direct exposure; turbulent water, weeds, maintenance equipment and animal traffics. Generally earth gravels and tiles are used as the protective material. Other materials like shotcrete and asphalt macadam have been used. Buried asphalt membrane lining: This type of lining forms a continuous impervious membrane, which is protected against damage by a soil or gravel coverings. The membrane is placed by spraying a heated high softening point asphalt on to a prepared sub-grade. The thickness of membrane is usually 5-8 mm and when cool a soil cover of about 300 mm is applied. The most common causes of failure particular to this type of lining are. • • •
Non-uniform thickness of membrane. Large rocks or clods piercing the lining and indicating poor sub-grade preparation. Sand and gravel mixed with membrane resulting from poor application of procedure.
Buried precast asphalt lining: Prefabricated asphalt linings are usually thin asphalt coated felts or fibre mats of 3-6 mm thickness. Common reinforcing materials include both organic types such as jute or hemp as well as inorganic types such as fibre glass and asbestos. These are usually supplied in rolls which is spread over the prepared subgrades and the overlapping joints are cemented with hot asphalt a soil cover is then applied to protect the membrane against damage. The buried prefabricated asphalt linings are reported to be prone to damage by temperature during lining. Further organic fibres used for reinforcement are prone to deterioration although inorganic materials have resistance to this. The results seem to indicate a large increase in seepage rate with time. Buried bentonite and clay membrane lining: This is spread as a membrane, 25-50 mm or more in thickness over the canal subgrade and covering with a 15-30 cm protective stable soil cover. If good distribution of particle size is obtained, coarse ground or pit run bentonite may be equally satisfactory, although for comparable results a greater quantity of material is required. Buried plastic film and synthetic rubber membrane lining: These linings include polyvinyl chloride (PVC); low density polyethylene (LDPE), high-density polyethylene (HDPE), butyl rubber polyethylene and coated fabrics. Out of all the types of tested so far, LDPE film appears to be the best. PVC lining has several limitations. It cannot
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be manufactured in wide width and further stability of this film is hampered by the migration of plasticizers, which are essential for extruding flexible PVC film. PVC films are too expensive compared to LDPE film. Due to its higher specific gravity, PVC gives 40% less film for a given weight compared to LDPE film. LDPE film lining which had been tried on experimental basis for the past several years is now extensively used in states like West Bengal, Rajasthan, Madhya Pradesh, Punjab, Haryana and the Irrigation departments of the other states. Arresting Seepage Interception of seepage had been tried by providing interceptor drain(s) along the canal. These drains, sometimes called seepage drains, are normally required on sloping land (over about 10%), along watercourses, or along the canals to control waterlogging in land below as shown in Fig.1. When the barrier is shallow, they should be placed on or close to impermeable layer as practical. Interceptors are required where the slope of the barriers converges with ground surface slope. The drain should normally be located above the wet area to intercept the greatest flow. Sufficient borings should be made to locate the barrier and source of seepage. Although the theory would indicate that the subsurface water should not pass by the drain, bridging may occur. Sealing of surface and variation in hydraulic conductivity can cause water to move past the interceptor. The location of the first drain below a canal where an irrigated field is adjacent to an unlined watercourse can be estimated from a procedure given by USBR (1978). The seepage from the canal, which is based on Darcy’s law for steady state flow is:
q(c) = KD
d(z) X
1
where, q(c) K D d(z) X
= canal seepage when the root zone depth at the edge of the irrigated field is maintained by a drain in m3/d/m length. = weighted hydraulic conductivity between the root zone depth and the barrier in m/d. = average height of the water table between the canal (d+h) and selected root zone depth above the barrier, H in m. = depth of the selected root zone depth at the edge of the irrigated field and water surface in the canal in m, and = distance from the centerline of the canal to the edge of the irrigated field.
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Irrigated fields
X
Centerline of canal
S
Root zone depth, d(z)
d(w)
K zone
h
Water table at beginning of irrigation
H D
drain d
barrier
Figure 1. Definition sketch of interceptor drain
All symbols and dimensions are shown in Fig. 1. The canal is on a hillside with the slope, s (b), and the distance to the first drain can be estimated by
S =K
(H 2 −d 2 ) 2q(c)
+
X
2
where, S R d
= distance from the canal centerline to the first drain in m, = vertical distance from the barrier to the selected root zone depth at the edge of the irrigated field in m, and = vertical distance between the barrier and the drain in m.
Irrigation recharge from the field (S-X) between the canal and the drain should be added to the canal seepage used in computing S from the above equation. The distance, X, must first be determined so as to compute q(d), the flow from the drain. Compute a new value of S to correct for the new flow rate, if necessary. The spacing for additional parallel drains required to maintain the water level at the desired height can be determined from drain spacing equation of level land. These methods give acceptable spacing for slope up to 10%. Playing much with the spacing between first drain and centerline of the canal may not be possible especially when it reaches in the farmer’s field. Researchers have advocated based on studies that if there is no obstruction the first drain should be placed as close to canal as possible. Toe of the embankment is the closest point where first drain can be installed but there may be difficulties while digging trench for laying down the drainpipe or operating heavy machinery for this purpose. About 8-10 m distance may be left out from the canal embankment and there the first drain can be installed. Going far away from the canal will minimize induced seepage and drain 98
discharge. Induced seepage becomes practically negligible small when the distance of the drain from the centerline of the canal is more than 75 m. Maximum interception is excepted when drain is installed in the closest vicinity of the canal. Where intercepted water has to be disposed off in natural outlet or to be pumped for irrigation there should not be any problem as either no energy cost is involved or pumped water is being utilized for irrigation purpose. Higher induced seepage may be useful to cover large area under irrigation. Depth of interceptor drain is more important for controlling the water table position. Shallow drain will not be able to lower the water table below its bottom depth hence depth of interceptor drain should be decided carefully: An example of calculating the spacing of the drain is given below: Problem 1. Determine the distance of the first drain from the centerline of a canal assuming the bottom width of the canal is 3.0 m, the canal side slopes are 2:1, average weighted K = 0.5 m/d, d = 6.1 m, H = 7.65 m; d(z) = 1.2 m, X = 18 m, depth of drain, h = 2.75 m, D = 8.25 m and the deep percolation is 9.4 mm during a period of 14 days between irrigations. Compute the regular spacing below the first drain. Solution 1. 1. Substituting the value of K, D, d(z) and X in Equation (1)
q(c)=KD
d(z) 1.2 =0.5 ×8.25× =0.275m3 /d/m X 18
2. Substituting above value of q(c) in Equation (2) (H2 - d2 ) 7.652 - 6.12 S=K + X=0.5× +18 2 q(c) 2×0.275 =37.4 m 3. Calculate deep percolation from irrigation, q(d), for the field width (S-X) above the drain as given below. q(d) = D .C .× = 9.4 ×
(S - X) 1000 × (Irrigation Interval)
(37.4 - 18) 1000 ×14
= 0.013 m
4. Calculate total q = q(c) + q (d) = 0.275 + 0.013 = 0.288 m3/d/m 5. Calculate second estimate of S by substituting q in Equation (2)
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(H2 - d2 ) (7.652 -6.12 ) + X= 0.5 +18 2 q(d) 2×0.288 (58.5225 -37.21) =0.5 +18 0.576 21.31 = 0.5 +18=36.5m 0.576 Bio-drainage S=K
Bio-drainage is much-debated topic to tackle the waterlogging problems by growing suitable exotic plant species. Bio-drainage had been proposed in some literature for the interception of seepage but no scientific data are available on the topic. How much area should be under bio-drainage to combat the waterlogging or for seepage interception? A design criterion of bio-drainage for seepage interception needs to be developed. Developing design criteria for interceptor drain/belt: How much area should be under bio-drainage to tackle seepage water? Number of trees/ width/ area to be covered under bio-drainage is need to be worked out on some basic criteria. Length of Bio-drainage Belt (L): Length of the canal, which is actually affected with the problem of waterlogging or acute seepage problem needs to be covered under bio-drainage. Establishing a bio-drainage belt in pockets or blocks will not be very effective to create drastic gradient to cause water flow over long distances. Hence the affected length must be covered with bio-drainage.
Width of Bio-drainage Belt (W): Width of the area over which plantation work has to be done is very critical and essential for success of the project. To work out/decide the width of bio-drainage belt canal seepage rate (Q) has to be worked out first. For the measurement of canal seepage available mathematical models (analytical or numerical) or water balance of the area can be done systematically. For large canals steady state seepage rate can be taken for deciding the width of bio-drainage belt. Evapotranspiration rate (ET) of plantations types selected for establishing biodrainage belt need to be available. Making a water balance of the area as under: Width of bio-drainage belt = W, [L] Length of bio-drainage belt = L, [L] Area of bio-drainage belt = W x L, [L2] Evaporation rate of the plant species = ET, [L/T] Volume of water extracted from the soil mass to T = W x L x ET x T meet the ET demand of plant species with in time Canal seepage rate =Q [L3/T] Volume of water seeped with in time T =Q x T [L3] Critical Period for Design: A period when seepage rate is maximum and evapotranspirative demand is minimum is termed as critical period and the width of
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bio-drainage belt should be decided on the basis of water balance analysis of this period. ET for such period can be termed as ETc and seepage as Qc. During the winter season due to low temperature evapotranspirative demand of the crop/plant is quite low. During winter season irrigation demand is also low and consequently supplies level in major canal remains high, which may result in high seepage losses. This period may be treated critical for deciding the width of bio-drainage belt. During the rainy season the water level in canal is also high and water table in the adjoining area also come closer to the ground surface thus simultaneous increase of water level in canal and adjoining area may nullify any increase in seepage rate. During winter season irrigation demand is less and water level in canal may remain high for longer period. During the same period the water table depth below ground surface also remains deeper compared to rainy season. Thus there is increase in effective gradient, which will increase the seepage rate. Evapotranspirative demand during this period is also low and there may be build-up in water table. Therefore winter season may be treated as critical period for deciding the width of bio-drainage belt. It will be more appropriate to analyze water balance specially the monthly seepage and evpotranspiration volume. Select the critical month and calculate width of biodrainage belt using above equation. Water balance for five years will be sufficient. Problem 2. Calculate the area of bio-drainage belt for intercepting canal seepage for the following data set.
1. Seepage rate to be intercepted through bio-drainage interceptor from both side of the canal = 6.8 liter/hour/m canal length. 2. Evapotranspiration rate during most critical period (winter season) = 5 liter per day from an area of 2.25 m2. 3. The length of canal contributing seepage = 3.2 km. 4. Length of canal contributing seepage = 850 m Solution 2. Follow the following steps for the calculation of the bio-drainage belt.
1. Seepage rate to be intercepted from one side of the canal = (6.8 l/h/m)/2 = 0.0034m3/(60x60)s/m = 3.4 x 10-3 x 2.78 x 10-4 m3/s/m = 9.452 x 10-6 m3/m/s. 2. Calculate average evapotranspiration rate from per unit area = (0.005 m3)/(24x60x60) m3/2.25 m2 = 5.0 x 10-3 x = 2.575 x 10-8 m3/m2/s. 3. Calculate width of bio-drainage belt using Equation (10) as below. q 9.452×10-6 W= c = =36.7m@37m ETc 2.575×10-7 4. Length of bio-drainage belt: Bio-drainage is recommended to be established throughout the affected reach of the canal, hence the length of bio-drainage belt is 850 m 5. The area under bio-drainage belt, A = W x L = (37 x 850) m2 = 3.1450 ha.
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Experience of Seepage Interception Interceptor drain: An interceptor drain was designed to capture 0.001204 m3/s seepage rate from a length of 800 m and drain of 1.60 m. Interceptor drain was to be discharged in a open surface drain with an average depth of 1.70 m below ground surface Considering n=0.014 for corrugated PVC drain pipe, seepage discharge Q=0.001204 m3/sec for 800 m length of seepage drain (whole discharge) and slope, S = 0.00031 and using Manning Equation drain diameter was calculated. Therefore the drain diameter becomes 11.42 cm. Pipe of this diameter was not available in the market. Nearest size available in the market is 144 mm, which may be used for installation.
Installation of 144 mm internal diameter pipe may be expensive if installed in whole reach of 800 m. To economize the interceptor drainage system pipe diameter should be calculated for two different reaches. Lower 400 m reach diameter is already calculated which is 144 mm. The discharge for upper 400 m reach will become (1/2)Q. Substituting the value seepage rate, slope and Manning’s roughness coefficient in above equation one will obtain a radius of 80 mm. Nearest diameter available in the market is 88 mm. In the upper 400 m reach 88 mm diameter drainpipe and lower 400 m reach 144 mm diameter drainpipe was installed during June 2003. Synthetic filter: Geo-textile filter of 3.5 mm ± 0.3 mm thick & opening (O90) 300 micron ± 10% was sleeved over the perforated PVC drain pipe manually prior to installation. At the joints the filter was overlapped and tied with the plastic rope to avoid slippage and entry of soil inside the pipe. A 10 cm sand layer was again placed over the pipe to avoid any choking of filter in sodic soil Seepage interception: Volumetric flow rate of intercepted seepage was measured directly from the interceptor pipe and open drains. Variation of water depth flowing in the canal and amount of seepage water arrested by the interceptor drain is shown in Fig.2. A power form relationship explained the variation of seepage water arrested by the drain and the depth of flowing water in the canal. Qdrain = 1837.2 H0.8072 11 [R2 = 0.9448] where, Qdrain = intercepted seepage flow rate liter per hour H = Depth of water in canal, m Water balance: Amount of seepage water arrested during different months from June 2004 to May 2005 is shown in Fig.3. Maximum volume of seepage water of 4825 m3 arrested during the month of March 2005. Minimum seepage was arrested during the rainy season. Actually due to high water level conditions in main open drain, interceptor drains became nonfunctional during rainy season.
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Figure 2. Variation of seepage rate with canal water depth.
Figure 3. Variation of seepage interception during different months. 5000 4500
Seepage volume, cu. m
4000 3500 3000 2500 2000 1500 1000 500 0 Jun. 04
Aug. 04
Oct.04
Dec.04
Feb. 05
Aprl. 05
Months
Figure 3. Variation of seepage interception during different months
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Open interceptor drain arrested maximum volume of seepage water of 5867 m3 during the month December 2004. Minimum seepage of 1102 m3 was intercepted during May 2004. Overall maximum seepage water of 7510 m3 was intercepted during January 2004 and 9344 m3 during January 2005 from both pipe drain and open drain interceptors. Total volume of seepage water arrested during first year of installation was measured to be 24084 m3 and 25781 m3 during the second year of installation of interceptor drain. Thus total volume of seepage water arrested through interceptor drain within two years of installation became 49865 m3. Total volume of seepage water intercepted by open drain was 14122 m3 for first year and 20844 m3 for second year of digging of drain thus making total volume of 34966 m3. Bio-drainage Interceptor Establishing bio-drainage belt: A bio-drainage belt of 1.2 ha area (400 m long and 30 m wide) was established during the March 2005. Row to row and plant-to-plant spacing was kept as 1.5 m. In one line 20 eucalyptus plants were planted using auger hole method of plantation. A power auger (tractor mounted) was used to dig a circular hole of 300 mm diameter in the soil to a depth of 600 mm from the soil surface. An input mixture was prepared by mixing 5 kg of gypsum, 5 kg of farmyard manure (FYM) and 10 kg of sand from the canal bed. After thorough mixing of basic ingredients, the homogeneous input mixture was filled in the dugout holes/pits. Biodrainage belt had a satisfactory growth up to two years but declined thereafter. Fig.4 shows the quarterly growth of plant heights of selected lines.
Figure 4. Quarterly growth of average plant heights of selected lines
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Plant water uptake: Four metallic lysimeters were installed for measuring plant water uptake. The average daily water uptake of the eucalyptus plant were measured to be 5.53, 3.50, 3.37, 5.57, 2.97, 2.63, 2.73, 4.61, 8.91, 11.67, 14.34, 21.76 liter/day/plant in the respective months from April 2004 to June 2005. Seepage interception: The range of water uptake by the bio-drainage belt was 34.859.1 mm during July to October 2004. The monthly water uptake during the month of November to February was 30.1-42.3 mm. Maximum water depth was extracted during the summer season i.e. from March 2005 to June 2005. Monthly water uptake ranged 90.5-141.9 mm from March 2005 to May 2005. The bio-drainage belt intercepted the highest depth of water (208.5 mm) during the month of June 2005. The total depth of water annually extracted by the bio-drainage belt comes out to be 880.8 mm from three years old plantation belt. Conclusions
Canal seepage can be controlled either through provision of some sort of living to prevent conveyance losses or arresting seepage losses before it joins the ground water. Advantages and disadvantages of different types of living have been discussed in details. Seepage water can be arrested by interceptor drain or biodrainage. The design and installation of interceptor drain have been explained with help of field study. Similarly methodology to estimate width and length of tree belt under bio-drainage has been developed and implemented for testing its feasibility. Bibliography
Lal,
Cheddi (2005). Develop design criteria of interceptor drain for preventing/minimizing waterlogging in areas along major canals. Progress during 2004-05 (Personal communication) Kapoor, A.S. (2000). Bio-drainage feasibility and principles of planning and design. Proc. 8th ICID int. Drainage Workshop, New Delhi. ICID, New Delhi. Vol. IV: 17-32. Manjunatha, M.V., Hebbara, M., Patil, S.G., Kuligod, V.B. and Minhas, P.S. (2000). Effect of tree plantation in control of canal seepage and shallow water table in saline Vertisols. National Seminar Environmental Pollution and management, Dharwad.
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Crop Tolerance to Waterlogging and Salinity Stress and Strategies for Conjunctive Water Use D. P. Sharma Central Soil Salinity Research Institute, Karnal - 132 001
The plants differ widely for the tolerance of different kind of stresses from sensitive ones, whose normal growth is inhibited by low stress to the most resistant, which grow profusely in different kind of stress conditions. Crop plants even exhibit differences in their resistance to water stagnation, salinity and salinity of the irrigation water. Four criteria are generally followed to evaluate comparative tolerance of crops to different kind of stresses: Germination of crops, Plant survival, Absolute plant growth or yield and Relative growth or yield. Large numbers of investigations on differential response of crops or varieties have been reported at germination stage and attempts made to extrapolate the tolerance limit for final performance. More than often-such attempts are likely to be frustrating because tolerance characteristics differ from one stage of growth to another. Plant survival has been used as a criterion by ecologists but without yield, plant survival alone has little value to the farmer. On the other hand, it can be useful criterion for plant breeders. Absolute plant growth or yield is of greatest interest to the farmers. However, this criterion does not permit comparison between crops because yields for different crops are not expressed in comparable terms. The relative growth or yield is defined as the yield on saline and waterlogged soils as a fraction of the yield on a non-saline/waterlogged soil under similar environment and nutritional conditions. This criterion is reliable provided the level of other essential factors such as nutritional factor or water does not affect yield reductions. The main difficulty with this method, however, is to decide at what level of yield reduction, different plants should be compared. A researcher comparing the salt tolerance at 10 % yield reduction may essentially end up differently than the other who is comparing the salt tolerance at 50 % yield reduction. Nevertheless, this criterion is favoured world over and is widely used for relative comparison. In addition to these four criteria, attempts have also been made to evolve a criterion based on metabolic parameters. Conjunctive use is defined as the use of limited quantity of fresh water most judiciously in combination with poor quality saline sodic waters. In general, the cyclic and mixing modes are two options for conjunctive use. Various strategies have been proposed to use various quality waters for irrigation of crops. Selection of a particular strategy depends upon the quality of irrigation water, soil type, crops to be irrigated and the agro-climatic conditions. Conjunctive use of such waters is more practical in areas where non-saline/sodic water is available during the early growing season but limited in supply to meet the crop water requirements for the entire irrigation season. In arid and semi-arid regions, underground waters are of poor quality and supply of fresh canal water is not sufficient to meet the irrigation requirements of the entire area. In such situations the conjunctive use of different quality waters may be useful for crop
106
production. This lecture summarize the effects of stress due to waterlogging and soil salinity and some strategies for conjunctive water use. Stress due to Surface Water Stagnation
Surface stagnation of rain/irrigation water in the croplands is assuming a serious dimension as a result of unplanned implementation of development projects, rising water table in irrigation commands, unrealistic drainage system design and inadequate maintenance of the drainage systems. The problem is even more severe in alkali lands under reclamation, where water continues to stand on the land surface for more duration than the normal lands. High sodium concentrations and high pH impart adverse soil physical properties leading to poor air-water relationships. Application of gypsum (CaSO4.2H2O and continuous cropping for 2-3 years result in the improvement of surface soil layers, but subsoil layers continue to exhibit poor water penetration, low water storage and limited water movement through the layers (Sharma, 1986). Most crops not adapted to wetland conditions receive a severe setback when water stagnates even for a short period. The extent of damage or yield reduction as a result of water stagnation depends upon the crop and its growth stage, duration of water stagnation/flooding, type of soil and prevailing agro-climatic conditions. In alkali soils where the problem of water stagnation is more acute after irrigation or rains, one can cite only a few experimental evidence that have been gathered in the past years to quantify the yield loss as a result of water stagnation (Sharma and Swarup, 1988, 1989b). To evaluate the effects of water stagnation on growth several crops, several field experiments were conducted at Karnal. The soils of this site were initially highly sodic but after the addition of gypsum and continuous rice-wheat cropping, the pH2 and ESP of the soils decreased in the range of 8.6-8.8 and 22-25, respectively in 030 cm soil depth. These crops were cultivated following recommended package and practices. Water stagnation treatments were applied at different crop growth stages for different period. In the drained treatment, excess water was drained in a drainage channel 12 hour after irrigation, in the second, third, fourth and fifth treatments, irrigation water was allowed to stand for 1, 2, 4 and 6 days, respectively. During the water stagnation period and thereafter, oxygen diffusion rates (ODR) were measured daily with an oxygen diffusion rate meter at a depth of 15 cm. Root and plant samples were analyzed for different nutrients. Surface water stagnation for 1, 2, 4 and 6 days reduced plant growth parameters, yield and yield components of different crops. The data in general reveal that water stagnation for more than one day is harmful to various crops (Table 1). It has also been shown that the adverse effects of water stagnation are relatively more when water stagnation occurs at the early growth stages than at the latter. Water stagnation decreased ODR and reduced ion uptake, especially of N, P, K, Zn, Cu and increased the absorption of Na, Fe and Mn. The general pattern of ODR depletion following water stagnation showed that in these soils, values were not only lower than the drained plots but low ODR values persisted for longer duration resulting in lower yield. It is believed that poor aeration due to water stagnation and imbalance in the nutrient uptake might have caused yield 107
reduction of the crops, although several other factors such as reduced root growth, ionic imbalance and/or nutrient stress might have contributed to the overall decline in the yield. Nitrogen deficiency triggered by flooding is considered to be an important cause of low yields (Swarup and Sharma, 1993). Studies have also shown that increasing the rate of top-dressed urea-N (50-75%) after water stagnation helps in alleviating the adverse effects of temporary water stagnation. Supplementing N also promoted uptake of N, P, K, Zn. Since, such a strategy cannot be adopted on large scale, it cannot be recommended as a long-term solution of the problem. The results of these studies clearly indicated that to ensure optimum yield of crops in partially reclaimed sodic soils excess irrigation water must be drained within one day of irrigation or rains. An integrated drainage system would be the most cost-effective and eco-friendly solution of the problem. A review of the available data on the yield of various crops as a function of water stagnation was made. The application of the Maas and Hoffman model yielded the threshold and slope values as reported in Table 2 (Gupta et al., 1992; Fig.1) It may be seen that in most cases the threshold is less than 1 day and decline in yield from 4.5% to 23% for each additional day of water stagnation. Table 1. Response of various crops to short-term water stagnation Duration of Grain yield (Mg/ha) water stagnation (days) Wheat Barley Mustard Pearl Sunflower millet Drained 4.41 3.65 1.43 2.22 1.86
Pigeon pea 1.41
1
3.70
3.52
1.31
2.08
1.62
1.35
2
3.63
3.39
1.20
1.89
1.50
1.22
4
3.13
3.18
1.12
1.74
1.38
1.16
6
2.35
2.75
1.02
1.63
1.29
1.11
CD (p = 0.05)
0.28
0.28
0.22
0.12
0.06
0.13
Vegetative
--
3.22
1.11
1.90
1.51
1.17
Flowering
--
3.37
1.32
1.98
1.55
1.34
CD (p = 0.05)
--
NS
0.14
0.10
0.04
0.10
Growth stages:
*
Vegetative : Flowering stages :: Barley - 25 : 65; Mustard - 30 :60; Sunflower - 50 : 80; Pigeon pea - 35 : 75; Pearl millet - 25 : 50 Days after sowing) (Source: Sharma & Swarup, 1988; Sharma & Swarup, 1989b; Singh et al., 2002, 2003; Thakur et al. 2003; Sharma et al., 2005)
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Table 2. Water stagnation tolerance of various crops at different locations in India Site Crop Water stagnation tolerance indices Threshold (days) Slope (%) DWS50 (days) Delhi Pigeon pea 1.6 23.2 3.8 Hisar Karnal
Ludhiana
Cow pea
0.8
6.6
8.4
Pigeon pea
0.5
9.2
6.0
Wheat
0.0
7.0
7.2
Barley
1.0
4.4
12.2
Mustard
0.5
6.8
7.9
Pearl millet
0.0
5.3
9.4
Wheat
1.9
9.2
7.3
Stress due to High Water Table
Since the soil is the living place for plant roots, soil environment characterized in term of salt and water regimes, soil aeration, temperature and soil tilth determine the crop growth. Although, the depth of water table has no direct effect on crop growth, but it indirectly effects crop growth by influencing the soil adaphic environment. Crop yields are often affected due to high water tables. For many crops and soils, it is considered desirable to have a depth to the water table at least 80 cm. However, shallow water table may not always be a curse, particularly when it is free from salinity hazard, as is the case in most humid regions. Water table contributes substantially towards the crop evapotranspiration. On the other hand, shallow water table causes the hazard of soil salinization, especially where the ground waters are brackish and potential evaporation is high. The gradual and irreversible salinization of the soil may have been the process responsible for the destruction of once thriving agricultural civilizations. The presence of water table at the soil surface or near/within the root zone, replaces air in the soil pores leading to an O2 deficiency. Oxygen deficiency affects the root growth and nutrients uptake by the growing plants. The optimum water table depth for various crops in non-saline areas is given in Table 3. Table 3. Optimum depth of water table for various crops in non-saline areas Crop Depth of water Crop Depth of water table table (cm) (cm) Soybean 125 Rice ≤ 30 Wheat
60
Gram
90
Barley
90
Maize
120
Sugarcane
60
Cotton
125
Cowpea
75
Pearl millet
125
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Water table affects O2 supply to the growing plants and nutrient uptake. For an example oxygen content of a heavy soil at depth of 23 cm was sharply reduced as the water table was raised from 90 to 30 cm depth and the cotton yield and nutrient uptake were decreased accordingly (Table 4). Table 4. Effect of water table depth on O2 content of soil air, yield and nutrient uptake Nutrient uptake by 5 plants (mg) Water table O2 at 23 cm (%) Cotton yield (g) N P K depth (cm) 30 1.6 57 724 85 1091 60
8.3
108
1414
120
2069
90
13.2
157
2292
156
3174
(Source: Meek et al., 1980) Stress due to Excess Salts in the Root Zone on Plant Growth
Excess salinity affects crop growth in three ways. First and most important, as the amount of salts increases, the water in the soil becomes less available to the plants even though the soil may appear quite moist. This is because the osmotic pressure of the soil solution increases with the increase in salt concentration and the plants are unable to extract water as readily as they can from a relatively non-saline soil. In addition to the osmotic effect of salts in the soil solution, at high concentration, absorption of an individual ion may prove toxic to the plants. Besides preferential absorption of one ion may also retard the absorption of other essential plant nutrients necessary for the normal growth of plants. It is believed that the adverse effects are usually due to cumulative effects of these factors although one may be dominating others in many cases. In many cases salinity problem occurs along with the problem of alkali. It is particularly true in the case of saline-alkali soils. Therefore, crop selection in such cases may have to be made on the basis of tolerance to soil salinity than alkali. The yield reductions due to excessive salts could be ascribed to the following three factors, which may influence plants singly or in combination: • A general osmotic effect in which growth and yield are determined by the osmotic pressure of the medium. • Imbalance in the uptake of ions • Toxic effects on specific plants due to accumulation of the causative ions. Since crops differ in their tolerance to salinity, selection of crops and cropping sequences for saline soils assumes significance in the overall management of saline soils. The selection of the first crop, therefore, will depend upon the degree of soil salinity after the basic reclamation measures such as land drainage; field levelling, bunding and leaching have been implemented. Since complete reclamation is not attained in the initial years, tolerant or semi-tolerant crops that can withstand expected salinity levels are preferred in the early phase of reclamation (Table 5).
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Table 5. Crop groups based on response to salt stress Resistant Group Sensitive Group ------------------------------------------------------------------------------Medium tolerant Highly tolerant Highly sensitive Medium sensitive Lentil Radish Spinach Barley Mash
Cow pea
Sugarcane
Rice (transplanted)
Chickpea
Broad bean
Indian mustard
Cotton
Beans
Vetch
Rice (direct sowing)
Sugar beet
Peas
Cabbage
Wheat
Turnip
Carrot
Cauliflower
Pearl millet
Tobacco
Onion
Cucumber
Oats
Safflower
Lemon
Gourds
Alfalfa
Taramira
Orange
Tomato
Blue panic grass
Karnal grass
Grape
Sweet potato
Para grass
Date palm
Peach
Sorghum
Rhodes grass
Ber
Plum
Minor millets
Sudan grass
Mesquite
Pear
Maize
Guava
Casuarina
Apple
Clover, berseem
Pomegranate
Tamarix
In arid and semi-arid regions of northwest India, the recommended cropping sequences for saline soils are pearl millet-barley, pearl millet-wheat, pearl milletmustard, sorghum-wheat or barley, sorghum-mustard, cluster bean-wheat or barley and cotton-wheat or barley. Pearl millet-wheat, pearl millet-barley, pearl milletmustard, sorghum (fodder)-wheat and sorghum (fodder)-mustard sequences are more remunerative in saline soils. Cotton based cropping sequences are not beneficial since the yield of the winter crops that follow cotton was low. In areas with water scarcity, mustard could replace wheat in the cropping sequence since its water requirement is low compared to wheat. Maas and Hoffman (1977) prepared a comprehensive table listing ECt, slope and ECo of many crops utilizing the piecewise linear model. Such comprehensive data for Indian conditions is lacking. Gupta (1992) collated the existing information on this subject and determined ECt, slope and ECo for several crops and soil/climatic conditions (Table 6). More comprehensive data are available for the Indian conditions in respect of crop tolerance to irrigation with saline water. Gupta and Yadav (1986) based on a review of the experimental evidence reported the critical limits of salinity of the irrigation water at which yield would decline by 10, 25 and 50 % of optimum yield that is expected with fresh water. The relative crop tolerance of wheat to salinity at Gohana is depicted in Fig. 2. Such data could be made use of in working out tolerance of a crop to soil salinity provided leaching fractions could be properly estimated.
111
Table 6. Crop tolerance to soil salinity for working out leaching requirement Slits Soil type Crop Threshold ES Slope (%) EC50 (dS m-1) (dS m-1) 5.7 29.0 4.0 Sample Sandy Wheat 9.3 15.0 6.0 loam Mustard 9.6 19.0 7.0 Barley 3.3 20.7 1.8 Karnal Sandy Green gram 11.0 6.9 3.8 loam bean 6.9 10.6 2.2 Mustard Sorghum Agra Sandy Wheat 8.2 19.8 10.7 loam Mustard 6.1 20.7 8.5 Berseem 3.5 12.5 7.5 Tomato 1.3 6.5 9.0 4.7 20.5 2.3 Dharwad Black clay Wheat 5.2 20.7 2.8 Safflower 14.9 3.9 2.1 Sorghum (w) 7.1 50.0 6.1 Itallian Millet 4.7 20.5 2.3 Indore Black clay Berseem 5.2 20.7 2.8 Safflower 14.9 3.9 2.1 Sorghum (w) 7.1 50.0 6.1 Italian millet 23.9 2.2 1.1 Sataria 6.5 11.2 2.0 Indore Black clay Berseem 12.8 5.0 2.8 Safflower 6.8 7.9 0.5 Maize Strategies for Conjunctive Use of Water
With the increasing problems of disposal of saline drainage water and expanding demands on high quality water for other purposes, reuse of saline drainage water for crop production has gained recognition. Results of various studies have indicated a potential for the reuse of saline drainage water for crop production. Various strategies can be adopted to use such water for irrigation. In arid and semi-arid regions, under ground waters are of poor quality and supply of fresh canal water is not sufficient to meet the irrigation requirements of the entire area. In such situations the reuse of saline drainage water may be useful for crop production. Several options are available for the reuse of drainage water in conjunction with good quality water. Some feasible alternatives are discussed in the following sections: Use of blended water for irrigation: Drainage water of higher salinities cannot be reused directly for crop production. Blending involves mixing two waters of different qualities to obtain water that is suitable for irrigation. The salinity attained after mixing should be within the permissible limits, based on soil type, crop to be grown and climate of the area. To use the blending strategy, a controlled way of mixing the water supplies must exist.
112
Figure 1. Relative tolerance of 3 rabi crops to surface stagnation
Figure 2. Effect of soil salinity on wheat yield at Gohana. Note the breakpoint at 4.5 dSm-1
113
Blended drainage water reuse was studied at Sampla location (Haryana) where a subsurface drainage system was installed at a depth of 1.75 m. Blended saline drainage water of different salinities (3, 6, 9, 12 and 18 dS/m) was used for all and only for post-plant irrigations of wheat (Table 7). Our results in a monsoon climate are consistent with the concept that both salt sensitive and salt tolerant crops can be grown in rotation if the non-saline water is used for irrigating the succeeding crops. Table 7. Mean relative grain yield of wheat and succeeding pearl millet and sorghum crops as affected by different salinity levels of post-sowing irrigation EC (dS/m) of irrigation water Wheat Pearl millet Sorghum fodder (%) (%) (%) 0.5 (Canal water) 100 100 100 6.0 (Blended drainage water)
95.8
98.0
96.1
9.0 (Blended drainage water)
90.3
94.1
90.1
12.0 (Blended drainage water)
83.7
86.3
80.3
18.8 (Blended drainage water)
77.8
77.3
70.4
(Source: Sharma and Tyagi, 2004)
Cyclic or rotational use of two waters: The cyclic use, also known, as sequential application or rotational mode is a technique, which facilitates conjunctive use of fresh and saline drainage effluent. In this mode, canal water is replaced with saline drainage water in a predicated sequence/cycle. Cyclic strategy has an advantage of unsteady state salinity conditions in the soil profile. This strategy may work better in arid climates with very low rainfall but it is of natural occurrence under the monsoon climate. Cyclic use of saline drainage water (ECiw 10.5-15.0 dS/m) and canal waters were used in pearl millet/sorghum-wheat rotation supported the suitability the strategy where canal water was used for pre-plant irrigation (Sharma et al., 1994). Pearl millet and sorghum received no further irrigation than monsoon rains in the season (Table 8).
Table 8. Mean relative grain yields of wheat and succeeding pearl millet and sorghum crops as affected by various cyclic modes of post-plant irrigations Mode of water application Wheat Pearl millet Sorghum fodder (CW-Canal, DW-Drainage Waters) (%) (%) (%) 4 CW 100 100 100 CW : DW (alternate)
94.4
97.0
91.8
DW : CW (alternate)
91.3
95.5
91.1
2 CW + 2 DW
94.3
96.4
92.8
2 DW + 2 CW
88.2
94.9
91.1
1 CW + 3 DW
83.6
91.9
87.2
4 DW
73.7
85.0
78.7
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Management Practices for Use of Poor Quality Waters
When using saline drainage water for irrigation many suitable management practices should be considered. An approach with rigid criteria will not be practical, since most management decisions are subjective and innumerable combinations exist. The management practices which are to be followed for optimal crop production, must aim at preventing the build up of salinity, sodicity and toxic ions in the root zone to level that limit the productivity of soils, control the salt balances in soil-water system as well as minimize the damaging effects of salinity on crop growth. The following practices are suggested: • • • • •
Availability of waters Analysis of poor quality water Crop substitution Pre-sowing irrigation Alternate area/Area switching
Salt Build-up in the Profile
When using saline drainage effluent for irrigation, the salt concentrates in the soil solution due to evapotranspiration and may accumulate in the soil. But if the salt accumulation does not exceed the threshold value of crop salt tolerance in the root zone, the crops will grow normally. Soil salinity was monitored in different studies, indicated that soil profile salinity increased with the increasing salinity of irrigation water (Sharma and Rao 1998). Observations indicated that salt build up did not occur over the years and much of the salts that were added during irrigation are leached out of the soil profile with the monsoon rains. This downward leaching of salts reduced the salinity levels within acceptable limits for good germination of next wheat crop. The leaching of soluble salts under the prevailing conditions was brought about by rainwater and a preplant irrigation and no extra irrigation water was applied for leaching of salts. If the monsoon rainfall is not sufficient for leaching the salts in the profile, in such cases a heavy (7-10 cm) pre-plant irrigation with canal water should be applied. The salinity profiles, measured before and after the monsoon rains, were used to develop a relation between salt removal and rain- water depth. The relations indicate that for the removal of 80% accumulated salts, build-up by the irrigation of 6, 9, and 12 dS/m salinity water, 0.51, 0.76 and 0.92 m of rain water per meter depth of soil will be required. The average annual rainfall of Sampla area during the past 15 years was 637 mm. This amount of rainfall and pre-sowing irrigations with canal water should keep the root zone salinity with in acceptable limits. In the areas provided with subsurface drainage system, the dynamics of soil salinity in the root zone is such that long- term salt accumulation will not occur and soil salinity will be controlled within crops salt tolerance limits. If some salts accumulate in the subsoil after 5-6 years, canal water should be used for irrigation for one or two years to prevent any salt accumulation at the lower depths.
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Long-term Effects on Soil Properties
Several studies have suggested that irrigation water containing salt concentrations exceeding conventional suitability standards can be used successfully on many crops for at least 6-7 years without a loss in yield. However, uncertainty still exists about the long-term effects of these practices. Long-term effects on soil could include soil dispersion, crusting, reduced water infiltration capacity and accumulation of toxic elements. The magnitude of these effects will, however depends on the quality of drainage water. Effects of irrigation with high salinity drainage effluent as available at Sampla drainage project area were monitored for six years on some soil properties (Sharma and Rao, 1998). Leaching of salts by monsoon rains reduced SARe and the remaining SARe values did not cause any alkali hazard to the succeeding crops. Similarly, no significant adverse effects were observed on saturated hydraulic conductivity and water dispersible clay after the monsoon rains. A slight decrease in hydraulic conductivity after monsoon leaching will not be a problem during the irrigation season since the negative effects of high SAR of drainage water is offset by the high salinity of the drainage water. Only slight variation in water dispersible clay after 6 years of irrigation with drainage water indicates minimum structural deterioration in soils irrigated with high salinity drainage water. Bibliography
Gupta, S.K. (1992). Leaching of saline soils. Bull. 17, CSSRI, Karnal. Gupta, S. K., Sharma, D. P., Tyagi, N. K. and Dubey, S. K. (2002). LavaniyaAkashriya Maridayon Ka Sudhar Avam Parbandh, CSSRI, Karnal, 152 p. Gupta, S.K., Singh, R.K. and Pandey, R.S. (1992). Surface drainage requirement of crops: Application of a piecewise linear model for evaluating submergence tolerance. Irrigation and Drainage Systems. 6:249-261. Maas, E. V. and Hoffman, G.J. 1977. Crop salt tolerant: Current assessment. Journal Irrigation Drainage Division, ASCE, 103 (IR): 115-34. Meek, B. P. et al. (1980). Cotton yield and nutrient uptake in relation to water table depth. Soil Science Society American Journal, 44 : 301-305. Sharma, D. P. (1986). Effect of gypsum application on long-term changes in soil properties and crop growth in sodic soils under field conditions. Journal Agronomy Crop Sciences, 156:166-172. Sharma, D. P. and Swarup, A. (1988). Effect of short-term flooding on growth, yield and mineral composition of wheat in a sodic soil under field conditions. Plant and Soil, 107: 137-143. Sharma, D.P. and Swarup, A. (1989). Response of pearl millet to short-term flooding in a moderately sodic soil under field condition. Journal Agricultural Sciences (Camb.),113: 331-337. Sharma D.P., Singh, K.N., Rao, K.V.G.K.and Kumbhare P.S. (1991). Irrigation of wheat with saline drainage water on a sandy loam soil. Agricultural Water Management, 19: 223-233.
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Sharma, D.P., Rao, K.V.G.K., Singh, K.N. and Kumbhare, P.S. (1994). Conjunctive use of saline and non-saline irrigation waters in semi -arid regions. Irrigation Science, 15: 25-33 Sharma, D. P. and Rao, K.V.G.K. (1998). Strategy for long term use of saline drainage water for irrigation in semi-arid regions. Soil and Tillage Research, 48: 287295. Sharma, D. P. and Tyagi, N. K. (2004). On farm management of saline drainage water in arid and semi-arid regions. Irrigation and Drainage, 53:87-103. Sharma, D. P., Singh, K. N. and Kumbhare, P. S. (2005). Response of sunflower to conjunctive use of saline drainage water and non-saline canal water irrigation. Archives of Agronomy and Soil Science, 51: 91-100. Sharma, D. P., Singh, M. P., Gupta, S. K. and Sharma, N. L. (2005). Response of pigeon pea to short-term water stagnation in a moderately sodic soil under field condition. Journal Indian Society Soil Science., 53: 243-248. Singh, M. P., Sharma, D. P., Gupta, S. K. and Sharma, N. L. (2002). Effect of time and duration of water stagnation on growth, yield and mineral composition of sunflower in a gypsum amended alkali soil. Current. Agriculture, 26:23-29. Singh, M. P., Sharma, D. P., Gupta, S.K. and Sharma, N. L. (2003). Response of sunflower to top-dressed nitrogen after short-term water stagnation in a gypsum amended alkali soil. Journal Water Management, 11:60-67. Swarup, A. and Sharma, D. P. (1993). Influence of top-dressed nitrogen in alleviating the adverse effects of flooding on growth and yield of wheat in a sodic soil. Field Crop Research., 35: 93-100. Thakur, N. K., Gupta, S. K., Sharma, D. P., Swarup, A. and Panda, S. N. (2003). A comparative assessment of tolerance of three rabi crops to water stagnation on soil surface. Journal Indian Society. Soil. Science, 51: 554-556.
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Drip Irrigation with Marginal Quality Land and Waters R. S. Pandey and C. K. Saxena Central Soil Salinity Research Institute, Karnal - 132001
Per capita land and water resources are decreasing at a very fast rate. These resources are also being degraded mainly due to unmanaged overexploitation in the wake of resource exploiting green revolution. Per capita land resource has decreased from 0.33 ha in 1951 to 0.13 ha in 2001. Similarly, per capita water availability assessed at more than 5300 m3 in 1951 had decreased to 1905 m3 in 1999 and is likely to be less than 1500 m3 by the year 2025. Therefore, to conserve water resource and to utilize salt affected land resource in a most productive manner, improved irrigation techniques including drip irrigation would play a very prominent role. Though the land area is constant like water, there is scope for utilizing the same in an intensified manner in project commands and rainfed areas to increase the production. Further, this can also be achieved by reclaiming the fallow, barren and uncultivable lands. All this would need water and hence optimum use of available water is very crucial. Research experiments on drip irrigation in India were initiated in the early seventies in many state agricultural universities and research organizations. The spread was quite fast during the last decade, when its coverage touched 0.3 M ha (Table 1). The highest coverage is in the state of Maharashtra followed by Karnataka, Tamil Nadu, Andhra Pradesh and Rajasthan. According to Sivanappan (1999) about 28.5 m ha could be covered under drip irrigation, which is likely to be achieved by the year 2020/25. However, at a annual compound growth rate of adoption of drip irrigation assessed at present at 12 per cent, it would take about 8 years to bring additional one M ha area under drip irrigation. Table 1: Growth of area (in thousand ha) under drip irrigation, India Year 1970 1985 1989 1994 1999 Area (,000) ha
Nil
1.5
12.0
70.9
300.0
2002 355.4
(Source: Kumar and Singh, 2002; Rao, 2002)
Inland and Coastal Salt Affected Soils
The extent of salt affected soils has been worked out by adding the figures obtained with the help of data base of the institute, literature survey, contact with various organizations for information and looking at various reports on land reclamation in states on latest figures of the waterlogged salt affected lands, the assessment of the coastal salt affected soil is 2.992 (≈3.0) m ha without area under mangrove and 3.667 m ha with area under mangrove (Gupta, 2005). It was reported that the total salt affected areas in the country were worked out after reconciling the 118
data from several sources. Total inland salinity is spread over an area of 5.407 m ha. The total area with coastal salinity and including area under the mangrove is 9.084 m ha. If the mangrove area is excluded than the area is 8.4 m ha. Marginal Quality Waters and Its Classification
State wise ground water potential, ground water utilization and percentage distribution of poor quality waters are shown in Table 2. Results of the survey of poor quality waters in the arid and semi-arid regions of the country indicate that they are used to the extent of 25 to 84% of the total ground water developed so far for irrigation. Estimate suggests that of the present ground water development of 13.5 m ha-m/year, poor quality ground water account for about 3.2 m ha-m/year. Irrigation with poor quality ground waters may cause salinity, specific ion toxicity or infiltration problem in soils. Such effects of irrigation may adversely affect crop production. Based on the characteristics of ground water in use with the farmers in different agroecological regions and the indices with their salinity, sodicity/alkalinity hazards on soils and crops, poor quality ground water can be broadly grouped into two categories of saline and alkaline waters (Table 3). Apart from salinity and alkalinity problems, ground water bodies may also face local pollution problem due to excessive amounts of specific ions such as nitrate, fluoride or toxic heavy metal etc. Table 2. State wise ground water potential, utilization and percentage distribution of poor quality waters in M ha-m /year State Utilizable Net Potential Low quality % Low quality ground water draught available ground use waters Punjab 1.31 0.93 0.36 0.38 41 Haryana
0.88
0.61
0.27
0.38
62
U. P.
9.27
2.68
6.59
1.28
47
Gujarat
2.03
0.69
1.34
0.21
30
Rajasthan
1.83
0.46
1.37
0.39
84
M. P.
5.95
0.79
5.46
0.20
25
Karnatka
1.30
0.18
1.12
0.07
38
Maharastra
3.45
0.66
2.80
-
-
Tamil Nadu
2.69
0.99
1.70
-
-
A. P.
3.66
0.74
2.92
0.24
32
Bihar
2.86
0.69
1.34
-
-
Others
2.15
0.09
2.06
-
-
41.85
13.50
28.35
-
-
Total
(Source: Ministry of Water Resources, GoI, 1988; adapted from Minhas and Gupta, 1992)
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Table 3 Grouping of poor quality ground waters Water quality Eciw SARiw (mmole/l)1/2 (dS/m) A. Good 0, we choose a higher discount rate (accept the project viability) and NPW8 dS/m. About 44% and 32% area respectively in Kolekhan and Bhana Brahmana had ECe >8 dS/m. About 23-34 % area in Kalayat had ECe between 4 and 8 dS/m and 14 % between 8 and 12 dS/m and the rest had an ECe, 4dS/m. Besides this, ECe at highly saline spots was as high as 60 dS/m. Drainage: A subsurface drainage system with 60-67 m spacing at 1.7 m depth using trencher was in operation in about 1200 ha area since 2001. The corrugated perforated polyvinyl chloride pipes were used for laterals and collectors. The diameters of lateral pipes 80 & 100 mm and collector pipes were 200-294 mm. An envelope materials viz. geo-textiles (300-400 microns) for laterals and nylon netting (60 mesh) for collector pipes were used.
201
Performance of Subsurface Drainage System
The monitoring and evaluation of the system to assess the impact of the drainage on water table depth, soil salinity and crop productivity were undertaken. Performance of subsurface drainage system was quite satisfactory. The depth to water table receded down below root zone, which was favourable for crop growth. The soil salinity reduced to considerable limit and had no adverse effect on crop growth. The yield of crops increased from 25 to 50 %. Reuse of saline drainage water can be possible for irrigating crops. Bibliography
Anonymous (2003). Haryana Operational Pilot Project – KMU for Reclamation of Waterlogged and Saline lands of Haryana. Final Progress Report. 105pp.
Figure 1. HOPP Kalayat Drainage Project Area
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