Subsurface drip irrigation and water management ...

In: Advances in Environmental Research. Volume 22 Editor: Justin A. Daniels, pp. 181-197

ISBN: 978-1-61470-743-1 © 2012 Nova science Publishers, Inc.

Chapter 7

Subsurface drip irrigation and water management under semiarid climate Douh Boutheina* and Boujelben Abdelhamid University of Sousse, Higher Institute of Agronomy of Chott Mariem, Tunisia

Abstract From the early days of irrigated agriculture, farmers and irrigation professionals looked after concepts and technologies to improve water utilization in agriculture. One of these concepts was the localized application of water directly to the root zone. Another concept was subsurface water application to avoid evaporation from the soil surface. The objective of this study was to evaluate how different irrigation depths applied with SDI affected the redistribution of soil moisture, agronomics’ parameters of maize in the semiarid climate of Tunisia. Data shows that with suitable management, subsurface drip irrigation at 0.35 m depth can achieve higher efficiency rates with limited water to maximize yields. Keywords: subsurface irrigation, maize, Tunisia, yield, soil moisture, sustainability. 1. INTRODUCTION As the population grows and urban water use increases, irrigated agriculture is being called on to produce more food using less water, and to do so without degrading soil and water resources (Skaggs et al., 2004). However, due to the current and expected limited water supplies, interest in subsurface drip irrigation (SDI) systems to irrigate row crops is growing (Caldwell et al., 1994; Lamm et al., 1995; Howell et al., 1997; Camp, 1998; Ayars et al., 1999; Lamm and Trooien, 2003).



The SDI is defined by ASAE S526.1 “Soil and Water Terminology” (ASABEStandards, 2007), as “application of water below the soil surface through emitters, with discharge rates generally in the same range as drip irrigation”. Subsurface irrigation is the practice of applying water to soils directly under the surface. Moisture reaches the plant roots through capillary action. When soil conditions are favorable for the production of cash crops on small areas, a pipe distribution system is placed in the soil well below the surface. This method of applying water is known as artificial subirrigation. Soils which permit free lateral movement of water, rapid capillary movement in the root zone soil, and very slow downward movement of water in the subsoil are very suitable for artificial subirrigation. The cost of such methods is very high. However, the water consumption is as low as one-third of the surface irrigation methods. The yield also improves. Application efficiency generally varies between 30 and 80 per cent. In several parts of the world, the moisture available in the root-zone soil, either from rain or from underground waters, may not be sufficient for the requirements of the plant life. This deficiency may be either for the entire crop season or for only part of the crop season. For optimum plant growth, therefore, it becomes necessary to make up the deficiency by adding water to the root-zone soil. This artificial application of water to land for supplementing the naturally available moisture in the root-zone soil for the purpose of agricultural production is termed irrigation. (Asawa G.L., 2008). The object of providing irrigation and drainage is to assist nature in maintaining moisture in the root-zone soil within the range required for maximum agricultural production. Irrigation management or irrigation scheduling can be done using three different approaches. The first approach, soil-based, may control the soil water content in the root profile by measuring it directly gravimetric method, neutron probes or Time Domain Reflectometry (TDR) or indirectly, using tensiometers. A second approach is canopy temperature-based via infrared thermometers on land or boarded on aircrafts and/or satellites. A third approach is weather-based, using weather data and mathematical models that calculate evapotranspiration (ET). In practice, a mix of these three approaches is commonly used. A literature review for these three approaches is given by Evett et al. (2008). Local information on the response of corn growth, yield and other crop–water dynamics with SDI is very limited. The agronomic response of the crop to irrigation with SDI is needed to be able to evaluate the economic and technical feasibility of using SDI under local conditions and provide scientifically based practical information to the users on best management practices for SDI-irrigated corn. The objective of this study was to evaluate how different irrigation depths applied with SDI affected the redistribution of soil moisture, agronomics’ parameters, yield, water use efficiency, and dry matter production of corn in the semiarid climate of Tunisia. The results will also be discussed in the context of other similar work at other locations. The Research supplements a larger body of knowledge. In some cases, existing information about SDI use in other regions and with other crops has been transferable. In other cases, it has not. As in many parts of the world, the interaction of climate, soils, and crop production presents unique combinations that require local research to fine-tune the production systems.



Historic of subsurface irrigation Buried, unglazed pots (fig. 1) allow water to seep through the clay’s micro pores and into the surrounding soil at a rate that is limited by the soil and the plant’s water uptake. This subsurface irrigation eliminates water losses to surface evaporation and infiltration through the soil, improving water savings by up to 70% over conventional surface irrigation methods.

Figure 1: Pitcher irrigation using an unglazed clay pot (Vukasin et al. 1995). In the mid-1950s, a small irrigation manufacturing firm in Watertown, New York, began to supply polyethylene tubing to water plants and flowers grown in greenhouses. By the early 1960s, plastic-pipe drip irrigation systems were extensively used in greenhouse research. Norman Smith, a cooperative extension agent from New York and Richard Chapin of the previous manufacture are credited with conducting the early pioneering work with plastic film mulch and surface drip irrigation for row crop production at the Old Westbury Gardens, Westbury Long Island, New York in 1963. The first field experiment in the United States with a subsurface drip irrigation system was established on a lemon orchard at Pomona, California in 1963 and on an orange orchard near Riverside, California in 1964 (Davis, 1974). The first research and demonstration study on a private grower’s trees was in an avocado orchard in San Diego, California in 1969. About the same time trials were started using drip irrigation and plastic mulch on strawberries and tomatoes also in and around San Diego (Davis and Bucks, 1983).



Colaizzi et al. (2009) stated that in 1984 cotton farmers installed the first SDI equipment in Texas HP. However, many of the early established SDI’s malfunctioned due to poor management in terms of root intrusion and inappropriate irrigation scheduling (Bhattarai, 2005). These issues were later solved by the development of antiroot intrusion emitters and maintenance techniques, leading to a faster increase of SDI adoption by farmers (fig. 2).

Figure 2: Subsurface drip irrigation system On 2007, Douh et Boujelben conducted an experimental trial comparing the effect of surface and subsurface drip irrigation on water saving and yield of eggplant at the High Institute of Agronomy of Chott Meriem Tunisia (Douh and Boujelben, 2010). The experimental results indicated that SDI leads to a greater yield making significant water saving 23.2% rather than surface drip irrigation. On 2008, a new irrigation technique for trees, vegetables and plants in containers was created by Chahbani, in Arid Regions Institute of Medenine-Tunisia. This technique consist on buried diffusers that can be manufactured using different raw materials plastic, cement, metals or ceramic (fig. 3). According to tests conducted by the researcher in the laboratory and field, conservation of irrigation water during the summer by this system is four times greater than that achieved by using drip irrigation technique. As a result, the frequency of irrigation is reduced at the same time promoting the control of its cost.



Figure 3: Buried diffuser (Chahbani, 2008)

2. MATERIALS AND METHODS

2.1. Experimental site Field experiment was conducted at the Higher Institute of Agronomy of Chott Mariem, Tunisia (Longitude 10°38E, Latitude 35°55N, altitude 15 m) from May to July 2010 (three months). The climate is typically Mediterranean with 230 mm annual rainfall and an average of 6 mm day-1 evaporation from a free water surface (Douh and Boujelben, 2010). In winter, the average minimum temperature is of 6°C and the average maximum is of 18°C, while in summer average minimum is of 23°C and average maximum is of 38°C. The soil is sandy loam with average basic infiltration rate of 14 mm h-1. Bulk density of soil was found to be 1.40 g cm-3 for the layer 0-60 cm. the porosity is calculated assuming a soil particle density (dp) of 2.65 Mg m-3 for mineral soils and Bd is bulk density. The field was precision graded to approximately 1 mm m-1 slope (table 1). Maize (Zea mays L.) was seeded the 1st of May with row spacing of 80 cm and inrow spacing of 40 cm and the whole planting area is 1000 m2 (25m*40m).



2.2. Experimental design and measurements The maize crop was irrigated with surface drip irrigation (DI) and subsurface drip irrigation (SDI) at different depths during the growing season. Drip tubing (GR type, 16 mm diameter) with 40 cm emitter spacing built in each delivering 4 L/h at 1bar pressure was used in DI and SDI treatments (10 drip tubing for each irrigation system). The subsurface laterals were buried at depths of 0.05, 0.20 and 0.35 m, respectively. The crop was irrigated twice a week by regarding estimated crop water requirements. Irrigation depth for each application was half the weekly water requirements. Weather data were obtained from a weather station located adjacent to the experimental area. Time Domain Reflectometry (TDR) technique was used to measure soil volumetric moisture using portable soil moisture monitoring system (TRIME FM). The vertical profile of soil water content in every tube was determined from measurements of volumetric soil water. Soil moisture content was measured daily and the gravimetric sampling technique and steel rings were used to calibrate the TDR display unit. Six measurement tubes were installed for each irrigation system. The measures were made by a layer of 10 cm in a tube of 1 m in length. The measurement tubes were located just under the dripper 0 and 20 cm apart from the dripper, respectively and in the middle of the in-row spacing at 0, 20 and 40 cm, respectively. The experimental design was presented in figure 4.

Figure 4: Experimental layout of the TDR tubes The data were obtained daily during the irrigation period at approximately 11:00 AM CDT. Water’s stock in soil is calculated as integrating the soil volumetric moisture relative to the domain D composed of the elementary soil volumes for a depth of 60 cm



(1) S: water’s stock in soil [L3/ drop] D: Domain or volume of soil [L3]. θ(x,y,z): soil volumetric moisture relative to the node point of coordinates x, y, z. dx, dy and dz take different values according to the grid bases to cover the set of the domain integration D. The variation of the soil volumetric moisture in the domain D between two instants t and (t+Δt) is (Δt= 1day): (2) We analyzed results from a completely randomized block designs with three treatments are the irrigation system’s depht (0.05 m, 0.20 m and 0.35 m), eight blocks for each treatment are the TDR tubes, six replications in each block and one factor the volumetric soil water contents. The volumetric soil water contents and the water’s stock in soil for the different emitter depth were analyzed using the Proc ANOVA (Analysis of Variance) procedure from the SAS Institute, (Cary, N.C.). Means were separated using a SNK test at the 0.05 probability level. 3. RESULTS AND DISCUSSION 3.1.

Soil characteristics

The soil physical properties were evaluated in the laboratory at the Higher Institute of Agronomy of Chott Meriem, to acquire baseline information regarding the study plots and for subsequent analysis pertaining to the irrigation scheduling and sensor evaluations. The results are presented in Table 1. Bulk densities at the layer of 20-25 cm depth were higher than the topsoil. This is an indication of compaction caused by machinery and human traffic. Table 1. Measured soil’s hydraulic parameters Layer Soil class % sand % silt Texture Analysis % clay Retention Water θr [%] content Saturated water θs[%] content Ks [cm h-1] Hydraulic conductivity Bd [g cm-3] Bulk density Porosity

0-20cm Sandy Loam 61 31 8 0,0640

20-60cm Sandy Loam 68 27 5 0,0589

60-100cm Sandy Loam 52 43 5 0,0600

0,3714

0,3711

0,3712

1.39

1.38

0.31

1,58 0,4037

1,66 0,3736

1,61 0,3924



3.2. Water’s dynamic in soil 3.2.1. Effect of SDI on redistribution of soil moisture Soil volumetric water content (VWC) used for the three irrigation treatments, measured with a Time Domain Reflectometry (TDR) system in one hour after irrigation. Soil VWC, measured in 30 points of the soil profile, were interpolated using Inverse Distance Weighing (IDW) multivariate method (Shepard, 1968). Inverse distance weighting (IDW) is a method for multivariate interpolation, a process of assigning values to unknown points by using values from usually scattered set of known points. Here, the value at the unknown point is a weighted sum of the values of N known points. A general form of finding an interpolated value u at a given point x based on samples ui =u(xi) for i = 0,1,...,N using IDW is an interpolating function: Where

is a simple IDW weighting function, as defined by Shepard, x denotes an interpolated (arbitrary) point, xi is an interpolating (known) point, d is a given distance from the known point xi to the unknown point x, N is the total number of known points used in interpolation and p is a positive real number, called the power parameter. Here weight decreases as distance increases from the interpolated points. Greater values of p assign greater influence to values closest to the interpolated point. For 0 < p < 1 u(x) has smooth peaks over the interpolated points xi, while as p > 1 the peaks become sharp. The choice of value for p is therefore a function of the degree of smoothing desired in the interpolation, the density and distribution of samples being interpolated, and the maximum distance over which an individual sample is allowed to influence the surrounding ones. For two dimensions, power parameters, for the interpolated values to be dominated by points far away, since with a density ρ of data points and neighboring points between distances r0 to R, the summed weight is approximately which diverges for R → ∞ and P ≤ 2.

For N dimensions, the same argument holds for p ≤ N. Shepard's method is a consequence of minimization of a functional related to a measure of deviations between tuples of interpolating points {x, u} and I tuples of interpolated points {xi,ui}, defined as:



Derived from the minimizing condition:

The method can easily be extended to higher dimensional space and it is in fact a generalization of Lagrange approximation into a multidimensional spaces. A modified version of the algorithm designed for trivariate interpolation was developed by Robert J. Renka and is available in Netlib as algorithm 661 in the tom’s library. Numerous studies have been conducted on water infiltration for subsurface drip irrigation in different depths. These studies were concerned with the soil water distribution patterns during infiltration into a dry soil assuming that a point source or single emitter was supplying water to the soil. Bresler et al. (1971) and Levin et al. (1979) showed that the wetted pattern in a sandy soil to be elongated in the vertical direction compared with the horizontal direction. Bar-Yosef and Sheikholslami (1976) found horizontal elongation of the wetting pattern in a clay soil. After irrigation, the horizontal advance of the wetting front for a loamy-sand was much less than the vertical advance, but water movement in silt loam was relatively uniform in all directions (Hachum et al., 1976). Water movement in a fine-textured soil may be limited, but vertical movement in a coarse-textured soil may be significant. A 1 L/h emitter discharge rate tended to give greater lateral water lateral movement during infiltration on a dry, bare silty loam than a 4 L h-1 rate (Mostaghimi et al., 1982). The larger emitter discharge rate resulted in deeper wetting during infiltration. Considerable additional redistribution of water occurred 48 h after the start of irrigation than at the end of the irrigation event. Under field conditions of continual wetting and drying, patterns of soil water content not only depend on soil texture and emitter discharge rate, but also on water management (irrigation frequency and amount of applied water), emitter spacing, lateral spacing relative to plant row spacing, lateral positioning with respect to the plant row, and plant extraction of soil water. Because of plant extraction of soil water, redistribution of soil water after irrigation may be minimal under some conditions. Water distribution was more favorable for weekly drip irrigations than daily drip irrigations (Earl and Jury, 1977). Under daily irrigation, lateral movement from the emitter was about 0.6 m and downward movement was about 0.6 m deep. Under weekly irrigation, lateral movement was about 1 m from the emitter and downward movement was about 0.75 m deep. Soil water patterns were determined in a sandy loam four days after cotton irrigation for driplines spaced every 2 m and place midway between plant rows (1 m plant row spacing) (Yaron et al., 1973). Irrigation amounts were 75% and 100% of the soil water deficit of an adjacent sprinkler-irrigated plot. An emitter discharge rate of 4 L/h and emitter spacing of 0.4 m was used for the three treatments. Wetting occurred down to at least 0.60 m for the three treatments. Lateral movement was about 0.50 m for both treatments. Patterns of soil water content under subsurface drip irrigation at 0.05m, 0.20m and 0.35m deep in a sandy loam soil were compared under water applications of 100% of the potential crop evapotranspiration (Plaut et al., 1985). Emitter spacing of the 4 L/h emitters was 0.40 m and driplines 0.60m.



The water content distribution in soil 2 hours after irrigation was based on depths and distances from the dripper (0.0) to plot the curves of equal water contents. Figures 5, 6 and 7 present Two-dimensional maps of experimental water content values (m3 m-3) for subsurface drip irrigation system buried respectively at 0.05 m, 0.20 m and 0.35 m at different depths. Soil water content for the drip irrigation system buried at 0.05 m (T1) is significantly higher around the dripper 12% away from the emitter decreases to 9% at 0.20 m from the dripper, at a depth of 0.05 m under the emitter (a). At 0.20 m of depth water percolates from the dripper located 5cm to achieve this depth, the water content under the emitter is of 13% (d). Soil water content is of 12% at 0.35 m deep under the dripper (j). For subsurface drip irrigation system (T2) the water content; at 0.05 m depth; varies between 7.5% and 11%. The water arrives through the capillary effect (b). At 020 m deep, under and around the emitter, the maximum water content is 16.5%, and is distributed outward (e). Water seeps in and reaches that depth. The water content is sufficient to ensure a good crop development (h). For subsurface drip irrigation system (T3), the water content varies between 7.5% and 10%. No effect of irrigation water at this depth and the curves are almost horizontal lines (c). At 0.20 m, soil water content arrives by capillarity, is maximal and reaches 20% (f). At 0.35 cm, the water content is significantly higher and exceeds 21%. The curves are spaced showing a smaller variation of soil moisture (i). For the T1 treatment, the soil profile was wet 9% to 13% water content down to at least 0.40 m beneath the emitters. Soil water content decreased with horizontal distance for all emitter placements. However, horizontal flow of water under subsurface drip irrigation buried at 0.35 m was the greatest at about the 0.60 m depth. Soil water content decreased in the upper part of the profile as water application decreased. Camp et al. (1987), proved that water movement above the subsurface dripline was limited for all water applications. Wetting patterns measured in a sandy loam indicated drier soil under surface drip than with subsurface drip irrigation. Measurements also revealed little or no redistribution of soil water after irrigation. This lack of redistribution was due to soil water extraction by the crop reducing or preventing any further lateral movement of soil water. Soil water patterns under surface drip irrigation were determined for two different bed configurations and dripline locations (Hanson and Bendixen, 1998). A narrow bed (1 m spaced bed with 1 dripline centered on bed) had an elongated vertical soil water pattern on a sandy loam with nearly constant soil water below the dripline to about 0.5 m deep. Soil water content decreased at horizontal distances greater than 0.1 m. Similar vertical elongation patterns were present for the wide bed configuration (1.5 m crop bed with 2 driplines/bed), but tended to have higher soil water contents near the soil surface. Soil water content again decreased with horizontal distance with more dry areas occurring midway between the dripline and at the edges of the bed. Results of Hachum et al. (1976) have led to the assumption that lateral movement of water from a dripline is greater in a fine-textured soil than for a medium or sandy soil. However, field measurements and observations have shown that the lateral movement in a fine-textured soil can be very small, sometimes less than about 0.15 m from the dripline. Explanations for this behavior are unclear, but it may be because lateral water flow in a fine-textured soil moves at a relatively slower rate than the rate of plant water uptake. In a bare soil where no plant water uptake occurs, lateral movement in a fine-textured soil may be considerable over a long period. Pulsed water applications have been advocated for improving distribution of water around driplines. Studies of this concept involved cycling irrigation water with irrigation events ranging



from a few minutes to 30 min/h. The main advantages to this approach are: (1) the ability to use emitters with large flow passages, thus reducing clogging problems, while maintaining low average application rates, and (2) better soil aeration. Zur (1976), Levin and Van Rooyen (1977), and Levin et al. (1979) found that soil water distribution around the dripline showed little difference between pulsed and continuous applications with similar average application rates. Camp et al., (1987), however, found a narrower and deeper wetted pattern for the continuous application than pulsed applications. Pulsed applications may be suitable for small drip irrigation systems, but can cause management and uniformity problems for large systems. Drip irrigators in California (USA) found that a significant percentage of the irrigation set time was spent filling pipelines when using short, frequent water applications. Also, the frequent applications resulted in substantial amounts of water draining from the irrigation system and collecting at the lower part of the field, thus, contributing to poor field-wide uniformity of applied water. These results indicate that pulsed drip irrigation may only be practical for small fields.

Figure 5: Two-dimensional maps of experimental water content values (m3 m-3) and root water uptake for subsurface drip irrigation system buried respectively at 0.05 m, 0.20 m and 0.35 m at 0.05 m depth.



Figure 6: Two-dimensional maps of experimental water content values (m3 m-3) and root water uptake for subsurface drip irrigation system buried respectively at 0.05 m, 0.20 m and 0.35 m at 0.20 m depth

Figure 7: Two-dimensional maps of experimental water content values (m3 m-3) and root water uptake for subsurface drip irrigation system buried respectively at 0.05 m, 0.20 m and 0.35 m at 0.35 m depth



3.2.2. Soil moisture distribution in different depths Mean of soil moisture distribution in different depths, for the subsurfaces systems at 5 cm (T1), 20 cm (T2) and 35cm (T3), are presented in table 2. The means are respectively 9,25±2,72 , 13,01±4,59 and 15,39±4,97 for T1, T2 and T3. Soil water content under T1 and T2 had large variation and higher trends for the 5 cm depth, ranging from a minimum of 7% to a maximum 17%, while at the depth of 20 and 35 cm varied from a minimum of 15% to a maximum of 26%. However, volumetric moisture content of soil varied between 18% and 33% for the depth 15 to 20 and 35 cm under T3. The water content values were equal with a slight difference lower than 6% which was relatively more stable than T1 and T2. In fact, the present study showed that soil water content increases after a rain or an irrigation. Nevertheless, water content decreases according to the time following an increase of needs of the plant and losses of water by evapotranspiration. The results show that soil moisture is relatively more stable for T3 than T1 and T2 with a slight difference except of water’s contributions. The study indicated that soil moisture content under subsurface drip irrigation at 35 cm depth was more uniform as compared to that at 5 and 20 cm; these results are confirmed by Singh (2007). The results provide evidence that 35 cm below the soil surface was so dry as it was hypothesized that SDI method would improve the water use efficiency of maize crop by minimizing the evaporative loss and delivering water directly to the root zone. Soil water content for the depth of 20 to 35 cm was higher in T3. These results are confirmed by Bajracharya and Sharma (2005) who put the same hypothesis to explain the amplification of water use efficiency of cucumber and tomato crops relatively to SDI. Changes between the pre- and post-irrigation soil sampling dates in the average volumic soil water content were determined for each depth of subsurface drip irrigation. Taking into account the average change in total soil water from all sampling depths and considering the same number of positions for each lateral orientation, there was greater increase in volumic soil water content for T3 than for T1 and T2 with statistically significant increases. The ANOVA allowed us to conclude a highly significant difference at the threshold of α = 5% for root length. Indeed, the SNK were classified into three groups. The first class consists of subsurface drip irrigation system buried at 35cm the second consists of subsurface drip irrigation system buried at 20cm and the third class contains the underground irrigation to 5cm. The difference between the average water content of the three treatments referred to lost by evaporation. 3.2.3. Water’s stock in soil Water’s stock in soil increased after irrigation or rain and decreased between two successive irrigations in absence of rain. This decrease of water stock became more rapidly as the climate became hotter and drier and the crops reached a more advanced vegetative stage. In the same way, table 2 provided evidence that water’s stock is much more important in T3 than in T1 and T2. The highest mean of the water’s stock in soil is registered for T3 30462,23±4625,79 cm3/plant, compared to 26977,90±3046,85 cm3/plant for T1 and 28568,43±3965,49 cm3/plant for T2. Therefore, the losses of water by evaporation were weaker for the underground irrigation at 35 cm. SDI offers many advantages over surface drip irrigation such as reduced evaporation loss and precise placement and management of water (Camp, 1998). Even though, the results indicated that T3 leads to a greater yield making significant water saving (12.9%) rather than T1. Whereas, water’s stock in soil is greater (5.9%) in T2 compared to T1 but this difference did not produce significant results. Sakellariou (2002) studied the water



saving and yield increase of sugar beet with subsurface drip irrigation and he found greater water economy of 16.6% for the SDI in comparison to surface drip. Table 2. Effect of SDI under three treatment on soil moisture and water’s stock in soil

Treatment

Water's stock (cm3/plant)

Soil moisture (%)

T1 (-0.05m)

26977,90±3046,85 b

9,25±2,72 c

T2 (-0.20m)

28568,43±3965,49 b

13,01±4,59 b

T3 (-0.35m)

30462,23±4625,79 a

15,39±4,97 a

3.3. Crop response to surface drip irrigation 3.3.1. Surface versus subsurface drip irrigation A few studies have compared crop yields between surface and subsurface drip irrigation. Maize yields were different between surface and subsurface drip irrigation at different depth 0.05 m, 0.20 m and 0.35 m. Figure 8 shows the difference between the average yield in surface and subsurface drip irrigation system at different depths. These results indicate that large yield differences exist between surface and subsurface drip at 0.05 m 0.20 m and 0.35 m. The ANOVA allowed us to conclude a highly significant difference at the threshold of α = 5% for depth of the dripline. Indeed, the SNK were classified into two groups. The first class consists of subsurface drip irrigation system buried at 0.35 m the second consists of subsurface drip irrigation system buried at 0.20 m, 0.05 m and the surface drip irrigation. Thus, the choice of drip irrigation system probably will often depend on factors other than yield and depth of applied water, some of which were considered earlier in this chapter. It is frequently assumed that evaporation of water from the soil will be less under subsurface drip irrigation than surface drip. This is probably true, it allows the reduction of evaporation and gives subsurface drip irrigation an advantage over surface drip in terms of water use and crop yield. The treatment T3 allowed us a gain of 29.5 % compared to the witness T0.

Figure 8: average yield in surface (T0) and subsurface drip irrigation system buried at 0.05 m (T1), 0.20 m (T2) and 0.35 m (T3) deep



Potato yield was slightly higher with subsurface drip irrigation (Sammis, 1980). Similar eggplant yields were obtained for surface and subsurface drip irrigation. The increased yield reached 40% compared to the surface drip 20 Kg/m2for surface drip irrigation and 28 Kg/m2 for subsurface drip irrigation buried at 0.15 m of lateral placement (Douh and Boujelben, 2010). In addition, similar lettuce yields were obtained under furrow, surface drip, and subsurface drip irrigation in sandy loam (Hanson et al., 1996). Sweet corn yield was slightly higher with subsurface than with surface drip irrigation (0.3 m depth), but the difference was not statistically significant (Bar-Yosef et al., 1989). There were no significant differences in cotton yield between surface and subsurface drip (0.40 m depth) for a clay loam soil (Plaut et al., 1985). Davis et al. (1985) also found no significant yield differences in processing tomato between surface and subsurface drip irrigation (0.45 m depth). No field corn yield differences occurred between surface and subsurface drip (0.3m depth) for a given amount of applied water, which ranged from deficit irrigation to adequate irrigation (Howell et al., 1995). Similar yields of processing onions and fresh-market onions were found between surface and subsurface drip irrigation for the same amount of applied water on a silt loam soil (Hanson and al., 2003). Caution should be exercised in extrapolating these results to soils that differ considerably in texture from those used in the experiments described for shallow rooted crops. While the previously cited study showed similar onion yields between surface and subsurface drip irrigation on silt loam soil, grower experience has shown lower onion yields under subsurface drip irrigation than surface drip irrigation for other soil textures. For silt loam soil, upward and lateral flow of water readily occurs around the drip line, but such movement may be limited for sandy soil and in some cases, clay loam soils. 4. Conclusion The observations were recorded on distribution of soil moisture content, water’s stock in soil and corn yield. This study indicated that soil moisture content under subsurface drip irrigation at 0.35 m depth was more uniform in comparison to that at 0.05 m and 0.20 m. Moreover, yield was higher in T3 (13.47 T ha-1). In fact, it increased about 29.5% when compared with T0 treatment. Subsurface drip irrigation allows uniform soil moisture, minimize the evaporative loss and delivery water directly to the plant root zone which increases use efficiency and yield. Further observations are needed to determine whether corn production with SDI is feasible in the arid region to develop recommendations for farmers choosing to adopt the method. SDI systems are capable of applying small amounts of water directly to the plant root zone where the water is needed, and can be applied frequently to maintain favorable root zone moisture conditions. Improvements in yield and quality, and reduction in production costs are some of the potential benefits of SDI. It offers many advantages over surface drip irrigation such as reduced evaporation loss, precise placement, management of water, nutrients and pesticides leading to more efficient water use, greater water application uniformity and an enhanced plant growth and crop yield. References 1. ASABE-Standards, 2007. Soil and Water Terminology. S526.3. ASABE, St. Joseph, MI.



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