1 2
Yield response of potatoes to variable nitrogen management by landform element and in relation to petiole nitrogen – A Case Study
3
A. P. Moulin1, Y. Cohen2, V. Alchanatis2, N. Tremblay3 and K. Volkmar4
4 5 6 7 8 9 10 11 12
1
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Corresponding author: A. P. Moulin
[email protected]
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Short title: Yield response of potatoes to variable nitrogen
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Key words: potato yield, spatial variability, nitrogen management
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Abbreviations: HSD Tukey’s honest significant difference, GPS Global Positioning
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System, GDD Growing Degree Days, P-days Heat units for potatoes, NUE Nitrogen Use
18
Efficiency
19
Agriculture and Agri-Food Canada, Brandon Research Centre, AAFC, Brandon, Manitoba, Canada, R7Y 5Y3 2 Agricultural Research Organization, Volcani center, Institute of Agricultural. Engineering, Bet-Dagan, Israel 3 Agriculture and Agri-Food Canada, Horticultural Research and Development Centre, Saint-Jean-sur-Richelieu, Quebec, Canada, J3B 3E6 4 Agriculture and Agri-Food Canada, Southern Crop Protection and Food Research Centre, London, Ontario, Canada, N5V 4T3
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Yield response of potatoes to variable nitrogen management by landform element and in relation to petiole nitrogen – A case study
23
A. P. Moulin1, Y. Cohen2, V. Alchanatis2, N. Tremblay3 and K. Volkmar4
24 25 26 27 28 29 30 31 32 33
1
Agriculture and Agri-Food Canada, Brandon Research Centre, AAFC, Brandon, Manitoba, Canada, R7Y 5Y3 2 Agricultural Research Organization, Volcani center, Institute of Agricultural. Engineering, Bet-Dagan, Israel 3 Agriculture and Agri-Food Canada, Horticultural Research and Development Centre, Saint-Jean-sur-Richelieu, Quebec, Canada, J3B 3E6 4 Agriculture and Agri-Food Canada, Southern Crop Protection and Food Research Centre, London, Ontario, Canada, N5V 4T3
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Recent increases in the cost of fertilizer N have prompted producers to assess the
36
potential to vary inputs within fields and during the growing season to produce the
37
highest marketable yield of potatoes (Solanum tuberosum L.). A study was conducted
38
from 2005 to 2007 near Brandon, Manitoba Canada, to assess the spatial variability of
39
potato yield in upper, middle and lower landform elements on a sandy loam soil in
40
response to a range of N fertilizer rates applied in the spring or in combination with an
41
application during the growing season. There was no clear trend with respect to the
42
effect of landform on potato yield. Nitrogen fertilizer increased total and marketable
43
yield relative to the control at rates from 75 to 225 kg ha-1 in split applications or applied
44
at seeding. No significant interaction between landform and fertilizer treatment was
45
observed. Petiole N concentration, determined late in the growing season, was correlated
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with potato yield though the correlation varied considerably between years. Petiole
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leaflet N concentration was affected by fertilizer on most sampling dates, but decreased
48
with time during the growing season. We conclude that although N fertilizer could be
49
applied during the growing season based on petiole leaflet N concentration deficiencies in
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mid July, there is no clear difference in potato yield due to split application relative to
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spring applications of N fertilizer at rates of 75 kg ha-1 or greater based on landform
52
elements for potato production likely due to the short growing season in Western Canada.
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INTRODUCTION
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Manitoba is currently the second largest potato producer in Canada, with an area of
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approximately 32,000 ha planted in 2009 (Statistics Canada 2010). With large areas of
57
land suitable for irrigated potato production and the potential for an expanding processing
58
industry, Manitoba could become the largest potato producer in Canada. The expansion
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of potato industry, however, has created some concerns about water contamination and a
60
reduction in profitability of N management for potato production due to a shallow water
61
table in the potato producing area and the high cost of N fertilizer.
62
Nitrogen management for potato (Solanum tuberosum L.) is important from both
63
production and environmental standpoints. Westermann and Kleinkopf (1985) and
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Errebhi et al. (1998) concluded that split N application, based on N sufficiency during the
65
growing season, would significantly improve N fertilizers use efficiency. In Canada,
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potatoes are often grown on coarse-textured soils, with high N rates applied at planting.
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In this environment, N can easily be leached below the rooting zone during heavy rainfall
68
and excess irrigation. This practice could contaminate ground water with NO3-N and
69
substantially reduce yields due to N deficiency. Errebhi et al. (1998) showed that lower
70
rates of N applied at planting combined with application of N fertilizer at emergence and
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hilling, reduced NO3-N leaching, increased N recovery by the crop and improved tuber
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yield. Meyer and Marcum (1998) and Bélanger et al. (2003) recommended petiole NO3-N
73
be monitored to correct N deficiency with split application of N during the growing
74
season.
75
Spatially variable application of inputs to crops is commonly based on sub-division of a
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field into 'management zones' – areas that may be treated uniformly (Whelan and
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McBratney 2000). Delineation of management zones (MZ) requires analysis of crop yield
78
and soil properties at a scale relevant to field production and spatial variability. Currently,
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four types of data are available: remotely-sensed images (Cohen et al. 2010), yield maps
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(mainly of grain crops), elevation maps and maps of properties such as apparent electrical
81
conductivity (EC) or soil NO3-N (Stafford et al. 1996; Fraisse et al. 2001; Boydell and
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McBratney 2002; Fridgen et al. 2004; Kitchen et al. 2005).
83
Delineation of MZ, based on yield, landform analysis or environmental factors often does
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not account for variations in observed yield due to the dynamic relationships between
85
crop, soil and environment, which change within and between seasons (Van-Alphen and
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Stoorvogel 2000). Soil N supply and crop N requirements were highly variable within
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management zones in several studies (Walley et al. 2001; Pierce and Nowak 1999;
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Fergusson et al. 2002). Because of temporal and spatial variability in soil N supply,
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strategies based on detecting crop N status at early, critical crop growth stages and
90
meeting crop N requirements with carefully timed fertilization may ultimately be more
91
successful in improving N-use efficiency than strategies which attempt to estimate soil N
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supply ahead of time (Van-Alphen and Stoorvogel 2000; Fergusson et al. 2002). In this
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context, leaf reflectance data correlated with petiole leaflet N concentration could be
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collected at critical periods during the growing season to recognize, to refine variable rate
95
application within management zones.
96
The potential for variable management of potatoes was discussed by Davenport and
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Hattendorf (2000), who identified the need for further research on this topic. However
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Cambouris et al. (2007; 2008) concluded that response to N fertilizer was similar in
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management zones delineated on the basis of soil conductivity. Koch et al. (2004)
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reported that variable-rate N management based on site-specific management zones was
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more economically feasible than conventional uniform N application. Significant multi-
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variate relationships between spatial variability of soil properties, elevation and potato
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yield were reported by Po et al. (2010). Based on a simulation of variable-rate N
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management for seed potatoes with the EPIC model, Watkins et al. (1998) postulated that
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economic and environmental benefits may accrue from split applications. However there
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are no published analyses of field studies in Western Canada for variable management of
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N for potatoes in relation to management zones. The objectives of this study were to
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assess: 1) the first objective was to assess the spatial variability of response in potato
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yield to rate and split application of N in management zones based on landform elements
110
and 2) the temporal variability of petiole N in relation to yield, management zone and
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fertilizer rate.
112 113
MATERIALS AND METHODS
114 115
Site description
116
A field was selected in 2004, on sandy textured soils 19 km northwest of Carberry,
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Manitoba, based on variability of soil fertility, landform elements and cropping history.
118
Replicated studies were located at one site in each year (2005, 2006 and 2007) within the
119
field for a total of three site-years. The field (49o57’10.62”N, 99o 36’ 05.32“ W, legal
120
location 28 11 16 W) selected for the study was in a cereal-cereal-potato rotation with
121
irrigated potatoes in the third year of production. Spring wheat (Triticum aestivum L.)
122
and fall rye (Secale cereale L.) were the cereal crops in the rotation. Cereal grain was
123
either harvested or cultivated in the fall. The field was tilled during the fall in preparation
124
for spring planting. Soils in the field were predominantly Orthic Black Chernozems in
125
the Stockton series, with a coarse sandy texture (Manitoba Land Resource Unit 1997).
126
Meteorological data (Table 1) were recorded at an Environment Canada station located at
127
Carberry MB, 19 km southeast of the site (Mohr et al 2011). Potato degree days (P days)
128
were calculated (Sands et al. 1979) according to equation 1:
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Pday 1 * 5 * PT 1 8 * PT 2 8 * PT 3 3 * P(T 4) ( 1) 24 where : T 1 T min 2 * T min T max 3 T min 2 * T max T3 3 T 4 T max T2
where : P 0 when T 7 o C
130
(T 21) 2 when 7 T 21o C P 10 * 1 2 (21 7) (T 21) 2 when 21 T 30 o C P 10 * 1 2 (30 21) P 0 when T 30 o C
131
Growing degree days (GDD) were calculated for the period from May 1 to September 30,
132
with a baseline of 7 o C recommended for potatoes (Manitoba Agriculture, Food and
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Rural Initiatives 2010a). Spatial variability of crop reflectance was determined from a
134
true color photograph taken of the 2004 cereal crop (ATLIS Geomatics Inc., August 3,
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2004) for the 2005 and 2006 sites and a near-infrared photograph in 2006 (Prairie Agri
136
Photo Ltd, July 17, 2006). These photographs were digitized and referenced with Didger
137
software (Golden Software 2001) to coordinates (UTM, zone 14, WGS84) determined
138
with a Trimble ProXR. Cluster analysis (binning method) was conducted with IDRISI
139
software (Eastman 2003) on a geo-rectified color photograph (2004 true color
140
photograph) of the site to classify the image in 3 nominal classes. The spatial distribution
141
of these classes was compared to landform analysis of digital elevation data collected
142
with ground based GPS (Trimble ProXRS) for the 2005 site. Digital elevation data for
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the 2005, 2006 and 2007 sites (SW, NE and SW 28 11 16 W) were processed to
144
characterize landform elements. Upper, middle and lower landform elements were
145
delineated from digital elevation data for the 2005, 2006 and 2007 sites with Landmapper
146
software (MacMillan 2000; 2003). Elevation was determined for the 2005 site with
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survey grade (0.5 m accuracy) GPS (Trimble Pro XRS). The 2006 and 2007 sites were
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surveyed for apparent electrical conductivity with a Veris sensor (Veris 3100).
149
Soil was sampled in a stratified grid at 13 locations per landform element (total of 39
150
locations per site-year) in 0-15, 15-30 and 30-60 cm depth increments in fall 2004, 2005
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and 2006 to characterize soil properties and fertility prior to application of fertilizer
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treatments in spring 2005, 2006, and 2007. Total organic and inorganic C, total soil N
153
and NO3-N were determined in the 0-15, 15-30 and 30-60 cm depth increments. Olsen P
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and K were measured in the 0-15 cm increment. Soil moisture at field capacity -30 kPa
155
was determined with a pressure plate (Dane and Hopmans 2002) and soil texture with a
156
hydrometer (Gee and Or 2002). Soil samples were analyzed in 2004 to 2006 for NO3-N
157
(2 M KCl extract, Technicon auto-analyzer), (modified Kelowna, P, K, S ICP 2004-2005)
158
and in 2007 for NO3-N (2 M KCl extract, Technicon auto-analyzer), PO4-P (NaHCO3,
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extract Technicon auto-analyzer), K (NaHCO3,extract atomic absorption), SO4-S (CaCl2
160
extract, Methylthymol blue, Technicon auto-analyzer). Soil standards were included with
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samples analyzed for NO3-N, Olsen P (APG 4022), K and SO4-S (APG 4052). Soil was
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sampled in each landform and analyzed for soil organic C and total N by combustion with
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a Carlo-Erba 1500 elemental analyzer. Soil pH was measured with a 1:2 soil:water
164
suspension (Hogg and Henry 1984).
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Experimental protocol
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The experimental design was a split block, with each site year considered a block with
167
one upper, middle and lower landform element per year (Littell 1996). Two treatment
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factors were studied: three landform elements (upper, middle and lower) and seven
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fertilizer treatments. Four replicates of seven N fertilizer treatments, organized in a
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randomized complete block design, were located in the upper, middle and lower landform
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elements in each site-year (2005, 2006 and 2007).
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Nitrogen fertilizer treatments (0, 75, 150 and 225 kg ha-1 N fertilizer) were based on the
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range recommended by Manitoba Agriculture Food and Rural Initiatives (2010b) and
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were applied to the plot areas shortly after seeding (May 13 and 16, 2005; May 10 and 11
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2006; May 18, 2007). The initial application of N fertilizer was followed by a second
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application in three treatments (75, 150 and 225 kg ha-1, July 22, 2005, July 5, 2006, July
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11, 2007) immediately before hilling. Treatments were organized in a randomized
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complete block design located within upper, middle and lower landform elements in each
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site-year. Fertilizer was broadcast with a Valmar in the form of urea followed by
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irrigation within the next one or two days. Fertilizer (P, K and S) was broadcast at a
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uniform rate in the plot area, based on soil analyses for fall 2004, 2005 and 2006, so as
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not to limit potato production. Nitrogen applied with monoammonium phosphate and
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ammonium sulphate fertilizer was 25.6 kg ha-1.
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Tillage, irrigation and pests were managed in the plot area, with practices used by the
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producer in the surrounding potato field. Plots were tilled with a Lely power harrow prior
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to planting. Fungicide-treated potato seed pieces were planted in 8 rows per plot using a
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six-row cup planter with 95 cm between rows and 36 cm within rows in plots 10.7 m long
188
by 7.6 m wide. Potatoes were hilled once during the growing season, usually between
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mid-June and mid-July depending on crop development. Rimsulfuron (Prism) and
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metribuzin (Sencor) were applied by the producer to control weeds in conjunction with
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management of the surrounding potato field as specified in the “Guide to Crop
192
Protection”, (Manitoba Agriculture, Food and Rural Initiatives. 2009). Plant emergence
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was visually assessed as relatively uniform in the field and within management zones.
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Water was applied to potatoes with a centre pivot, to maintain 75% of available soil water
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(Field capacity – permanent wilting point) based on the producer’s management of the
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surrounding field (J. Adriaansen pers. comm. 2009). Potato plots received 230 mm of
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irrigation water in 2005 and 320 mm in 2006 (data not recorded 2007) (J. Adriaansen,
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pers. comm. 2009).
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Potatoes were harvested in mid-September without desiccation. Two non-border rows,
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9.1 m each in length, of potatoes were dug in each plot with a mechanical digger, bagged,
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weighed and removed. Marketable potato yield (tubers with diameter greater than 4.4 cm;
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main yield: tubers with a diameter five cm and greater; small yield: tubers with diameter
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4.4 cm but less than five cm, which are further divided into two sub-categories based on
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length: less than 7.6 cm long and greater than 7.6 cm long; bonus: diameter greater than
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five cm and weigh more than 0.28 kg) and total yield were determined in each plot.
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During the growing season (June 13, July 12, July 26, August 19 2005; June 8, June 19,
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July 5 and July 18, 2006; July 4, July 25 and July 31, 2007) 14 leaflet samples stripped
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from the petiole from the fourth leaf from the top of the potato plant (Zebarth et al. 2003)
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were collected in each plot (seven samples from each of two locations in each plot) and
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were saved for N and NO3-N analysis. Laboratory analysis of petiole leaflet N
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concentration was conducted with a Carlo Erba 2500 elemental analyzer in 2005 and
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2006 and a Carlo Erba 1500 elemental analyzer in 2007. In addition, petiole leaflet NO3-
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N was determined for samples collected on July 25, 2007. Petiole leaflets were oven
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dried at 55 oC and were ground to pass a two mm screen prior to analysis. Using a
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method similar to Zebarth et al. (2003), a 0.1 g subsample was extracted with distilled-
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deionized water using a 50 ml water extract ratio and 30 min shaking time. The extract
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was diluted 1:4000 using an automated diluter and NO3-N concentration in the extract
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determined on a Lachat Flow Injection Analyzer following reduction of NO3-N to NO2-N
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with hydrazine sulphate (Lachat Method 12-107-04-1-B).
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Soil NO3-N, PO4-P, K and SO4-S were also determined from samples from three
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locations per plot bulked by depth increment (0-15 cm, 15-30 and 30-60 cm) after harvest
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in 2005 and 2006. Additional soil samples were collected in the 60-90 cm depth
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increment after harvest in 2006. Soil was sampled for 0-15, 15-30 and 30-45 cm depths
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after harvest in 2007 due to the presence of a buried power line located diagonally across
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the plot area. Soil nitrogen supplying capacity was estimated from soil samples (0-15
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cm), collected from the control treatment in each of 4 replicates within three landform
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elements in each year. In two separate analyses, subsamples were extracted with either
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hot or cold 2 M KCl to determine total NH4-N and NO3-N release and background NH4-
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N concentrations (Campbell et al. 1997; Burger and Jackson 2003). The difference
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between hot and cold extracts was used to estimate soil N supplying capacity. Extracts
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were analyzed with a Technicon auto-analyzer.
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Data were analyzed with residual maximum likelihood in a mixed model for replicates,
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site years, landform element and fertilizer treatment for a split block design. Replicates
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nested within landforms, site years and related interactions were considered random,
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while landform elements, fertilizer treatments and the interaction were fixed (Littell et al.
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1996, Milliken and Johnson 2002; 2009). Significant fixed effects (P < 0.05) in the mixed
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model and random effects (proportion of variance of mixed model > 20%) were
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compared with Tukey’s honest significant difference (HSD). Repeated measures of
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petiole leaflet N concentration during the growing season were analyzed within plots in a
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combined analysis across years with the MANOVA procedure in JMP and with analysis
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of covariance with cumulative GDD and P days separately as independent variables. The
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Mauchly Criterion was used to test for sphericity of repeated measures during the
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growing season and an adjusted Greenhouse-Geisser method was used in cases where it
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was significant (SAS Institute 2009). Normality and heterogeneity of variance were
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assessed with leverage plots of the mixed model. All statistical analyses were conducted
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with JMP v 8.0.2 and SAS Enterprise 4.01 (SAS Institute 2009 a, b).
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RESULTS
248 249
Soil properties and landform elements
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The majority of landform elements (47.6%) in the study area were in the middle-slope
251
position with the remainder primarily in the upper (20.8 %) and lower (22.2%) landform
252
elements. Slope gradient ranged from 0.5 to 2.0% (35.5%) and 2.0 to 5.0% (33.8%) for a
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significant proportion of the field, which reflects the undulating dissected landscape at the
254
site. Clay content ranged from 91.0 mg g-1 in lower landform elements to 37.0 mg g-1 in
255
upper landform elements with 158.0 mg g-1 in lower landform elements and 66.0 mg g-1
256
in upper landform elements. Field capacity at 33 kPa was higher in lower compared to
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upper landform elements. Soil pH (0 to 15 cm) ranged from 6.8 for the lower slope
258
position to 7.1 for the upper slope position.
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Soil fertility
260
Soil residual NO3-N, determined in fall prior to planting, was generally low and varied
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significantly between landform elements delineated with analysis of true color air
262
photographs. For example, soil NO3-N (0-15 cm) in the upper slopes prior to the
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experiment in was 5.8 kg ha-1 in 2005 and 3.7 kg ha-1 in 2006 significantly less than 13.6
264
kg ha-1 and 11.8 kg ha-1 in the lower slopes respectively. In 2007 residual soil NO3-N (0-
265
15 cm) was 9.7 kg ha-1 in the lower landform, significantly higher than 2.1 kg ha-1 and 2.4
266
kg ha-1 for the middle and upper landform elements respectively.
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Soil N supplying capacity was very low for the 0-15 cm depth increment, ranging from 0
268
kg ha-1 to 10 kg ha-1, with little or no NO3-N released (0 kg ha-1). There was a significant
269
interaction between year and landform with the highest supplying capacity (10 kg ha-1)
270
occurring in the lower slopes in 2007.
271
Soil organic carbon and total nitrogen
272
Soil organic C and total N varied significantly between landform elements, with trends
273
similar to soil NO3-N. Analyses for 2005 show that soil organic C concentration (0-15
274
cm) was significantly higher (24 mg g-1) in the lower slope position, relative to the upper
275
slope position (6 mg g-1), similar to 2006 and 2007, with the highest value (51 mg g-1) in
276
the lower slope position for 2007. Total soil N (0-15 cm) varied from 1.8 mg g-1 in the
277
lower slope position to 0.8 mg g-1 in the upper slope position in 2005 similar to 2006 and
278
2007. Significant differences were observed between upper and middle slope positions
279
for soil organic C and total N for the 2006 though not for the 2005 or 2007 sites.
280
Soil conductivity
281
Soil conductivity (0-30 cm) in the field ranged from 1 to 40 mS m-1 in 2006 and 2007
282
with a few outliers near 90 mS m-1 and is typical for sandy soils in this area. All data
283
were below the critical level of 100 mS m-1 at which agricultural production is reduced
284
(Henry 2003) and indicated that salinity did not limit potato production at these sites.
285
Precipitation and temperature
286
Growing season precipitation in the study area was higher than long-term (19601990)
287
climate normals (Mohr et al 2011) in 2005 and lower in 2006 and 2007 (Table 1) with
288
considerable variability in monthly rainfall (June and July) between years. Mean
289
monthly temperatures were higher in 2005 to 2007 than long-term climate normals.
290
Cumulative P days and GDD varied between years (Table 1) and in relation to the climate
291
normals (Potato days 916, GDD 1390).
292
Potato Yield
293
Potato yield varied significantly due to fertilizer N (Tables 2 and 3). However residual
294
NO3-N in fall prior to planting plus nitrogen added with P and S fertilizer (25.6 kg N ha-1)
295
and low levels of hot KCL extractable N, do not account for the yields observed for the
296
controls (Table 4), based on the assumption that 5.7 kg N Mg-1 potato tubers (Manitoba
297
Agriculture, Food and Rural Initiatives 2010b). Control yields ranged from 20.4 to 51.10
298
Mg ha-1. Unaccounted N ranged from 75.6 to 242.8 kg ha-1 N (Table 4).
299
Application of fertilizer N at rates over 75 kg ha-1 N fertilizer increased total yield
300
significantly relative to the control for most combinations of site-years and landform
301
elements, . Potato yield did not significantly respond to the range of fertilizer rates above
302
75 kg ha-1 N fertilizer. The interaction between fertilizer N treatments, landform elements
303
and site-year was not significant and did not account for a large proportion of the total
304
variance of the mixed model. Contrasts for fertilizer response by landform effects were
305
not considered due to the lack of statistical significance of the interaction (Table 2).
306
Addition of fertilizer significantly increased total and marketable yield of potatoes (Table
307
5) relative to the control. The highest response in total and marketable yield occurred
308
with an application of 225 kg ha-1 N fertilizer at seeding, though this was not statistically
309
different than other N fertilizer rates (Table 5).
310
The interaction of site year with landform accounted for 28% of variance for total yield
311
and 22 % of variance for marketable yield. Potato yield was lower on upper relative to
312
other slope positions in 2005 and 2006 though this effect was not observed in 2007. This
313
was attributed to low soil N and soil organic matter relative in upper relative to lower
314
slope positions. Site-year accounted for 35% of variance for total yield and 42 % of
315
variance for marketable yield. Higher yields in 2006 (Table 5) were attributed to higher
316
accumulated P-days and earlier seeding date (Table 1) relative to 2005 and 2007. The
317
interaction between landform, site-year and fertilizer treatment accounted for a very low
318
percentage of the overall model variance (< 2%). In general yield was lowest in the upper
319
compared to the lower landform element though this was not consistently significant in
320
an analysis for all site years (Table 5).
321
Petiole Nitrogen
322
Potato petiole leaflet N concentration varied significantly during the growing season and
323
from year to year in response to landform and N fertilizer (adjusted Greenhouse-Geisser
324
method, P = 0.0193) with distinct differences as the growing season progressed in
325
relation to time of application and landscape (Table 6, 7, 8, 9, 10). Petiole leaflet N
326
concentration increased from upper to lower slope positions (Table 6), with fertilizer
327
(Table 7), and decreased with time during the growing season (Table 8) though there was
328
no interaction of landform with fertilizer treatment in analysis independent of repeated
329
measures (Table 7). The interaction of landform with fertilizer was significant when
330
analyzed with repeated measures (Time) as an effect (Table 8). Split application of N
331
fertilizer increased petiole leaflet N concentration relative to spring application (Table 7)
332
in combined analysis across site-years and landform elements. In general, N fertilizer at
333
rates greater than 75 kg ha-1 significantly increased petiole N. Petiole leaflet N
334
concentration averaged across treatments decreased during the growing season (Table 8,
335
9) though the trend varied within and between years. The highest petiole leaflet N
336
concentration was observed on June 8 and 19, 2006, the year with highest total and
337
marketable production. Petiole leaflet N concentration also decreased linearly with time
338
measured as P days or GDD, in an analysis of covariance with site-year and fertilizer
339
treatment. The correlation of petiole leaflet N concentration with total and marketable
340
potato yield was significant (P < 0.0001) for all dates except July 5, 2006 but the degree
341
of correlation was low within and between years with the exception of July 12, 2005
342
(Table 11).
343
Petiole NO3-N
344
Petiole NO3-N, determined in 2007, was similar to those for petiole leaflet N
345
concentration, with an interaction between fertilizer rate and landform. Analyses of
346
petiole NO3-N and petiole leaflet N concentration were significantly correlated (P
347
0.0001, r2 = 0.77).
348
DISCUSSION
349
There are few published reports for variable management of potatoes in landform based
350
management zones. Whitley and Davenport (2003) found that variable management of N
351
fertilizer in potatoes based on spatial variability of soil organic matter reduced N leaching
352
potential during the early part of the growing season, though this effect did not persist
353
during the entire growing season. Cambouris et al. (2008) assessed variable management
354
based on two management zones, for rate and timing of N fertilizer application on potato
355
tuber yield, distribution and specific gravity. The criteria for classification of zones in that
356
research were based on soil electrical conductivity related to clay substrata. The optimal
357
rate and timing of N fertilizer was similar between zones, though potato tuber yield, size
358
and specific gravity varied significantly (Cambouris et al. 2007; 2008). Successful
359
variable application of N fertilizer to flax (Linum usitatissimum L.), wheat and canola
360
(Brassica rapa L.) based on landform elements has been reported in the literature by
361
Beckie et al. (1997) but similar studies are not available for potatoes. Potato yield varied
362
significantly in response to N fertilizer management independent of landform elements
363
and displayed variability in this study, similar to results reported for wheat and canola in
364
western Canada (Beckie et al. 1997; Kucher et al. 2005a, b; Pennock et al. 2001).
365
Stevenson et al. (2001) concluded that the response of grain yield to landform element
366
was complex and varied due to the influence of several variables such as soil water
367
content, soil N availability during the growing season and plant disease in the landscape.
368
The effect of spring applied and split application of N fertilizer treatments on potato yield
369
and petiole leaflet N concentration in this study reflects the short growing season
370
characteristic of the potato growing area of Manitoba. Love et al. (2005) found no
371
significant difference in yield with split application relative to spring applied N fertilizer
372
for Bannock Russet and Gem Russet potato varieties, in contrast to regions with longer
373
growing seasons (2 to 3 weeks) (Westermann and Kleinkopt 1985). In this study total
374
and marketable yields increased in 2006 relative to 2005 and 2007, which was attributed
375
to the higher accumulation of P-days. However results from this study were similar to
376
those of Love et al (2005) and did not show a temporally or spatially consistent
377
significant increase in potato yield due to split application of N fertilizer. Precipitation
378
was higher in July 2005 and 2007 relative to 2006, and the efficacy of N fertilizer applied
379
in the split application during that month may have been reduced with higher rainfall and
380
subsequent leaching. In contrast, Love et al. (2005) reported that Russet Burbank
381
demonstrated a positive trend toward higher yields with two-thirds of the N fertilizer
382
applied early, though this effect was not statistically different from application at
383
planting. Love et al. (2005) inferred that improved control over N leaching minimized
384
the differences in N-use efficiency between pre-plant and split N applications based on a
385
study by Stark et al. (1995). The absence of any response of potatoes to split application
386
of N fertilizer was also attributed to short growing seasons by MacLean (1984) and
387
Zebarth et al. (2003). High levels of N fertility, reflected by the yields for controls in this
388
study, may also have reduced the potential for response to application of fertilizer.
389
However these high levels of N fertility were not correlated with soil test N, soil organic
390
matter, or hot KCl extractible N. Further research is required to characterize N cycling in
391
these soils.
392
The variability of the relationship between petiole leaflet N concentration status and
393
potato yield in response to fertilizer and landform for this study is attributed to rapid plant
394
development over the short growing season. Petiole nitrate-nitrogen concentration has
395
been used as means to determine the requirement for in-season application of fertilizer
396
(Love et al. 2005). Similar to the results of this study, Gardner and Jones (1975) and
397
Westcott et al. (1991) showed that petiole NO3-N concentrations decreased rapidly during
398
the growing season and changed with the rate of N fertilizer applied. Furthermore
399
concentrations vary depending on the time of sampling, location on leaf sampled and
400
cultivar (Williams and Maier 1990; Vitosh and Silva 1996). Petiole leaflet N
401
concentration was higher in lower relative to upper landform elements in July and August
402
2005 but not 2006 or 2007. However the correlation of petiole leaflet N concentration
403
with potato yield was low though statistically significant. In addition, petiole leaflet N
404
concentration did not vary significantly between landform elements or fertilizer rates
405
until later in the growing season in mid July 2005 but not for other years.
406
Split application of N for potatoes at midseason may not benefit producers in short
407
growing seasons characteristic of Manitoba and western Canada. Nitrogen fertilizer
408
similarly increased total and marketable yield at rates from 75 to 225 kg ha-1 in split
409
applications or applied at seeding relative to the control. Split application of N fertilizer
410
did not provide a significant advantage over that applied at seeding. Furthermore
411
deficiencies in petiole N, relative to the control, did not appear till later in the growing
412
season thus there is a narrow window for diagnosis and split application of fertilizer.
413
However split application of N should be considered in terms of the environmental
414
benefit of reduced leaching. CONCLUSIONS
415 416
The potential for variable management of N fertilizer is primarily with respect to
417
management in terms of spatial trends in landform element and application at seeding.
418
Although the correlation between petiole leaflet N concentration and potato yield is
419
statistically significant and could be used to calculate as a predictor of yield, the
420
relationship is weak and varies between years. Furthermore, split application of N
421
fertilizer does not provide a significant advantage in production over that applied at
422
seeding, though leaching may be reduced. Yield response to N fertilizer was observed
423
relative to the control, for rates from 75 to 225 kg ha-1 N applied at seeding or in split
424
applications. No interaction was observed between landform and fertilizer rate, or timing
425
of application.
426
Producers may use landform elements or similar related to delineate zones of high and
427
low yield, with the objective of focusing inputs on those areas which produce the highest
428
marketable yield and net income. However the response to N fertilizer may not be
429
consistent from year to year. Further research is required to assess N cycling to account
430
for high productivity in soils with low organic matter, soil test N and no application of N
431
fertilizer.
432 433 434
ACKNOWLEDGEMENTS
435
The authors wish to acknowledge the contribution of John and Jack Adriaansen, potato
436
producers in the Brandon area, who provided land, seed and pesticide management to the
437
project at no cost. In addition the technical assistance of Grant Gillis, Shirley Neudorf,
438
Josh Price and Roger Fortier, casuals (Kyle Able, Bryce Granger, Shaun Parkins), interns
439
(Lisa Bidinosti and Patricia Garrod) and summer students (Hayley Haberoth, Mark
440
Fenwick, Duane Allen, Blair Yaremchuk) at the Brandon Research Centre is
441
acknowledged. Dean James and Duaine Messer and Rod Lunggren (Semi-Arid Prairie
442
Agricultural Reseach Centre, Swift Current Saskatchewan) conducted laboratory analyses
443
in 2007. Technical staff from the Canada Manitoba Centre for Crop Diversification
444
provided equipment and assistance with potato harvest. Mitch Long and Nicole Rabe in
445
cooperation with John Van Oosterveen from PFRA, supervised students from
446
Assiniboine College and conducted elevation and conductivity surveys. This project was
447
supported by the Research Grant Award No. CA-9102-06 from BARD-AAFC - The
448
United States - Israel Binational Agricultural Research and Development Fund and
449
Agriculture and Agri-Food, Canada.
450
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602 603
Table 1 Total precipitation, monthly mean temperature, cumulative potato days and growing degree days (oC) from Carberry, Manitoba, 19 km south east of the study site Precipitation Temperature Cumulative Potato Days z (mm) (oC) (o C) Month 2005 2006 2007 Climate 2005 2006 2007 Climate 2005 2006 2007 Normal Normal
Cumu 2005
x
May June July August September Total 604 605 606 607 608 609 610
z
58.0 123.2 92.6 25.0 10.4 321.0
79.8 29.4 9.8 44.6 50.0
67.4 89.2 39.2 35.2 20.4
54 76 69 71 45
9.5 16.3 18.5 16.5 12.9
11.7 17.2 19.8 18.7 12.5
9.4 16.5 20.3 16.6 12.1
1. w 16.2 19.1 17.6 11.6
116.4 335.2 571.8 784.1 935.4
140.9 363.0 592.0 824.1 962.5
263.0 257.1 315
P days calculated for May 1 to September 30, based on Sands et al.1979, Raddatz et al.1996 GDD calculated C for May 1 to September 30, with a baseline of 7 o C recommended for potatoes by Manitoba Agriculture, Food and Rural Initiatives 2010. http://www.gov.mb.ca/agriculture/climate/waa50s03.html x Mohr et al 2011 Climate normals for Carberry station w Mohr et al 2011 Climate normals for Carberry station, The mean temperature for May (1961-1990) was not available for the Carberry weather station. Data from nearby stations reported mean temperatures for May (1961-1990) of 11.4 to 11.6oC. y
64.2 284.5 518.8 735.7 869.1
154.5 434.4 793.6 1091.3 1318.3
611 612
Table 2. Analysis of variance of total and marketable potato yield (Mg ha-1), for fixed effects fertilizer treatment and landform combined across site year Yield (Mg ha-1) Total
Marketable
613 614
Factor F Ratio Prob > F Landform 3.375 0.139 Fertilizer 6.747 0.003 Landform*Fertilizer 1.372 0.245 Landform 2.912 0.166 Fertilizer 5.639 0.006 Landform*Fertilizer 0.903 0.557
615 616
617 618 619 620 621 622
Table 3. Effect of fertilizer treatment on total and marketable potato yield (Mg ha-1) combined for landform and site year Fertilizer treatment (N Total Potato Marketable Potato -1 seeding-N at seeding Yield (Mg ha ) Yield (Mg ha-1) hilling kg ha-1) y 225 45.3A 33.9A 150 44.9A 33.4A 75-225 44.1A 32.1A 75-150 45.7A 32.6A 75-75 43.8A 31.3AB 75-0 42.1AB 29.2AB 0-0 38.9B 25.6B x SE 3.6 4.5 z Fertilizer treatments followed by the same letter are not significantly different (P≤0.05) Tukey HSD test y N fertilizer applied shortly after seeding, May 13 and 16, 2005, May 10 and 11, 2006, May 18, 2007 second application July 22, 2005, July 5, 2006, July 11, 2007 x SE standard error
623 624
Table 4. Residual NO3-N and total potato yield (Mg ha-1) for control treatments by landform and site year Slope position site year
Residual NO3-N
Total NO3-N residual and fertilizer N
2.
625 626 627
Yield from residual NO3-N and z fertilizer N
Total measured yield Mg -1 ha
-1
kg ha
3.
-1
Mg ha
Lower 2005
32.40
58.00
10.18
47.10
36.92
Middle 2005
14.60
40.20
7.05
31.90
24.85
Upper 2005 Lower 2006 Middle 2006 Upper 2006 Lower 2007 Middle 2007 Upper 2007
15.10 22.90 10.30 7.90 27.90 5.40 6.40
40.70
7.14
20.40
13.26
48.50
8.51
51.10
42.59
35.90
6.30
47.50
41.20
33.50
5.88
40.30
34.42
53.50
9.39
44.70
35.31
31.00
5.44
31.20
25.76
36.40
30.79
32.00 5.61 -1 calculated from 5.7 kg N fertilizer Mg potatoes (Manitoba Agriculture, Initiatives 2010b) z
Total – residual N yield Mg -1 ha
Food and Rural
628 629
630 631 632 633
Table 5. Effect of site year and landform element on total and marketable potato yield (Mg ha-1) Site Year Total Potato Marketable Potato -1 Landform Yield (Mg ha ) Yield (Mg ha-1) 2005_Lower 48.9B 33.3BC 2005_Middle 40.5CD 23.8C 2005_Upper 28.6E 12.6E 2006_Lower 54.4A 42.3A 2006_Middle 50.1AB 37.0AB 2006_Upper 46.4BC 34.6BC 2007_Lower 42.8CD 33.5BC 2007_Upper 41.2CD 32.6BC 2007_Middle 39.0D 30.6D y SE 1.2 1.2 z Site year and landform followed by the same letter are not significantly different (P≤0.05) Tukey HSD test y SE standard error
634 635
636 637
Table 6. Multivariate analysis of variance for petiole leaflet nitrogen concentration between factors (N mg g-1) Factor F Ratio Prob > F Site Year 295.7 0.0001 Landform 14.4 0.0001 Fertilizer 17.5 0.0001 Fertilizer*Site Year 5.4 0.0001 Fertilizer*Landform 0.8 0.6949 Fertilizer*Landform*Site Year 1.2 0.2264 Landform*Site Year 6.3 0.0001
638 Table 7. Contrasts with repeated measures for effect of fertilizer on petiole leaflet 639 nitrogen concentration (N mg g-1) Fertilizer Fertilizer Spring vs 150 vs 225 75 vs 150 75-225 vs 75-150 vs -1 -1 (kg ha ) vs No Split kg ha kg ha-1225 ha-1 150 kg ha-1 Fertilizer Application x 225 50.7A 50.7A 50.7A 50.7A 150 x 50.6A 50.6A 50.6A 50.6A 50.6A 75-225 w 50.5A 50.5B 50.5A 75-150 w 51.7A 51.7B 51.7A 75-75 w 49.9A 49.9B x 75 48.2A 48.2A 48.2B 0 45.0B Prob>F
