Topographically Controlled Yield Response of Canola to Nitrogen Fertilizer

Abstract

The effect of topographical position on the yield response of canola ( Brassica rapa var. Maverick) to N fertilizer was evaluated in a 3‐yr field study in Saskatchewan, Canada. The hummocky, glacial till research site was stratified into three topographically defined landform complexes (convex, linear, and concave). Five N treatments (0, 0.5, 1.0, 1.5, and 2 times the recommended soil test rates; treatments will be referred to as 0×N, 0.5×N, 1×N, 1.5×N, and 2×N, respectively) were randomized in replicated blocks, and each block spanned the three landform complexes. Substantial yield differences occurred among the study years and were associated with year‐to‐year differences in spring soil moisture. Canola seed yields (averaged across years and treatments) increased from 0.53 Mg ha −1 in convex complexes to 0.95 Mg ha −1 in linear, and 1.42 Mg ha −1 in concave landform complexes. The greatest yield responses to N occurred in the concave landform units in years where spring soil moisture was high. The N fertilizer rate required to achieve the economically optimum yield was significantly correlated to spring available moisture (required N rate [kilogram per hectare] = 40.9 + 14.87 [spring available water {in centimeters} water to 60‐cm depth], R 2 = 0.73, sig. = 0.003) but was not significantly related to spring (i.e., preseeding) available soil N. The results confirm earlier studies indicating the importance of spring available water for crop production in the northern Great Plains, and suggest that intensive spring sampling for soil moisture conditions may be the most useful diagnostic tool for the implementation of a variable rate N program in this region.