On-farm spatial characterization of soil mineral nitrogen, crop growth, and yield of canola as affected by different rates of nitrogen application

Understanding the spatial variability of soil mineral nitrogen (SMN) and crop growth is an important step for implementing precision nitrogen (N) management technologies for canola production. A 3 yr field experiment in Ontario investigated the within-field spatial variability of SMN in relation to growth parameters and yield. Each year, large strips in a commercial field were randomly assigned a preplant N treatment (0, 50, 100, and 150 kg ha(-1)), with three replicates of each. Our data showed that SMN varied widely among field-strips receiving different treatments and also within strips receiving the same N rate, indicating significant spatial variability in N availability at the field- and strip-scale. Some crop measurements exhibited wide variations in parallel with the SMN dynamics. At the early flowering stage, SMN contents displayed a strong relationship with plant height and branch numbers. Although grain yield showed a positive response to N, the inconsistent yield increase with increasing N supply was likely due to the inherent variations in soil N supply among years and fields, indicating an inefficient use of the uniformly applied preplant fertilizer N by the crop. The strong associations between SMN and crop parameters or yield provided a substantial evidence for implementing in-season variable rate N application.