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

Since nitrogen (N) is often the limiting nutrient for high N demanding crops such as canola (Brassica napus L.), N fertilization is the most decisive factor to achieve optimum grain yields and profits. However, the availability of N to crops involves complex process controlled by edaphic, environmental and management factors. Nitrogen fertilizer management in a cool and humid environment as found in eastern Canada is even more important due to the significant spatial and temporal variability of both soil N supply and crop growth factors in the field. However, the spatial variation in soil properties is not generally considered in traditional N-fertilizer application; it is often based on a single rate of application across the entire field regardless of soil type and other variables. There appear to be no studies assessing the applicability of yield monitors in canola crop production. The purpose of this study is to better understand the interactive effects of SMN supply and crop growth parameters on grain yields in commercial canola fields. The specific objectives were to: (1) assess the effects of N fertilizer application on the spatial patterns of SMN, crop growth parameters and grain yield of canola; and (2) determine the dynamic relationships among SMN, plant growth parameters and yield.

This study examined the spatial variability and dynamic responses of soil mineral N (SMN), crop growth measurements, and yields of canola to different rates of preplant N applications. Both SMN contents and grain yield varied significantly across field-strips that received different N treatments and within field-strips that received the same N treatment, indicating a substantial spatial variability in soil N supply power. The inconsistent responses of grain yield of canola crop to preplant fertilizer N application was likely due to the influence of large spatial variability of the field. Overall, strong associations between SMN contents and crop parameters measured at early flowering stage, and grain yield provide substantial evidence for in-season variable rate N application for canola crop production in eastern Ontario.