Optimizing nitrogen application rates for winter canola in Mississippi

Abstract

The production of canola (Brassica napus L.) in the United States is low, whereas the demand is high. Most US canola research is centered in the Midwest, with minimal to no research in Southern states including Mississippi. Therefore, a study was conducted in Mississippi to assess the feasibility of canola as a double crop with soybean (Glycine max L.) rotation and determine its optimum nitrogen (N) requirement. After canola was harvested, soybean was planted within the same experimental plots. In total, six N treatments (0 [control], 34, 67, 101, 135, and 168 kg N ha⁻¹) were applied to canola and replicated four times across all site-years in a randomized complete block design. The application of N increased seed yield, aboveground biomass, and N content compared to the control in canola. Across all site-years, the highest seed yield was 1726 kg ha⁻¹ at 168 kg N ha⁻¹. Moreover, N uptake, plant height, and test weight were highest at 135 kg N ha⁻¹, which were 76%, 21%, and 44% greater than control, respectively. Oil content and seed weight were inversely related to N rates indicating dilution with increased N. Overall, 141 kg N ha⁻¹ was found to be the agronomic optimum nitrogen rate, and no further supplementation was deemed necessary to maximize canola yield in Mississippi. Additionally, the following soybean crop benefitted from the N applied to canola and produced greater yields. This study establishes that canola has the potential for double cropping without adversely affecting subsequent soybean yield, provided optimum N rates are applied.