Evaluating the application of controlled release urea for oilseed rape on Brassica napus in a regional scale: The optimal usage, yield and nitrogen use efficiency responses

Abstract

The use of controlled release urea (CRU) was proposed as a promising approach to improve crop yield and nitrogen use efficiency (NUE) of crops in varying regions. However, such beneficial effects have not been well assessed in winter oilseed rape (Brassica napus L.), which usually has a period longer than 200 days. In this regional scale study covering 9 site-years, the effects of CRU for oilseed rape (CRUrape) application on seed yield, NUE, N physiological efficiency (NPE) and the recommended application rate were investigated, in comparison with conventional urea (CU). Oilseed rape plants were grown with either CRUrape or CU applications with five N rates (0, 60, 120, 180 and 240 kg N ha−1). The results showed that CRUrape N release coincided well with oilseed rape N demand. The CRUrape application generally increased seed yield relative to CU, and such effects were more pronounced at higher N rates (180 and 240 kg N ha−1) because of the sufficiency N supply over the whole growing season and thus higher pods per plant. While the low N rates (60 and 120 kg N ha−1) could not supply adequate N at early development stage. Obvious N source × N rate interaction was observed. Moreover, the N source × site-year interaction was significant. The yield increase by CRUrape over CU varied considerably among site-year, suggesting CRUrape effects may depend very much on the target environmental conditions. Further analysis revealed that precipitation before wintering and accumulative temperature over the over-wintering contributed to variations in such CRUrape effects. The oil yield was remarkably increased by 12.4% and 7.1% by CRUrape relative to CU at 180 and 240 kg N ha−1, because of the benefits of seed yield and oil concentration. The NUE and NPE of CRUrape were higher than that of CU as the N rate increased to 180 kg N ha−1. The recommended N application rate of CRUrape was different from that of the CU in 5 of 9 site-years. The mean optimal N rate for the region investigated was quite similar for CRUrape and CU (203 and 201 kg N ha−1, respectively), but CRUrape application with optimal N rate could enhance the average grain yield by 7.2% and the related gross profit by 17.8%, respectively. In conclusion, the CRUrape application could be used as a feasible strategy to improve oilseed rape seed yield, oil yield and NUE in the investigated region.