Effects of controlled release urea application on yield, nitrogen recoveryefficiency of rapeseed and soil inorganic nitrogen content

Four field trials were conducted to study the effects of the controlled release urea (CRU) application on yield, nitrogen recovery efficiency of rapeseed and soil inorganic nitrogen concentration in the main rapeseed zone of China in the 2009-2010 rapeseed growth period. The special purpose was to provide evidence for the CRU application in rapeseed fields. The results show that the application of CRU promotes the growth of rapeseed significantly and enhances the nitrogen supply in the whole period. Compared to the treatment with total N as base fertilizer (UB), the SPAD value, plant height and green leaf number of individual plant are increased significantly under the fertilization. The application of CRU increases the yield of rapeseed by 7.1%-19.7%, and the factors for the increase are branch number, pod number and high position of first nodes. The nitrogen accumulation amount and nutrient recovery efficiency are increased by 16.9%-27.3% and 12.2-17.7 percentage points compared to the UB treatment, and the NO3--N concentration, total inorganic nitrogen (Nmin) in tillage layer soils are increased by 149.3%-296.1% and 40.5%-145.9%. There are no significant differences in the growth indexes, yield and dry matter amount between the CRU treatment and the treatments of total N split application(UD), while the N accumulation and N recovery efficiency have increasing trends. Therefore, the effect of the total N split application on rapeseed could be achieved by CRU.