Effects of CRU application on the yield, nitrogen recovery efficiency of rapeseed and soil nitrogen Balance
Rapeseed is one of the main oil crops, it occupied 50% of total planting area and 41% of total oil output of whole oil crops in China. At present, the labor cost occupied 50% of total investment in rapeseed planting, as winter rapeseed usually needs 2-3 fertilizer top dressing operation in its long growing season. Therefore, reduce labor cost and make the operation simple become more and more important in rapeseed planting.
Supported by IPNI China program, the project cooperators in Huazhong Agricultural University conducted 4 field experiments to study the effect of controlled release urea (CRU) on the yield, nitrogen recovery efficiency and soil nitrogen balance in the main rapeseed planting areas along Yangtze River valley in recent years. The results showed that application of CRU promoted growth of rapeseed significantly and guaranteed the nitrogen supply in the whole growing period. The SPAD value (leaf green grade), plant height and green leaf number of individual plant increased significantly compared to the treatment with total N as basal fertilizer (UB). The application of CRU increased the yield of rapeseed by 0.9%-19.7%, for it promoted branch number, pod number and first nodes high. Results also showed that the nitrogen accumulation amount and nutrient recovery efficiency were increased by 16.9%-27.3% and 12.2-17.7 percentage points compared to that of the UB treatment. The NO3-N concentration, total inorganic nitrogen in tillage layer soil were increased by 149.3%-296.1% and decreased by 17.7-61.3 kg/ha after the experiment. Nitrogen fertilizer recovery efficiency of CRU treatment was increased by 22.6-51.0 percentage points compared to that of the UB treatment. There was no significant difference in the growth indices, yield and dry matter amount between the CRU treatment and the treatment total N split application (UD), while N accumulation and N recovery efficiency were increased. After the experiments, the soil TIN and N recovery efficiency of CRU treatment were increased by 16.7-51.3 kg/ha and 11.5-30.4 percentage points compared to that of the UD treatment. Therefore, CRU application not only promoted rapeseed growth and seed yield, but also improved soil N fertility and saved labor cost.
