Effects of controlled-release nitrogen fertilizers on yield and quality of Chinese cabbage and their related mechanisms

The effects of different controlled-release nitrogen fertilizers (CRNFs) supply on yield and quality of Chinese cabbage (Brassica campestris L. var. pekinensis) were studied in field experiment. Relationship between nitrogen release from CRNFs and nitrogen uptake by Chinese cabbage, and the characteristics of fertilizer coat were also discussed. The results showed that the yield of Chinese cabbage was significantly increased by 8.2%16.8% with CRNFs application, compared to the urea supply. Vc content in the head leaves at harvest stage was 1.80(mg/kg) at average with CRNFs application, 24.8% higher than that of urea treatment. NO3--N contents were significantly decreased by CRNFs treatments, which were 14.3%39.9% lower in rosette leaves at rosette stage and 12.1%21.4%in head leaves at harvest stage, compared to urea treatment. The yields, NO3--N content and Vc content of Chinese cabbage leaf were almost changeless when CRNFs were half supplied. It was confirmed that nitrogen was released slowly and continuously from the inner part of CRNF granules. When CRNFs were applied at early stage, nitrogen was still supplied at medium and later stage for Chinese cabbage. The characteristics of nitrogen release of CRNF were apparently determined by thickness of granule coat, number and diameter of pores on coat surface.