Effect of N and K Fertilizers on Yield and Quality of Greenhouse Vegetable Crops1

The application of large amounts of fertilizers, a conventional practice in northern China for the production of vegetable crops, generally leads to substantial accumulation of soil nutrients within a relatively short period of time. A fixed field experiment was designed to study the effects of nitrogen (N) and potassium (K) fertilizers applied to optimize the yield and quality of typical vegetable crops. Application of N and K fertilizers significantly increased the yields of kidney bean. The largest yields were obtained in the first and second years after application of 1 500 kg N and 300 kg K2O ha−1. In the third year, however, there was a general decline in yields. Maximum yields occurred when intermediate rates of N and K (750 kg N and 300 kg K2O ha−1) were applied. However, no significant differences were observed in the concentrations of vitamin C (VC) in kidney bean among different years and various rates of fertilizer treatments. Yields of tomato grown in rotation after kidney bean showed significant responses to the application of N and K in the first year. In the second year, the yields of tomato were much lower. This suggested that the application of N fertilizer did not have any effect upon tomato yield, whereas application of K fertilizer did increase the yield. Application of K fertilizer was often associated with increased sugar concentrations.