Nutrition Characteristics and Fertilization Indices of Nitrogen, Phosphor and Potassium for Major Vegetables in Fujian Ⅱ. Vegetable's Response to Fertilizations and Garden Soil's Available NPK Fertilization Indices

Based on the results of field experiments on the vegetables'response to N,P and K,soil fertilization indices of available N,P and K in vegetable gardens in Fujian were established.Soil fertility of the croplands was classified as high,medium and low grades according to the vegetable yield from 148 field experiments conducted in a test area.The results showed that the average contribution rate of soil nutrients to the growth of vegetables was(50.9?12.8)%.It decreased significantly when the soil fertility declined.A significant linear relationship existed between the yield on the control and fertilized areas.Leafy vegetables,melon,fruits,root-stock and onion-type vegetables were used in this study.Their yields increased significantly in response to the NPK fertilization.The effect of the NPK application increased significantly as the soil fertility declined.The extent and net gain from N fertilization were significantly greater than those from K,and those from K significantly greater than those from P.The value/cost ratios(VCRs)of N fertilization for leafy and onion-type vegetables were significantly higher than those of P or K.The VCRs of P for the root-stock vegetables,melon and fruits were significantly higher than those of N and P.The critical application levels of alkali-hydrolyzable N,Olsen-P and available K to achieve high yield for leafy vegetables were found to be 243 mgg-1,52 mgg-1 and 150 mgg-1,respectively.And those for other vegetables were 276 mgg-1,47 mgg-1 and 132 mgg-1,respectively.These recommended application levels were all significantly higher than for grains and oil crops.The results provided a scientific basis for soil evaluation and fertilization optimization for vegetable gardens in Fujian.