THE CHANGES OF CROP YIELD AND SOIL FERTILITY WITH LONG-TERM FERTILIZER APPLICATION

A number of long-term fertilizer experiments were laid out by China National Network on Evaluation of Chemical Fertilizer Use around 1981. Results from 70 experiments, are summarized in this paper. The main objective of conducting these experiments is to monitor the changes of crop yield and soil fertility with successive use of chemical fertilizer and organic manures alone, or in their comb -ration. It is indicated that only when NPK fertilizers are used together can a high and stable yield be kept, a more higher yield can be obtained if organic manure is added.In general, the effect of N fertilizer is higher than of P and K fertilizer, and effect of P and K fertilizers varies with soils and crops. The effect of organic manure is increasing with application years because of its accumulated impacts. According to the changes of soil physical, chemical and biological properties, soil fertility can be improved obviously by use of organic manure,and also improved by integrated use of NPK fertilizers. A proper fertilizer formulation is put forward for maintaining balance of nutrients and increasing yield and fertility.