Abstract:A long-term field experiment with fixed site was conducted to study the effects of imbalanced fertilization on soil fertility,fertilizer use efficiency and nutrient balance in rice-wheat cropping systems was studied.The results showed that the content of soil organic matter and total nitrogen declined in the treatment without fertilization for 11 years,while it were increased in each treatment with chemical fertilizer application,among which organic matter content for NPK balanced fertilization treatment was the highest.Soil available P content was substantially increased for all treatments with phosphate fertilizer application compared with background value before experiment.Soil slowly available K content was lower than background value before experiment in all treatments whether potash fertilizer was applied or not,among which soil slowly available K was highest with straw returning to the soil.Imbalanced application of N,P and K induced a reduction of crop yield and the efficiency of chemical fertilizer,as well as depletion of soil nutrients.Applying N 150(kg/ha) per cropping season could maintain soil nitrogen fertility;Applying P2O5 60—75 kg/ha per cropping season could cause P surplus.Soil potassium was deficient for all treatments except the treatment of straw returning in rice-wheat cropping systems.