| Effect of continuous application of chemical and/or organic fertilizer on productivity and soil fertility, as well as nutrient (N, P, K) cycling and nutrient balance in rice-wheat cropping systems was studied by using field, pot, lysimeter experiments and laboratory analysis. The purposes of this study were to quantify the input/output of nutrient resource and its related change in crop productivity, soil fertility and system sustainability, in order to provide detailed information for nutrient resource use and management. The main results were as follows:During 10 years of the rice-wheat rotation, application of NPK chemical fertilizer or combination of NPK chemical with organic fertilizer could maintain or even increase crop productivity and soil fertility in rice-wheat cropping system. Under above conditions the high sustainable yield for rice and wheat and high efficiency of N fertilizer could be achieved year by year, while the content of soil organic matter and N, P were increased, and the balance of soil available K could be maintained. Inbalanced application of N, P, and K chemical fertilizer led to a reduction of crop yield and the efficiency of chemical fertilizer, as well as depletion of soil nutrients.The rice-wheat rotation repeated transitions from anaerobic to aerobic growing conditions, which greatly affected soil nutrient remove, transport and accumulation. Soil mineral N contents were low and did not show tendency of accumulation in 0-100cm soil profiles after 10-years continuous application of N fertilizer. The remaining P fertilizers in soil after long-term applied P fertilizers had been transformed into inorganic phosphorus of Ca2-P- Cag^ Al-Ps Fe-P and O-P, which were mostly available for rice and wheat. When soil P got exhausted the O-P became the main available P for rice and wheat. The accumulated P in soil had obvious downward transportation. The release of soil slowly available K and soil K-supplying capacity were improved during flooding period.In the rice-wheat cropping systems, continuous application of N fertilizer alone resulted in a reduction of crop yield and N use efficiency. Balanced supply of N and PK nutrient could increase both yield and N use efficiency, grain yield of rice and wheat were increased by 8kg and 10kg per 1 kg N applied, fertilizer N recovery rate were increased by 34.5 + 9% and 40 ?% for wheat and rice in ten years, respectively. N input from environment to rice-wheat cropping system amounted to 126 kg/hm2, which was not neglectable for optimized nutrient management. The N removal by rice and wheat harvest made up 30-38% of nitrogen input from N fertilizer applied to the soil-crop system. The rates of nitrogen left in the soil and lost by volatilization and leaching were in the range of -5.9%~36.4%, and 38%~76% respectively. Combinations of N, P and K fertilizers or NPK with organic manure could greatly reduce the losses of nitrogen by volatilization and leaching, thus increase (he rales of nitrogen absorbed by crops and stored in the soils. The losses of nitrogen by volatilization were significantly larger than by leaching which accounted for 3-4% of the total N applied. The strongest downward transport and leaching of nitrogen occurred in the period of wheat seedling growth, control the rate of Nfertilizer were the mostly approached for reduction of N leaching.The fertilizer P recovery efficiency and agronomic use efficiency of wheat were 27.1% and 13 kg, respectively, which were larger than that of rice, namely 19.5% and 10kg, respectively. The P efficiency of rice and wheat was increased with the prolongation of the experiment. The residual P in soil accounted for 70-80% of applied P fertilizers, which increased soil available P content in a average rate of 2.8 mg/kg annually. The proposition of P uptake by rice and wheat from soil were 60-70% and 40-50%, respectively, soil P-supplying capacity were improved during flooding period, so that the P fertilizer rate for rice could be reduced during rice growth season.Purple soil has quite...
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