| Nutrients cycle is one of the most essential functions in an ecosystem. The amount of nutrients cycle is indicator of the promary chararteristics of metabolism in farming ecosystem. Soil organic matter is one of the most important factors that affect the soil productivity and soil nitrogen is an. essential nutritional element for crop growth. Since rice is one of the main farming crop in the red soil hilly region of south China, it is necessary to understand the characteristics of nutrients cycle, its yield-increase effects and its contribution to food production of China, and its effect on the cycling and transformaation processes of soil C and N, in order to establish the better cyc'e of nutrients, reasonably utilize the available resource and adjust and control the balance of soil C and N in the rice cropping systems of red soil region of China. The experiment was conducted based on the long-term experiment-the effects of different fertilization systems on soil productivity and environments in rice cropping system of red soil region of South China at Taoyuan Experimental Station of Agroecosystem Research. The characteristics of nutrient cycling was pointed out, its yield-increase effects and its contribution to food production was illustrated under the fertilization systems developed and the nutrients recycled, and the transformation processes of soil C and N was proved up in the rice cropping system of red soil region of China, by means of analysis of the 12-year soil nutrients, crop yield, the cycle and transformation processes of C and N. A model was developed according to the organic C dynamics, and was tested by the long-term experiment. The results indicated it could promote the cycle of soil C and N, increase the content of soil organic matter, improve the quality of soil organic matter, heighten the activity of the pool of soil C and N, strenthten the cycle and transformation of soil nutrients, and increase the systems productivity only depended on organic residues cycled and used in red paddy system. The detailed results were summarized as follows:1. The output of NPK nutrients is much larger due to harvesting rice. The output of N range from 88.2k g/hm2 to 231.0 kg/hm2, its average is 172.6 kg/hm2. The output of P changes from 21.5 kg/hm2 to 55.7 kg/hm2, its average is 38.3 kg/hm2. The output of K varies from 105.6 kg/hm2 to 282.2 kg/hm2, its average is 184.6 kg/hm2. The output of NPK nutrients is 61.9 kg/hm2, 11.8 kg/hm2 and 162.0 kg/hm2 by rice straw, respectively. Their percent to the output of rice harvested is 35.9%, 30.8% and 87.8%, respectively.2. The most NPK nutrients are returned back to soil using organic material cycle in rice cropping system of red soil of China. The returned amount of NPK is up to 127.6 kg/hm2, 40.4 kg/hm2 and 262.6 kg/hm2, respectively. Their percent to the output of rice harvested are 55.2%, 72.5% and 93.0%, respectively. Soil nutrients reveals deficit under chemical fertilizer (N 230kg/hm2, P 40kg/hm2, K 162kg/hm2) is applied only while NPK nutrients indicate surplus based on NPK applied and using organic material cycle in rice cropping system of red soil.3. Three jumps of soil productivity are observed with development of fertilization systems and the productivity is increased 15% each jump in rice cropping system of red soil. Compare with non-fertilization treatment, the productivity of the organic material cycle treatment is increased 56.8%, it is first jump of productivity developmental process since fertilization systems improved in human history. The productivity of fertilization system with NPK combination is heightened 62.5%, it is second jump of productivity as chemical fertilizer is applied in agriculture. The productivity of fertilization system with NPK+C is enhanced 80.1%, this is third jump based on organic material cycle and NPK fertilizer enter the agro-ecosystem in turn. The rice yield is increased 62.5% due to chemical fertilizer application, on other words, the contribution rate of chemical fertilizer application is 38.4% in yield-...
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