| Rice is one the three most important crops (rice, wheat and maize) in China and it accounts for 40% of the summer crops, about 40 million hectare per year. Waterlogged cultivation of rice is a traditional way, which can ensure the rice yield to be very high and long-term stable. However, more than 80% of the freshwater used in agriculture finds its way to rice production in waterlogged soil in China. In Jiangsu province, for example, where it receives 800~ 1000mm precipitation annually, irrigation of 10,500~ 15,000 m3 of freshwater per hectare is still needed for one crop season of rice and more irrigating freshwater is needed in the area with less rainfall. Much work has been done on water-saving cultivation of rice crop, i.e., intermittent irrigation, which saved 20~60% of freshwater compared with traditional waterlogged cultivation, varying with the different precipitations in different areas.A novel cultivation system of rice crop in aerobic soil is showing its great potential in water saving agriculture, especially in the areas which receive more than 800 mm of precipitation annually. The rice cultivated in aerobic soil is a complete revolution in the rice cultivation system, in which the rice crop (not upland variety but traditional paddy rice variety in waterlogged soil with high yield) is grown during whole growth stage in a soil with water content being 70~85 % of water holding capacity (WHC). Our previous three years' field experiments showed that almost the same grain yields of rice crop could be obtained in aerobic cultivation as in waterlogged only if the soil was mulched with crop straw. In Jiangsu province, for example, the yield of rice grain of 8738 kg hm'2 in aerobic cultivation could be obtained and only 11% reduction was found compared with that in waterlogged cultivation with the same rice cultivars. About 90~100 % of freshwater irrigated could be saved in aerobic cultivation compared with waterlogged one and 11% reduction in grain yield of rice cultivated in aerobic soil is nothing in terms of the freshwater saved.The novel cultivation of paddy rice variety in aerobic soil reveals a great potential not only for water-saving agriculture but also for the rice intercropping with legumes, both of which are closely related to sustainable development of agriculture. In this study, field experiments were carried out to investigate yield advantages in intercropping system of peanut with rice crop cultivated in aerobic soil in 2001 and 2002 and the effects of intercropping system on soil N fertility were also studied in field condition. Pot experiments were then done to examine the biological nitrogen fixation (BNF) by peanut and N transfer from peanut to rice in the intercropping system using 15N-isotope dilutionmethod with N fertilizer application rates of 15, 75, 150, 225 and 300 kg N hm-2 in 2001 ~ 2002, and the contribution of peanut root decomposition to N transfer was investigated as well. The main results were as follows:1. Two-year field experiments showed that the relative advantage of intercropping, expressed as land equivalent ratio (LER), was 1.41 in 2001 and 1.18-1.36 in 2002, respectively. Yield of rice was significantly increased in intercropping system while that of peanut were not significantly different in intercropping and monocropping system. The yields of rice grain and peanut, for example, were increased by 29~38 % and 4~7% in intercropping system compared to the respective component crop in monocropping system, respectively. The N concentration of rice (21.2 g kg"1) under monocropped condition was significantly (P=0.05) lower than under intercropped (26.9 g kg"1) condition, while there was no significant difference of N concentration of peanut between mono- and intercropping. Compared to the rice in monocropping system, an increasing of 27.4 % of N concentration in rice plant was obtained in intercropping when the rice was harvested, which resulted in a higher chlorophyll content of the rice leaves. Thus, the chlorophyll content of rice leaves were...
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