Experimental Study on Water and Nutrient Transformation in the Paddy Ecosystem of the Yangtze Valley
长江流域稻田生态系统的水分和养分转换过程

The located experiment was conducted in Taoyuan Experimental Station of Agroecosystem Research of the Chinese Academy of Sciences. The result indicated both fertilization systems and water management pattern significantly affected the transformation processes and production efficiency of the nutrient and water. The production efficiency was 4.5 kg/kg for N fertilizer application only, but 8.8 kg/kg and 8.0 kg/kg for NP and NPK fertilizer combined, respectively. The yield-increase rate was 56.8% in the organic residue recycle case, however it could be up to 80.1% based on organic residue combined application with NPK fertilizer. The yield-increase rate was 62.8% with fertilizer application development and 80.1% with inorganic-organic fertilizer combined. In other words, in the case of optimum fertilization system, the largest contribution portion of inorganic fertilizer applied was 38.4% while that of inorganic-organic fertilizer combined was 44.4%. There were obvious differences in water transformation in paddy fields with different irrigation patterns. Water distribution in the paddy field with control irrigation (CI) showed that transpiration and evaporation accounted for 1/2, plowing and preparing land for 1/6, plant constitution for 1/21, field leakage for 1/14, and other environment consumption (maintenance) for 1/5. Whereas, the proportion of plowing and preparing land and field leakage was too large under rain-fed (RF) conditions. Water needed for irrigation was about 5838 m 3 /hm 2 and the annual variation efficiency of irrigation water required was 8.3%, of which 71% for growing late rice. Irrigation between July and September consumed 68% of the total water required. Irrigation production rate was 3.67 kg/m 3 in rice biomass and 1.48 kg/m 3 in grain output. It was concluded that for growing double harvest rice in the Yangtze Valley, the thinner water layer must be kept in early rice and the periodical ration irrigation was very important for late rice.