Nitrogen Flow in Farming-Feeding System and Its Environmental Impact in China
中国种养系统的氮流动及其环境影响

By applying Nitrogen Flow Model for Farming-Feeding System (NFM-FFS) which integrates soil full nitrogen balance model with inventory analysis for agricultural pollution, nitrogen flow in China farming-feeding systems and its environmental impact are analyzed. In 2003, although surface nitrogen surpluses, nitrogen deficit in agricultural soil system in China is estimated to be 623.9×104t, and 13.7 kg/hm2 averagely, which implies that soils in China farming-feeding systems are at the risk of nitrogen content decline and potential soil degradation as a whole. With a intense nutrient input in arable land and no extra fertilizer input in grassland in China, there is a nitrogen surplus of 1761.9×104t, averagely 142.8 kg/hm2, while grassland has a deficit of 2385.7×104t, averagely 90.7 kg/hm2. As a result, existing negative impact of cropping activities on water environment as well as grassland degradation may be effectively abated by balancing nitrogen input between arable land and grassland. Total nitrogen loss from China farming-feeding system is 2266×104t, including 495.8×104t exported into surface water by drainage and surface runoff, and 102.4×104t into groundwater by leaching. Lost nitrogen is to be deposited in rivers, lakes and marine system, and is less likely to return to farming-feeding system. Fertilizer should be the priority of rural pollution control and management because of its dominant contribution to nitrogen export into water environment from farming-feeding system.