Nitrate accumulation in agricultural soils and groundwater of the North China Plain

摘要

This paper discusses the changes in fertilizer use and cropping systems over the last two decades. We summarize N input -output balances of various cropping systems and discuss how soil and climatic conditions and changes in fanners' practices contribute to nitrate accumulation in soils, and to nitrate leaching and nitrate contamination of groundwater. Currently, mean N fertilizer use in the North China Plain is higher than the national average. The presence of light textured soils and shallow ( < 15 m) groundwater aquifers, and the practice of excessive fertilization and flood irrigation all contribute to leaching of nitrate from topsoil to subsoil to shallow groundwater. Among all factors, fertilization had the most significant effect on nitrate accumulation in soil and nitrate contamination of groundwater. Nitrate contamination of shallow groundwater occurs especially in vegetable production system in greenhouses. More than 90% of the shallow groundwater wells in areas with intensive greenhouse vegetable production have nitrate-N concentrations that exceed 11.3 mg per litre. We conclude that improvements in farm management can drastically decrease the accumulation of nitrate in soils and groundwater while maintaining or improving agricultural productivity.