洞庭湖区氮肥外部成本及稻田氮素经济生态最佳投入研究

【目的】以中国粮食主产区之一的洞庭湖区为研究对象，研究氮肥的外部成本和稻田经济生态最佳投入量。【方法】采用环境影响经济评价方法估算氮肥的外部成本，运用外部不经济性原理和生产函数模型方法研究兼顾农户经济效益、生态效益的稻田适宜施氮量。【结果】2002年洞庭湖区因氮肥施用不当带来的渔业损失0.1×107元，饮用水源污染损失1.02×108元，旅游业损失0.9×107元和居住环境损失0.3×107元。每公斤纯氮的外部成本约为0.41元。兼顾生产与农户经济效益的施氮量为138 kg•ha-1，兼顾生产与生态效益的施氮量为137 kg•ha-1。【结论】洞庭湖区实际施氮量已经达到并超过农户经济效益最佳施氮量和生态施氮量，氮肥给生态环境带来的负外部影响应引起足够的重视，建议政府在一些氮肥高投入、高污染的县（市）征收环境税。

Studies on the External Costs of and the Optimum Use of Nitrogen Fertilizer Based on the Balance of Economic and Ecological Benefits in the Paddy Field System of the Dongting Lake Area

【Objective】Study on designing the tax of nitrogen fertilizer can provide one of the new ways for controlling nitrogen fertilizer non-point source pollution. 【Method】The tax design of nitrogen fertilizer was discussed by utilizing the external theory and the demand elasticity theory.【Result】The results showed that the 11 counties (cities and districts) which the farmland nitrogen application in the Dongting Lake area surpassed the average ecological fertilization dosage are listed to the taxation scope of nitrogen fertilizer tax, the ecological environment loss will reduce 0.07×108 Yuan and the revenue will increase 0.89×108 Yuan in the country after levying on nitrogen fertilizer. The economic benefits, which brought about by the increasing of the food supplies production, will be 0.58×108 Yuan and the net social benefit will be 1.58×108 Yuan after the revenue collecting. The variation scope of the increasing expenditure of farmers will range from 0.95％ to 1.49％. The increasing income of farmers will take up -5.93％ to 8.41％ of the net total income. The 6 counties (cities or districts), Huarong, Miluo, Anxiang, Lixian, Nanxian and Yuanjiang, in which the nitrogen application surpassed the ecological fertilization dosage and decreases the food supplies production are listed to the N fertilizer tax collecting scope, the ecological environment loss will reduce 0.06×108 Yuan and the revenue will increase 0.49×108 Yuan in the country after levying on nitrogen fertilizer. The economic benefits, which brought about by the increasing of the cereals production, will be 1.25×108 Yuan and the net social benefit will be 1.85×108 Yuan after the revenue collecting. The variation scope of the increasing expenditure of farmers will range from 1.01％ to1.49％. The increasing income of farmers will take up 2.57％ to 8.41％ of the net total income. The coefficient of price elasticity of nitrogen fertilizer demand is 0.21, which instructed that the market demand and supply are in lack of elasticity in the short period and the impact of nitrogen Fertilizer manufacturers is subtle. 【Conclusion】Considering from the entire social welfare, taxation of nitrogen fertilizer will have more advantages than the disadvantages in the Dongting Lake area. It is more appropriate to list the Nitrogen application surpassing the average ecological fertilization dosage and the food supplies production not decreasing areas as the nitrogen fertilizer tax collecting scope.