1996年和2011年全球农产品贸易中氮素流向和流量的变化

为了更有效地利用资源同时保护环境，有必要了解新时期全球养分的分布特征。本文通过量化不同农产品中所包含的氮，研究比较了全球肥料氮、植物性食品氮、动物性食品氮和饲料氮等在1996年和2011年的流量和流向变化。结果表明，与1996年相比，全球氮素贸易量增加了1 371.3万t，到2011年达到3 380.1万t。从产品来看，肥料氮、饲料氮、植物性食品氮对增量的贡献分别为59.3%、19.7%和18.7%，说明能源和土地是氮素流量变化的关键因素。从区域来看，北美和南美对肥料氮进口增量的贡献为39.5%和28.5%，其加强了矿产依赖型的氮肥产品进口，而增加了土地依赖型的植物性食品和饲料出口；而亚非发展中国家与地区则相反，其对植物性食品氮和饲料氮进口增量的贡献为44.7%和21.3%。向以矿产换土地模式的转变加剧了亚非发展中国家与地区的食物安全和能源安全问题，而氮素的跨地区运输又加剧了所有地区的环境问题。因此，各国应据此思考本国食物安全、能源安全和环境安全的最优氮管理策略。

Transformation of Quantities and Directions of Nitrogen Contained in the Worldwide Trade of Agricultural Products in 1996 and 2011

In order to make use of resources more efficiently and better protect the environment it is necessary to understand features of the global nitrogen(N)distribution. We analyzed N trade flow from fertilizers, food of vegetal origin, food of animal origin and feed in 1996 and 2011 at a global scale by quantifying N contained in agricultural products. The results indicate that the total amount of global N trade reached 33.8 million tons in 2011, a 13.7 million ton increment compared with that in 1996. Among all categories, N from fertilizers, feed and food of vegetal origin contributed 59.3%, 19.7% and 18.7%, respectively, to the increment in the total amount of the global N trade. This implies that land and energy are key factors impacting variation in N flow. From a regional perspective, North and South America contributed 39.5% and 28.5% to the increment of fertilizer-N import, respectively. They largely increased fertilizer-N imports(resource-dependent products)and exported more and more N from food of vegetal origin and feed(land-dependent products). However, regions like Asia and Africa behaved in the opposite way: they contributed 44.7% and 21.3%, respectively, to the increment in N imports from food of vegetal origin and feed. Exchanging resources for land has exacerbated the problems of food and energy security in Asia and Africa, while transporting N-containing products across the world induces environmental problems worldwide. Therefore, each country should select an optimal N management strategy based on the results above to ensure the security of food, energy and the environment.