河北省不同利用方式农田土壤氮磷环境风险分析

弄清不同利用方式农田土壤氮磷养分平衡状况,进而明确其环境风险特征,为进一步指导土壤养分管理及环境政策制定具有重要意义。研究以河北省的粮田、果园和菜地为研究对象,通过分析三种利用方式氮磷的输入、化肥和有机肥的分配比例及氮磷养分的盈余状况,并结合化肥使用环境风险指数,评价三种不同利用方式化肥氮磷的环境风险类型。结果表明,氮总输入量为菜地明显高于果园和粮田,磷总输入量为菜地和果园明显高于粮田,且粮田和菜地氮磷输入主要以化肥为主。三种不同利用方式农田氮磷均呈盈余状态,其中氮盈余率为果园(532.6%)明显高于菜地(61.5%)和粮田(31.6%),磷盈余率为菜地(700.4%)和果园(615.7%)明显高于粮田(66.6%)。化肥氮磷的环境风险指数均为菜地(0.83)明显高于粮田(0.59-0.62),三种不同利用方式下化肥氮磷的环境风险类型均达低度风险及以上,特别是菜地达严重风险。为了农业的可持续发展,河北省粮田应控制氮磷肥的投入,果园和菜地应加大减少氮磷肥化肥投入,以减少对环境的潜在危害。同时为了更好地培肥地力,在控制施肥总量的前提下应加大粮田和菜地有机肥的投入比例。     

Changes of the rice distribution and the functions of the food control system in Japan

Japan's Food Control System was established in 1942 during World War II in order to cope with the shortage of food. The system has been maintained in order to secure a stable supply of rice, a staple food and key crop in the country. The functions and roles of this system change gradually according to fluctuations in the rice market. Since the establishment of the ‘voluntary rice-marketing system’ in 1969, Japan's marketed rice has been classified into the following three types: (1) Government-marketed rice (GM rice): the government purchases from rice growers and sells to wholesalers. (2) Voluntarily marketed rice (VM rice): rice assemblers' organizations sell directly to wholesalers. (3) Freely marketed rice (FM rice) which is an illegal practice. Recent trends have witnessed decreased sales of GM rice and increases in the sales of VM and FM rice, thus resulting in the weakening of government control of the rice supply. The goods markets for VM rice instituted in 1990 introduced to a greater degree the market mechanism of price controls for rice. At the same time, the government's control of rice distribution was relaxed to allow new access to rice dealers and to promote free trade between sellers and buyers. Although the Food Control System in Japan has changed significantly, it will be retained since it protects the rice supply and paddy field agricultural system.