放牧草地生态系统中氮素的损失和管理

对于大多数放牧草地，Ｎ素都是限制生产力的最重要因素之一，而生态系统中Ｎ素的损失量又很大，Ｎ素以ＮＯ－３、ＮＨ３、Ｎ２Ｏ等形态进入水圈和大气圈，不仅造成了生产上的资源浪费，而且对全球环境和人类健康都产生了深远的影响。本文将对草地生态系统中Ｎ素损失的主要过程（如氮挥发、反硝化和ＮＯ－３淋溶等）及影响因素研究的进展情况进行简要地综述，然后对ＩＭＧＡＲＳＳ项目研究中关于Ｎ素损失研究部分提出一些建议。草地生态系统中Ｎ素损失的主要途径包括：土壤、植物、动物排泄物和肥料的氨挥发；生物和化学反硝化；淋溶；动物体和动物产品对Ｎ素的固持；动植物残体和动物排泄物的燃烧；动物以排泄物形式将Ｎ素从生产区转移到非生产区；通过土壤侵蚀而损失等。放牧加速了草地生态系统中Ｎ素的损失速率。从全球角度分析ＮＨ３的来源后认为，生物残体燃烧是最大的ＮＨ３源，其次是自然土地。对欧洲ＮＨ３来源的研究表明，与人类活动有关的ＮＨ３挥发总量的大部分来源于牲畜排泄物的氨挥发。由于方法的限制，对田间条件下的反硝化测定较少，动物排泄物对Ｎ２Ｏ的贡献及对全球变化影响的研究数据较少。但研究表明，草地尿、粪斑处Ｎ２Ｏ释放速率很高，动物排泄物可能是最重要的Ｎ２Ｏ源。在半干

Nitrogen Loss and Management in Grazed Grassland

Nitrogen is one of the most important factors to limit grassland productivity, meanwhile nitrogen loss is substantial in ecosystem Nitrogen loss in the forms of NO - 3 , NH 3 , N 2 O into water and atmosphere not only causes great resource waste, but also impacts global environment and human health The main paths of nitrogen loss in grazed grassland ecosystem include: ammonia emissions from soil, plant, animal excreta and fertilizers; biological and chemical denitrification; nitrogen retention in animals and animal products; leaching; burning of animal and plant residues and animal excreta; animal transfer of nitrogen from productive areas to non-productive areas in the form of animal excreta; soil erosion etc Grazing increases the rate of nitrogen loss in grassland From global data analysis, biomass burning is biggest source of emitted NH 3 , then natural land emission From Europe data analysis, most anthropogenic NH 3 emissions comes from animal excreta Because of methodological restriction, few denitrification studies were conducted in field conditions The contributions of animal excreta to global environment changes and N 2 O pool is not fully understand N 2 O emission rate is very high in urine and dung patches, and animal excreta perhaps is the most important source of N 2 O Leaching loss is low in semi-arid region Other nitrogen loss ways may be dominated depending on the conditions of climatic, utilization types etc The main practices to minimize nitrogen loss can be realized through optimum management of grassland, grazing system, plant factors etc Changing the nitrogen management may causes maximum 70% reduction in N 2 O release Many studies on nitrogen loss processes have been conducted in agricultural ecosystem, but less in grassland ecosystem It is necessary to establish nitrogen loss models in medium scale in grassland nitrogen loss studies