中文摘要：

中国农业生产是以农户为单位进行的,农户氮素利用及平衡对农业生产和农村环境有非常重要的影响.本研究选择三峡库区秭归县张家冲小流域,对农户农田氮肥施用量、农户购买的饲料与食物、人畜粪便排放等进行了调查,并对农户氮素循环特征进行了分析.结果表明,根据该流域农户氮素流动的特点,可将其分为养殖型农户、柑橘种植户、茶叶种植户、蔬菜种植户、传统种植户5种类型;其氮素负荷大小顺序为养殖型农户〉蔬菜种植户〉柑橘种植户〉茶叶种植户≈传统种植户,以氮计分别为（363±129）、（355±127）、（345±107）、（152±60）和（151±73）kg.（hm^2·a）^-1;不同农户农田氮素循环分析表明,单位面积农田氮盈余变化在（102±68）303±134kg·（hm2·a）^-1之间,大小顺序为蔬菜种植户〉柑橘种植户〉茶叶种植户〉养殖型农户≈传统种植户,分别为（303±134）、（262±100）、（111±46）、（102±68）和（103±67）kg·（hm2·a）^-1;在农户氮负荷中,居民生活排放的氮占28%,农田氮盈余占72%,说明农田是主要的氮污染源,生活污染也是不可忽视的.该地区的养殖型农户、蔬菜种植户和柑橘种植户对水体质量威胁较大,是氮素污染重点防治对象;实地调查农户生产与生活的方法能清晰地明确农业生态系统中氮循环的不同环节和估算循环流量,有利于揭示区域氮素循环特征.

英文摘要：

In China,the agricultural activities are often carried out by single family,and the balance of nitrogen in every farm may have great effect on agricultural production and environment.A farm survey was carried out on the amounts of chemical fertilizers consumed,the amounts of food and feed purchased,and the livestock manures used in Zhangjiachong watershed of Three Gorges Reservoir Area for each farmer.According to the characteristics of nitrogen flow,farms in this watershed could be divided into 5 types： breeding specialized farms,orange-growing farms,tea-growing farms,vegetable-growing farms and traditional farms.Differences in environmental nitrogen load were observed among the five farm types in the following order： breeding specialized farms 〉 vegetable-growing farms 〉 orange-growing farms 〉 tea-growing farms ≈ traditional farms,being（363±129）,（355±127）,（345±107）, （152±60） and（151±73） kg·hm2·a^-1 respectively by nitrogen.Nitrogen cycle for different farm fields showed that field surplus nitrogen ranged from （102±68） to（303±134） kg·hm2·a^-1 among different farms.Among the five farm types,the field surplus nitrogen followed the order of vegetable-growing farms 〉 citrus-growing farms 〉 tea-growing farms 〉 breeding specialized farms ≈ traditional farms,being（303±134）,（262±100）,（111±46）,（102±68） and（103±67） kg·hm2·a^-1.The nitrogen from farm life activities accounted for 28% of the total N load,while the field surplus nitrogen was 72%.It was estimated that field nitrogen consumption was the predominated nitrogen pollution source in the watershed.However,the farmer＇s daily life pollution should not to be neglected.Breeding specialized farms,vegetable-growing farms and orange-growing farms were the high potential pollution sources for the water environment in the watershed,and the major attention should be paid to these types of farms.Field survey on farm nitrogen cycle is of significance in evaluating the nitrogen flows in the a