| 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)-1 respectively by nitrogen. Nitrogen cycle for different farm fields showed that field surplus nitrogen ranged from (102±68) to (303±134) kg·(hm2)-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)-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 farmers 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 agro-ecosystems and revealing the characteristics of nitrogen cycling in the region. |
