Abstract: Nitrogen flow in farming is one of the most important factors affecting the human environment,especially water environment.A regional nitrogen flow model was established for analysis of nitrogen budget of the farming-feeding system in the Wuliangsuhai Lake watershed,Inner Mongolia Autonomous Region in 2006 and its influences on the local environment.Results indicate that input of nitrogen in the watershed mainly comes through the farmland system and only a little through the pasture system.In the former the input is much higher than its output,leaving a surplus of 4.03×104 t or 85.0 kg·hm-2,while in the latter the input is lower than the output,resulting in a deficit of 593 t or 0.99 kg·hm-2.The massive loss of nitrogen is a primary factor causing degradation of the local pastures.In addition,the surface runoff in the watershed brings as high as 9.25×103 t of nitrogen into the surface water every year,posing a great pressure on the local water environment.Fertilizer application in the farming system is the primary source of the nitrogen in the surface water.It is,therefore,recommended that the priority of the management of the local water environment should be laid on control of the agricultural non-point source pollution.

Key words: nitrogen, nitrogen flow, Wuliangsuhai Lake watershed, regional environment, water environment, farming-feeding system