Abstract: 【Objective】The objective of this paper is to study the nitrogen (N) nutrient flow of crop-livestock system (CLS) and evaluate its related environmental effects in Yunnan province, increase the utilization efficiency of N, improve the agricultural eco-environment, and to provide a scientific basis for making the policies obeying the agricultural development law in Yunnan province. It is also of strategic importance to realize the sustainable development of social eco-economics.【Method】the temporal differentiation characteristics of N flow of CLS in terms of time series were analyzed based on the NUFER model (nutrient flows in food chains, environment and resources use). the spatial distribution of N flow of CLS in 16 prefectures of Yunnan province in 2014 were analyzed based on GIS from the perspective of spatial pattern.【Result】N inputs of CLS in Yunnan province increased year by year from 1995 (2.1×10⁶ tons) to 2014 (3.5×10⁶ tons). The applications of N fertilizer and the imports of feed primarily caused the increasing of N inputs to CLS. The N uptake amount of main products of farmland and that of animal production systems showed the same increasing trends along time, and the multiples of which were 2.1 and 8.5 times from 1995 to 2014, respectively. The N uptake amount increased a lot in 2000 and 2006, because of the expansion of the crop growing area and livestock breeding scale, and the improvement of the planting techniques and also the mode in the development of agricultural and animal husbandry of Yunnan. N flow of CLS in Yunnan province exhibited great imbalance, and the input of N presented a distribution characteristic showing high inputs in the center and the gradual decreasing trends towards the surrounding area. N uptake amount coordinated with the status of the regional social economic development. The more the developed region economy, the higher the N uptake amount. The significant reasons of N losses in CLS were the ammonia volatilization which attributed to the runoff, erosion and leaching caused by terrain condition and some unreasonable fertilization patterns. According to the characteristics of input, uptake and loss of N in Yunnan province, four types of N flow were divided as follows: high input with high discharge (Dali, Kunming and Honghe), high input with low discharge (Qujing, Lijiang, and Chuxiong, etc.), low input with high discharge (Diqing and Zhaotong, etc.) and low input with low discharge (Nujiang and Puer).【Conclusion】 Due to the traditional fertilization approaches which led to the excessive fertilization and the consequent great amount of N entering into the atmosphere through ammonia emission, and also due to the runoff and leaching effect of N from the urines and feces of livestock, the economic benefit of agricultural production was reduced and the environment was also contaminated. The N losses were higher in Dali, Kunming and Honghe based on the spatial distribution characteristics. Therefore, there are several aspects which should be amended like improving the pattern of fertilization, upgrading the utilization efficiency of fertilizer, improving the livestock breeding mode and also increasing the amount of urines and feces returning to the fields. Different CLS N optimized management techniques should be adopted according to the characterizes of different areas, and other approaches such as increasing manure nutrient cycling, improving the efficiency of N nutrient, decreasing fertilizers and exogenous feed requirements and reducing the discharge quantity into air and water should also be conducted in order to realize the reasonable cycling of nitrogen in the CLS.

Key words: crop-livestock system, nitrogen nutrient flow, NUFER model, environmental effects, Yunnan Province