Abstract: Based on the Breeding - Farmland- Crops system, a regional farmland livestock and poultry carrying capacity model was developed by integrating the theory of field nutrient balance and reasonable combined application of organic manure and inorganic fertilizers. The model was used to evaluate rationality of the number of pigs currently kept in the pens of the region and to predict pig carrying capacity of the region. A case study was performed of Chifeng City, assuming that the ratio of organic manure and inorganic fertilizer in combined fertilizer in combined fertiliztion was 5︰5, and that the fertilization kept surplus of N and P₂O₅ nutrients unchanged in the farmlands now under cultivation. On such as basis, the model was tested. The results show that if based on N balance, the number of pigs in pen could be increased by 0.436 million and the regional pig carrying capacity up to 6.308 million pigs and if based on P₂O₅ balance, the number of pigs in pen could be increased by 3.693 millions and the regional pig carrying up to 10.413 million pigs. Songshan, Wengniute , Kalaqin , Ningcheng and Aohan on the south bank of the Xilamulun River are the major areas that have the potential to increase the number of pigs in pen. In consideration of the pressure from the environment, the N-based prediction can be recommended as the basis for calculation of potential increment in the number of pigs in pen and pig carrying capacity of Chifeng City.

Key words: farmland nutrient balance, combined application of organic manure and inorganic fertilizer, livestock and poultry carrying capacity, model