Pig farm-cropland configuration under typical waste treatment modes- A case study of anaerobic liquid fermentation following solid-liquid separation of waste

Nutrient loss during the processing of livestock and poultry manure is significantly different under different modes of manure disposal, subsequently influencing nutrient utilization in farmlands. Separation of solids from liquids before anaerobic fermentation of liquids is currently the main mode of treatment of poultry manure in China. Studies on the configurations of pig farm and croplands under solid and liquid waste disposal modes following the separation and the subsequent anaerobic fermentation of liquid manure is greatly important to reduce pollution by livestock excrement and promote sustainable development of animal husbandry. The purpose of this study was to determine the optimal farmland area needed for large-scale pig farm, and to provide the scientific basis and reference for establishing a sustainable agro-ecological mode of crops and animals. Based on the proportions of pig population and pig nitrogen and phosphorus discharge data for different types of swine, the rate of nutrient loss during waste treatment, and then nutrient demands by different crops, the areas of farmlands for waste consumption and the carrying capacities of farmlands with different planting patterns were estimated under typical anaerobic fermentation of liquids following the separation of solids from liquids of waste in a farm with 10 000 pigs. In order to avoid environmental pollution, the optimal farmland area needed for a large-scale pig farm was determined based on calculated maximum farmland areas from crop nitrogen and phosphorus requirement. The results showed that under anaerobic fermentation of liquid after solid-liquid separation of waste, the configuration of a 10000-pig farm needed an area of at least 12.4-13.7 hm² of grain/oil cropland, 14.2-17.9 hm² solanaceous vegetable field or 16.4-51.3 hm² orchard/seedling field for safe disposal of biogas slurry. One hectare of grain/oil cropland, solanaceous vegetable field or orchard/seedling field was enough for the disposal of liquid waste produced respectively by 730-803 heads, 559-704 heads or 195-609 heads of pig. For entirely safe disposal of manure fertilizer and biogas slurry, a 10000-pig farm needed at least an area of 299.3-312.9 hm² grain/oil cropland, 145.1-179.0 hm² solanaceous vegetable field or 553.1-1 343.8 hm² orchard/seedling field. Accordingly, one hectare of grain/oil cropland, solanaceous vegetable field and orchard/seedling field was enough for the disposal of manure fertilizer and biogas slurry produced respectively by 32-33 heads, 56-59 heads and 7-18 heads of pigs. The above results suggested that waste use patterns and crop types of ambient farmlands should be rationally determined according to breeding quantity of pig farm and its surrounding farmland area.