Assessment of land carrying capacity of animal production in Beijing from a wider perspective of combination of planting and animal breeding

A strong market demand is ever increasing for animal protein in China. Correspondingly, this increase inevitably requires the expansion of animal farming industry. However, a trade-off is also highly necessary between the livestock/poultry manure and environmental pollution. Arable land can serve as a disposal site of animal manure in some regions. Furthermore, an optimal combination of planting and animal breeding is also critical to achieve the win-win goals of environmental protection and aquaculture development. Therefore, it is very necessary to accurately estimate the land carrying capacity for animal manure in modern agriculture. In this study, a systematic evaluation was made on the amount of manure production and nitrogen, phosphorus nutrient resources within the animal wastes in 2018 using the livestock and poultry breeding data in Beijing Statistical Yearbook. Six types of land were taken as the sites for the consumption of livestock and poultry manure, including grain field, vegetable field, orchard, available woodland, available grassland, and unused land, compared with only arable land was considered in the previous studies. Both Statistical Yearbook and ArcGIS were used to estimate the above-mentioned land resources. The nitrogen and phosphorus nutrient demand per unit area in the various land types were analyzed comprehensively, thereby to calculate the land carrying capacity of animal breeding industry in the study area. The results showed that the total amount of livestock and poultry manure was 3.801 million tons in Beijing in 2018, where the nitrogen and phosphorus nutrient resources were 5 289.8 and 26 118.2 t, respectively. In terms of nitrogen and phosphorus, the total amount of animal breeding was equivalent to 4.53 million and 5.13 million pig equivalents, respectively. Nevertheless, nitrogen was the significant limiting factor of pollution from the perspective of environmental protection. The total areas was about 218 408.8 hm2 available for the animal manure accommodation land in the six types of land. Among them, a major of arable land, the grain and vegetable field reached 112 000 hm2, accounting for 52% of the total area of land. The available area of orchard field, woodland, grassland, and unused land were 59 000, 37 600, 9 171.2, and 79.6 hm2, respectively. The nutrient requirement value of nitrogen and phosphorus per unit area were 308.9 and 72.9 kg/hm² for the grain field; 404.2 and 122.9 kg/hm² for the vegetable field; and 250 and 55 kg/hm² for the orchard field. Assuming that the plant nutrients were supplied only by organic fertilizer from animal manure, the maximum land carrying capacity for animal breeding was 6.752 million pigs equivalent, if only arable land (including grain and vegetable field) were used as the accommodation sites for livestock and poultry manure. If the six types of land were all used concurrently for the consumption of animal manure, the maximum land carrying capacity for animal breeding increased to the equivalent of 10.89 million pigs, 1.61 times of that of arable land. Assuming that the plant nutrients were provided 50% by organic and 50% by chemical fertilizers, the maximum land carrying capacity for animal breeding was reduced to the equivalent of 3.376 million pigs equivalent, if only arable land was used as the accommodation field of livestock and poultry manure. In this case, the breeding scale exceeded the carrying capacity of arable land in 2018, where it may cause environmental pollution. Fortunately, the land carrying capacity was 5.45 million pigs equivalent for the six kinds of land concurrently, 20.1% more breeding potential, compared with the actual breeding amount in 2018. Therefore, it is necessary to increase the replacement ratio of organic fertilizer to chemical fertilizer during this time, thereby to fully utilize the multiple types of land to absorb livestock and poultry manure. The finding can provide insightful ideas for the long-term coordinated development of environmental protection and animal breeding industry.