Spatiotemporal characteristics of the bearing capacity of cropland based on manure nitrogen and phosphorus load in mainland China

The discrepancy between livestock breeding and crop planting in integrated crop-livestock system (ICLSs) usually cause nutrients surpluses to the arable land. Evaluation of regional land bearing capacity and identification of environmental critical regions associated with livestock in China are benefit to nationally- and regionally-specific livestock rearing. This study was conducted to demonstrates the changes in livestock industry from 1996 to 2016 in China and identify the environmentally critical regions of livestock farming by calculating the indexes of bearing capacity of cropland based on nitrogen (IN) and phosphorus (IP). The results revealed that the scale of livestock and poultry farming, manure production, and manure nutrients has increased over the past two decades. The livestock and poultry breeding quantity was 1290.8 million heads with a manure production of 4238.0 million tons in 2016. The manure N and P were 12.0 and 1.9 million tons with an increase of 5.8% and 5.9%, respectively. The N and P demand of crops from manure were 29.1and 4.5 million tons with an increase of 31.5% and 27.2%, respectively. The bearing capacities based on N and P were 2668.9 and 2554.7 million heads in pig equivalent, respectively. On the national level, the IN and IP were 0.43 and 0.45, respectively, which is categorized as Grade II. Livestock rearing in China was still within the bearing capacity of cropland. Both the Northeast and Northwest regions were categorized as Grade I, while Southeast region, Southwest region, the Middle and Lower Reaches of the Yangtze River and the North China were categorized in Grade II. There is still enough space for expansion of livestock and poultry farming in the Northeast and Northwest regions. In the North China region, Southwest region, the Middle and Lower Reaches of the Yangtze River, and the Southeast region, manure generated can be accommodated without any expansion in livestock breeding quantity. While livestock industry in Sichuan, Yunnan, Beijing and Tianjin need to be strictly controlled because of the grade of IV and V.