Optimizing the scale of planting and breeding on the county scale based on soil carbon balance

Abstract: Black soil region can serve as the main production area of commodity grain in Northeast China. There is the soil quality decline of cultivated land in recent years, such as the thinner and harder land. Among them, the efficient return of agricultural waste as a carbon source can be an important way to improve soil quality. However, it is still lacking in the regional, agricultural production system model using the regulation of the carbon cycle between plant and animal, in order to promote the return of carbon to the field for the recovery of black land fertility. This study aims to improve the soil organic matter content of black land for recovery. The research object was selected as Qiqihar City located in the hinterland of Songnen Plain in Heilongjiang Province of China. The soil carbon budget of each county was calculated to compare the difference between the soil carbon input and output of different crops. The agricultural carbon balance model was established for plant and animal husbandry using multi-objective linear programming. The least carbon emission and the highest economic benefit were taken as the main targets, while the efficient use of agricultural and waste resources was the secondary target. As such, the balance between soil carbon emission and carbon input was determined, according to the situation of each county. The results showed that the adjustment plan in each county was optimized to reduce the rice planting area, while increasing the cow farming scale and maize planting area with high biomass. There was no decrease in the soil carbon pool of farmland after the full utilization of the waste of cultivation and breeding industry. However, the scale of plant and animal husbandry at the county level should be adjusted, according to the local conditions. Taking Nehe City with a large soil carbon deficit as an example, the maize planting area increased by 46.4%, while the scale of beef breeding should be reduced by 63%, and the scale of cows, pigs, sheep and poultry breeding increased by 85%, 54%, 75%, and 71%, respectively, in order to balance the carbon input and agricultural economic benefits. Take Longjiang County with a small soil carbon deficit as an example, the rice planting area, and the beef and pigs breeding industry should be reduced by 334% and 179%, respectively, while the corn and soybean planting area increased by 4% and 88%, respectively, and the scale of cows, pigs, and poultry increased by 39%, 26%, and 41%, respectively. The organic materials returned to the field were replaced by 33%-59% of the fertilizer nitrogen input after the planting and breeding scale, particularly for the higher soil quality and the soil nitrogen carrying capacity. Moreover, the soil nitrogen-carrying capacity of the three main crops showed an increasing trend, except for the maize planting in Kedong and Keshan County. The agricultural "carbon balance" development model can be expected to serve as the scientific basis for the efficient utilization of agricultural waste resources. The finding can also provide a strong reference to realize the "double carbon" strategy in the black soil area.