System dynamic model and scenario simulation of land carrying capacity for livestock and poultry manure

To implement systematic evaluation of land carrying capacity for livestock and poultry manure, prejudge its development trend and inspect the implementation effects of different emission reduction policies, this paper conducts the design and simulates different scenarios of land carrying capacity system model for livestock and poultry manure. Based on analyzing various subsystems of social economy, livestock and poultry breeding, crop planting and land carrying, and their elements, we established a system dynamic model of land carrying capacity for livestock and poultry manure, taking Shijiazhuang City as an example, which was an important city of animal husbandry in north of China. The system operation results indicated that: The model had good stability and reality, the error between the simulated value and the measured value was generally less than 10%. Therefore the model was effective. The system dynamic model was used to simulate the carrying capacity of livestock and poultry farming land in Shijiazhuang City from 2007 to 2025 under different scenarios. Five scenarios were designed. Scenario1: Inertial trend development condition, adjusting the economic structure of the animal husbandry, the investment in environmental protection, the proportion of manure and fertilizer and the mode of coordinated development, the simulation results show that: the output scale of animal husbandry and planting has increased, but the output growth of planting is inferior to that of livestock and animal husbandry, making it difficult for planting to consume nitrogen and phosphorus emissions by animal husbandry, and bringing more land carrying pressure. Scenario 2: Adjusting the economic structure of animal husbandry, both nitrogen and phosphorus balance carrying capacity present a downward trend, but phosphorus balance carrying pressure still exists. Scenario 3: Adjusting the environmental protection governance investment, nitrogen balance carrying is in the loadable state. Although the phosphorus balance carrying pressure is obviously decreased, only 8 years are loadable. Scenario 4: Adjusting the manure use ratio, nitrogen balance carrying is in the loadable state. The phosphorus balance carrying with improvement over the initial situation is still overloaded. Under the coordinated development mode, both nitrogen and phosphorus balance carrying pressure present a downward trend, both nitrogen and phosphorus balance carrying capacity are at the loadable level. It can be found through comparative analysis that the coordinated development mode has the best effect. This study provides support for carrying out monitoring and evaluation of livestock and poultry pollution and establishes an assessment mechanism for livestock and poultry breeding pollution on one hand. On the other hand, this paper provides scientific basis for the regulation and control of animal husbandry development in major livestock cities and other resources and environment overloading areas. © 2019, Editorial Department of the Transactions of the Chinese Society of Agricultural Engineering. All right reserved.