| In order to solve the problems of serious agricultural non-point source pollution,low utilization rate of agricultural wastes and backward agricultural economic development,Chongqing has built some agricultural science and technology parks aiming at circular agriculture.At the same time,in order to protect the ecological environment,Chongqing requires the total amount control of livestock and poultry breeding and zero emission of breeding pollution.In order to promote the popularization value of the circular agriculture development pattern of the agricultural science and technology park in the restricted breeding area,this study selected the core area of Bishan national agricultural and science park in Chongqing as the research area,constructed the evaluation index system based on the theory of agricultural ecology,and evaluated the input-output characteristics and input-output efficiency of material,energy,value and emergy in the agricultural system of the park:(1)By calculating and analyzing the material flow index of organic carbon and nitrogen in the circular agriculture system of the agricultural science and technology park,it can be seen that the operation of the aquaculture subsystem depends on the external material input,and the system has poor self-sufficiency;The plant subsystem and fermentation subsystem have low utilization efficiency of agricultural waste and high dependence on chemical fertilizer.(2)Based on the calculation and analysis of energy flow index in agro-ecosystem,it is found that the energy demand of aquaculture subsystem is strong,but its economic energy output effect is poor.The planting subsystem is highly dependent on the input of inorganic energy,the self-sustaining ability of the system is poor,and the utilization level of non-economic energy is insufficient.(3)Based on the value stream analysis of the economic benefits of the circular agriculture system in the agricultural science and Technology Park,the cost profit rate is 55.72%,the economic output-to-input ratio is 1.56,and the internal rate of return is13.36%.The profit level and capital use efficiency of the system are high.At the same time,the payback period of the system is 5.03 years,and it has certain anti-risk ability.(4)By analyzing the emergy index of the circular agriculture system in the park,it can be seen that although the system has sustained economic benefit output,the problem of planting and breeding structure is prominent,and the degree of resource recycling is low.The pressure of agricultural production activities on the ecological environment in the park is at a medium level,and its sustainable development potential is insufficient.Based on the theory of nutrient balance,combined with the evaluation conclusion and the requirements of agricultural development in restricted breeding areas of Chongqing,a multi-objective linear programming model was established to optimize the planting and breeding structure of the study area,and the optimization scheme was obtained by using WINQSB software.In the optimization scheme,the breeding scale is 3.64 times of that before optimization,in which the broiler breeding scale is reduced by 38.10%,and the earthworm breeding scale is greatly increased.Before and after the optimization,the total planting area changed slightly,the vegetable planting area only increased by 0.84%,and the grain crop planting scale changed relatively large.After optimization,rice increased by 20.29%,corn and beans decreased by 31.56% and47.37% compared with before optimization.Through the agroecological evaluation of the optimized scheme and the analysis of the index value changes before and after the optimization,we can draw the conclusion that the material flow,energy flow,value flow and emergy index values of the optimized circular agriculture system in the study area are significantly better than those before the optimization.Among them,the level of resource utilization of agricultural waste is improved,the efficiency of energy utilization is improved,the selfsufficiency is enhanced,and the impact of agricultural production activities on the environment is reduced.With the improvement of risk-resisting ability and profitmaking ability,the sustainable development ability of the system is further promoted.It can be seen that the material and energy flow efficiency and the eco-economic benefit of the agricultural system have been improved greatly after the optimization of the planting and breeding structure of the circular agricultural system. |
