Quantitative Simulation Of Agricultural Land Use System At Different Scales

Since the reform and opening-up policy,the high intensive agricultural land use pattern has improved the land income and ensured the food security in China,while also causing serious environmental problems.Nowadays,how to coordinate the relationship between food security and agricultural environmental protection has become a major challenge in the current process of agricultural development in China.In the current situation,a good solution is to regard agricultural land use as a system and conduct an overall and systematic study of agricultural land use system on multi-angle,multi-scale and multi-effect.In this study,we began with the definition of agricultural land use system which was analyzed comprehensively.Then,supported by the basic theory of man-land relationship,sustainable land utilization,complex system and farmer household rational decision,based on the framework of farmer household manage unit-small catchment-region,using linear programming model,agent-based model,export coefficient model,substance flow analysis and 3S technology,a quantitative simulation system of agricultural land use system was established,achieving the goal of quantitatively simulate the effect of agricultural land use system change on food security and environmental pollution.The main results are as follows:(1)Analysis of agricultural land use systemThe conceptual framework of agricultural land use system in this study was established which included four parts:input,land use process,output,and feedback.According to the conceptual framework and scale features of agricultural land use system,the goals of agricultural land use system simulation at three different scales are:at the farmer household management unit scale,taking farmers as the research object,simulate their decision-making process and analyze the effect of farmers decision behavior on food security and environment pollution;at the small-catchment scale,by simulating the agricultural land use system,we researched the effect of land use change on river water quality which is the foundation for controlling water quality environment by regulating farmers behavior;at the regional scale,by simulating the change of agricultural land use system,we studied how to maximize both the socioeconomic and eco-environmental benefit,providing the basis for agricultural sustainable development policy-formulation for the government.(2)Simulation of agricultural land use system at the farmer household management unitAs a case study of Taojiang County of Hunan Province,this study randomly selected 399 households by stratified sampling.According to the main source of income and operation scale,the households were divided into 8 types:off-farm,traditional,hobby,part-time,farming-oriented,professional,large-scale and breeding-specialized household.Then the land use behavior and management characteristics of each household were analyzed respectively.The results suggested that factors included market,policies,technology,physic,society and household characteristics had important effect on the choice of crop cultivation;while laborers in a household,age of household head,farmland area and main source of income influenced the farmland transfer decision-making behavior significantly.On the basis of this,a decision model of household land use based on linear programming method and a model of agricultural land use environmental effect at field scale based on SFA method were conducted.We selected 9 indicators from 3 aspects of society,economy and environment to establish the index system of comprehensive effect of agricultural land use,then analyzed and compared the comprehensive effect of agricultural land use of different household types.It suggested that under the current technic-economic condition,professional household type had better comprehensive effect of agricultural land use.(3)Simulation of agricultural land use system at the small catchment scaleBased on the case-study analysis of the small catchment of Taojiang County in Hunan Province,to simulate the effects of rural household livelihood transition on non-point source(NPS)pollution from 2000 to 2014,a model combining an agent-based model(ABM)and an improved export coefficient model(IECM)was developed.The simulated results revealed that the transition of household livelihood strategies occurred with the changes in the prices of rice,pig,and labor.Thus,the cropping system,land-use intensity,resident population,and number of pigs changed in the small catchment from 2000 to 2014.As a result of these changes,the total nitrogen load discharged into the river increased initially and then decreased.Results also suggested that rural living,livestock,and precipitation alternately became the main causes of NPS pollution in the small catchment.Despite some limitations,the coupled model provides an innovative way to simulate the effects of rural household livelihood transition on NPS pollution with the change of socio-economic factors,and thereby identify the key factors influencing water pollution to provide valuable suggestions on how agricultural environmental risks can be reduced through the regulation of the behaviors of farming households in the future.(4)Simulation of agricultural land use system at the regional scaleTo assess the comprehensive impacts of agricultural land use system changes on food security and environmental effect,and establish effective and environment-friendly subsidy policies,this research constructed an agent-based model(ABM)and selected Daligang Town as the case study site.It suggested that cultivated land resource transferred to scale-farming household occurred as the farmland circulation,while the double cropping rice proportion and total rice yield increased.The environmental output of nitrogen loss by volatilization,de-nitrification,runoff and eluviation decreased initially then increased,but the growth rate of nitrogen surplus is lower than the decrease rate.In addition,the validation result was well within the acceptable limits,indicating the reliability of the proposed model.On the basis of that,according to the realities of situation and the growth rate of subsidy in the past decade,based on the coupled ABM-SFA model,the effect of agricultural land use system change under different policy scenarios on food security and environment sustainability from 2014 to 2029 was studied.The scenario analysis revealed that the four scenarios generated different variations in cropping systems,rice yield,and environmental effect.Among the four different policy scenarios in Daligang,the TD scenario was considered the best,because it had a relatively high rice yield,fairly minimal use of fertilizers and pesticides,and a lower level of subsidy.