| The Tarim Watershed is located in the inland arid regions of Northwest China. The water scarcity and continuing deterioration of ecology have recently become the main restricting factors to sustainable socio-economic development in this area. Agricultural water accounts for about 95% of total water consumption, which lead to a shortage of ecological water, and the water use efficiency was quite low. So, based on ensuring food security, ecological security and water security, increasing efficiency of agricultural water use and decreasing consumption of agricultural water became the key factors to solve conflict between agricultural and ecological water consumption and alleviate the water shortage and ecological deterioration in the basin. In this study, for important issues of low efficiency of agricultural water use, unreasonable planting structure and excessive water consumption, a multi-objective optimization model based on the high water utilization efficiency and its corresponding evaluation system were built by analyzing the water resources, agriculture water consumption and planting structures in Tarim watershed. The macro-control mechanism of agro-planting structures optimization was addressed to provide theoretical basis for planning and policy analysis of future agro-planting structures in the basin, even in the arid desert oasis area.1. Through semi-structure interview, questionnaire investigation and on-site investigation among water administrative departments, technicians and farmers, a large number of information and data such as planting structures, agricultural water consumption, environment, developing planning and statistical data in the basin were collected. The survey results showed that the panting ratio of grain, economic crops and forage crops lack of coordination. The forage crops cultivation proportion was too small and the cultivation area of high water consuming crops was too large and so the water production efficiency was too low. The social and ecological benefits were hardly considered, and the agricultural planting structures based on high efficient water resource utilization were not founded to counter the problems of the extremely dry climate and increase the water-use production.2. Draw on the theories of sustainable development, system engineering and crop planting structure optimization, taking high efficient water resource use as core aim, considering the largest net output, the heaviest food yield, the biggest ecological benefits and the highest water production, a multi-objective model based on high water use efficiency and planting structure optimization in Tarim watershed was built, in which eight constraint conditions were selected from five aspects such as farmland area, the amount of water resources useable for agriculture, social demand, the net output of planting industry. Taking Wensu, an important agricultural county in this basin, for example, the solution was got by using PSO (particle swarm optimization) method of the whole set non-inferior solution model. The results showed that optimizing the agricultural planting structure can still lead to high water-saving benefits, while the net output of planting industry, total grain yield, ecological efficiency and water use production were increased to some extent. The total amount of water consumption for planting industry was 24.543 billion cubic meters in 2005. According to the results of optimizing simulation of Wensu, if the planting structure was not optimized, the planting industry will consumpt 24.125 billion cubic meters water in 2010 and 22.549 billion cubic meters water in 2015. Otherwise, after optimization, the total water consumption amount for planting industry could be reduced to 20.829 billion cubic meters in 2005, 19.260 billion cubic meters in 2010 and 18.129 billion cubic meters in 2015. The saved water could not only meet the rapid growth in the water use for industry and daily life, but also provide some water for the ecology which are suffering continued deterioration in the basin.3. The benefits assessment was an important part for optimizing the planting structure. A 3-layer evaluation system was set up, including the target layer, rule layer and index layer. The target layer was the planting structures rationality. There are 4 aspects in rule layer, such as the high use efficiency of water resources, social equality, economic rationality and ecological security. The index layer contains 24 basic indexes. Using the methods of AHP (improved analytic hierarchy process) and MATLAB procedure to solve the evaluation model, the results showed that after the optimization for the planting structure, the rationality of planting structure increased by 24.8% in 2005, 23.2% in 2010 and 26.3% in 2015 respectively compared to those before. At the same time, by optimizing the planting structure, the economic, social and ecological benefits of the planting industry were increased to some extent, and the utilization efficiency of water resources was improved significantly. Tanking together, it was feasible to make planting structure optimized. The results of optimizing the planting structure were proved to be reasonable and feasible.4. Base on analyzing the obstacles for optimizing the planting structure in Tarim watershed, such as the dispersion of rural production, conflict among different administrative regions, low price of agricultural water and low literacy levels of local farmers, we proposed that if only gradually establishing and improving mechanism of plan and market combination, compensation and motivation for agriculture, sci-tech investment in agriculture, land transferring, social participation and optimal sale-order-production et al., the optimization of planting structure could be effectively implemented.
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