Agricultural Planting Structure Optimization Based On The Efficient Use Of Water Resources

China's total water resources are numerous, but the per capita consumption is less than normal, while the spatial and temporal distribution of water resources is lack of coordination with the water demand, and the contradiction between supply and demand is becoming increasingly acute. Northwestern China is one of the regions whose water shortage is most serious and ecological environment is most vulnerable, and agricultural water use accounts for the largest proportion. Therefore, it has an important effect on sustainable use of water resources and ecological environment improvement to study how to efficiently use water resources in Northwestern China. From the perspective of water resources management, such as agricultural planting structure and irrigation system optimization, this paper explored the means of efficiently using agricultural water resources by calculation and analysis of agricultural water-saving potential , taking Minqin county as an example, and Minqin is in the downstream of Shiyang River Basin whose problems of water shortage and ecological environment deterioration are most serious. The main contents and conclusions are as follows:(1)Analysis research progress on the optimization of agricultural planting structure water distribution between crops at home and abroad systematically.Problems Proposed are researchs in this area are not comprehensive and the construction of multi-crop species modeling is relatively complex ect.(2)Based on the analysis of the status of water resources development and use in Minqin county, it was proposed that in agriculture water use, there were some issues, just as Agricultural planting structure and irrigation system is unreasonable,ecological water can not be guaranteed, recycling rate of water resources is high, The contradiction between water rights is obvious,so further research of the agricultural water resources optimization is needed to realize the efficient and sustainable use of water resources.(3)The calculation model of regional agricultural water saving potential was established, then the calculation methods of theoretical and practical water saving potential was got. Theoretical water saving potential is the difference between the actual irrigation water use and irrigation water requirements in current year. The calculation results of agricultural water saving potential in Minqin county showed that there are only 102.09,42.08 and 47.53 million cubic meters of water space in 50%, 75% and 95% hydrological year respectively,which is still a big gap to"the Comprehensive Restoration Plan of the Shiyang River Basin in the Recent Period"requirements.This shows that the problem of water shortage can not be solved by the traditional water-saving mode, and water requirements of local planning was not satisfied, so it is essential to adopt a new approach, adjusting agricultural planting structure and irrigation system to achieve water savings.(4)Based on previous studies of planting structure and irrigation system optimization theory,a two-tier optimization model based on Large Scale System Theory is established.The first layer is an optimization model for crop irrigation system based on Jensen model. The second layer is an optimization model for crop planting structure based on nonlinear optimization theory.Water production functions of the main crops in Minqin are calculated by the first layer of the model. And then these functions are substituted into the second layer of the model, the optimizations of planting areas and irrigation rations is obtained by optimizing.And then the results are put into the first Layer of the model and the best optimized irrigation system for each crop is obtained. The structure of the model is simple and easy to use.(5)By selecting the digital data in 75% level years, the satisfactory results are achieved through model calculation. The results show that in Minqin region, by optimizing the planting structure and irrigation system under the condition of irrigation area invariable, 109 million cubic meters water resources will be saved and the local farmers'income will increase by 1607 yuan. In response to the demand in the agriculture water saving proposed in"the Comprehensive Restoration Plan of the Shiyang River Basin in the Recent Period", under the circumstance of planting area reduction, the agriculture water will save 293.53 million cubic meters, reduced by 39.102 percent than present situation, and also, the increased income of local farmers will be 364.2 yuan. Compared with the status quo,the optimal planting structure increased the acreage of Bailan melon, pepper and cotton etc,whose cost is relatively high and crop irrigation is relatively less, reduced the acreage of alfalfa, wheat, corn and watermelon and other crops wose cost is relatively low and crop irrigation is relatively high.