| The existing water resources are increasingly in short supply,the contradiction of water use is prominent,and agricultural production is greatly restricted.Studying to determine the reasonable irrigation time and irrigation amount(ie irrigation system)of crops under limited water supply conditions is an important measure to improve water use efficiency and increase agricultural production efficiency.According to the distribution of water resources,soil conditions and climatic conditions in Shanxi Province,Shanxi Province is divided into seven research areas: Datong Shuozhou District,Xinzhou District,Jinzhong District,Changzhi District,Lvliang District,Linfen District and Yuncheng District.In this paper,winter wheat reseeding summer corn and spring maize were taken as the research object,soil hydrothermal dynamic transport model was selected to simulate soil temperature and water.The crop growth model was used to simulate the yield.Taking the maximum benefit as the goal,the analysis proposed the province’s regional economic irrigation system.Main research conclusions:(1)The experimental data of spring maize and winter wheat re-broadcasting maize(2015-2017)were selected,and the water and heat coupled model and crop growth model were used to simulate the crop water and yield,and the model parameters were determined.The fitting effect between the simulated and measured values of soil moisture content is good,the correlation coefficient R value can reach 0.869,and the consistency index reaches 0.81.The results of the crop growth model parameters are good,and the correlation coefficient R of the above-ground dry matter simulation and measured values can reach 0.966.The results of the model parameter verification are also good.The correlation coefficient R of the soil hydrothermal model parameter verification results can reach 0.820,and the consistency index reaches 0.84.The correlation coefficient R of the crop growth model parameter verification results can reach 0.7861.The results show that the soil hydrothermal model and crop growth model used in this study are reasonable and feasible.(2)Based on the potential evaporation,crop coefficient and daily rainfall values of the representative station series(1954-2017)of the seven sub-regions of Shanxi Province,the irrigation water requirement for winter wheat re-seeding corn and spring maize growth period was calculated.Frequency analysis was performed to identify five typical years(5%,25%,50%,75%,and 95%).(3)According to the optimization of irrigation system for different typical years,the optimization of irrigation system is a nonlinear planning problem due to the complexity of crop water demand and production calculation.The minimum interval between adjacent irrigation times is 7 days.The optimization calculation under different water supply conditions was carried out by using the exhaustive method.On this basis,the economic irrigation system for the divided crops was determined with the goal of maximizing the net benefit per unit area.(4)Based on the numerical simulation method,the farmland soil hydrothermal coupling model and the crop growth model were organically combined,and the economic irrigation system and irrigation water limit of the typical planting spring maize and winter wheat double-cropped maize in different hydrological years in Shanxi Province were determined.As an exploratory study,the corresponding analysis gives the irrigation low limit for limited water supply irrigation.(5)In this paper,the algorithm is improved.The non-saturated Darcy’s law is directly applied to the layered soil.The water balance equation is established by the average of the water flux at the beginning and end of the period,so as to solve the layered soil moisture content at the end of the period.Iterative calculation is used to avoid the use of the difference of the basic equations of soil water motion and the solution of the three-diagonal equation,which makes it easier to understand and perform the algorithm.At the same time,this study establishes the irrigation system expressed daily,which is more in line with the actual irrigation system than the current irrigation schedule expressed in the crop growth period.On this basis,the lower limit of economic irrigation and the lower limit of dynamic irrigation for different crop growth periods are also proposed. |
