Autumn Irrigation Schedule In Hetao Irrigation District Based On SWAP-SHAW Coupling Model

Recently,more and more attention has been paid to the water saving in agriculture.The agricultural water consumption in large scale irrigation area is high and the problem of water waste is serious.As an important grain and oil production base in China,Hetao Irrigation District is a typical seasonal frozen soil area.Its geographical environment,high groundwater level and high salinity of groundwater lead to unique irrigation method,namely autumn irrigation.In order to obtain a suitable autumn irrigation schedule,and ensure water saving on the basis of the effect of autumn irrigation,this thesis simulated the autumn irrigation system in Hetao irrigation district.Due to the lack of crop model for seasonal frozen soil area,in this thesis,the SWAP model which is a popular crop model and SHAW model which is a water,heat and salt transportation model are coupled to obtain the SWAP-SHAW coupling model which can be used to simulate in seasonal frozen soil region.Based on SWAP model,the SWAP-SHAW coupling model modified the SWAP model according to the method of water,heat and salt transportation used in SHAW model.This thesis presents the coupling process and gives a brief description of the key numerical calculation procedure.The modification of SWAP model mainly includes:modified the heat transfer equation in the original SWAP model,added the term of the latent heat of phase change of soil water,present iterative method for heat transfer calculation,and adjusted the temperature of the first frozen soil;presented the method to determine whether the soil is frozen and calculate the soil liquid water content and the ice content by using the temperature and the total water content;modified soil thermal characteristics and soil matric potential for frozen soil.Using the materials of indoor frozen soil experiments by predecessors and outdoor monitoring data to validate the coupling model,the validation result showed that the coupling model can simulate the soil temperature,soil water content and salt content well and reflect the dynamic process of water,heat and salt in the process of soil freezing.The SWAP-SHAW coupling model was used to simulate the autumn irrigation schedule in Hetao Irrigation District.The effects of different drainage conditions on the growth and development of wheat were analyzed.At the same time,the salt dynamics and the growth and development of wheat in next spring were analyzed under different autumn irrigation quota in soil with different degree of salinization.Simulation results show that for severe saline soil,the reasonable autumn irrigation quota is 100m~3/-133m~3/mu,for moderate saline soil,the reasonable autumn irrigation quota is 67m~3/mu-100m~3/mu,for mild saline soil,reasonable autumn irrigation quota is 33m~3/mu-67m~3/mu.In the reasonable range of autumn irrigation quota,wheat was almost not affected by salt stress before the first irrigation next year,and the relative yield could reach a high level.