Numerical Study On Surface Drip Irrigation And Subsurface Drip Irrigation

Drip irrigation is one of the most effective irrigation methods in arid areas.In this study,soil water movement is simulated under different irrigation methods using both HYDRUS-1D and SWMS₂D software,and attempts are made to infer soil hydraulic parameters using an inverse analysis model.The results from this study are helpful to further understand soil water movement under various irrigation methods,and provide evidence for choosing appropriate irrigation methods and designing rational irrigation scheduling.Numerical simulations are carried out for six soils including clay,clay loam and loam with various irrigation rate and time using HYDRUS-1D software.The corresponding responses of soil water content are studied at the end of irrigation and 24h after irrigation before runoff occurs.It shows that:1)soil water content is related to soil texture and the amount of irrigation;2)great re-distribution occurs for soils with good drainage capacity;3)soil wetting depth after water re-distribution is dependent on,and varies in a linear manner with,the amount of irrigation for a given soil.Systematical numerical simulations are conducted for both surface irrigation and sub-irrigation with SWMS₂D software.The soil hydraulic parameters are estimated using the pedo-transfer functions?PTFs?proposed by Saxton et al.and Woston et al..The results reveal that the PTFs by Saxton et al.are superior to those by Woston et al..Good agreement is achieved between simulated values of soil water content with measurements with the Saxton's approach.Although overall the simulated values of soil water content are smaller than measurements,the model is capable of re-producing the measurement to a great extent.However,significant discrepancies between simulation and measurement are found with Woston's approach,indicating that such a approach is not suitable for the studied soil.An inverse analysis model is developed.Preliminary attempts are made to infer soil hydraulic parameters using the data from the surface irrigation experiments,and the inferred parameters were verified with an independent dataset from other experiments.It shows that the results are encouraging for both the inverse analysis case and the validation case,and good agreement is achieved of soil water content between simulation and measurement.The calculated indices for evaluating model performance are satisfactory.It suggests that the inverse analysis method proposed in this study is not only feasible,but also has a great potential for further study.