Field Evaluation Of Drip Irrigation And Fertigation Performance And Simulation

The trend of increasing commended area and complex hydraulic influence factors are the most important factors in individual drip irrigation system of northwest arid area of China.For large-scale irrigation system management,the way to reduce the operating pressure,and the uniformity of water and fertilizers applied,being pressure equalization through the system is a concern to designers and users.Accordingly,investigate the space-time characteristics of water and fertilizer distribution in system,and make confirm the main factors of water distribution in different irrigation period,should therefore be concerned in drip irrigation system optimization.The objectives of this study contained three parts:irrigation system investigation,water supply method control experiment and simulation experiment by EPANET,to evaluate the drip irrigation and fertigation performance of a large-scale irrigation system,and put forward the optimization of laterals layout.On-site investigation that was conducted for two-years in a drip irrigation system of 153 ha in Xinjiang province.Three scales of drip irrigation system were selected to evaluate space-time characteristics of water and fertilizer distribution.At system scale,the experiment ascertained irrigation schedule and water distribution in the different subregions.Three typical subunits were selected and referred to as S1,S2,and D3,in S1 and S2,water was fed from both ends of laterals while water was fed from one end of lateral in D3,to investigate the uniformity and consistency of water and fertilizers applied.Besides the effect weight of manufacture variation,hydraulic deviation and clogging were confirmed in lateral scale.A five-month control experiment was conducted to evaluate the effects of water supply method in lateral on water and fertilizer performance for drip irrigation while using different pressure tank.Two lateral layouts(feeding water from one end of laterals(A1)and from both ends of laterals(A2)),four lateral lengths(70(L1),100(L2),130(L3)and 160 m(L4)),five inlet pressures(0.02(P2),0.04(P4),0.06(P6),0.08(P8)and 0.10 MPa(P10)),three tank pressure(0.02(D1),0.07(D2)and 0.12 MPa(D3))and two types of emitters(Labyrinth(T1)and Plain(T2))were considered in this study.The distributions of water,fertilizer,and pressure were determined during the experiment.Furthermore,different water supply modes under the lateral scale and system scale of EPANET were established to evaluate the influences of terrain deviation and system control scale on water distribution.The main conclusions of this study are as follows:(1)In the early stage of irrigation period,the water distribution uniformity of each subregion under the large-scale drip irrigation system is generally less than 80%,and decreased with the subregion area and the distance from the head pivot increase.In general,the hydraulic deviation increased the risk of nonuniformity of water applied,the effect weight analysis result illustrated that factor weight range 0.41 to 0.47.In the late stage of the irrigation period,emitters clog is the main factor affecting the fluent performance with a weight rate 0.44 to 0.62.(2)During the measurement for each subunit,the evaluation result showed feeding water from both ends of the laterals can significantly improve water volume and fertilizer distribution uniformity.In the S2 subunit,6%of water application uniformity reduced and 0.13 hydraulic deviation weight increased was found while changed the water supply method to feeding water from one end,in the middle stage of the irrigation period.(3)The control experiment result demonstrated that the discharge deviations for the A2 treatments were great improving of water application uniformity and fertigation uniformity were observed for the treatments with water fed from one end of laterals.An approximate 60%increase of the allowable maximum lateral length was determined for the system with water fed from both ends of laterals than water fed from one end of laterals while the allowable discharge deviation was set as 20%.The uniformity of water application and fertigation for the A2 treatments were 1%-9%and 1%?8%higher than those for the A1 treatments,respectively.The ANOVA results indicated that the lateral layout imposed a significant effect on the water application uniformity and fertigation uniformity at a significance level ofp<0.05.(4)EPANET could accurately simulate the different pressure tank performance and water distribution in the drip irrigation system verified by the result of the control experiment.The lateral and system simulated results showed that higher Christiansen uniformity coefficients(Cu)for the irrigation water were observed for the two-way water supply arrangement,under the condition of favoring slope 80%of the allowable maximum lateral length was determined for the system with water fed from both ends of laterals than with water fed from one end of laterals and 65%increase were found in adverse slope.While the allowable Christiansen uniformity coefficients(Cu)was set as 80%,the system control area was 1.69 to 1.82 times of that water was fed from one end of lateral,indicating a better performance of feeding water from both ends of the laterals.