Simulation Research On Soil Water Infiltration Under Ridge-furrow Irrigation

Ridge-furrow irrigation was birthed and developed in accompany with ridge-furrowintercropping fields. The ridge-furrow configuration is built by shaping the soil surfacewith alternate ridges and furrows along the contour. In ridge-furrow irrigation, the flowwater only transports on furrows and supplies water to crops. The flow water on furrowsinfiltrates into ridge-furrow configuration by capillarity forces, and lateral infiltrated watervolume must meet the needs of the plants grown on the ridges of soil or raised beds.Improper ridge-furrow irrigation design and management in fields has some disadvantages,such as interference infiltration, higher deep water percolation, and lower irrigationuniformity. Soil water dynamics and distribution under ridge-furrow configuration canprovide guidance to design the appropriate width ratio of furrows to ridges in ridge-furrowintercropping fields. Soil infiltration characteristics in ridge-furrow irrigation wereinvestigated in laboratory experiment by using rectangular soil chambers. Soil watermovement was numerically simulated by using HYDRUS-2D software. The effects ofvariables—soil physical properties, cultivation technique parameters, and irrigationtechnique parameters—on irrigated soil infiltration process and wetting patterns werequantitatively evaluated. The optimized artificial neural networks model was developed topredict soil infiltration characterization under ridge-furrow irrigation. The appropriatewidth ratio of furrows to ridges under ridge-furrow irrigation was investigated byoptimized method and simulated calculation, which provide theoretical guidance toirrigation technique optimization and management in field experiments. The mainly resultsare as follows:(1) Soil water movement equation was revised to simulate water infiltration inridge-furrow irrigation based on variably saturated flow theory. Soil hydraulic parametersin heavy loam soil and sandy loam soil were deduced. The initial and boundary conditionswere determined in ridge-furrow irrigation. Soil water movement equation was solved byusing HYDRUS-2D software and accurately simulated soil water dynamics under ridge-furrow irrigation. There were higher simulated precision in cumulative infiltrationand wetting distances, while a low simulated precision was shown in soil water distributionin ridge-furrow irrigation through the hydrodynamic model.(2) The effect of different variables on soil water distribution and cumulativeinfiltration was investigated by using numerical simulation. Soil texture had a significanteffect on soil water distribution and cumulative infiltration during the same ridge-furrowirrigation event. Ridge-furrow irrigation design and optimization is relied on soil texture,and the irrigation method should be implemented in finer soil. Film-covering furrowregulated water distribution between ridges and furrows. The vertical infiltration distancewas significantly reduced, while lateral infiltration distance was increased. Film-coveringfurrow should be implemented in ridge-furrow irrigation fields. Furrow size had an effecton soil water distribution and cumulative infiltration. We should select narrow furrows forcrops with deep rooting depth and wide furrows for crops with shallow rooting depth.Furrow water depth had an effect on lateral infiltration distance and cumulative infiltration.Lateral infiltration distance and cumulative infiltration tended to increase with increase offurrow water depth. The higher furrow water depth is recommended in ridge-furrowirrigation to improve water use efficiency and irrigation uniformity.(3) The effect of different variables on soil infiltration characteristics and infiltrationmodels were quantitatively evaluated by using statistical methods. Ridge-furrow irrigationwas conducted in laboratory experiment, and the path analysis method was applied toquantify the effect of variables on cumulative infiltration. The results showed that51.62%,47.2%,38.12%, and6.44%of variability in cumulative infiltration was explained by totalvariations in wetted perimeter, bulk density, flow section area, and initial soil water content.The principal component variables were bulk density and wetted perimeter underridge-furrow irrigation. The performance of four infiltration models—Philip model,Kostiakov model, Kostiakov-Lewis model, and Horton model—was investigated on thebasis of evaluation indices. The Kostiakov-Lewis model provided the best description ofthe relationship between cumulative infiltrations with infiltration time. A furrowcumulative infiltration model taking wetted perimeter into consideration was developed.The validations by experimental data indicated that the variation of cumulative infiltrationagainst infiltration time could be effectively simulated by the furrow cumulative infiltrationmodel.(4) The spatial moment analysis method was applied to quantify the effect of variableson the wetting pattern. The results showed that the wetting pattern was like an ellipse with a long axis in the horizontal direction. The longitudinal coordinate of the mass center of theellipse, zc, the long axis, σ_x, and the minor axis, σ_z, were increasing with the increase ofinitial soil water content, respectively, and the area of the ellipse was also increasing.Initial soil water content had a minor effect on the ellipse characteristics compared withother variables. Soil texture had a significant effect on the ellipse characteristics. zc, σ_x, andσ_zwere increasing with the increase of furrow size, and the area of the ellipse was alsoincreasing. σ_xand σ_zwere increasing with the increase of furrow water depth, and the areaof the ellipse was also increasing. However, zcwas decreasing with the increase of furrowwater depth because of higher water depth. The eccentricity of higher furrow water depthwas greater and lateral infiltration distance was further.(5) Back propagation artificial neural network (BP-ANN) model in ridge-furrowirrigation was established based on water moments data to predict irrigated soil infiltration.The Bayesian arithmetic was used in the BP-ANN model. The results showed that theoptimized BP-ANN model is reasonably accurate and can provide an easy and efficientmean of estimating complex soil water distribution in ridge-furrow irrigation.(6) The method of determining the appropriate width ratio furrows to ridges wasproposed in ridge-furrow irrigation. Soil water distribution in different ridge widths wassimulated in ridge-furrow irrigation by using numerical simulation. The appropriate widthratio of furrows to ridges was determined by soil water content matching principle. The60cm:75cm and60cm:70cm width ratio of furrows to ridges are recommended in heavyloam soil and sandy loam soil in ridge-furrow irrigation, respectively. These results canprovide guidance to reasonable design of irrigation design and field extension inridge-furrow intercropping fields.