Modeling Soil Moisture and Flow Dynamics of Variably Saturated Heterogeneous Lateritic Porous Media under Wheat Crop

Abstract

Soil moisture plays a significant role in hydrologic systems and agriculture by serving as an important input parameter in major hydrologic process modeling. As limited field studies on investigating soil moisture dynamics and flow processes under wheat cultivation are reported, especially in heterogeneous lateritic soils, the present study was conducted to understand the flow dynamics in a heterogeneous vadose zone under wheat cultivation. Proper field instrumentation was created, and detailed investigations were carried out to determine layer-wise soil physical properties as well as to monitor daily perched water table and moisture content in each layer during two wheat growing seasons. Further, a HYDRUS-1D model was developed to simulate the effects of wheat crop growth and irrigation on the vadose-zone flow dynamics. Analysis of the results revealed that the soil moisture at shallow depths up to 0.30 m shows significant temporal fluctuations due to plant water uptake and the percolation of water to deeper depths. At deeper depths, consistently high moisture content was prevalent throughout the crop growing season with little percolation beyond 0.30 m depth due to the presence of relatively impermeable layers at varying depths. Saturated moisture content was found to be the most sensitive model parameter. The HYDRUS-1D model simulated drying and wetting events reasonably well in the entire flow domain before and after the application of irrigation water except at deeper depths. Mostly downward water flux was found to be dominant after the 1.3-m deep soil layer with only a small fraction of water percolating beyond the 1.3-m soil layer, whereas significant upward water flux dominated in the upper soil profile. Results of this study can further aid in designing an efficient demand-based irrigation schedule for the wheat crop grown in the lateritic region, thereby helping in formulating an efficient irrigation management plan.