Applications of HYDRUS and the Proposed SWMRUM Software in Simulating Water Flow with Root Water Uptake Through Soils

Numerical models are frequently used for simulation of water movement in soils. Soil water flow simulation models require a description of root water uptake as a sink term. In this study, two water flow models including the proposed SWMRUM model and the HYDRUS software were compared based on the field measurement in an apple orchard. Probe-type time domain reflectometry (TDR) was used to measure soil volumetric water content within radial (R) and depth (Z) vectors. Root water uptake model includes root density distribution function, potential transpiration and soil water stress-modified factor. A root water uptake sink term was developed, and entered into a soil water dynamic model to enable simulation of water flow in soil via numerical solution of Richards equation. The outputs from the two models were compared against the measured water content data. Simulated and measured water contents were in excellent agreement. Analysis of residual errors, differences between the measured and simulated values, was performed to evaluate the model performance, based on the maximum error (ME), root mean square error (RMSE), coefficient of determination (CD), modeling efficiency (EF), and coefficient of residual mass (CRM). Results showed that maximum root water uptake was 0.04 m3m-3d-1 at 25-30 cm depth and the minimum was 0.005 m3m-3d-1 at 80 cm depth.