EVALUATION OF MACROSCOPIC ROOT WATER UPTAKE MODELS USING LYSIMETER DATA

Abstract

Three macroscopic root water uptake models (MolzRemson, Feddes, and SelimIskandar) have been widely usedin modeling water flow in soilplant systems. In this article, we use evapotranspiration data and soil water content dataobtained from lysimeter measurements and root distribution data obtained in a nearby wheat field to evaluate the accuracyof these root water uptake models in predicting the soil water content profiles in the winter wheat field. To account for therole of root distribution, we modified the MolzRemson model and the SelimIskandar model with the Feddes reductionfunction, and the Feddes model with the root length density. These models, with and without modifications, were thenindividually incorporated into the soil water flow equations as a sink term. The flow equations were solved numerically withthe measured evapotranspiration data as input, and the predicted soil water content profiles were compared with the measuredprofiles to evaluate the validity of the root water uptake models. The comparison showed that: (1) the average deviation ofthe MolzRemson (linear version) model, the Feddes model, and the SelimIskandar model could reach as high as 25%, andthe nonlinear version of the MolzRemson model performed slightly better, with an average deviation of 13%;(2) modifications made to the MolzRemson models and the SelimIskandar model did not achieve any improvement in themodel predictions, but the modified Feddes model significantly improved the prediction accuracy, reducing the averagedeviation to 5.6%.