An exponential root-water-uptake model with water stress compensation

Modelling soil water flow under cropped conditions requires a description o f water uptake by plant roots. Most macroscopic root-water-uptake models di stribute potential transpiration across the root zone based on the root dis tribution pattern, without accounting for the distribution of water stress in the soil profile. An exponential root-water-uptake model was modified by incorporating a weighted stress index which accounts for both root distrib ution and soil water stress. This new model. called water stress compensati ng exponential root-water-uptake model, is represented as a function of pot ential transpiration, soil water availability and root-length density. The root length fraction in the various soil layers can be estimated from its v alue in the surface (0-10 cm) layer. Both the exponential- and the water st ress compensating- root water uptake models were incorporated in the Soil-W ater-Atmosphere-Plant (SWAP) simulation model, and tested against soil wate r content data from a long-term crop rotation experiment in the semi-arid r egion of western Canada. The results showed that the new water stress compe nsating model simulated soil water contents significantly better than the e xponential model. especially during the second half of the growing season a t the lower depths (60-120 cm). The model is user-friendly and application oriented, and can be used for various cereal crops. (C) 2001 Elsevier Scien ce B.V. All rights reserved.