The role of roots in controlling soil water extraction during drought: an analysis by simulation

Four hypotheses about the magnitude of root restrictions to water uptake were tested by comparing simulated water uptake with that measured in an experiment where the water supply was varied. We conclude that the effect of root restrictions is large, and often underestimated in wheat simulation models. When drought is moderately severe to severe, this results in substantial overestimates of water uptake and soil water depletion. In less severe conditions, the effect is less obvious because standard potential evaporation equations underestimate demand, so that root restrictions are partly included in the calculations. We show how the incorporation of quite simple hypotheses into simulation models can substantially improve the simulation of water uptake, including the development of soil water depletion profiles, These results require further experimental investigation. (C) 1999 Elsevier Science B.V. All rights reserved.