Quantifying root water extraction by rangeland plants through soil water modeling

We used soil water modeling as a tool to quantify water use of non-cultivated plant communities based on easily measured field data of soil water contents, soil hydraulic properties, and leaf area index. The model was applied in the mixed-grass prairie, considering a dynamic and non-uniform root distribution, the effect of soil water stress on plant water uptake, as well as the compensation effect of root water uptake. The simulation was conducted for the 111 days from mid May to early September of 2009. A good agreement between the model simulated and field measured soil water contents was obtained, with a maximum rooting depth estimated within the depth range of 1.3-1.6 m. The results suggest that a reasonable estimate of soil water retention parameters, and especially the use of the root uptake compensation significantly improved both numerical accuracy in predicted soil water dynamics, and the biological importance in the predicted seasonal root water extraction. In particular, the model gave a reasonable simulation of the seasonal progression of the drying zone in the soil profile in the summer of 2009. The method and analyses used in this paper may be useful in a wider context of soil-plant relationships.