REGULAR ARTICLE Quantifying root water extraction by rangeland plants through soil water modeling Xuejun Dong & Bob D. Patton & Anne C. Nyren & Paul E. Nyren & Lyle D. Prunty Received: 22 December 2009 / Accepted: 19 April 2010 / Published online: 7 May 2010 # Springer Science+Business Media B.V. 2010 Abstract We used soil water modeling as a tool to quantify water use of non-cultivated plant communi- ties 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 simulat- ed 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 progres- sion 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. Keywords Computer simulation . Mixed-grass prairie . Richards equation . Root water extraction . Soil water flow . Water stress compensation Introduction The ability to quantify plant root water use is essential for sound management policies with regards to both production and the environmental impacts of the soil- plant system (Wang and Smith 2004). The “macro- scopic” root water uptake models incorporating dynamic and non-uniform root distribution and water uptake capabilities have been used in various culti- vated crop ecosystems (Feddes et al. 1978; Li et al. 2001; Mathur and Rao 1999; Ojha and Rai 1996; Prasad 1988; Wu et al. 1999; Yadav et al. 2009b; Zuo et al. 2004). However, the use of these models in rangelands, and other native ecosystems where many plant species coexist, faces a major difficulty due to the lack of accurate and site-specific root distribution and rooting depth data. Yet in rangelands, a better understanding of major ecological processes, such as photosynthesis and carbon sequestration (Emmerich 2007; Svejcar et al. 2008; Williams et al. 2000), nitrogen mineralization (Biondini et al. 1998), forage Plant Soil (2010) 335:181–198 DOI 10.1007/s11104-010-0401-7 Responsible Editor: Rafael S. Oliveira. X. Dong (*) : B. D. Patton : A. C. Nyren : P. E. Nyren Central Grasslands Research Extension Center, North Dakota State University, Streeter, ND 58483, USA e-mail: xuejun.dong@ndsu.edu L. D. Prunty Department of Soil Science, North Dakota State University, Fargo, ND 58105, USA