Nonlinear Root-Water Uptake Model

Quantifying root water extraction by rangeland plants through soil water modeling

“…This same trend was further developed later in the season, as shown by both the measured and simulated data on Fig. 6 A comparison between the fractional root distribution function of Li et al (2001) and the normalized root density distribution of Ojha and Rai (1996) using root shape parameters l=0.5 and β=1.75, respectively. Data are predicted water uptake rates from 80 soil depth increments equally divided within an assumed 1-m root zone under (a) an optimal uptake condition (with a soil water potential h=−5 m) and (b) a water stress condition (with h=−80 m).…”

“…The model-simulated soil water contents were further compared with the field measured data through the soil water profiles on four selected days Table 2 Final parameter values obtained from a simulation-based searching method for maximum rooting depth (L m ), root distribution exponent (β or λ), simulated total transpiration, as well as the minimum average relative discrepancy (ARD) and the root mean square error (RMSE) between model simulated and field measured soil water contents on a mixed-grass prairie during the summer of 2009 Ojha and Rai (1996) 2. Same as 1, except that a physicoempirical model of Arya and Paris (1981) was used to predict water retention curves for depth intervals from 0.15 m to 0.76 m of the soil 3.…”

“…where h is soil matric potential (m), c ¼ @q @h À Á the soil water capacity (m -1 ), K the hydraulic conductivity (m s -1 ), z the vertical coordinate originating from the soil surface and positive downwards (m), and S(z,t) is the volume of water taken by plant roots from unit volume of soil at location z and time t (Ojha and Rai 1996;Mathur and Rao 1999;Wu et al 1999;Zuo et al 2004;Liu et al 2005;Yadav and Mathur 2008). It has a unit of s -1 and can be estimated by:…”

“…3). The normalized root density L nrd as a function of normalized rooted soil depth z r was computed using the nonlinear equation of Ojha and Rai (1996), namely,…”

“…The "macroscopic" root water uptake models incorporating dynamic and non-uniform root distribution and water uptake capabilities have been used in various cultivated 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.…”