Abstract
Abstract. How much water can be taken up by roots and how this depends on the root and water distributions in the root zone are important questions that need to be answered to describe water fluxes in the soil–plant–atmosphere system. Physically based root water uptake (RWU) models that relate RWU to transpiration, root density, and water potential distributions have been developed but used or tested far less. This study aims at evaluating the simulated RWU of winter wheat using the empirical Feddes–Jarvis (FJ) model and the physically based Couvreur (C) model for different soil water conditions and soil textures compared to sap flow measurements. Soil water content (SWC), water potential, and root development were monitored noninvasively at six soil depths in two rhizotron facilities that were constructed in two soil textures: stony vs. silty, with each of three water treatments: sheltered, rainfed, and irrigated. Soil and root parameters of the two models were derived from inverse modeling and simulated RWU was compared with sap flow measurements for validation. The different soil types and water treatments resulted in different crop biomass, root densities, and root distributions with depth. The two models simulated the lowest RWU in the sheltered plot of the stony soil where RWU was also lower than the potential RWU. In the silty soil, simulated RWU was equal to the potential uptake for all treatments. The variation of simulated RWU among the different plots agreed well with measured sap flow but the C model predicted the ratios of the transpiration fluxes in the two soil types slightly better than the FJ model. The root hydraulic parameters of the C model could be constrained by the field data but not the water stress parameters of the FJ model. This was attributed to differences in root densities between the different soils and treatments which are accounted for by the C model, whereas the FJ model only considers normalized root densities. The impact of differences in root density on RWU could be accounted for directly by the physically based RWU model but not by empirical models that use normalized root density functions.
Highlights
Root water uptake (RWU) is a vital process for plant functioning since it conditions nutrient transport and balances transpiration
Water stress led to smaller root system conductances in the Couvreur model (C model) and a reduction of the root water uptake (RWU) for less negative soil water potentials in the FJ model
The C model, which is based on a physical description of the flow in the soil–root system, represented the effect of the differences in root system development on RWU directly since we related the root system conductance to the root length
Summary
Root water uptake (RWU) is a vital process for plant functioning since it conditions nutrient transport and balances transpiration. Estimations of RWU are needed to make predictions of crop water use, to assess water and nutrient use efficiency as a function of root architecture and environmental controls, and to design efficient water and nutrient resource management in agricultural practices (Molz, 1981). Quantifying RWU for water and nutrient management in different regions and climates continues to be a challenge due to the lack of knowledge of key RWU parameters and appropriate description of the RWU process (Vereecken et al, 2016). Different soil water balance models have been developed that allow RWU to be estimated using different parameterizations of the root system and water uptake mechanisms. The availability of field-plot-scale experiments in different soil
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