Revisiting the wet and dry ends of soil integral water capacity using soil and plant properties

The integral water capacity (IWC) approach takes into account various soil physical limitations for calculating plant available water. However, the IWC approach cannot distinguish the differences in water uptake between various plants. Therefore, the objectives of this study were i) to modify the approach to include plant physiological properties to redefine the wet and dry ends of the IWC, called IWCplant and ii) to evaluate the performance of the IWCplant approach using experimental data. The restrictions imposed by poor soil aeration and rapid drainage flux were calculated using both soil and plant properties to modify the wet end of the IWC. The soil hydraulic resistance was considered to redefine the dry end of the IWCplant. Based on these approaches, physically meaningful weighting functions were developed for three proposed limiting factors at both ends of the wet and dry ranges of soil. Experimental data were obtained from a greenhouse trial with wheat and canola plants in two soil textures (sandy loam and clay loam) for 2 years. The IWCplant obtained values of 0.202 and 0.205 m3 m–3 for wheat and 0.189 and 0.194 m3 m–3 for canola in sandy loam and clay loam soils, respectively. These differences in the IWCplant between wheat and canola in the same soils demonstrate the importance of plant properties to estimate actual plant available water using IWC. These differences would be even more appreciable for root systems with a wider range of different properties.