On quantifying hydraulic conductance at the soil–root interface

This study sought to test a widely used hypothesis in water transport from soil to root: the soil textural effect on soil–root interfacial conductance can be quantified by the degree of soil water saturation. This hypothesis is inferred from basic soil physics and is commonly used in modelling root water uptake. However, it has never been subjected to rigorous experimental test. In the current study, the soil texture effect on the interfacial hydraulic conductance was evaluated on well‐watered pot‐grown cotton plants, with soil particle size ranges of 0–0.05, 0.05–0.1, 0.1–0.2, 0.2–0.3, 0.3–0.45, 0.45–0.6 and 0.6–1 mm in seven treatments, in addition to hydroponics. However, our experimental results showed that the volumetric soil water content, not degree of saturation, is the best explanatory variable for quantifying the interfacial effect on hydraulic conductance. Further analysis indicated that if temporal change of this interfacial effect on hydraulic conductance is the subject of concern, degree of saturation may still be a valid option. If soil textural or spatial variation in root water uptake is the subject of concern, volumetric soil water content is best suited to quantifying the interfacial effect on hydraulic conductance. Copyright © 2013 John Wiley & Sons, Ltd.