The Effects of Texture on the Resistance to Water Movement within the Rhizosphere

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Abstract
A growth chamber study was designed to investigate the relative importance of the resistances involved in water movement within the rhizosphere. The components considered are the soil, the soil‐root interface, and the root itself. The plant species used was sunflower (Helianthus annus L.), grown in three soils of different texture. After several weeks of growth all water application was stopped and the soil allowed to dry by transpiration alone. Relevant destructive measurements were carried out during the course of the drying period, one pot being sacrificed for each set. Measurements included transpiration rate, soil and xylem water potential, rooting density, and hydraulic properties of the soils. As the soil dried, total resistance to water movement was found to increase most rapidly in the coarsest textured soil and least rapidly in the finest textured soil. A steady state model was used to partition the total resistance between the various resistive components. This enabled the root plus interfacial resistance to be quantified in terms of soil texture and water content.