Root hydraulic resistance: Implications in modelling nutrient and water uptake

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Abstract
This paper reviews 3 recent experiments dealing with root hydraulic resistance of cotton and discusses their implications in modelling the mass flow of ions through the soil‐root interfacial zone. A value of 4.7 x 10‐7 cm3/cm•s, which has been assumed in one ion uptake model, is approximately correct for cotton grown in soil that was kept continuously moist, but root uptake rate varies with root age, type of rooting media, soil water content and with frequency and severity of soil drying around the root. Mass flow rate radially through the root material was about 1/2000 of the assumed ion uptake value when the rooting media had been dried severely. These major shifts in root conductivity as the soil dries will have major consequences in the proportionality between mass flow and diffusion of ions through the soil‐root interfacial zone in cotton.
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