Root‐Sink Descriptions of Water Supply to Dryland Wheat1

Abstract

AbstractSoil water content changes were supplemented with calculations of water flow between soil layers to provide an improved description of water uptake by dryland wheat (Triticum aestivum L.). This root‐sink description of water use, recognizing both measured change in water content and vertical redistribution (upward or downward) of water by flow between soil layers, is needed for a better understanding of plant‐soil and atmospheric factors involved in water stress when the wheat plant must rely on stored soil water for long periods. Water content changes were estimated from neutron meter measurements. Soil water flux was estimated from field measurements of both hydraulic conductivity and hydraulic head gradients; unsaturated conductivity beyond the range of field measurement was calculated with the pore interaction model of Marshall matched to field measured values at 250 mb. Seasonal water‐uptake patterns, determined by the root‐sink description, differed from those shown by only water content measurements. Peak water‐use rates did not coincide with maximum leaf area index, but coincided with the period from heading to completed head extension. Water flux in the profile was important for supplying water during grain filling and was critical in this layered soil, which restricted rooting to depths less than 150 cm.