Water uptake by plants as influenced by distribution of soil water in the root zone

Typescript (photocopy).A model of root water uptake is described and was tested experimentally. The model proposes that the local rate of water uptake by the root system of a plant is directly proportional to the difference between the water potential of the soil surrounding the roots and the water potential of the foliage, to the fractional root density of the root system, and inversely proportional to the hydraulic resistance of the entire plant per unit leaf area. The model was tested experimentally, by first determining the hydraulic resistance of cotton plants grown in single, homogeneous containers, then, by calculating the water uptake of cotton plants of which the root system was divided over two containers, which differed in regard to the soil water potential, and comparing the values so obtained with directly measured ones. The specific hydraulic resistance of cotton plants to water flow was measured to be 0.7E09 s. This value is within the range of values reported in the literature for a number of plant species. The results of the model predictions agreed well with measured rates of water uptake from each container, both absolutely, and as a ratio of the two values. Therefore, it was concluded that, as the measured value of the resistance appears to apply to the split root system plants as well, the form of the proposed model is correct