Transport of water in the soil-plant-atmosphere system.
An approximate solution is presented of the differential equation describing soil-moisture flow towards a root absorbing water at a periodically varying rate. Combined with hypothetical plant characteristics it is used to form a model of the hydraulic behaviour of a crop. The characteristics specified are depth of penetration of roots, density of rooting, the internal resistance of the crop to the flow of water, and the critical value of leaf-water potential associated with stomatal closure. The level of leaf-water potential in relation to environmental conditions, and the rate of transpiration from the crop when leaf-water potential falls to the critical value, are determined by the "supply function" which is a measure of the ability of the soil-crop system to supply water to the evaporating surfaces within the leaves. The variation of this function with the water content of the soil is examined for different values of the parameters involved, and the behaviour of the soil-crop model under constraints representing those imposed by the external environment is discussed.