A MACROSCOPIC-SCALE MODEL OF WATER UPTAKE BY A NONUNIFORM ROOT SYSTEM AND OF WATER AND SALT MOVEMENT IN THE SOIL PROFILE

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Abstract
A dynamic numerical model, based on the transport equations for water and noninteracting solutes in a porous medium and written in IBM S/360 CSMP language, was designed to compute the movement of water and salts in a soil profile in the presence of an active root system. The inputs are soil and root system hydraulics, initial water content and solute concentration, density and distribution of active roots in the soil profile, and the climatically imposed evapotranspiration rate with its diurnal fluctuation. The output provides the patterns of soil moisture depletion and of water potential distribution in the soil and the water potential in the plant as needed to maintain various transpiration rates, as well as the flow of water and salt though the bottom of the root zone. The model is illustrated for a number of combinations of root densities and resistances, profile depths, initial soil water contents, solute concentrations and evaporativity levels. The pattern of soil moisture depletion and plant-water status is seen to be a combined function of soil, plant and climatic factors which can be mapped out systematically and quantitatively by dynamic simulation, for a wide range of environmental conditions. Much experimental research is yet required to obtain the appropriate input information for models of this kind and to validate their results.

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