Response in Plant Water Status to Integrated Values of Soil Matric Potential Calculated From Soil Water Depletion by a Field Bean Crop

Abstract

Water deficits were induced in a field bean crop using Polythene rainout shelters to study the crop response to changes in soil matric potential integrated over the zone of soil water extraction. Integrated values of soil matric potential (Ψ_m,s) were derived from the values of matric potential (Ψ_m,s) at four separate depths weighted according to the corresponding rates of water depletion at the time of measurement. Linear relationships existed between Ψ_m,s and variations in leaf water potential before sunrise (Ψ_d) and in the afternoon (Ψ_a). The total resistance to daily water flow in the soil-plant system was found to increase linearly with falling Ψ_m,s. The water flux from separate soil layers indicated that the deeper the layer, the greater the resistance to water uptake from soils at a given value of soil water potential. Such an increase in resistance with soil depth, which considerably reduced the availability of soil water in the deeper soil layers, was attributed mainly to plant factors.