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

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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 (Ψm,s) were derived from the values of matric potential (Ψm,s) at four separate depths weighted according to the corresponding rates of water depletion at the time of measurement. Linear relationships existed between Ψm,s and variations in leaf water potential before sunrise (Ψd) and in the afternoon (Ψa). The total resistance to daily water flow in the soil-plant system was found to increase linearly with falling Ψm,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.