Plant Measurements as Indicators of Crop Water Deficit1

An irrigation experiment was conducted with southern peas [Vigna sinensis L. (Endl.) var. ‘Burgundy’] utilizing lysimeters in which the soil water balance could be controlled. The purpose of the experiment was to compare certain plant measurements as indicators of crop water deficit. Plant measurements made on stressed and non‐stressed plants throughout the growing season were leaf‐water potential, leaf‐air temperature differential, and leaf‐diffusion resistance. Leaf‐water potentials were measured by the pressure chamber method on well‐exposed leaves. Leaf temperatures were measured by infrared radiometry and a diffusion porometer was used to measure leaf‐diffusion resistance. Tensiometers were used to determine the soilwater potential and to time the irrigations. The plant response data taken throughout a day were sensitive to water deficits during the late vegetative stage; however, the measurements were less responsive when the leaves aged, indicated by plants in the pod development stage. The change was particularly evident in the leaf‐water potential measurements. All three plant measurements did indicate water deficit to some degree. Leaf‐diffusion resistance was the least responsive, and leaf‐water potential was the most responsive. Results relating leaf‐water potential to leaf‐diffusion resistance and soilwater potential are also given.