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Effect of Aerial Environment and Soil Water Potential on the Transpiration and Energy Status of Water in Wheat Plants¹

Water stress is an important factor limiting wheat (Triticum aestivum L.) growth on the Canadian prairies. To determine the effect of evaporative demand and soil water potential on transpiration and leaf water status, Thatcher wheat was grown under four combinations of air temperature and relative humidity in a loam and a clay soil. Transpiration rate, leaf water potential, leaf water content, and soil water potential were determined. The relationship between transpiration rate and soil water potential depended on evaporative demand and soil texture. The decline in the transpiration rate from its maximum commenced at higher soil water potentials under conditions of higher evaporative demand and was more gradual on the clay than on the loam soil, presumably due to the higher capillary conductivity of the former. Permanent wilting occurred at soil water potentials of –20 to –25 bars on the loam soil and at –45 to –50 bars on the clay soil. At these potentials the capillary conductivities of both soils were about equal. Resistance to Water flow in the plant decreased with increased temperature, while changes in relative humidity had no consistent effect. The total resistance to water movement in the plant and the soil increased with decreasing soil water potential and decreasing air temperature. The relationship between leaf water potential and relative water content was affected by aerial environment and soil texture.

Key Words: Leaf water characteristic • Potential evapotranspiration • Crop factor

² Former Graduate Research Assistant (now, Research Associate, Department of Agronomy and Soils, Washington State University, Pullman, Wash. 99163) and former Associate Professor of Soil Science, (now Soil Physicist, Taiwan Sugar Exp. Sta., Tainan, Taiwan).

Received for publication April 3, 1971.