Environmental Influences on the Leaf Temperatures of Two Soybean Varieties Grown under Controlled Irrigation¹

Abstract

Remote sensing techniques have been suggested as a possible tool to the agricultural research worker. In addition, plant leaf temperatures (a quantity capable of being measured by remote sensors) give an indication of the plant's response to the environment. For these reasons, an experiment was conducted in the field to investigate the relations between plant leaf temperatures and soil moisture stress and various environmental parameters. Leaf temperatures (TL) of two soybean [Glycine max (L.) Merr.] varieties grown under controlled irrigation were measured with an infrared thermometer during a 9‐day experiment. On a given day relative leaf water content (RWC) and TL were highly correlated. When TL's were examined over different days, vapor pressure deficit (VPD) and air temperature (TA) were found to affect TL· TL increased with decreasing values of both RWC and VPD. Interactions involving both VPD and TA with RWC were observed. TL increased with increasing TA; however, the amount of increase of TL seemed related to the leaf's level of RWC. This was related to increased transpirational cooling (stomatal conductivity) at higher levels of TA. The two varieties in this experiment were significantly different with respect to TL, but the degree of significance was related to VPD.

Variable upper and lower crop water stress index baselines for corn and soybean

“…This method is based on the fact that the difference between canopy and air temperatures (T c −T a ) increases when crops are under water stress, in response to decreased evapotranspiration, which serves as a cooling mechanism for the crop (Wolpert 1962;Gates 1964;Linacre 1964;Conaway and van Bavel 1967;Fuchs and Tanner 1966;Carlson et al 1972). It is known that (T c −T a ) is linearly related to air vapor pressure deficit (VPD) .…”

Evapotranspiration Obtained from Remote Sensing Methods

“…Aston and van Bavel (1972) proposed the canopy temperature variability method but did not provide actual values which would signal the onset of stress. They and Carlson et al (1972) showed that (T c -T a ) values are negatively correlated with relative leaf water content. They also stated that this value was valid only when the canopy cover was nearly complete.…”

Heat stress in food legumes: evaluation of membrane thermostability methodology and use of infra-red thermometry

“…Tanner (1963) suggested that the temperature difference between stressed and unstressed plant leaves gave a quantitative indication of differences in transpiration potential. Leaf temperature was associated with leaf water content (Carlson et al 1972) and the gradient of temperature between leaf surface and air boundary (DT C-A ) increased following irrigation (Ehrler 1973). Gardner et al (1981) reported that canopy temperature closely followed ambient air temperature, and the profile of leaf and air temperature of stressed and unstressed canopy were similar.…”