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

Abstract

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 (T L ) 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 T L were highly correlated. When T L 's were examined over different days, vapor pressure deficit (VPD) and air temperature (T A ) were found to affect T L· T L increased with decreasing values of both RWC and VPD. Interactions involving both VPD and T A with RWC were observed. T L increased with increasing T A ; however, the amount of increase of T L seemed related to the leaf's level of RWC. This was related to increased transpirational cooling (stomatal conductivity) at higher levels of T A . The two varieties in this experiment were significantly different with respect to T L , but the degree of significance was related to VPD.