A hand‐held infrared thermometer was used to measure the leaf canopy temperature of 20 soybean [ Glycine max (L.) Merr.] genotypes under both irrigated and nonirrigated conditions. In 1980, 14 canopy temperature measurements were made end 9 were made in 1981. Canopy temperature differentials (T d = canopy temperature ‐ air temperature) were consistently larger under dryland conditions. Values of T d were averaged, within a year, to derive the mean canopy temperature deviation (T̄ d ). T̄ d was found to be correlated negatively with yield in both the irrigated and dryland treatments in 1980, but not correlated significantly with yield in either irrigation treatment in 1981. In 1980, evaporative demand was great, with air temperatures abnormally high, and moisture was limiting, with rainfall well below normal. A reversal in environmental conditions occurred in 1981 with air temperatures at or below normal and rainfall above normal. In both years, genotypic differences for T̄ d existed, but genotypic response was not the same across years. The lack of association of T̄d with yield in 1981 seemed to be due to the lack of moisture stress and the relatively low evaporative demand that existed in that season.
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Harris et al. (1984) studied this question.