Canopy temperature bias from soil variability enhanced at high temperatures

Abstract

Maize canopy temperature was monitored on a continuous basis for two growing seasons in a limited-irrigation maize experiment with seven separate irrigation treatments and four replicates of each treatment. Soil electroconductivity (EC) was measured and mapped to quantify the variation in soil texture throughout the plots and was correlated with the average field capacity of the soil (R2 = 0.51). At lower canopy temperatures, indicating little or no water stress, very little difference was observed between replicates within the same treatment. However, at higher temperatures, soil texture had a greater influence on temperature, with soils having lower EC (and therefore lower water-holding capacity) showing more water stress. More specifically, at canopy temperatures above 29°C, the influence of soil texture biased the temperature by up to 2.0°C over the EC range of 16.9 to 40.2 mS m-1; at mean canopy temperatures of 35°C, this bias could be more than 5.0°C between field replicates. Results similar to the continuous infrared thermometry were found using nadir thermal images. This study demonstrates the importance of understanding the potential effects of soil variability on canopy temperature, which could have profound implications for spatially variable field-based management using thermal imaging or similar technologies.