Infrared Thermometry for Maize Water Stress: Soil Effects and Alternative Indices.

A non-stressed crop will transpire the available water through its leaves, but a water-stressed crop will reduce and gradually shut down transpiration thus creating a warmer canopy. Infrared thermometers (IRTs) are an affordable tool for researchers to monitor canopy temperature in a continuous manner. In this two-year maize experiment, six treatments of regulated deficit irrigation levels were evaluated. The objective of this study was to evaluate these six treatments in terms of soil influence on canopy temperature, and also to evaluate and compare six stress indices commonly used to quantify water stress: three “spot” indices where one daily reading is assumed representative of the day and three indices that evaluate water stress over time. Results showed that soil texture has an influence on canopy temperature, even within the same treatment, as coarser soils have smaller water holding capacity and are therefore more prone to water stress. Diurnal fluctuations of canopy temperature converged at nighttime regardless of treatment giving an opportunity to indirectly verify proper calibration, while daytime and early afternoon temperatures saw the most divergence, thus ideal time to obtain spot index values. Index values were compared to soil water deficit.