The utilization of thermal infrared radiation measurements from grain sorghum crops as a method of assessing their irrigation requirements

Abstract

Field studies on irrigated grain sorghum (Sorghum bicolor L. Moench) crops were conducted in California for three years to evaluate the use of thermal infrared measurements to estimate water use and detect crop stress. These studies were conducted on a Yolo loam soil with different rooting volumes to limit the water availability. Data show that the stress-degree-day index (midday comparison of canopy-air temperature differences) provides a valid indicator of crop stress, and that the canopy-air temperature difference increases rapidly above zero when more than 65% of the available water is depleted. The canopy-air temperature difference is also related to leaf-water potential, with an increase above zero when the potential decreases below − 1.1 MPa (=11 bars). Improvement of the performance of the stress-degree-day index through compensation for environmental variability was achieved by including measurements of the plant water stress which are related to available water extracted. It is concluded that remote sensing of emitted thermal radiation offers a promising technique which can be incorporated into irrigation management programs.