Submitted to: Hortechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/6/1996
Publication Date: N/A
Interpretive Summary: Measuring the temperature of a crop's leaves, relative to air temperature, has been shown to be a good way of monitoring whether plants have sufficient water or not. As the water supply runs low, the leaves warm up. However, when trying to apply this technique to thermal video cameras mounted in airplanes a problem arose. Exposed bare soil around each plant can get very hot, resulting in a thermal image with misleadinly warm temperatures. In this report, a new approach is described which uses cameras sensitive to red and near infrared light to estimate the amount of bare soil present and compensate for its effect. This information will enable growers to use water more efficiently as well as improve yields and quality in some cases, which benefits all users of food and fiber.
Technical Abstract: Water application efficiency can be improved by directly monitoring plant water status rather than depending solely on soil moisture measurements or modeled ET estimates. Plants receiving sufficient water through their roots have cooler leaves than those that are water stressed, leading to the development of the Crop Water Stress Index based on hand-held infrared thermometry. However, substantial error can occur in partial canopies whe a downward pointing infrared thermometer measures both leaf temperature and the temperature of exposed, hot soil. Mathematically comparing red and near infrared reflectances provides a measure of vegetative cover. Combined with radiant surface temperature, this information gives a two- dimensional index capable of detecting water stress even with a low percentage of canopy cover. Thermal, red, and near infrared images acquired with airborne sensors over subsurface drip irrigated musk melon (Cucumis melo L.) fields demonstrated the method's ability to detect areas with clogged emitters, insufficient irrigation rate, and system water leaks.