Plant and air temperatures in differentially-irrigated corn

Abstract

Studies by Jackson et al. (1977) and Idso et al. (1977) indicate that wheat is not stressed for water unless leaf temperature exceeds air temperature. One objective of the study reported here was to determine relationships between leaf temperature and air temperature within corn canopies as a function of water stress. A second objective was to evaluate the effects of varying levels of plant water stress on crop temperature. A third objective was to establish the relationship between plant water stress and crop temperature in corn ( Zea mays L.) with the aim of providing practical water resource management tools. Meteorological, physiological and phenological measurements were made in nine plots of corn, grown on Valentine fine sand (Typic ustipsamment) at the Sandhills Agricultural Laboratory located near Tryon, Nebraska. Each plot received one of seven different irrigation treatments. Canopy temperatures were measured with an infrared thermometer at midday throughout the growing season. Air and leaf temperature measurements were made on an hourly basis with thermocouples. Physiological and phenological observations were made weekly. The average midday difference in canopy temperature between stressed and non-stressed areas was as large as 7.0°C. In fully-irrigated plots, the standard deviation of midday canopy temperature was about 0.3°C but in non-irrigated areas it reached, at times, 4.2°C. It is concluded that a standard deviation of temperature in a plot exceeding 0.3°C signals that some plants are experiencing water stress. This behaviour can indicate the need for irrigation. Daily profiles of leaf and air temperature in stressed and non-stressed canopies were found to be similar. Profiles tended to be lapse before crop cover was complete and inverted later in the season. At any level within the stressed canopy, plants were warmer than at the same level within the non-stressed canopy. The midday temperature of sunlit leaves of non-stressed and moderately stressed plants was generally 1–2°C below air temperature. The temperature of sunlit leaves in severely stressed plants was as much as 4.6°C above air temperature. It was observed that corn plants may be subject to water stress and still be cooler than air temperature.