Detecting Water Stress in Differentially-irrigated Tomato Plants with Infrared Thermometry for Cultivation of High-Brix Fruits

Abstract

An application of water stress to tomato plants is effective for increasing fruit-brix, but diagnostic information is essential for the optimum irrigation management. The applicability of infrared thermometry to the water-stress management in tomato cultivation is investigated. Leaf temperatures with the infrared thermometer and thermography, physiological response, growth and fruit quality were measured in five differentially-irrigated tomato plants; a well-watered plot irrigated with 90% of the potential water uptake, and four types of water-stressed plots, i.e., the combination of two levels of irrigation water (30% and 60%) and two treatment periods (12 days and 53 days). The potential amount of transpirational water uptake could be reasonably estimated by a subirrigation apparatus. A significant increase of the fruit-brix was found in the water stressed plots, especially in those with severer and longer stress treatments. The infrared thermal imagery was shown to be effective in the visual detection of water-stressed tomato plants. Photosynthesis and transpiration rates were significantly lowered in the water-stressed plots and were closely coupled with the elevated canopy temperature or less canopy-air temperature difference, which can be measured by the infrared thermometry on remote and real time bases. Results suggested that the management of water-stress in the greenhouse fruit-vegetables could be one of the most feasible applications of infrared thermometry.