Use of infrared thermography to detect water deficit response in an irrigated cotton crop

Abstract

Infrared thermography is a plant water stress sensing technique that allows acquisition of thermal infrared images of crop canopies with a thermal infrared camera at a high spatial resolution and a thermal resolution of 0.1 degree C. Canopy temperature is considered as an indicator of plant water stress and is also used as a tool for irrigation scheduling. In this field study the potential of using infrared thermography to detect water deficit in cotton crop under various irrigation treatments was investigated and also the relationship between canopy temperature and soil water within root zone was explored. Irrigation treatments (T50-T85) were designed to allow soil water depletion down to 50%, 60%, 70% and 85% of the plant available water capacity in soil. Due to the variation in rainfall distribution over the growth period, T85 treatment did not receive any irrigation water. Measurements of profile soil water and canopy temperature were made in 3 replicated plots of 4 irrigation treatments using a randomized block design. In this field experiment we used infrared thermography to measure canopy temperature and profile soil water with a neutron probe on six occasions during the entire period of cotton growth. Results indicated that thermal imagery was successful in distinguishing irrigated (i.e. T50) and unirrigated (i.e. T85) treatments, with a strong correlations between soil water within the root zone and canopy temperature as measured with the infrared camera. Due to the close correspondence between canopy temperature and soil water within root zone, estimation of crop water stress indices relating to stomatal conductance (IG) and improved crop water stress index (ICWSI) may not be necessary for irrigation scheduling. Similarities in the pattern of spatial variation in canopy temperature and soil water over the entire crop field could be used to determine soil water deficit such that precise quantity of water can be delivered at various parts over the experimental field. Overall, thermography provided a more rapid and convenient approach to detection of crop water deficit stress with potential for commercial application.