Abstract
The direct examination of plant canopy temperature can assist in optimizing citrus irrigation management in greenhouses. This study aimed to develop a method to measure canopy temperature using thermal imaging in one-year-old citrus plants in a greenhouse to identify plants with water stress and verify its potential to be used as a tool to assess citrus water status. The experiment was conducted for 48 days (27 November 2019 to 13 January 2020). We evaluated the influence of five levels of irrigation on two citrus species (‘Red Ruby’ grapefruit (Citrus paradisi) and ‘Valencia’ sweet orange (Citrus sinensis (L.) Osbeck)). Images were taken using a portable thermal camera and analyzed using open-source software. We determined canopy temperature, leaf photosynthesis and transpiration, and plant biomass. The results indicated a positive relationship between the amount of water applied and the temperature response of plants exposed to different water levels. Grapefruit and sweet orange plants that received less water and were submitted to water restrictions showed higher canopy temperatures than the air (up to 6 °C). The thermal images easily identified water-stressed plants. Our proof-of-concept study allowed quickly obtaining the canopy temperature using readily available equipment and can be used as a tool to assess citrus water status in one-year-old citrus plants in greenhouses and perhaps in commercial operations with mature trees in the field after specific experimentation. This technique, coupled with an automated system, can be used for irrigation scheduling. Thus, setting up a limit temperature is necessary to start the irrigation system and set the irrigation time based on the soil water content. To use this process on a large scale, it is necessary to apply an automation routine to process the thermal images in real time and remove the weeds from the background to determine the canopy temperature.
Highlights
Irrigators usually use weather, plant, and soil-based irrigation management methods.the direct examination of some plant physiological factors is paramount for optimizing irrigation rather than focusing on soil or weather factors [1]
The water availability in the soil can be correlated to canopy temperature using infrared thermometry as a proxy for plant water status, as the canopy represents the aboveground portion of a plant [4,5]
The technique creates a thermal index that allows assessing the water availability in the canopy and determining the amount of water needed by irrigation
Summary
Irrigators usually use weather-, plant-, and soil-based irrigation management methods. The direct examination of some plant physiological factors is paramount for optimizing irrigation rather than focusing on soil or weather factors [1]. Stomatal conductance and stem water potential are standard parameters to monitor the plant water status relative to the soil water content, these measurements are time consuming and cannot be automated [2,3]. A reliable indicator for detecting water stress related to plant transpiration is needed. The water availability in the soil can be correlated to canopy temperature using infrared thermometry as a proxy for plant water status, as the canopy represents the aboveground portion of a plant [4,5]. Plants tend to present a higher leaf temperature when compared to those under adequate water availability [6]
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