Infrared canopy temperature of early-ripening peach trees under postharvest deficit irrigation

Canopy temperature measurements with infrared thermometry have been extensively studied as a means of assessing plant water status for field and row crops but not for fruit trees such as peaches. Like in many regions of the world, the lack of water is beginning to impact production of tree fruit such as peaches in the San Joaquin Valley of California. This is an area where irrigation is the only source of water for agricultural crops in the summer growing season. A two-year field study was conducted to assess plant water stress using infrared canopy temperature measurements and to examine its feasibility for managing postharvest deficit irrigation of peach trees. Twelve infrared temperature sensors were installed in a mature peach orchard which received four irrigation treatments: furrow and subsurface drip irrigation with or without postharvest water stress. During the two-year period, measured midday canopy to air temperature differences in the water-stressed postharvest deficit irrigation treatments were in the 5-7 °C range, which were consistently higher than the 1.4-2 °C range found in the non-water-stressed control treatments. A reasonable correlation (R2 = 0.67-0.70) was obtained between stem water potential and the canopy to air temperature difference, indicating the possibility of using the canopy temperature to trigger irrigation events. Crop water stress index (CWSI) was estimated and consistently higher CWSI values were found in the deficit irrigation than in the control treatments. Results of yield and fruit quality assessments were consistent with the literature when deficit irrigation was deployed.