Citation: Wang, D., Gartung, J.L. 2010. Infrared canopy temperature of early-ripening peach trees under postharvest deficit irrigation. Agricultural Water Management. 97:1787-1794. Interpretive Summary: California has been under an extended drought due partly to below average precipitation, partly to early Sierra Nevada snowmelt (higher night-time temperatures as a result of global climate change) that reduces water availability during the summer growing season. Approximately 10,000 ha of commercially-grown peach trees in central California depend on this water as the primary source of water supply. The objective of this study was to evaluate characteristics of canopy temperature of early-ripening peach trees with respect to soil water content and stem water potential measurements under different irrigation regimes, including postharvest regulated deficit irrigation. The study was conducted in a 1.6 ha peach orchard at the USDA-ARS San Joaquin Valley Agricultural Sciences Center located near Parlier, CA. The experimental design was a randomized block with furrow and subsurface drip irrigation treatments as the main effect and levels of postharvest deficit irrigation the sub-effect. A total of six replications were used, with each replication including the four irrigation treatments or a total of 24 treatment plots for the study. Twelve infrared temperature sensors were installed in three of the six replicated plots within the peach orchard to measure canopy temperatures. Stem water potential and soil water content were measured approximately weekly after peach harvest for the 2007-2008 and 2008-2009 growing seasons. Marketable-sized fruits were picked by a commercial harvesting crew. For the experimental plots, peach yield and fruit quality were measured for each treatment. Deficit irrigation treatments clearly showed higher canopy temperature values than the non water stressed treatments throughout the postharvest period for both 2007 and 2008. A reasonable correlation was obtained between stem water potential and the canopy temperature to air temperature difference. The relationship has potential for guiding irrigation scheduling.
Technical Abstract: 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 ºC range, which were consistently higher than the 1.4-2 ºC range found in the non water-stressed 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. Results of yield and fruit quality assessments were consistent with the literature when deficit irrigation was deployed. The next step is to develop a mechanism to use canopy temperature for managing irrigation scheduling in peaches.