Infrared Canopy Temperature of Peach Trees under Deficit Irrigation.

An early-season peach, “Crimson Lady” (Prunus persica (L.) Batsch), is generally harvested in late May to early June in central California.  To reduce water use, regulated deficit irrigation may be applied to these trees for the remaining and also most water demanding season (mid June to November).  A field study was initiated to evaluate an infrared thermometer (IRT) system for evaluating water stress in peach trees and potential application for irrigation management.  The field site was located at the USDA-ARS San Joaquin Valley Agricultural Sciences Center near Fresno, CA.  Four irrigation treatments (F1, F2, S2, S5) were selected for the study, where F1 represents furrow irrigation replacing 100% ET, F2 is furrow irrigation triggered by stem water potential reaching 20 bars, S2 is subsurface drip irrigation replacing 100% ET, and S5 is deficit irrigation replacing only 25% ET.  Each treatment was replicated three times in a randomized-block experimental design, so a total of 12 plots were used in the study.  Each treatment plot consisted of three rows with eight trees per row.  Twelve IRT sensors were installed in the field, one per plot, by mounting them on 2” galvanized metal pipes 18 feet (5.5 m) above the soil surface.  All sensors mounted on the pipe were pointed southward at 30º from NADIR with the center of FOV aimed at the middle three trees of the center row.  Results clearly showed higher canopy temperature in the water deficit treatments F2 and S5 than in non-stressed F1 and S2 treatments.  Because of a longer irrigation cycle in F2 than S5, a gradual temperature rise and relatively rapid decline responding to irrigation events were also observed.  The next step is to develop an appropriate algorithm for irrigation management of the early maturing peaches with canopy temperature being a key input.