Water Use Dynamics of Peach Trees under Postharvest Deficit Irrigation

Abstract

Postharvest deficit irrigation is a potential strategy for conserving valuable fresh water for production of early season tree fruit crops such as peaches. However, water use dynamics under deficit irrigation conditions that can be described as seasonal changes in crop evapotranspiration (ET_c) and crop coefficient (K_c) are largely unknown. A three-year field study was carried out in a 1.6 ha peach orchard to determine seasonal ET_c and K_c characteristics. The orchard was divided equally into 72 plots, in which 12 randomly selected plots received deficit irrigation and the remaining 60 plots received full irrigation. A Bowen ratio flux tower was installed in the orchard to make meteorological measurements for estimating an integrated ET_c for the orchard. The study showed that from July to August 75-85% of the daily net radiation was used by latent heat or partitioned into ET_c. The average monthly cumulative ET_c was 151 mm in June, 162 mm in July, and 155 mm in August. K_c values under deficit irrigation conditions or termed as Deficit_K_c was computed as ratios of the ET_c over potential evapotranspiration or ET_o, and were compared with K_c derived from a lysimeter study under non-water stressed conditions or termed as Lysimeter_K_c. The maximum Deficit_K_c values were 0.90, 1.03, and 1.07 for the three field seasons but all were smaller than 1.20, the maximum Lysimeter_K_c. The study demonstrated that water stress under deficit irrigation can be characterized in K_c values. The approach may be used to detect if portions of an orchard or the entire orchard are under water stress. Conversely, the method may provide guidance on deploying deficit irrigation practices with pre-determined Deficit_K_c.