Effects of tree size on water use of peach (Prunus persica L. Batsch)

A short-term experiment was conducted to determine the effects of reducing tree size on peach tree water use (TWU). Tree size was progressively reduced by de-branching an individual isolated tree over a 15-day period. TWU was measured at 15-min intervals using heat pulse sap flow sensors located at eight positions in the trunk sapwood. Measures of TWU were compared with estimates derived from reference crop evapotranspiration (ETo) and the area of shade cast by the tree on the soil surface (ASH). ASH was estimated prior to each de-branching event using a combination of photographs of the tree taken from the direction of the sun, and measures of fractional radiation interception in the area of shade cast by the tree. TWU and ETo averaged 39.5 l/day and 4.7 mm/day, respectively, in the 6-day period prior to de-branching. Effective canopy cover (ECC; estimated as ASH measured at solar noon) was 5.8 m2 in that period. Five de-branching events reduced TWU and ECC by >95%. To account for the daytime variation in ASH, we used effective area of shade (EAS), calculated from estimates of ASH at solar noon and 3 h each side of solar noon. Kcb, the basal crop coefficient defined by Allen et al. [Crop evapotranspiration: guidelines for computing crop water requirements (FAO irrigation and drainage paper 56). Food and Agriculture Organisation of the United Nations, Rome, 1998], was related to EAS by Kcb = 1.05 EAS. These data for an isolated tree suggest that the transpiration component of orchard water use may be related to ETo using estimates of effective fraction of shade on the soil surface.