Evaluation of Pecan Transpiration in a Southeastern US Orchard Using the Sap Flow Method

The present study determines pecan tree transpiration using the sap flow technique in a microirrigated pecan orchard. It documents for the first time the contribution of pecan tree transpiration to the orchard’s water use in the hot and humid climate of Georgia. The tree transpiration is derived from sap flow data on a daily basis and calibrated against tree transpiration using a combination of eddy-covariance and microlysimeter measurements. Results show that trees consumed 46% to 84% of the monthly water use of the orchard during the June–October period. The pattern of intraseasonal variation of pecan transpiration is associated with the influence of weather conditions, especially the vapor pressure deficit. The present study suggests that high pecan transpiration took place from June through August (nut sizing and early kernel filling stages) with peak values reaching ∼4.5 mm/day in the first half of July (mid nut sizing). The transpiration decreased in September during late kernel filling and post-kernel filling. The results also suggest that the crop coefficient increased throughout the growing season, possibly reflecting the influence of crop load: the relative evaporative demand becomes higher with crop load development. This information represents a step forward in understanding how pecan trees use water in the humid southeastern United States.