A study of trickle irrigation rates and irrigation timing on young pecan, Carya illinoensis (Wang) K. Koch, trees

Abstract

Irrigation rate and frequency studies were conducted under field conditions during the 1975 and 1976 growing seasons to determine if the formula Q = A x E x C, [Where Q = Daily water requirement in liters. A = Area covered by tree canopy in square meters. E = Class A pan evaporation in mm per day. C = Constant (0.7 or 70% of the area covered by the tree canopy).] can be used to determine the daily water requirement of pecan trees. Additional studies were conducted to measure the difference in performance of young pecan trees when they were watered daily vs. weekly. The leaf water potential was measured to determine the water status of the trees in each treatment. Potential measurements were made with a pressure chamber apparatus. The data generated from two years rate studies did not conclusively prove that the planning formula Q = A x E x C could be used to determine the daily water requirement of young pecan trees. The calculated rates of 5.4 and 8.4 1/day were determined to be optimum in 1975 and 1976 respectively. Water puddled around the irrigation emitters at higher than calculated rates. Water potentials in August 1976 averaged the same for trees receiving no water and those receiving 11.34 and 15.12 1/day. These observations indicate that most of the trees in these experiments which received more water than the calculated rate were stressed from excessive soil water and the trees which received less than the calculated rate did not grow as much. Trees in the irrigation frequency experiment received 19 cm of rain during the experiment and no significant difference between any of the treatments was found. The pressure chamber proved to be an efficient way to measure plant water potential in the field but its use as a tool for determining irrigation rate efficiency was found to be limited as the apparatus cannot distinguish between stress caused by the lack of soil moisture and stress caused by excessive soil moisture.