The influence of drip irrigation on vegetative growth, yield, nut quality, and leaf water potential of mature pecan trees, Carya illinoensis (Wang) K. Koch

Abstract

Twenty-five year old Stuart pecan trees were drip irrigated during the 1976 and 1977 growing seasons. Treatments consisted if 132, 283 and 454 liters per day and a control which received no supplemental irrigation. The area under 12 trees from the trunk to the outer root perimeter was covered with 0.125 mm black polyethylene film to exclude direct rainfall. The high rate of drip irrigation water significantly increased yield, percent kernel, nut size, shoot length, and leaflet area over the non-irrigated control, but it did not influence cross sectional area of tree trunks. In many cases, the covered treatments had better growth and more yield than the uncovered treatments. Water potential was measured in the field with a pressure chamber on biweekly intervals and was found to be directly proportional to the amount of water applied with the control trees showing an average of -25 bars, and the 454 1/day treatment having an average water potential of -13 bars. A growth chamber study indicated that the accumulation of ABA was inversely proportional to water stress. At the end of the experiment the water stressed seedlings accumulated 318 n gm ABA compared to 224 n gm ABA in the control. Water potential of stressed plants average about -18 bars while that of the control averaged -11.7 bars.