CROP DEMAND INCREASES POTASSIUM UPTAKE BY MATURE PRUNE TREES

Abstract

Two heavily-cropping, twelve-year-old prune trees (Prunus domestica L., syn. `Prune d'Agen') were compared with two adjacent trees which were defruited during stage II of fruit growth (28 May). Trees were uprooted, dissected, and processed to determine total nonstructural carbohydrates, tree nutrient contents and within-tree distribution at the time of fruit maturity (28 July). Trees defruited 2 months earlier contained 5 times as much starch and 2.5 times as much total nonstructural carbohydrates (TNC) in leaves and perennial tree parts as did cropping trees at the time of fruit maturity.Cropping trees absorbed about 90 g more K during stage III of fruit growth than did defruited trees during the same interval (28 May -28 July). Vegetative trees parts (i.e., trunk, branches, roots, and leaves) in cropping trees generally had lower K contents than did defruited trees at the time of fruit maturity. Fruit demand for K was associated with increased K uptake from the soil despite reduced levels of TNC in the roots and the probability of reduced root growth. Potassium uptake by heavily cropping trees was not resource limited when K was supplied regularly through the drip irrigation system.