NUTRIENT-UPTAKE BY CROPPING AND DEFRUITED FIELDGROWN FRENCH PRUNE TREES

Four adjacent heavily cropping 12-year-old 'Petite d'Agen' prune (Prun us domestica L.) trees were selected, and two of the trees were defrui ted in late spring (28 May) after the spring growth flush and full lea f expansion. Trees received K daily through the drip-irrigation system , and N-15-depleted (NH4)2SO4 was applied twice between the dates of d efruiting and fruit maturation. Trees were excavated at the time of fr uit maturity (28 July) and fractionated into their component parts. Th e following determinations were made after tree excavation and sample processing: tree dry weight, dry weight distribution among the various tree fractions (fruit, leaves, roots, trunk, and branches), tree nutr ient contents, within-tree nutrient distribution, total nonstructural carbohydrates (TNCs), and recovery of labeled N. Trees only recovered almost-equal-to 3% of the isotopically labeled fertilizer N over the 6 -week experimental period. Heavily cropping trees absorbed almost-equa l-to 9 g more K per tree (17% of total tree K content) during the 2-mo nth period of stage III fruit growth than defruited trees. The enhance d K uptake in heavily cropping trees was apparently conditioned by the large fruit K demand and occurred despite greatly reduced levels of s tarch and TNCs relative to defruited trees. Fruit K accumulation in he avily cropping trees was accompanied by K depletion from leaves and pe rennial tree parts. Except for K, fruited and defruited trees did not differ in nutrient content.