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  • Author or Editor: S. Ponchner x
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Four adjacent heavily cropping 12-year-old `Petite d'Agen' prune (Prunus domestica L.) trees were selected, and two of the trees were defruited in late spring (28 May) after the spring growth flush and full leaf expansion. Trees received K daily through the drip-irrigation system, and 15N-depleted (NH4)2SO4 was applied twice between the dates of defruiting and fruit maturation. Trees were excavated at the time of fruit maturity (28 July) and fractionated into their component parts. The 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 nutrient contents, within-tree nutrient distribution, total nonstructural carbohydrates (TNCs), and recovery of labeled N. Trees only recovered ≈3% of the isotopically labeled fertilizer N over the 6-week experimental period. Heavily cropping trees absorbed ≈9 g more K per tree (17% of total tree K content) during the 2-month period of stage III fruit growth than defruited trees. The enhanced K uptake in heavily cropping trees was apparently conditioned by the large fruit K demand and occurred despite greatly reduced levels of starch and TNCs relative to defruited trees. Fruit K accumulation in heavily cropping trees was accompanied by K depletion from leaves and perennial tree parts. Except for K, fruited and defruited trees did not differ in nutrient content.

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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.

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