Graduate Thesis Or Dissertation
 

Nitrogen partitioning and remobilization in field-grown apple trees

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  • Uptake and cycling of nitrogen (N) in mature trees are not well understood. Fertilizer-N uptake, partitioning, and use-efficiency were studied in standard strain 'Topred Delicious' and spur strain 'Redspur Delicious' mature apple trees {Malus domestica Borck) on 'Malling 7A' (M.7A) rootstocks. The treatments consisted of a ground application in spring, a preharvest ground application in August, a foliar spray in fall, or a combination of each of the last two treatments with the first. When soil-applied in spring, labeled N (¹⁵N) was allocated preferentially to above ground tissues and to a lesser extent to roots of both strains. The amount of newly absorbed soil-N allocated to above ground tissues decreased as the season progressed, little ¹⁵N from preharvest ground applications reached the leaves, fruit, buds, or branches, while roots were heavily labeled. Total fertilizer-N recovery in the trees was similar regardless of the time of fertilizer application. However, losses of ¹⁵N to fruit removal, leaf fall, and pruning were most severe when N was applied in spring and minimal for the pre-harvest timing compared to all others. About a third of the variability in recovery was due to variation in tree size. When recoveries were adjusted to account for size differences, spur-type trees tended to be more efficient at utilizing fertilizer-N. When ¹⁵N-urea was applied in April to young apple leaves, the label was not exported. Labeled N from fall urea sprays was exported from the leaves to the buds, but was restricted to the treated spurs and branches. Foliar urea sprays immediately after harvest contributed more N to the buds than later applications. Mobilization of ¹⁵N from storage in various tree parts was assessed. In moderately vigorous trees, N stored in aerial parts of the tree was mobilized first, followed by simultaneous mobilization of root and soil N. Utilization of root reserves depended on the N status of the tree. When the buds were low in N but the roots had adequate N reserves, root to shoot N transport started early in winter.
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file details KHEMIRAHABIB1996.pdf 2017-08-15 Pubblico Scaricare