Nitrogen, defoliation and new growth in almond (Prunus dulcis (Mill) D.A. Webb) nursery plants Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/6108vd52x

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  • The relationships between nitrogen (N), defoliation, and plant growth in nursery plants were studied using almond {Prunus dulcis (Mill) D. A. Webb) trees. In several experiments the effects of N source and availability on tree growth, N uptake, N remobilization, and nonstructural carbohydrates (TNC) were investigated to determine the most efficient and effective methods and timing for N fertilization. The influence of chemical defoliants (CuEDTA and ZnSO₄) and foliar urea applications on defoliation, N reserves, and new growth performance was also assessed to determine optimal methods for promoting early defoliation without negative effects on tree growth and quality. Nitrogen from both reserves within the plant and fertilizer applications in the spring was found to be important for enhancing new growth of almond nursery trees during establishment after transplanting. N fertigation during the growing season or foliar urea applications in the fall increased the N reserves in trees, resulting in increased new growth the following spring. Applications of N fertilizer in the spring increased new growth regardless of the amount of reserves in the plant. Young almond trees were found to take up N from the soil as early as two weeks after transplanting. Maximum N uptake occurred during the period of rapid new shoot growth. For trees with low N reserves, spring-applied nitrogen fertilizer was found to be particularly important for promoting new growth. Almond trees accumulated N dynamically in the form of amino acids and protein. Increasing N availability increased concentrations of both free and total amino acids prior to winter storage. However, protein was the main form ofN stored in almond nursery trees. The synthesis of amino acids and proteins occurred at the expense of carbohydrates, and the amount of TNC used to assimilate N increased as the N availability increased. Both CuEDTA and ZnSO₄ were found safe and effective for promoting early defoliation in almond nursery trees, however, CuEDTA was more effective than ZnSO₄. Foliar urea application prior to or with defoliant treatments was found to promote early defoliation and improve N reserves, without affecting the new growth of almond nursery trees.
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