Abstract
The annual dynamics of whole mature almond tree nutrient remobilization in spring and the accumulation of nutrients in perennial tissues during the year were determined by sequential coring, tissue sampling, nutrient analysis, whole tree excavation and biomass estimation for trees grown under four nitrogen rate treatments 140 kg ha−1 N (N140), 224 kg ha−1 N (N224), 309 kg ha−1 N (N309), and 392 kg ha−1 N (N392) over 2 years. Whole tree perennial organ N content was greatest in dormancy then declined through bud swell, flowering and fruit set, achieving the lowest total whole tree nutrient content of perennial organs by March 12 [12–14 days after full bloom (DAFB)] coincident with 60–70% leaf expansion. During this period no net increment in whole tree N content (annual plus perennial N) was observed indicating that tree demand for N for bud break, flowering, fruit set and leaf out was met by remobilized stored N and that there was no net N uptake from soil. Remobilizable N increased with increasing N application up to N309 and was maximal at 44.4 ± 4 kg ha−1 and 37.5 ± 5.7 kg ha−1 for the optimally fertilized N309 in 2012 and 2013 respectively. Net increases in perennial organ N (stored N) commenced 41 DAFB and continued through full leaf abscission at 249 DAFB. Total annual N increment in perennial organs varied from 25 to 60 kg ha−1 and was strongly influenced by N rate and tree yield. N remobilized from senescing leaves contributed from 11 to 15.5 ± 0.6 kg ha−1 to perennial stored N. Similar patterns of nutrient remobilization and storage were observed for P, K, and S with maximal whole tree perennial storage occurring during dormancy and remobilization of that stored P, K, S to support annual tree demands through to fruit set and 70–100% leaf development. Net annual increment in perennial organ P, K, S commenced 98 DAFB and continued through full leaf abscission at 249 DAFB. Organ specific contribution to remobilizable and stored nutrients changes over the growing season are presented. Details of the pattern of perennial organ nutrient allocation, storage, and remobilization provides a framework for the optimal management of nutrients in almond with relevance for other deciduous tree species.
Highlights
Deciduous trees cycle nitrogen (N) and other nutrients by remobilizing them from the senescing leaves into woody tissue and by storing a portion of accumulated nutrients in perennial organs
The objectives of this study were to (1) determine the size of storage pool of N, P, K, S, B, and other elements under different N application levels, (2) To determine which organs are used for nutrient storage in almond trees, (3) to document the timing of nutrient remobilization and storage, and (4) to determine the contribution of leaf nutrient remobilization into the storage pool during senescence
As determined by a net decrease in N in perennial organs, started at bloom (February 28th and continued until fruit set March 12th) for all N rates, there was an increase in the N content of the perennial tissues except for the low N rate treatment (N140) which showed a lower N content in perennial tissues at kernel fill in 2012 (August 17th) which represents a high N demand time
Summary
Deciduous trees cycle nitrogen (N) and other nutrients by remobilizing them from the senescing leaves into woody tissue and by storing a portion of accumulated nutrients in perennial organs. Deciduous species tend to store N in the wood and bark of roots or the trunk (Millard and Grelet, 2010). Stored nutrients play a pivotal role in the nutrition of the tree at a time when soil nutrient uptake is limited by environmental factors, lack of transpiration and restricted root growth (Basile et al, 2007). Initial tree growth in the spring utilizes remobilized N rather than N uptake by roots due to suboptimal conditions, abundance of stored N and absence of leaves (Millard and Neilsen, 1989; Millard and Grelet, 2010)
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