ISHS Acta Horticulturae 448: III International Symposium on Mineral Nutrition of Deciduous Fruit Trees
FOLIAR NITROGEN UPTAKE AND WITHDRAWAL FROM PEACH LEAVES DURING SENESCENCE |
| Authors: | M. Tagliavini, P. Millard, M. Quartieri, B. Marangoni |
| Keywords: | foliar uptake, leaf abscission, N nutrition, N withdrawal, Prunus persica, peach, nitrogen, senescence |
| Abstract:
Fruit trees benefit from a post-harvest supply of N which can increase N storage within the tree during winter and so make a major contribution to tree growth and fruit set the following year. The most common way to supply post-harvest N is through the soil, a technique that may increase the potential risk of nitrate leaching during the following winter and spring. Foliar application of nitrogen to the tree canopy represents an environmentally-friendly way to supply post-harvest N, although the effectiveness has not been fully investigated. Nitrogen uptake from leaves and withdrawal in autumn can be accurately assessed by techniques that use fertilisers enriched with 15N as a tracer. We have used 15N applications to test the hypothesis that the N status of the tree affects both the uptake of foliar-applied N and its withdrawal during leaf senescence. The study was carried out with one year-old nectarine trees (24 in total) of the cv. StarkRedGold, grafted on peach seedlings GF 305 and planted in 40 1 plastic pots. Twelve trees each received 40 g of N through bi-weekly soil fertigations from May to September (HN), while the remaining received 12 g each (LN). Only two shoots per tree were allowed to grow. The differential supply affected the N status of the trees, whose leaves in summer had average N concentrations of 4.2 % and 3.1% in HN and LN, respectively. Canopy sprays of a 2 % solution of urea enriched with 19.41 atom % 15N were applied at the beginning of September on one of the two shoots per tree and a few days after, representative leaf samples were collected to measure the amount of 15N and original N present before senescence started. The shoots were then covered in a net and abscised leaves collected three times a week. Leaf samples were bulked and analysed to determine the amounts of both fertilizer N and original N withdrawn. Results indicate that: (1) peach leaves are able to retain approximately 40 % of the N applied to the canopy, regardless of N status; (2) the N taken up by the leaves is withdrawn to the perennial organs with higher efficiency than the original N present in the treated shoot prior to leaf senescence; (3) at leaf abscission, the leaves treated with foliar sprays of urea contained more nitrogen per leaf area than those untreated. Therefore, the total amount of N withdrawn by senescing leaves was similar in the treated and not treated shoots. | |
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