Leaf absorption, withdrawal and remobilization of autumn-applied urea-N in apple

Abstract

Six-year-old well-nourished Jonagold/M9 apple (Malus domestica) trees were sprayed 7 d after harvest with a 2% urea solution enriched with 9.9% atom 15N. Through 3 d of the absorption period, leaves absorbed 19.2% of the intercepted urea 15N. This low absorption could be in part due to unfavourable conditions, i.e., low temperatures (daily mean ≈5°C) and windy conditions following treatment During leaf senescence, 48% of the urea 15N absorbed was withdrawn from leaves and most of that (95%) remained in the treated branch section. Of this portion, 65% of the urea 15N was found in dormant bark, 29% in wood, and 6% in flower buds. In the following spring, 46% of the stored urea 15N was remobilized for growth of the flower buds when sampled at the "pink" stage of bud development. This accounted for 3.8% of total N in these tissues. This contribution did not influence flower quality, estimated by the length of the period between flower opening and petal fall and the level of fruit set.