Export of urea N was quantified after 15 N-enriched urea was applied to ‘Manzanillo’ olive leaves ( Olea europaea L.). Labeled N derived from foliar urea applications to mature trees in October 1982 and March 1983 constituted 4.3% and 23.0%, respectively, of the nitrogen composition of olive flowers at anthesis (May 1983). Labeled N applied to leaves following anthesis was translocated to fruit within 3 days. Export of N from treated leaves was greatly reduced when developing fruit and shoot tips were removed. Preloading of leaves with standard urea (before foliar application of labeled urea) increased leaf N by 30% and increased slightly the translocation of labeled urea N to the fruit 2 to 4 weeks later. The nitrogen status of small, potted ‘Manzanillo’ plants did not influence subsequent absorption of foliage-applied urea; however, nitrogen deficiency reduced translocation of labeled urea N from the treated leaves to new shoots and, to a lesser extent, roots. Olive leaves represent storage organs for N and release N in response to the metabolic demands of developing reproductive and vegetative organs.
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Klein et al. (1984) studied this question.