STORAGE OF FOLIAR-ABSORBED NITROGEN AND REMOBILIZATION FOR SPRING GROWTH IN YOUNG NECTARINE (PRUNUS-PERSICA VAR. NECTARINA) TREES

The effectiveness of spraying foliage with urea to provide nitrogen (N ) to augment the seasonal internal cycling of N in young nectarine tre es (Prunus persica (L.) Batsch var. nectarina (Air. f. Maxim.), cv. St ark Red Gold) was studied. One-year-old trees were grown with contrast ing N supplies during the summer and foliage was sprayed with a 2% ure a solution labeled with N-15 just before leaf senescence started. Afte r leaf abscission had finished, the trees were repotted in sand and gi ven no further N. Remobilization of both labeled and unlabeled N for l eaf growth the following spring was quantified. Leaves absorbed betwee n 58 and 69% of the N-15 intercepted by the canopy irrespective of tre e N status. During leaf senescence, the majority of N-15 was withdrawn from the leaves into the shoot and roots. Remobilization of N-15 the following spring was also unaffected by tree N status. About 38-46% of N-15 in the trees was recovered in the new growth. More unlabeled N ( derived from root uptake) was remobilized for leaf growth in the sprin g than was withdrawn from leaves during canopy senescence the previous autumn. Therefore, soil-applied N augmented N storage pools directly, and contributed more to N remobilization the following spring than di d foliar-absorbed N-15.