SEASONAL UPTAKE OF N-15-NITRATE AND DISTRIBUTION OF ABSORBED NITROGENIN PEACH-TREES

The absorption and distribution of N was measured monthly throughout a calendar year in 3-year old peach trees (Prunus persica (L) c.v. Mayc rest) grafted on Nemaguard rootstock. Plants were grown on siliceous s and in 500-L pots and fertilized with a solution containing N-15 enric hed KNO3. During flowering and fruit set (March) approximately 7% of N found in new growth came from the fertilizer and the remainder came f rom the N stored in the old organs. Maximum N absorption took place du ring the periods of fruit ripening and maximal vegetative growth (May to August). This nitrogen was relocated from leaves to woody tissues a nd stored as reserve-N before leaf fall. In the following growth seaso n reserve-N was used for flower development and new shoot growth. The N absorbed during plant dormancy was quite low and remained in the ste m bark and roots mainly as soluble-N.