Timing of nitrogen uptake affects winter storage and spring remobilisationof nitrogen in nectarine (Prunus persica var. nectarina) trees

Two-year old nectarine trees (Prunus persica, Batsch, var. nectarina, cv. S tarkredgold on GF305 rootstock) planted in pots each received five applicat ions of 1.0 g N-15 labelled urea either from mid May to mid July (early upt ake) or from mid August to the beginning of October (late uptake). All tree s were supplied with a corresponding amount of unlabelled urea when they di d not receive the labelled N. In autumn, all abscised leaves were collected and during winter randomly selected trees were harvested and divided into main organs. The remaining trees were transplanted into similar pots filled with sand; they received no N fertiliser and were harvested in May to eval uate the remobilisation of N. Total N and N-15 abundance were determined in each organ. Nectarine trees took up similar amounts of N in the 'early' an d in the 'late' period; however, more labelled nitrogen was recovered in th e perennial organs during the winter when trees received the labelled N in the 'late' than in the `early' period. Some 73-80% of the N present in the dormant trees was stored in the roots, which contained almost twice the amo unt of labelled N taken up 'late' than that absorbed 'early'. Nitrogen for spring growth was remobilised predominantly from the roots and accounted fo r some 43-49% of the labelled N recovered in the tree during winter. Result s suggest that the nitrogen taken up 'late' in the season is preferentially stored in roots and used by peach trees to sustain new growth the followin g spring.