Distribution of 15N applied to the soil in the 'Bing'/'Gisela®6' sweet cherry (Prunus avium L.) combination

Labeled nitrogen (N) was applied as ammonium nitrate ((NH4NO3)-N-15-N-15; 10% atom) to 6-year-old sweet cherry (Prunus avium L.) trees of the combination 'Bing'/'Gisela (R) 6' ('GI (R) 6') at three different developmental stages, which constituted the treatments (TR), in equal amounts of N (120 kg ha(-1)). TR included: TR1 = accelerated shoot growth (30 days after full bloom, DAFB, Year 1), TR2 = early post-harvest (105 DAFB, Year 2) and TR3 = late post-harvest (165 DAFB, Year 2). The fertilizer was applied to the soil surface in the root zone. The N content in the trees was determined after the destructive harvest of seven replicates per TR 40 days after N application. Trees were divided into different organs (i.e., buds, fruits, current-season shoots, wood from the trunk and branches, fruiting spurs, non-fruiting spurs and roots (fine and thick)). The total N-15 recovered (mg) from whole trees was higher 30 and 105 DAFB than the amount recovered 165 DAFB. Wood from the trunk and branches had the highest NDFF% values, which varied from 0.35% (165 DAFB) to 3.82% (30 DAFB). The nitrogen derived from fertilizer (NDFF%) values for fruits, current-season shoots and fine roots were also high. The highest N use efficiency (NUE%) was observed 30 DAFB (5.5%), and the lowest occurred 165 DAFB (2.1%). The phenological stage at the time of application to the soil influenced N uptake by the tree as well as the N distribution among its organs. The results demonstrate that the source-sink relationship at a particular phenological stage has an effect on the uptake, distribution and accumulation of N applied to the soil in the semi-vigorous combination 'Bing'/GI (R) 6'. Therefore, N supply to commercial sweet cherry orchards using 'Gl (R) 6' as rootstock should consider nutritional strategies that follow the phenology and the source-sink relationships predominant at a particular stage during the growing season. N applications after fruit harvest to increase storage reserves should consider the reduction in NUE% of whole trees towards fall. As example, N applications early after harvest should be focused in supporting flower bud development, while N applications late after harvest should promote N storage in woody structures and root. (C) 2016 Published by Elsevier B.V.