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

• Phenology influences N uptake and distribution in ‘Bing’/‘GI®6’ sweet cherry.
• 15N recovery from whole ‘Bing’/‘GI®6’ sweet cherry trees declined toward fall.
• Nitrogen use efficiency in ‘Bing’/‘GI®6’sweet cherry trees declined toward fall.
• The highest nitrogen use efficiency was observed 30 DAFB.

Labeled nitrogen (N) was applied as ammonium nitrate (15NH415NO3; 10% atom) to 6-year-old sweet cherry (Prunus avium L.) trees of the combination ‘Bing’/‘Gisela®6’ (‘GI®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 15N 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®6’. Therefore, N supply to commercial sweet cherry orchards using ‘GI®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.