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In a field trial with the Spur variety Super Chief® Sandidge, three different levels of nitrogen supply (50, 100, 150 kg ha(-1)) in combination with 3 rootstocks (M9 at 8333 trees ha(-1), M26 at 5555 trees ha(-1) and Pi80 at 4166 trees ha(-1)) were compared with respect to soil nitrogen dynamics, leaf nutrient levels, tree vigour and yield. The experimental orchard was planted in 2007 and the trial lasted until 2014. The data collected in this period revealed no significant effect of nitrogen levels above 50 kg ha(-1) year-1 on tree vigour and fruit yield, whereas clear differences emerge with respect to the different planting systems (rootstock/planting density). The observed soil nitrogen dynamics indicate that a considerable amount of mineral nitrogen may be lost by leaching from the very permeable soil at the site of the experiment, in particular in the case of high fertilizer applications and humid climatic conditions. Leaf nitrogen contents were not significantly affected by fertilizer rates.

SummaryIn a ®eld experiment on `Golden Delicious' apple trees, different combinations of labelled (10 at. % 15N) urea concentrations (4, 20 and 40 g l±1) and spray volumes (1500, 300 and 150.l ha±1) were used in mid summer to foliar apply 920.mg N per tree by the following treatments: 1) low concentration-high volume, 2) medium concentration-low volume, 3) high concentration-ultra low volume. The fate of urea-N sprayed on leaves was followed during a 5.d period from spraying by determining 15N concentration on leaf samples collected at different timings and on entire branches, previously girdled. Basal and apical leaves were sampled 1, 5, 24, 48 and 120.h after spraying. Leaves intercepted on average 24.mg labelled N per m2 of leaf area, regardless of treatment and leaf age. Leaf N uptake within 48.h was highest when urea was sprayed at low concentration-high volume. At the end of the experiment (120.h), however, no signi®cant effect of treatments on leaf uptake was recorded. Urea-N penetrated at higher r...