Guidelines in European Union for N management in orchards aim to limit fertilizer applications under threshold limits, in order to reduce N losses to the environment, but at the same time to attain optimum tree growth, high yield and good fruit quality. The experiment was carried out at the Wilanów Research Farm, situated in the postglacial valley of the Vistula River, on a fertile silty loam alluvial soil. The soil of the field assigned for the experiment was at the depth of 0–20 cm, slightly acid (pHKCl = 6.0), showed high available Mg (16.6 mg%) and P (6.6 mg%) contents, medium available K (19.6 mg%) and a low K/Mg ratio (1.2). Considering a low ratio of K to the other kations as well as occasionally appearing K deficiency symptoms in the neighbouring orchard, before tree planting potassium salts were applied at the rate of 200 kg K2O ha-1. Throughout all the years of studies potassium, magnesium and phosphorus fertilizers as well as liming soil were not applied. 'Jonagored' apple trees on M.9 rootstock were planted in spring 2000, spaced 3.5 × 1.5 m. From spring 2000, five fertiliser treatments were applied: (1) N-0 (check); (2) N-50 (50 kg N ha-1), over the whole orchard area in early spring); (3) N-100 (100 kg N ha-1, over the whole area, in early spring); (4) N-100delayed (100 kg N ha-1, in early spring, starting from the fourth year after planting 2004); (5) N-100sward (100 kg N ha-1, in early spring, starting from the fourth year after planting, in sward alleyways only). Nitrogen was applied as ammonium nitrate, before the start of vegetative growth. After 10 years, the higher dose, i.e. 100 kg N ha-1 applied from the first year after planting resulted in the smallest trunk cross-sectional area (TCSA), during when the same dose starting from the fourth year after planting resulted in the highest TCSA. N fertilization did not significance effect on growth of the trees as compared with not fertilized control. The first yield was harvested in the 3rd year after planting (2002), but in any year neither dose or mode of N fertilisation had any significant effect of yield. The cumulative yield for the years 2002–2009 and fruit size did not depend on N fertilization either. No significant response to nitrogen fertilization was noted on cropping efficiency coefficient for eight years of bearing in relation to the final trunk cross-sectional area.
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