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Nitrogen fertilization is a basic agrotechnical orchard treatment, and affects quality and size of the crops. The aim of this study was to assess the impact of nitrogen fertilization on the yield and quality of sour cherry fruit of the ‘Łutówka’ cultivar. The course of climatic conditions in relation to the timing of flowering and fruiting was analyzed. The trials were carried out in three different experimental sour cherry orchards (quarters) with different planting dates (1999, 2001 and 2002) located at the experimental orchard of the Poznań University of Life Sciences in Poland. In each orchard, three levels of fertilization were used: control without fertilization, fertilization at a dose of 60 kg N ha−1 and fertilization at 120 kg N ha−1. Increasing the dose of N did not have a significant effect on sour cherry yield. However, it resulted in a reduction of fruit weight, extract content, acidity and TSS/TA ratio, whereas the brightness (L*) and redness (a*) of the fruit surface color increased. Temperature and precipitation had the greatest influence on the course of flowering, fruiting and fruit ripening. Particularly important was the course of climatic conditions at the beginning of the growing season, especially during flowering, when there is a high risk of spring frosts. The timing of flowering and fruiting was correlated with the sum of active temperatures. The greatest relationship for the flowering date was found for SAT (sum of active temperatures) when the base temperature equals 11 °C and the temperature for the harvest date equals 9 °C.
Rutkowski et al. (Fri,) studied this question.