Effect of nitrogen application and crop load on external and internal fruit quality parameters of apples

The aim of the study was to investigate the effect of nitrogen application rate and crop load on individual external (fruit colour) and internal fruit quality parameters (mineral composition, fruit flesh firmness, soluble solids, titratable acidity and starch degradation index). Apple trees in their second to fifth growing year of the Golden Delicious cultivar were fertilized either with 60 or 105 kg N/ha and loaded with crop loads of 100 %, 70% or 40 % of the initial fruiting potential of young trees. A higher crop load and a higher nitrogen rate significantly reduced fruit coloration, fruit flesh firmness, soluble solids and acid content, although the influence of crop load was less evident in the case of higher fertilization. Fruit skin colour parameters were strongly correlated to nitrogen rate and crop load, where crop load mainly affected the colour parameters L* and b*, while parameter a* depended on nitrogen rate. A higher nitrogen rate significantly increased the nitrogen concentration in fruit. Positive correlations between fruit mass, fruit skin colour and soluble solids content were confirmed. Although nitrogen rate of 105 kg N/ha may worsen some individual fruit quality parameters, its positive role on quality equalization should be recognized.