Vegetative and productive responses of organic apple (Malus domestica L.) to fossilized red guano and a controlled-release fertilizer

Abstract

Fossilized red guano and organic controlled-release fertilizers are among the N fertilizers that can be used in organic production. There is little information about the impacts of these fertilizers on the vegetative growth, fruit yield and quality, and mineral contents in fruits. The objective of this study was to assess the responses of increasing levels of N fertilization with fossilized red guano and a controlled-release fertilizer (Fertil®) on the vegetative growth, fruit yield, quality and mineral composition of 'Granny Smith' apples grown under organic management. Treatments included the application of increasing levels of N fertilization (100, 120 and 170 kg N ha-1) applied 50% during early spring and 50% during early summer. In general, trees with higher levels of N fertilization showed greater terminal shoot length and trunk cross-sectional area (TCSA) than those of the control treatment. Yield ranged from 60.0 to 62.0 kg tree-1, as well as fruit mineral concentration and ratios were not affected by the treatments. Leaf mineral concentrations were affected only in the case of N. Bitter pit incidence was low (1.4 in a scale 1-4), and therefore not statistically significant. Both fertilizers proved effective in enhancing vegetative growth compared to the control. Fertilizer applications did not affect tree cropping, fruit firmness, TSS, starch index, fruit ground color and incidence of physiological disorders.