Conventional vs. organic soil management practices in German apple orchards: Correlation between bitter pit disease incidence and nutrient status

Apple orchard soils in Germany face numerous challenges, including pest and disease control and soil nutrient management, leading to the potential accumulation of potentially toxic elements (PTEs). Producing high-quality fruit requires effective management of these challenges, which is additionally intensified by the impact of changing climate and associated weather patterns. One example is bitter pit (BP) disease, a significant disorder in apple orchards that results in substantial economic loss when symptoms manifest in the fruit.

This study aimed to assess macronutrient ratios in German apple orchards and explore the relationship between BP disease incidence and variations in fruit composition across orchards with diverse locations and management practices. Soil and composite plant samples (apples, leaves, and branches) were collected from 16 apple orchard sites (a total of 32 sample sites) in the Eastern region of Germany, encompassing both conventional and organic farming systems (CFS and OFS). MP-AES was used for total macronutrients and trace element plant and soil analysis, and relevant physiochemical soil properties, such as pH, EC, OM, and carbonate content (%) or texture, were examined. Data were evaluated using bioaccumulation (BAF) and translocation (TF) factors, Pearson correlation coefficient, and principal component analysis (PCA).

The study revealed that fruits with an elevated Mg+K/Ca ratio were more affected by BP incidence. Based on PCA, a correlation between orchard location (region), management practices (CFS and OFS), and BP occurrence was observed. We conclude that macronutrient ratios, especially the Mg+K/Ca ratio, play a crucial role in BP disease development in apple orchards, and orchard location and management practices influence these ratios. Knowledge regarding these correlations can support the development of strategies for preventing and managing BP disease, leading to enhanced apple orchard productivity and reduced economic losses.