Phosphorus sprays applied six weeks post petal fall can be used to increase fruit firmness improving long-term storage potential at the same time.
Calcium has a major role to play in maximizing apple quality by providing firm fruit. Cell wall integrity and cell-to-cell adhesion is improved, resulting in a tougher flesh that is less prone to bruising or tissue breakdown.
Soil applied calcium nitrate is very effective in improving fruit firmness. When using foliar applications, the more sprays the better, provided that products such as calcium nitrate don’t deliver too much nitrogen, creating nutrient imbalances and loss in quality.
Trials suggest that for firmness, the critical value of calcium in apple at harvest is higher than the 5mg/100g fresh weight recommended for minimizing bitter pit.