Remedy in case of calcium deficiency in apple trees
Apple trees suffering from calcium deficiency often show symptoms such as early bitter pit, characterized by a spongy texture beneath the skin without rot. Red and black spots that appear before harvest must be carefully distinguished between invasive diseases and physiological conditions. Invasive diseases cause rapid expansion of these spots, leading to internal rot, while calcium-deficient spots remain as sunken, blackened areas without rot—commonly referred to as "bitter acne." Gently peeling the skin with a knife can help identify the issue: if the flesh feels spongy, it indicates calcium deficiency during fruit enlargement; if the subcutaneous tissue appears normal, it suggests deficiency during ripening.
Calcium-deficient apples may also lose cell-to-cell adhesion, causing soft cell walls and middle lamellae, which lead to cell rupture. Besides bitter pit and bitter acne, other symptoms include water core, blossom end rot, and fruit softening, all of which can occur before harvest.
The causes of calcium deficiency in apple trees are both internal and external. Internally, calcium moves slowly within the plant, and its transport through the xylem depends on leaf transpiration. Leaves at the top, with strong transpiration, tend to have higher calcium levels, while lower branches, shaded areas, and weak buds receive less. The phloem has limited ability to redistribute calcium, so mature leaves cannot provide much to younger tissues or fruits. This is why calcium deficiency first affects the apical and young tissues.
Externally, long-term use of chemical fertilizers depletes soil nutrients, especially medium and trace elements, leading to severe calcium deficiency. Excessive nitrogen, phosphate, or potassium fertilizers can also inhibit calcium uptake. Drought reduces soil moisture below 50% of its capacity, weakening transpiration and affecting calcium transport. Waterlogging can similarly cause calcium deficiency. During periods of heavy rain before harvest, fruit expansion is rapid, but lack of sunlight can hinder calcium movement, resulting in red and black spots, bitter acne, and other issues.
To prevent and treat calcium deficiency:
1. Reduce reliance on chemical fertilizers. Use organic manure and high-quality compost as base fertilizer, along with 30-40 kg of siliceous calcium per acre (such as calcium magnesium phosphate). Over time, this improves soil fertility and calcium content.
2. Apply calcium to the soil in March, during the root’s first growth peak, at 20-25 kg per mu.
3. Foliar sprays with amino acid calcium (300 times dilution) or chelated calcium solutions are effective. Spray 5–6 times during key growth stages—bloom, fruit set, and bagging—for immediate results.
4. Prune to improve light penetration in the canopy, especially for inner and lower branches.
5. Ensure adequate watering during droughts. Maintain soil moisture at 60–70% of its maximum holding capacity. If irrigation isn’t possible, use grass or holes to store water.
6. Thicken the soil layer under the tree and maintain proper drainage to avoid water accumulation.
7. Before harvest, if prolonged rain occurs, spray the fruit with 300-times diluted amino acid calcium on dry days.
8. Just before harvesting, apply 300–400-times diluted amino acid calcium to prevent red and black spots, bitter pit, water core, and other storage-related issues.
By combining soil, foliar, and cultural practices, farmers can effectively manage calcium deficiency in apple trees and improve fruit quality.
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