What are the control methods for calcium deficiency in apple trees?
Symptoms of calcium deficiency in apple trees: bitter pit formed in the early stage, with a spongy texture under the skin but without rotting. The red spots and black spots formed before harvest should be distinguished as to whether they are an infectious disease or a physiological disorder. The red spots and black spots formed by infectious diseases rapidly expand and penetrate deep into the flesh and rot. The red spots and black spots formed by calcium deficiency are sunken and shriveled into black scars without rotting, also known as bitter pit. Gently peel off the skin with a knife; if the tissue under the skin is spongy, it is a symptom of calcium deficiency formed during the fruit enlargement stage. If the flesh under the skin is normal, it is a symptom of calcium deficiency formed during the fruit ripening stage. In calcium-deficient apples, because the intercellular binding effect disappears, the cell walls and middle lamella soften and the cells rupture. Not only do the above calcium deficiency symptoms appear before harvest, but during storage bitter pit, water core, and symptoms such as cracked skin and soft, dark skin are also prone to occur.
Causes of calcium deficiency: First, severe calcium deficiency in the soil; second, the transport of calcium is affected by climatic factors.
1. Calcium ions move very slowly within the plant, and supplementing calcium from the soil is also a very slow process. The transport of calcium within the xylem depends on the transpiration of the leaves; mature leaves have strong transpiration and are relatively rich in calcium. Terminal buds, weak buds, and branches in the inner canopy and lower layers with poorer light have less calcium because of weaker transpiration. The transport of calcium within the phloem is very weak, and the calcium in mature leaves basically cannot be reused by young leaves, root tips, shoot growing points, and fruit. Therefore, when an apple plant is deficient in calcium, it first shows in the root tips, growing points, young leaves, and the newly formed tissues of the fruit. This is the internal cause of calcium deficiency in apples.
2. Looking back at historical experience and the reality of calcium deficiency symptoms appearing in recent years, the external causes of calcium deficiency in fruit trees are: ① Long-term reliance on chemical fertilizers for fertilizing fruit trees has left the available secondary and trace elements in the soil nearly exhausted, and the soil has already become severely calcium-deficient. ② Large applications of nitrogen fertilizer or phosphorus and potassium fertilizers inhibit the absorption of calcium. ③ Severe drought, when soil moisture drops below 50% of the soil's maximum water-holding capacity, leaves wilt, that is, transpiration function weakens, affecting calcium transport. ④ Waterlogging from accumulated water can cause deficiency symptoms of calcium and other elements to appear at the same time. ⑤ During the rapid fruit enlargement stage before harvest, long periods of continuous rain without sunlight affect calcium transport, and severe calcium deficiency symptoms such as red spots, black spots, and black scars will appear.
Control of calcium deficiency:
1. Move away from the mistaken approach of relying mainly on chemical fertilizers. Apply base fertilizer in autumn, mainly farmyard manure and high-quality organic fertilizer, with 30-40 kg of silicon-calcium fertilizer (such as calcium-magnesium phosphate fertilizer, superphosphate, etc.) applied per mu. By increasing soil organic matter and secondary and trace elements to build soil fertility, increase the available calcium content in the soil. Because calcium ions are transported very slowly within the tree, results may not be obvious in the same year. But persisting for several years is the inevitable path to fundamentally solving calcium deficiency.
2. Soil calcium supplementation. In March, before the first root growth peak, apply 20-25 kg of calcium nitrate per mu as a topdressing.
3. Foliar calcium supplementation. Use amino acid calcium at 300 times dilution or other chelated calcium liquid fertilizers. Spray the fruit 5-6 times during the apple bud break stage, before flowering, at flowering, at the young fruit stage, and after bag removal. This is a shortcut for calcium supplementation and can achieve good results in the same year.
4. Through pruning, create good light conditions for the inner canopy and lower branches of the tree crown.
5. Water promptly when drought occurs. For orchards without irrigation conditions, implement grass mulching or hole-stored fertilizer and water so that the soil always maintains 60%-70% of maximum water-holding capacity.
6. Thicken the soil layer under the tree canopy, build good drainage ditches inside and outside the orchard, and drain promptly when the rainy season arrives to prevent water accumulation and waterlogging under the trees.
7. During the fruit enlargement stage before apple harvest, if there are long periods of continuous rain (plum rain weather), seize the rainless days and make time to spray the fruit with amino acid calcium at 300 times dilution, mainly spraying the fruit and wetting the fruit bags.
8. After apple harvest and before putting the fruit into cellars (storage), spray or wash the fruit with amino acid calcium solution at 300-400 times dilution to prevent symptoms such as red spots, black spots, bitter pit, cracked skin, soft dark skin, and water core during storage.