Identification and Prevention of Deficiency Diseases of Four Trace Elements in Bean in Greenhouse
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Zinc deficiency symptoms include a fading of the central leaf area, with veins becoming more prominent compared to healthy leaves. As the condition progresses, the areas between the veins gradually lose color, and the leaf margins turn from yellow to brown. The internodes shorten, and the top of the stem develops clustered lobules, while the leaves slightly curl outward and fail to bloom. Zinc deficiency is often triggered by excessive light exposure. Even if zinc is present in the soil, an overabundance of phosphorus can interfere with its uptake. Additionally, high soil pH reduces zinc solubility, making it unavailable for plant absorption. Diagnosis of zinc deficiency can be confused with potassium deficiency, as both cause yellowing. However, in potassium deficiency, yellowing starts at the leaf margins and moves inward, whereas in zinc deficiency, yellowing begins from the center and spreads outward. Severe zinc deficiency may also result in shortened internodes near the growing tip. To prevent this, avoid excessive phosphate fertilizers. If needed, apply 1–1.5 kg of zinc sulfate per acre. For emergency treatment, spray a foliar solution of 0.1%–0.2% zinc sulfate.
Boron deficiency symptoms involve the atrophy and browning of growth points, with new leaf buds and petioles appearing pale, stiff, and easily folded. Upper leaves curl outward, and their margins turn brown. Careful observation of leaf veins reveals signs of atrophy, and the pod epidermis becomes lignified. Boron deficiency is common in dry soils, where absorption is hindered. Soils with low organic matter and high pH are also prone to boron deficiency. Excessive potash fertilizer can further impair boron uptake. Diagnosis typically shows symptoms in upper leaves, with no yellowing of the veins. The growth point may become shriveled or withered, resembling calcium deficiency. However, in calcium deficiency, the veins turn yellow, while in boron deficiency, the veins remain green. To manage boron deficiency, pre-apply boron fertilizer, ensure proper irrigation, and increase organic matter in the soil. In emergencies, spray a foliar solution of 0.12%–0.25% borax or boric acid.
Iron deficiency manifests as yellowing of young leaves, with the veins turning pale and the leaf tissue turning white. In severe cases, entire leaves may become yellow and dry without necrotic spots or death. This condition often occurs in alkaline soils, especially when there's an excess of phosphate or other heavy metals like iron and copper. Soil that is too dry or too wet, or under low temperatures, can reduce root activity and lead to iron deficiency. Diagnosis involves checking soil pH; if the rhizosphere is alkaline, iron deficiency is likely. Yellowing of the leaves, either in patches or uniformly, suggests iron deficiency. To prevent this, avoid using alkaline fertilizers and maintain soil pH between 6 and 6.5. Keep soil moisture balanced. For immediate relief, spray a foliar solution of 0.1%–0.5% ferrous sulfate or 100 ppm iron citrate.
Molybdenum deficiency causes poor plant growth, with young leaves showing yellowing between the veins and margins. Leaf tips may wither, and plants may flower without producing fruit. This deficiency is common in acidic soils. Diagnosis focuses on the location of symptoms, which typically appear in the upper leaves. Testing the soil pH can confirm acidity in the rhizosphere. A "flower without fruit" phenomenon is also a key indicator. To control molybdenum deficiency, apply 0.05%–0.1% ammonium molybdate solution at 50 kg per acre, spraying once during seedling and again during flowering.