Zinc deficiency in soil is commonly caused by several factors. First, soils derived from parent materials low in zinc, such as those formed from granite, are prone to this issue. Second, calcareous soils, which are prevalent in northern regions, include types like cotton soil, bauxite soil, fluvo-aquic soil, cinnamon soil, and brown soil. These soils often have a high pH, which reduces the availability of zinc, making them a major cause of zinc deficiency in China. Third, calcareous paddy soils with high organic matter content can also limit zinc availability due to the adsorption capacity of organic matter. Fourth, excessive use of phosphate fertilizers and environmental stress that limits root development can further contribute to zinc deficiency.
Zinc-deficient soils can lead to various physiological disorders in crops. For example, when trees lack zinc, new growth becomes small and stiff, resulting in clustered leaves, known as "rosette disease." In rice, zinc deficiency causes "hollow grains," stunted growth, delayed tillering, reduced root systems, and poor grain filling. Maize suffering from zinc deficiency shows leaf chlorosis, white tassels, delayed silking, and poorly developed ears. Besides rice, corn, and fruit trees, crops like flax, wheat, peanuts, soybeans, and peas are also vulnerable to zinc deficiency.
To address zinc deficiency, common methods include applying zinc sulfate or zinc oxide. Soil application is the most widely used approach, and it's best done during plowing before sowing or transplanting. The recommended rate is typically 1.5–5.0 kg per mu (about 0.067 hectares) of zinc sulfate. Foliar sprays are effective for fruit trees and vegetables, especially when symptoms appear. A concentration of 0.05–0.1% zinc sulfate is generally suitable for early crop growth, while fruit trees may benefit from a 0.5% solution. Seed treatments, such as soaking seeds in a 0.1% zinc sulfate solution or using a coating for rice and cotton, are also common. Mixing 2–4% zinc oxide suspension is an economical option. However, when using industrial waste-derived zinc sulfate, care must be taken to avoid heavy metal contamination like cadmium and lead. The residual effect of zinc in the soil usually lasts 3–5 years, and plant analysis is a reliable way to determine if additional zinc fertilizer is needed.
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