Zinc is a universally recognized essential micronutrient for plants, with a content generally below 1/1000 in plant tissues. Although crops have a low demand for micronutrients like zinc, they are just as crucial as macronutrients for crop growth and development. Plants mainly absorb zinc from the soil, and fertilizers can improve or maintain the zinc content in soil and plants.
Zinc can promote crop growth and increase yields; enhance crop resistance to abiotic stresses such as drought and high temperature; improve crop resistance to diseases and pests; and boost the nutritional quality of crops. When plants are deficient in zinc, zinc in old leaves can be transferred to younger leaves, but the transfer rate is relatively low. Therefore, zinc deficiency symptoms mainly appear at the shoot apex and young leaves. The main manifestations are: stunted plant growth, short internodes, delayed growth period; small and clustered leaves; interveinal chlorosis in middle and lower leaves. Plants sensitive to zinc deficiency include legumes, citrus, rice, corn, fruit trees, sorghum, etc. Rice with zinc deficiency will suffer from dwarf disease, corn will have white seedling disease, and apple trees will exhibit little leaf disease and rosette growth.
However, excessive application of micronutrients can lead to crop toxicity. Crops suffering from zinc toxicity will show leaf yellowing and brown spots.
There are four methods of zinc fertilizer application. The first and most commonly used method is direct spraying. The second is soil application, including broadcasting, band application and hole application. The third is seed treatment, such as seed soaking, seed dressing and seed coating. The last one is root dipping treatment for transplanted crops.
Common zinc fertilizers on the market currently include zinc sulfate, zinc oxide, zinc nitrate, zinc carbonate and various compound foliar fertilizers.