Foliar fertilizer is a type of nutrient supplement applied directly to the surface of plant leaves, allowing the foliage to absorb essential elements. This method offers quick results, high efficiency, reduced application rates, and is easy to use, making it widely adopted in modern agriculture. However, improper use due to a lack of understanding can lead to waste or even damage to crops. To ensure effective application, several key factors should be considered.
First, selecting the right foliar fertilizer depends on the specific needs of the crop. There are various types available, including nitrogen, phosphorus, potassium, micronutrients, amino acids, humic acid, and growth regulators. Before choosing, it's important to analyze the soil's nutrient content and pH level. In some cases, testing the plant itself or observing symptoms of deficiency can also guide the choice. For example, if base fertilization is insufficient, nitrogen-, phosphorus-, and potassium-based foliar fertilizers are recommended. When sufficient base fertilizer is used, focus should shift to trace elements. Cotton’s bud drop is often linked to boron deficiency, so applying boron fertilizer 2–3 times during the budding stage can help. Similarly, tomato blossom end rot is caused by potassium deficiency, so spraying potassium dihydrogen phosphate 15–20 days after fruit set can be beneficial.
Second, solubility is crucial. Foliar fertilizers must dissolve completely in water; otherwise, undissolved particles may not be absorbed and could harm the leaves. Therefore, choose high-quality products with less than 5% insoluble matter.
Third, the pH of the solution should be appropriate. Most foliar fertilizers work best within a pH range of 5–8. Too acidic or too alkaline solutions can harm the plant and reduce nutrient uptake.
Fourth, concentration matters. The solution must be neither too weak nor too strong. A low concentration may not provide enough nutrients, while a high concentration can burn the leaves. For instance, urea is typically sprayed at 1–2% for corn, 0.5–1% for vegetables and fruits, and no more than 0.2% for seedlings. Trace element sprays usually range from 0.3–0.5%, with lower concentrations for zinc, copper, and molybdenum.
Fifth, some foliar fertilizers are unstable and cannot be stored long-term. For example, ferrous sulfate can oxidize quickly, reducing its effectiveness. To prevent this, add a small amount of vinegar or mineral acid when preparing the solution to keep it acidic and stable.
Sixth, timing is important. Spraying in the evening during calm weather helps the solution stay on the leaves longer, improving absorption. Avoid spraying during heavy rain, as the solution may wash off.
Finally, the timing of application should match the crop’s growth stage. Applying foliar fertilizer during critical periods, such as the late growth stage of wheat or rice, can boost grain yield. During fruiting, watermelon benefits from foliar sprays that help reduce flower drop and improve fruit set.
By following these guidelines, farmers can maximize the benefits of foliar fertilization while minimizing risks.
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