Foliar fertilizers are specifically designed for direct application to plant leaves, hence they are also referred to as leaf or foliar fertilizers. Commonly used ingredients include urea, potassium dihydrogen phosphate, calcium superphosphate, potassium sulfate, borax, ammonium molybdate, and sulfuric acid. Other substances like zinc, rare earth elements, ammonium bicarbonate, ammonia, ammonium chloride, and calcium magnesium phosphate fertilizer should generally be avoided for foliar sprays due to potential damage or inefficiency.
The concentration of the foliar solution is crucial. Too high a concentration can cause fertilizer burn, while too low may not deliver the desired results. Ideal concentrations vary depending on the type of fertilizer and crop. For example, urea is typically applied at 0.5% to 2%, potassium dihydrogen phosphate at 0.3% to 0.5%, and potassium sulfate at 1% to 1.5%. Different crops may require different concentrations; for instance, rice and other grasses benefit from 1.5% to 2% urea, while sweet potatoes, potatoes, and peanuts perform better with 0.4% to 0.8%.
Timing is also important. The best time for foliar feeding is during calm evenings when the leaves can remain wet for 30 to 60 minutes, allowing maximum nutrient absorption. Avoid spraying during rainy days, before rain, or in the morning when dew is present. If it rains within three hours after spraying, reapplication is needed once the weather clears, but at a reduced concentration.
For effective application, both sides of the leaves should be sprayed evenly, using fine droplets. Pay special attention to the underside of upper leaves and areas where new growth is active, as these parts absorb nutrients more efficiently. In some plants with thick cuticles on the upper surface, extra care should be taken to spray the lower side to ensure proper absorption.
It’s recommended to apply foliar fertilizers at least twice, as each application delivers only a small amount of nutrients. For nutrients with limited mobility in the plant, such as iron, boron, calcium, and phosphorus, more frequent applications are necessary.
Mixing two or more types of foliar fertilizers can improve efficiency and save time. However, it’s essential to ensure that the mixture does not cause adverse reactions or reduce effectiveness. Always test combinations before large-scale use.
Finally, adding a wetting agent, such as a mild soap or quality detergent, can enhance the performance of foliar fertilizers. These agents help reduce the surface tension of the solution, allowing it to spread more evenly and penetrate the leaf surface more effectively. This step is especially beneficial for plants with thick or waxy cuticles.
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