Basics of Foliar Application
Posted on June 02, 2020
Foliar feeding or foliar fertilization is a term describing the application of necessary plant nutrients to the above ground, living plant parts. Its purpose is not to replace soil fertilization, but rather to supplement plant nutrient needs during shortages and/or critical growth stages. Foliar feeding is intended to delay natural senescence processes shortly after the end of reproductive growth stages. Foliar feeding targets the growth stages where declining rates of photosynthesis and the leveling off of root growth and nutrient absorption occur. It attempts to aid translocation of nutrients into seed, fruit, tuber or vegetative production. Foliar feeding can be an effective management tool to favorably influence pre-reproductive growth by compensating for environmentally induced stresses such as adverse growing conditions and/or poor nutrient availability.
Early foliar applications can make an already good crop better, either by stimulating more vigorous regrowth or by increasing the yield potential. The practice is a highly efficient and timely method of applying needed plant nutrients and a means of compensating for soil or environmentally induced nutrient deficiencies.
CROP GROWTH STAGES
It is important to apply foliar fertilizer at the proper growth stages. Foliar applications should be timed to provide needed nutrients during the yield determining growth stages. Multiple, low rate applications may show the most favorable crop yield responses. Monitor crop growth on a weekly or even on a daily basis for proper determination of the targeted growth stage. Regular plant tissue testing is essential to identify those nutrients that are most limiting crop growth.
Generally, crops that are nutritionally sound will be more likely to respond to foliar feeding. This is due to better tissue quality (allowing for maximum absorption of nutrients into leaf and stem) and faster growth (translocatable nutrients will be moved rapidly to the rest of the plant). Crops under heat or moisture stress show less response to foliar fertilizer applications. When the stress is removed and the crop begins to recover, foliar applications may be resumed successfully.
Environmental influences, such as time of day, temperature, humidity and wind speed influence the physical and biological aspects of foliar applications. Warm, moist and calm conditions favor highest plant tissue permeability.
- Time of day: Ideal conditions are most likely found during the evening hours and early morning.
- Temperature: 65-85 degrees F, 70 degrees is ideal.
- Humidity: Greater than 70% is best.
- Temperature + humidity: 140-160.
- Wind speed: Less than 5 mph.
Not all fertilizers are suitable for use in foliar applications. The objective is for maximum absorption of nutrients into the plant tissue with a minimum or no foliage damage. Fertilizers should meet the following standards:
- Low salt index: Reduces or eliminates potential tissue damage from fertilizer burn.
- High solubility: Reduces the volume needed for application. Liquid fertilizers are the easiest to work with.
- High purity: To eliminate interference with spraying, solution compatibility or unexpected adverse effects on foliage.
SURFACTANTS AND OTHER SPRAY ADDITIVES CAN HAVE A POSITIVE EFFECT
Consult product labels for appropriate uses and follow all instructions. Always run compatibility tests on the products that will be sprayed together before mixing into the spray tank.
Reference: Foliar Nutrition, Midwest Laboratories, Inc., Omaha, NE, 1995.
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