It's that time of the season when many producers wonder if foliar fertilization could help improve soybean growth and grain yield, and some also wonder about corn. They wonder if preplant fertilization was adequate; if late planting dates, replanting and cold or excessively wet conditions limited early nutrient uptake; or if assumed adequate soil nutrient levels may limit yield when growing conditions are excellent.

Foliar fertilization should be viewed as a complement to preplant fertilization or a "rescue" treatment. Only a very small fraction of the needed amount of nutrients can be applied to the foliage because high nutrient concentrations in the leaf surface have toxic or salt-induced damaging effects, and repeated applications would be too costly.