The choice to foliar feed crops is a management decision each farmer needs to make based on personal preferences. Before considering these products, we need to first consider the return on the investment and chance for success.
When considering foliar fertilizing corn and soybean we need to categorize which nutrients we are fertilizing, cost per pound nutrient applied and crop symptomology. The first things to consider are macronutrients, nitrogen, phosphorus, potassium. Nutrient uptake from macronutrients is more efficient taken up from the soil profile. Macronutrients are utilized in larger quantities by plants so small amounts applied as foliars are less effective then being taken up from the soil solution.
Micronutrients in very small amounts can be absorbed by plant leaves or taken up from the soil solution. We also need to understand that for nutrients to be absorbed by plant leaves. those products need to penetrate the waxy cuticle or enter the stomata of the leaf. Most nutrients in the plant are moved with water. Plants that show moistures stress are not efficient at transporting nutrients in the plant. This is not to say on occasion that foliar feeding plants that exhibit nutrient deficiency may respond in color to application. However, this does not always translate to a yield increase. If you feel micronutrients could be beneficial, the best application is in a band at planting or post emerge.
If I was going to consider other nutrients in Iowa to look at for a yield increase, I would start with sulfur applications on corn and alfalfa. The other place, I would consider would be zinc in corn but after consulting a soil test result for zinc (PM 1688).
Looking at research in Iowa foliar fertilizer applications have shown limited success. Extensive testing has been done in the Midwest with foliar applications in 47 trials on corn with boron, manganese, zinc, or mixtures, and none of these trials showed a yield increase. For soybeans in over 63 trials, only one showed a significant yield increase. That is not to say plants cannot benefit from these applications, try to set your farm up with success by tissue sampling (CROP 3153) “Phosphorus and Potassium Tissue Testing in Corn and Soybean” prior to application.
Despite how we feel about “poor” Iowa soils, we still have high quality soils for corn and soybean production in Iowa compared to surrounding states.