Strong commodity prices have encouraged producers to look for ways to increase their yields even if it is only for a few bushels. Retail businesses have of wide array of available foliar fertilizers for producers to try to get those few bushels. Before using a foliar program one should review university research summaries and ask if the concept is sound.
University research has not shown a consistent response to foliar fertilizers. There have been sites that have seen a yield response and some that have seen a yield loss. For most sites there has been no yield change (Ohio data has not shown a yield gain or loss). When a yield response has been seen, researchers were often unable to explain why it worked at one site and not others. Soybeans have been more responsive than corn. Universities generally do not recommend foliar programs since the research results have been inconsistent, unrepeatable and unpredictable.
There are limitations to a foliar program. Crop leaves are made for photosynthesis and not nutrient absorption. A foliar has to be absorbed by the leaf before it dries by entering stomata openings or passing through the cuticle – neither one an easy process. Because of this limitation, it is highly unlikely that a plant would have the ability to absorb large amounts of any given nutrient. Thus a foliar program would be impractical to correct major deficiencies for the macronutrients (N, P, K, Ca, Mg, or S). However, a savvy marketing program often adds a small amount of N or S to a foliar for visual impact (causes the leaves to look greener giving the impression one is getting a benefit from the foliar, but generally no increase in yield). If too much N has been added tissue burn may occur.
If a soil is truly not able to provide roots a micronutrient, foliar application may be viable option since the crop only needs a very small amount. This critical amount would have to enter the leaf through the same restricted pathways as mentioned above. However, available micronutrients should easily be provided to roots in fields where the soil has the optimum pH range, has adequate organic matter, has proper soil moisture, and has followed a balanced nutrient program based on soil tests.
University research is a one tool a producer has to select production practices. There are many new foliar programs and products available each year that universities’ have not evaluated. If a producer selects one of these programs, they should leave at least one strip that does not receive the foliar program for a yield check to confirm potential benefits. OSU Extension will work with any producer, consultant or retailer who would like to set up an on-farm evaluation of these programs or products.
Producers should be suspicious of programs that recommend foliar products based on plant analysis. There have been instances where a company pulls tissue from a field for analysis and then recommends a producer to apply certain foliar products based on that analysis, regardless of crop condition or growth stage. No university research supports this type of nutrient recommendation. Plant analysis is a diagnostic tool and not a fertilizer recommendation program. Nutrient sufficiency levels were not established or correlated to make a fertilizer recommendation but to evaluate a crop at a specific stage of development. Tissue analysis is an interpretive tool, not an absolute yes or no answer tool. When properly used as a diagnostic tool, plant tissue should be collected from a normal area and the area of concern along with a soil sample for analysis from the two areas.