Except for iron and zinc, micronutrients not warranted
Boron application is much promoted; however, the probability of profitable response is extremely low. Applying boron in the seed furrow can be toxic at germination and emergence. Building soil test boron levels is not feasible as it is easily leached from the soil. Irrigation typically supplies enough boron to meet crop needs.
In some parts of the Corn Belt, glyphosate-tolerant soybean often respond to soil and foliar application of manganese. In trials conducted in southeast and south central Nebraska soybean did not respond to manganese application. In Kansas there was a response to both soil- and foliar-applied manganese at one of four locations. A case of very serious manganese toxicity due to misapplication by a dealership has been verified in Nebraska.
Crop response to chloride application has occurred in Kansas. There were no yield increases with chloride application in trials conducted with corn in southeast to south central Nebraska and with winter wheat in western Nebraska.
Copper and Molybdenum
There is no evidence of crop response to copper and molybdenum in Nebraska.
Interpreting Micronutrient Test Results
What if foliar analysis indicates a micronutrient deficiency? Such results are often used to promote micronutrient application. Treat these results with caution.
First, foliar nutrient concentration can vary with rate of growth, growth stage, variety, weather conditions, and time of day. With many samples taken and several nutrients considered, there is potential for seeing occasional low levels, even with high soil fertility conditions.
Second, labs and service companies differ greatly in their interpretation of foliar analysis results with some considering low to be anything below an average result, and others basing their interpretation on research relating plant response to nutrient application relative to the tissue nutrient levels. Foliar analysis for agronomic crops in Nebraska should be used to guide soil testing and additional foliar analyses for future crops but, it is not a sole justification for a nutrient application.
Could you have an exceptional situation for response to micronutrients? Such claims are common, often with a high level of certainty. If you are doubtful, do your own trials, but don’t limit yourself to a mere one time, side-by-side comparison which many find to be convincing. Spatial technology makes replicated on-farm trials often easy to conduct. Even with such trials, repetition on three or more fields or years is encouraged for confidence in small yield effects. Extension Educators can help you design such a trial and interpret the results. We would also appreciate you sharing your results with us.