Secondary and Micronutrients for Corn and Soybean Production in Kentucky.

With the exception of zinc (Zn), micronutrients seldom limit corn and soybean production in Kentucky.  However, recent tissue analysis data collected from fields in south central Kentucky had levels of boron (B), copper (Cu), sulfur (S), and Zn below established critical concentrations.  These observations seem to be confined to soils derived from sandstone and siltstone parent materials.  A study was established in 2008, and continued in 2009, in two corn-soybean fields in Russell County.  In 2008, treatments included B, S, and Zn as well as higher than recommended levels of potassium.  A Cu treatment was added in 2009 because of extremely low tissue Cu concentrations observed in 2008.  In 2008, B and Zn fertilization increased their tissue concentrations above critical levels for both corn and soybean.  Tissue S concentration was slightly greater than the critical level for both crops; however, added S increased tissue levels only in soybean.  Yields of both crops were not influenced by any of the fertilizer treatments in 2008, likely due to extremely dry growing conditions from flowering to maturity. Significant differences found in the 2009 cropping season will be discussed.  These results should help growers decide when secondary and micronutrient applications may be necessary for maximum yield.