July 7, 2011

Not usually. Research findings of the past 10 years from Nebraska and neighboring states indicate a low probability of profitable soybean response to foliar application of nutrients if soil fertility is well managed. With the exception of iron chlorosis, there also is a lack of field evidence of profitable response to foliar application when tissue analysis indicates a below average or deficient level in the plant. If test results indicate low nutrient levels, use this information to re-evaluate soil fertility management practices.

There is a puzzling amount of interest in foliar boron (B) application to soybean, considering the lack of evidence of response to soil or foliar application of B. There is abundant evidence of high soybean yields without B application. If there is a response to B application, it is most likely on sandy soil that has less than 1% organic matter, a pH over 6.5, and less than 0.7 ppm soil test B.  We have not determined a critical soil test B level in Nebraska or neighboring Corn Belt states due to lack of response. Suggested critical levels elsewhere are commonly 0.3 to 0.5 ppm, but New Jersey advises 0.75 ppm for corn.

Is there a special case for manganese (Mn) application on glyphosate-tolerant soybean varieties? There is some evidence that response to Mn application is more likely on glyphosate-tolerant soybean compared with non-GMO varieties, but does this apply to Nebraska?

Nathan Nelson, associate professor of Agronomy at Kansas State University, evaluated foliar and soil application of Mn at nine site-years; response was similar and generally very small (non-significant) over seven site-years for glyphosate-tolerant varieties compared with susceptible varieties. However, there was a response of the glyphosate-tolerant varieties for two years of experimentation at Scandia, Kan.

In Nebraska Mark Bernards, extension irrigated weeds specialist, compared four resistant varieties with four non-resistant varieties for response to foliar applied Mn. In Bernards study there was no Mn effect on yield for either variety set. The evidence indicates a low probability of response of glyphosate-tolerant soybean to soil or foliar Mn application in Nebraska.

In-field Testing

The availability of new foliar products, such as those with some slow-release N, and increasing yields may increase the probability of profitable returns to foliar application. With support from the Nebraska Soybean Board, NACHURS, and other funding sources, the effect of foliar application of N (immediate and slow availability N), P, K and micronutrients is being evaluated at four soybean field day sites in Nebraska. The topic will be addressed at the Soybean Management Field Days August 16-19.

Producers interested in foliar application of nutrients to soybean are encouraged to do their own comparison. Leave at least six strips throughout the field without foliar application. Using yield monitors or weigh wagons at harvest, compare the grain yields of the six strips without application to six strips with application. Please share your results with us.

Charles Wortmann, Extension Nutrient Management Specialist, Lincoln
Keith Glewen, Extension Educator, Saunders County
Charles Shapiro, Extension Soils Scientist - Crop Nutrition, Haskell Agricultural Laboratory, Concord
Tim Shaver, Extension Nutrient Management Specialist, West Central REC, North Platte