Do Soybeans Respond to Micros?

A recent Minnesota research study said soybean yield doesn’t respond to a broadcast application of boron, chlorine, manganese and zinc.

Deficiency of micronutrients can reduce crop yield and, perhaps, grain quality and composition. Since the run-up in soybean prices and focus on increasing yields, there has been an interest in applying micronutrients, due to the belief that deficiencies might exist. And each retailer has access to a myriad of products that can remedy this perceived shortage.

The question is, “Do micronutrient applications make a difference in soybeans?” We know that corn is sensitive to zinc shortages and applying zinc is common practice. We also know that soybeans are sensitive to manganese shortages, but much of that is more temporary and related to a glyphosate induced tie-up.

In this Minnesota study micronutrients were broadcast across the soil surfaces and incorporated prior to planting. The researchers reported the following results:

• Broadcast applications of B, Cl and Zn increased tissue nutrient concentration, but Mn did not
• Addition of B, Cl, Mn and Zn did not increase soybean grain yield
• Soil tests for B, Cl and Zn don’t predict soybean grain yield response
• No predictive relationship exists between B, Cl, Mn and Zn tissue concentration and yield

The authors wrote, “Results from these studies indicated that the need for micronutrients to increase soybean grain yield is unlikely except potentially for manganese where a response to manganese may be possible when the DTPA test is less than 20 mg/kg (ppm).”

In this study, the authors concluded that it’s is unlikely that micronutrients will increase soybean grain yield. I know that other university studies often report similar findings under controlled small plot research on university research farms. However, private company research will refute this. And increasing tissue test concentrations to be sure there is never a deficiency in-season is no guarantee of an increase in yield.

Applying micronutrients to soybeans, either preplant broadcast or foliar applied, has shown a real mixed bag of results and will add about an $8 to $10 investment (about a bushel) to generate 3 to 5 bushels in return. That return should always be the goal.

My advice—do your homework before deciding. Look at soil and tissue tests to see if micronutrients are lacking and then do your own on-farm testing to see if you can get a yield response and if it produces a profitable economic return.

Research citation: Sutradhar AK, Kaiser DE, Behnken LM. Soybean response to broadcast application of boron, chlorine, manganese, and zinc. Agron J 2017;109:1048-1059. View article at http://dx.doi.org/doi:10.2134/agronj2016.07.0389.

Soybean agronomist Daniel Davidson, Ph.D. posts blogs on agronomy-related topics. Feel free to contact him at djdavidson@agwrite.com or ring him at 402-649-5919.