Iron deficiency chlorosis in soybeans is an issue addressed in the North Dakota State University Soybean Soil Fertility circular (SF1164) revised in November 2019. First, if you haven’t checked out this revised circular, please do. You can find it by Googling “Dave Franzen NDSU” and then clicking on the “Extension Publications and Programs” link about half-way down the page.
Next, the circular addresses the use of cover crops with soybean at time of planting to reduce the severity of IDC. I know a few farmers who have tried this in the past with success and others that will be trying it this year — so let’s talk about it.
A bushel of an easily killed small grain cover crop (like oats or barley) can be seeded near the date of soybean planting as a management tool for IDC. How it works is, the small grain takes up excess moisture and nitrogen that can enhance IDC in the plant. Manage the situation by terminating the small grain cover crop with herbicide either when the conditions are dry enough to cause concern for the soybean crop (meaning termination early) or terminate by five leaf stage of the small grain if conditions are wet.
Research on this practice has been done in three states, giving us confidence in this practice for the Northern Plains region. At the Minnesota research site, seeding an oat cover crop with soybean resulted in as high as 40 bushels per acre more soybean than where oats were not used in a wet season (Table 9 in the Soybean Soil Fertility circular shows the results). I think it’s safe to say that most of us are experiencing wet soil conditions this spring, so this may be a good practice to put in place this spring.
Salinity also increases severity of IDC in soybeans, so let’s address that also because we are seeing salinity rear its ugly head this spring (especially when the wind blows and dries out the soil). We know that soybean plants are not tolerant of salts, so your first management approach is to avoid planting soybeans in saline soils. Use a more salt tolerant, small grain crop or perennial in saline areas. However, if you are insistent on planting soybeans in marginally saline soils (still only talking about an electrical conductivity of less than 2 millimhos per centimeter), including an oat or barley cover crop at time of planting may help. It won’t work miracles, so keep that in mind, but like I said, if you’re going to do it anyways, add in some small grains with your soybeans to help manage the situation.
If you try cover crops with soybeans, please let us know how it goes by posting photos on Twitter and tagging @NDSUsoilhealth or texting or emailing pictures to Dave or me.
Editor's note: Dave Franzen, NDSU Extension Soil Specialist, contributed to this column. Abbey Wick is an Extension soil health specialist at North Dakota State University.