With corn and soybean harvest approaching, many folks are planting their cover crops, or planning to plant their cover crops as soon as they can. The biggest question we are getting these days is whether cover crop seeding recommendations need to be changed because of the dry conditions in many parts of Iowa.
The quick answer is that cover crop seeding recommendations remain the same: aerial and broadcast seeding methods require a slightly greater seeding rate than drill seeding. If there is not enough soil moisture or a rain within a week of seeding, there will be diminished and variable stand establishment across the field. To minimize this, you might consider drill seeding over aerial and broadcast seeding. Typically, drill seeding results in more uniform stands across the field with the consequence of less fall biomass production due to a later seeding date. Even later planting due to drilled seeding results in soil health improvements from spring growth of winter cereals.
Regardless of how you are going to seed, it is important to get the cover crops out in the fields. Cover crops play a crucial role in building soil moisture by improving water infiltration and aggregate stability. Additionally, they have the added benefit of scavenging residual soil nitrogen. Winter cereal grains such as winter rye, wheat, and triticale, are the preferred cover crop for their exceptional ability to use residual soil nitrogen. This is an extremely important characteristic following drought years where nitrogen leaching and crop nitrogen uptake are both potentially lower.
Iowa State University research conducted by Dr. Matt Helmers at Gilmore City, Iowa, show seasonal spring nitrate concentrations from 2011 to 2015 were the highest in 2013 (wet spring following a dry 2012). In the conventionally tilled system, nitrate concentration in drainage was 23.7 mg/L. When cover crops were added to the system, the nitrate concentration was reduced by 51% to 11.5 mg/L.
While establishing cover crops in dry conditions may be a challenge, these are the situations where the impact of cover crop can provide big benefits.
Mark Licht is an Iowa Learning Farms team member and Assistant Professor and Extension Cropping Systems Specialist at Iowa State University.