The benefits of cover crops are undeniable: helping to protect from soil erosion during the “brown” months, uptaking nutrients that would otherwise be vulnerable to leaching, forage value for livestock, and, over time, helping to build soil organic matter. Cover crops can be readily integrated into corn and soybean cropping systems, as farmers are doing on hundreds of thousands of acres across Iowa. However, up front there are a number of important management considerations that must be taken into account:
This blog post will focus on the first question above. There are three major types of winter cover crops used in Iowa: brassicas, grasses, and legumes. Over the last few weeks, we’ve introduced the “Top 10” cover crop species in Iowa, and we’re in the process of highlighting each of those in individual blog posts. So let’s get the low down on using grasses as winter cover crops!
When considering grasses as cover crops, there are wide variety of species to consider:
- Cereal Rye
- Oats
- Winter Barley
- Sorghum Sudangrass
- Winter Triticale
- Winter Wheat
- Annual Ryegrass
Grasses are the most abundantly utilized type of cover crop in Iowa, offering many benefits to the user. First and foremost, the ease of establishment in the fall is a definite plus! Grasses can be successfully established via a variety of seeding techniques, including drilling, broadcast seeding, overseeding, and aerial seeding. With sufficient moisture for germination, they tend to quickly establish a nice green carpet across the surface of the field, while also establishing an extensive root system underground.
While they do not grow a taproot that helps break up compaction like the brassicas, the quick-growing grasses have a more fibrous root system with outstanding abilities to hold soil firmly in place, anchor corn and soybean residues in the field, and promote water infiltration. Further, the grasses like to scavenge vulnerable nitrogen in the soil profile. Two cover crop grasses are featured in the Iowa Nutrient Reduction Strategy, with cereal rye and oats offering nitrate-nitrogen reduction rates of 31% and 28%, respectively.
Grasses tend to produce large amounts of residue. Depending on the grass species chosen, some will winter kill (e.g. oats) while others are winter hardy (e.g. cereal rye, winter wheat, winter triticale), offering the opportunity for additional biomass growth in the spring. Another benefit offered by winter hardy cover crops is the potential for helping with weed suppression in the spring as the cover crops can outcompete weeds for resources including light, moisture, nutrients, and space.
For these overwintering cover crops, they must be terminated in the spring prior to planting your corn or soybean crop, whether that be via herbicide (e.g. glyphosate), mowing, tilling, or rolling. If using a glyphosate herbicide, the general recommendation for termination is 14 days in advance of planting to minimize adverse impacts on the following corn crop.
To the best of our knowledge, Iowa Learning Farms and Practical Farmers of Iowa have the longest on-farm cover crop research and demonstration project going on in Iowa, investigating the use of cereal rye as a winter cover crop across the state. In 25 of the 28 site-years of this study, farmers experienced no adverse impacts to corn yield following a cereal rye cover crop. The three instances in which corn yield was reduced by the cover crop occurred only in the first two growing seasons of the trial (2009 and 2010). Farmer inexperience with terminating cover crops or adjusting the planter to plant into the cover crop residues could have contributed to the yield losses in these instances. Want to dig in deeper? Full results of this ongoing study (through Year 6) can be found in the document Winter Cereal Rye Cover Crop Effect on Cash Crop Yield.
Cost is always an important consideration in evaluating conservation practices on the farm, and even more so with the tighter margins that farmers are facing today. Grasses are a big plus in the cover crop world as they offer a significantly lower cost in comparison to other cover crop species.
How about seeding rates, seeding dates, and other considerations? Check out the USDA-NRCS’s recommendations in Cover Crops: A Guide for Iowa Producers and Cover Crop Recommendations from Practical Farmers of Iowa. Another excellent resource is the Midwest Cover Crops Council webpage, which includes information on a variety of cover crop research trials as well a robust cover crop selector tool.
In summary, cover crop grasses are versatile, well-tested across the state of Iowa, and offer numerous benefits to the producer. As our friends at Practical Farmers of Iowa like to say, “Don’t Farm Naked!”
Additional Cover Crop Resources:
Cover Crops in Iowa: A Quick Guide (Iowa Learning Farms)
Iowa Learning Farms Cover Crop Resources page
Cover Crops: A Guide for Iowa Producers (USDA-NRCS)
Cover Crop Recommendations (Practical Farmers of Iowa)
Cover Crop Business Directory (Practical Farmers of Iowa)
Overview of Nonlegume Cover Crops (SARE)
Managing Cover Crops Profitably: Third Edition
Iowa Learning Farms 
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