Choosing a cover crop seed blend

Our new season of Carbon College has launched, including an entire course on cover crops. Check out the video above as well as this article to explore choosing the right cover crop seed blend. For more on cover crops and carbon farming, explore Carbon College’s free video courses.

Once you decide cover cropping is right for you, one of the first choices you’ll need to make is the specific cover crops you’ll be growing. The seed or seed blend you choose for your cover crops is a key decision, and you’ll want to gather some information before you make your selection. 

When evaluating different cover crop seeds, the first factor to consider is the soil challenge(s) or production challenge(s) you want to improve. Different cover crops are best for different situations. Below, we discuss nine common soil challenges as well as the best cover crop options to tackle each of them. 

If you want to reduce erosion, your best bet is a quick-to-establish species like grasses with fibrous roots to hold in soil. You can also combine grasses with light rates of brassicas that’ll help break compaction and improve infiltration over time, further reducing erosion.

Ideal species to reduce weeds are grasses that can establish quickly and produce allelopathic toxins. They’ll minimize weed germination while also outcompeting weeds. Cereal rye, triticale, and annual rye are especially good at this. Hairy vetch, once established, can pull down already established weeds due to its vine and climb nature. Alfalfa can also choke out other species when planted in a thick stand.

Poor nutrient cycling is a common problem because most soils don’t cycle nutrients well due to an inadequate microbial profile. This is exacerbated when high carbon cover crops are planted. To combat this issue, choose species with lower C:N ratios like legumes, brassicas, and broadleaves. Also, make sure to terminate high carbon cover crops while in early to mid vegetative stages to promote nutrient cycling.  As your microbial population begins to grow and overall soil health improves, you may need to transition back into using heavy carbon cover crops to keep the workforce fed. 

To reduce low nitrogen availability, select legumes to fix nitrogen. You can also mix in a small amount of brassicas and grasses to improve gas exchange so that free-living nitrogen-fixing bacteria can thrive.

If you’re dealing with compaction, poor water infiltration, or low gas exchange, brassicas are your best bet for penetrating hard pans. Grasses like cereal rye, annual ryegrass, and sorghum sudan can find breaches in hardpans and break them up. Some broadleaf species like sunflowers, okra, safflower, and sugar beets have deep taproots that can also break up compaction. However, they usually require warm conditions and a longer growing window to be cost effective.

Low productivity is a broad category that encompasses many of the soil and production challenges we’ve already covered. Multi-species mixes, when given adequate time to grow, will help improve low productivity. However, you’ll need to gather more information on soil limitations to make a clear decision on species selection and ultimately combat the root cause of low productivity.

Cover crops can also help with drought conditions. For areas with low rainfall or sandy soils with low organic matter, choose cover crops that are highly water efficient and will establish quickly and protect the soil surface. Good options are barley, oats, camelina, peas, and millets. For areas with adequate rainfall but a long duration between rain events, choose species that improve infiltration and improve soil structure, like mixes that have both fibrous and tap roots. 

If you’re looking to expand forage or pasture space, the cover crops you choose will depend partly on when you plant them. For summer planting, warm season species will generate the largest amount of biomass when given the right conditions to grow. Optimum species include millets, BMR/ grazing species, forage soybeans, and cowpeas. For fall planting, cool season species will likely have better grazing in the spring as little biomass is accumulated above ground for most planting dates. Generally, cool season grasses like triticale, cereal rye, and winter wheat will be your best option here.

And finally, to reduce insect or disease pressure, many brassicas, especially members of the mustard family, can produce toxins that are harmful to microbial pathogens. This can reduce soil borne disease pressure in cash crops following a mustard-heavy cover crop blend.

Here’s that information condensed into a table:

After you’ve determined what soil condition or conditions you want to improve, you can think about other factors, such as climate conditions, the application equipment you want to use, and how you’ll be terminating the cover crop.

If you’re looking for more resources on choosing a cover crop seed, there are many available. Check out Indigo Ag’s Cover Crop Selector, as well as the USDA Cover Crop Chart. Also, speak with farmers in your area who’ve been using cover crops. Often they’ll have the best insight into what works and what doesn’t in your area.