Crop Spotlight: Unlock the Benefits of Cover Crops
Aug 31, 2023
Growing season went well. The harvest was great. Now, looking at your freshly-harvested fields, you give a contented sigh: it’s time to let them rest. Of course, you still have work to do—winterizing your pivots, for example. Still, until winter passes and it’s time to plant again, you can leave the fields and focus on other aspects of your operation. But what if you could put those fields to work over winter and make life easier a few months from now?
That’s where cover crops come in. We’ve talked before about ways to cut fertilizer costs—and depending on where you operate, with a bit of effort at the end of the season, you can seriously reduce your future fertilizer needs.
Benefits of cover crops
There’s a reason cover crops are also known as “green manure.” Growing these crops over winter does wonders for your soil’s nutrition and composition. Certain plants scavenge nutrients (especially nitrogen) as they grow and scatter them when they die. Others “lock in” nutrients (again, especially nitrogen) and can be mown or plowed before death, preventing nutrient loading. And as leftover biomass decays, it increases soil’s organic matter—improving water infiltration and water and nutrient capacity. As an added bonus, cover crops prevent erosion—and their roots break up compacted or clayey soil.
The end result: soil that’s rich (but not too rich) in nutrients and better-positioned to absorb and retain irrigation. That’s more food for your crops, less fertilizer required. The difference can be substantial. Consider these survey results from the USDA. In 2019–2020, cotton farmers who used cover crops saved 53% on fertilizer costs.
Different types of cover crops
There are two categories of cover crops: those that survive the winter to continue growing in spring and those that die once temperatures drop. Which kind you use depends on your needs and priorities.
Frost-killed and winter-killed crops die at the first frost and midwinter temperatures, respectively. They can generate a lot of biomass before they die and are easily tilled under once spring arrives, so you can start planting right away. However, since they die in the cold, you’ll need to plant earlier in order to generate a useful amount of biomass. They’re best planted in fields that hold spring vegetables, or undersown in summer crops like corn.
Winter-hardy crops can be planted later, making them usable in more fields. Many of them also lock in more nitrogen than winter-killed crops. But they require more work in spring—you’ll have to actively mow them to stop growth—and disposing of their biomass can hold up planting. Plus, if you don’t terminate these crops soon or thoroughly enough, they can act like weeds, returning and competing with your cash crops for resources.
There’s also the crop type to consider:
Grasses and winter cereals are fantastic for scavenging nutrients from soil, providing shade and adding biomass.
Legumes, meanwhile, fix nitrogen and other nutrients at their roots, replacing nutrition depleted by hungry crops. The more biomass you grow, the more nitrogen you get.
Brassicas provide many of the same benefits as grasses, but their remains break down more readily in the spring.
The category, type and species you choose will depend heavily on your farm’s unique circumstances, your needs and priorities, as well as the hardiness zone in which you operate. Think carefully about the crops you choose; you may not be growing it for cash, but you’ll still want to grow as much of it as possible.
8 common cover crops
Now that you know the categories and types of cover crops, let’s review some of the most popular plants:
Winter wheat is an excellent choice of winter cereal for cover. Its robust root system and dense ground cover control soil erosion while scavenging excess nitrogen. Residue from its stalks, leaves and stems provide a lot of biomass. Plus, it’s slower to mature than other cereals, so there’s no hurry to kill it when spring arrives. It even releases allelopathic chemicals into the soil, which makes it great for weed suppression, but be careful—if you don’t remove it thoroughly enough, those chemicals can stick around and hamper cash crop growth.
This cereal lives up to its name, germinating in temperatures as cold as 33 degrees (and surviving down to 30 below!). You can plant it late in the fall and still expect large volumes by spring, making it perfect for cover after a late harvest. It alleviates soil compaction, sequesters nitrogen and other nutrients for nutrition management, and can even provide forage for livestock. Like wheat, it has allelopathic properties, so hold off on planting for two weeks after termination.
Oats won’t produce quite as much benefit on their own as winter wheat or winter rye, but they’re still a popular cover crop. They’re inexpensive, fast-growing, generate a lot of biomass and will survive a few hard frosts (dying at 20 degrees). After winter-kill, the residue makes excellent winter mulch—and once spring arrives, the remains can be easily incorporated into the soil, boosting organic matter and adding back any sequestered nutrition.
Buckwheat has a lot going for it: it thrives in many different kinds of soil, grows fast and excels at scavenging nutrients (especially phosphorus) which release once it breaks down. Plus, its dense canopy protects soil from erosion and provides excellent weed control. However, buckwheat terminates quickly in cold weather, so it’s better suited for early planting or milder climates.
This winter-hardy legume pulls a lot of nitrogen from the air—and excels at scavenging other micronutrients, too. Plus, its long taproots break up thicker soil, improving infiltration. The resulting residue upon termination makes for highly nutritious mulch. Just make sure to terminate it at or after the bud stage to get the most nitrogen possible.
Another winter-hardy option, hairy vetch fixates a lot of nitrogen—and its substantial biomass is great for weed suppression and erosion control. Consider planting it in late summer to get the most biomass (and thus the most nitrogen) possible by spring. It’s also usable for forage, but keep it away from poultry or horses—it can be fatal.
Winter peas don’t do as much weed suppression or nutrient scavenging as other plants on this list, but like other legumes, they’re excellent nitrogen fixers. They’re also hardy, capable of tolerating temperatures as low as zero degrees. Plus, they’re excellent for forage—and a tasty snack for humans! After termination, their residue easily incorporates and releases nitrogen for the next crop of lucky plants.
While grasses and legumes remain more common, brassicas like canola are growing in popularity. Like wheat, canola has a deep root system that scavenges everything from nitrogen to potassium. The roots prevent erosion and lock the nutrients into the soil once the plant terminates. And while its biomass is dense enough to outcompete weeds, it quickly decomposes and easily incorporates into soil once spring arrives.
And that’s just scratching the surface. There are a lot of species to choose from, far more than we can talk through in one article. You can also sow multiple kinds of cover crops at once, further increasing the possibilities. Again, it all depends on your needs, your region and your priorities. Regardless of your choices, however, the end result is the same: a little more to do over winter, a lot more nutrition in your soil, and a lot less fertilizer in your fields next year.
As you consider what cover crops might work best for your farm, reach out to your local Zimmatic™ dealer—they’re in an excellent position to provide insight on your hardiness zone, local soil quality, and the unique irrigation needs of cover crops. And keep up with our blog for more stories like this one.
Finally, take another look at your fields and ask yourself: wouldn’t this look better with some rows of winter wheat?