If you drive by the fields at Dee River Ranch, in Aliceville, Alabama, the mixture of crops may look strange: On a given day, owner Annie Dee is kneeling in the field, pulling out small radish plants between massive sunflowers. But these radish plants have been doing a mighty job – they’re supporting the giant sunflowers growing beside them. At Dee’s ranch, located on about 4,000 hectares near the Mississippi-Alabama state line, the focus is on corn, wheat, sunflowers and soybeans, as well as cattle. Still, some passersby stop at the farm and ask questions about what they see as the odd mixture of plants on the fields. “People are curious about why and how farmers use cover crops,” Dee says. “As time goes by and farmers using cover crops are more successful, other farmers will follow.”
Researchers agree that cover crops are one of farming’s best tools. “This is because they provide many different environmental benefits,” explains Dr. Robert Myers, Associate Professor at the Plant Science Division at the University of Missouri. “First, they help to keep the soil in place, so you don’t have the erosion. Secondly, they help keep nitrogen and phosphorus in the field, where the crop can use it instead of getting into our water supply. And they also help with climate change by sequestering carbon in the soil. That is a really big environmental aspect of cover crops.”
As time goes by and farmers using cover crops are more successful, other farmers will follow.
Farming’s Strategic Cover
Cover crops are non-profit “in-between” crops, usually planted just a few weeks after the harvest of the main crop, and before the next is sown. There are three main categories of cover crops. One is legumes, such as clover, pea and vetch. Legumes live in symbiosis with bacteria which capture nitrogen and make it available to the neighboring crops. The second type of cover crop includes grasses such as cereal rye, wheats, barley and triticale; these are also the most popular cover crops in the US. Instead of being harvested for grain, these grasses are grown only for vegetative cover and removed before they produce any seeds. The third category of cover crops is mustards. One that has really become popular in the US is the radish; after cereal rye, radishes are the second most used cover crop in the US. Besides radish, other known and useful cover crops include turnips, canola and rapeseed.
Small plants – big effects
Alongside his faculty role in the Plant Science Department at the University of Missouri, Dr. Myers also serves as Regional Director for the US Department of Agriculture’s Sustainable Agriculture Research and Education Program (SARE). SARE helps US farmers be more sustainable in their management practices. One of the major practices they promote is cover crops. “We have a variety of programs to help farmers with cover crops,” explains Dr. Myers. “The simple things are that we do have books and shorter publications on how to use cover crops. Perhaps more importantly, we give out funding and grants to organizations and farmers to try cover crops. We also fund universities and non-profit organizations to do research and education on cover crops,” says Dr. Myers.
The reason why Annie Dee started with cover crops was to get away from tillage and increase the fields’ organic matter. The Dee River Ranch has been a no-till farm for over 20 years. Dee, herself, was awarded the “National No-Till Innovator in the Crop Production Category” in 2017. “With cover crops, we also increased organic matter and thus the water holding capacity of the soil,” she adds. “Cover crops also increased the microbial activity and the cation-exchange-capacity (CEC) of the soil,” a measure of how many cations (positively-charged ions) can be retained on soil particle surfaces. A soil’s CEC influences its ability to hold onto essential nutrients – calcium, magnesium and potassium – and it provides a buffer against acidification.
Cover crops also offer farmers additional options in weed control, which mean they might have a growing role in the herbicide resistance management. “Research at the University of Illinois demonstrated that a uniform cover crop of cereal rye (seeded at 45 kilograms per hectare) before soybeans can provide 98 percent control of marestail, also known as horseweed,” says Chad Watts, Executive Director for the Conservation Technology Information Center (CTIC), located in West Lafayette, Indiana. The CTIC provides reliable information to support environmentally responsible and economically viable decision making in agriculture. “Cover crops take up space and sunlight, and therefore suppress the germination of weeds,” Watts continues. “Some of the cover crops also sequester chemicals to the soil, which inhibit the germination or even the growth of these grasses.
No sunlight without shadow
Many farmers, however, have reservations about cover crops. Above all, they see problems with their established farm crops. “The number one thing that keeps farmers from using cover crops is having enough time to plant them in the fall, because farmers are busy with harvesting their summer crops and getting the fields ready for the next year,” explains SARE’s Dr. Myers. However, he adds, there are solutions for this. “Farmers can put cover crops into the field before harvesting the previous crop – for example, by using a crop duster to fly the seeds over the field while the corn is still out there. They can do this maybe a month before the corn is harvested, and then the cover crops will start growing.” Annie Dee is also convinced of this technique. “We've had great success by flying over our fields to spread the cover-crop seed up to a month before harvesting both corn and soybean plants. This method gets the seeds below the crops, which helps give the seeds contact with the soil and gets them growing as soon as the cash crop is removed.”
The second biggest thing that holds back farmers is the cost of the seed, which is roughly 60 US dollars per hectare. One solution in the US is government programs that pay for the cost of the seed, to make the cultivation of cover crops attractive to the farmers. “These programs are not enough to pay for all the area of cover crops the farmers want to plant,” explains Dr. Myers. “It is enough, however, to help farmers getting started.”
The usage of cover crops in the USA is steadily increasing. From 2010 to 2018, the usage has risen about 15 percent per year.
Both getting started and staying with it are crucial. While Annie Dee now successfully uses cover crops, she did not succeed from the beginning. “At the start, we sowed the cover crops too densely. We learned that it’s easier if you take less seeds and get a lower density of plants. This makes it easier to terminate the cover crops when it’s time to remove them before the main crops are sown. You have to experiment at the location where you farm and find out what will work for you.”
The future of cover crops lies in the soil
Dr. Myers sees good prospects for cover crops in the future. “The big new focus in sustainable farming and cover crops is soil health and biology. Knowing about the microbes, the fungi and the earthworms needed for soil health leads many farmers to have more interest in using cover crops.”
Currently in the US, cover crops are cultivated on less than ten percent of the nation’s total agricultural area. But their use is increasing steadily, by about 15 percent per year in the last eight to nine years. “Right now, we have about eight million hectares of cover crops in the US, far more than we ever had before,” Dr. Myers says. And as the next generation of farmers begins taking over US farms – the average age of the US farmers is close to 60 – there is an understanding that new cultivation techniques are needed and desired, in order to farm sustainably. “The next generation of young farmers has to be trained and educated,” Dr. Myers notes. “This is a big issue, but it’s also a big chance. As they begin their farming careers, cover crops will certainly be part of their ongoing learning.”
Importance of cover crops in Europe
To receive funding from the so-called second pillar of the Common Agricultural Policy (CAP; a system of agricultural subsidies) of the EU, farms in Europe with more than 15 hectares of farmland have to generally designate 5 % of the arable land as ecological focus areas since 2015. Cover crops are one opportunity in order to comply with this provision. In Germany, for example, the proportion of cover crops out of all ecological measures was 68 % in 2015.
Sources: Deutscher Bauernverband; Zinngrebe et al. (2017): The EU’s ecological focus areas – How experts explain farmers’ choices, in Germany. Land Use Policy, Vol. 65, p. 93-108