Cover crops are a hot topic in agricultural circles. Ironically, interest isn’t due to a major research breakthrough, nor does it stem from cover crops being new on the scene. (They’ve been grown for generations.) Instead, many attribute the heightened curiosity to a soil health message that’s resonating with the right crowd. Dean Baas, a senior research associate with Michigan State University (MSU) Extension, conducts cover crop and organic agriculture research and education. As a member of the Midwest Cover Crops Council (MCCC) executive committee, Baas advocates for cover crop usage among farmers. Recently he has noticed a substantial change in perception.
“As little as two years ago, if you asked a group of farmers what’s the primary benefit from growing a cover crop, a large majority would have said to prevent erosion and keep the soil in place. Now, with recent surveys, they’re saying it’s to improve soil health,” he said. “To have soil health beating out soil erosion indicates to me that there is definite interest in improving soils, and it’s high on farmers’ minds.”
Some of the shift is the result of educational campaigns, including the United States Department of Agriculture (USDA) Natural Resources Conservation Service’s “The Science of Soil Health.” Started in fall 2013, it encourages landowners to talk with farmers about how they are working to build sustainable soil and productive land. The campaign discusses soil health management practices including diverse rotations, no-till and cover crops.
Planted to provide a protective green blanket when land is normally barren or lifeless, cover crops help create a year-round habitat providing food and shelter for wildlife as well as beneficial organisms in the ground. Cover crops help retain the nutrients from the previous crop and pass them on to the next. They also take in carbon dioxide from the atmosphere and release clean oxygen in exchange.
MSU researchers and Extension educators, like many across the nation, report a rise in requests to speak about the benefits and use of cover crops, largely from growers, commodity organizations, agri-businesses and seed companies. MSU nematologist George Bird, who conducts research in integrated pest management and soil biology, has been studying cover crops since 1968. In the past 18 months, he has received 30 invitations to speak about soil health, a topic that invariably leads to cover crops.
“Cover crops and soil health are the two hottest topics in the north central region in 2015, unless someone wants to throw in colony collapse,” Bird said. “Ten years ago, there were very few seed companies interested in cover crops. Today, there are dozens, plus many more in the works. It can even be diffcult to get the varieties you want. You may have to find a company halfway across the country to do that.”
In addition to various speaking engagements, Bird has organized a 2015 Short Course for Agribusiness that focuses on cover crops and soil health. It is ideal timing — the United Nations declared 2015 “The International Year of Soils.” A project funded by the Environmental Protection Agency from 2010 to 2013, the Great Lakes Cover Crop Initiative, is adding to interest as well. With the catchy slogan “Keeping it green keeps the water clean,” the initiative demonstrated the effectiveness of cover crops and conservation tillage systems to decrease agricultural nonpoint source pollution.
It also informs producers in the Lake Michigan, Lake Erie and Lake Huron watersheds about implementation of cover crops and conservation tillage systems on nearly 37,000 acres. Baas was co-principal investigator on the project, and MSU Extension educators Paul Gross and Christina Curell contributed significantly. The Conservation Technology Information Center’s (CTIC) $1.07 million project, which includes three Michigan farmers, is also garnering attention. It is aimed at examining the economic, agronomic and environmental benefits of cover crops. The ultimate goal is to help the United States reach 20 million acres of cover crops by 2020, an increase of 17 million acres.
Despite considerable publicity, incorporation of cover crops into agricultural systems is nowhere near the norm. The National Agricultural Statistics Service recently started collecting survey data on cover crops. In Michigan, the report revealed that cover crops accounted for 6.5 percent of farmland in the 2012 growing season — fifth in the nation.
“At the end of the day, cover crop use is still at a very low percentage,” Baas said. “It is nowhere close to being a common farming practice in Michigan. Word is getting out, the message is being heard and you see pockets of people incorporating them into their systems. But there is still a long road ahead.”
Research delves into soil health
Researchers are focusing on ways to use cover crops to bring diversity to the crop system, to reduce reliance on fertilizers, herbicides and pesticides, and to determine the impact of cover crops on overall farm economics. Some of the work is funded by commodity groups to benefit their respective grower members. But cover crops do not have a formal organization advocating on behalf of their usage, a factor that Baas said plays into the lack of adoption and research funding.
MSU researchers, however, are studying the impact of cover crop use on everything from row crops to orchards and carrots to Christmas trees. Field trials are also taking place at MSU AgBioResearch research centers from Traverse City to Frankenmuth and south to Benton Harbor. Alexandra “Sasha” Kravchenko, professor in the MSU Department of Plant, Soil and Microbial Sciences (PSMS), received both her undergraduate and doctoral degrees in soil science.
In addition to soil fertility studies, Kravchenko is looking at ways that cover crops can help mitigate climate variability as part of a large-scale project, Climate and Corn-based Cropping Systems Coordinated Agricultural Project (CSCAP), funded by the USDA.
“To me, there seems to be the beginning of a comeback occurring in soil research,” she said. “We came to the realization that while what we do know about soils might be good enough for business as usual, it’s not enough to anticipate future impacts of variable climate.”
CSCAP encompasses 140 researchers at 10 Midwestern universities, including fellow MSU researchers Bruno Basso from the Department of Geological Sciences and Andrey Guber from the Department of PSMS who work on modeling; Martin Chilvers from the Department of PSMS working on the integrated pest management portion; and Marilyn Thelen from MSU Extension on the outreach component.
The group is focused on understanding the mechanisms by which cover crops increase soil carbon sequestration, how they impact greenhouse gas emissions and how they influence corn yields and soil nitrates. Kravchenko is conducting trials at two experimental sites, one in Mason and the other at Kellogg Biological Station. Each has diverse topography in order to examine cover crop performance and effects in a real-life terrain, such as topographically variable landscapes that Michigan farmers face. This past spring researchers began collecting soil samples from the experimental fields and will begin comparing it to data from 2011 when the project started.
“We’re seeing some positive changes in soil organic matter when cover crops are used,” she said. “But we’re not quite there yet. Cover crops are a tool but they don’t work overnight. It takes several years to produce the noticeable, beneficial effects.”
CSCAP goals are to safeguard crop production’s most basic components — fertile soil and fresh water — maintain crop yields, reduce emissions of atmospheric greenhouse gases that are responsible for climate change, and to train a new generation of scientists. Like Kravchenko, Baas and Bird agree that continued cover crop research is needed. They are collectively thankful that the soil health message has not fallen on deaf ears.
“We, as researchers, have spent much of the recent past justifying the use of cover crops and quantifying the benefits,” Baas said. “So much so that I believe, to a certain extent, that this message has been beaten to death. I no longer run into farmers at meetings who say, ‘But why should I plant a cover crop?’ Now they say, ‘I see the benefits. Now, help me make them work in my production system.’”
No one-size-fits-all solution
A poll of Midwest farmers conducted by the CTIC reveals that one major barrier to cover crop adoption is cost. There is a strong perception among farmers that cover crop seed is expensive. A large majority — 71 percent — seeded their cover crops at an average cost of $12 per acre. Seed cost is substantially higher — $25 per acre — in the Midwest. Other challenges cited included time to plant and manage cover crops, terminating the crops and selecting the right varieties. Some also complained of problems with slugs.
The most desired benefits cited were increased soil organic matter, reduced soil erosion, reduced soil compaction, weed control and a natural nitrogen source. Bird, who started work on cover crops as a graduate student at Cornell University, said he informs farmers of three basic principles he calls “Bird’s three laws of cover cropping”:
Decide on your objective.
Select the proper cultivar.
Manage the cover crop, with particular emphasis on timing and objective.
“You must know that alfalfa is not just alfalfa. Clover is just not clover. Potatoes are not just potatoes,” he said. “There are varieties within each, and they all have different genetic attributes. For instance, oil-seed radish has been bred by Germans as trap crops for sugar beet cyst nematode control. For the past decade or so, Michigan sugar beet growers have been using three specific varieties of oil seed radish as an integral part of soil management. But if you use any other variety, you end up making the entire system worse.”
An added layer of complexity is that what works for one farmer doesn’t necessarily work for another, not even the neighbor next door. In his studies, Bird has found that some cover crops have shown potential to be conducive to beneficial organisms; others damage them. Some can be highly attractive to beneficial organisms; others attractive to pests. He cautions that each agronomic cover crop variety needs to be evaluated under local conditions by one or more highly respected growers with a significant interest in soil health.
“There is not a one-size-fits-all answer,” Baas adds. “But what I point out is that nearby farmers do not necessarily do the same thing to their cash crops. Some fall till, others spring till. There are good years and bad years. Some people say they tried cover crops but quit because they failed miserably. I remind them that this happens with cash crops, but they don’t stop growing them.”
The researchers agree there is a fairly steep learning curve. Although not all are successful the first few years, Baas said most growers eventually get the hang of it. Having curiosity, tenacity and the ability to learn from mistakes is of utmost importance. On average, it takes three to five years of cover crop use before a farmer begins to see benefits such as increased yield. It also requires added time and labor to plant the crops after harvest, a time when most farmers are in need of a break.
“I remember a survey response years ago that said, ‘So what do you want me to do — finish harvesting my crops or plant cover crops?’ That’s a real battle,” Baas said. “A lot of people plant cover crops after harvest. Then you have a year like last year when they’re harvesting in November. So there is the time management part of the equation, too.”
In general, the researchers say that the farmers finding the most success with cover crops incorporate them into their production plans without stopping to question if they’re going to or not.
A reemerging industry of sorts
Cover crops were used several generations ago to manage nutrients in the soil at a time when chemical pesticides and fertilizers were nonexistent. Farmers used cover crops to control weeds, provide nitrogen and keep the soil in place. They also grew them for forage when farms were more diversified, growing both plants and animals. But as technology advanced, cover crops eventually phased out of many farming systems. Now with interest in soil health and soil productivity surging, perceptions of cover crops are changing.
One of the major differences is transitioning from thinking of something that was once a cash crop in its own right to growing it for purposes other than immediate economic gain. Baas said cover crop breeding is a research area that he believes could be very helpful moving forward.
“The majority of cover crops were never bred or developed as cover crops,” he said. “There are many reasons why you breed a crop — high yields, low lodging and short stock, for example. For cover crops, you want a lot of biomass, an early-maturing variety and shade tolerance. If we could do some breeding, we could probably get some better cover crops.”
After searching for decades, Bird has found that some varieties of a cover crop called pearl millet help deter the most prevalent root lesion nematode (Pratylenchus penetrans) in Michigan. The nematode invades a variety of hosts, including fruit, vegetable and field crops. Bird and his colleagues are also looking at a cover crop called dwarf essex rape to help ward off a tree fruit disease that is particularly devastating to cherries and apples. He says cover crops are gaining popularity because they are a natural way to control insects and diseases, an alternative to using synthetic chemical pesticides and fungicides.
“Today some of the most progressive farmers I know are going one step further beyond soil health and trying to figure out how to develop a bio-based agriculture,” Bird said. “They’re going to let the biology and the soil provide the things needed for our crops. And so when you go into a system with something designed to kill, you’re going to have all kinds of unexpected consequences.”
Bird said finding a cover crop that is a trap for soybean cyst nematode, the No. 1 limiting factor of soybean production in the United States, would be a major cover crop discovery. But he said he knows of only two scientists in the world — one in Germany and the other in Denmark — breeding cover crops specifically for nematode control. While farmers await more research news, researchers are anticipating this summer’s release of results from an online national cover crop survey, sponsored by the USDA Sustainable Agriculture Research and Education program, the American Seed Trade Association and Corn+Soybean Digest. The information will provide further information on cover crop usage and research needs.
All farmers — whether they use cover crops or not — were invited for the third consecutive year to share their thoughts on this increasingly popular management practice. Baas, Bird and Kravchenko agree that more work needs to be done to help advise farmers, especially those in regions such as Michigan, where soils can vary tremendously even across short distances.
“Within Michigan, because of its glacial history, soils can vary substantially even in a small space,” Kravchenko said. “Whether the soil is stony, sandy or heavy clay, it plays a big role in determining how beneficial or how feasible to manage the cover crops will be. This is a big component of this puzzle we’re trying to figure out.”
More from 2015: International Year of Soils
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