Cover crops take their place in mainstream agriculture

Sunday, March 4, 2012

As more and more farmers embrace the practice, appreciation is building for the sometimes surprising ability of these shoulder-season plantings to enhance the performance of cash crops

by MARY BAXTER

Last year, after Kim Lennox's daughter earned the Queen of the Furrow title at the Normanby Plowmen's Association's annual match in southern Grey County, she asked her dad a question: the only attraction at the plowing match was plowing. Had they ever thought of adding something else?

Lennox, an association director, put the question to the board. "We have this land available and we have a no-till drill, let's go ahead and try something." The board agreed and that something ended up being five demonstration plots of cover crops – buckwheat, oats, oats and tillage radish, winter rye, and an oat pea mixture – on the Brusso family Ayton farm that hosted the 2011 match.

"I think it worked out pretty good," says Adam Brusso, who farms with his father Ken at Ayton.

Slowly and steadily, cover crops are working their way into mainstream agriculture. Appreciation is building across North America for the sometimes surprising ability of these shoulder-season plantings to enhance the performance of cash crops.

One of their most enthusiastic proponents lives in the windswept ranch country of Montana. Jill Clapperton is a rhizosphere ecologist who once worked for the Agriculture and Agri-Food Canada research station in Lethbridge, Alta. She has lectured about soil health to farm groups and is the founder of Worm Watch, a soil ecosystem education program aimed at school children. Today, she runs a land resource consulting business.

Organic farmers often use cover crops to add nitrogen, but for a long time conventional farmers weren't interested, she says. Farmers questioned the sense in dedicating space to a crop that wasn't harvested and didn't earn them money. "Then, with some of the research, people started to understand that it wasn't just about growing nitrogen. There were these other effects."

Cover crops help prevent soil erosion and add organic matter to the soil. Scientists have also found that growing three to four species together kick-starts physical changes in the soil structure and its chemical properties after just a few months of growing. Other studies show that crops grown after a cover crop may experience increased test weight or yield and, on grain analysis, demonstrate a nutrient content increase.

For the scientific community the phenomenon is puzzling. "We haven't been able to explain it, but we have known about it for quite some time," Clapperton says, citing research as far back as 1901.

Clapperton suspects ecology's intermediate disturbance hypothesis is at work. It posits that a shock to an ecosystem helps maintain and perpetuate productivity. She uses the example of fire being used to rejuvenate crops. In the same way, cover crops, even if grown for a short period of time, give soil a complete change.

Another factor may be the interaction of plants. Every plant has a unique combination of chemicals it leaks to the ground through the roots by which it attracts a microbial community to protect itself, she explains. In native ecosystems, plants existed in communities. Each "did a job that benefitted the entire community." Moreover, certain plants always associated with each other. These benefited from each other but didn't compete.

In agriculture, however, monocultures are necessary to generate food volume, she says. So adding cover crops between commercial crops is a way to introduce the beneficial effect of a plant community. "It's about creating some kind of a mix or looking at adding something to the system that it doesn't have all the time, so all of these organisms waiting in the soil for this have a chance to grow up and multiply again."

It's the ultimate insurance, because now there are different organisms in the soil so, no matter what's grown, "they've got something to protect them; they've got the organisms in the soil that will benefit them."

Buckwheat for phosphorus
The practice is embraced around the world. In Brazil, farmers grow a cover crop right up to the time when they seed their commercial crop. The crops reduce pest pressure by interrupting the pests' natural cycles.

Identifying cover crops that will address the farm's needs is key. If tapping into more phosphorus is the desired result, Clapperton suggests buckwheat, which has deep roots and accumulates phosphorus. Oats and rye grass will accumulate available nitrogen so, if excess nitrogen is the challenge, then these crops will scavenge it and prevent it from leaching.

Using eight different plants to create the mixed cover seems to be the magic number to achieve the most boosts for the crop to follow, she says. But diversity comes with a price – about $30 to $40 for an acre of cover crops, she estimates – and it produces a messy-looking field which some farmers might find difficult to tolerate. And even though it's called a "crop," this is not one that can go to seed, she warns. Doing so might create a new weed problem.

Moreover, when plants go to seed, they draw nutrients from their roots into their above-ground biomass and seeds. "So we actually lose some of the benefits of the cover crop at that time."

Yet even a single cover crop will provide a benefit as long as it offers the cropping system a change from the commercial crop. For example, "if you're a cereal farmer, then put a broadleaf in," she advises. "Don't go putting a cereal in. Put something in that is actually going to benefit everything."

Tom Oegema, who grows corn, soybeans, winter wheat and edible beans near Talbotville in Elgin County, sticks to one cover crop at a time. "We've done them forever," he says.

He uses red clover to add nitrogen, organic matter and prevent erosion, seeding it into wheat as soon as the snow melts. He kills the clover with glyphosate in the fall, and then works it into the ground with a disc chisel.

"The disc chisel does a great job of rooting up the red clover . . . and it mixes it with the soil, so the decomposition can begin. It leaves enough clover residue on so that it's not like bare soil," he says. A corn crop follows in the spring and, when it's time to side-dress, he assigns a nitrogen credit to where the red clover was located.

One year, Oegema had problems killing the clover. He was advised to use the herbicide dicamba. "It's not cheap and you have to be careful with how much you use in terms of residue for growing corn or whatever other crop you might want to grow there," he says. Now, as a precaution, he uses a slightly higher rate of glyphosate and is satisfied with the results.

Each year, Oegema spreads turkey manure on about 100 acres. Because of its powerful odour, the manure is plowed under with a roll-over moldboard plow and then seeded with oilseed radish (it's the only time in the farm operation that the moldboard is used). The work takes place on a harvested wheat field in the second half of August and he uses a grass seed box mounted on a rotating harrow to seed.

Oilseed radish needs lots of nitrogen to thrive and is also supposed to be a nematicide, he says. It boasts a substantial taproot which creates drainage, aeration holes and worm holes. Deep winter cold will kill it, so there's no problem with competing growth in the spring. There's not a lot of lignin in the plant's walls. Once frozen, it ruptures and degrades quickly, leaving enough cover to prevent soil erosion in winter but little residue by spring.

"You could plant directly into it in the spring if you wanted to, but usually we had to come in with a burn-down to get any weeds that had escaped," Oegema says. But be warned: when the radish plant first ruptures, it releases a pungent odour for about a day.

Up until last year, Oegema grew a variety of oilseed radish that had a lot of top growth, but not big taproots. Now, he uses tillage radish, which is about twice as expensive. "It concentrates its growth into the roots and tubers, so you have huge turnip-like roots, deep tap roots. There is still top growth, but not nearly as much as with the other variety and it does not flower as readily."

Provincial crop specialists tell him radishes lose a lot of nitrogen in the winter. "I think they're right," he says. He gives some nitrogen credit to radish and manure in the next year's corn crop, but not as much as he would to a spring application of nitrogen.

Cover crops for 30 years
At the other end of the cover crop diversity scale is father and son farming duo Eric and Max Kaiser.

The Kaisers grow corn, winter wheat and soybeans on the north shore of Hay Bay on the Bay of Quinte near Napanee. They had used cover crops, primarily volunteer wheat, for 30 years. Then Eric Kaiser, long involved with the Innovative Farmers Association of Ontario, heard Clapperton speak at the organization's annual conference. He also visited the farm of Pennsylvania farmer Steve Groff, another well-known proponent of cover crops and who markets tillage radish. "We started putting more emphasis on what was in the cover crop," he says.

The family also has an egg layer operation and is located next to a cottage development. Given the farm's heavy clay soil, as well as its proximity to residential development and water, August is the safest time of year for spreading liquid poultry manure. They incorporate the manure into the ground after wheat harvest and then broadcast the cover crop seed using a fertilizer spreader at a rate of 110 pounds per acre.

Next, Kaiser uses a cultivator and packer to mix and pack the seeds into the surface. In the mixture could be oats, barley, peas, tillage radish and sunflowers. "Any left-over corn seed we have from planting plots we throw in and the same with soybeans," he says. There will be winter wheat too, blown out the back of the combine.

Around Oct. 20 they spray with glyphosate. "Then that brown mat stays there over the winter and we plant corn into it in the spring."

The approach is always evolving and has been tied to the family's shift away from tillage (they switched to total no-till in 2001). Early on, they realized that allowing green material to persist into spring wasn't an option. "The clay stays wet and sticky and you end up slotting," says Kaiser. (Slotting refers to the seed trench not closing properly.) "It's also a great place for cutworm moths to land – they like that green stuff," he adds.

The Kaisers switched to tillage radish from oilseed radish after finding that the latter damaged some of their tiles. Buckwheat was eliminated because it goes to seed too quickly. They also planted cover crops into standing corn without success. Now, Kaiser is considering adding phacelia, a fern-like crop used extensively in Europe, to the mix.   

One of the cover crop's key roles is to preserve nitrogen from the chicken manure for the spring's corn crop. The crop reduces the need for other inputs and helps prevent the escape of other nutrients into the broader environment.

The Kaisers apply phosphorus once every three years. Other than that, they use nitrogen and a small amount of liquid starter on wheat and corn. "We tend to stay fairly stable on our soil tests," Kaiser says. A problem with quack grass experienced early on is non-existent today.  
Bumper crops possible

Research done in the 1960s and 1970s on plant properties and how they can influence one another reveals that, if you get the combination right, you can produce bumper crops, says Clapperton. She acknowledges that, with the advances of technology in today's growing fields, this effect might not be as pronounced as it once was. But it still exists.   

And studies also show that growing some plants all the time may prove even more beneficial. Corn shares the same mycorrhiza as some clovers and legumes. If the mycorrhiza, a symbiotic relationship between soil fungi and plants, is present all the time, the corn will benefit and not require as much phosphorus.

Clapperton refers to one recent study where corn was planted next to a living crop of lentils, vetch and peas. The corn had more copper, zinc and micronutrients than corn where the cover crop was killed earlier. "We're slowly starting to understand more and the literature is starting to support the use of that," she says.

But providing farmers with prescriptions similar to those for fertilizers is still in the distant future, Clapperton says. "Our goal is to be able to say: ‘Well, you live in this area, so here are the plants you can choose from, here are what these plants will do for you and here are what these plants' properties are.' Then you could pick plants that would actually work for you." BF

SIDEBARS:

Integrating cover crops with livestock
Kim Lennox, who farms in Grey County near Ayton, first planted cover crops about six years ago as a way to control weeds on a rented acreage whose owner forbade the use of pesticides. Now, he's also using them to extend the grazing season for his sheep flock and beef herd. He plants winter rye after corn and allows the animals to graze on it in early spring before either burning it down or plowing it under with a moldboard plow to prepare for another crop.
"The one problem with grazing, say, winter rye in the spring is that, if it's a wet spring like this past one, those animals will create compaction and then it will be more difficult to no-till into it," he says.
Lennox is a member of the Normanby Plowmen's Association, which last year planted five demonstration plots of cover crops on their plowing match site – buckwheat, oats, oats and tillage radish, winter rye, and an oat pea mixture. The area experienced quite dry weather conditions in late summer and, after one month of growth, the buckwheat had the best response, while tillage radish struggled with flea beetle infestations. BF

When choosing cover crops, grow something that you can manage
Jill Clapperton, a rhizosphere ecologist based in Montana, says clover cover crops have some drawbacks. A cover crop is often grown to add nitrogen to the soil, but it is challenging to get going and takes a while to produce nitrogen.

It's the same with legumes, Clapperton adds, explaining that the plants have to be close to flowering to produce enough nitrogen for it to be worthwhile. Moreover, many farmers don't want clover in the corn, which means it should be grown for only a short time. If nitrogen is the goal, she suggests winter peas or even fava beans planted as an early spring crop.

If you're considering seeding into a cover crop, why not consider lentils? University of Guelph studies have shown that spacing of corn is important, because corn plants don't like to touch other corn plants during germination and don't like touching some weeds. But they seem to tolerate legumes like lentils, Clapperton says. She warns, however, that these may carry some of the diseases that affect soybeans.

Lentils are low-growing, not competitive and can be seeded a lot earlier than corn. Researchers tried peas, but these bent the corn and were too aggressive, she says.

There's no right answer for what you choose to put in your cover crop or how you add it to your cropping schedule. But if there's any question of being able to get to them in time to kill them off, Clapperton advises choosing something low-growing that's not going to be overly competitive with your commercial crop. A lot of people use annual rye grass, she notes. "That's really competitive and, if you don't kill it, you're going to have a problem."

If you don't want the hassle and can't be right on top of the crop, then don't grow something like that, she says. "Grow something that you know you can probably manage or grow something for the winter that's going to kill itself. That's the beauty of living in a northern climate." BF

The nitrogen calculator: a handy way to measure the value of a clover crop plowdown
by DON STONEMAN

The solar array and the red clover crop on Dave Start's farm south of Woodstock have something in common. Both provide measurable amounts of energy to his farm.

A chemical reaction in the solar panels converts the sun's energy to electricity, which flows to the power grid. Another chemical reaction, photosynthesis, uses the sun's energy to fix nitrogen from the atmosphere in the soil at the clover roots. Start sprays and tills the clover in the fall, his payback coming in greatly reduced nitrogen costs for the following year's corn crop. A meter measures the electricity that is going to the grid from Start's panel and his local utility pays him for it. However, measuring the value of the nitrogen from red clover is more complicated.

Start estimates the value of that nitrogen by using the Ontario Corn Nitrogen Calculator.

According to the nitrogen calculator, a clover crop plowdown is worth 73 pounds of nitrogen per acre, according to Greg Stewart, corn specialist with the Ontario Ministry of Agriculture, Food and Rural Affairs. That is "not quite double, but almost" the 40 pounds of N credited to a plowdown in the 1980s, Start says.

Start says many farmers give little credit, if any, to the nitrogen produced by a green manure plowdown and Stewart agrees. In an average meeting of growers, he figures "maybe 25 per cent" of the growers are familiar with the nitrogen calculator tool. Probably even fewer farmers actually use it and follow its recommendations, and they spend more on nitrogen than they need.

Start grows 850 acres of crops, split nearly equally into soy and edible beans, wheat and corn. Corn is planted on the acres that grew wheat the previous year. Red clover is frost-seeded into the wheat in March. Start sprays with a burndown in the fall and usually conservation tills the field, either in the fall or in the spring, depending upon the soil.

Start is as concerned about nitrogen leaching as he is about economics. He grows crops on the Thornton well field, owned by Oxford County near the village of Sweaburg. The well field is the source of drinking water for the nearby city of Woodstock and nitrate levels in the aquifer is a particular concern.

Farmers need to be thinking about nitrate levels in their soil if they are applying larger amounts of nitrogen than crops are removing. "I think the data is pretty clear that, over time, you are going to build excessive soil nitrate levels. When you do that, it becomes a risk for the aquifer below," Start says.

A two-year project in 2009 and 2010 at the well fields revealed that a corn crop following red clover and receiving 45 per cent less nitrogen, as indicated by the Ontario Corn Nitrogen Calculator, had similar yields to plots with full nitrogen applications and no cover crop.

Part of Start's strategy for managing soil nitrate levels is to side-dress an application later in the season, when the crop is able to use it.

Technicians from Agri-Food Laboratories soil-test Start's corn at the five-leaf stage and he aims to apply the appropriate amount of Urea Ammonium Nitrate (UAN) at the six-leaf stage. Start says the turnaround time for the test is two or three days at most. "We are ready to apply when we get that testing done," he says. But he admits that there is a weather risk to side-dressing. If there is a torrential rain and you can't get on the field for a week, "you are really running to catch up," he says.

Putting on overly high rates of nitrogen is "a very poor way of ensuring high corn yields from an economic point of view," Start believes. Focusing on early planting, good herbicide programs, good hybrid selection, and proper starter fertilizer and micronutrients are better ways of spending the dollars budgeted for inputs.

Start thinks farmers are going to be considering their nitrogen applications more in the future. "The economics will help," he says, with nitrogen following oil prices upwards. For now, at least, the economics of high-priced corn dictate that farmers aren't going to risk a 15-bushel-per-acre yield drop and reduce their nitrogen applications.

For farmers unwilling to commit to the nitrogen calculator tool, "the best thing they can do is to put in a zero nitrogen strip," Start says. The strip can be as simple as one pass of the planter down the field, with no more nitrogen applied to the strip than is in the planter.

Start's farm is largely Huron silt loam with the odd sandy or clay knolls. He seeds red clover onto frozen ground and some snow in March, using a tractor with a three-point hitch seed applicator. Start isn't worried about spreading clover on snow. The seed won't wash away unless a torrential rain and snow melt also moves a lot of soil.

In most years, Start sprays the red clover in late fall and follows with conservation tillage in December or the following spring, depending upon the soil type.

Last December, Start used a mouldboard plow because he couldn't get his herbicide on in the fall. It was wet and windy. "We've got to kill the clover," he stresses.

He says that soil sampling last June, following a wet May, showed that the red clover plowdown from the previous fall still hadn't broken down to the point where the nitrogen could be available to the plant, or leached away for that matter. That's not what happens in some production systems, where farmers have to reapply their nitrogen after it is leached away, he says. BF