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The Role Of Cover Crops In Healthy Soil

Want healthier soil, higher yields and lower input costs? Then take a page from Mother Nature’s playbook.

That was the message from the recent Cover Crop Field Day in Bangor, Saskatchewan, organized by the Parkland Holistic Management club.

The highlight of the tour was the farm of Garry Richards who, after taking a holistic management course, changed his pasture management practices and doubled the productivity of his grassland over the past five years. That got him interested in cover crops; he grew his first one on 80 acres in 2009.

“It’s mixing different plants to mimic nature in their diversity,” said Richards. “Each plant has a specific job to help the soil. With a cover crop, half of it is harvested by the livestock and the rest goes back to the soil.”

MIXED BAG

The list of cover crop benefits is almost as long as Richards’ cover crop seed mix, which in 2009 was purple top turnip, oilseed radish, crown millet, Siberian millet, sunflower, taproot, alfalfa, soybeans, sorghum Sudan grass, yellow sweet clover, Berseem clover, yellow peas, and oats.

But Richards’ main focus is improving his bottom line by boosting the organic matter and nutrient levels in his soil, improving its structure, and encouraging beneficial organisms in order to lower input costs and increase yields. He applied normal amounts of fertilizer on the barley this year but expects he will eventually boost fertility levels to the point he won’t need any – although he estimates that could take five or more years.

“The first few years are an investment in your land. Later on, we hope to see a return on that investment,” he said. “I think once we get a better idea of our seed blend, we will achieve what we hope without inputs except for a glyphosate burnoff in the spring.”

The exceptionally wet year also meant he had to use fungicide, although he said the barley grown on the 80 acres appeared to have a lower level of disease.

The crop hadn’t been combined at the time of the tour so Richards didn’t have this year’s yield numbers, but soil expert Dr. Jill Clapperton said cover crops are a definite money-maker.

“Once we get the mixtures right it will start paying for itself in less than three years,” said Clapperton, who was the guest speaker at the field day.

So how do cover crops work? Once again, the list is long.

SOIL’S NATURE

It starts with the nature of soil itself. Although soil is partly bits of weathered rock and minerals, it’s largely plant material transformed by roots and microbial activity. While they grow, plants and microbes create a mutually beneficial environment – a process scientists call metabiosis.

A former AAFC researcher and now a private consultant, Clapperton knows a lot about these relationships.

“Roots modify soil structure and are the connection between the plants, soils and organisms; all are interconnected,” Clapperton told the 100 farmers at the field day.

Roots, she said, don’t just extract nutrients from the soil that the plant needs to grow, but also perform other functions, such as protecting the plant from diseases or pests.

“In corn, for example, when insects start to eat the roots, the corn sends out signals through the soil to attract nematodes to parasitize the insect larvae,” says Clapperton, owner of Earth Spirit Land Resource Consulting in Florence, Montana.

“Plants have very effective ways to protect themselves.”

TEXTURE BUILDERS

Then you have bacteria, which help to hold soil particles together, and fungi, which break down the woody residues of plants and help give soil its crumbly texture.

“Bacteria and fungi are the principle agents in decomposition, and they make the nutrients available from organic matter and begin the nutrient cycling process,” she noted.

Next come protozoa, voracious eaters of bacteria and fungi that recycle 18 per cent to 20 per cent of the nitrogen in these organisms, increasing nitrogen content in the soil by up to 45 per cent.

Nematodes, which many think of as a problem, are actually beneficial in soil and very important as they eat bacteria, fungi and insect larvae that could result in disease, she said.

BENEFICIAL INSECTS

There is also a host of beneficial insects above the soil, such as mites, spiders and beetles (which are effective predators of pests), and below it, such as night crawlers and earthworms. The latter, which can live in healthy soil for up to 10 years, have a major fan in Clapperton.

“Earthworms are the ecosystem engineers,’” she said. “They modify soil habitat and drainage capacity dramatically, and pull organic matter from the surface and bury it.”

Given all these factors, the reason for the wide range of plants in a cover crop become obvious – putting more items in the mix ups the level of beneficial activity. For example, adding turnips and radishes helps to aerate soil and releases compounds that aid in the decomposition of the fibrous plant residues.

The stumbling point is the cost. Richards forked out a hefty $27 an acre to seed his cover crop in 2009.

He continues to tweak the cover crops he is growing. This year, he added Cicer milk vetch, winter triticale and forage rape, and eventually hopes to bring the cost of seed down to around $20 an acre. The vetch has proven to be a great nitrogen fixer and also helps reduce bloating, but he felt that the oat content in the mix was too high. Clapperton recommends that oats, while an important element in the cover crop for forage, should not exceed more than 30 per cent of the mix.

REDUCED INPUTS

The final goal of a cover crop or any other type of holistic management system should be to eliminate inputs, said Clapperton.

“We change the dynamics when we fertilize and also the way we release nutrients, so we try to simplify a truly dynamic system and we just need to accept that it works.”

Among the participants checking out the “before and after” grazing effects on Richards’ fields and examining his soil were Manitoba producers from the South West Grazing Club near Shoal Lake, who attended thanks to assistance from the Agri- Extension Environment Program. MAFRI, in co-operation with Ducks Unlimited Canada and the Manitoba Forage Council, provides funding through the program to encourage the adoption of environmentally sustainable agricultural practices.

The Manitoba Zero Tillage Research Association has also been conducting cover crop experiments – they call it poly-cropping – using a similar seed mix to Richards.

Manitoba’s 31 grazing clubs are already at the forefront of innovative pasture management techniques, including rotational grazing, forage establishment and remote watering systems, said Michael Thiele, co-ordinator of the South West Grazing Club.

While ideally suited for mixed farming operations, grain producers can also employ cover crops if there is an opportunity to bring livestock from neighbouring farms onto their fields.

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“Soil health dictates how the ecosystem functions, which in turn affects what services the soil provides.”

– SOIL MICROBIOLOGIST, DR. JILL CLAPPERTON

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