NIPAWIN, Sask. – Growing a crop that won’t be harvested may seem alien to many prairie producers, but it is a necessity for an increasing number of organic farmers.
Green fallow or green manuring with the legume chickling vetch is one way to replace traditional nitrogen-fixing cover crops in organic production.
Clovers and alfalfa are good at fixing nitrogen and preventing soil erosion, but are hard to kill without herbicides.
AC Greenfix may be the answer. It is a chickling vetch, also known as grasspea or grassy pea vine, and was developed by Agriculture Canada’s research centre in Swift Current, Sask.
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The crop provides a heavy ground cover about 60 days after planting, which discourages weed growth, and performs well with little moisture.
With only 200 millimetres of rain, it will fix an average 75 pounds of nitrogen into most soils through its shallow-rooting system.
Clovers use more moisture and send down deeper roots, making them more invasive as a fallow rotation.
Eric Klassen of Johnson Seeds in Arborg, Man., has the Canadian rights to distribute the seed, which is registered as a green manure crop in Canada.
“It doesn’t have that big tap root going down deep and taking out subsoil moisture,” he said.
Indianhead black lentil, which is the only other registered green manure crop, produces less nitrogen and dry matter than the vetch. AC Greenfix also has greater resistance to drought and disease than clovers and Indianhead black lentil, according to a seven-year study at Swift Current.
Cereals grown on Greenfix stubble produced as good as on mechanically fallowed fields and yielded 59 percent better than those on cereal stubble.
Greenfix is tilled into the soil at between six and eight weeks of growth, leaving about 25 percent of the plant material on the surface to reduce erosion. Its short growing season allows for field moisture accumulation in August, a time when other cover crop legumes are still fixing nitrogen and growing.
“With good rains and sufficient phosphorus, the nitrogen fixed by AC Greenfix on wheat stubble has reached as high as 210 pounds per acre,” said Bix Biederbeck of Agriculture Canada.
“Indianhead lentils produced just 63 lb. per acre in the same tests. For organic growers working lighter soils, the crop has the potential of substantially increasing wheat yields while protecting against erosion.”
Greenfix, treated with a standard pea or lentil inoculant, is generally seeded at 70 to 80 lb. per acre along with phosphorus. With seed prices reported to be about 25 cents a pound, it will cost about $19 per acre to seed.
This is more expensive than traditional fertilizers, but it solves a problem for organic producers.
“For the organic grower there is no need to seed the crop in fall, like they might have to do with alfalfa,” Biederbeck said.
“That can be appealing.”
Klassen said he has had some interest from organic seed growers and feels there will be a market for organic sources of nitrogen that can control weeds with little loss of moisture.
