Organic practices show promise for conventional systems
Cutting down on purchased inputs may be appealing, but research-based recommendations
for organic or low input farming practices are lacking.
November 22, 2007 By Helen McMenamin
Organic and low input practices are gathering interest with growers because of low commodity prices. However, researchers are just starting to unravel what works and what does not, based on long-term rotation studies. Cover crops such as sweet clover offer low cost benefits over conventional fallow – better soil health, weed suppression and residual nitrogen. And diverse cropping systems support diverse soil biology, which can be a benefit in
low input systems.
A study at Agriculture and Agri-Food Canada’s Lethbridge research centre is looking into the feasibility and potential benefits of these systems.
Nine years into the study, scientists are seeing some patterns, but they caution that the first phase of the study, three full rotations (12 years), is not yet complete.
The researchers have set up replicated plots of three basic rotations, withfallow in alternate years, once in four years or no fallow with organic and conventional versions. They also have continuous wheat as a baseline treatment. The organic rotations include cover crops rather
The conventionally grown crops receive about 50lb/ac nitrogen. Each phase of every rotation is grown every year to ensure weather patterns do not mask the impact of a particular rotation. Unsuccessful treatments are kept in the study for four years so all plots in that rotation suffer equally.
Soil ecologist, Jill Clapperton is enthusiastic about the benefits of cover crops as a replacement for fallow. “Nature keeps soil covered all the time,” she says. “Cover is vital for soil health. We’ve been able to manage cover crops to fit available moisture, so we haven’t sacrificed yield.”
Clapperton explains that the researchers have seen big differences in soil quality among the rotations. The more diverse rotations, the more diversity there is under the ground. More diverse soil biology can reduce the impact of soil pathogens because most species are beneficial.
The number of species of bacteria, fungi, insects and other small animals living in healthy soil is so large that researchers cannot count them all. Instead, they assess microbial communities chemically, or use indicator species like earthworms or nematodes.
“Most nematodes are good,” says Clapperton. “They graze on bacteria and fungi and, as they digest them, they recycle N back into the soil for plants to use. Nematodes are responsible for 34 percent of nitrogen cycling in the soil. And, because they move in water films, they are usually close to plant roots where they can be particularly useful.”
Sweet clover has been the best cover crop for the dry conditions at Lethbridge. It is underseeded in wheat or linola, and hayed or plowed down the following year. Berseem clover and red clover did not establish or grow well at Lethbridge, although these and
other annual clovers have been effective cover crops for suppressing weeds in the Parkland.
“Growing sweet clover is an organic farming practice that could fit in any system with fallow,” says weed scientist, Bob Blackshaw. “It grows well, even in a dry year. While it’s growing and for up to six weeks after it’s mowed, it has an allelopathic effect on weeds, producing a chemical that prevents weeds from growing. The effect carries over to the following spring when we have fewer weeds because the plots were so clean the previous year.”
In the organic rotations without herbicides, perennial weeds, especially Canada thistle, have become a problem. Growing sweet clover in alternate years eliminates them almost entirely.
For farmers, sweet clover weevil is rarely a problem because the insects are very weak fliers, except when it is grown on adjacent fields in successive years. In the closely spaced research plots, the insect has reduced sweet clover hay yields.
Even so, the cover crop has left 30 to 85 pounds N per acre, according to soil tests, which show only 30 to 50 percent of the N that is accessible to the following crop.
“That amount of N is adequate for our wheat-sweet clover rotation,” says Blackshaw. “We see signs of N deficiency with sweet clover once in four years, even though we apply compost and grow pea-barley silage as well. Although cereal-pea silage mixtures have been dependable producers with low inputs, silage harvest seems to be too early for the pea nodules to fix very much N.
We’ve switched to Austrian winter pea to lengthen the period of N fixation.”
Blackshaw describes their efforts at no-till organic cropping as a miserable failure. Clapperton sees reasonable yields from two years of direct seeded crops as an indication the practice has potential. At the end of that rotation cycle, the researchers switched to using as little tillage as possible. That means tilling before seeding and sometimes, in the organic rotations, using a rotary harrow for weed control.
Fall tillage is used only when justified by pressure from perennial weeds and when there is plenty of straw. Clapperton likes to avoid fall tillage because it is hard on earthworms and other soil fauna.
The inclusion of linola has been the economic salvation of the organic rotations, according to Blackshaw. Premiums for organic wheat, peas and barley are too small to compensate for lower returns from lower fertility and greater weed pressure in organic systems. “We don’t consider things that don’t work a problem,” says Blackshaw. “Finding what doesn’t work is as important as finding what does work. We can take the risk so farmers can avoid it. Some things show up relatively early, others take longer. For example, we’re just starting to see a build-up of root rot in our continuous wheat plots.”
Blackshaw explains that, for the most part, rotation studies are a long-term effort that do not offer quick answers. Their real value often comes years later, after almost everyone has lost interest in them. “They’re really a legacy we’re building for future generations.”