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Organic Agriculture Centre of Canada聽

Organic farmers and researchers are seeking methods of reducing tillage. Negative effects of tillage are well known: making soil more prone to erosion, killing soil organisms, and the cost in fuel and time.聽 However, tillage is important in reducing weed populations, improving nutrient cycling, burying residues and terminating green manures. Finding ways to retain these benefits, while reducing tillage is a challenge for organic research.

Although many no-till and reduced till techniques are effective on organic farms, many people feel that tillage is still required to terminate and incorporate a green manure crop. Finding alternatives to incorporation, and finding ways to reduce the amount of tillage needed to terminate a green manure will move organic farmers closer to organic no-till. Several techniques are being tried.

Wide blade cultivator
The idea of using a wide blade cultivator to undercut weeds and leave the soil surface largely undisturbed is not new. Charles Sherwood Noble, an Alberta farmer introduced this concept in the 1930鈥檚 to promote soil conservation. In semiarid regions, the Noble blade has been as good as zero till at retaining soil organic carbon that was lost using more intensive cultivation methods. The blade cultivator left up to 85% of crop residues on the soil surface and effectively controlled annual weeds.

Blade roller
The blade roller rolls over the green manure crop, crimping it with the blades. The crop remains attached to the soil, but dries out and dies, leaving a mulch cover. This technology has been used in Latin America for reduced tillage, and has been promoted widely by the Rodale Institute.

Initial tests at Carman, MB have had mixed results. Use of the roller to terminate an oat-pea green manure was very successful.聽 When rolled in late July, most of the plants were killed. They provided a nice cover that was still providing benefits 12 months later.聽聽

The downside was that some of the nitrogen benefits of the green manure were lost. More of the nitrogen (roughly 5-10%) was lost to the air when the crop was rolled, rather than tilled. There was also less nitrogen available to the following wheat crop, which subsequently yielded less when the green manure was rolled than when it had been tilled.

In Saskatoon, terminating with the blade roller resulted in less weed re-growth and in less green manure re-growth than either mowing or tillage.聽 In one year, wheat yields were lower following use of the crimper roller, but this was not true over the entire test.

Terminating with livestock
Perhaps the most creative approach to terminating green manures is to return to nature鈥檚 system: grazing. Approximately 80% of the nutrients that livestock graze are returned to the soil, and livestock provide an economic benefit as well.聽

In a test at Carman MB, grazing at full bloom effectively terminated all legume green manures. The effects on nitrogen differed in the two test locations.聽 Yield of the subsequent wheat crop was not reduced by grazing in this test.

Mulches to suppress weeds
If green manures are laid on the soil surface, rather than incorporated, they may provide the additional benefit of being a weed suppressing mulch. In trials at the University of Manitoba, alfalfa applied to a growing wheat crop provided strong nitrogen benefits, helped conserve soil moisture, and usually suppressed annual weeds.

At the Agriculture and Agri-Food Canada research station at Lethbridge, yellow sweetclover residues remaining after termination of growth continued to provide excellent weed suppression. Weed densities in April before planting the succeeding wheat crop were 75 to 97% lower in yellow sweetclover than in untreated fallow treatments.

Research is beginning to find effective ways of reducing or eliminating tillage for green manure termination, and using that green manure as a weed suppressing, water retaining, mulch. Scientists working with the Organic Science Cluster, a federally funded research initiative, are continuing this research. It has the potential to provide organic farmers with more ways to nurture and steward their soil. 聽Results are just beginning to come in, and verification of these data will take time. The goal is to use the information to help producers reduce tillage, yet retain many of its benefits in organic systems.

This article was written by Brenda Frick on behalf of the OACC with funding provided by Canada鈥檚 Organic Science Cluster (a part of the Canadian Agri-Science Clusters Initiative of Agriculture and Agri-Food Canada's Growing Forward Policy Framework).聽 The Organic Science Cluster is a collaborative effort led jointly by the OACC, the and industry partners. For more information: oacc@dal.ca or 902-893-7256.


Posted March 2012