Reducing Tillage in Organic Agriculture on the Prairies

By Iris Vaisman

Is it possible to reduce tillage in organic crop production while maintaining the benefits of green manures and keeping weed populations in check? In organic crop production, tillage is a key tool in terminating and incorporating green manures, and is also a major tool for weed control. However, tillage has been shown to decrease organic matter, increase the risk of erosion, and dry out soil.

Researchers at the University of Manitoba are exploring the roller crimper as an option for reducing tillage in organic agriculture. The roller crimper was developed by farmers in South America as a method to terminate green manures. The roller crimps green manure stems and lays them flat. The green manure plant eventually dries and is killed. The residue left on the soil surface creates a barrier that can suppress weeds and reduce water evaporation. The green manure still contributes nutrients to the soil, and builds soil organic matter. Farmers ‘roll’ their green manure crops and seed their cash crop directly into the mulch in a single operation. In recent years, the Rodale Institute in Pennsylvania has been experimenting with the roller, seeding corn and soybeans directly into rolled hairy vetch or rye. Plans for building a roller are on the Institute’s website and now a variety of models are being tested around the United States.

University of Manitoba researcher Dr. Martin Entz and graduate student Iris Vaisman are assessing whether the roller crimper is suitable for green manure termination on the prairies. Typically, organic farmers seed green manures in the spring and terminate the green manure at full bloom. The green manure is tilled to incorporate it into the soil, providing nutrients for subsequent crops. But what would happen if the green manure was rolled instead of tilled? What if it remained on the surface instead of being incorporated?

University of Manitoba researchers are asking several questions about the effect of the new roller system: What effect would it have on the yield of subsequent crops? Would the nitrogen be as available? Would nitrogen be lost to the air? Will this suppress the weeds? What about soil moisture? Does it really reduce erosion?

To investigate these parameters, in the summer of 2007 at the Carman Research Station, researchers grew a pea and oat intercrop as a green manure. Beginning at pea flowering, the green manure was terminated by rolling, tilling, or a combination of the two. In the following spring, they seeded hard red spring wheat into the different plots. Initial results show that wheat yield and grain protein were the same, regardless of whether the green manure was tilled or rolled. There was also no significant difference in soil moisture. While total weed densities were also not affected by tillage, weed species did vary with various treatments .

In a separate experiment, researchers compared chickling vetch, hairy vetch, and Indian Head black lentil. Each green manure was both rolled and tilled. Rolling killed most of the chickling vetch and lentil; they had limited regrowth. The hairy vetch continued to grow after being rolled and produced a large amount of biomass. Wheat was seeded into the plots in the spring. While there was very little ground cover from the rolled chickling vetch and lentil, the rolled hairy vetch provided a thick mulch that appeared to be suppressing weeds. The thick mulch also delayed the development of the wheat, and researchers are waiting to see how that will affect the yield at harvest.

These initial studies indicate the potential for reducing tillage while maintaining benefits of a green manure crop. Researchers are learning that coupling the right species of green manure with the roller will be the key to maximizing its benefits. Researchers are continuing their work this summer.


Iris Vaisman is a graduate student at the University of Manitoba. She welcomes your comments at 204-474-6236 or by email at iris.vaisman@gmail.com.


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Posted October 2009