There is an abundance of research documenting the negative effects of tillage on soil.
But according to Diane Knight from the University of Saskatchewan, tillage associated with organic food production is more palatable.
“There’s something about being organic that makes tillage less bad,” Knight told people at the Organic Alberta conference in Spruce Grove Alta.
No-till systems have many advantages such as greater biological activity and diversity, better soil structure, increased organic matter, and better nutrient retention.
As a result, organic producers are frequently called to task for their excessive tillage.
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A common myth is that organic producers have simply replaced herbicide use with tillage.
In fact, weed management on organic farms employs many useful tools, such as diverse rotations, increased seeding rates and appropriate cultivar selection.
Although many organic producers have decreased their dependence on tillage, it remains an important tool.
Some researchers and producers are experimenting with no-till organic systems, but these have not yet been entirely successful for field cropping on the Prairies.
Does this mean that organic farms are destined to have poor soil quality?
According to Knight, soil quality is the result of many biological, chemical and physical properties.
Only one factor – soil organic matter – is easily influenced.
Organic matter includes plant and animal material from crops, green manures, animal manures, compost, straw and other materials.
It includes biological material that is breaking down, slowly decomposing and is relatively stable within the soil.
Soil organic matter is important because it provides soil structure and food for soil organisms, including soil mites, bacteria and fungi.
Such organisms are crucial in the cycling of nutrients, and thus in soil fertility.
Knight emphasized the importance of arbuscular mycorrhizal fungi, or AMF, a beneficial fungus.
These fungi are important in helping many crop plants gather nutrients, and are an important indication of soil biological health.
She said some research suggests that soils on organic farms support more of the beneficial AMF than conventional farms do.
In one study, the amount of crop colonized by AMF was three to six times greater on organic farms than it was on neighbouring non-organic farms.
These results may come as a surprise to many.
Tillage does damage AMF, primarily by cutting through its slender threads (or fungal hyphae) but apparently there other factors at play.
AMF form relationships with most plants.
These partnerships bring an array of benefits to the plants, including protection from plant diseases, promotion of growth and greater access to nutrients such as phosphorus, calcium, zinc and copper.
The partnership brings benefits to the AMF as well.
The plant roots supply various polysaccharides to the AMF. These sugars are crucial food to the AMF, but they do take energy for the plant to produce. If there is an overabundance of nutrients, plants are less likely to form AMF partnerships.
According to Knight, AMF form relationships with about 80 percent of land plants.
Legumes, with the exception of lupins, are especially likely to form relationships with AMF.
Maximizing legumes in rotations increases the amount of AMF in the soil.
Plants in the canola-mustard-cabbage family do not form relationships with AMF.
These plants decrease the amount of AMF in the soil, as do phosphorus fertilizers.
These two factors probably account for the reduced levels of AMF on non-organic or conventional farms.
The benefits of AMF are not limited to improving plant growth.
They also improve soil quality.
The tiny threads of AMF extend throughout the soil and secrete substances that act like glue between soil particles.
When soil is glued together into stable soil aggregates, these make the soil “fluffy” and porous.
Soils with high aggregate stability are less prone to compaction, resist erosion, and have better aeration and water nutrient retention. As well, plant roots grow better within them.
High aggregate stability is a factor in good soil structure.
Organic rotations tend to emphasize legumes, both as crops and green manures, and often eliminate canola.
Organic producers generally don’t use highly soluble phosphorus fertilizers.
Soils under organic management tend to have higher aggregate stability, and more diverse and active soil organisms.
This seems to counteract many of the potentially negative effects of tillage on organic farms, although tillage should still be used judiciously.
Brenda Frick, Ph. D., P. Ag. is an extension agrologist and researcher in organic agriculture. She welcomes your comments at 306-260-0663 or email organic@usask.ca.
