Look after your soil microbes

Guelph researchers mapped soil microbial communities and the practices that were most beneficial. Tillage practices, fertility treatments and different crop rotations were all part of their analysis.

Advances in genome analysis tools are providing a more comprehensive understanding of how microbial communities interact with crops and different production practices, and how farmers could help improve crop profitability.

University of Guelph microbiologists looked into soil composition and how farmers could foster the growth of useful microbes for better crops, and environmental resiliency.

Headed by soil and environmental microbiology Dr. Kari Dunfield, the research team leveraged long-running crop trials at Elora and Ridgetown to map what microbial communities look like in different agricultural soils in southern Ontario. The now-complete 5-year project compared changes in microbial communities across several cropping systems and has provided yet more evidence that less tillage and greater diversity in the field support healthier communities below ground.

“The soil microbiome sometimes gets bundled in with soil health,” Dunfield says. “But soil health is just the tip of an iceberg. It’s an indicator that represents the biological component in your soils. It’s only now we are starting to consistently know what’s in the soil in agricultural systems.”

Dunfield says that working in some of the long-term crop trials in Ontario was a huge opportunity from a microbial point of view, because microbial communities constantly change.

“In a system where we could really get at what organisms are there consistently with a given crop was really important – especially in Ontario soils and Ontario conditions, because we know it really depends on where you are,” she says.

OVERARCHING CONCLUSIONS

Tillage practices, fertility treatments, and different crop rotations were all part of the researchers’ analysis.

Overarching conclusions include:

• In fields treated with high rates of nitrogen year over year, the bacterial biomass of microbial communities increased, while fungal biomass decreased. The change, however, was small.
• There was a detectable increase in soil organic carbon and bacterial nitrifiers in surface soils (between 0 and 5 centimetres in depth) 5 years after shifting to conservation tillage.
• Conventional tillage changed the types of microbes observed in soil. Decreases in organisms associated with nutrient cycling and crop water uptake were identified as being particularly hard hit.
• In conventional tillage systems, the inclusion of winter wheat in rotation spurred higher populations of microorganisms associated with plant growth promotion. This suggests diversifying corn-soybean rotations with wheat could help maintain beneficial soil biological function, when tillage is necessary.
• Long-term (35-year) corn monocropping is associated with what Dunfield calls “a unique microbial community,” that had a lower diversity of fungal pathogens.

WINNING FORMULA

Taken together, such findings suggest reduced tillage, higher crop diversity (such as winter wheat and cover crops), and more active cropping rotations are a win for bacteria and fungi beneficial to crop production.

This conclusion tracks with other research, including the higher decomposition rates observed in fields with less tillage and higher crop diversity.

The broader point, according to Dunfield, is that the project has helped answer persistent questions about the complexity of soil systems, and why it can be so challenging to promote production-supporting microorganisms.

The research also highlights the importance of understanding trends in microbial communities before taking specific corrective efforts, such as applying specific microbes to the field as an input.

“In [University of Guelph – Ridgetown Campus Prof.] Laura Van Eerd’s cover crops trials with radish, for example, there’s an observable yield effect in crops from including the radish, but not a clear reason why that’s happening,” Dunfield says. “We can go in there and see increases in the number of organisms known to cycle nutrients, providing stress tolerance to the plants. Now we’re starting to ask what are we doing for these organisms?”

This research was supported by the Natural Sciences and Engineering Research Council of Canada. •