ONTARIO GRAIN FARMER RESEARCH 11 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. • “Now we’re starting to ask what are we doing for these organisms? - Dr. Kari Dunfield
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