| | The soil world is wildly diverse. It teems with a multitude of organisms like soil mites, nematodes, bacteria and fungi. These organisms carry out a wide variety of functions that affect nutrient cycling, soil health and crop yields. Like detectives in a mystery story, Alberta researchers are exploring how agricultural practices affect soil organism communities.
In a two-year pilot study at five Alberta sites, researchers are focusing on two components of the soil biological community:
- Microarthropods,which include such creatures as spider mites, soil mites and springtails; and
- Smaller organisms like protozoa, fungi and bacteria.
Both components are involved in “the primary decomposition of residues and materials that are added to the field. They are at the start of nutrient cycling and nutrient availability,” explains Jason Cathcart, Soil Conservation Specialist and Coordinator of the AESA Soil Quality Program. He is a member of the pilot’s joint research team from Alberta Agriculture and Food and Agriculture and Agri-Food Canada.
Four of the sites have been selected from among the 45 long-term sites in the AESA Soil Quality Program’s province-wide benchmark monitoring program. The four sites are all in the Mixed Grass ecoregion in southern Alberta but have different agricultural management regimes. The fifth site is the long-term crop rotation study near Three Hills. Data from the 120 plots at that site allow comparisons of practices, like direct seeding versus conventional tillage.
Based on the literature, the researchers expect the soil organism communities will likely be different under different kinds of agricultural management, but exactly how they might differ is not known.
Cathcart says, “We carefully selected sites where we would expect to find differences among the soil organism communities.” The preliminary results from the pilot’s first year in 2005 suggest that there are indeed differences. If those results continue for the second year, the researchers hope to scale up the project to include additional sites from the AESA benchmark program.
To study the soil organism communities, the researchers take soil samples at the five sites each fall. In the lab, they use a separation technique to collect the microarthropods and then identify them under a microscope. And they use a technique called phospholipid fatty acid analysis (PLFA) to identify the major categories of organisms like bacteria, fungi and protozoa.
After identifying the types and numbers of soil organisms in each soil sample, the researchers analyze how that data relates to the agricultural practices at the site.
The pilot also has a landscape dimension. Each benchmark site has long-term data for three sampling locations: upper slope, mid slope and lower slope. “The pilot is collecting samples from the upper and lower positions. That allows us to investigate whether the community of soil organisms changes as a result of different landscape positions, which means the organisms would be exposed to differences in soil characteristics (e.g., organic material and soil moisture levels),” says Cathcart.
The researchers could add yet another dimension if they decide to scale up the study using other AESA benchmark sites. Cathcart explains, “We’ll be able to look at the information on a regional basis. For example, does the soil microorganism community in the Peace Lowlands differ from that in the Mixed Grasslands in the south, and if so, how does it differ?”
For Cathcart, the research is a little like being a “supersleuth”, trying to pin down which practices are stressing different types of soil organisms and which practices are helping to sustain them. “For instance, we expect that direct seeding will be less stressful for the organisms because rarely does something come in and rip their houses apart; whereas the community living in the conventional tillage system will likely be adapted to having their houses destroyed all the time. So there’s the excitement of trying to identify what communities are living at each location and why.”
Give your soil community a helping hand
When the soil organism community is thriving, it contributes to higher crop yields and reduced crop input requirements. Cathcart outlines how some agricultural practices affect the health of soil organism communities:
- Practices that increase soil community diversity and abundance include: applying nutrients (whether as livestock manure, green manure or commercial fertilizer), controlling soil erosion, maintaining a diversity of crops, and reducing or eliminating tillage.
- Practices that decrease soil community diversity and abundance include: applying pesticides, not controlling erosion, using monoculture cropping, and frequently tilling the soil.
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