When discussing beneficial critters, it’s easy to forget about the ones we don’t see, especially those below ground. Yet the soil is where it all starts, so they deserve recognition and admiration too. From cycling and retaining nutrients to improving structure, suppressing disease and moving and holding water, air and carbon, soil fauna do an incredible amount of work providing essentials for plant growth.
A healthy soil is an amazingly diverse, self-regulating ecosystem with a long list of creatures interacting with one another. When given appropriate conditions, their work generates soil rich in available nutrients, with favorable and stable pH, and good structure necessary for healthy root growth and critical water- and air-holding pore space.
The list of soil creatures is long, and their diversity and populations vary dramatically, not only from one biome to the next, but also from one plot to the next. Each prairie, field, forest or back yard has a unique mix of vegetation, microclimate, soil type and management practices, and with it, a unique food web. Yet within each soil food web there are common tasks that must be done. Following are the shared job titles, a few of the beneficial workers and the jobs they do.
Decomposers and Mutualists: Bacteria and Fungi
The decomposers take essential first steps to breaking down plant residue, while mutualists enhance plant growth. Bacteria and fungi retain nutrients in their biomass, create new organic compounds, help bind soil in beneficial aggregates, convert forms of nitrogen and aid in control of disease causing organisms. Some fungi even deliver nutrients and water to the plant.
Bacterial- and Fungal-feeders: Protozoa, Nematodes and Microarthropods
These guys (springtails, mites, etc.) are the grazers. As they work they release numerous nutrients, including plant-available nitrogen, control multiple disease-causing and root-feeding pests and energize and regulate bacterial and fungal populations.
Shredders: Earthworms and Macroarthropods
Shredders (millipedes, pill bugs, etc.) do just that while they feed on bacteria and fungi. This aids in breaking down residue and their burrowing and fecal pellets enhance soil structure. Their guts and fecal pellets also provide habitat for beneficial bacteria.
Higher-level Predators: Predatory Nematodes, Macroarthropods
Population control is the main role of the predators (centipedes, beetles, ants, spiders, etc. and mammals like voles, mice and shrews). Their burrowing also contributes to soil structure.
The vast majority of soil organisms are beneficial, but there are some organisms that can cause damage to plants. These include certain nematodes and various larvae that feed on roots, as well as disease-causing bacteria and fungi. Yet a biodiverse soil does a great job of controlling the populations, usually limiting their impact to tolerable levels.
We greatly affect the biodiversity, and the resulting effectiveness, of our soil by how we treat it. If we treat it like dirt, instead of living soil, we pay the price. Excessive traffic and over-tilling leads to compaction and limited pore space. Over-watering can create anaerobic conditions. Reliance on chemical pesticides and fertilizers creates artificial, often uninhabitable conditions. All of these negatives greatly limit, inhibit or eliminate a large portion of these valuable creatures and the benefits they provide.
To maximize your soil’s potential, be kind to it and its inhabitants. Use a diversity of plants (especially natives), add organic mulch and compost, allow at least some plant litter to remain, water properly, limit tilling, limit foot and machine traffic and limit or avoid chemical applications. Then sit back and marvel at the diverse soil ecosystem and the extensive and essential behind-the-scenes work it does.
Kendall Weyers, Nebraska Statewide Arboretum, plantnebraska.org