Mycorr-what? An Introduction to the Soil Food Web

When you sit down to enjoy a big plate of spring greens, do you stop and thank the nematodes for your dinner?  How about the flagellate protozoa or the arbuscular mycorrhizal fungi?  They are hard to pronounce, yes, and hard to remember when you don’t have a microscope handy. Without their largely invisible, yet crucial, functions in ecosystems, however, we couldn’t sustain our food production for long.  On the flip side, if we consciously tend to these micro-biotic ‘livestock’ in our gardening practices, we can produce healthier plants and better harvests.

Known collectively as ‘the soil food web,’  the bacteria, fungi, protozoa, nematodes, arthropods, and everybody else living underground cycle the nutrients that plants need to grow.  It’s a friendly business relationship: plants secrete some of the sugars, proteins, and other compounds they make during photosynthesis through their roots.  This buffet attracts beneficial soil organisms to the root zone where they perform many jobs for the plants, such as scavenging for nutrients and water, fixing atmospheric nitrogen into plant-usable forms, breaking down organic matter, aggregating soil particles so roots can easily penetrate soil, and out-competing pathogenic microbes.

And just like life above ground, these organisms are constantly eating each other!  Protozoa graze on bacteria, nematodes munch protozoa, arthropods shred up organic matter, and fungi eat, well, lots of things. All of this eating leads to…ok, you know what it leads to, but did you know that plants access those little packages of nutrients, especially high in nitrogen, that are left behind after digestion?  The plants feed the soil organisms, the soil organisms supply the plants, and together they keep the nutrients cycling instead of being lost as runoff or leaching into the water table.

A soil system in which only inorganic salt-based fertilizers are added, or one in which chemical pesticides are over-utilized results in soil organisms’ death; the biotic cycle breaks down and leaves a damaged system that requires constant human input to maintain any level of productivity. Excessive tillage also interrupts soil organism life cycles by damaging the mycorrhizal hyphae (fungal networks that bear resemblance to plant root networks) that can extend through meters of soil to ferry phosphorous and  other nutrients back to plant roots. Excessive tillage also ‘burns’ up soil organic matter by introducing excessive oxygen to deeper layers of soil resulting in unsustainable aerobic activity.

So when thinking about how to improve the health and productivity of your garden, consider feeding the soil first. Replenish garden soils by adding back organisms and food for them in the form of organic matter.  There are many different ways to inoculate soil with beneficial organisms: applying compost (check out Vermiblend: it’s an all-star with earthworm castings, kelp, and mycorrhizal fungi!), compost tea (an aerated brew with extra high populations of microbes: we make it in-store or can set you up to make your own), or powdered inoculant like Rooters Mycorrhizae.  Once the soil food web is established, keep it healthy by incorporating cover crops, mulches, and natural mineral and organic fertilizers into your gardening system to provide a diversity of foods.

By Martha Morris

Stay tuned for more articles about nurturing the beneficial soil organisms in your garden and check out the sources for this post to learn more:

“Caring for the Soil as a Living System” by Mark Schonbeck (http://vabf.files.wordpress.com/2012/03/caringforthesoil.pdf)

“Soil Biology” by Dr. Elaine Ingham (http://soils.usda.gov/sqi/concepts/soil_biology/soil_food_web.html).

We also offer a great book on the soil food web: Teaming with Microbes: An Organic Grower’s Guide to the Soil Food Web by Jeff Lowenfels and Wayne Lewis.