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Soil Health: Shifting the Carbon-Nitrogen Balance (Part I)

By Liz Clift

Whether you’re adding carbon-rich materials to soil for ecological restoration purposes, trying to figure out how to make your compost more efficient, or perhaps figuring out why last year’s chop-and-drop mulch in your garden isn’t breaking down the way you expected it to, it’s important to understand carbon to nitrogen ratios (C:N).

Carbon and nitrogen are both necessary for plant growth—and an imbalance can lead to slower or stunted growth, or make an area more hospitable to certain types of weeds. In addition, the relative levels of carbon or nitrogen on a site impact how quickly mulch—including grass clippings, leaves, crop residue, etc.—decomposes.

If you’ve never spent much time in prairies, here’s a sampling of plants and birds

How does this factor into restoration ecology?

One of the hurdles of restoration ecology is what to do with pioneer species (aka weeds) we don’t want colonizing a piece of land. Vigorous weed growth can be a sign of high levels of nitrogen in the soil, relative to carbon. By increasing the levels of carbon in the soil, it’s possible to effectively manage nitrophilic weeds (such as cheatgrass, Bromus tectorum), even with a reduced (or no!) use of herbicides.

By focusing on increased soil health through increased carbon supplementation, it is possible to shift the competitive balance. Increasing soil carbon mimics later successional stages of soil ecology, which generally favors native plant growth. Often, native plants can more easily establish and thrive in low nitrogen environments, which allows them to begin the process of out competing nitrogen-loving weed species—some of which produce many more seeds than native species.

Sawdust and wood chips, when used as an incorporated soil amendment, provide opportunities to increase carbon in the soil, as do fire-regimens that allow for controlled burns of prairies or woodlands. Controlled burns, unlike wildfires, generally burn at a lower temperature, which leaves the microbiota of the soil intact. Although controlled burns are not always understood as a management technique by the public at large, it’s critical that we remember fire used to be a standard part of most ecosystems.

If we face public resistance to incorporating woodchips, sawdust, or a fire-regimen (or other forms of carbon supplementation), we will do well to remember that this is an opportunity to talk with people about soil health and why we’re doing what we’re doing. For those of us who work in grasslands, it’s especially important to note that increasing carbon in the soil has been shown to be effective at facilitating prairie restoration.

Great Ecology employees have successfully applied carbon supplementation as part of oil pad reclamation, and are currently applying the process at some Denver-area park sites as a means to reduce weed species proliferation and reduce operations and maintenance costs.

Part II of this blog will cover the role of carbon and nitrogen in agricultural restoration and compost.

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