In our new Feature series, “A Closer Look”, we take a deeper dive into a specific topic relevant to our issue’s theme. This time, Dustin Hilderman is taking a look at soil, and the importance of the carbon cycle. Even if you’re not a farmer or working in the agricultural industry, you’ll likely find it interesting—we did.
Just a few generations ago, when the prairies were first broken, pioneering farmers were able to produce good yielding, high protein crops without the addition of synthetic fertilizers. However, years of conventional farming practices like monocropping and heavy tillage have interrupted natural regenerative processes—carbon, nitrogen and water cycles—which restore soil fertility.
As a result, farmers and gardeners alike, have had to increasingly rely on synthetic applicants and invasive farming techniques which focus on control—control of nutrient levels in the soil (synthetic fertilizer and soil sampling), control of biodiversity (tillage, herbicides, pesticides and fungicides) and control of water (irrigation). However, nature is fickle. Attempting to micromanage soil health through modern technology is becoming increasingly expensive and financially risky—particularly, if mother nature decides not to play fair.
In an effort to promote land rejuvenation and increase soil health, many researchers are now suggesting a more symbiotic approach to land management.
Enter the carbon cycle. In its simplest form, the carbon cycle (as it relates to agriculture) begins with plants drawing carbon from the atmosphere, processing it into organic compounds and depositing (sequestering) organic carbon in the soil. This organ carbon provides a number of functions necessary for the structural, physical, and biological health of soil.
As many conventionally farmed soils produce a net loss of carbon—meaning more carbon is taken off the land in the form of seed, straw or silage than monocrops are able to sequester back into the soil—establishing a healthy carbon cycle is central to this approach. According to Dr. Christine Jones, soil ecologist and founder of amazingcarbon.com, “the solution lies in the adoption of management practices that increase levels of stable carbon in the soil … when levels of soil carbon increase, so too does organic nitrogen.”
Dr. Jones offers five basic principles for carbon sequestration in soil restoration.
Green is good—and year-long green is even better.
As noted by Jones, “every green plant is a solar-powered carbon pump.” Plants draw in CO2 from the atmosphere and process it with water and sunlight to produce organic compounds, which eventually make their way into the soil where the organic carbon provides a variety of services for a healthy microbial community. The greener foliage on the cropland, the more organic carbon being deposited into the soil.
On the flip side, bare soil leaches stored organic carbons back into the atmosphere. Jones warns, “If you can see the soil it is losing carbon—and nitrogen!”
There is an entire complex ecosystem thriving in the soil. Just under the surface, hundreds of species of microbes are at work, building soil aggregates, transporting nutrients and protecting their host from various pests.
One microbe in particular, mycorrhizal fungi, is the star of the show. This fungus establishes nutrient networks which it uses to tap into soil-locked nutrients—organic nitrogen, phosphorus, sulfur, calcium, copper, zinc and more—which the network then exchanges for organic carbon, thus moving carbon collected in the atmosphere into the soil.
Diversity is not dispensable.
As each plant produces its own blend of organic compounds, diversity above ground quite literally feeds diversity below ground. Multiple root types break up hard packed soil and host different types of microbes. In turn, these microbes improve soil structure and protect the plant from pests and disease.
Jones goes on to argue that, “the belief that monocultures and intensively managed systems are more profitable than diverse biologically-based systems does not hold up in practice. Monocultures need to be supported by high and often increasing levels of fertilizer, fungicide, insecticide and other chemicals that inhibit soil biological activity.”
Limit chemical use.
A healthy mineral cycle is part of a healthy soil ecosystem. Jones claims that an established mycorrhizal network can supply up to 90 percent of the nitrogen and phosphorus that plants require. While it may feel counterintuitive, too much synthetic fertilizer can actually inhibit soil rejuvenation.
For example, the presence of synthetic fertilizer reduces the liquid carbon deposited in the soil as the plant has easy access to nitrogen and phosphorus and no longer needs to rely nutrient exchanges with microbial communities. In other words, spoon-feeding the plant starves the microbes.
As synthetic fertilizers are becoming increasingly expensive, farmers are looking to reduce input costs while maintaining productivity. Learning to exploit natural mineral cycles is a good option.
The integration of animal grazing to cropland has numerous benefits for both animals and soil. Beyond the obvious benefits of free fertilizer and additional pasture land, controlled animal grazing also increasing the amount of organic carbon transferred to the soil.
Jones notes that as long as 50 percent of the green leaf is maintained, the photosynthetic capacity of the plant is sufficient to allow “the rapid restoration of biomass to pre-grazed levels.” This principle is visible on your front lawn—grass grows the fastest just after it is cut. Rapid plant growth requires nutrients. The quicker the growth means the more frequently the plant exchanges nutrients with microbes. The more frequent the exchange, the more organic carbon is deposited in the soil.
Ultimately, as Jones notes, “the carbon, nitrogen and water cycles are intrinsically linked. It is not possible to change one with changing all three.” This means taking steps to improve the efficacy of any one cycle should have positive repercussions on the other two. For example, selecting broad leaf cover crops with deep root systems will help break up hardpan soil and increase water infiltration while the addition of green leaf sequesters organic carbon into the soil, which in turn feeds the microbial community.
As more and more “cost saving” technology enters the market, learning to exploit the symbiotic nature of the soil ecosystem, may be the best way for farmers to reduce input costs while maintaining productivity.
Jones, Christine (2018) Light Farming: Restoring carbon, nitrogen and biodiversity to agricultural soils. Conference Proceedings: No-till on the Plains 2018