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That's what she said

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Let’s Sequester More Carbon in Our Soil


At a PLAN-Boulder forum on Friday, March 18, 2016, Boulder artist, mini-farmer and environmental activist Elizabeth Black informed the audience that agricultural land in the United States has the capacity to sequester 11 percent of American greenhouse gas (GHG) emissions, according to one expert, while another expert asserts that it could sequester 100 percent of American GHGs.

Soil Health: Soybeans Planted into Winter Wheat Stubble, Natural Resource Conservation Center,

Soil Health: Soybeans Planted into Winter Wheat Stubble, Natural Resource Conservation Center,

Either way, that is a lot of carbon removed from the atmosphere, and the costs of soil sequestration are much lower than they are through the use of industrial methods to sequester carbon deep underground. Black said that it costs $20 to $30 to sequester a ton of carbon dioxide in soil using natural methods, while the cost of carbon catchment and storage deep underground at a project being built in Texas will be $276 to $340 per ton of carbon dioxide. Underground sequestration processes also consume a lot of energy.

Black, who grows vegetables and trees (including Christmas) at her tiny farm in North Boulder, is advocating that Boulder County and the City of Boulder emphasize soil sequestration of carbon in their policies and that they amend the Boulder Valley Comprehensive Plan in that respect. She also is trying to encourage property owners, particularly farmers and ranchers, to use practices to sequester carbon in their soil.

Black explained that through the process of photosynthesis plants split the carbon in carbon dioxide from oxygen. The oxygen is emitted back into the air through the leaves, while the carbon moves to the plants’ roots. There the plants release carbon sugars into the soil, which are consumed by microbes; and the microbes deliver minerals to the plants. The microbes excrete humin, which enriches the soil.

Black said that in a spoonful of healthy soil, there are four billion bacteria, 2,000 yards of fungal filament, 400,000 protozoa, 2,000 nematodes, 1,000 arthropods, as well as worms and algae. She noted that David Johnson, a prominent molecular biologist at New Mexico State University, claims that optimal soil health requires fungi, rather than bacteria, to be favored.

Unfortunately, Black revealed, the soil in this area is new. The top soil was created only 11,000 years ago. Beneath it lies a layer of clay and rocks. The drainage and soil nutrition are poor, and alkalinity is common. Agriculture has often exacerbated these natural disadvantages. Plowing breaks the fungi and volatilizes carbon. Mono-culture limits the variety of microbes, and pesticides and herbicides destroy them.

Not only does soil sequestration of carbon improve the atmosphere, Black declared, but it also improves the soil. Black observed that for every one percent increase in soil organic material, the capacity of the soil to hold water increases by an inch of water. The effect is similar to increasing rainfall by an inch, she noted.

Black expounded four general principles for increasing the health of soil:

  1. Keep it covered as much as possible, or, in other words, avoid bare dirt
  2. Disturb it as little as possible
  3. Keep plants growing throughout the year
  4. Diversify plants as much as possible

She praised the value of compost and manure and also suggested applying fertilizer, but only in limited amounts.

She also recommended a variety of more specific techniques for farming, grazing, and stewardship of forest land in Boulder County:

  • Prompt reforestation of burned areas while considering likely, future climate change (she claimed that if temperatures in Boulder rise by 3.5 degrees Celsius, our future climate will resemble Albuquerque’s current one, and different seed sources and spacing will be needed for our trees)
  • Forest-thinning and conversion of the slash into biochar, which can be buried and reduces the carbon dioxide created by organic waste
  • Green waste compost
  • Creating compost without turning it, which tends to break up helpful fungi
  • “Mob grazing” of cattle, which involves concentrating cattle in relatively small pastures by using temporary, electric fencing and then excluding them from those areas for long periods of time. This technique causes grass to grow more vigorously
  • No-till farming
  • Strip-till farming
  • Mulch tillage
  • Conservation crop tillage using at least four different crops
  • “Cover crop cocktails” of up to 50 different types of plants to be planted when the soil would normally be bare. It is turned under, grazed, or crushed before the main crop is planted in the spring.

Black conceded that building soil organic material requires more expensive equipment and more skilled labor than do traditional approaches to farming. She acknowledged that agricultural laborers can rarely afford to live in Boulder County and usually must commute from elsewhere. She called for strong partnerships between landowners and lessees of agricultural and grazing lands and contended that more research is needed on Colorado ecosystems, soils and climate, including baseline studies of the health status of soils.

Most urbanized Americans spend their lives attempting to avoid dirt; and when we think about it we do so only in order to figure out how to remove it from our surroundings. Maybe we need to change our attitude and learn to appreciate dirt if we are going to successfully co-exist with the natural world.

Black, who as part of another campaign has given away 4,000 tree seedlings to Boulder residents, is eager to spread her message to all those who are interested. She can be contacted at

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