What a difference twenty years make.
On April 23rd, U.S. Agriculture Secretary Tom Vilsack announced a major voluntary, incentive-based effort to address climate change by reducing greenhouse gas emissions, expanding renewable energy production, and increasing carbon sequestration in partnership with various agricultural producers across the nation. Specifically, this effort aims to achieve a net reduction of 2% of greenhouse emissions by 2025, or the equivalent of taking 25 million cars off the road, according to the press release.
While this goal is not particularly ambitious, frankly, it does represent a startling change from the type of conservation priorities on federally owned lands that I encountered when I co-founded the Quivira Coalition nearly twenty years ago. It’s an important indication not only how serious climate change has become as a policy issue, but also a testament to how far soil carbon has risen as a climate change mitigation strategy. If you had told me as recently as 2010, when I began researching a book on soil carbon, that the Secretary of Agriculture would be supporting publicly the implementation of practices that sequestered carbon in soils, I would not have believed you.
But here’s what the press release said: “USDA intends to pursue partnerships and leverage resources to conserve and enhance greenhouse gas sinks, reduce emissions, increase renewable energy and build resilience in agricultural and forest systems.”
Here are some of the USDA’s Building Blocks for Climate Action announced at the April press conference:
- Soil Health: Improve soil resilience and increase productivity by promoting conservation tillage and no-till systems, planting cover crops, planting perennial forages, managing organic inputs and compost application, and alleviating compaction. For example, the effort aims to increase the use of no-till systems to cover more than 100 million acres by 2025.
- Grazing and Pasture Lands: Support rotational grazing management on an additional 4 million acres, avoiding soil carbon loss through improved management of forage, soils and grazing livestock.
- Stewardship of Federal Forests: Reforest areas damaged by wildfire, insects, or disease, and restore forests to increase their resilience to those disturbances. This includes plans to reforest an additional 5,000 acres each year.
- Urban Forests: Encourage tree planting in urban areas to reduce energy costs, storm water runoff, and urban heat island effects while increasing carbon sequestration, curb appeal, and property values.
Twenty years ago, goals like these would have made all of us fall out of our saddles. Words like adaptation, mitigation, sequestration and even resilience were not on anyone’s agenda, much less the words climate change. At the time, we worked mainly on improving land health – the ecological processes that sustain life in rangelands and riparian areas. Mostly, we focused on living things above the ground, such as plants, animals and people. The microbial subsurface universe was terra incognita for many of us. And carbon? Wasn’t that just some element on a Periodic Chart?
How the times have changed.
It’s especially heartening to see the Secretary of Agriculture support rotational grazing. One of Quivira’s principle goals was to spread the news about the multiple benefits short duration, management-intensive cattle grazing, now generally called holistic planned grazing. We took a lot heat from a lot of quarters for our advocacy, including from employees of the USDA’s Forest Service. For a while in the mid-2000s, Quivira was a grazing permittee on the Santa Fe National Forest where we attempted to ‘walk the talk’ of progressive land management. Our hopes for implementing a planned grazing system on the allotment, however, were met with a large amount of indifference (i.e. passive opposition) by the local Forest Service district office. To see the Secretary of Agriculture now become an advocate for the very system we tried to implement is both exciting and bittersweet.
AS a result of this experience, I’ll remain skeptical until I see the Secretary’s words actually reach the ground.
It’s the same with his support for no-till farming systems. On a conventional farm, a tractor and a plow are required in order to turn over the soil and prepare it for seeding and fertilizing, a process the often requires three passes of the tractor over the field. In a no-till system, a farmer uses a mechanical seed drill pulled behind a tractor to plant directly into the soil, requiring only one pass. The drill makes a thin slice in the soil as it moves along, but nothing resembling the broad furrow created by a plow. The soil is not turned over and any growing plants or crop residue on the surface are left largely undisturbed, which is a great way to reduce erosion and keep soil cool and moist, especially during the hot summer months.
These are all good reasons why no-till has grown in popularity with farmers around the world.
One of the major disadvantages of no-till, however, is its lack of weed control. When farmers don’t plow, the weeds say “thank you very much” for all that undisturbed soil and grow vigorously. To kill weeds in a no-till system, many farmers apply chemical herbicides to their fields. Lots of it. They also spray pesticides to keep the bugs in check. Additionally, many no-till farmers use genetically modified seeds, often in combination with the synthetic herbicides. All of this is verboten in an organic farming system, of course, which brings us to the Holy Grail of regenerative agriculture: organic no-till. It combines the best of both worlds—no plow and no chemicals. It operates on biology – plus the tractor and the seed drill.
I doubt Vilsack has organic no-till in mind with this new effort to fight climate change, but who knows? After twenty years, at least it’s a start!
In this graphic, replace the words ‘organic matter’ with ‘carbon’ and see how it all links together.
To explain how the USDA’s new policy on carbon sequestration in soils might work, it’s worth a quick review of a protein in the soil called glomalin, one of nature’s superglues.
The story starts with mycorrhizal fungi, which are long, skinny filaments that live on the surface of plant roots with which they share a symbiotic relationship, trading essential nutrients and minerals back and forth. This fungi-root mutualism reduces a plant’s susceptibility to disease and increases its tolerance to adverse conditions, including prolonged drought spells or salty soils.
Fungi in general are best known to humans as the source of mushrooms, yeasts, and the molds that make cheeses tasty, ruin houses in humid climates, and produce antibiotics. Like plants, animals, and bacteria, fungi form their own taxonomic kingdom. There are an estimated 2 to 5 million individual species of fungi on the planet, of which less than 5 percent have been formally classified by taxonomists.
Carbon molecules, in the form a sugar called glucose, pass from plant roots into a mycorrhizal fungus where they eventually makes their way to one of its hyphae – hairlike projections that extend as much as 2 inches into the soil in a never-ending search for nutrients. Then, in a process that is not completely understood by scientists, the carbon molecule is extruded from the hyphae as a sticky protein called glomalin.
As a plant grows, hyphae break off and the now free-floating glomalin quickly binds itself to loose sand, silt, and clay particles. Soon, small clumps of glomalin-glued particles form larger and larger aggregates, kind of like a vast, intricate tinker toy construction. As the aggregates grow bigger they become stronger and more stable, making the soil increasingly resistant to wind and water erosion. This process also makes the soil more porous (fluffy), with lots of tiny pockets in between the tinker-toy aggregates, and this facilitates oxygen infiltration, water transport, micro-critter movement, and nutrient transfer.
Next stop: humus – carbon rich soil, dark, rich, and sweet-smelling.
You can feel glomalin, by the way. It’s what gives soil its tilth—the smooth texture that tells experienced farmers and gardeners that they are holding great soil in their hands. To create tilth, the soil engine needs both biology and chemistry working together, and glomalin is the glue that binds them.
Glomalin itself is a tough protein. It can exist up to fifty years without decaying or dissolving. When locked into the stable tinker-toy structure of humus, it can persistent for even longer periods of time. Healthy soils have a lot of glomalin, which means this: since glomalin is 30 to 40 percent carbon, it is the ideal safe–deposit box for the long-term sequestration of atmospheric carbon dioxide. This is what scientists call “deep carbon”—the kind that stays in the soil for decades, or longer. There are fewer hungry microbes this deep in the soil, which adds to the stability and longevity of the carbon storage.
It’s a simple equation: lots of deep glomalin = lots of secure carbon storage. It’s also a fragile equation, however. A plow can destroy this safe-deposit box in a heartbeat, releasing its carboniferous contents back into the atmosphere. Plows also tear mycorrhizal fungi into bits, slaughtering them in droves, putting an end to our unsung heroes.
No one knew glomalin existed until it was discovered in 1996 by Sara Wright, a soil scientist with the US Department of Agriculture’s Agricultural Research Service in Maryland. She named it after glomales, the taxonomic order that includes arbuscular mycorrhizal fungi. Not only did she uncover its role in soil-building and carbon sequestration, but a subsequent four-year research project under her direction demonstrated that levels of glomalin could be maintained and raised with regenerative farming practices, including no-till planting.
In the study, Wright observed that glomalin levels rose each year after no-till was implemented, from 1.3 milligrams per gram of soil (mg/g) after the first year to 1.7 mg/g after the third. A control plot in a nearby field that was plowed and planted each year had only 0.7 mg/g. In a further comparison, the soil under a fifteen-year-old buffer strip of grass had 2.7 mg/g of glomalin. She also discovered that some plants don’t attract arbuscular fungi to their roots, including broccoli, cabbage, cauliflower, mustards, rapeseed, and canola.
Before 1996, determining the carbon content of a farm’s soil was largely based on measuring its soil organic matter (SOM), which is roughly 58 percent carbon. Thanks to the discovery of glomalin, soil carbon can now be measured quite precisely. This sort of data is very useful in determining how much deep carbon a specific farming or ranching practice is sequestering. It has economic implications as well, since carbon trading markets, such as the ones recently established in California could potentially use levels of glomalin as a “currency” to pay landowners for mitigating carbon dioxide pollution.
Here’s an idea: employ a farming or ranching practice that is known scientifically to increase levels of glomalin and get compensated financially!
That’s what I would recommend to Secretary Vilsack, anyway.
Here’s an electron microscope image of glomalin (the small spherical shapes) on a fungus:
