If you’ve heard that grazing is good for the planet because it can sequester more carbon in the soil, you’re not alone. The hypothesis goes like this: When livestock take a bite of grass, the grass plant sloughs off an equal amount of root mass below ground. That dead material is full of carbon. Microbes in the soil eat the carbon, and turn it into a stable substance so the carbon is safely sequestered below ground. So grazing creates more forage, more meat production, and a healthier climate.
It’s an interesting hypothesis, and hypotheses are where all scientific discovery begins. Someone has an idea about how a process works, and then sets up tests and experiments to see if the idea holds water. So, on behalf of our On Pasture community, we decided to look into it.
We started where all researchers start: with a review of what scientists have already discovered from working on this topic. There’s a LOT out there.
So far, we’ve read over 100 scientific papers published between 1998 and 2016. Each of those papers cite at least 50 additional papers that supported them in their work. And, of course, each of those support papers cite even more papers. It’s a lot to digest.
Let’s start with the basics of what the research tells us. We’ll go into more detail in future articles.
What we’ve learned from our reading so far:
Grazing itself does not seem to have much influence on increasing carbon in the soil.
The carbon cycle is very complex and there are lots of things influencing how carbon gets into the soil, how long it stays there, and what makes it head back into the atmosphere. Our reading has revealed that precipitation, soil type and its potential for absorbing more carbon, as well as the kind of vegetation growing in the pasture, all determine what happens to a much greater degree than grazing does.
It turns out that, though grasslands cover about 1/3 of the planet, there are other agricultural lands with greater potential to sequester carbon. The more degraded a soil is, the higher its potential for improvement. Dr. Rattan Lal, who has studied environmental quality and sustainability, and soil degradation and restoration for over 50 years, says, “…the potential of SOC [soil organic carbon] sequestration is in the following order: degraded soils and desertified ecosystems > cropland > grazing lands > forest lands and permanent crops.” (Pg. 14 of Lal – Soil carbon sequestration to mitigate climate change, April 2004, Geoderma 123 (2004) 1-22.)
Here’s another important piece:
While grazing may not be the silver bullet, it’s an important part of the carbon cycle.
Good grazing produces food and fiber while keeping the soil covered with vegetation, improving water storage, preventing erosion and nutrient migration, and maintaining water quality. These are all vital ecosystem services. Good grazing management is also important to allowing the seasonal uptake of carbon to be as great as it can be, and to ensuring that the carbon we’ve got in the soil doesn’t oxidize and head back into the atmosphere at a greater rate.
Done poorly, grazing can have negative effects. Grazing too early in the season reduces the leaf surface area that’s so important for the seasonal uptake of carbon into the soil. Practices that encourage shorter rooted vegetation over longer rooted plants also reduce seasonal uptake. Finally, grazing so that we leave the soil bare through the winter can turn grasslands into carbon sources.
So, is soil the answer?
Let’s check back in with Dr. Lal for the answer to that question:
“People should know that soil is part of the solution, and agriculture can be part of the solution,” he says. “That’s an important message.”
To figure out how large a role agriculture can play, Dr. Lal looked at the global soil carbon pool, historic carbon loss and the capacity of the world’s degraded agricultural soils to store carbon. He looked at strategies like woodland regeneration, no-till farming, cover crops, improved grazing, and compost, sludge and manure applications, and calculated how rapidly they could increase the soil carbon pool. His estimate, reported in Geoderma, is that the global potential of soil organic carbon sequestration through these practices is .9 (plus or minus .3) gigatons of carbon per year.
That’s a lot. But it’s only one-fourth to one-third of the estimated 3.3 gigatons in annual increase of atmospheric CO2.
So soil may not be THE answer. But it is part of the answer. And the best part of this answer is that as we work on our part of the answer, we’re restoring degraded soils, enhancing forage and food production, purifying surface and ground water, and reducing the rate of enrichment of atmospheric CO2. That’s a pretty good thing.
Stay tuned next week as we look more closely at what research tells us about grazing and soil carbon.