Rotational grazing is one part of regenerative agriculture. This style of grazing involves moving livestock to portions of the pasture, called paddocks, while the other portions rest. The result of holistically planned grazing is carbon sequestration, improved soil health and topsoil growth.
How cool is that? This is ultimately why we want to start a farm – we want to be soil builders.
Before discussing how rotational grazing has these amazing environmental impacts, make sure you check out the first soil blog post where I reviewed the important plant and mycorrhizal fungi relationship and the carbon phases.
As a brief recap – mycorrhizal fungi are in the soil and colonize plant roots. In properly managed soil (soil that has not been conventionally farmed), plants and mycorrhizal fungi have a symbiotic relationship. Plants use carbon dioxide (gas phase of carbon) during photosynthesis to create sugars. Plants send some of these sugars (liquid phase of carbon) to mycorrhizal fungi for their food source. In exchange, the mycorrhizal fungi provide the plants with a wide array of nutrients (more nutrients than synthetic fertilizers provide). This simple carbon form then undergoes humification to form more stable, complex polymer structures (solid carbon) deeper in the soil. This humification process is building more topsoil. Carbon is sequestered from the gas, to the liquid, then to a solid phase through this beautiful, mutually beneficial plant-root relationship.
Many people think soil takes a long time to grow since a study reports that if you let land just sit without any chemical inputs or animal impact, it takes approximately 500 years for an inch of fertile topsoil to form (1).
But, a big but, farms that practice regenerative agriculture report growing topsoil inches in just a few years! For example, Gabe Brown, who has a regenerative farm with rotational crops and grazing, grew 3 inches of topsoil in just 4 years. We do not have 500 years to improve our soil health – we need the faster option of regenerative agriculture!
So how does animal impact/grazing lead to carbon sequestration?
High density, livestock grazing can be used to build soil. This is consistent ancestrally where ruminants would travel in large groups, and would move around due to predators. They would not return to a particular grass area for quite some time, leaving time for ample grass recovery.
So how does this work?
Plants consider an animal bite as a wound, which requires a healing process. The plant needs nutrients to repair this wound. They obtain these nutrients from the soil from the mycorrhizal fungi. So, the plant exudes some of the sugars generated during photosynthesis to attract and feed the carbon hungry microbes. This process will maximize the photosynthetic capacity of plants to increase carbon secretions. Plants will pull more carbon out of the atmosphere in the gas form, and push it down to the mycorrhizal fungi so that it can get the nutrients it needs to heal from the wound. The result – carbon is pushed into the soil and is transformed to the solid phase.
This situation is very similar to humans and hormesis, where we need a little bit of stress (like exercise) to operate at our best. Similarly, plants need a little bit of stress, otherwise they tend to be lazy and not work for their nutrients.
But, there is a delicate balance – overgrazing can be harmful similar to how over exercising and living in a chronic state of stress is not good for our health. If 50% of the aboveground biomass is removed from livestock, root growth is not affected. But if 60% is removed… root growth is cut in half! Gabe Brown allows his cattle to remove around 30-40% of above ground biomass before rotating to ensure he does not hit that 60% mark.
The resting time between animal impact is key to allow time for the grass to recover from the ‘wound’. This is like muscle building and working out – muscles need ample recovery time between workouts in order to build back up stronger.
In conventional farming, plants don’t work for their nutrients and don’t have these animal bites. The plants instead get a limited set of nutrients from expensive chemicals. Plus, tillage destroys these mycorrhizal fungi networks limiting the plant root-mycorrhizal fungi relationship.
When the plant root-mycorrhizal fungi relationship is still in place (in regenerative agricultural practices), the plants are able to obtain significantly more nutrients. (Which is why plants grown with conventional practices during this day and age have less nutrients!)
In summary, the goal of rotational grazing is to apply a small stress to a pasture with animal impact, and then rotate the animals to a new pasture. A plant that has been grazed will photosynthesize more and pump more liquid carbon into the soil compared to a plant that has not been grazed. This in turn will build more soil since carbon sequestration and soil building go hand in hand.
--> Plants pull more carbon out of the atmosphere to maximize photosynthesis
--> Plants will thus send more carbon to the soil to attract mycorrhizal fungi to obtain the nutrients needed to heal from the animal bite
--> Humification transforms that carbon to a stable, solid form and builds new soil.
Ruminants are a big part of this, but animal impact is just one aspect of regenerative agriculture. More posts on regenerative agriculture to come! Stay tuned!