Recently the NRCS hosted a seminar on the soil health and production benefits of mob grazing. Over 400 people from around the country joined to listen to Doug Peterson, Missouri’s State Soil Health Specialist (and past State Grazing Specialist), speak about the practice.
Peterson, who farms in northern Missouri said in many parts of the country soils have been degraded.
“In many cases we’ve probably lost half of our soil organic matter.”
Purchased amendments like lime and fertilizer will improve soils, but Peterson challenged participants to consider those inputs as capital investments, rather than annual costs.
He asked, “How can we improve our soils without that annual expense?”
He answered that question by referring to the work of Alan Savory, who proposed that the only known tool to heal the land is animal impact. Peterson concurred with Savory that animal impact — though perhaps not the only tool — is a very economical and natural tool for improving the land.
Animal impact includes everything livestock does to the land — hoof action, saliva deposits, “all the physical things they do besides how much grass they eat.”
Animal impact can help manage and restore croplands as well as grasslands, Peterson said.
How is soil built in a natural system? Peterson used the example of bison. When predators are present near a group of bison, they cause the herd to stick close together — trampling the forage.
Then the herd leaves the area, not to return for some time.
That basic template — close trampling of a tight group, followed by a long rest period — is the model for mob grazing.
Trampling plants helps build soil by feeding the soil biology and speeding mineralization of nutrients in forage trampled to the earth.
Peterson measures animal impact by calculating pounds of animal live weight per acre. He made these categorizations: managed intensive grazing as using up to 50,000 pounds of live weight per acre, high stock density as using 50,000 – 250,000 pounds of animal live weight per acre, and ultra high stock density as using 250,000 pounds or more of live weight per acre.
Stock density doesn’t directly correlate to how often you move your herd, Peterson said. Instead it refers to “how compressed we have that livestock on a given area.”
You could change paddocks six times per day or just once a day — your strategies and goals will likely be different at different times of the year — and still be achieving high stock density.
To achieve the benefits of high stock density, however, you will probably want to rotate paddocks at least once a day, and use rest periods that measure in months or years.
By practicing this type of grazing, Peterson said, you can “achieve some of what the bison did when they were harassed on the prairie — without the stress, obviously.”
Peterson recommends a minimum of 100,000 to 150,000 pounds live weight per acre for grass farmers wanting to practice high stock density in the eastern part of the U.S.
High stock density improves soil health by increasing organic matter, which among other things helps moderate pH — reducing a high soil pH or increasing a low soil pH. Changes in soil surface pH can help change a sward’s species composition and ultimately increase a field’s productivity.
There are four principles behind optimizing soil health, Peterson said: minimize disturbance, promote living roots, keep the soil covered, and add diversity.
Disturbances can be physical or chemical. The biggest disturbance on grassland, Peterson said, is typically haying.
Grazing, too, is a disturbance that impacts plant succession. In a forage environment, Peterson suggests promoting a succession that includes perennials rather than annuals, yet remains herbaceous (not woody and shrubby). That kind of succession can be attained, Peterson said, by lengthening rest periods.
As for promoting living roots, Peterson notes that the exudates of roots are the primary food source for a number of soil organisms, including bacteria, nematodes, fungi, and worms. So having living roots — something you can promote with longer rest periods — will help grow that feed trough for your soil livestock.
“Do you, with purpose and with thought, plan on feeding your soil livestock?” Peterson asked?
By moving to say two to three grazing events per year, you may be able to develop a thatch of decomposed litter on the soil surface. That mulch will not only feed soil biology but also control soil temperature and reduce water runoff.
Keeping soil covered will also moderate soil moisture evaporation, keeping water in the soil for plant growth rather than escaping into the atmosphere. The trampling that comes with high stock density grazing will put more mulch on the soil surface.
Having a diversity of plants in your grassland — cool and warm season species, grasses and broadleafs — is important, Peterson said. Even if a plant is never grazed, it could bring up minerals to feed other plants. Lengthening the rest period between grazing helps increase diversity.
By selecting for plant diversity and practicing high density stocking, Peterson has been able to double the amount of average annual forage production in northern Missouri, from 8,000 to 16,000 pounds of forage per year.
High density grazing also needs to include an awareness of the competitive pressure of animals within your herd.
Peterson gave the example of “scorched-earth grazing,” in which not enough forage is provided to a group of animals, forcing the weaker animals — like calves — to get outcompeted by stronger animals — like cows.
Thus, if you have a mixed herd, Peterson said, make sure the weakest animals have the opportunity to graze adequately.
Ultimately, to pull profit from the land, Peterson said, you need to put organic matter back into the soil, reversing a trend of the past 100 years where we have been extracting organic matter. High density stocking is a great tool for increasing soil organic matter, forage productivity, and ultimately your farm’s own profitability.