When I first started learning about grazing management, the concept that most blew my mind was animal impact.

Not anymore.

I've seen it with my own eyes, and scientific documentation is growing steadily.

For those uninitiated to the term, animal impact is the cumulative effect of plant biting, saliva, urination, defecation, trampling and all the other things grazing animals do to plants and their habitat.

The idea that these things can be positive when applied in the right ways and right timing can best be understood by thinking about the immense herds in which ruminants lived and traveled in significant portions of the year, and the apparently high organic matter in prairie soils that resulted and are now degraded all over the world.

These days, those of us in the livestock industries should think about applying animal impact in terms of animal herd density, or stock density. That refers to the number of animals present in a paddock at one time, and it effectively compounds herd effect.

Personal experience

I saw this very visibly the growing season of 2011, the year after I grazed the small pasture near my house at super-high stock density the fall of 2010. You can find one of my blogs from that timeframe describing those initial experiences on BeefProducer.com.

All my grazing that fall was done at 200,000 pounds per acre of stock density and above. When I could spare the time, I used stock densities up to 1,000,000 pounds. In that droughty year, on the worn-out soils, that meant I usually had to just stand and watch the cattle graze and then move them as soon as they became listless and the forage was well-cropped. In other words, it only took a few minutes.

The amazing result I saw the next year was a tremendous crop of purple top, a mid-seral forage that's relatively high quality and loved by cattle. It was dramatically obvious: Where the cattle had grazed between the temporary fences, the purple top was dominant that first year. Under the fences it was mostly windmill grass, a locally prominent foxtail, and a mix of weeds typical of "go-back" farm ground.

Since then, I have grazed cattle on this pasture every year except this year, and at moderately high stock densities ranging from 20,000 to 250,000 pounds per acre. The forage type and quality continue to improve visibly, soil samples suggest the soil is improving, and forage volume is improving. Yet I've never seen so dramatic a change as I did that first year when I applied the most animal impact.

Scientific evidence

Moreover, studies by a group of scientists and ranchers working in several projects are showing high stock-density management develops soil much more quickly than lighter-density "rotation" grazing.

Allen Williams, a private consultant, grazier, and partner in the land management firm Standard Soil, shared the figures from a research project he helped conduct.

Williams and other scientists are comparing the effects of management on the soils of three farms/ranches in Mississippi, and are expanding the efforts to other regions of the country.

Williams explains the first set of data were collected in the fall of 2014 using three farms in northeast Mississippi. The farms agreed to participate in a multi-year study. They are in close proximity to each other and have the same soil types, topography and annual average rainfall. The primary difference is the grazing strategy employed by each farm.

The three farms selected were:

Farm 1 – Practices Adaptive Multi-Paddock Grazing (AMP) for the past five years. Prior to that, the farm was alternately in row crops, dairy and CRP for the last several decades. Stock density for the AMP grazing over the past five years was strategically alternated between 100,000 pounds per acre and over 500,000 pounds per acre, with cattle being moved either daily or multiple times a day to fresh pasture.

Starting soil organic matter at the beginning of AMP grazing five years ago was 1.5%-1.6%. A cow-calf operation has been maintained on the farm for the past five years with the cattle used as a tool for land improvement as well as for beef production.

Farm 2 – Practices a grazing methodology with high stocking rates (HCG), in which the cattle are rotated to fresh pasture once every two to four weeks. The farm has been continuously in pasture and grazing for the past 50 years, alternating between cow-calf and stocker grazing. Farm 3 – Practices continuous grazing with low stocking rates (LCG). Cattle are free to graze most the farm without restriction to movement. This farm has been in continuous grazing (primarily cow-calf) for the past 40 years.

Many scientists have said for many years that soil organic matter (SOM) cannot be improved. The data from this trial show differently.

On the AMP farm, which uses high stock-density grazing and heavy animal impact, SOM was 4.26% in the top 6 inches and 1.98% at 36 inches. The AMP farm started five years before the study began with an average of just 1.5% SOM in the top 6 inches, so the SOM has increased almost threefold within a five-year period.

SOM from five years ago was not available for the HCG and LCG farms. Williams and the other researchers estimate the current SOM on the HCG and LCG farms is about the same as it was five years ago since management has been static.

On the HCG farm, SOM ranged from 3.28% in the top 6 inches to 0.82% at 36 inches.

On the LCG farm, SOM ranged from 2.72% in the top 6 inches to 0.68% at 36 inches.

Animal impact and the way you choose to manage grazing makes a huge difference. Data and empirical evidence show the more you can apply these principles, the faster you can make improvements.

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