Recent Data Supports Soil Health Benefits of Adaptive High Stock Density Grazing

by: Allen R. Williams, Ph.D.

In the fall of 2014 soil data was collected from three distinct cattle farms located in Northeast Mississippi. The farms were in very close proximity to each other and were comprised of the same soil types, topography, and annual average rainfall. The only primary difference was the grazing strategy employed by each farm.
The three farms selected were:

• Farm 1 – Practicing Adaptive High Stock Density Grazing (AHSD) for the past five years. Prior to that the farm was alternately in row crop, dairy, and CRP for the last several decades. Stock density during that time period would strategically alternate between 100,000 lbs/acre and over 500,000 lbs/acre, with cattle being moved daily to fresh pasture. Soil conditions were poor in year 1 with soil organic matter averaging less than 1.5%. A cow/calf operation has been utilized on the farm for the past five years with the cattle being used as a tool for land improvement.
• Farm 2 – Practicing a more conventional grazing methodology (CG-Good) with two to four week planned rotations of cattle from pasture to pasture. Land has been continuously in pasture and grazing for the past 50 years alternating between cow/calf and stocker grazing.
• Farm 3 – Practicing continuous grazing methodology (CG-Poor) where cattle have been free to graze the majority of the farm without restriction to movement. This farm has been in continuous grazing (primarily cow/calf) for the past 40+ years.
  

In early November of 2014, a team of scientists collected soils data from each farm on the same day. Random locations were selected on each of the three farms and soil pits were dug to a depth of three feet. Soil samples were collected for analysis within every six inch layer from the soil surface down to three feet (36 inches). Observations were made and recorded pertaining to root structure and development, presence of soil organisms, soil texture, and soil aggregation.

Immediate observations were that root structure and development, including root depth and mass, were significantly greater at the AHSD farm compared to the CG-Good and CG-Poor farms. Root growth was observed all the way down to and past the three foot depth on the AHSD farm. On the other farms, root growth did not reach the three foot depth. In addition, there were noted differences in apparent soil life with earthworms immediately present in the soil of the AHSD farm. Earthworm populations were significantly lower at the CG-Good and CG-Poor farms. Likewise, soil texture, aggregation, and appearance was significantly better at the AHSD farm when compared to the CG-Good and CG-Poor farms.

Laboratory analysis of the soil samples from each farm revealed even more startling differences. Table 1 shows the difference in soil pH between the three farms. On the AHSD farm, soil pH was a constant 7.8-7.9 from the top six inches down to 36 inches. On the CG-Good farm, soil pH ranged from 5.8 in the top 12 inches to 7.0 at 36 inches. On the CG-Poor farm, soil pH ranged from 5.6 in the top 12 inches to 4.9 at 36 inches.

Table 1: Soil pH on Three Sampled Farms to Depth of 36 inches.



Table 2 shows the result of analysis for Total Soil Carbon from each of the three farms. The AHSD farm had total soil carbon measurements ranging from 4.67% in the top 6 inches to 1.42% at 36 inches. The CG-Good farm had a range in Total Soil Carbon from 1.64% in the top 6 inches to 0.41% at 36 inches. The CG-Poor farm had Total Soil Carbon measurements ranging from 1.36% in the top 6 inches to 0.34% at 36 inches. So, on the AHSD farm, Total Soil Carbon was significantly higher all the way down to the three foot depth. On the CG-Good and CG-Poor farms, Total Soil Carbon dropped sharply with samples taken at deeper depths.

Table 2: Total Soil Carbon to Depth of 36 Inches.



Table 3 shows the soil organic matter (SOM) results from the three farms. On the AHSD farm, SOM was 4.26% in the top 6 inches and 1.98% at 36 inches. As stated earlier, the AHSD farm started 5 years ago with an average of just 1.5% SOM in the top 6 inches, so the SOM has increased almost 3 times within a 5 year period. On the CG-Good farm, SOM ranged from 3.28% in the top 6 inches to 0.82% at 36 inches. On the CG-Poor farm, SOM ranged from 2.72% in the top 6 inches to 0.68% at 36 inches.

Table 3: Soil Organic Matter to a Depth of 36 Inches.



Table 4 shows the Carbon Assessment per acre in terms of KG of carbon per square meter, toms of carbon per acre, and tons of CO2 equivalent per acre. The AHSD farm had a total of 51.41 tons of carbon per acre, whereas the CG-Good had 28.71 tons/acre and the CG-Poor farm had 22.16 tons/acre. In tons of CO2 Equivalent per acre, the AHSD farm had 188.13 tons/acre while the CG-Good and the CG-Poor farms had 105.07 and 81.09 tons per acre, respectively.

Table 4: Carbon Assessment Per Acre Down to 36 inches.



In summary, results show that with just 5 years of AHSD grazing, significant results can be achieved in terms of building soil organic matter, soil carbon, and overall soil health. Even with what are considered (by traditional standards) good grazing practices, AHSD grazing appears to yield results and benefits that far exceed more relaxed grazing rotations. The ability to build such significant differences within a relatively short period of time make AHSD grazing an attractive tool for land improvement and remediation.