Developing a Pasture Soil Carbon Assessment Method For Farms Adding Multi-Species Grazing.

A group of cooperating WV farmers added sheep to their cattle operations from 2010 to 2012. This multi–species grazing activity was evaluated for its suitability as a conservation practice. Funding for this project was provided by a USDA NRCS Conservation Innovation Grant program. The literature indicates that the addition of sheep to a cattle grazing system has a positive influence on pasture soils in the humid temperate Eastern USA. The effects include increased macro-nutrient cycling, increased buffering of soil pH, soil respiration values will increase along with populations of soil invertebrates such as earthworms and rotifers. These soil effects provide better season long balance in pasture forage growth, quality and the nutritional needs of co-grazing livestock. This added biological activity in the pasture soils and increased plant growth provides a potential method of increasing soil carbon if the multi-species grazing system is maintained.
Four of our cooperating farmers were provided a baseline soil carbon determination on a pasture field that had active multi-species grazing occurring as well as a non-grazed hay field for each farm. The hay field was chosen as a control, typically in West Virginia, harvest occurs twice a year and after second cutting the re-growth is underutilized. These permanent hay fields would have a less dynamic nutrient cycling process compared to the pasture fields and thus would tend toward a static soil carbon content over time. The pasture fields with the introduced co-grazing practice would have a greater ability over time to sequester carbon.
Additionally, two pasture fields were evaluated for soil carbon content on a farm that has had greater than 30 years of multi-species grazing and a pasture that has had greater than 30 years of cattle only. These two pasture fields were sampled to demonstrate the potential long term soil carbon assimilation potential with farms using multi-species grazing systems.
The soil sampling method that was used for this study was developed by NRCS for their “Rapid Assessment of U.S. Soil Carbon for Climate Change and Conservation Planning”. The total soil carbon determination from each pedon sample point was averaged to give a field carbon content. The soil carbon units are presented in metric tons of carbon per hectare. The mean carbon content for the long term multi-species pasture was 127 metric tons per hectare compared to the mean carbon content of the long term cattle grazing pasture having a carbon content of 95 tons per hectare. Baseline soil carbon content of cooperating farmers pasture field averaged 86 metric tons per hectare. The least significant difference is 50 tons per hectare. Data shows no significant difference at a (p = 0.1555). These pasture soils show a high variability of soil carbon content, both within fields and across the sampled fields.