Grazing animals on site increase the variability in our data.

In these 2 graphs, sites were divided into 2 groups: 35 sites with grazing animals and 21 sites without grazing animals on-site at some point during the year. We then graphed each site's 3-years'-worth of soil organic matter data by connecting the 3 years of data from each site with a vertical black line. When the 3-year variability of soil organic matter data is compared between sites with and without grazing animals, sites with grazing animals clearly show more variability in SOM data, year to year.
Grazing animals deposit manure and urine in small exact locations.  If that exact location is sampled one year and then not the next, that could change lab results significantly.