Livestock Increase Soil Organic Carbon in the Northern Great Plains

Managing grasslands to sequester carbon is of global importance, but effects of grazing on soil organic carbon (SOC) stocks remain uncertain. We quantified effects of livestock grazing (grazed or not for 9−26 yr) and soil texture on SOC stocks (kg × m−2) of 20 sites in a temperate grassland. We also quantified the effects of livestock grazing on SOC concentration and bulk density. Percent sand explained a considerable amount of the variation in SOC stock (r2 = 0.45 to 0.59). In addition, SOC stocks were 12% less in areas rested from livestock grazing (i.e., not grazed) than annually grazed. Soil carbon concentrations were also 10% less in rested than grazed areas. Bulk density was 2% less in areas rested from grazing, but bulk density was greater at sites with longer periods of rest. We also detected a grazing treatment and rest duration interaction, indicating that bulk density differences between grazing treatments tended to be greater at sites with longer periods of rest. Compared with no grazing, moderate grazing tended to increase SOC stocks and concentrations. Although compaction (i.e., increase in bulk density) is generally regarded as an indicator of declining soil health, minor compaction may help reduce mineralization of SOC and ultimately increase SOC stocks. We discuss methodological improvements needed for a next generation of grazing land experiments to better resolve how best to manage livestock and sequester carbon.