Grazing management effects on inorganic C storage in rangelands. Reeder, Jean^*,1, ¹ USDA-ARS, Fort Collins, CO, USA

ABSTRACT- Research has established that grazing management can affect soil C storage in pastures and rangelands. Studies to date have focused on the influence of management on soil organic C (SOC). Although soil inorganic C (SIC) is a large component of C stored in semi-arid and arid ecosystems, it has been virtually ignored with the assumption that SIC is relatively static and not influenced by grazing management. However, recent studies on a short-grass steppe indicate that grazing management can influence SIC more than SOC. In a fence-line comparison of long-term heavy grazing to long-term exclusion of livestock grazing, the profile (0-90 cm) of an Olney sandy loam soil was 7.5 Mg/ha higher in SOC and 16.8 Mg/ha higher in SIC with heavy grazing than where livestock grazing was excluded. The large difference in SIC in these adjacent soil profiles is the result either of a decrease in SIC where livestock grazing was excluded, or an increase in SIC with heavy grazing, or a combination of both. Preliminary assessment of the C isotopic signature of SIC in these soil profiles indicates that the source of the high SIC with heavy grazing is parent material carbonates rather than newly fixed SIC, and that the difference in SIC with grazing management is more likely the result of a decrease in SIC where exclusion of livestock grazing changed plant community composition and soil water dynamics, rather than the result of an increase in soil profile SIC with prolonged heavy grazing.

KEY WORDS: grazing management, inorganic C, C storage