ARS | Publication request: LONG-TERM GRAZING INCREASES SOIL INORGANIC CARBON IN A SHORT-GRASS STEPPE

Submitted to: Ecological Society of America Proceedings
Publication Type: Proceedings
Publication Acceptance Date: February 29, 2004
Publication Date: August 1, 2004
Citation: Reeder, S.J., Larson, M., Williams, D.G., Morgan, J.A., Mosier, A.R. 2004. Long-term grazing increases soil inorganic carbon in a short-grass steppe. Ecological Society of America Proceedings. Paper No. 97-9.

Technical Abstract: We investigated the influence of long-term (56 years) livestock grazing on the inorganic carbon (C) content of the plant-soil system (to 90 cm depth) in the short-grass steppe of northeastern Colorado. Grazing treatments included continuous season-long (May-October) grazing at heavy (60-70% utilization) and light 20-35% utilization) stocking rates, and non-grazed exclosures within each grazing treatment. The heavy stocking rate resulted in a plant community dominated (75% of biomass production) by the C4 grass Bouteloua gracilis, whereas 47% of biomass production in grazing exclosures was from cool-season grasses, forbs, and sub-shrubs utilizing the C3 photosynthetic pathway. Mass of soil inorganic C (SIC) was slightly but significantly higher at 0-60 cm depth in the light grazing treatment (0.8 Mg C ha-1) compared to that in the non-grazed exclosure (1.5 Mg C ha-1), whereas mass of SIC was higher at 30-90 cm depth in the heavy grazing treatment (39.9 MG C ha-1) compared to its exclosure (25.3 Mg C ha-1). We hypothesized that the large increase in SIC with heavy grazing was due to a combination of newly sequestered SIC and redistributed parent material SIC from deeper in the soil profile. Stable C isotopes of SIC in the soil profile indicated a slight increase in C4 respiration signal in carbonates in the heavily grazed treatment compared to the non-grazed exclosure at the 45-60 cm depth, below the primary rooting zone of B. gracilis. This suggests that a portion of the SIC in the heavily grazed treatment is newly fixed CO2 (i.e. within the last 50 years and associated with the grazing-induced shift in plant community). Inorganic C has been neglected in studies of C distribution and dynamics in native and agroecosystems. Our results indicate the importance in semi-arid and arid ecosystems of including inorganic C in these assessments.