Submitted to: Soil and Water Conservation Society Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 12/28/2006
Publication Date: 7/26/2006
Citation: Schuman, G.E., Lachlan, I.J., Derner, J.D., Stahl, P.D., Vance, G.F. 2006. Dynamics of long-term organic carbon storage in northern mixed-grass rangelands. In: Soil and Water Conservation Society Proceedings "Rocky Mtn Rendezvous II. p. 58-59. Keystone, CO, July 22-26, 2006.
Technical Abstract: Soil organic carbon (SOC) dynamics were assessed in replicated pastures of northern mixed-grass prairie that were continuous season-long grazed at light and heavy intensities or excluded from grazing after 10 and 20 years following grazing initiation (1982). Grazing at light and heavy intensity increased SOC to 60 cm after 10 years compared to no grazing. However, significant SOC was lost from the heavy grazing treatment during the next 10 years compared to light or no grazing. Previously stored SOC mass decreased by 30% in the heavy grazing treatment indicating that this grazing intensity had significant negative impacts on C cycling during the extended (2000-2003) drought period that occurred during the second 10 year period. This loss in C was supported by carbon dioxide (CO2) flux measurements that showed lower net CO2 assimilation under heavy grazing at a nearby shortgrass praire site. Heavy grazing shifted the plant community from predominately C3 grasses in the light and no grazing pastures to one dominated by C4 grasses, primarily blue grama. This warm-season species produces significantly less aboveground biomass and has a root system considerably shallower than C3 grasses. This research has demonstrated that proper grazing management can enhance SOC storage on northern mixed-grass prairie, whereas heavy grazing shifts the plant community to a vegetation state that is prone to losses of carbon during extreme climatic events. It remains to be determined, however, if this plant community has the potential to regain lost carbon during drought recovery years.