Submitted to: Meeting Abstract
Publication Type: Proceedings
Publication Acceptance Date: November 20, 2002
Publication Date: November 20, 2002
Citation: REEDER, S.J. RESPONSE OF ORGANIC AND INORGANIC CARBON AND NITROGEN STOCKS TO LONG-TERM GRAZING MANAGEMENT OF THE SHORTGRASS STEPPE. MEETING ABSTRACT. 2002. Technical Abstract: We investigated the influence of long-term (56 years) grazing on organic and inorganic carbon (C) and nitrogen (N) contents of the plant-soil system (to 90 cm depth) in shortgrass steppe of northeastern Colorado. Grazing treatments included continuous season-long (May - October) grazing by yearling heifers at heavy (60-75% utilization) and light (20-35% utilization) stocking rates, and non-grazed exclosures. The heavy stocking rate resulted in a plant community that was dominated (75% of biomass production) by the C4 grass blue grama (Bouteloua gracilis,), whereas excluding livestock grazing increased the production of C3 grasses and prickly pear cactus (Opuntia polycantha). Soil organic C (SOC) and organic N were not significantly different between the light grazing and non-grazed treatments, whereas the heavy grazing treatment was 7.5 Mg ha-1 higher in SOC than the non-grazed treatment. Lower ratios of net mineralized N to total organic N in both grazed compared to non-grazed treatments suggest that long-term grazing decreased the readily mineralizable fraction of soil organic matter. Heavy grazing affected soil inorganic C (SIC) more than the SOC. The heavy grazing treatment was 23.8 Mg ha-1 higher in total soil C (0-90 cm) than the non-grazed treatment, with 68% (16.3 Mg ha-1) attributable to higher SIC, and 32% (7.5 Mg ha-1) to higher SOC. These results emphasize the importance in semi-arid and arid ecosystems of including inorganic C in assessments of the mass and distribution of plant-soil C and in evaluations of the impacts of grazing management on C sequestration.