Response of Organic and Inorganic Carbon and Nitrogen to Long-Term Grazing of the Shortgrass Steppe

• Published in: Environmental management (New York) Vol. 33; no. 4; pp. 485 - 495
• Main Authors: Reeder, J.D, Schuman, G.E, Morgan, J.A, Lecain, D.R
• Format: Journal Article
• Language: English
• Published: United States Springer Nature B.V 01-04-2004
• Subjects: Animals; Biomass; Bouteloua gracilis; Cactaceae; carbon; Carbon - analysis; carbon sequestration; Cattle; Colorado; Desert Climate; Ecosystem; Environmental management; Feeding Behavior; Grasses; grassland soils; grasslands; Grazing; heifers; Herbivores; Inorganic carbon; Livestock; long term experiments; Nitrogen; Nitrogen - analysis; Opuntia; Opuntia polyacantha; Opuntia polycantha; Organic Chemicals; Organic matter; Pasture management; Plant communities; Plants, Edible; Poaceae; sandy loam soils; Soil; Soil organic matter; soil-plant interactions; Soils; Steppes; stocking rate; Great Plains region; Colorado; USA, Colorado
• ISSN: 1432-1009; 0364-152X; 1432-1009
• DOI: 10.1007/s00267-003-9106-5

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 nongrazed 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 nongrazed treatments, whereas the heavy grazing treatment was 7.5 Mg ha-1 higher in SOC than the nongrazed treatment. Lower ratios of net mineralized N to total organic N in both grazed compared to nongrazed 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 nongrazed 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 semiarid 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.