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United States Department of Agriculture

Agricultural Research Service

Title: Response of Organic and Inorganic Carbon and Nitrogen Stocks to Historic Grazing Management of the Shortgrass Steppe

Authors
item Reeder, S
item Schuman, Gerald
item Morgan, Jack
item LECAIN, DANIEL

Submitted to: Meeting Abstract
Publication Type: Proceedings
Publication Acceptance Date: January 20, 2003
Publication Date: January 10, 2003
Citation: REEDER, S.J., SCHUMAN, G.E., MORGAN, J.A., LECAIN, D.R. RESPONSE OF ORGANIC AND INORGANIC CARBON AND NITROGEN STOCKS TO HISTORIC GRAZING MANAGEMENT OF THE SHORTGRASS STEPPE. MEETING ABSTRACT. 2003.

Technical Abstract: We investigated the impact of 57 years of grazing management on the organic and inorganic carbon (C) and nitrogen (N) contents of the plant:soil system (to 90 cm) of shortgrass steppe at the Central Plains Experimental Range, Nunn CO. Grazing treatments included continuous season-long grazing by yearling heifers at heavy and light stocking rates, and non-grazed exclosures. The heavy stocking rate resulted in a plant community dominated by blue grama (Bouteloua gracilis, 75% of biomass production), whereas excluding livestock grazing increased the production of annual forbs and grasses. Grazing intensity did not affect the content or distribution of organic N in the soil profile, and had only a small effect on soil organic C (SOC), with 3.8 Mg ha-1 more SOC in the 15-30 cm depth of the soil profile under heavy grazing compared to light or no grazing. Although SOC was fairly resistant to change by grazing management, grazing intensity strongly influenced soil inorganic C (SIC) content. Total soil C was significantly higher (23.8 Mg ha-1) in the soil profile (0-90 cm) under long-term heavy grazing compared to long-term light grazing or exclusion of grazing, with 68% (16.3 Mg ha-1) attributed to an increase in IC, and 32% (7.5 Mg ha-1) due to an increase in OC. Future studies to evaluate stable C isotopic composition of SIC and SOC will help elucidate the sources of the increased SIC in the soil profile of the heavily grazed treatment. We hypothesize that the observed increase in SIC with heavy grazing is a combination of newly sequestered C and redistributed SIC from deeper in the soil profile.

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