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Title: STOCKING RATE EFFECT ON SOIL CARBON AND NITROGEN IN DEGRADED SOILS

Author
item Potter, Kenneth
item Daniel, John
item ALTON, W - SAMUEL R NOBLE FOUNDATION
item Torbert, Henry - Allen

Submitted to: Journal of Soil and Water Conservation Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/13/2000
Publication Date: 5/20/2001
Citation: Potter, K.N., Daniel, J.A., Altom, W., Torbert, H.A. Stocking rate effect on soil carbon and nitrogen in degraded soils. Journal of Soil and Water Conservation Society. 2001. v. 56. p. 233-236.

Interpretive Summary: Concern over global change resulting from greenhouse gasses in the atmosphere has increased in recent years. Atmospheric carbon dioxide is a major factor, having doubled in the last century largely from burning fossil fuels, but also from losses of carbon from soils. Recent attempts have been made to determine if, with proper management, agricultural contributions to atmospheric CO2 could be reduced or if agriculture may even serve as a sink for carbon. Grazinglands comprise about 40 percent of the United States. This enormous amount of land provides the potential, with the proper management, to sequester carbon in the soil that may otherwise be in the atmosphere. We conducted a study to determine the effect of cattle stocking rate on the carbon content of two contrasting soils in southern Oklahoma. After ten years of varying stocking rates, the lighter textured soil contained greater amounts of carbon with grazing than without grazing. The heavier textured soil, in contrast, had less carbon in the soil with grazing than without grazing. Soil properties should be considered in assessing the potential of grazinglands to sequester carbon, especially if payments for carbon storage are initiated.

Technical Abstract: Grazinglands, which comprise about 40 percent of the United States, have been proposed as possible sinks for carbon to aid in reducing agriculture's impact on global climate change. The purpose of this study was to determine the impact of stocking rate on soil carbon and nitrogen content resulting from 10 years continuous management by the Noble Foundation near Marietta, Oklahoma. Treatments consisted of rotational grazing with four stocking rate levels: light, moderate, heavy and non- grazed. Two soils, a Durant loam (Udertic Argiustolls) and a Teller silt loam (Udic Argiustolls) located within common paddocks were sampled to 60 cm and the organic carbon and total nitrogen content determined for selected depth increments. Total organic carbon mass in the surface 60 cm of the Durant soil, averaged across stocking rate treatments, was 95.7 t ha**-1 compared to 56.7 t ha**-1 in the Teller soil. The soils responded differently to stocking rate. In the heavier textured Durant soil, organic carbon decreased as stocking rate increased, with the non- grazed exclosure having the greatest amount of soil carbon. In contrast, the lighter textured Teller soil had similar amounts of organic carbon in the soil profile with all stocking rates, but less without grazing. Total soil nitrogen followed similar trends as the soil organic carbon. Soil properties should be considered to accurately assess the potential of grazinglands to sequester carbon.