Submitted to: Soil Science Society of America Special Publication Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 6/21/2007
Publication Date: 2/1/2009
Citation: Schuman, G.E., Ingram, L.J., Stahl, P.D., Derner, J.D., Vance, G.F., Morgan, J.A. 2009. Influence of Management on Soil Organic Carbon Dynamics in Northern Mixed-Grass Rangeland. In: Soil Carbon Sequestration and the Greenhouse Effect, 2nd Ed., SSSA Special Publication 57. ASA-CSSA-SSSA, Madison, WI. Book Chapter. Interpretive Summary:
Technical Abstract: Grazing rangelands can influence plant community structure, soil chemical and physical properties, and the distribution and cycling of nutrients within the plant-soil system. Studies initiated in 1982 at the High Plains Grasslands Research Station near Cheyenne, Wyoming, have shown that after 12 years of season-long grazing, the total C mass of the belowground plant-soil (0-60 cm) system was not affected when compare to a non-grazed treatment. However, significant increases in the mass of C in the primary root zone (0-30 cm) of the soil were evident in the grazed treatments. Carbon dioxide exchange rates (CER), as measured by a gas-exchange chamber, indicated that (CER) was as much as 2 times greater from mid-April through the end of June for the grazed compared to non-grazed treatment. This increase in CER was most closely related to a green vegetation index, which indicated earlier spring green-up in grazed pastures. We hypothesize that grazing removed and/or prevented the accumulation of dead plant material, and reduced litter, thereby resulting in a warmer soil and enhanced light penetration and growth of green shoots in the spring. However, when sampled after 21 years, which included 7 years of below normal precipitation during the last 10 years, significant soil organic C was lost from the heavily grazed treatment. In 2003, soil organic C and N contents were significantly higher in continuously light grazed sites than continuously heavy grazed and exclosure sites. In addition, soil lignin contents within exclosures suggested lower rates of decomposition than grazing treatments, with the lignins in humic substances extracted from the grazed sites exhibiting greater degradation. These data indicate that grazing can significantly affect C balance and composition of rangeland ecosystems, with grazing at proper stocking rates enhancing soil C and the potential for soil C-sequestration.