Grassland gets another boost from new study
The science about grazing just keeps getting better.
Money spent on science in the global warming/climate change debate is actually providing some great material for grazing managers, says Alan Franzluebbers, an ecologist with the USDA Agricultural Research Service in Watkinsville, Ga.
“For producers, soil carbon sequestration is really about how you’re affecting your land and how your management choices can actually benefit your land,” Franzluebbers says.
He recently reviewed an extensive list of research projects on carbon sequestration in lands used for grazing, haying, cropping and forest throughout the Southeastern states. The area stretches north from eastern Texas to eastern Kansas, east to Kentucky and Virginia, and south to Florida.
Much of the research was Franzluebbers’ own. The good news is Franzluebbers found grazing nearly always builds soil organic carbon levels. Moderate grazing does so more than heavy grazing.
He and his colleague, John Stuedemann, measured only continuous stocking. They did not test planned rotation grazing, although such a project is now beginning at the ARS research station at El Reno, Okla.
Land-use comparisons indicated grassland stored about the same amount of carbon in soil as forest, and both grassland and forest stored more carbon than cropland in the “warm, humid climate” where the studies were concentrated.
This data helps defeat the argument of vegetarians/animal agriculture critics, and it also shows the potential for well-managed grazing to actually be self-elevating.
“For every 10 units of carbon you store in the soil, you also store about 1 unit of nitrogen,” Franzluebbers says.
Scientific study has remained fairly consistent on this point since the 1950s, he adds. Therefore, building soil organic matter, which stores carbon in the soil, also builds the amount of soil nitrogen. In turn, of course, that adds opportunity for expanded soil life, which helps increase nutrient cycling and the overall availability of most or all soil fertility.
Here are some of the findings from Franzluebbers’ study of the warm and humid grazing lands:
• Rate of soil carbon sequestration with grazed Kentucky 31 tall fescue was three times greater than with hayed coastal bermudagrass and two times greater than with grazed bermudagrass.
• After 15 years of management, grazed bermudagrass fields had 6,700 pounds per acre more soil carbon than neighboring hayed bermuda-grass fields.
• Ungrazed and unharvested forage stored a little more soil carbon over eight years than hayed forage, but much less than either heavily or moderately grazed forage.
• Under warm, humid conditions, accumulation of soil carbon appears to slow after about 20 years and may eventually reach saturation, meaning soil will not store any more carbon beyond what has already been “banked,” unless management improves further for the better.
• Fescue with heavy endophyte infestation stores more carbon but suppresses microbial activity in the soil.
• Type of fertilizer does not greatly affect the amount of carbon stored in the soil. However, since broiler litter is an organic source of nutrients with high carbon content, soil organic matter can be expected to increase further at a rate of 10% of the carbon content in broiler litter. For example, application of 3 tons of broiler litter per acre per year would contain about 900 pounds of carbon; therefore, soil carbon would increase by 90 pounds per acre per year (10% of 900 pounds).
• Overall, the data showed establishing perennial-grass pastures can sequester soil organic carbon at rates varying from 250 to 1,250 pounds per acre per year.
This article published in the MAY, 2010 edition of BEEF PRODUCER.