Title: Assessment of grassland management methods for balancing soil C sequestration with native grass biomass production Authors
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: January 19, 2010
Publication Date: July 18, 2010
Citation: Riedell, W.E., Osborne, S.L., Schumacher, T.E., Pikul Jr, J.L. 2010. Assessment of grassland management methods for balancing soil C sequestration with native grass biomass production. In: Proceedings Soil and Water Conservation Society 65th Annual Meeting, p.48. July 18-21, 2010. St. Louis, MO. Interpretive Summary: Grassland management techniques that affect forage production may also potentially affect soil organic carbon. Despite the importance of grassland management in maintaining productivity, relatively little information is available that quantitatively describes the effects of long-term management options on soil organic carbon. More effective management of grassland that has been converted from cultivated cropland will require a better understanding of the effects of fire and mowing on grassland biomass productivity and soil characteristics. There currently are 1.2 million hectares in South Dakota and Minnesota enrolled in Conservation Reserve Program. This region is also slated to provide cellulosic feedstocks for biofuels. Thus, scientific inquiry on management options for native grass mixtures planted into previously-cultivated cropland and the effects these management options have on soil organic carbon are important priorities. This study was conducted to measure the effects of grass canopy management treatment (burning in early spring, mowing and residue removal in mid- to late-summer, or no management) and native grass species composition (mixtures of cool season species, warm season species, or combined cool and warm season species) on soil and grass canopy carbon and nitrogen in cropland recently converted to grassland. This experiment reveals that grassland management treatments (annual spring burning, late summer haying, and no management) and grass species composition treatments (cool season, warm season, and cool+warm season mixtures) had important independent and interactive effects on biomass production as well as on C grass canopies and soil in previously row-cropped plots that were converted to perennial native grasses. While soil C accumulation appeared to be independent of the grass species composition of the plots, methods used to manage grass canopies had significant effect upon the rate of soil C accumulation during the first 9 years after grass plot establishment. In this context, the choice of grassland management methods when converting cropland to grassland should be based upon consideration of grass biomass utilization as well as soil C accumulation
Technical Abstract: Grassland management (annual spring burning, late summer haying, and no management) and grass species composition (cool season, warm season, and cool+warm season mixtures) had important independent and interactive effects on biomass production and soil C sequestration in soil previously row-cropped then converted to perennial native grasses. During the last 2 yr of the 9-yr experiment, shoot biomass from the burn (2730 kg ha-1) and mow (3421 kg ha-1) canopy management treatments were less than no management (4655 kg ha-1). Burn treatment biomass contained 1189 kg C ha-1, mow contained 1433 kg C ha-1, while no management contained 2014 kg C ha-1. Soil C sequestration was independent of grass species composition. Soil C sequestration rates, which increased in strong linear fashion after initial grass establishment, were 387, 503, and 711 kg C ha-1 yr-1 for burn, mow, and no management treatments, respectively. Thus, the choice of grassland management methods when converting cropland to grassland should be based upon consideration of grass biomass utilization as well as soil C sequestration. No canopy management would be recommended if the primary goal was to increase soil C sequestration. If the goal was to use harvested grass biomass as a feedstock, an annual late-summer haying treatment could be recommended with the understanding that this would be less efficient at increasing the soil C sequestration rate. A spring burn treatment would be recommended if the goals were restoring or maintaining dominance of C4 warm season grasses in mixed grasslands while only slowly increasing soil C sequestration.