Enhancing the soil organic matter pool through biomass incorporation

A study was installed in the Upper Coastal Plain of South Carolina, USA that sought to examine the impact of incorporating downed slash materials into subsoil layers on soil chemical and physical properties as compared with the effect of slash materials left on the soil surface. Baseline levels of slash were estimated by establishing transects within harvested stands and estimating the quantity of down wood and stumps. An equivalent quantity of biomass and two times the baseline levels were incorporated into subsurface soil layers by a CMI RS 500B reclaimer/stabilizer. Two sites were examined which differed in soil textural composition: sandy vs. clay. Site differences had no impact on machine productivity and machine costs were estimated at $US 521 ha−1 and $US 633 ha−1 on the ‘sandy’ and ‘clay’ sites, respectively. The feasibility of the CMI for biomass incorporation is low due to high unit area costs but increased machine productivity would reduce costs and improve its potential. Biomass incorporation improved carbon and nutrient content of each site, especially on the sandy site. Slash levels had an impact on nutrient content but the differences were not statistically significant. For the sandy site, improvements in soil physical properties were evident in response to incorporation and machine planting operations. Bulk density and soil strength were reduced in response to biomass incorporation and tillage to levels that would not limit root production. The differences in soil physical response between incorporated treatments were minimal and not statistically significant.