Changes in Labile Fractions of Soil Organic Matter After Six Years of Corn Production for Cellulosic Ethanol.

Three physical fractions and one humic acid fraction of soil organic matter were extracted from a corn field outside Ames, IA, to determine how labile soil carbon pools changed after aboveground corn biomass had been removed for two and six years at three rates (0, 50, and 100%). In the surface 0-15 cm depth, masses of the light fraction and the 53-um particulate organic matter were greatest with least removal of corn biomass after six years, while no trend was evident after two years. In the 15-30 cm depth, rate of biomass removal had no effect on fractional masses in either year  The mobile humic acid (MHA) fraction attained its greatest mass with 50% biomass removal, especially in the lower soil depth.  This trend was stronger after six years than after two years. Visible light absorption and carbohydrate concentrations of the MHA did not indicate any effect of biomass removal on MHA composition. Soil N and organic C stocks were also greatest with 50% biomass removal.  Carbohydrates contributed to this C accumulation while showing little change in the balance of microbial to plant carbohydrates.  Trends in amino acid concentrations will be reported.