Root Inputs Drive Carbon Sequestration Differences in Corn and Prairie.

Corn and prairie are two potential biofuel feedstocks that are being compared for energy potential and environmental performance.  Included in the evaluation of environmental performance is the potential for the systems to sequester carbon (C).  It is known that carbon sequestration is highly dependent upon C input by roots. Measurements of root accrual, distribution, and recalcitrance were made in corn-based cropping systems and prairie-based systems that were either fertilized with 84 kg N ha-1 or not fertilized.  Annual root sampling down to 1 m showed unfertilized prairie systems accrued the greatest amount of root biomass over three years (9 Mg ha-1) while fertilized prairie had less root biomass (3.2 Mg ha-1) and corn had the least amount of root biomass (0.90 Mg ha-1).  Most root biomass in the prairies was distributed in the top 15 cm, but prairie root biomass still exceeded corn root biomass at 1 m depth.  Accrued unfertilized prairie roots had the greatest C:N ratios, ranging from 38 to 89 across years and depths, while fertilized prairie had lower C:N ratios (28-52) and corn had the lowest C:N ratios (20-25).  These data show that prairie roots, especially when unfertilized, are likely to contribute to a higher potential of C sequestration than corn because they provide higher inputs of C that is less available for mineralization.  Focusing on root biomass and root characteristics may be a good approach to comparing C sequestration potentials in different systems.