Print PageThe initial transition to biofuel cropping systems is accompanied by shifts in plant residue inputs that may influence decomposition dynamics and long-term soil carbon storage. However, the fate of these new carbon inputs in biofuel cropping systems is unknown since distinct litter chemistries, microbial communities and edaphic characteristics under various conversion scenarios are likely to moderate decomposition rates. This is further complicated by differences in land-use histories, which likely maintain biotic and abiotic legacies that influence decomposition following biofuel crop conversion. We initiated a litter decomposition experiment in the spring, 2010 in southwest Michigan to assess how decomposition rates of various biofuel litter inputs are mediated by initial litter chemistry, biotic and abiotic land-use legacies, and extant biofuel crop species. Switchgrass, mixed prairie, and corn were each planted in fields that were previously under either continuous corn cultivation or managed prairie for over 20 years. Litterbags of corn, switchgrass, and prairie-grass were deployed at each field site for serial destructive sampling over the course of a 2-year period. For each of 4 sampling times in the first season, soil and litterbags were analyzed for extracellular enzyme activity, microbial biomass, and mass of litter remaining.
Results/Conclusions
An initial assessment of enzyme activity and microbial biomass results indicate that land-use history and crop species were strong moderators of decomposition dynamics. Sites that were historically corn had lower enzyme activity and microbial biomass in both litter and soil compared to the historical grasslands. Further research is needed to identify whether differences between sites are driven more by the biotic legacies of historical management practices or edaphic soil properties such as texture. Among current crops, corn had the highest enzyme activities irrespective of site history. The effect of litter species on litter decomposition dynamics was not as strong or consistent as the effects of site or current cropping system. While prairie litter resulted in higher enzyme activity compared to corn and switchgrass litter, microbial biomass was greater in corn litter. Differences in enzyme activity and microbial biomass across crop species may be partly explained by the fact that switchgrass and prairie-grass fields were in their first year of establishment with low plant biomass compared to the corn fields. Our results suggest that during the preliminary stages of transition into biofuel cropping systems, crop species and site characteristics, including but not limited to historical land-use practices, should be considered when assessing soil carbon decomposition dynamics.
