Influence of switchgrass management on soil microbial biomass and fatty acid methyl ester content in soil

Abstract

Switchgrass is a fairly new source of commercial biofuel feedstock. Its production can potentially preserve soil health and microbial functions in ecosystems. There is an increasing demand for large scale biomass production, making the relationship between crop production and soil health more important. Microbial biomass abundance and ratios can be an indicator of broader soil health, as they provide a measure of the living portion of soil organic matter. The goal of this study was to evaluate relationships between switchgrass production and the soil microbial community. Composite soil samples from three established switchgrass plots and adjacent uncultivated mixed grass plots were used for microbial biomass analysis, as well as fatty acid methyl ester (FAME) analysis. Compared to the adjacent unmanaged soils, switchgrass managed soils had a significantly lower microbial abundance indicated by the content of microbial biomass carbon, nitrogen and phosphorous, as well as total FAME. Microbial composition and community structure was also altered by switchgrass management. Data showed significantly lower microbial biomass C/N ratios and changes in the concentration of FAME indicator groups in the switchgrass managed soils than the adjacent unmanaged ones. More specifically, switchgrass management led to reduction in the abundance of gram positive bacteria, gram negative bacteria, actinobacteria, and saprophytic fungi, but promoted the growth of arbuscular mycorrhizal fungi.