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Chemistry and Microbial Functional Diversity Differences in Biofuel Crop and Grassland Soils in Multiple Geographies

Watrud, Lidia S., Reichman, Jay R., Bollman, Michael A., Smith, Bonnie M., Lee, E. Henry, Jastrow, Julie D., Casler, Michael D., Collins, Harold P., Fransen, Steven, Mitchell, Robert B., Owens, Vance N., Bean, Brent, Rooney, William L., Tyler, Donald D., King, George A.
BioEnergy research 2013 v.6 no.2 pp. 601
Geographical Locations, sustainable agriculture, soil sampling, soil chemistry, microbial biomass, grasslands, grassland soils, genes, functional diversity, energy crops, ecosystem services, correlation, chemistry, Sorghum bicolor, Panicum virgatum, agricultural soils, copper, genetic variation, nitrates, soil ecology, soil microorganisms, species diversity, sulfates
We obtained soil samples from geographically diverse switchgrass (Panicum virgatum L.) and sorghum (Sorghum bicolor L.) crop sites and from nearby reference grasslands and compared their edaphic properties, microbial gene diversity and abundance, and active microbial biomass content. We hypothesized that soils under switchgrass, a perennial, would be more similar to reference grassland soils than sorghum, an annual crop. Sorghum crop soils had significantly higher NO₃ ⁻ -N, NH₄ ⁺ -N, SO₄ ²⁻ -S, and Cu levels than grassland soils. In contrast, few significant differences in soil chemistry were observed between switchgrass crop and grassland soils. Active bacterial biomass was significantly lower in sorghum soils than switchgrass soils. Using GeoChip 4.0 functional gene arrays, we observed that microbial gene diversity was significantly lower in sorghum soils than grassland soils. Gene diversity at sorghum locations was negatively correlated with NO₃ ⁻ -N, NH₄ ⁺ -N, and SO₄ ²⁻ -S in C and N cycling microbial gene categories. Microbial gene diversity at switchgrass sites varied among geographic locations, but crop and grassland sites tended to be similar. Microbial gene abundance did not differ between sorghum crop and grassland soils, but was generally lower in switchgrass crop soils compared to grassland soils. Our results suggest that switchgrass has fewer adverse impacts on microbial soil ecosystem services than cultivation of an annual biofuel crop such as sorghum. Multi-year, multi-disciplinary regional studies comparing these and additional annual and perennial biofuel crop and grassland soils are recommended to help define sustainable crop production and soil ecosystem service practices.