Soil microbial activity under different grass species: Underground impacts of biofuel cropping

Microbial and plant communities interact to determine local nutrient cycling rates. As lands are converted to bioenergy crops, including corn and cellulosic grasses, focus has been on changes in soil carbon sequestration. Little attention has been paid to impacts of such land conversion on the activity of belowground communities. We hypothesized that in addition to affecting soil organic carbon (SOC), monoculture species establishments have appreciable effects on microbial community activity, as evidenced by N and C mineralization rates. We compared soil microbial response in soils under long-term corn (Zea mays L.) production to soils under 10-year old monocultures of four warm-season perennial grasses (switchgrass (Panicum virgatum L.), coastal bermudagrass [Cynodon dactylon (L) Pers.], sideoats grama [Bouteloua curtipendula (Michaux) Torrey] and buffalo grass [Bouteloua dactyloides (Nutt.) Columbus]). All assayed perennial systems had higher SOC and water extractable organic C (WEOC) than the annual corn system. However, of all the perennial grasses, switchgrass soils had the lowest SOC and WEOC values, and the lowest 28-day C and N mineralization rates. This study indicates that soil microbial activities under buffalograss stands are more active than those under sideoats grama, switchgrass, coastal bermudagrass, or corn.