Carbon dynamics subsequent to establishment of switchgrass

It is necessary to develop new, dean and renewable biofuels to mitigate the greenhouse effect and reduce dependence on nonrenewable fossil fuels. Swit chgrass (Panicum virgatum L.) has been chosen by the US Department of Energ y as its model herbaceous energy crop in the Southeast due to high yields, low production costs, economic benefits, and little competition from existi ng enterprises. However, knowledge of its influence on soil carbon (C) dyna mics is limited, as no systematic study of soil C dynamics in switchgrass c ulture has been conducted. Our objective was to determine C dynamics subseq uent to switchgrass establishment and the impact of cultural practices (row spacing and harvest frequency) on C biogeochemical characteristics in a sa ndy loam soil (Typic Paleudult) and a clay loam soil (Typic Hapludult). Res ults indicated that soil C characteristics changed over time after switchgr ass establishment. Carbon mineralization, microbial biomass C, C turnover, and % microbial biomass C in organic C was generally higher approximately 2 years after switchgrass planting than after its initial establishment in a sandy loam soil. Specifically, C mineralization increased by 112 and 254% at depths of 0-15 cm and 15-30 cm, respectively; microbial biomass C increa sed by 168% in the top 15 cm of soil; and C turnover increased by 116 and 2 55% at 0-15 cm and 15-30 cm, respectively. Microbial biomass comprised 0.76 +/- 0.09% and 0.75 +/- 0.19% of soil organic C in 0-15 cm and 15-30 cm dep ths, respectively, of sandy loam soil, while it made up 1.37 +/- 0.22% and 1.11 +/- 0.19% of soil organic C in the same soil depths in day loam soil. Harvesting once resulted in more C turnover than harvesting twice in the sa ndy loam soil. Linear regression between soil C characteristics and switchg rass root weight, root C, and root nitrogen (N) returned to soil support th e conclusion that soil C accumulation is positively related to root input. It appears that switchgrass establishment may have dual benefits as a sourc e of renewable energy and as a means of improving soil quality. However, lo nger periods of study will be required to elucidate substantial gains in so il quality owing to switchgrass culture. (C) 2000 Elsevier Science Ltd. All rights reserved.