Soil carbon dioxide fluxes in established switchgrass land managed for biomass production

Abstract

Switchgrass ( Panicum virgatum L.) grown for biomass feedstock production has the potential to increase soil C sequestration, and soil CO 2 flux in grassland is an important component in the global C budget. The objectives of this study were to: (1) determine the effects of N fertilization and harvest frequency on soil CO 2 flux, soil microbial biomass carbon (SMBC), and potentially mineralizable carbon (PMC); and (2) evaluate the relationship of soil CO 2 flux with soil temperature, soil moisture, SMBC, and PMC. Two N rates (0 and 224 kg ha −1) were applied as NH 4NO 3 and cattle ( Bos Taurus L.) manure. Switchgrass was harvested every year at anthesis or alternate years at anthesis. The data were collected during growing season (May–October) 2001–2004 on switchgrass-dominated Conservation Reserve Program (CRP) land in east-central South Dakota, USA. Manure application increased soil CO 2 flux, SMBC, and PMC during the early portion of the growing season compared with the control, but NH 4NO 3 application did not affect soil CO 2 flux, SMBC, and PMC. However, seasonal variability of soil CO 2 flux was not related to SMBC and PMC. Estimated average soil CO 2 fluxes during the growing periods were 472, 488, and 706 g CO 2–C m −2 for control, NH 4NO 3–N, and manure-N plots, respectively. Switchgrass land with manure application emitted more CO 2, and approximately 45% of the C added with manure was respired to the atmosphere. Switchgrass harvested at anthesis decreased soil CO 2 flux during the latter part of the growing season, and flux was lower under every year harvest treatment than under alternate years harvest. Soil temperature was the most significant single variable to explain the variability in soil CO 2 flux. Soil water content was not a limiting factor in controlling seasonal CO 2 flux.