Carbon controls on nitrous oxide production with changes in substrate availability in a North American Grassland
Tiemann, L.K., and S.A. Billings. 2008. Soil Science 173:332-341
Abstract
Fluxes of nitrous oxide (N2O) are governed by the availability of substrate nitrogen (N), soil moisture, and soil organic carbon (SOC) concentration. Grassland management techniques such as fertilization and haying can influence both SOC and soil N transformations. In mesic grasslands, where SOC can be high compared with drier regions, it is unclear to what extent heterotrophic denitrifiers will respond to such
management practices. Biomass removal via haying can reduce SOC, whereas fertilization decreases C:N ratios of plant residues, which can decrease or increase heterotrophic microbial activity, respectively. We experimentally manipulated haying and fertilization regimens on a grassland in northeastern Kansas and measured resulting inorganic N availability, field fluxes of N2O and potential denitrification, and litter
C:N ratios to assess how these management practices may influence soil N2O evolution. We observed N2O fluxes that were an order of magnitude larger than those reported in drier grassland systems with lower SOC. The largest N2O fluxes observed were in fertilized and fertilized/hayed plots, immediately after precipitation events. Haying periodically mitigated N2O fluxes. Denitrification enzyme activity was lower in hayed plots than unhayed plots, and greater with glucose-C additions, indicating that the C substrate in these soils is an important driver of denitrification. The N2O fluxes that represented at least 0.1% of available inorganic N exhibited a weak negative relationship with C:N ratios of litter in fertilized/hayed plots, suggesting that the lower C:N ratios associated the shift to C3 plants with fertilization may promote soil N2O production, in addition to SOC and inorganic N availability.
Key Words
Grassland; N2O; fertilization; haying; soil organic carbon
