Miscanthus x giganteus (miscanthus), a perennial rhizomatous grass with a C4 photosynthetic pathway, has the potential to reduce greenhouse gas (GHG) emissions as it sequesters carbon into soil. Although fertilizer application to miscanthus sometimes increases yield, especially after five growing seasons, unintended impacts of GHG emissions resulting from the application of fertilizer has also been documented. This study evaluated the effects of four different fertilization treatments (digestate from a biodigester, synthetic nitrogen fertilizer, hydrochar from hydrothermal carbonization of digestate, and a control) on soil GHG emissions of an established miscanthus stand grown on abandoned agricultural land. Four replicate 10x10 m2 miscanthus plots at two sites were divided into 3x3 m2 subplots. Collars were placed in random locations in every subplot in site A and B to represent the four treatments (digestate, nitrogen fertilizer, hydrochar and control). Soil greenhouse gas fluxes were sampled in all treatments using the static chamber methodology. The samples were analyzed with a gas chromatograph to determine the concentration of each CH4, CO2, and N2O. Aboveground biomass yield was also measured.
Results/Conclusions
There were no significant differences in biomass yield among the four treatments. Average biomass yield varied from 20.2 Mg/ha to 23.5 Mg/ha between the four treatments. Even though there was no significant difference between CO2 fluxes in the four treatments over the growing season, the hydrochar treatment reduced CO2 fluxes by up to 34% compared to the control treatment. Applying digestate to miscanthus resulted in a CH4 source while nitrogen and hydrochar treatments produced CH4 sinks. While fertilizer treatments had no significant effect on N2O fluxes, soil differences between sites affected N2O fluxes significantly (p-value=0.006). The control and digestate treatments acted as sources of N2O fluxes while the hydrochar and nitrogen treatments were sinks of N2O fluxes. Overall, fertilization did not improve biomass yield but the hydrochar treatment appeared to be a better alternative at reducing GHG fluxes when compared to the other treatments.