Impact of Amendment with Hog, Cattle Manure, and Biochar on N2O, CO2, and CH4 Fluxes of Two Contrasting Temperate Prairie Agricultural Soils

Liquid hog manure (LHM) and solid cattle manure (SCM) are valuable soil amendments for the nutrients and organic matter they augment. However, desire to mitigate the N2O, CO2, and CH4 fluxes attendant with their use has led to the question of whether biochar co-applied with LHM and SCM could mitigate these greenhouse gas fluxes. A split-plot design was used at two agricultural field sites with contrasting soil types (Brown Chernozem and Black Vertisol) in Saskatchewan, Canada, to assess the effect of LHM and SCM (100 kg N ha(-1)), alone and in combination with two different biochars applied at 8 Mg C ha(-1); produced using either slow or fast pyrolysis of willow (Salix spp.) feedstock. Intact cores were collected from the plots and the N2O, CO2, and CH4 fluxes were measured during a 6-week (42 days) lab incubation. The impact of manure amendment on greenhouse gas fluxes, was more apparent with LHM than SCM; reflecting higher inorganic N content, narrower C:N, and more easily mineralizable carbon in LHM. Co-applying biochar with the manure sources reduced the manure-related N2O emissions 31.5 to 43.1% and increased CH4 consumption 94.1% to 2.1 x compared with manure alone. Regardless of soil type, neither biochar co-applied with the manures affected the net CO2 fluxes compared with manure alone. The N2O emissions were principally influenced by the impact of biochar addition on NO3-N supply and pH, while the net CO2 fluxes were controlled by the opposing effects of heterotrophic (i.e., CO2 production) and postulated autotrophic (i.e., CO2 consumption) respiration. The CH4 consumption was related to the NH4-N supply and its influence on autotrophic methanotrophy.