PRS Publications

Impact of amendment with hog, cattle manure, and biochar on N₂O, CO₂, and CH₄ fluxes of two contrasting temperate prairie agricultural soils

Hangs, R. D. and J. Schoenau. 2023.

Abstract

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 associated 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 and Black) 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 six-week lab incubation. The cumulative N₂O emissions (37.9-1956.8 mg m^-2 ), net CO₂ fluxes (665.2-1233.2 g m^-2 ), and CH₄ consumption (28.3-90.0 mg m^-2 ) were consistent with previously reported Canadian temperate agricultural soils, with and without LHM, SCM, or biochar addition. 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. Overall, 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× compared with manure alone. Regardless of soil type, neither of the biochars 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 autotrophic (i.e., CO₂ consumption) respiration. The CH₄ consumption was related to the NH₄ -N supply and its influence on autotrophic methanotrophy. Co-application of biochar along with manure, particularly the combination of slow pyrolysis biochar and LHM, decreased N₂O emissions and increased CH₄ consumption in these young temperate prairie soils; presumably, through enhanced abiotic sorption and biotic N immobilization, in addition to promoting greater methanotrophic activity.