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Abstract:
Bio-char, biomass that has been deliberately charred to slow its rate of decomposition, has been proposed
as an amendment with the potential to sequester carbon and improve certain soil properties. Slow
pyrolysis (temperature 500 C) and hydrothermal carbonization (low temperature, high pressure) are
two efficient methods to produce bio-char with high yield and are applicable to a broad range of
feedstocks. Chars made using slow pyrolysis (PC) and hydrothermal carbonization (HTC) of the same
feedstock material (corn, C4) differed in physical appearance, chemical properties and decomposition
behavior. We added these HTC and PC chars as amendments to three soils with C3-derived organic
matter that differed in clay content, pH, and land use (managed spruce forest, unmanaged deciduous
forest and agriculture), and compared their impacts on carbon sequestration and net greenhouse gas
(CO2, 13CO2, N2O and CH4) emissions. HTC addition (1% w/w) significantly increased CO2 emissions in all
three soils (p < 0.001), with much of the extra C derived from HTC decomposition. In contrast, PC
addition (1% w/w) had almost no impact on deciduous forest soil and actually decreased CO2 emission
from the agricultural soil. HTC treatment resulted in increased CH4 emission from all soils but reduced
N2O fluxes in the agricultural and spruce forest soils. PC amendment had no significant effect on CH4
emission, and resulted in intermediate levels of N2O emission (between control and HTC treatments).
Although both HTC and PC chars were produced from the same feedstock, PC had markedly higher potential for carbon sequestration than HTC.
