Pig slurry acidification and separation techniques affect soil N and C turnover and N2O emissions from solid, liquid and biochar fractions

• Solid fraction from acidified pig slurry had higher N availability in soil.
• Advanced slurry separation techniques increased N availability from solid fractions.
• Acidification resulted in liquid fraction with increased soil N2O and CO2 emissions.
• Biochar produced from slurry solids produced lower C and N turnover than raw solids.

The combined effects of pig slurry acidification, subsequent separation techniques and biochar production from the solid fraction on N mineralisation and N2O and CO2 emissions in soil were investigated in an incubation experiment. Acidification of pig slurry increased N availability from the separated solid fractions in soil, but did not affect N2O and CO2 emissions. However acidification reduced soil N and C turnover from the liquid fraction. The use of more advanced separation techniques (flocculation and drainage > decanting centrifuge > screw press) increased N mineralisation from acidified solid fractions, but also increased N2O and CO2 emissions in soil amended with the liquid fraction. Finally, the biochar production from the solid fraction of pig slurry resulted in a very recalcitrant material, which reduced N and C mineralisation in soil compared to the raw solid fractions.