Short-term effects of biochar and salinity on soil greenhouse gas emissions from a semi-arid Australian soil after re-wetting

Arid and semi-arid soils often show a pulse of soil greenhouse gas (GHG) emissions upon re-wetting - whether from irrigation water or rainfall. We used a laboratory incubation to elucidate interactions of salinity, biochar amendment, and simulated wetting intensity in emissions of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) in a semi-arid Australian soil. A factorial experimental design was used with three main factors: irrigation water salinity (using NaCl, control or similar to 0.9 dS m(-1), 5 dS m(-1) and 10 dS m(-1)), biochar amendment (0% and 5% by mass of Eucalyputs polybractea biochar) and soil moisture (25%, 50%, 75% and 100% of water holding capacity, WHC-a proxy for wetting intensity after irrigation or rainfall). The strongest single regulating variable of rates of soil CO2 emission was WHC (+171% increase between 25% and 100% WHC). Salinity reduced CO2 emissions (relative to controls) by -19% at 5 dS m(-1) and-28% at 10 dS m(-1). Soils amended with biochar produced less (-10%) CO2 emissions. All treatments showed negative CH4 emissions (or CH4 oxidation) that were only influenced by WHC. Soil N2O emissions increased with salinity (+60%), while biochar additions reduced them slightly (-12%). N2O emissions were not influenced by WHC. Overall, results showed that biochar additions can mitigate some of the pulse effects of rainfall on emissions (similar to 10% in term of global warming potential across all treatments).