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

Abstract 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 (CO 2 ), methane (CH 4 ), and nitrous oxide (N 2 O) in a semi-arid Australian soil. A factorial experimental design was used with three main factors: irrigation water salinity (using NaCl, control or ~ 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 CO 2 emission was WHC (+ 171% increase between 25% and 100% WHC). Salinity reduced CO 2 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%) CO 2 emissions. All treatments showed negative CH 4 emissions (or CH 4 oxidation) that were only influenced by WHC. Soil N 2 O emissions increased with salinity (+ 60%), while biochar additions reduced them slightly (− 12%). N 2 O emissions were not influenced by WHC. Overall, results showed that biochar additions can mitigate some of the “pulse” effects of rainfall on emissions (~ 10% in term of global warming potential across all treatments).