Effects of biochar addition on greenhouse gas emissions and microbial responses in a short-term laboratory experiment

Biochar application to soil has drawn much attention as a strategy to sequester atmospheric carbon in soil ecosystems. The applicability of this strategy as a climate change mitigation option is limited by our understanding of the mechanisms responsible for the observed changes in greenhouse gas emissions from soils, microbial responses, and soil fertility changes. We conducted an 8-wk laboratory incubation using soils from PASTURE (silt loam) and RICE PADDY (silt loam) sites with and without two types of biochar (biochar from swine manure [CHAR-M] and from barley stover [CHAR-B]). Responses to addition of the diff erent biochars varied with the soil source. Addition of CHAR-B did not change CO2 and CH4 evolution from the PASTURE or the RICE PADDY soils, but there was a decrease in N2O emissions from the PASTURE soil. Th e eff ects of CHAR-M addition on greenhouse gas emissions were diff erent for the soils. Th e most substantial change was an increase in N2O emissions from the RICE PADDY soil. Th is result was attributed to a combination of abundant denitrifi ers in this soil and increased net nitrogen mineralization. Soil phosphatase and N-acetylglucosaminidase activity in the CHAR-B-treated soils was enhanced compared with the controls for both soils. Fungal biomass was higher in the CHAR-B-treated RICE PADDY soil. From our results, we suggest CHAR-B to be an appropriate amendment for the PASTURE and RICE PADDY soils because it provides increased nitrogen availability and microbial activity with no net increase in greenhouse gas emissions. Application of CHAR-M to RICE PADDY soils could result in excess nitrogen availability, which may increase N2O emissions and possible NO3 leaching problems. Th us, this study confi rms that the ability of environmentally sound biochar additions to sequester carbon in soils depends on the characteristics of the receiving soil as well as the nature of the biochar.