Contrasting effects of wheat straw and its biochar on greenhouse gas emissions and enzyme activities in a Chernozemic soil

Biochar produced from plant biomass through pyrolysis has been shown to be much more resistant to biodegradation in the soil as compared with the raw biomass, such as cereal straw that is routinely shredded and discharged on to farm fields in large amounts. Biochar application to soil has also been reported to decrease greenhouse gas (GHG) emissions, although the mechanisms are not fully understood. In this study, the emissions of three main GHGs (CO2, CH4, and N2O) and enzyme activities (urease, β-glycosidase, and dehydrogenase) were measured during a 100-day laboratory incubation of a Chernozemic soil amended with either straw or its biochar at rates of 0.67 and 1.68 % (based on the amount of C added) for the low and high rates, respectively. The biochar application dramatically reduced N2O emissions, but CO2 or CH4 emissions were not different, as compared with the un-amended soil. At the same C equivalent application rate, CO2 and N2O emission rates were greater while CH4 emission rates were lower in straw than in biochar application treatments. The activities of both the dehydrogenase and β-glycosidase significantly declined while that of urease significantly increased with the biochar as compared with the straw treatment. We conclude that pyrolysis of cereal straw prior to land application would significantly reduce CO2 and N2O emissions, in association with changed enzyme activities, while increasing the soil C pool through the addition of stable C in the form of biochar.