Biochar impacts on nutrient dynamics in a subtropical grassland soil: 2. Greenhouse gas emissions.

Land application of biochar reportedly provides many benefits, including reduced risk of nutrient transport, greenhouse gas (GHG) emission mitigation, and increased soil C storage, but additional field validation is needed. We evaluated the effectiveness of biochar in controlling the lability of nutrients in agricultural land. This study was designed to evaluate the impacts of biochar co-applied with various N and P sources on GHG fluxes from a subtropical grassland. Nutrients (inorganic fertilizer and aerobically digested Class B biosolids) were surface applied at a rate of 160 kg plant available N ha-1  yr-1 with or without biochar (applied at 20 Mg ha-1 ). Greenhouse gas (CO2 , CH4 , and N2 O) fluxes were assessed using static chambers and varied significantly, both temporally and with treatments. Greenhouse gas fluxes ranged from 1,247 to 23,160, -0.7 to 42, and -1.4 to 376 mg m-2 d-1 for CO2 , N2 O, and CH4 , respectively. Results of the 3-yr field study demonstrated strong seasonal variability associated with GHG emissions. Nutrient source had no effect on soil CO2 and CH4 emissions, but annual and cumulative (3-yr) N2 O emissions increased with biosolids (8 kg N2 O ha-1  yr-1 ) compared with inorganic fertilizer (5 kg N2 O ha-1  yr-1 ) application. Data suggested that environmental conditions played a more important role on GHG fluxes than nutrient additions. Biochar reduced CO2 emissions modestly (<9%) but had no effects on N2 O and CH4 emissions.