Agro-residue biochar and N fertilizer addition mitigates CO2-C emission and stabilized soil organic carbon pools in a rain-fed agricultural cropland

Scarce carbon dioxide (CO2) emission data, soil organic carbon (Corg) and labile Corg pool index for croplands in sub-Saharan Africa (SSA) limits our ability to define regional CO2 flux and mitigation prospects provided by biochar amendment. Hence, we conducted a two-year field scale study quantifying effects of biochar (12 t ha−1), biochar (12 t ha−1) and N fertilizer (90 kg N ha−1), N fertilizer (90 kg N ha−1) alone and control (no amendment) on Corg, Corg pools, lability index (LI) and CO2 emissions of a humid tropical alfisol under rainfed rice cultivation. Results clearly demonstrate that biochar amendment combined with N fertilizer significantly increased Corg, particulate organic carbon, and particulate organic carbon to organic carbon proportion. Furthermore, this combination decreased dissolved organic carbon, dissolved organic carbon to organic carbon proportion, easily oxidizable carbon, easily oxidizable carbon to organic carbon proportion, microbial biomass carbon, microbial biomass carbon to organic carbon proportion, LI, and CO2 emission when compared to other treatments. Our findings established relationship between labile Corg pools and CO2 emission. Overall, our study suggest that application of biochar and N fertilizer addition can decrease CO2 emission from SSA croplands under rainfed rice cultivation, increase essential labile Corg pools, protect labile Corg pools sensitive to losses and sequester Corg with positive implication for global change mitigation and soil quality improvement.