Exploring the potential of sugarcane straw biochar: Insights into N2O emissions and microbial functional genes

Sugarcane straw has been considered a promising cost-effective feedstock for bioenergy production through pyrolysis. Straw-based biochar is a by-product from biomass pyrolysis that has the potential to mitigate nitrous oxide (N2O) emissions. However, the understanding of how biochar influences N2O emissions remains limited. This study assessed the effects of sugarcane straw-based biochar on soil N2O emissions and its interaction with functional genes associated with N2O production and consumption in tropical conditions. A greenhouse experiment was conducted for 60 days to evaluate the following treatments: control (CTR), N fertilizer (NF), NF + 15 Mg ha-1 straw (NF + S); NF + 5 Mg ha-1 biochar (NF + B5); and NF + 10 Mg ha-1 biochar (NF + B10). Results showed that N2O emissions were 73 % higher in the NF + S than in the biochar treatments. However, biochar treatments did not reduce N2O emissions compared to NF. Soil N-NH4 +availability was reduced under NF + S but was greater in biochar treatments at initial sampling time-points. High soil C content was observed in the NF + B10. Although NF + S increased sugarcane biomass, it registered the highest N2O-yield scaled emission. N2Oyield scaled emissions in NF + B5 and NF + B10 were 63 % and 62 % lower than in NF + S. The NF + S increased the abundance of AOB-amoA genes, suggesting that nitrification was the major N2O-producing pathway. Conversely, biochar effects on soil N2O emissions were not correlated with nitrification or denitrification genes. Thus, converting sugarcane straw into biochar is feasible strategy to reduce N2O emissions and increase soil C sequestration in tropical soil.