Carbon stability and mitigation of fertilizer induced NO emissions in soil amended with biochar.

Biochar is a promising tool for an efficient and low environmental impact agriculture since can offer both soil carbon (C) sequestration and mitigation of nitrous oxide (NO) emissions. The extent of biochar C stability after soil amendment and efficiency in reducing NO emissions from an external nitrogen (N) source were accessed through laboratory incubations. A clay loam soil was amended with chicken manure (CM), sewage sludge (SS), eucalyptus sawdust (ES) and filter cake (FC) feedstocks and corresponding slow-pyrolysis (400°C) biochars at 5gCkg soil in combination with two N fertilizer rates (0 and 140mgNkg soil). Carbon dioxide (CO) and NO emissions were measured during 60days. Biochars and feedstocks CO emissions were described by an exponential first order kinetics model. For C mineralization an interaction effect was observed for feedstock source and organic amendment. Lower values of mineralizable C was found for biochars than corresponding feedstocks, except for ES. Carbon losses in 60days of incubation totaled between 0.8 and 9.4% and 2.4 and 32% for biochars and feedstocks, respectively. Regarding to NO emissions, only CM-biochar impacted emissions with a two-fold increase in non-fertilized soil. When NHNO was co-applied, biochars reduced fertilizer induced NO emissions, reaching a seven-fold reduction in SS-biochar treatment. The fertilizer emission factor (EF) decreased with biochar amendments as well, varying between 0.01 and 0.08% of the fertilizer N emitted as NO, which shows the biochar potential to reduce fertilizer induced NO emissions, with major reduction by SS-biochar mitigating 87% of the soil-fertilizer emissions. Such potential could be explored by designing biochars based on feedstock chemical and structural properties, including a mixed feedstock source biochar that promotes C sequestration and mitigates NO emissions.