Carbon stability and mitigation of fertilizer induced N2O 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 (N2O) emissions. The extent of biochar C stability after soil amendment and efficiency in reducing N2O 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 degrees C) biochars at 5 g C kg(-1) soil in combination with two N fertilizer rates (0 and 140 mg N kg(-1) soil). Carbon dioxide (CO2) and N2O emissions were measured during 60 days. Biochars and feedstocks CO2 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 60 days of incubation totaled between 0.8 and 9.4% and 2.4 and 32% for biochars and feedstocks, respectively. Regarding to N2O emissions, only CM-biochar impacted emissions with a two-fold increase in non-fertilized soil. When NH4NO3 was co-applied, biochars reduced fertilizer induced N2O emissions, reaching a seven-fold reduction in 55-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 N2O, which shows the biochar potential to reduce fertilizer induced N2O emissions, with major reduction by 55-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 N2O emissions. (C) 2017 Elsevier B.V. All rights reserved.