Effects of biochar and dicyandiamide combination on nitrous oxide emissions from Camellia oleifera field soil

Greenhouse gas emissions from agricultural soils contribute substantially to global atmospheric composition. Nitrous oxide (N₂O) is one important greenhouse gas induces global warming. Nitrification inhibitors (NI) or biochar can be effective soil N₂O emission mitigation strategies for agricultural soils. However, due to differences in crop physiological traits or agricultural management, the effectiveness of mitigation strategies varies among agricultural systems. Camellia oleifera is a woody oil plant widely grown and requires intensive N input, which will potentially increase N₂O emissions. Thereby, mitigation of N₂O emissions from C. oleifera field soil is vital for sustainable C. oleifera development. Besides NI, incorporation of C. oleifera fruit shell-derived biochar into its soil will benefit waste management and simultaneous mitigation of N₂O emissions but this has not been investigated. Here, we conducted two studies to examine effects of biochar addition and NI (dicyandiamide, DCD) application on N₂O emissions from C. oleifera field soil with different N (urea or NH₄NO₃) and incubation temperatures. Biochar effects on nitrification rates varied among N treatments. Biochar applied in combination with DCD further reduced nitrification rates (for urea treatment, decreased from 1.1 to 0.3 mg kg^-1 day^-1). Biochar addition consistently increased soil N₂O emissions (for urea treatment, increased from 0.03 to 0.08 ng g^-1 h^-1) and their temperature sensitivity. DCD application reduced soil N₂O emissions with greater reductions with urea application. In future cultivation of intensively managed C. oleifera gardens, NI should be applied to mitigate N₂O emissions if biochar is added, especially when urea is used.