Bamboo biochar does not affect paddy soil N2O emissions or source following slurry or mineral fertilizer amendmenta 15N tracer study

Nitrogen (N)-containing fertilizers, such as slurry and ammonium nitrate (NH4NO3), can significantly increase soil nitrous oxide (N2O) emissions following addition to agricultural soil. Biochar amendment to soil has been observed to suppress N2O emissions in a number of studies. However, the effect varies depending on many factors, including when biochar is added to soil concurrently with organic or mineral fertilizers. An incubation was conducted in which bamboo biochar (created at 800 degrees C) was added to an ex-rice paddy soil (1% rate) concurrently with dairy cattle slurry or NH4NO3 (100 mg N kg(-1)). At three time points, following biochar amendment, N-15-labelled NH4NO3 (50 mg N kg(-1)) was added to the soil to determine the N2O emissions derived from nitrification and denitrification in the 24 h that followed (at 70% water filled pore space; days 0, 7, and 28). Nitrous oxide emissions from slurry-amended soils were much greater than those from NH4NO3-amended soils, as well as the proportion of soil N2O emissions derived from denitrification. Biochar amendment did not significantly affect soil N2O emissions or consistently affect the percentage of soil N2O emissions derived from nitrification in slurry or NH4NO3-amended treatments. The lack of N2O-emission suppression with biochar amendment may have been due to the relatively-low addition rate of a biochar that had a low content of volatile organic carbons and redox-reactive organic/inorganic compounds, and did not greatly increase the pH of the acidic soil (pH5). These results suggest that bamboo biochar produced at such a high temperature may not be suitable for mitigation of soil N2O emissions.