Nitrous oxide emissions from an Andosol upland field amended with four different types of biochars

The application of biochar can affect the nitrous oxide (N2O) emissions from soil. Although laboratory studies reported that biochar applications can reduce N2O emissions, the number of field-based studies is still limited. Therefore, in the present study, we investigated the effects of four different types of biochars and their interactions with a variety of environmental parameters on N2O emissions from an Andosol field over a 2-year period (2015–2016). The field experiment consisted of five treatments: chemical (mineral) fertilizer without biochar (CF), chemical fertilizer with rice husk biochar (RH), chemical fertilizer with chipped bamboo biochar (BA), chemical fertilizer with chipped hardwood biochar (HW), and chemical fertilizer with chipped wood briquette biochar made from a mixture of softwood and hardwood sawdust (SH). Biochar was applied at a rate of 25 t ha−1. The NH4+–N and NO3−–N adsorption capacity of biochars before application was also measured. NH4+–N adsorption capacity differed among the biochars, while biochars showed very little NO3−–N absorption capacity. The cumulative N2O emission of biochar treatment to that of the CF treatment during the N2O peak period (17 days) after biochar and fertilizer application increased with the increase of NH4+–N adsorption capacity of the biochar. However, biochar application did not affect the cumulative N2O emission over 2 years in the field condition. The lack of significant differences may have been due to Andosol CEC (31.3 cmol(+) kg−1), which was higher than that of the biochars (4.52–19.65 cmol(+) kg−1), and also high pH-buffering capacity of Andosol.