The combined effects of nitrification inhibitor and biochar incorporation on yield-scaled N₂O emissions from an intensively managed vegetable field in southeastern China

Abstract. An experiment was conducted to study the influences of nitrification inhibitor (NI) and biochar incorporation on yield-scaled N₂O using the static chamber method and gas chromatography in an intensively managed vegetable field with seven consecutive vegetable crops from 2012 to 2014 in southeastern China. With an equal annual nitrogen (N) application rate (1217 kg N ha^-1 yr^-1), six treatments under three biochar amendment rates – namely, 0 t ha^-1 (C0), 20 t ha^-1 (C1) and 40 t ha^-1 (C2) – with compound fertilizer (CF) or urea mixed with NI of nitrapyrin as chlorinated pyridine (CP) were studied in these field experiments. The results showed that, although there was no significant influence on soil organic carbon (SOC) content or total nitrogen (TN), nitrapyrin could result in a significant increase in soil pH during the experimental period. Nitrapyrin significantly decreased cumulative N₂O emissions by 15.9–32.1% while increasing vegetable yield by 9.8–41.9%. Thus, it also decreased yield-scaled N₂O emissions significantly. In addition to the differential responses of the soil pH, biochar amendment significantly increased SOC and TN. Compared with the treatments without biochar addition, the cumulative N₂O emissions showed no significant difference in the CF or the CP group treatments but increased slightly (not significantly) by 7.9–18.3% in the CP group treatments. Vegetable yield was enhanced by 7.1–49.5% in the CF group treatments compared with the treatments without biochar amendment, while there was no significant difference in the CP group treatments, and the yield-scaled N₂O emissions were thus decreased significantly. Furthermore, treatments involving with nitrapyrin and biochar incorporation slightly increased yield-scaled N₂O emissions by 9.4%, on average, compared with CP-C0. Therefore, the application of nitrapyrin could serve as an appropriate practice for increasing vegetable yield and mitigating N₂O emissions in intensively managed vegetable fields and should be further examined in various agroecosystems.