Mitigation of nitrous oxide emissions by 3,4-dimethylpyrazole phosphate and 3,4-dimethylpyrazole succinic acid with reduced fertilizer application time while maintaining cabbage yield in Andosol fields

Previous studies have reported that nitrification inhibitors are effective in reducing nitrous oxide emissions. However, no studies have reported the effectiveness of 3,4-dimethylpyrazole phosphate, and 3,4-dimethylpyrazole succinic acid in Andosol fields. Thus, the effects of nitrification inhibitors—dicyandiamide, 3,4-dimethylpyrazole phosphate, and 3,4-dimethylpyrazole succinic acid—on cabbage yield, nitrogen use efficiency, soil inorganic nitrogen, nitrous oxide emissions, and methane uptake were investigated in Andosol fields for six crop seasons over three years. The results showed that dicyandiamide inhibited nitrification only at temperatures lower than about 20°C and under relatively dry conditions but not at higher temperatures or under high rainfall. In contrast, 3,4-dimethylpyrazole phosphate and 3,4-dimethylpyrazole succinic acid effectively inhibited nitrification for all crop seasons. 3,4-dimethylpyrazole phosphate and 3,4-dimethylpyrazole succinic acid were effective in reducing nitrous oxide emissions (P < 0.05), but not dicyandiamide. Nitrification inhibitor application did not affect methane uptake by soil. Even though nitrification inhibitor applications did not increase the cabbage yield or nitrogen use efficiency, they could reduce the fertilizer application time (i.e., two fertilizer application times for urea vs only one basal fertilizer application time for nitrification inhibitor treatments). Additionally, 3,4-dimethylpyrazole phosphate and 3,4-dimethylpyrazole succinic acid maintained the yield even at a low nitrification inhibitor rate (0.5 % of applied nitrogen). Moreover, the former maintained yield at even a low nitrogen rate (175 kg N ha⁻¹, 70 % of the local standard application rate of 250 kg N ha⁻¹). Our results demonstrated that the nitrification inhibitors were effectively reduced the fertilizer application time, thus saving labor costs. Particularly, 3,4-dimethylpyrazole phosphate could reduce the nitrogen rate by 30 % compared to conventional nitrogen rates. These results suggested that 3,4-dimethylpyrazole phosphate and 3,4-dimethylpyrazole succinic acid application can be an effective way to ensure yield and reduce nitrous oxide emissions while saving labor costs.