Effects of 3,4-dimethylpyrazole phosphate and dicyandiamide on nitrous oxide emission in a greenhouse vegetable soil

A laboratory study was conducted to determine the effect of 3,4-dimethylpyrazole phosphate (DMPP) and dicyandiamide (DCD) on nitrous oxide (N2O) emission, mineral nitrogen (NH4+-N, NO3--N) contents, as well as ammonia oxidizing and denitrifying microbes in a greenhouse vegetable soil. Five treatments were established at 55% and 75% water filled pore space (WFPS): no fertilizer; urea; urea + manure (UM); urea + manure + DCD (UMDCD) and urea + manure + DMPP (UMDMPP). The application rate of urea and manure was 1800 kg N/ha and 1000 kg N/ha, respectively. DMPP and DCD were applied at the rate of 0.5% and 2% of urea-N application rate, respectively. Compared to UMDCD treatment, UMDMPP treatment significantly reduced N2O emission and NO3--N content and delayed ammonia oxidation, and showed a stronger inhibition effect on ammonium-oxidizing bacteria at both WFPS. Moreover, the copy numbers of nirS and nirK genes decreased significantly in the presence of DMPP at both WFPS, but were not affected by DCD. These results suggest that the application of DMPP is more effective than DCD on N2O mitigation in high N level vegetable soil, although the application rate of DMPP was one quarter that of DCD.