Soil N2O emission and microbial activity in a potato cropping fertilized with DMPP-added nitrogen fertilizers.

In this work we evaluated the effects of 3,4-dimethylphyrazole phosphate (DMPP), a nitrification inhibitor, on N2O emission and microbial activity of a soil cropped to potato in Southern Italy. The experiment consisted in two treatments applied: control (C) and DMPP plots. The nitrogen fertilizer was supplied in three events: at 0 Day After Sowing (DAS; 100 kg N ha-1), at 57 DAS (30 kg N ha-1), and at 71 DAS (30 kg N ha-1). Soil N2O emission was monitored by both dynamic and static chambers. Microbial biomass and basal respiration were determined as CO2 evolution. No statistical difference in N2O fluxes measured with dynamic chambers between C and DMPP plots was found. However, after the first fertilization event, the average N2O fluxes measured with static chambers were higher in DMPP plots than in C plots. Microbial biomass significantly decreased in DMPP plots as compared to C plots, whereas an opposite trend for basal respiration was observed. After 57 and 71 DAS the microbial biomass was similar between C and DMPP plots, whereas basal respiration resulted statistically lower in DMPP plots than C plots. During these periods, average DMPP N2O fluxes were also comparable or lower. Overall, our data evidence a stressful condition for soil microbes and in particular for nitrifiers when a higher DMPP quantity is supplied. On the contrary, when lower quantities of DMPP-added fertilizers are supplied the effectiveness of DMPP in reducing soil N2O emission is guaranteed by reducing the nitrifiers activity without negatively affecting their growth.