Influences of nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) and application method on nitrogen dynamics at the centimeter-scale

Abstract Nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) could be used to reduce nitrogen (N) loss and improve N use efficiency in agroecosystems. However, the DMPP effect on N dynamics at the microscale remains largely unknown. A microcosm experiment was conducted to evaluate the effects of DMPP and fertilizer application method on N fate, including 15 NH 4 + -N, ( 15 NO 3 − + 15 NO 2 − )-N, MB 15 N and N losses at the centimeter-scale. The isotope labelled 15 N-urea was applied to soil with or without DMPP. Two fertilizer application methods were compared, including mixed with soil (mix-application) or concentrated on the soil surface (spot-application). After 28 days of incubation at 28 °C, DMPP amended with urea significantly increased soil pH and 15 NH 4 + -N concentrations but decreased ( 15 NO 3 − + 15 NO 2 − )-N concentrations in both horizontal and vertical directions compared with urea application alone. Such effect was more obvious within 0–2 cm and weakened with increasing distance from the fertilizer zone. DMPP addition significantly increased N losses compared with urea application alone, which is mainly due to the increased ammonia volatilization caused by high pH and NH 4 + concentrations. The application method of urea and DMPP also had different effects on N performance, depending on the distance and spatial directions of microsites. And the N losses in the mix-application treatment (32%) were significantly lower than in the spot-application treatment (37%) when urea was applied alone. We concluded that DMPP addition significantly slowed down nitrification processes, and urea mixed with soil is better than concentrated on the soil surface in reducing N losses when urea was applied alone.