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

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 (NH4+)-N-15 -N, ( (NO3-)-N-15 + (NO2-)-N-15 )-N, (MBN)-N-15 and N losses at the centimeterscale. 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 (spotapplication). After 28 days of incubation at 28 degrees C, DMPP amended with urea significantly increased soil pH and (NH4+)-N-15 -N concentrations but decreased ( (NO2-)-N-15 + (NO2-)-N-15)-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 NH4+ 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.