Release, movement and recovery of 3,4-dimethylpyrazole phosphate (DMPP), ammonium, and nitrate from stabilized nitrogen fertilizer granules in a silty clay soil under laboratory conditions

In model experiments under laboratory conditions the release of 3,4-dimethylpyrazole phosphate (DMPP; ENTEC), NH4+-N, and NO3--N from the ENTEC-fertilizer granules placed on a silty clay soil was studied. The air-dried soil contained in Petri dishes was moistened to 18% or 24% water holding capacity, and incubated for 10 days at 4°C, 15°C or 25°C after placing the granules in the centre of the plates. Plates without granules served as controls. At appropriate intervals, soil cores were taken at 5-20 and 25-40 mm distance from the granules and analysed for DMPP, NH4+-N and NO3--N. Amongst the three fertilizer ingredients, NO3- was found to be the most mobile showing a fairly uniform distribution in both soil zones during 10 days of incubation. Under the different temperature and moisture conditions, more than 80% of DMPP remained within the 0- to 5-mm region around the granule. Between 5% and 15% of DMPP was found in the 5- to 20-mm region, and <3% moved into the 25- to 40-mm region. Increasing temperature and moisture facilitated the movement of DMPP in soil. NH4+ diffused faster than DMPP and showed a recovery of up to 13% in the 25- to 40-mm region under the given conditions. NH4+ was separated from the DMPP within 10 days, as revealed by an increase in the NH4+-N to DMPP ratios. An intensive N2O flux was observed within the 5- to 20-mm zone of the fertilizer granules, which was ascribed to heterotrophic denitrification rather than nitrification.