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

Abstract

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.