Understanding the variability in performance of the nitrification inhibitor 3,4-Dimethylpyrazole phosphate in Australian agricultural soils

Helen Suter1, Charlie Walker2, Deli Chen1

1 Faculty of Veterinary and Agricultural Sciences, The University of Melbourne, Burnley Campus, 500 Yarra Boulevard, Richmond, Victoria 3121, http://fvas.unimelb.edu.au/ Email: helencs@unimelb.edu.au

2 Incitec Pivot Fertilisers, PO Box 54, North Geelong, Victoria 3215, Australia


The nitrification inhibitor 3,4-Dimethylpyrazole phosphate (DMPP) is being widely used across Australian agricultural systems to reduce nitrogen loss from soils, particularly targeting the greenhouse gas nitrous oxide, and to improve nitrogen use efficiency. However, the effectiveness of DMPP is variable and the reason for this has been unclear. A laboratory investigation was undertaken using 30 soils collected from a range of agricultural land uses to identify the key drivers influencing the performance of DMPP. Average nitrification over 14 days across all treatments ranged from -4.61 to 26.89, with a median of 2.57 mg NO3N produced/g soil/day. Cumulative N2O emissions ranged from 0.01 to 7.74 mg N2O-N/g soil. However only 3 soils contributed to high emissions and the remaining soils had < 0.63 mg N2O-N/g soil. DMPP effectively reduced average nitrification by 9-100% (average of 42%) and N2O emissions by 0-100% (average of 55%) Only manganese and the interaction between organic C and clay influenced DMPP’s efficacy at reducing nitrification, having a negative impact. The efficacy of DMPP at inhibiting N2O emissions was positively related to pH, Cu and Zn and negatively related to Fe. The results suggest that further investigation of the soil metal-inhibitor interaction, and the role of metals in soil microbial function (nitrifiers and denitrifiers) is required to understand when the DMPP will work best.