3,4-Dimethylpyrazole Phosphate Applied on Ammonium Sulfate Nitrate and Urea Reduces the Nitrification Process in Three Tropical Soils: An Incubation Study

Objectives: Nitrification inhibitors applied to soil can reduce nitrogen (N) fertilizer losses by delaying the nitrification process and reducing nitrate losses to environment with enhanced N- fertilizer management. In this study, laboratory-scale experiments were carried out in order to evaluate the efficiency of nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) applied on urea and ammonium sulfate nitrate (ASN) sources under three tropical soils (Typic Quartzipsamment, Typic Hapludox and Rhodic Hapludox - contrasting soil textures). Methods: Soil samples were incubated over 60 days and the content of nitrate (N-NO3-), ammonium (N-NH4+) and pH variations were assessed periodically. In addition, N-NO3- and N-NH4+ percentage and nitrification inhibition were assessed. Results: 3,4-Dimethylpyrazole phosphate application delays the nitrification process across all three tropical soil types, being more evident in the sandytextured soils (Typic Quartzipsamment > Typic Hapludox > Rhodic Hapludox). DMPP application reduced the N-NO3- and N-NH4+ percentage in both ASN and urea sources, mainly between 15 and 30 (ASN) and between 7 and 30 days after N fertilization ( urea). However, 45 days after N fertilization, inhibition of the nitrification process by DMPP is unlikely, regardless of N source. Conclusions: The nitrification process tended to be more intense when conventional urea was applied compared to conventional ASN. Therefore, the use of DMPP would benefit more urea than ASN mainly in sandy-textured soils, where the nitrification was observed to be increased.