Effect of various doses of 3,4-dimethylpyrazole phosphate on mineral nitrogen losses in two paddy soils

Abstract

Nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) has been widely proposed to reduce nitrogen (N) loss and improve N availability in paddy soil. However, little knowledge exists regarding the optimum dose of DMPP required for inhibiting nitrification in different soil types. In undisturbed soil columns under greenhouse conditions, dynamics of ammonium (NH4+–N) and nitrate (NO3−–N) in floodwater and leachate, and ammonia (NH3) volatilization were studied in two paddy soils (hydragic and gleyed), amended with urea-N at 180 N kg/ha with DMPP applied at 0, 0.45, 0.675, and 0.90 kg/ha (0.25%, 0.375%, and 0.5% of urea-N, respectively). The source of DMPP was Entec® 46 (46% urea-N and DMPP at 0.5% of urea-N) that was mixed with pure urea (fertilizer mixture). DMPP application rates and soil types significantly influenced NH4+–N and NO3−–N concentrations in floodwater and leachate; however, DMPP application rates did not significantly impact NH4+–N concentrations in floodwater. Results indicate that concentrations of both NH4+– N and NO3−–N in leachate and floodwater were peaked between 10 and 20 days after fertilizer application. Increased DMPP application rates increased floodwater and leachate NH4+–N concentrations, while significantly decreasing NO3−–N concentrations in floodwater and leachate, with largest decrease seen in the 0.90-kg/ha DMPP treatment. NH3 emissions were observed after fertilizer was applied and decreased gradually, with no significant differences in response to the DMPP amount. The total N losses via leaching and NH3 emission were significantly decreased at treatments of 0.675 kg/ha and 0.90 kg/ha DMPP, and positively correlated with sand fraction in soil. Compared with the gleyed paddy soil, higher total N loss was observed in the hydragic paddy soil, which was related to the higher sand fraction of the hydragic paddy soil and the better behavior of DMPP in this soil type. Considering economic factors, mineral N concentrations in floodwater and leachate, together with N losses via leaching and volatilization, application of 0.675 kg/ha DMPP could significantly inhibit nitrification in the hydragic paddy soil while application of 0.90 kg/ha DMPP was shown to be the best choice to inhibit nitrification in the gleyed paddy soil.