Evaluation of 3,4-dimethylpyrazole phosphate as a nitrification inhibitor in a Citrus-cultivated soil

The objectives of this work were to evaluate the inhibitory action on nitri fication of 3,4-dimethylpyrazole phosphate (DMPP) added to ammonium sulphat e nitrate [(NH4)(2)SO4 plus NH4NO3; ASN] in a Citrus-cultivated soil, and t o study its effect on N uptake. In a greenhouse experiment, 2 g N as ASN ei ther with or without 0.015 g DMPP (1% DMPP relative to NH4+-N) was applied 6 times at 20-day intervals to plants grown in 14-l pots filled with soil. Addition of DMPP to ASN resulted in higher levels of NH4+-N and lower level s of NO3--N in the soil during the whole experimental period. The NO3--N co ncentration in drainage water was lower in the ASN plus DMPP (ASN + DMPP)-t reated pots. Also, DMPP supplementation resulted in greater uptake of the f ertilizer-N by citrus plants. In another experiment, 100 g N as ASN, either with or without 0.75 g DMPP (1% DMPP relative to NH4+-N) was applied to 6- year-old citrus plants grown individually outdoors in containers. Concentra tions of NH4+-N and NO3--N at different soil depths and N distribution in t he soil profile after consecutive flood irrigations were monitored. In the ASN-amended soil, nitrification was faster, whereas the addition of the inh ibitor led to the maintenance of relatively high levels of NH4+-N and NO3-- N in soil for longer than when ASN was added alone. At the end of the exper iment (120 days) 68.5% and 53.1% of the applied N was leached below 0.60 m in the ASN and ASN + DMPP treatments, respectively. Also, leaf N levels wer e higher in plants fertilized with ASN+DMPP. Collectively, these results in dicate that the DMPP nitrification inhibitor improved N fertilizer efficien cy and reduced NO3- leaching losses by retaining the applied N in the ammon iacal form.