LAUSR

Commercial nitrification inhibitors (NIs), namely nitrapyrin, 3,4-dimethylpyrazol phosphate (DMPP) and dicyandiamide (DCD), are ineffective at high temperatures. Therefore, it is imperative to explore new compounds that can be commercialised as effective NIs for warm climatic conditions. The aim of the present study was to compare the potential of 4-amino-1,2,4-triazole (ATC) with the two commercial NIs DMPP and DCD to delay nitrification of (NH4)2SO4 in an alkaline calcareous soil incubated under aerobic conditions at warm temperatures (35 and 25°C). Inhibitors were incorporated in (NH4)2SO4 granules and nitrification inhibition was calculated on the basis of net NH4+-N disappearance and net NO3–-N accumulation. At 35°C, the inhibitory effect of DCD and DMPP persisted only for 1 week, whereas ATC was effective up to 4 weeks. At 25°C, the inhibitory effect of ATC, DMPP and DCD was comparable. In another set of experiments, different concentrations of ATC (0.25–6% of N) were tested at three different temperatures (35, 25 and 18°C). At 35°C, ATC applied at 2% of N caused 63% inhibition for 2 weeks, whereas at a rate of 4–6% of N the inhibitory effect of ATC persisted up to 4 weeks (63–84% inhibition). At 25°C, ATC application at a rate of 1% of N caused 64% inhibition for 2 weeks; increasing the application rate to 2–6% of N prolonged the inhibitory effect up to 4 weeks (55–94% inhibition). At 18°C, a much lower concentration of ATC (0.25–0.5% of N) was required to achieve ≥50% inhibition for 2–4 weeks, whereas increasing the application rate to 2% of N caused 93% inhibition for 4 weeks. The results of the present study suggest that although commercially available NIs are ineffective at high summer temperatures, ATC may have the potential to be commercialised as an effective NI for warm as well as moderate climatic conditions.