4‑Methyl-1-(prop-2-yn-1-yl)‑1H‑1,2,3-triazole (MPT): A Novel, Highly Efficient Nitrification Inhibitor for Agricultural Applications

Nitrogen fertilization in agriculture has serious environmental consequences, including production of the greenhouse gas nitrous oxide (N₂O), pollution of groundwater with nitrate (NO₃⁻), and river eutrophication. Nitrogen use efficiency can be increased by amending fertilizers with inhibitors to slow microbial nitrification processes, which transform ammonia to NO₃⁻. Unfortunately, commercial inhibitors have failed to perform reliably across various agroecosystems for reasons not well understood. Using a combination of bacterial studies and soil incubations, we demonstrate here that 4-methyl-1-(prop-2-yn-1-yl)-1H-1,2,3-triazole (MPT) exhibits superior nitrification inhibitory properties. Unlike the commercial reversible inhibitors, MPT acts as a mechanistic, irreversible inhibitor of the key enzyme ammonia monooxygenase, enabling effective retention of ammonium (NH₄⁺) and suppression of NO₃⁻ and N₂O production over 21 days in several agricultural soils with pH values ranging from 4.7 to 7.5. A bacterial viability stain and a suite of freshwater and terrestrial ecotoxicity tests did not indicate any acute or chronic toxicity. Real-time quantitative polymerase chain reaction (qPCR) analysis revealed an enhanced inhibitory effect of MPT on both ammonia-oxidizing bacteria and archaea. Thus, MPT outperforms currently available nitrification inhibitors and has great potential for broad application in various agricultural settings.