Biological nitrification inhibitors show low persistence in agricultural soils: the role of pH and soil microbiota

Biological nitrification inhibitors (BNIs) are plant-derived compounds, emerging as sustainable alternatives to synthetic nitrification inhibitors (SNIs). Yet, their environmental fate, and particularly their persistence in agricultural soils, a key determinant of their performance, remains unknown. We studied the dissipation of five BNIs — sakuranetin, 6-methoxy-2(3 H)-benzoxazolone (MBOA), 2,7-dimethoxy-1,4-naphthoquinone (zeanone), 2-methoxy-1,4-naphthoquinone (MNQ, a zeanone analogue), and 1,9-decanediol— in 10 soils differing in texture, pH and organic carbon content. All BNIs showed limited persistence (DT50 < 8 days), except in the most acidic soil (pH 4), where dissipation was markedly prolonged, with zeanone showing the longest persistence (DT50 = 88 days). Soil fumigation, tested on two representative soils—one acidic and one alkaline—selected based on their slowest and fastest dissipation rates, significantly slowed dissipation of all BNIs in the acidic soil, but only of sakuranetin and MBOA in the alkaline soil, suggesting complex interactions between biotic and abiotic soil factors that control BNI dissipation. Amongst soil parameters, pH exerted the strongest and most consistent effect on BNI persistence in soil, with faster dissipation of zeanone, MNQ and MBOA at higher soil pH, whereas texture-related parameters, particularly silt and clay content, influenced the persistence of sakuranetin. Overall, our findings provide benchmarking knowledge on BNI persistence in soil, with direct implications for their agronomic performance and their integration into sustainable nitrogen management strategies. Future studies should evaluate BNI fate under realistic field conditions where competing processes in the plant rhizosphere such as exudation and degradation will ultimately determine their persistence and dynamics.