Soil Type Controls the Effects of the Nitrification Inhibitor DMPP on Nitrate Leaching and Mineral N Retention Under Simulated Heavy Rainfall

ABSTRACT Background Nitrate (NO 3 − ) leaching is a major nitrogen (N) loss pathway in agriculture and may increase with more frequent heavy rainfall. Nitrification inhibitors, such as 3,4‐dimethylpyrazole phosphate (DMPP), can reduce these losses, but their effectiveness under frequent heavy rainfall events remains unclear, which limits their targeted use in N management. Aims This study aimed to investigate the effect of DMPP on nitrate leaching and soil mineral N (SMN) retention under repeated simulated heavy rainfall events and to assess to what extent its effectiveness depends on soil type and temperature. Methods In a column experiment, three arable soils from northwestern Germany with contrasting textures—GO (silty clay loam), KL (silt loam), and OS (sandy loam)—were studied using ammonium sulfate nitrate (ASN) or urea ammonium nitrate (UAN), each with and without DMPP. Nitrogen was applied at 327 mg N per column, corresponding to 180 kg N ha −1 . The experiment was conducted at 10°C and 20°C and included 14 simulated rainfall events of 20 mm over 7 weeks. After each event, percolate was collected to quantify NO 3 − leaching, and at the end, SMN (SMN = NO 3 ‐N + NH 4 ‐N) was analyzed. Results NO 3 − leaching was mainly determined by soil type and temperature. Substantial leaching occurred only in soil GO, particularly at 10°C, whereas losses remained low to very low in soils KL and OS. In GO, DMPP reduced cumulative NO 3 − leaching by 43% with UAN and by 13% with ASN at 10°C. In KL and OS, DMPP mainly increased NH 4 + retention and SMN. Higher temperature was associated with lower cumulative NO 3 ‐N leaching, particularly in GO and OS, consistent with enhanced microbial nitrate reduction under persistently wet, oxygen‐limited conditions. Conclusions Overall, DMPP reduced NO 3 − leaching where nitrification remained relevant and mainly increased NH 4 + retention otherwise. This supports targeted DMPP use under nitrification‐driven leaching risk, whereas complementary soil and water management strategies may become more important under persistently wet conditions.