Nitrogen stabilizers and crop rotation affect chemical properties and relative abundance of nitrification and denitrification genes in boreal podzolic soils.

Nitrogen (N) is an essential macronutrient required to enhance plant growth and yield. However, 50-70% of applied N is lost in cropping systems. N stabilizers can reduce these losses by modulating microbial N transformation processes, yet their effectiveness in boreal podzolic soils remains understudied. A field experiment was conducted to evaluate the effects of N stabilizers and short-term crop rotation on soil mineral N and the relative abundance of key genes involved in nitrification and denitrification processes, 15 days after N application. Treatments included five N sources (control (CT), urea (UR), and three stabilizers: a urease inhibitor [N-(n-butyl)-thiophosphoric triamide (NBPT)], a nitrification inhibitor [nitrapyrin], and a dual inhibitor [NBPT + dicyandiamide]) and three crop rotations (corn-corn (c-c), corn-wheat (c-w), corn-faba bean (c-fb)). N stabilizers differentially affected soil mineral N relative to urea: the urease inhibitor (Agrotain (AG), urea coated with N-(n-Butyl) thiophosphoric triamide [NBPT]) increased NH₄+ availability, consistent with reduced NH₃ loss, whereas the nitrification inhibitor (eNtrench (EN), urea coated with nitrapyrin) delayed the nitrification process and the dual inhibitor (SuperU (SU), urea coated with dicyandiamide and NBPT) increased NH₄+ availability and delayed the nitrification process, again consistent with reduced NH₃ loss. Importantly, all N stabilizers significantly suppressed the relative abundance of nitrification and denitrification genes relative to urea. Among crop rotations, c-fb rotation (which received the lowest N rate) reduced NH4+ and NO3- concentration and the relative abundance of amoA AOB, amoA AOA, nxr-nitrospira, and nirK genes compared to c-c rotation. The nosZ gene abundance was highest in urea-amended c-w rotation and lowest in control treatment across all rotations. We conclude that N stabilizers and c-fb rotation effectively suppress the relative abundance of nitrification and denitrification genes in boreal podzolic soils; lower gene abundances under c-fb rotation were associated with the lower N input, though rotation and N rate effects could not be separated.