Nitrite intensity explains N management effects on N2O emissions in maize

• In spite of its central role in soil N2O production, NO2− is seldom measured.
• We quantified NO2− separately from NO3− dynamics under multiple treatments in maize.
• N2O was correlated with NO2− intensity (NO2I) but not with intensities of NH4+ or NO3−.
• Treatments that reduced NO2I also reduced N2O emissions.
• More scrutiny should be given to NO2− separately from NO3− in experiments and models.

It is typically assumed that the dependence of nitrous oxide (N2O) emissions on soil nitrogen (N) availability is best quantified in terms of ammonium (NH4+) and/or nitrate (NO3−) concentrations. In contrast, nitrite (NO2−) is seldom measured separately from NO3− despite its role as a central substrate in N2O production. We examined the effects of three N fertilizer sources and two placement methods on N2O and N dynamics in maize over two growing seasons. Cumulative N2O emissions were well-correlated with NO2− intensity (NO2I) but not with NO3− (NO3I) or NH4+ (NH4I) intensity. By itself, NO2I explained more than 44% of the overall variance in N2O. Treatment effects on N2O and NO2I were similar. When conventional urea (U) was applied using mid-row banding (MRB), both N2O and NO2I increased by a factor of about 2 compared to broadcast/incorporated (BI). When polymer-coated urea (PCU) was the N source, MRB placement increased both N2O and NO2I compared to BI only in the wetter of the two years. When urea with microbial inhibitors (IU) was the N source, N2O and NO2I were lowest across both years and were less affected by placement than U or PCU. A 50/50 mix of IU and U reduced N2O and NO2I compared to U alone, suggesting that a mixed N source may provide an economical N2O mitigation strategy. Our results show that practices which reduce NO2− accumulation have the potential to also reduce N2O emissions, and that separate consideration of NO3− and NO2− dynamics can provide more insight than their combined dynamics as typically quantified.