Dynamics of nitrite in acidic soil during extraction with potassium chloride studied using ¹⁵ N tracing

Nitrite is well known to be unstable, including during soil extraction with KCl (especially in acidic soils), but the source and fate of NO₂ ^- in the short duration of the extraction process remain unclear.

A series of ¹⁵ N-tracing studies explored NO₂ ^- transformations during KCl extraction in acidic and alkaline soils. Tests considering multiple factors assessed the interactions of such factors as soil sterilization, extraction time, and pH adjustment. After addition of ¹⁵ NO₂ ^- , ¹⁵ NH₄ ⁺ , and ¹⁵ NO₃ ^- tracers, the concentrations and isotopic compositions of N₂ O, N₂ , NH₄ ⁺ , NO₃ ^- , NO₂ ^- , and dissolved organic nitrogen (DON) were measured to investigate the production and consumption of NO₂ ^- .

Nitrite was stable in alkaline soils during KCl extraction. In contrast, changes did occur in acidic soils during KCl extraction: NO₂ ^- declined rapidly in the first 10 min of extraction although the subsequent rate of decrease lessened as the extraction time progressed. Significant dilution of ¹⁵ NO₂ ^- suggested high rates of NO₂ ^- production and even higher rates of consumption. The soil's organic N was the only source of NO₂ ^- and also its main destination. Soil sterilization showed that NO₂ ^- processes during extraction were chemical, not microbial. The pH adjustment of acidic soil stabilized its NO₂ ^- .

Overall, the pH adjustment of KCl solution appears favorable for investigating NO₂ ^- dynamics. For example, this work recommends an extraction solution comprising a 4:1 mixture of 2.5 M KCl solution and pH 8.4 buffer, which was more convenient to operate than the method reported by Stevens and Laughlin.