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

Rationale: Nitrite is well known to be unstable, including during soil extraction with KCl (especially in acidic soils), but the source and fate of NO in the short duration of the extraction process remain unclear.

Methods: A series of N-tracing studies explored NO 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 NO , NH , and NO tracers, the concentrations and isotopic compositions of N O, N , NH , NO , NO , and dissolved organic nitrogen (DON) were measured to investigate the production and consumption of NO .

Results: Nitrite was stable in alkaline soils during KCl extraction. In contrast, changes did occur in acidic soils during KCl extraction: NO declined rapidly in the first 10 min of extraction although the subsequent rate of decrease lessened as the extraction time progressed. Significant dilution of NO suggested high rates of NO production and even higher rates of consumption. The soil's organic N was the only source of NO and also its main destination. Soil sterilization showed that NO processes during extraction were chemical, not microbial. The pH adjustment of acidic soil stabilized its NO .

Conclusions: Overall, the pH adjustment of KCl solution appears favorable for investigating NO 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.