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Hydroxylamine (HA) is a crucial intermediate in the first step of nitrification, i.e., the oxidation of ammonium to nitrite. Due to its reactivity, HA may play a key role in soil N2O emission. To determine soil HA concentrations and to explore the correlation between soil HA concentrations and N2O emission rates, we developed a novel, extremely sensitive method based on fast extraction of HA from the soil at pH1.7, oxidation of HA to N2O with Fe3+ and analysis of the N2O with gas chromatography (GC). The new method was tested on soil samples from a temperate Norway spruce forest, comparing soil HA concentrations with N2O emission rates determined with microincubations of the soil samples in GC vials. Our results demonstrate that the new GC method is extremely sensitive, being able to detect soil HA contents as low as 0.3 μg N kg-1 dry soil. HA content in the forest soil samples ranged between 0.3 and 34.8 μg N kg-1 dry soil. Moreover, N2O emission rates were significantly correlated with soil HA content (r²=0.80), suggesting a key role of HA in N2O formation under aerobic conditions. [ABSTRACT FROM AUTHOR]

Abstract: The binding of the pesticide metabolite aminobenzothiazole (ABT) to a model humic acid was studied. It is shown that, by comparing quantum chemically calculated and experimental 15N NMR chemical shifts, proton transfer occurs in complexes of ABT with aminobenzoic acid (AB) and thiophene carboxylic acid (TC). For extended structures, i.e. the crystalline form of AB–ABT and TC–ABT, only in the latter proton transfer is observed, in agreement with previously reported analysis based on IR spectroscopy. Thus it is concluded that in the bimolecular complexes as model systems for structures found in humic substance, here specifically AB–ABT, proton transfer may be different as compared to the crystalline state. Moreover, it was shown that combining experimental NMR work and quantum chemical calculations can reveal the presence of proton transfer. [Copyright &y& Elsevier]