Formation of nitrous oxide and dinitrogen by chemical decomposition of hydroxylamine in soils

Abstract

Soil properties affecting formation of nitrous oxide (N 2O) and dinitrogen (N 2) by chemical decomposition of hydroxylamine (NH 2OH) in soils were studied using 19 soils selected to obtain a wide range in properties. It was found that production of N 2O by chemical decomposition of NH 2OH in soils is more rapid than production of N 2 and that, except with calcareous soils, N 2O production greatly exceeds N 2 production. Studies of the correlations between various soil properties and formation of N 2O and N 2 by decomposition of NH 2OH showed that production of N 2O was very highly correlated with exchangeable and oxidized Mn in the soils studied, and that production of N 2 was very highly correlated with pH, CaCO 3 equivalent, exchangeable Ca 2+, and oxidized Mn. Production of N 2 in neutral and acidic soils was highly correlated with both exchangeable and oxidized Mn, and production of N 2 in calcareous soils was significantly correlated with oxidized Fe. The deductions from these correlations that Mn compounds are involved in the reactions leading to formation of N 2O and N 2 by chemical decomposition of NH 2OH in soils, and that CaCO 3 and Fe compounds are involved in the reactions leading to formation of N 2 in calcareous soils, were supported by studies of N 2O and N 2 production through reactions of Mn and Fe compounds with NH 2OH in the presence and absence of CaCO 3. Production of N 2O via chemical decomposition of NH 2OH in soils greatly exceeds production of N 2O through chemical decomposition of nitrite (i.e. via chemodenitrification), and the amount of N 2 produced by decomposition of NH 2OH in most soils exceeds the amount produced by decomposition of nitrite. Work reported indicates that, if N 2O is formed in soils through nonbiological transformations of NH 2OH produced by soil microorganisms, very little of this gas is generated by the reaction of NH 2OH with nitrite frequently postulated as a mechanism of N 2O production in soils (NH 2OH + HNO 2 → N 2O + 2H 2O).