Gaseous Nitrogen Evolution During Nitrification of Ammonia Fertilizer and Nitrite Transformations in Soils

Abstract

AbstractThe biological oxidation of NO2‐ is inhibited when alkaline‐hydrolyzing N fertilizers are band‐applied to soils, and NO2‐ may accumulate. Nitrogenous gases can be evolved with NO2‐ is added to soil. The aim of the work described here was to determine if gaseous‐N losses could occur via chemical transformations of NO2‐ during nitrification in soils treated with NH3 fertilizer.Evolution of N2, N2O, and NO + NO2 occurred during nitrification in three soils treated with aqueous NH3. Losses occurred when measured soil pH was > 7.5. The highest gaseous‐N loss amounted to 16.5% of applied‐N (1156 µg N applied/g of soil) in a calcareous soil incubated for 28 days at 30°C. Nitrogen was the major gaseous form of N evolved in all soils. In two soils, NO2‐ did not accumulate to more than 13 µg N/g of soil, but substantial N2 emission was measured. Addition of the nitrification inhibitor, nitrapyrin, with the fertilizer, prevented NO2‐ accumulation without preventing nitrification. This treatment prevented N2O evolution and markedly reduced loss of N2 and NO + NO2.Evolution of N2, N2O, and NO + NO2 occurred in the three soils following NO2‐ addition. Loss of N2 was very sensitive to soil pH, and markedly increased with increasing acidity. However, N2 was readily evolved when soil pH was slightly alkaline. Evolution of NO + NO2 was inversely related to pH, but N2O loss was highest in the most alkaline soil (pH 8.4). The marked similarities within individual soils of the patterns of gaseous‐N losses obtained for NH3 and NO2‐ treatments, strongly suggest that similar processes were operating. Gaseous‐N evolution was similar in γ‐irradiated and nonirradiated soils treated with NO2‐. These results, together with the effect of nitrapyrin, suggest that gaseous‐N losses can occur via chemical transformations of NO2‐, when the competitive biological oxidation of NO2‐ by Nitrobacter is inhibited.