Suppression of methane oxidation in aerobic soil by nitrogen fertilizers,nitrification inhibitors,and urease inhibitors

Concentrations of CH₄, a potent greenhouse gas, have been increasing in the atmosphere at the rate of 1% per year. The objective of these laboratory studies was to measure the effect of different forms of inorganic N and various N-transformation inhibitors on CH₄ oxidation in soil. NH ₄ ⁺ oxidation was also measured in the presence of the inhibitors to determine whether they had differential activity with respect to CH₄ and NH ₄ ⁺ oxidation. The addition of NH₄Cl at 25 g N g^-1 soil strongly inhibited (78–89%) CH₄ oxidation in the surface layer (0–15 cm) of a fine sandy loam and a sandy clay loam (native shortgrass prairie soils). The nitrification inhibitor nitrapyrin (5 g g^-1 soil) inhibited CH₄ oxidation as effectively as did NH₄Cl in the fine sandy loam (82–89%), but less effectively in the sandy clay loam (52–66%). Acetylene (5 mol mol^-1 in soil headspace) had a strong (76–100%) inhibitory effect on CH₄ consumption in both soils. The phosphoroamide (urease inhibitor) N-(n-butyl) thiophosphoric triamide (NBPT) showed strong inhibition of CH₄ consumption at 25 g g^-1 soil in the fine sandy loam (83%) in the sandy clay loam (60%), but NH ₄ ⁺ oxidation inhibition was weak in both soils (13–17%). The discovery that the urease inhibitor NBPT inhibits CH₄ oxidation was unexpected, and the mechanism involved is unknown.