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. NH4+ oxidation was also measured in the presence of the inhibitors to determine whether they had differential activity with respect to CH4 and NH4+ oxidation. The addition of NH4Cl at 25 mug 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 mug 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 mumol 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 mug g-1 soil in the fine sandy loam (83%) in the sandy clay loam (60%), but NH4+ 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.