CH4 oxidation in two temperate arable soils as affected by nitrate and ammonium application

The short-term effect of NaNO3 or (NH4)(2)SO4 application on CH4 oxidation was measured under laboratory conditions with sieved soils collected from the top layer (0-12 cm) of a loamy and a sandy soil. The soils were incubated in sealed flasks and the CH4 and CO2 concentrations in headspace were measured periodically. On each gas sampling date the soils were analysed for inorganic N, electro-ultrafiltration organic N, and pH. NH4+ application to the loamy soil inhibited CH4 oxidation entirely whereas in the untreated control soils CHS concentration decreased linearly with a rate of -41 nl CH4 l(-1) h(-1); NO3- application to this soil caused a small but significant reduction in CH4 uptake. The CH4-oxidizing ability of the sandy soil was low, even in the control. This was mainly a result of the disturbed soil structure after sieving. Both NH4+ and NO3- treatments completely inhibited CH4 uptake in this light-textured soil. The adverse impact of NH4+ persisted during the entire incubation, although in the loamy soil only 17% of the NH4+ added was recovered after 168 h. The negative effect of NO3- was probably caused by an increase in osmotic potential. Immediate inhibition of CH4 oxidation after inorganic N addition was demonstrated in two arable soils, although the effect was directly related only in part to soil N transformations.