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

The short-term effect of NaNO₃ or (NH₄)₂SO₄ 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. NH ₄ ⁺ application to the loamy soil inhibited CH₄ oxidation entirely whereas in the untreated control soils CH₄ concentration decreased linearly with a rate of-41 nl CH₄ l^-1 h^-1; NO ₃ ^sup- 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 NH ₄ ⁺ and NO ₃ ^sup- treatments completely inhibited CH₄ uptake in this ligh-textured soil. The adverse impact of NH ₄ ⁺ persisted during the entire incubation, although in the loamy soil only 17% of the NH ₄ ⁺ added was recovered after 168 h. The negative effect of NO ₃ ^sup- 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.