Cultivation, nitrogen fertilization, and set-aside effects on methane uptake in a drained marsh soil in Northeast China.

To evaluate the effect of cultivation, nitrogen fertilizer, and set aside on CH₄ uptake after drained marshland was converted into agricultural fields, CH₄ fluxes and CH₄ concentrations in soil gas werein situmeasured in a drained marsh soil, a set-aside cultivated soil, and cultivated soils in Sanjiang Plain of Northeast China in August 2001. Over the measuring period, the highest CH₄ uptake rate was 120.7±6.2 μg CH₄ m⁻² h⁻¹ in the drained marsh soil and the lowest was 29.5±4.9 μg CH₄ m⁻² h⁻¹ in the set-aside cultivated soil, showing that there was no significant recovery of CH₄ uptake ability 5 years after cultivation activity was stopped. CH₄ uptake rates were significantly less in the cultivated soils than in the drained marsh soil by 30.1–74.6%, which resulted mainly from cultivation and partly from nitrogen addition. A significantly negative correlation between CH₄ flux and bulk density in the cultivated soils tilled by machine suggests that cultivation reduced CH₄ uptake through compaction, because of the enhanced diffusion resistance for CH₄ and O₂. Nitrogen fertilization slowly reduced but persistently affected CH₄ uptake even after long-term application of nitrogen. [ABSTRACT FROM AUTHOR]