The influence of tillage on CH4 consumption is not always consistent; nor is it easy to distinguish from that of concurrent management changes. Tillage may suppress CH4 oxidation by several mechanisms: it enhances immediate mineralization, generating NH+, which may inhibit CH4 oxidation; it tends to dry the soil, suppressing microbial activity; it reduces gas diffusion into the soil via macropores; and it disturbs microbial habitat by affecting soil structure (Hütsch, 1998). Adopting NT, therefore, may sometimes enhance CH4 oxidation.
The influence of NT on CH4 consumption, however, may depend also on other, interactive factors. For example, Cochran et al. (1997) noted an interaction between tillage and soil water contents. Early in the season when soil water contents were high, CH4 consumption was lower in NT than in tilled plots. These high water contents, particularly in the NT plots, may have restricted gas diffusion into the soil, reducing CH4 supply to methanotrophs or favouring CH4 production by restricting oxygen availability. During the remaining season, soils were quite dry, apparently suppressing methanotroph activity more in tilled than in NT soils. Kessavalou et al. (1998) attributed short-term reductions in CH4 oxidation immediately after tillage partly to soil drying. Venterea et al. (2005) observed that tillage increased or decreased CH4 uptake, depending on the fertilizer N treatment. After conducting a limited number of studies, Six et al. (2002) estimated that CH4 consumption would be 20% greater in NT than in tilled soils.
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