Methane oxidation kinetics and diffusivity in soils under conventional tillage and long-term no-till

Abstract

Long-term no-till (NT) farming can improve the methane (CH4) oxidation capacity of agricultural soils, but the relative contribution of soil biological and physical properties on this outcome remains unclear. This understanding is especially important in fine-textured and poorly-drained soils where gas transport can limit expression of the potential for biological CH4 oxidation. A study was conducted to assess gaseous diffusivity (Ds), CH4 oxidation capacity (initial CH4: ~3μLL−1) and other oxidation kinetic parameters (Km, Vmax, Th) in a well-drained (WD) and a poorly-drained (PD) soil under forest (WL), plow till (PT) and long-term NT (50y). Regardless of study site, CH4 oxidation capacity (μgCH4-Ckg−1h−1) was significantly higher in NT (0.26) than in PT soils (0.06), and approached (74%) the level in forest soils. Half saturation constants (Km) and thresholds for CH4 oxidation (Th) were lower in NT (Km: 100.5; Th: 0.6μLCH4L−1) than PT soils (Km: 134; Th: 2.7μLCH4L−1) suggesting a shift in the affinity of methanotrophs for CH4 in soils under long-term NT. Irrespective of soil drainage, Ds was significantly higher in NT (2.97×10−3cm2s−1) than PT soils (1.32×10−3cm2s−1). CH4 oxidation rates in intact soil cores were positively related to Ds (r2=0.64, P<0.002), and were also lower than in sieved soils, suggesting diffusion restriction of CH4 oxidation. This limitation was most pronounced in the PD soils under PT (CH4 consumption in cores was only 6% of that in sieved soils); thus, this combination of soil type and tillage would be least favorable to CH4 uptake at the field-scale. Overall these results confirm the positive impact of NT on both the biological and physical soil attributes essential for CH4 uptake in croplands. Long-term implementation of NT farming could therefore contribute to the mitigation of CH4 emission from agriculture.