Effects of grassland management on the emission of methane from intensively managed grasslands on peat soil

Methane (CH₄) is the most important greenhouse gas next to CO₂ and as such it contributes to the enhanced greenhouse effect. Peat soils are often considered as sources of CH₄. Grasslands on the other hand are generally considered to be a net sink for atmospheric CH₄. The aim of this study was twofold: (i) to quantify the net CH₄ emission of intensively managed grasslands on peat soil in the Netherlands; and (ii) to assess the effects of grassland management, i. e. drainage, nitrogen (N) fertilization, and grazing versus mowing, on CH₄ emission rates. Net CH₄ emissions were measured weekly or biweekly for one year with vented closed flux chambers at two sites, one with a mean ground water level of 22 cm below surface and one with a mean ground water level of 42 cm. On each site there were three treatments: mowing without N application, mowing with N application, and grazing with N application. The dominating species was perennial ryegrass (Lolium perenne L.). Net CH₄ emissions were low, in general in the range of - 0.2 to 0.2 mg CH₄ m⁻² d⁻¹. In the relatively warm summer of 1994, consumption of atmospheric CH₄ peaked at 0.4 mg m⁻² d⁻¹. On an annual basis, the sites were net consumers of atmospheric CH₄. However, the consumption was small: 0.31 to 0.08 kg CH₄ ha⁻¹ yr⁻¹. Effect of mean ground water level was significant, but small. There were no significant effects of withholding N fertilization for some years and grazing versus mowing on net CH₄ emissions. We conclude that grassland management of intensively managed grasslands on peat soil is not a suitable tool for reducing net CH₄ emissions.