Dairy cow excreta patches change the boreal grass swards from sink to source of methane

Abstract

We studied the annual methane (CH4) flux rates from experimental excreta patches on a boreal dairy pasture in Eastern Finland. The CH4 fluxes were measured with a chamber technique during snow free seasons and with gas gradient technique during winter from timothy-meadow fescue sward with mineral N fertilization (220 kg ha-1) and from grass-white clover mixture without mineral N addition. The simulated dung and urine patches were applied in June or August two consecutive grazing seasons. The measurements were carried out for a year following each application except for the last application period, measurements were extended to two years. There were no significant differences in CH4 fluxes between plant species. CH4 emissions originated mainly from the fresh dung pats. The annual CH4 fluxes from the control sites without excreta were on average -0.60 ± 0.1 kg CH4 ha-1 (net uptake) and with the excreta 0.47 ± 0.3 kg CH4 ha-1 (net emission). Thus, excreta originating from dairy cows can turn boreal swards from weak sinks to small sources of CH4. However, these CH4 emissions from pasture are only 0.2% of the total CH4 emissions from a dairy cow.