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

Abstract

We studied the annual methane (CH 4 ) flux rates from experimental excreta patches on a boreal dairy pasture in Eastern Finland. The CH 4 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 CH 4 fluxes between plant species. CH 4 emissions originated mainly from the fresh dung pats. The annual CH 4 fluxes from the control sites without excreta were on average -0.60 ± 0.1 kg CH 4 ha -1 (net uptake) and with the excreta 0.47 ± 0.3 kg CH 4 ha -1 (net emission). Thus, excreta originating from dairy cows can turn boreal swards from weak sinks to small sources of CH 4 . However, these CH 4 emissions from pasture are only 0.2% of the total CH 4 emissions from a dairy cow.

Quantifying Beetle-Mediated Effects on Gas Fluxes from Dung Pats

“…Absolute flux rates of CO 2 , CH 4 and N 2 O in chambers with dung were observed to be high compared to emissions from agricultural soils in general [4], [11], [12], [33] – and compared to the fluxes observed in our control chambers without dung. However, the elevated fluxes from individual pats were of relatively short duration (Fig.…”

“…These studies also found significant fluxes of CO 2 , CH 4 and N 2 O from dung (e.g. [5], [9], [10], [12], [33]). CH 4 emissions from the dung of grazing dairy cows have been observed to be particularly high, ranging from 300 to 2040 mg CH 4 m −2 over the first ten days [4].…”

“…CH 4 emissions from the dung of grazing dairy cows have been observed to be particularly high, ranging from 300 to 2040 mg CH 4 m −2 over the first ten days [4]. Even if dung only covers a fraction of the pasture surface, the overall CH 4 budget of a boreal pasture switches from a CH 4 sink into a CH 4 source when emissions from dung pats are taken into account [12]. These considerations highlight the importance of including dung pats, and the factors influencing gas fluxes from them, in studies of agricultural GHG emissions.…”

“…Yet, most studies on GHG fluxes from dung consider the impacts of abiotic conditions, such as temperature and moisture (e.g. [9], [10]), or of plant and soil interactions [11], [12], whereas the role of the dung fauna has received considerably less attention. While recent findings suggest that the activity of earthworms may increase emissions of N 2 O and CO 2 from dung pats [13], [14], and increase the rate of CH 4 production in soils [15], [16], the potential for other invertebrates to modify emissions of GHGs is little explored (but see [17]–[19]).…”

Eddy covariance methane flux measurements over a grazed pasture: effect of cows as moving point sources

“…Therefore the soil fluxes referred to here are the combination of fluxes from the soil microbial community and fluxes from dung/urine which normally dominate the pure soil fluxes (Flessa et al, 1996). Emissions from cattle dung were estimated to be 0.778 g CH 4 head −1 d −1 (Flessa et al, 1996) and from Finnish dairy cows to 470 g CH 4 ha −1 over a 110 day grazing period (Maljanen et al, 2012). The soil flux in the present study (16 g ha −1 d −1 ) is around 3 times higher than the corresponding flux calculated with the literature numbers (Flessa et al (1996): 5 g ha −1 d −1 and Maljanen et al (2013): 4.3 g ha −1 d −1 ).…”