Cattle methane emission and pasture carbon dioxide balance of a grazed grassland
McGinn, S.M., Beauchemin, K.A., Coates, T., McGeough, E.J. (2014). Cattle methane emission and pasture carbon dioxide balance of a grazed grassland, 43(3), 820-828. http://dx.doi.org/10.2134/jeq2013.09.0371
Grasslands constitute a major land use globally and are a potential sink of atmospheric carbon dioxide (CO2). They are also an important habitat for wildlife and a source of feed that supports ruminant livestock production. However, the presence of ruminants grazing these grasslands is also a source of methane (CH4) that contributes to buildup of greenhouse gases in the atmosphere. Our study measured enteric CH4 from 40 confined heifers in 1-ha paddocks using a dispersion model and CO2 exchange from an adjacent grassland site using a micrometeorological technique. The study was conducted at a mixed prairie grassland located in southern Alberta, Canada. The mean (standard error) CH4 emission was 189 (± 6) g animal-1 d-1 over four campaigns (over a 3-yr period). The daily averaged CO2 exchange from the grassland peaked at +2.2 g m-2 h-1 (sink) in early July and declined to negative values (source) in mid-August. Annually, the grazed grassland was either a net sink for carbon (C) at +40 kg C ha-1 or a small source at -7 kg C ha-1 depending on a cattle stocking density of 0.1 or 0.2 animals ha-1, respectively. However, in basing the exchange on CO2 equivalence (CO2_eq), both stocking densities resulted in the grazed grassland being a source of greenhouse gas of -9 or -338 kg CO2_eq ha-1 y-1. This study illustrates the need to consider the cattle CH4 emissions and the stocking density when evaluating the environmental sustainability of grazed grasslands.
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