Mitigation the greenhouse gas balance of ruminant production systems through carbon sequestration in grasslands.

Soil carbon (C) sequestration (enhanced sinks) is the mechanism responsible for most of the greenhouse gas (GHG) mitigation potential in the agriculture sector. Carbon sequestration in grasslands can be determined directly by measuring changes in soil organic carbon (SOC) stocks and indirectly by measuring the net balance of C fluxes. A literature search shows that grassland C sequestration reaches on average 5 ± 30 g C/m 2 /year according to inventories of SOC stocks and –231 and 77 g C/m 2 /year for drained organic and mineral soils, respectively, according to C flux balance. Off-site C sequestration occurs whenever more manure C is produced by than returned to a grassland plot. The sum of on and off-site C sequestration reaches 129, 98 and 71 g C/m 2 /year for grazed, cut and mixed European grasslands on mineral soils, however with high uncertainty. A range of management practices reduce C losses and increase C sequestration: (i) avoiding soil tillage and the conversion of grasslands to arable use; (ii) moderately intensifying nutrient-poor permanent grasslands; (iii) using light grazing instead of heavy grazing; (iv) increasing the duration of grass leys; and (v) converting grass leys to grass-legume mixtures or to permanent grasslands. With nine European sites, direct emissions of nitrous oxide (N 2 O) from soil and of methane (CH 4 ) from enteric fermentation at grazing, expressed in carbon dioxide equivalents (CO 2 eq), compensated 10 and 34 percent of