Carbon cycling and sequestration opportunities in temperate grasslands

Abstract

Abstract. Temperate grasslands account for c. 20% of the land area in Europe. Carbon accumulation in grassland ecosystems occurs mostly below ground and changes in soil organic carbon stocks may result from land use changes (e.g. conversion of arable land to grassland) and grassland management. Grasslands also contribute to the biosphere±atmosphere exchange of non-CO 2 radiatively active trace gases, with¯uxes intimately linked to management practices. In this article, we discuss the current knowledge on carbon cycling and carbon sequestration opportunities in temperate grasslands. First, from a simple two-parameter exponential model ®tted to literature data, we assess soil organic carbon¯uxes resulting from land use change (e.g. between arable and grassland) and from grassland management. Second, we discuss carbon¯uxes within the context of farming systems, including crop±grass rotations and farm manure applications. Third, using a grassland ecosystem model (PaSim), we provide estimates of the greenhouse gas balance, in CO 2 equivalents, of pastures for a range of stocking rates and of N fertilizer applications. Finally, we consider carbon sequestration opportunities for France resulting from the restoration of grasslands and from the deintensi®cation of intensive livestock breeding systems. We emphasize major uncertainties concerning the magnitude and non-linearity of soil carbon stock changes in agricultural grasslands as well as the emissions of N 2 O from soil and of CH 4 from grazing livestock.

Modeling vegetation and carbon dynamics of managed grasslands at the global scale with LPJmL 3.6

“…Both mechanisms are intentionally used in European livestock systems to maximize herbage digestibility by sowing suitable forage cultivars and frequent grazing (Soussana et al, 2004).…”

“…The frequency of biomass removal and its fate (complete removal as feed to other locations or partially remaining in the form of manure on the plot) have effects on the productivity of the grass itself and on the carbon and water budget of the grassland (Soussana et al, 2004;Herrero et al, 2016).…”

“…For intensive grazing in Europe (about 2 livestock units per hectare -LSU ha −1 ), Soussana et al (2004) report a harvest fraction of 60 % of the aboveground dry matter production and less for lower livestock densities. The digestible part of the ingested carbon (up to 75 %) is respired shortly after intake (Soussana et al, 2004). A total of 25-40 % of the carbon intake is non-digestible and returned to the grassland in the form of excreta (Soussana et al, 2004).…”

“…The digestible part of the ingested carbon (up to 75 %) is respired shortly after intake (Soussana et al, 2004). A total of 25-40 % of the carbon intake is non-digestible and returned to the grassland in the form of excreta (Soussana et al, 2004). Thus, management includes also the possibility to apply manure which is either directly dropped by livestock or spread by machinery.…”

“…Similar to option G D , the removed carbon is divided into a harvest flux (incorporation into animal body and animal respiration) and a manure application to the soil pool which is subject to mineralization there. The portion of the grass intake that remains on the grassland as manure (which is incorporated into the fast soil carbon pool) is 25 % (Soussana et al, 2004).…”