• The role of the farmers
• In climate change mitigation
• Carbon storage
• Carbon sequestration in biomass
• Carbon sequestration in the soil
• In watershed protection services
• In biodiversity conservation
• Preserving agriculture landscape

In climate change mitigation

Carbon sequestration in the soil

All soils contain organic or inorganic carbon.  The extent of additional carbon that can be sequestered depends on cropping system and geographical conditions

Figure 2.1 – Potential to sequester additional carbon in soils on croplands(6) click on the picture to enlarge

All soils contain carbon, deposited in some organic or inorganic form or dissolved in groundwater.  Organic carbon storage, in the form of soil organic matter, is the balance between the addition of dead plant material (leaf and root litter) and losses from decomposition processes.  Inorganic carbon is stored in carbonates both in solid form and dissolved in groundwater. 

Although soil inorganic carbon is relatively stable, it will release carbon dioxide if the carbonates become exposed through erosion.  In addition, irrigation can cause inorganic carbon to become unstable, thus the release of carbon dioxide from inorganic sources is seen as a major problem if irrigation is used in any system that is trying to store carbon.  Furthermore, groundwater in arid lands often contains concentrations of carbon dioxide that are much higher than in the atmosphere, so when it is used for irrigation, carbon dioxide is released to the atmosphere.

The extent of additional carbon that can be sequestered depends on the cropping system and geographical conditions.  The areas with significant “soil carbon gap” indicate locations where soil carbon levels are currently low but medium-to-high technical potential for sequestration exists.  Such locations are shown in Figure 2.1 provides a preliminary perspective on where cropping systems could be changed to achieve significative soil carbon sequestration.

Changes in agricultural management practices can accelerate or reverse the degree of sequestration: planting of cover crops or mulch farming combined with zero tillage and agro-forestry will increase below ground carbon sequestration, although the effects can differ quite dramatically by location.(7) Currently various voluntary carbon market standards trade offsets generated from soil carbon sequestration -see box 2.1- and these represent about 20% of the overall voluntary carbon market(8)

Box 2.1. Grassland management options generating offsets for the voluntary carbon market(9)

measures to enhance soil C stocks from practices that increase belowground inputs or slow decomposition increasing forage productivity (e.g. through improved fertility and water management) introducing species with deeper roots and/or more root growth and reducing degradation from overgrazing

measures to reduce soil N2O emissions by enhancing the N use efficiency of targeted crops, reducing the need for added N as fertilizer or manure: improved timing of application (e.g., split application) improved formulations (e.g. slow release fertilizers, nitrification inhibitors) and improved placement of N

lowering N2O and CH4 emissions by reducing fire frequency and/or intensity

reduce emissions of CH4 and N2O from grazing animals by: improving livestock genetics improving the feed quality (e.g.introducing new forage species, feed supplementation); and/or by managing stocking rates and distribution (rotational and seasonal grazing)

Payments for Environmental Services from Agricultural Landscapes - PESAL
is a project funded by the FAO Netherlands Partnership Programme © FAO 2010