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Safe disposal of surplus runoff at low velocity involves the use of some land-forming and engineering techniques, including terraces, waterways, diversion channels, drop structures, chutes, and so forth. Similarly, vegetative strips are used as filter strips for riparian zone management and as shelter belts for wind erosion control. Development of more sustainable grazing systems leads to a reduction of soil erosion rates (Ash et al., 1996; Scanlan et al., 1996; Tenberg et al., 1998). For more detail, see Sections 4.4.2.3 and 4.4.3.3.
Use and Potential
Terracing and other engineering structures are widely used on sloping lands
all over the world. Runoff management to control soil erosion by water and shelter
belts to control wind erosion are important strategies to decrease the risk
of soil erosion. There are several soils and ecoregions where conservation tillage
is not applicable and adoption of these erosion control measures is essential.
Many of these techniques are also used in conjunction with conservation tillage.
Erosion control enhances the productivity of these lands.
Current Knowledge and Scientific Uncertainties
Potential SOC sequestration through erosion-control measures depends on an increase
in biomass productivity through conservation of water and efficient use of fertilizer
and farm chemicals. Initial energy input that is required for the installation
of engineering techniques is offset by long-term benefits of erosion control
and enhanced productivity. Although the productivity benefits of erosion control
measures are known, improvements in the SOC pool are not widely established.
Improved grazing management systems, which reduce erosion, also lead to increases
in the SOC stock (Kelly et al., 1996; Tongway and Ludwig, 1996).
Methods
Methods for the measurement of SOC sequestration through erosion control involve
soil sampling for periodic assessment of SOC stocks and estimation of the reduction
in depletion of the SOC resulting from decreased soil erosion. The SOC input
can also be measured by using established empirical relations for specific soil
types and farming systems within an ecoregion.
Time Scale
The effects of erosion-control measures are cumulative and occur over a long
time, so changes in SOC stocks need to be measured over a period of 25-50 years
through periodic assessment. The rate of SOC sequestration may vary among ecoregions
and can be high for shelter belts and contour hedgerows.
Monitoring, Verifiability, and Transparency
Monitoring and verification of SOC sequestration must be carried out by using
ground truthing through periodic measurements of SOC stock in benchmark sites.
Adoption of these measures can be verified through remote-sensing techniques
and ground truthing through local extension organizations. Installations of
terraces, waterways, shelter belts, riparian protection zones, and other engineering
devices are conspicuous, easily checked, and verified through a combination
of measures that involve remote sensing and ground truthing. The empirical relations
developed for estimating the rates of SOC sequestration can be verified through
soil sampling and analysis for benchmark soils in principal ecoregions.
Removals
Maintenance of engineering devices is critical to their performance and effectiveness.
Defective installation and poor maintenance can exacerbate soil erosion. Therefore,
regular maintenance of these installations is critical to ensure the benefits
of engineering devices.
Associated Impacts
There are numerous ancillary benefits and associated impacts. Important among
these impacts are increased productivity; improved water quality; reduced use
of fertilizers, especially nitrates; decreased siltation of waterways; reduced
methane emissions; associated reductions in risks of flooding; and increased
biodiversity in shelter belts and riparian zones.
Relationship to IPCC Guidelines
The effects of erosion-control practices (other than for reduced tillage) on
changes in soil carbon stocks are not included in the Guidelines.
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