Wednesday, 9 November 2011

Agricultural Carbon Sinks for climate change mitigation

A carbon sink is a natural or artificial reservoir that gathers and stores carbon containing chemical compounds for an indefinite period. Agricultural carbon sinks also called agriculture carbon sequesters refers to agricultural farms, ranches and forests which absorb CO2, the most important global warming gas emitted by human activities. According to the greenhouse effect theory, the discharge into the atmosphere of large quantities of carbon dioxide (CO2) and other green house gases eventually warms the planet causing climate change. This is due to destruction of the ozone layer which whose function is to reduce the strength of the radiation or sun rays reaching the earth.
Increased concentration of CO2 and other greenhouse gases in the atmosphere has led to global warming. Average global temperatures increased by about 1 degree in the 20th century, contributing to the thawing of the permafrost, rising ocean levels and extreme weather according to scientist. Currently there is increased global concern of greenhouse gas emissions and scientists are researching on ways to limit the amount of CO2 entering the atmosphere; Therefore there is a global drive to limit CO2 emissions into the atmosphere through Carbon Capture and Storage (CCS) technologies, in order to mitigate climate change. Carbon sequestration is the process through which agricultural and forestry practices remove carbon dioxide (CO2) from the atmosphere and deposit it in a reservoir.Agriculture  Carbon sequestration activities can help to prevent global climate change by enhancing carbon storage in soils and trees, preserving existing soil and tree carbon, and by reducing emissions of CO2, methane (CH4) and nitrous oxide (N2O).

In order to comprehend CO2 emissions from the soil, it is important to understand the carbon cycle in farm systems.  Normally CO2 in the atmosphere is absorbed by plants, and it is transformed into carbohydrates, cellulose and other sugars, during the process of photosynthesis.  The plant uses some of the carbon compounds to meet its energy needs and converts the rest back into CO2.  Some of the carbon remaining in the plant is then removed from the system when the plant is harvested; the rest ends up in the ground and is transformed into CO2 again by microbes in the soil.  This cycle is identical in all crop systems, but the quantities of CO2 involved vary depending on climate, soils and type of plant.  The cycle is slightly more complex on farms where animals are raised because instead of being removed from the system, a considerable amount of the plant matter is used as bedding or animal feed.  Then carbon is released in various ways such as removal by the animals in the form of CO2, removal in form of animal products (e.g. meat), and a significant amount is returned to the ground in the form of manure.

The soil is a great carbon sink in form of organic matter and various farming practices enhance carbon sequestration in the soil. Therefore creation of a soil carbon sink calls for adoption of land management practices that increase the organic carbon content of the soil. This includes:-
·        Use of minimum tillage , common in conservation agriculture, which minimizes soil disturbance reducing the amount of CO2 released into the atmosphere ;
·        Cover cropping as temporary cover between seasons;
·        Crop rotation and intercropping;
·        Soil conservation using contour terraces or vegetative strips;
·        Rotation grazing and high-intensity short-term grazing which involves concentrating livestock in small paddocks for days at a time so they graze lightly but evenly which encourages roots to grow deeper into the soil;
·        Planting of shrubs and trees as windbreaks;
·        Use of farmyard and compost manure to increase soil organic matter;
·        Conversion of marginal farmland to perennial grasses or trees;
Therefore Soil carbon sequestration is a good way of reducing agricultural greenhouse gas emissions, and creation of a market for reducing carbon emissions would enable farmers to benefit economically from the process. Use of the above land management practices enables the soil to capture more CO2 than it emits; in effect CO2 is removed from the atmosphere and stored in the soil. As matter of fact, soil Carbon sequestration is a multi- purpose strategy with several co-benefits which include:-
1.      Reduced atmospheric CO2 and climate change mitigation;
2.      Improved agricultural productivity;
3.      Food security improvement;
4.      Increased farm income;
5.      Improved water conservation;
6.      Reduced soil erosion;
7.      Increased farm profitability;
8.      Environmental conservation;
9.      Poverty reduction;

Forests are carbon stores or carbon sinks when they are increasing in density or area. Growing trees sequester large amounts of carbon dioxide from the atmosphere through the process of photosynthesis. The carbon is used to build the plant and the oxygen is released back into the atmosphere. Forest fires and deforestation releases absorbed carbon back into the atmosphere, due to rapidly increased oxidation of soil organic carbon.