What is
Carbon Sequestration?

What is Carbon?

Carbon is a very common element found in minerals like diamonds and graphite, in salts like carbonates, and also in the tissues of all living things. Carbon atoms make up the backbone of all organic compounds. These include sugars, starches, cellulose, fats, proteins and even fossil fuels like oil and coal that formed from plants that grew many millions of years ago.

Organic compounds store a lot of energy in their molecules. We therefore use them as fuels to give us energy (sugars, starches and fats), to keep us warm (wood and coal) or to power our vehicles and industries (oil, petrol and natural gas). We need oxygen to break down organic compounds and liberate the stored energy. This process is called oxidation and includes both respiration and combustion. When organic compounds are oxidised, carbon dioxide gas is produced as a waste product.

Plants absorb carbon dioxide from the air and use the energy of sunlight to convert it into energy-rich organic compounds like carbohydrates. This process, called photosynthesis, ensures that carbon continues to cycle in the environment.

Carbon Dioxide and Climate Change

Carbon dioxide is known as a "greenhouse gas". It is one of the gases that can trap heat in the earth's atmosphere, preventing it from escaping into space. By trapping escaping heat, greenhouse gases help to keep the earth warm. Unfortunately, levels of these gases have been rising steadily since the beginning of the industrial age, since:

• We have been burning huge quantities of fuel, including fossil fuels, releasing carbon dioxide into the atmosphere.
• We have been destroying vast tracts of vegetation, including tropical rainforests, thus reducing the rate of photosynthesis that removes carbon dioxide from the atmosphere.

As a result of this, the earth is getting warmer and the global climate is changing. In South Africa, we face the prospect of large parts of the country becoming hotter and drier, while other parts will experience more frequent and extreme flooding. Climate change will affect farmers - and we must therefore do all we can to reduce the levels of carbon dioxide in the atmosphere and slow the effects of climate change.

Carbon Sinks - Reversing the Process

Certain agricultural practices have contributed to the increasing levels of carbon dioxide in the atmosphere. However, farmers can also play an important role in helping to reverse this process by "fixing" carbon in plant and animal tissues and by returning organic carbon to the soil. These stores of organic carbon are known as "carbon sinks", because they "drain" carbon dioxide from the atmosphere and hold it for a period in a form that does not contribute to global warming.

Carbon sinks may be relatively temporary or permanent. For example, grasslands are more temporary carbon sinks than forests because the grazing and burning of grasses causes rapid turnover of organic matter. Trees grow more slowly and store organic carbon for many years in woody tissues. However, they too may one day be burned as fuel or die and rot, releasing carbon dioxide into the atmosphere. Soil is the ultimate carbon sink: it contains organic matter derived from plants, animals, fungi and bacteria. About 60% of organic carbon in the soil occurs in a form that binds tightly to clay particles and cannot easily be dislodged. Soil enriched with organic matter is therefore a very stable carbon sink as it can store large amounts of carbon for a very long time.

By managing the land to increase organic carbon in the soil, farmers can fight global climate change and at the same time benefit from richer, more productive soil.

Protect the Vegetation - Revitalise the Soil

• Vegetation cover protects the soil from the impact of raindrops that fall to earth at great speed and do enormous damage to the structure of the soil at a microscopic level. Raindrops break up clumps or aggregates of clay. The tiny clay particles clog up pores in the soil, forming a crust that water cannot penetrate. This reduces infiltration and soil moisture, and increases soil erosion.
• Vegetation traps carbon in plant tissues and increases the amount of organic matter that can return to the soil. This increases the populations of soil organisms, the rate of decomposition and the levels of nutrients released into the soil. Soil organic matter also helps to maintain clay aggregates and improve both soil structure and water-holding capacity.
• Ploughing and tilling expose huge surface areas of the soil to air and to the warmth of the sun. This results in more rapid oxidation, breaking down organic matter in the soil and releasing carbon dioxide into the atmosphere.

Manage the Land to Increase Stored Carbon

Returning organic carbon to the soil is not only good for reducing levels of carbon dioxide in the atmosphere; it also directly benefits agricultural productivity:

• Minimum tilling conserves organic matter, stabilises the soil structure and reduces erosion while increasing levels of organic carbon in the soil.
• Returning organic matter to the soil enhances its fertility, improves its water-holding capacity and stimulates plant growth.
• Using existing standing crops as mulch and animal wastes as fertiliser reduces input costs of fertiliser.
• Restoring degraded lands to natural veld increases biological diversity and enhances ecological processes and resilience of ecosystems.
• Using renewable sources of energy rather than fossil fuels reduces the overall carbon load in the atmosphere. For example, in terms of the relative amounts of carbon currently absorbed from and released into the atmosphere, it may be preferable to burn firewood grown in wood-lots rather than coal.

Fact sheet

Click here to view our fact sheet on carbon sequestration.