Could the prospect of earning revenue from carbon markets encourage smallholder farmers in Africa to adopt more sustainable and productive land management practices? Louis Verchot, lead scientist for climate change at the World Agroforestry Centre, believes it could. His evidence is based, in part, on the findings of a long-term research project in Kenya.

“One of the key constraints preventing small farmers from taking advantage of emerging carbon markets has been the lack of knowledge about how to measure carbon stocks, especially in the soil,” explains Verchot. “To address this, we have been putting together projects that are designed to measure carbon sequestration in agroforestry systems.” One of these has focused on soil organic carbon – one of the major carbon pools in the global carbon cycle – at two sites in Western Kenya.

The experiment, which lasted six years, compared carbon storage in improved fallow systems – these involved the intercropping of maize and nitrogen-fixing legumes – with carbon storage in control plots of continuous maize and naturally regenerated fallow. The treatments were conducted on sandy soils at Teso and on silty-clay soils at Luero, under conditions of tillage and no tillage. “If you are going to establish a market for soil carbon,” explains Laure Dutaur, a soil scientist at the World Agroforestry Centre, “it is important to know not only the quantities of carbon in the soil and where it comes from, but where it is in the soil and the extent to which it is protected from degradation.”

The experiment found that the soil carbon content was significantly higher in the improved fallows than in the control plots. The increase in carbon in the top five centimetres was largely associated with the addition of above-ground inputs, notably the leaves and litter of the nitrogen-fixing species. These were incorporated into the soil prior to the sowing of each maize crop. “While most of the organic matter was found in the coarse fraction in both soil types, the greatest concentrations of carbon were in the micro-aggregates,” explains Dutaur. “This is important as the carbon in the micro-aggregates is less subject to degradation, and more stable, than carbon in the macro-aggregates.” There was little difference between the till and no-till treatments, although Dutaur speculated that this might be because tillage was done with a hand hoe rather than large machinery, as would be the case on most commercial farms.

The research has important implications both for the emerging carbon trade market, which is designed to tackle global warming (see also pages 13-17), and for small farmers. Under the European Union’s Emission Trading Scheme, European companies can purchase carbon credits from industrial sources in developing countries to offset their own carbon emissions, but not from forestry, agricultural or agroforestry projects. One of the main reasons the EU has excluded these schemes is because methods for measuring carbon stored in soils are considered too unreliable. According to Verchot, this no longer holds true.

The research in western Kenya can serve as a model of how to measure soil carbon accurately, and we now have a much better understanding of the processes by which soil carbon is sequestered. “Using agroforestry systems such as improved fallows is a good way of creating stable carbon stocks,” explains Verchot. “The systems have the added attraction of improving soil fertility and increasing crop yields, and in that way they can help to reduce poverty.”

The quantities of carbon sequestered in the soil are relatively modest, especially when compared with the potential of tree-planting schemes. However, this shouldn’t preclude small farmers from pooling their carbon and making collective arrangements with companies seeking to buy carbon credits. “Incentives don’t have to involve direct cash payments to individual farmers,” says Verchot. “A group of farmers might sell their carbon in return for a better road, or books for the local school, or advice from the extension services that they would otherwise have to pay for.”

The research is providing a loose consortium of non-governmental organizations – the Carbon for Poverty Reduction Alliance – with some of the tools it needs to help small farmers participate in the carbon market. Members of the consortium are keen to make carbon markets work so that they favour sustainable land management, encourage rural development and conserve the environment. While the NGOs are responsible for liaising with farmers’ organizations, the World Agroforestry Centre is providing technical support and helping to train the trainers.

Further reading
Verchot L, 2007. Opportunities for Climate Change Mitigation in Agriculture and Investment Requirements to Take Advantage of these Opportunities. A report to the UNFCCC Secretariat Financial and Technical Support Programme. Nairobi: World Agroforestry Centre.
http://worldagroforestry.org/Library/listdetails.asp?id=50515

Dutaur L, Verchot L, 2007. A global inventory of the soil CH4 sink. Global biogeochemical Cycles, vol 21. http://worldagroforestry.org/Library/listdetails.asp?id=50349

Nature magazine’s ‘Research highlights’: Sizing up the sink by Anna Barnett. http://www.nature.com/climate/2008/0801/full/climate.2007.76.html

For more information,
contact Laure Dutaur,
l.dutaur@cgiar.org