Agricultural practices in tropical areas that limit the Greenhouse Effect

FRANCE'S IRD, in collaboration with Brazil's Laboratory of Environmental Biogeochemistry, headed by Professor Carlos Cerri from the Centre of Nuclear Energy and Agriculture (CENA) at the University of Sao Paulo, conducted a study from 1998 to 2003 in the State of Sao Paulo.

Study results indicate that using the non-burning method for sugarcane harvesting can help limit human-generated greenhouse gas emissions. The greenhouse effect is a natural phenomenon that keeps the Earth's temperature at approximately 15 C instead of - 18C.

The sun's light penetrates the atmosphere and is partially absorbed by the Earth's surface, which then emits infrared rays, the majority of which are trapped in the atmosphere by the greenhouses gases: carbon dioxide (Co2), methane (CH4) and nitrous oxide (N2O).

However, human activities (industrial and agricultural practices) have caused the atmosphere's concentration of greenhouse gases to increase.

The comparative and quantitative study of these two management methods (burning and non-burning) showed that the adoption of the non-burning method quickly induced increased storage of carbon in the soils and a reduction of total methane emissions.

The absence of leaf burning also eliminates the emission into the atmosphere of significant amounts of the two other greenhouse gases, CH4 and N2O. If the whole of the surface area devoted to sugarcane in Brazil was managed using the non-burning system, the annual sequestration of carbon would represent about 15% of the emissions ascribable to the use of fossil fuels in the country.

Throughout the world - with the exception of India, where sugarcane is cultivated as an annual crop - sugarcane is burned prior to harvest to facilitate manual chopping and collecting of the stalks (removal of sharp-edged leaves, scaring off of potential predators such as snakes, etc.).

However, this practice immediately releases all of the carbon contained in the leaves (composed of 50% carbon) into the atmosphere. "When the non-burning method is used to harvest sugarcane, the leaves remain on the atmosphere. "When the non-burning method is used to harvest sugarcane, the leaves remain on the ground.

When they decompose, approximately 10% of their carbon is sequestrated as a relatively stable organic matter: mulch", explains Christian Feller, former director of the research unit "Carbon Sequestration in Tropical Soils" at the IRD of Montpellier.

Furthermore, the non-burning system increases soil fauna diversity and limits erosion. Just three years of the non-burning system are sufficient to restore a diversity and a faunal activity equivalent to those of the initial soil.

Already, a law passed in 1997 (decree of May 2000) requires the State of Sao Paulo (which supplies half of Brazil's sugarcane production) to progressively switch over to a non-burning harvesting system. In the meantime, the IRD and its Brazilian partners are pursuing the study over larger surfaces than those studied up to the present.

- Delphine Barrais

Websites: Institute for Research and Development (IRD): www.ird.fr

Centre of Nuclear Energy and Agriculture (CENA): www.cena.usp.br