Greenhouse effect: pastures trap carbon

09/03/2010 - Article

Forests are not the only ecosystems capable of trapping carbon. Pasture could also be a good candidate. In French Guiana, measures are currently being undertaken to quantify their carbon storage capacity, with the help of two flow towers that have been set up on grassland.

They are in the dock! Ruminants are accused of contributing to the greenhouse effect, particularly via their methane emissions expelled by their burps. However, in French Guiana, the establishment of grassland is one of the agricultural development systems being used to increase local cattle production and meet the needs of future demographic growth. Yet, pasture is synonymous with deforestation and a reduction in carbon (C) storage.

In temperate zones, grassland stores nearly 65 tonnes of carbon per hectare

How can ruminant production systems be set up in a way that limits greenhouse gas emissions? “Animal production is responsible for 18% of greenhouse gas emissions, according to an FAO report. Grassland compensates for part of the emissions by acting as a carbon sink” , says Vincent Blanfort, a grassland agro-ecologist for CIRAD.
While the Amazonian forest has considerable potential for trapping carbon–up to 300 tonnes per hectare in French Guiana–the estimated quantity of carbon stored in the soil of grassland in temperate zones is almost 65 tonnes per hectare. One tonne of carbon per hectare per year can be added in some conditions. Therefore, in French Guiana and more generally in Amazonia, it is important to know what becomes of carbon in the soil after the forest has been transformed into grassland and to understand how these pastures can continue to store carbon in the soil.

Flow towers for trapping C02 in grassland

The agro-ecologist will be conducting his research on livestock farms in French Guiana on pasture resulting from deforestation. It is part of the CARPAGG project (greenhouse gases and carbon in grassland in French Guiana), funded by the European Regional Development Fund (ERDF) and CIRAD. The aim of the study is to measure the quantities of CO2 in the atmosphere, with the help of two flow towers, equipped with sensors: "If the flow observed goes down, this shows that the plants absorb C02 via photosynthesis and store it ", says Vincent Blanford. "If it goes up, it shows that the plants and the pasture system with the cattle breathe and emit CO2 ". This is the mechanism with which grassland accumulates carbon in the soil. In fact, the humus produced by the plant cycle contains almost 50% carbon, which means there is that much less CO2 in the atmosphere.

These experiments will help identify the carbon dynamics in pasture and define the management practices that allow partial compensation for the carbon losses resulting from their establishment (which was to the detriment of the forest). In the medium term, the project should provide an original set of references that could be applied in other Amazonian contexts, such as Brazil.

This article was published in issue No. 1 of Agronews – French Guiana edition, which came out in March 2010.