Agriculture and Soil Carbon: A Critical Part of Climate Change Mitigation

Previous global accords and discussions on climate change have not included agriculture. Specifically, they have left out the role that soil plays as an enormous storehouse of carbon, and what that means in terms of mitigating carbon emissions and the greenhouse effect.

The omission of agriculture as a player in the fate of soil carbon stocks has been largely due to difficulties regarding ways to measure soil carbon levels and stability on site, in undisturbed soil samples. Until recently, such measurements were only possible within the laboratory, using sophisticated and expensive equipment.

But now, there are new techniques, which have the potential of providing cost effective and reliable measurements. Scientists at CIP and EMBRAPA have applied and validated a new method for measuring soil carbon, using a system that is portable, affordable, and reliable. It uses a new device, developed by EMBRAPA-Agricultural Instrumentation, employing laser-induced optical techniques to measure the carbon levels and their stability in whole soil samples. The device is so light and convenient that it can be used directly in the field.

Scientists from CIP and EMBRAPA tested soil carbon levels using the device in a variety of agricultural and land use systems in southern Peru. The samples represented the most common agroecosystems found in tropical areas worldwide. The results showed wide variations in the levels and stability of carbon stored in the soil depending on factors such as land use, crops grown, water content, elevation, and agricultural practices. For example, wet grasslands and peatlands from highland plateaus contained 4-times the amount of carbon found in primary rainforest soil, the common standard against which levels are compared. In contrast, areas planted with potato, maize, or olive trees held only half to three-quarters of the amount of content stored in rainforest soil. There are also important differences in the chemical structure stability of the carbon found in different soils; less stable carbon is more common in the samples found in the high-altitude grassy plateaus and is more likely to escape into the atmosphere if the soil is disturbed.

The implications for carbon emissions are great. “Undisturbed soil is a natural carbon sink,” explains CIP’s Roberto Quiroz, who was one of the Principal Investigator’s for the study. However, activities such as plowing release carbon from the soil into the atmosphere as carbon dioxide (CO2), a major greenhouse gas. So, if a farmer transforms a high-altitude grassland into cropland, for example, there will be a net loss in the amount of carbon retained in the soil and an increase in the amount of CO2 escaping into the atmosphere.

In fact, in tropical mountain regions, such as the Andes, poor farmers are already planting their crops further up the mountain and converting grassland to cropland, because warming trends due to climate change are increasing the threat of crop pests and disease at lower altitudes.

“We have tools and means to help mitigate these effects, and to transform an environmental risk into an opportunity for retaining soil carbon while improving the livelihoods of poor farmers,” says Quiroz.

CIP scientists and partners are working on three such strategies: 1. developing more stress-resistant crops, so that farmers can continue to grow them in existing fields at lower elevations; 2. using crop management techniques (e.g., mulching, water management) and diversified farming systems that balance soil carbon losses with methods to capture and retain soil carbon; and 3. implementing financial incentives and other techniques that reward farmers for improved stewardship of natural carbon sinks and soils. They are also continuing to test and streamline their portable device so that it can be adapted more easily and widely for broader use.

Agriculture accounts for 31% of total carbon emissions. Fully 88% of those could be reduced – including 74 % in developing countries. “But agriculture must be part of the climate change discussion,” emphasizes Quiroz. “It’s more than part of the problem; it’s a big part of the solution”.

December 10, 2009

For more information, please contact:
Valerie Gwinner
Head, Communications and Public Awareness Department
International Potato Center (CIP)
v.gwinner@cgiar.org
Tel: +51 1 317 5334

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