Better farming practices could help
agriculture bury about 10 percent of atmospheric carbon from
emissions caused by human activity over the next 25 years --
while improving soil, crop and environment quality, slowing
erosion and desertification, and enhancing biodiversity.
The key is to build up plant matter in the
soil. This would pull more carbon dioxide out of the air and
convert it into plant matter, which is largely carbon -- a
process called carbon sequestration. It would also improve soil
quality, reduce soil erosion and make farming more productive
and sustainable, according to a report, Soil carbon
sequestration for improved land management, recently
published by FAO.
Carbon dioxide is the
most prominent "greenhouse" gas. Carbon
sequestration can be used to partially offset a country's
carbon dioxide emissions, helping it meet its commitments under
the Kyoto Protocol, the mechanism for implementing the UN
Framework Convention on Climate Change.
The Protocol's Clean Development Mechanism allows
developed countries to offset some of their emissions by funding
climate-friendly projects in the developing world. This offset
process, in its infancy, will eventually
"credit" agricultural development that
increases plant matter, and thus carbon sequestration.
Reversing the damage
Agriculture also emits carbon dioxide when
tillage, often unnecessary, exposes organic matter in the soil.
This soil organic matter -- which is mainly carbon -- then rots
back into carbon dioxide. In one experiment at Rothamsted
Highfield in the United Kingdom -- part of the world's
oldest existing agronomic experiment, started in 1843 --
converting grassland to arable land cut the soil carbon content
by 55 percent over 20 years due to tillage. That carbon had gone
back into the atmosphere as carbon dioxide. Wind or water
erosion can do the same. But this can often be reversed.
"Forests store more carbon than
farmland, but farmland has the potential to increase its carbon
storage, whereas mature forests may do so at lower
rates," says Jacques Antoine, an FAO soil scientist who
worked on the report.
organic matter in farmland also improves soil structure,
allowing water to reach the crop's roots rather than
running off the surface, taking precious topsoil with it.
Reducing or eliminating tillage can protect soil organic matter.
So can leaving crop residues in place after harvest. A technique
known as conservation agriculture integrates all of these
But crop residues may be needed
for animal feed. Or leaving them on the ground may delay
re-sowing. The economics of farming are harsh, especially in the
developing world. So the report looks at the big picture for
several different farming systems, such as agroforestry, grazed
grassland and arable land.
it. Measure it
On paper, the
best way to bury carbon productively is agroforestry --
combining trees and crops, together or in sequence. Agroforestry
can replace slash-and-burn agriculture, which accounts for much
of the deforestation in the developing world, and the trees
provide income. Agroforestry could be suitable for up to 300
million hectares of degraded farmland in the tropics. But trees
and crops can compete for moisture and nutrients, so
agroforestry must be well managed to be profitable.
Grasslands could be as useful in practice. The
world's estimated 3.2 billion hectares of grasslands could
store as much soil carbon per hectare as forests. But about 70
percent are degraded, often through overgrazing. Stopping
overgrazing is the key, followed perhaps by improving degraded
grassland by planting it with legumes or grass species with
deeper root systems. These activities could increase carbon
sequestration -- and provide more sustainable grazing, and thus
Still, arable land remains
crucial. Buildup of soil organic matter can be encouraged
through better crops and agronomic practices, including
minimizingtillage, leaving crop residues in place, mulching and
using manure and even sewage sludge as fertilizer.
Before any of this can figure in carbon audits,
researchers need better measurement tools. They must assess
when, how and where carbon is best sequestered, the success of
current afforestation and rehabilitation projects, and how much
soil organic matter is built up in plant roots. And they need a
mass of other scientific and socio-economic data.
FAO helps gather this information through the
Terrestrial Carbon Observation Initiative and the Global
Terrestrial Observing System. These systems, which monitor and
collect data on environmental phenomena, are operated jointly by
various institutions, with FAO hosting the secretariats.
True green revolution
The report concludes that soil carbon
projects offer "an opportunity for semi-arid and
sub-humid regions to meaningfully participate in climate
mitigation, while improving human well being." It calls
for cooperation between the United Nations and other
organizations and the bodies responsible for implementing UN
conventions on climate change, desertification and biodiversity.
Such collaboration will result in "a true green
revolution," says the report.
"Agriculture in the developing world can do
much to mitigate climate change while becoming more sustainable
and productive," says Mr Antoine. "Soil carbon
sequestration for improved land management is the first route
map towards that goal."
28 March 2002