The climate can be
given a helping hand by taking organic soils out of rotation.
Photo: Mogens H.
Greve
(December 17, 2015) Drained
organic soils are a considerable source of greenhouse gases, particularly CO2
and nitrous oxide. These emissions make up six per cent of the total Danish
greenhouse gas emission.
Growing agricultural crops on organic (peat) soils is not
good for the climate. When organic soils are drained and cultivated the organic
matter in the soil will decompose which leads to emissions of greenhouse gases.
This emission makes up as much as 6 percent of Denmark’s total greenhouse gas
emission. The good news is that we can do something about it.
- Reducing the emission from cultivated organic soils is an
obvious choice to achieve greenhouse gas emission reductions from agriculture,
says Professor Jørgen E. Olesen from the Department of Agroecology at Aarhus
University.
Decomposition of
organic matter releases greenhouse gases
Organic soils – and raised bogs – have a high organic matter
content which consists mainly of the detritus from plant roots and other plant
residues. The reason that the organic matter is not broken down is because
these soils have a naturally high water content which limits the amount of
oxygen available.
Over the last couple of centuries most of the Danish organic
peat soils have been drained and cultivated. These soils have often initially
been very fertile, but because some settling of the soil takes place over time,
the water table on these areas is often very high, which can create problems
for their further cultivation or means they have to be redrained.
Over time the carbon content of cultivated organic soils
will fall. Today, some of the cultivated formerly organic soils have become
mineral soils that no longer produce significant emissions from the
decomposition of organic matter.
An inventory of the land uses on organic soils in 2013 shows
that roughly 81,000 ha are in rotation and 27,000 are used for permanent
grassland. Around 67,000 ha of this area have an organic carbon content of more
than 12 percent where the greenhouse gas emissions are particularly large if
cultivated.