NEWS
Crop leftovers can store huge
amounts of carbon: insights
from Uganda
Reprinted From: http://bit.ly/37c3ZkM
Dries Roobroeck
F
armers in countries like Uganda
could help fight climate change –
and improve their crop yields – by
adding agricultural waste to their fields.
The process removes carbon from the
atmosphere and stores it in the soil.
It’s a strategy proposed under the Unit-
ed Nations Framework Convention on
Climate Change and shown to have
strong potential, especially in sub-Sa-
haran Africa, in recent research done by
myself and colleagues from Makerere
University in Uganda and the University
of Natural Resources and Life Sciences
in Austria.
Soils can absorb carbon dioxide from
the air through a process called carbon
sequestration. This is when more carbon
is added to the soil than it loses. Carbon
dioxide is lost from soils to the atmos-
phere when plant material, manure and
other organic matter decomposes.
Biochar – plant matter that’s been
burned using only a little oxygen – is
an excellent way to add carbon to soil.
Many of the world’s soils already hold
charred organic matter which originates
from natural and human-made vegeta-
tion fires. Biochar is good at storing car-
bon in soils because its natural break-
down happens very slowly, unlike raw
residues or manure. This means it can
remove carbon from the atmosphere
over a long period of time.
A number of carbon sequestration pro-
jects using biochar are already taking
place in North and South America, Asia
and Europe. For instance by 2020, using
biochar from the natural waste of home
gardens and public parks, Sweden’s
capital city will remove as much carbon
dioxide as 3,500 cars emit in a year.
In sub-Saharan Africa, biochar from
farming residues – like husks, hulls,
leaves, branches and straw – could be
used for the same purpose. But few
studies have assessed how much of this
material is available for biochar and how
much carbon it could store in soils.
Grassroots
Vol 19
No 4
Figure 1: A sample of biochar NCAT (Photo credit:CAES/Flickr)
In our paper we shed more light on this.
We looked at how much residue was left
over from maize, sorghum, rice, millet
and groundnut crops on eastern Ugan-
dan farms.
We found that, when converted into
biochar, these “leftovers” have signifi-
cant potential for storing carbon in soils.
Adding biochar from crop residues to
soil on one hectare (2.5 acres) of land
could offset between 16% and 80% of
the 4.6 tons of carbon dioxide emitted
by one vehicle in the US each year.
Biochar has the added benefit of im-
proving soil fertility and crop produc-
November 2019
tion in tropical climates. So this strategy
– to use biochar to remove warming
gases from the atmosphere – will ben-
efit farmers.
Making biochar
When crops grow and are harvested,
they leave behind large amounts of resi-
due which has many valuable uses: it can
be added to soil to make it more fertile,
or used in animal feed, for construction,
or to generate heat and power.
Despite its uses, farmers in sub-Saha-
ran Africa burn a lot of crop residues in
fields because recycling the waste in-
20