*Originally published here
on the CCAFS blog
As year 2015 has
been earmarked as the International Year of Soils to highlight the urgent need
for better soil management, many are promoting conservation agriculture (CA) as
a key solution for African farmers. Yet, a slow adoption in sub Saharan Africa raises
questions on the effectiveness of CA and the true value of such cropping practices
for smallholder farmers. A new CCAFS report, based on collaboration with IFAD
and CIRAD, gives some answers.
Will CA help respond to
the urgent need to preserve our soils?
Out of over 930 million people
living in sub Saharan Africa (SSA), about two thirds depend on rain fed
smallholder agriculture for their livelihoods. Fragile soils, growing aridity
and unsustainable practices like overgrazing, soil-depleting crop cultivation
and firewood collection are rampantly degrading over two thirds of African land
[UN
Economic Commission for Africa].
Fighting this land degradation has recently yet again been
listed in the development priorities
by representatives of the Least Developed Countries in Cotonou. In SSA countries like Uganda, research shows that better
land management practices are linked to reduced rural poverty.
Conservation agriculture
(CA), which was initially developed as a response to the US Dust Bowl in the
1930s, is one of the approaches increasingly promoted on smallholder farms in
sub-Saharan Africa (SSA) to tackle this land degradation and improve soil
health. Proof of its popularity, the First African Congress on CA took place
in March in Zambia, where CA is already practiced on more than 5% of cultivated
lands.
CA combines three cropping
practices to help reduce erosion and water run-off, increase soil fertility and
ultimately the crop yields. These consist of minimum or no-tillage to reduce
soil disturbance; permanent soil cover, using crop residues as mulch; and crop
rotations or intercropping, especially with nitrogen-fixing legumes.
Many experiments across the globe have shown the very positive impact CA can have on
crop yields and livelihoods. In the Kulunda Steppe
in Siberia, where half of the 42 million hectares of cropland are degraded, farmers
were suffering from decades of declining yields. Scientists in this region began experimenting
with CA three years ago and have already seen
yields rise by around 20 to 25%. These encouraging results suggest CA could
offer a relatively inexpensive solution to prevent the next Dust Bowl in the Russian
Steppes.
But, to what extent could
small farmers in SSA benefit from CA, and in which conditions? To help set the
story straight, a CCAFS report has just been published following the analysis
of 41 studies identified as comparing CA with conventional tillage based
practices in various agro-ecologies and climate conditions of SSA.
This meta-analysis of existing data helps us better understand what conditions
result in positive crop responses to CA practices as well as identify the
factors that limit the adoption and impact of CA and potential solutions to
address these.
Yes, CA can bring long term benefits for farmers if all
three components are practiced
A key finding was that by combining no tillage with mulching, a farmer
will yield on average 300 kg more per hectare in the first three years and even
more thereafter, compared to conventional practices. However harvests will be
lower in the long run if he practices only no tillage without soil cover and
crop rotation.
Another finding is the
importance of the use of fertilizer as a condition of success for CA farmers.
Farmers yielded about 400 kg more per hectare through practicing CA when nitrogen
fertilizer application was higher than 100kg per hectare. Given that the
majority of SSA farmers apply much less fertilizer, on average around 8kg per
hectare, this calls for the appropriate use of small quantities of fertilizer
such as fertilizer microdosing, to benefit fully
from CA’s potential.
CA could improve farmer livelihoods and resilience
Scientists attribute the
positive yield impact (up to 300 kg more per hectare) of the combination of no-tillage,
mulch and crop rotation to several benefits of crop rotation such as better
soil structure, less pests and the biological nitrogen fixation which occurs
when legumes are used as a rotational crop.
The impact of CA
will vary depending on seasonal rainfall. Overall, the meta-analysis shows
greater yield gains in rainfall above 1,000mm than in drier conditions. However,
some studies claim the opposite as heavy rains on mulched soils often induce
aeration problems and waterlogging.
CA has been praised
as a good climate change mitigation and adaptation technique. In particular, it has beenpromoted as
a technology to cope with more erratic rainfall, due to the effects mulching
seems to have on soil-water-balance. But this may be overstated.
“The results of
this study do not show clear evidence of this potential,” said Marc Corbeels, a
researcher at CIRAD (French Agricultural Research Centre for
International Development) who led the study. “On average, yield benefits from CA were relatively
low under dry climates in SSA: 140 kg per hectare,” he explained.
Long-term
experiments on no till have shown that up to 10 tons of additional carbon could
be sequestered in soil. However a recent CIMMYT study of the carbon sequestration
potential of no tillage practices concludes that its impact on mitigation has
been overstated.
Still, CA advocates crop
rotation as well as no tillage and the positive impact of crop rotation in
climate change adaptation is widely accepted. Many
long-term field studies have directly compared continuous
maize cultivation with a legume based rotation. A replicated controlled
experiment in Canada found legume based rotation provided an additional 20 tons of soil organic carbon per hectare
after 35 years. Rotation with
legumes also adds organic nitrogen to the soil and breaks the lifecycle of pest
and diseases, reducing the need for “carbon costly” chemical
fertilizer, pesticides and herbicides, further contributing to climate change mitigation
Another CA benefit of
promoting legumes in crop rotation or intercropping is nutrition. Research in Malawi found that families intercropping pigeonpea in their maize fields
were more likely to get enough calories even during dry years than families
practicing maize monoculture.
But CA may not fit for all: understanding adoption
constraints
Despite its success in
some regions, CA is not being widely adopted in SSA. Among
the adoption issues identified is that the use of crop residues as mulch/soil
cover competes directly with other very important uses such as fodder to feed
animals in mixed crop-livestock farms. Poor families also often use maize,
sorghum or millet stalks as cooking fuel.
"It is important
that the study highlights adoption constraints like these so we can identify
potential solutions to ensure CA is being practiced where it is most suitable
for the smallholder farmer," adds Stephen Twomlow, a Climate and
Environmental Specialist from the International Fund for Agricultural
Development (IFAD) which helped fund the study.
The greater benefit may vary depending on the farm. A crop
residues trade-off analysis in West Africa found that while some farmers may get
better returns by using
crop residues for fodder, others benefit more from its use for mulching and
nutrient recycling.
Some agronomists
point out that CA may not suit all
soils. The analysis suggests that CA works better on loamy soils compared to
sandy and clay soils. Poorly drained soils are in general inappropriate as
mulch can cause waterlogging and crop diseases.
Despite crop rotation
benefits, farmers resist introducing legume rotation in continuous crop
monocropping (eg maize monoculture in Malawi) due to the lack of legume markets
for sales. Unless there is a ready market for the grain, smallholder farmers in
SSA tend to grow grain legumes on a small proportion of their farm land, just
for subsistence, and certainly not enough to provide a rotation across the
farm. This highlights the need for policies, infrastructure and new markets to
encourage better adoption of legume rotation practices. A successful example of
this is in Ethiopia where policies supporting better seed access, training and
markets have led farmers to dramatically increase chickpea cultivation
alongside teff.
Sustainable farming
practices like CA has a crucial role to play in SSA, where there will be 1.5
billion mouths to feed by 2050, in a drier and more fragile environment with
increasingly scarce resources. Providing tailored advice for each region is key
and despite evident benefits in many situations, CA may not be the solution for
all.
Download the report
Meta-analysis
of crop responses to conservation agriculture in sub-Saharan Africa by Marc Corbeels (CIRAD), Raymond Kofi
Sakyi (Georg-August-Universität), Ronald Franz Kühne (Georg-August-Universität)
and Anthony Whitbread (Georg-August-Universität).
The research was undertaken with funding from the International
Fund for Agricultural Development (IFAD).
