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Land degradation and agriculture in the Sahel of Africa: causes, impacts and recommendations

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The Sahel region is largely dependent on agriculture as the main economic activity, with about 80-90% of the population actively engaged in agriculture. Land degradation is however a major environmental issue affecting the region, with negative consequences on agriculture. Unsustainable agricultural practices in the region in turn promote land degradation. This paper discusses the major environmental issues relating to land degradation and agriculture in the Sahel. It attempts to provide a descriptive report on the interactions between land degradation and agriculture based on a desk review of various scientific journals and reports on agriculture and land degradation in the Sahel region. Land degradation in the Sahel is characterised by soil degradation, mainly due to wind erosion. This is favoured by climatic factors such as drought and diminishing rainfall, compounded by anthropogenic factors, including population growth, agricultural intensification and overgrazing. Climatic and anthropogenic factors may act independently or have effects on each other. These factors result in the reduction of vegetation cover, decrease in fallow periods and a reduction in the balance between fallow areas and cultivated fields, which are vital to maintaining soil fertility and reducing losses from erosion. Agroforestry, integrated farming and practices that promote vegetation cover are proposed as sustainable land practices in the Sahel region. These will provide soil cover to protect soils against agents of erosion, increase agricultural productivity per unit land area and diversify farmers' sources of income, resulting in benefits for agricultural production and addressing land degradation.
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Journal of Agricultural Science and Applications (J. Agric. Sci. Appl.)
J. Agric. Sci. Appl. Volume 3, Issue 3. 2014 PP. 67-73 DOI: 10.14511/jasa.2014.030303 © American V-King Scientific Publishing
67
Land degradation and agriculture in the Sahel of
Africa: causes, impacts and recommendations
Stephen Doso Jnr
P.O. Box SA 199, Somanya, Ghana.
E-mail: paafioteye@yahoo.com. Tel: +233 0245135514.
Abstract: The Sahel region is largely dependent on agriculture as the main economic activity, with about 80-90% of the population actively
engaged in agriculture. Land degradation is however a major environmental issue affecting the region, with negative consequences on
agriculture. Unsustainable agricultural practices in the region in turn promote land degradation. This paper discusses the major environmental
issues relating to land degradation and agriculture in the Sahel. It attempts to provide a descriptive report on the interactions between land
degradation and agriculture based on a desk review of various scientific journals and reports on agriculture and land degradation in the Sahel
region.
Land degradation in the Sahel is characterised by soil degradation, mainly due to wind erosion. This is favoured by climatic factors such as
drought and diminishing rainfall, compounded by anthropogenic factors, including population growth, agricultural intensification and
overgrazing. Climatic and anthropogenic factors may act independently or have effects on each other. These factors result in the reduction of
vegetation cover, decrease in fallow periods and a reduction in the balance between fallow areas and cultivated fields, which are vital to
maintaining soil fertility and reducing losses from erosion.
Agroforestry, integrated farming and practices that promote vegetation cover are proposed as sustainable land practices in the Sahel region.
These will provide soil cover to protect soils against agents of erosion, increase agricultural productivity per unit land area and diversify
farmers' sources of income, resulting in benefits for agricultural production and addressing land degradation.
Keywords: agriculture; agroforestry; anthropogenic factors; land degradation; integrated farming; Sahel.
1 Introduction
Land degradation is a major environmental issue affecting
the Sahel region of Africa (UNEP, 2012). Land
degradation has negative consequences on agriculture.
Unsustainable agricultural practices in turn promote land
degradation (Olsson et al., 2005). With agriculture being
the main economic activity in the Sahel (Suttie et al.,
2005), the effects of land degradation can be significant
(UNEP, 2012). This paper discusses the major
environmental issues relating to land degradation and
agriculture in the Sahel. The next section describes the
Sahel region and the subsequent sections discuss how
agriculture and land degradation affect each other. The
potential causes and their impacts are identified, and
recommendations suggested.
2 The Sahel Region
The Sahel is a semi-arid grassland and shrubland transition
zone stretching across the African continent between the
Sahara desert to the north and the tropical savannas to the
south (Herrmann, 2005). It covers parts of Senegal,
Mauritania, Mali, Burkina Faso, Algeria, Niger, Chad,
South Sudan, North Sudan and Eritrea (UNEP, 2012). The
Sahel climate is characterised by a long dry season and a
short humid season (Nicholson, 1995). The ecosystem is
greatly controlled by rainfall, which is variable and
unpredictable. The mean annual rainfall ranges from 200
mm in the north to 600 mm in the south (Visser and Sterk,
2007). The rainy season is intense and lasts for about 4
months with prolonged dry periods (Giannini et al., 2008).
The vegetation cycle responds to the rainfall seasonality,
with plant growth usually occurring in the humid months
(Hulme, 2001). The vegetation is characterised by sparse
vegetation cover from the Saharan biome which increases
towards the Sudanian and Guinean biomes. The species
consists of thorny shrubs interspersed between annual and
perennial grasses at the north which changes to taller
vegetation with more trees towards the south (Herrmann,
2005). Agriculture is the main backbone of the economies
of the countries forming the Sahel region (UNEP, 2012).
Figure 1 shows the Sahel region of Africa.
Figure 1. The Sahel region of Africa.
Journal of Agricultural Science and Applications (J. Agric. Sci. Appl.)
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3 Agriculture in the Sahel
The economies of the countries in the Sahel region are
largely dependent on agriculture, with about 80-90% of the
population actively engaged in agriculture (UNEP, 2012).
Crop production and agropastoralism are the main
economic activities in areas with rainfall of about 600 mm
whiles in areas with rainfall of about 400 mm, rearing of
livestock is the main economic activity (Mortimore and
Turner, 2005). Rainfall variability increases as the total
rainfall decreases, making agriculture in the low rainfall
areas vulnerable to recurrent droughts. In areas with
rainfall greater than 300 mm, the availability of nutrients,
mainly nitrogen and phosphorus, are the limiting factors
for biomass production (Aune and Bationo, 2008).
The Sahelian soils are mainly sandy (Bationo et al., 2014)
with the dominant soil types being Entisols and Alfisols
(Kang, 1985). Phosphorus and nitrogen are mostly
deficient (Bationo et al., 2014; Breman et al., 2001). Table
1 shows some soil properties in the Sahel. In the southern
part of the Sahel, agriculture is more diversified and
includes subsistence crops such as cassava, sorghum and
maize, and cash crops such as cowpeas, peanuts, wheat,
sugar cane and cotton. In the northern portion, the
subsistence crops are millet, sorghum and sometimes
maize, with the main cash crop being cotton. In the
parkland areas in the north, trees are also harvested for a
variety of products (UNEP, 2012).
Agriculture is mainly rain fed, and the field sizes are
usually small. Agriculture in the Sahel is characterised by
extensification, labour intensification and capital
intensification (Carswell, 2000). Extensification occurs
where land is readily available and farmers expand their
cultivated areas to increase production (Aune and Bationo,
2008). For example, pearl millet production increased in
Niger and Mali due to extensification, as yields did not
change for about 30 years. Land for pearl millet cultivation
in Mali increased to 1.5 million hectares in 2005, from
0.54 million hectares in 1970. In Niger, millet lands
increased from 2.3 million hectares in 1970 to 5.9 million
hectares in 2005 (FAO stat, 2007). As land becomes
limited as a result of population growth, fallow periods are
decreased and labour increased to boost production. The
labour per unit land area is increased for practices
including land preparation, manure application and
harvesting. For capital intensification, inputs such as
agrochemicals, fertilizers and agricultural equipment are
increased. Some farmers practice both capital and labour
intensification on different portions of their farmlands
(Aune and Bationo, 2008). A combination of
extensification and intensification are also used,
particularly for food crops (Aune and Bationo, 2008).
Pearl millet yields in Burkina Faso increased from 500 kg
ha-1 between 1976 and 1985 to 750 kg ha-1 between 1996
and 2005 whiles the cultivated land area increased by 41%
during the same period (FAO stat, 2007). Generally,
agriculture is becoming more market-oriented in the Sahel.
The percentage of farm products brought and sold on
markets rose from 20% in 1950 to about 50% in 2000
(Cour, 2001).
Table 1. General soil properties in the Sahel (Bationo
and Mokwunye, 1991; Kang, 1985; Vanlauwe et al.,
2014).
Property
Characteristic
Structural stability
Poor
Nutrient holding capacity
Low
Water retention capacity
Low
Organic matter content
Low
Effective cation exchange capacity
Low
Drought susceptibility
High
Texture
Coarse
Towards the northern part of the Sahel, pastorialism
dominates, with about a quarter of the population engaged
in animal husbandry. High stocking densities and
overgrazing are common, which affects the growth pattern
of grasses. The livestock varies among the ethnic groups,
with the Tuareg favouring camels whiles the Fulani prefer
cattle (UNEP, 2012). The Tuareg live at the fringe of the
desert and are divided into many groups. The exclusive
transhumant herders occupy lands not suitable for crops to
the north of the agropastoralists, who live close to their
fields. The agropastoralist Fulanis occupy the southern
part of the Sahel, and rear small ruminants like sheep to
provide meat for their families as the cattle are for capital,
investment and prestige. The transhumant Fulanis travel
through the lands of farming communities as their cattle
feed on the stovers and fallows on farmlands (Suttie et al.,
2005). The cattle help manure these farmlands through
their droppings as they graze.
In the southern, humid parts of West Africa, grazing is
hindered by the presence of ticks and particularly tsetse
flies, the vector for trypanosomiasis (Suttie et al., 2005).
Transhumant Fulanis are increasingly settling in some of
these areas by clearing trees and bushes to control the
tsetse flies. Grazing lands have been damaged through
human population increase, expansion of croplands into
marginal areas, and deforestation for firewood. This has
been aggravated by recurrent droughts, particularly in
1968 and in the early 1980s (Suttie et al., 2005). Fire is
often used as a tool to promote palatable grasses for the
grazing animals. The laterite plateaus are not cultivated;
they are used for grazing and as sources of firewood
(UNEP, 2012).
4 Land degradation in the Sahel
The Sahel is one of the most severely affected regions
from land degradation and desertification in the world
(UNEP, 1992). The region has experienced severe drought
and increasing deterioration of soil quality and vegetation
cover (Geist and Lambin, 2004). The United Nations
Conference on Environment and Development defines
desertification as land degradation in the arid, semiarid and
dry sub humid areas due to various factors including
climatic variations and human activities (UNCED,
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69
1992/93). Land degradation is the reduction in the physical,
chemical or biological status of land which may affect its
productive capacity (Eswaran et al., 2001). Land
degradation has adverse impacts on agricultural
productivity, the environment and food security (Eswaran
et al., 2001). Land degradation has resulted in the loss of
the soil's productive capacity which is a great concern to
the local people (Bielders et al., 2001) who are mainly
subsistence farmers. Excessive exploitation of firewood
and unsustainable agricultural practices including
overgrazing and over-cultivation have in turn contributed
to land degradation in the Sahel region (Olsson et al.,
2005). The main form of land degradation in the Sahel is
soil degradation through soil erosion and consequent
nutrient loss, soil physical degradation through crust
development, and salinization (UNEP, 2012).
4.1 Soil degradation
Soil degradation is the main form of land degradation in
the Sahel (Niemeijer and Mazzucato, 2002). UNEP’s “An
Ecosystem Approach to Restoring West African Drylands
and Improving Rural Livelihoods through Agroforestry
based Land Management Interventions” project identified
generally low soil organic carbon (SOC) content in the
Segou region of Mali using infrared spectroscopy. SOC is
a key indicator of soil condition in terms of nutrient status
and availability, soil physical properties, and water holding
capacity. The median SOC content was 3.12 g kg-1 in
topsoils (0-20 cm) for all sites. Cultivated areas where
found to have lower SOC in the topsoil compared to semi-
natural areas which are not cultivated or managed. This
was attributed to high sand content in the cultivated areas
and also as a direct consequence of cultivation (UNEP,
2012).
Wind erosion is the main contributor to soil degradation in
this region (Mainguet and Chemin, 1991). Wind erosion
causes considerable loss of soil and nutrients in the Sahel,
sometimes greater than the effect of water erosion (Visser
et al., 2005a). The soil sediments are transported by wind
through suspension, saltation and creep (Visser and Sterk,
2007). The finest soil particles are carried away as
suspended dust which can travel for thousands of
kilometres (Sterk et al., 1996). The finest soils contain
relatively higher proportions of organic matter and
nutrients in the topsoil, leading to considerable losses
(Leys and McTainsh, 1994). Relatively larger particles are
transported by saltation which bounces over the surface of
the soil up to heights of about 2 meters. These also result
in considerable nutrient losses as soil particles transported
by saltation are usually aggregates of the finer nutrient-
rich particles (Sterk et al., 1996). This however occurs
over relatively shorter distances. Coarse sand particles
bombarded by the saltating particles are transported by
creep over distances ranging from centimetres to a few
meters, keeping contact with the soil surface due to their
size. Creep does not result in considerable nutrient losses
as the coarse sand particles are poor in nutrients (Visser
and Sterk, 2007).
Vegetation in bush fallows (Bielders et al., 2002) and
valley sites (Visser et al., 2005b) adjacent to crop fields
trap the saltation materials. With a balance between the
fallow area and cultivated fields, saltation may result in
local redistribution of nutrients and soil particles which
remains
Figure 2. Laterite plateau in Segou town, Mali (UNEP,
2012).
in the system (Rajot, 2001). This may lead to declining
fertility in the crop fields and build up of nutrients in the
decrease of fallow periods and cultivation of new farm
lands including marginal lands reduces vegetation cover
leading the higher losses of saltation material. Farmers
may benefit in the short term by cultivating these new sites
but with time, these lands are also exposed to the forces of
erosion. As more land gets under cultivation, the balance
between fallow and cultivated area is reduced leading to
net losses of saltation materials from the system (Rajot,
2001).
High evaporation rates in the Sahel causes surface crust
development and the formation of laterites. These are
sometimes several metres thick, or form lumps, resembling
rocks. Water generally infiltrates poorly through these
hardened soils resulting in high runoff during rainfall
(UNEP, 2012). These laterite areas have high soil physical
constraints, including restricting root penetration. The
predominant vegetation in these areas is shrubby,
distributed in dense thickets, as seen in Figure 2. The
infiltration capacity on the laterites depends on the shrub
cover densities. The high rate of evaporation is also
promoted by the removal of vegetation cover which
exposes the bare soil. Such exposed and frequently heated
soils, with very little organic matter are also unfavourable
for soil fauna. Soil fauna increase water percolation in
soils through their movements. Crusts are also formed by
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70
termites in high clay soils in the form of mounds. The
activities of the termites results in localized improved rates
of infiltration and higher soil nutrient content. This leads
to the formation of fine-scale mosaics where more water
demanding plants grow (UNEP, 2012).
Water erosion in the Sahel region occurs through splash,
sheet, rill and gully erosion. This is influenced by the
topography, mainly slope gradient and surface
characteristics of the land, including the size of the soil
particles, degree of particle cohesion and the nature of
vegetation cover. Raindrops detach soil particles through
splash erosion which are further transported through sheet
erosion. Sheet erosion transports the fine nutrient-rich top
soil particles and organic matter down slope which can be
transported up to thousands of kilometres. The turbulence
of sheet flow can be increased by wind driven rain drops
falling into the flow. Clay, silt, nutrients and organic
matter are selectively carried away by sheet erosion when
runoff is low over gentle slopes, which is characteristic of
the Sahel region (Roose and Barthes, 2001). Larger
particles are transported by rolling or sliding over land
surface due to the force of the running water. These are
coarse sand particles which contain low nutrients.
Saltation materials break up in the water and the fine
particles are transported through suspension in sheet
erosion (Visser and Sterk, 2007). Water erosion is limited
in sediment transport off fields as compared to wind
erosion. Pools form over the fields, reducing runoff and
causing the soil sediments to settle. This results in local
redistribution of sediments (Visser et al., 2005a).
4.2 Causes of land degradation in the Sahel
Land degradation in the Sahel is considered to be caused
by climatic factors such as drought and diminishing
rainfall, and human activities (Herrmann et al., 2005). The
main human factors are pressure from population growth,
agricultural intensification and to some extent migration.
Though climatic and human factors may act independently,
they can also have effects on each other. Recurrent
droughts, together with low soil fertility are some of the
main factors for people migrating from their villages.
Droughts in the Sahel have sometimes been attributed to a
response of the regional atmospheric circulation to
anthropogenic factors such as overgrazing, over-
exploitation of trees for fuel wood and expansion of
agriculture to marginal lands, which have affected
vegetation cover (Charney, 1975 as cited in Giannini et al.,
2008).
4.2.1 Climate
Changes in climate may cause changes in land use
practices (Mazzucato and Niemeijer, 2000) which may
contribute to land degradation processes. Trends and
variability in rainfall in the Sahel directly and indirectly
affect crop production, vegetation, land degradation
processes and the functions of the entire ecosystem (Boko
et al., 2007). There has been an estimated reduction in
rainfall of about 20 to 30% in the Sahel region in the
second half of the 20th century (Batterbury and
Warren, 2001). In Burkina Faso, it was found that
farmers reallocated their fields from upland areas as an
adaptation to declining rainfall. Some farmers abandoned
farms in higher areas as yields where no longer adequate
due to declining rainfall (Mazzucato and Niemeijer, 2000).
The declining rainfall is also linked to a concentration of
farming in sandy areas. Sandy soils have a relative
advantage in dry areas (Reenberg, 1994). Lands have been
extended through shifting farms from one type to the other
compelled by climatic events (Mazzucato and Niemeijer,
2000).
The drought in the late 20th century in the Sahel represents
one of most striking shifts in climate (IPCC, 2007).
Satellite imagery of the effects of the severe droughts in
the Sahel between 1983 and 1984 showed a shift of the
desert southward into the Sahel region (Olsson et al.,
2005). Severe droughts affect the soil structure by causing
the land to develop cracks and also affect crop production.
The droughts also caused migration. Migrations in Burkina
Faso commenced in the 1980 as a consequence of severe
droughts which affected the central and northern portions
of the country, resulting in considerable losses of crop and
livestock to farmers. Since then, there has been increased
migration to less drought areas in the south, west and east
of the country as a livelihood diversification strategy. The
size of crop land in the southern part of Burkina Faso has
increased at annual rate greater than 1% since 1986 to
2006, caused mainly by population size and distribution of
migrants (Quedraogo et al., 2009).
4.2.2 Anthropogenic factors
Pressure from population increase is considered to be the
root cause of land degradation (Geist and Lambin, 2004).
Demographic growth for the Sahel region increased from
1.5% per year to 3% per year between the 1950s to the
1990s resulting in a three-fold increase in population in the
20th century. This represents one of the highest
demographic growths in the world (Raynaut, 2001). The
total population for Burkina Faso for instance, increased
from 5.6 million 1975 to 13.7 million in 2006 (INSD, 2007
as cited in Van Vliet et al., 2013). It is estimated that over
90% of Burkinabes are engaged in subsistence agriculture
(Van Vliet et al., 2013). Population growth has resulted in
the intensification of agriculture on existing farmlands and
increased cultivation of marginal lands. The higher
demand for food due to population growth has caused a
decrease in fallow periods which declines the fertility of
the soil, and consequently a decline in productivity
(Mazzucato and Niemeijer, 2000). Farmers are then forced
to cultivate new lands. Natural woody savannah lands have
increasingly been converted to rain-fed cultivated lands
due to this (Raynaut, 2001).
Expansion of cultivation to marginal lands increases
degradation of upland field areas. These are then
abandoned for new lands (Reenburg, 2001). Agricultural
expansion, particularly groundnut cultivation, has resulted
in the decline of fallow lands and savannah vegetation in
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71
the Sahelian part of Senegal (Van Vliet et al., 2013). A
trend spanning 40 years shows a steady increase in crop
lands and eroded bare soils leading to a drastic decline in
woody vegetation cover in Kouonkaba village in the
Sahelian region of Mali (Ruelland et al., 2010). Increase in
cultivated land area in the Sahelian portion of Niger
between 1950 and 1998 also resulted in a 7 to 16%
increase in eroded land at the detriment of the savannah
(Seguis et al., 2004). Other human activities that have
contributed to land degradation in the Sahel include
excessive exploitation of firewood and overgrazing
(Olsson et al., 2005).
4.3 Recommended sustainable agricultural
and land management practices
Agroforestry can be practiced as a more sustainable land
use practice in the Sahel compared to conventional
agriculture. Agroforestry involves the deliberate use of
trees in association with crops, pasture or livestock
(Breman and Kessler, 1997). Agroforestry would be more
beneficial in the Sahel as the use of external inputs in
agriculture is relatively low. Productivity in agriculture
can be increased by expanding the land area on which
productivity depends or by increasing the yield per unit
land area. In the Sahel where cropland is continuously
becoming limited due to population increase and land
degradation, the latter will be the favourable option.
Agroforestry has an advantage over non-agroforestry land-
use systems in achieving this goal by making more
effective and efficient use of land resources. The different
layers of trees and crops make more efficient use of above
ground resources such as sunlight whiles the different
rooting patterns of the trees and crops make more efficient
use of below ground resources such as nutrients and water
(Buck et al, 2010).
The inclusion of nitrogen fixing trees in agroforestry
technologies adds nitrogen to the soil. Also, litterfall and
the addition of prunings from the trees add organic matter
to the soil. Organic matter improves soil physical
conditions such as the soil structure, soil aeration and
drainage. The tree canopy, in addition to the mulch layer
of leaf litter and tree prunings can reduce soil erosion by
reducing the impact of wind and rain drops on the soil
((Jose, 2009). The tree roots also reduce soil erosion by
providing physical barriers which reduce run off and also
by increasing infiltration of water into the soil (Buck et al.,
2010). The shading effect of tree canopies and mulch
provide a favourable microclimate for microbial activities
in the soil which help in breaking down organic matter and
improving soil physical conditions. Mulching also reduces
weed proliferation. Agroforestry also provides cheap
sources of fodder, fruits, fuelwood, poles, timber and
medicinal herbs to the farmer depending on the trees used
(Pimentel and Wightman, 2010).
Integrated farming involving mixed farming practices
where the output from one farm component is used as an
input for other components can help maximize land use
per unit area. This is very vital in the Sahel where
favourable croplands are limited. Integrated farming
involving both crops and livestock can have both
environmental and economic benefits. This can help
improve soil fertility per unit land area through internal
recycling of nutrients, and consequently improve crop
yields. Livestock can either graze on crop residues or the
residues can be collected and fed to the livestock in their
housing. Manure from livestock housing can in turn be
collected together with straw, feed left over and household
waste and used on the crop fields. This can help improve
soil organic matter and fertility and also serve as mulch.
Mulch can help reduce soil erosion, conserve soil moisture
and promote the activities of soil organisms. Livestock
such as camels and cattle can further be used in land
preparation and carting farm produce and fuelwood to
homes. Integrated farming can also diversify farmers'
sources of income and provide back up during crop
failures.
Practices that promote vegetation cover such as the use of
trees and hedges as windbreaks, the use of cover crops on
slopes and green manuring can help protect soils from the
agents of erosion. Vegetation increases the fluid drag on
air stream which reduces the near surface wind velocity
causing deposition of suspended dust particles. Vegetation
has also been shown to reduce wind velocity gradient
above the canopy which causes friction velocity to fall
below the threshold for re-suspension of settling dust
particles. A two-year study in New Zealand showed that
dust deposition in vegetated areas was significantly
improved by 199.86 kg ha-1 to 108.04 kg ha-1 in bare
areas (McGowan and Ledgard, 2005). Vegetation can
effectively trap large amounts of suspended soil particles.
This dust when washed off by rains can return to the
underneath soils with the accompanying nutrients and
become available for plant use (Visser and Sterk, 2007).
5 Conclusions
Climatic factors such as declining rainfall and persistent
droughts can have negative effects on agriculture and
promote land degradation processes. In the Sahel,
agricultural extensification and intensification due to
population growth and unsustainable agricultural practices
that reduce vegetation cover on lands have contributed to
land degradation. Soil degradation through soil erosion is
the main form of land degradation in the Sahel, resulting in
nutrient loss, soil physical degradation and salinization and
consequently reducing agricultural productivity.
Extensification and the decrease of fallow periods may
yield benefits for farmers in the short term. In the long
term however, land degradation is exacerbated through
exposing newly cultivated lands to the forces of erosion, a
decline in soil fertility and the reduction in the balance
between fallow and cultivated areas, leading to net losses
of saltation material in the system.
With land degradation being a major problem in the Sahel,
the use of sustainable agricultural and land use practices
that promote vegetation cover on lands can help protect
soils from erosion. These practices include agroforestry,
growing of cover crops, grasses and drought resistant trees.
Integrated farming is proposed to maximize land use per
Journal of Agricultural Science and Applications (J. Agric. Sci. Appl.)
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72
unit area and diversify farmers' sources of income as
favourable croplands are limited in the region. Practices
that promote organic matter additions to soils such as
mulching and addition of organic manure can also have
positive benefits for both agricultural production and
addressing land degradation.
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... Poor vegetation cover reduces soil water infiltration capacity and indirectly speeds up the process of land degradation (Carmona et al., 2013;Kairis et al., 2015). Studies in Ethiopia (Mekuria et al., 2007), Kenya (Ovuka, 2000), South Africa (Vetter, 2007) and the Sahel region (Doso, 2014), for example, have traced increased land degradation -which worsened existing soil erosion -to overgrazing. Because of loss of vegetation cover that resulted in decreased quantity and quality of pastures, some subsistence livestock farmers in SSA have been constrained to stall-feed their livestock (Nkonya et al., 2011;Ovuka, 2000), which has enormous financial implications for poor farmers. ...
... Farmers in SSA have adopted several soil conservation techniques to improve soil fertility and enhance land rehabilitation (Doso, 2014;Guteta and Abegaz, 2016;Mekuria et al., 2007;Seitz et al., 2019;Zougmoré et al., 2000;Zougmoré et al., 2014). For example, farmers in Chencha and Arbaminch, Gamo Gofa zone, Ethiopia, use a combination of various traditional management practices such as terracing, manuring, fallowing and crop rotation to control soil erosion and improve soil fertility (Assefa and Hans-Rudolf, 2016). ...
... Soil erosion and the resulting land degradation is one of Africa's environmental challenges that have severely impacted rural livelihoods (Doso, 2014;Nkonya et al., 2016;Nyamekye et al., 2018;Vetter, 2007). The situation is no different for local farmers in KwaMaye. ...
Article
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... However, agroforestry can be practiced as a significant soil conservation technique for sustainable land use in agriculture both in developed and developing countries compared to traditional farming in agriculture (ICRAF, 1993;Stephen, 2014). Agroforestry includes trees along with crops, pastures and livestock (Stephen, 2014). ...
... However, agroforestry can be practiced as a significant soil conservation technique for sustainable land use in agriculture both in developed and developing countries compared to traditional farming in agriculture (ICRAF, 1993;Stephen, 2014). Agroforestry includes trees along with crops, pastures and livestock (Stephen, 2014). The practice of agroforestry helps in maintaining soil fertility, water holding capacity, erosion control, biodiversity, carbon sequestration and leaching of nitrate (NO3) (Reisner et al., 2007). ...
... However, the environmental benefits of agroforestry depend on the topographic condition, intensity of management and selection of crops and tree species (Palma et al., 2007b). Agroforestry is more effective way than non-agroforestry practices to achieve the objectives of soil conservation by using the land resources effectively (Stephen, 2014). Several strata of trees with crops ensure proper use of above ground materials such as sunlight from the sun while different patterns of rooting in regard to the trees and crops help to accelerate efficient use of underground resources like nutrients and water (Kawy and Ali, 2012). ...
... Benjaminsen et al., 2010;Ickowicz et al., 2012;Bouaré-Trianneau, 2013;Bonnet and Guibert, 2014;Doso, 2014;Hiernaux et al., 2014;Kiema et al., 2014;Daouda 2015;Koutou et al., 2016; Nilsson et al., 2020;Zoma-Traoré et al., 2020 ...
... The ever-increasing human population is one of the pressing issues in modern agriculture as it has become a global challenge to feed around 9 billion people by 2050 [1] Moreover, rapid decline in the soil productivity coupled with increased urbanization and human population has reduced the available cropland [2,3]. The scarcity of the existing cropland further threatens the food security and nutrition needs of the growing population. ...
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Low availability of native soil phosphorus (P) is a major constraint limiting sustainable crop production especially in alkaline calcareous soils. Application of organic manure in this regard has gained attention of the scientific community. Yet, the potential of fermented animal manure in improving P use efficiency and subsequent crop yield has not been assessed. This pot experiment was designed to study the performance of wheat under application of non-fermented and fermented animal manure in combination with 0, 45 or 90 kg·ha−1 phosphorus in the form of diammonium phosphate (DAP). Results show that non-fermented animal manure and split dose of phosphorus fertilizer improved plant quantitative attributes including plant growth, yield and nutrient uptake parameters. However, the placement of fermented animal manure combined with the full amount of P (90 kg·ha−1) fertilizer gave the mean highest value of fertile tillers per pot (12) and their grain yield (5.2 g). Moreover, plant physiological parameters were enhanced with fermented animal manure and the recommended rate of P fertilizer compared with the control. Likewise, the biochemical properties of wheat grain such as fat, fiber, ash and protein contents were increased by 1.24, 2.26, 1.47 and 11.2%, respectively, in plants receiving fermented animal manure and P fertilizer (90 kg·ha−1). Furthermore, co-application of fermented animal manure with P (90 kg·ha−1) into soil improved phosphorus uptake from 0.72 to 1.25 g·pot−1, phosphorus usage efficiency from 0.715 to 0.856 mg·pot−1, and soil phosphorus extent from 7.58 to 16.1% over controls. It is thus inferred that this new approach resulted in release of P from fermented manure that not only reduced fixation but also enhanced the growth, yield, physiology and nutrient uptake in wheat.
... In Sub-Saharan Africa (SSA), persistent problems of hunger and malnutrition, poverty and inequalities against declining landbased resources and climate change are now commonplace in rural and periurban areas. Widespread problems related to land degradation, declining soil fertility, loss of biodiversity, and loss of resilience in agro-production systems, have been well documented (e.g., Bationo, Waswa, and Kihara 2015;Chappell and Bernhart 2018;Doso Jnr 2014;Henry, Murphy, and Cowie 2018;Mlih et al. 2016). From an agricultural production perspective, the SSA, therefore, presents a paradox of hungry and malnourished farming families. ...
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Agroecology is an approach that seeks to improve the integration of food systems through environmentally sustainable production systems. This paper explores the key practices considered to define agroecological farming in Bikita District of Masvingo in Zimbabwe. It reviewed the literature on agroecology and presented a criterion that informed analysis to distinguish between agroecological and non-agroecological farmers. Agroecological farmers mainly comprised resource-constrained farmers who sought to tap on their natural environment, local knowledge, and social networks to move away from conventional agricultural practices to achieve similar food and nutrition security and livelihood objectives as their non-agroecological counterparts. They differed from their non-agroecological counterparts mainly with respect to the diversity of crops grown, agronomic techniques used, and primary sources of income. Major challenges for farming households practising agroecological approaches include a lack of capacity for sustained adherence to agroecological principles (e.g., in the context of otherwise conventional systems; for all intents and purposes, existing extension messages and support mechanisms do not favour agroecological farming). These farmers, therefore, practice agroecological farming against institutions and policies that do not recognize agroecological farming. There is therefore currently ‘no level playing field for farmers and promoters of agroecological practices in Bikita as in many areas in Zimbabwe.
... In Africa, several countries still face accelerating declines in agricultural yield due to unsustainable agricultural practices that are exacerbated by environmental factors, including climate change, rainfall variability, soil quality degradation, and recurrent droughts (Doso Jnr 2014; Lema and Majule 2009). These environmental factors result in detrimental effects on soil fertility and ecosystem functioning, as well as vegetation structure (Doso Jnr 2014;Lema and Majule 2009). Given that the agricultural sector plays a pivotal role in most economies, and the nonrenewable nature of soil (Doran and Zeiss 2000), sustainable strategies must be developed to help mitigate negative soil quality and yield potential at the time new crop areas are explored. ...
Article
Purpose Legumes have been used to improve soil fertility however, most legume research focuses on crop and not forage legumes. Forage legumes, including Pisum sativum L., increase the nutritional value in pastures and provide high amounts of soil protein and minerals required for plant growth. We investigated the effects of varying soil composition on plant growth, symbiosis establishment, and nutrient acquisition. We also aimed to compare phenolic compound production, since phenolics are reported to play a vital role in plant defense, pollination/dispersal, and symbiosis with quorum-sensing plant growth-promoting bacteria. Methods Using quantitative techniques, we evaluated the effect of nutrient deficiency in plant-microbe symbiosis, nutrition and carbon costs, as well as the phenolic concentrations in P. sativum. Four distinct regional soils in KwaZulu-Natal (KZN), geographically covering grassland and savannah ecosystems, were used as growth substrates. Results Plants maintained their root dry weights and growth rates across the four soil types. Low pH, total cations, and high exchange acidity in Bergville soil resulted in decreased total plant dry weights. P. sativum grown in Izingolweni soils relied more on atmospheric N fixed by endophytic/associative bacteria from the genera Cupriavidus, Paenibacillus, Cohnella, and Bacillus, while those grown in Hluhluwe soils relied on soil N. Conclusion Plant associative microbes might modulate nutrient availability for plant uptake in nutrient poor grassland and savannah ecosystems. P. sativum acclimatized to changes in soil nutrient concentrations and pH in the studied ecosystems by changing N source preferences and phenolic concentrations. The acclimatization of plants is likely modulated by the presence of rhizospheric microorganisms interacting with the plants.
... Agriculture is the main source of livelihood for the majority of people living in the Sahel region. (Stephen, 2014). ...
Chapter
Groundwater is an important resource for food production, drinking water supply, drought mitigation, and economic development especially for rural communities around the world. The rapid expansion in agricultural groundwater use in the last few decades has transformed rural economies in large parts of the developing world, in particular South Asia and North China. The main reason why groundwater is increasingly gaining prominence as a water source is the high natural storage capacity; the water quality is often good; the infrastructure is more affordable to poor communities, with a higher resilience to inter-annual variability when compared to surface water, which enables it to be used even during times of drought. In recent time, the use of agricultural groundwater has expanded but little is known about its contribution or linkages in enhancing rural livelihoods for future planning in the Sahel region. Published literature indicates that groundwater used on a 1–2 million hectares of cropped area, yields a direct 1.5 - 3% contribution to the livelihoods of the rural population in sub-Saharan Africa. While data are lacking, it is difficult to justify the role of groundwater in improving rural livelihood in the Sahel region. This book chapter seeks to understand the linkages between groundwater resources development and the improvement of rural livelihood aiming to provide guidance for policies and investments in innovative water interventions. Through the review of the growing body of existing literature combined with analysis of secondary data (from FAO databases, FEWS NET, World Bank etc.) and practical project experience in Niger, the study concluded that to assess the added value of agricultural groundwater use in support of rural livelihoods in the Sahel region should be based on sustainable livelihoods framework and Livelihood zoning models that have typically been applied in Asia. The study recommends the collection of more data that are in line with the different capitals of the sustainable livelihoods framework for better analysis and to generate evidence based results.
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The study assesses the farmers’ use of Global System for Mobile (GSM) for communication among farmers in agricultural extension programs in Taraba State, Nigeria. Specifically, the objectives include: identify key areas in which GSM are used for communication in agricultural extension programs activities, determine the frequency of usage of GSM for information exchange between farmers and extension personnel; and ascertain farmers’ satisfaction in the use of GSM in obtaining information in the various agricultural extension programs. The population for this study included all beneficiaries/farmers under the agricultural extension programs in Taraba state, Nigeria. Purposive sampling was adopted because of the accessibility of the selected three Local Government Areas (LGAs), (ArdoKola, Jalingo & Lau) throughout the year. Five Fadama User Groups (FUGs) were randomly selected from each LGA to constitute fifteen FUGs for the study. From each FUG, ten respondents were drawn randomly to give a sample size for the study. In the Fadama III project, respondents’ key areas of communications with personnel of the project included: group formation (88%), mobilization of members for participation in Fadama III programs and activities (87.3%), awareness creation of Fadama III intervention (82.7%), capacity building activities (81.3%), convening of Fadama User Group (FUG)/FCA meetings (81.3%), sub-project preparation and management (80.7%), advisory services and input support services (80%), environmental/social screening friendly practices (72.7%), asset acquisition activities (68%), record-keeping activities (66%), small-scale community infrastructure activities (63.3%) and financial management (61.3%). Farmers indicated their satisfaction in obtaining information o;n capacity building activities by the use of GSM with the (M = 1.21), advisory services and input support activities (M = 1.28), asset acquisition activities, (M= 1.16), mobilization of members for participation in Fadama III activities (M = 1.40), convening FUG/FCA meetings ( M = 1.43), financial management (M=1.09), record-keeping activities (M = 1.17), awareness creation of Fadama III intervention (M = 1.27), group formation (M = 1.37) and environmental/social screening and environmentally friendly practices ( M = 1.17). The main challenges included no GSM phones provided by Fadama III to farmers (M = 1.37), low level of education of farmers (M = 1.55), erratic power supply (M = 1.41), high call tariff (M = 1.11), poor network coverage (M = 1.24), lack of maintenance e.g recharging (M = 1.11), and fluctuating services by the service providers (M = 1.16). The study suggested that the Information and communication unit of the Fadama III project should collaborate with other media outfits and extension units to disseminate agro-information to the benefits of the Fadama III beneficiaries.
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This paper describes the opportunity for combining climate action and improved food and nutritional security as mutual elements of rural development projects, with particular reference to the situation in the African Sahel. This progress is achieved by identifying climate-smart agricultural production technologies and bundling them into solutions for inclusion within larger projects and programs. Seventeen (17) such technologies are offered in this chapter that represent genetic innovations, improved soil and water management, and directed improvement across landscapes. Examples of the efficacy of these technologies are presented based on results from the African Agricultural Transformation Program (TAAT) with specific reference to improved cereal production. An example of the deployment of TAAT technologies for millet and sorghum involving 83,620 households managing 123,863 ha led to nearly 200,000 MT of increased food production worth about $42 million. This effort led to an estimated annual increase of 177,279 MT CO2e in biomass and soil worth $3.9 million, assuming buyers could be found. The relationship between three principal drivers of agricultural transformation, the public, private, and farming sectors, is considered in terms of how these different technologies are mobilized and deployed. The potential for increasing food supply and carbon gains under current agricultural investment levels across the Sahel by International Financial Institutions, about $683 million per year, is described. This chapter then offers recommendations in how improved rural development projects combining climate action and food security in the Sahel may be designed in the future.
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This paper introduces a special issue of Global Environmental Change: Human dimensions on the Sahel of West Africa. It reviews the seminar to which the papers were presented, and brings together some conclusions. Despite the quarter century of research into the West African Sahel that followed the great droughts of the 1970s, there are still strong disagreements about how to achieve more prosperous, yet sustainable livelihood systems in the region. There are conflicts between those who believe in indigenous capacities to maintain rural livelihoods, those who believe that various forms of external support are necessary, and those wedded to a vision of a Sahel directed by regional urban growth. Under economic and cultural globalisation, the future of this region is, at best, unclear. The papers in this collection do agree that Sahelian environments are diverse, and that Sahelian people cultivate and exploit diversity and flexibility. They also suggest that there are no quick-fix development solutions, except to build upon this historical diversity with renewed purpose.
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Land use/cover change (LUCC) is a major indicator of the impact of climate change and human activity, particularly in the Sahel, where the land cover has changed greatly over the past 50 years. Aerial and satellite sensors have been taking images of the Earth's surface for several decades. These data have been widely used to monitor LUCC, but many questions remain concerning what type of pre-processing should be carried out on image resolutions and which methods are most appropriate for successfully mapping patterns and dynamics in both croplands and natural vegetation. This study considers these methodological questions. It uses multi-source imagery from 1952 to 2003 (aerial photographs, Corona, Landsat Multispectral Scanner (MSS), Landsat Thematic Mapper (TM) and Satellite Pour l'Observation de la Terre (SPOT) 5 images) and pursues two objectives: (i) to implement and compare a number of processing chains on the basis of multi-sensor data, in order (ii) to accurately track and quantify LUCC in a 100 km2 Sahelian catchment over 50 years. The heterogeneity of the spatial and spectral resolution of the images led us to compare post-classification methods aimed at producing coherent diachronic maps based on a common land-cover nomenclature. Three main approaches were tested: pixel-based classification, vector grid-based on-screen interpretation and object-oriented classification. Within the automated approaches, we also examined the influence of spectral synthesis and spatial homogenization of the data through the use of composite bands (principal component analysis (PCA) and indices) and by resampling images at a common resolution. Classification accuracy was estimated by computing confusion matrices, by analysing overall change in the relative areas of land use/cover types and by studying the geographical coherence of the changes. These analyses indicate that on-screen interpretation is the most suitable approach for providing coherent, valid results from the multi-source images available over the study period. However, satisfactory classifications are obtained with the pixel-based and object-oriented approaches. The results also show significant sensitivity, depending on the method considered, to the combinations of bands used and to resampling. Lastly, the 50-year trends in LUCC point out a large increase in croplands and erosional surfaces with sparse vegetation and a drastic reduction in woody covers.
Article
The Sahel has been subject of considerable environmental research and development efforts, specifically since the droughts of the 1970s and 1980s. This article uses a meta-study approach to summarize knowledge of crop land change, the documented driving forces, and the perceived impacts. The analysis of case studies shows that crop land has increased in the majority of cases mainly due to population increase. However, despite population increase, crop land has been stable in some areas, particularly where land availability is a limiting factor or where farmers are able to intensify their farmers from expanding their plots or because households have diversified their activities. The study shows the huge gap in the scientific literature concerning actual measurements of crop land change in the Sahel, which is in contrast to the attention given to crop land changes in theoretical and policy discourses. On the basis of the poor documentation available on crop land change and the contrasting results observed, we point out the need to exercise caution with regard to simple narratives about crop land change.
Article
To assess the mass budget of aeolian sediments transported by wind (erosion vs. deposition) at the scale of village land units (25 kmX25 km), measurements were carried out during 3 years (from 1996 to 1998) in a cultivated field and in a fallow area simultaneously. These were located in the Sahelian zone of Niger with an average annual rainfall of 560 mm. The vertical upward fluxes of particles <20 mu m exported from the study area were estimated from the horizontal sediment fluxes measured using BSNE sand catchers. This mass of exported dust was compared with the vertical downward fluxes of particles of the same size range (<20 mu m) measured using passive CAPYR collectors. Values of deposition recorded in the field and in the fallow were similar. In the field, wind erosion reached its maximum in May and June when the vegetation cover was minimal. In the fallow area, wind erosion was always very low in comparison with the field. It occurred during the strongest storms when the grass cover was minimal. Nevertheless, the net balance between deposition and erosion was highly positive in the fallow areas. These results have been extrapolated at the scale of the village land units based on the current land use. At this scale, the balance was positive for the arable land, indicating a net deposition of aeolian sediments of +0.36 t ha (super -1) yr (super -1) . However, the complete disappearance of fallow land would result in a balanced budget for the arable land.
Article
While addressing the issue of field encroachment and land use pattern changes in the desert margin regions, the paper proposes to develop a model which recognises land use pattern changes as event-driven. The picture that underpins development efforts and policy papers for environmental improvement in the Sudan–Sahel region often describes changes in agricultural landscape systems as a unidirectional expansion of fields onto marginal land in response to population pressure and resource degradation. It is proposed that models of land use pattern trajectories as well as of resilience of land use systems have to recognise a strong random element related to unforeseeable events.
Article
A simple theory of 'desertification' is found inadequate for understanding the complexity, diverse patterns and flexibility of farmers' responses to change in environmental conditions and population growth in the Sahel. These include long term transitions in farming practices, in management of natural resources and in income diversification. This paper reviews evidence relating to deforestation, woodland and rangeland degradation to show that in certain areas, a transition to intensified land use, although initially involving a loss of woodland, has led to the planting or protection of useful trees on farms and maintained biomass levels. Livestock numbers have been maintained, despite declining rainfall and loss or apparent degradation of rangeland, by development of more integrated livestock, arable and marketing systems. The possibility of these trends having impact on Sahelian 'greening' is discussed.