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Erosion control in the northern Sahelian zone around the Doti marches in Burkina Faso: valley farming


In this zone with under 400 mm of rainfall, conditions contrast greatly with those in Sudanian zones. Rainfall is more erratic and falls on a small area. While there are several methods of collecting rainwater or runoff to grow trees and cereals in the wide runon areas in the Mediterranean environment of the northern Sahara where rain falls during the cold season, water conservation strategies are few and less easily apparent in the tropical Sahelian zone where rain falls in the hot season. Strategies focus on choosing crops according to the soil (millet on sand, sorghum on loam and in the bottom lands, and irrigated gardens around the wetlands) and on taking advantage of storms when these occur (very light tillage, but with repeated sod-seeding, requiring very little seed [3 kg/ha] or work [9 h]) with large areas being sown, although a good proportion may be abandoned when it comes time to do the hoeing.

A frequent survival strategy is short-distance migration in order to gather wild crabgrass or water-lily bulbs. Homes are on the cultivated fields from November to August, near granaries and milking places. Herds are systematically moved to temporary pastures.

This region depends essentially on the extensive pasturing of herds, which are moved as seems most advantageous. The use of crop residues and even animal excrete as fuel demonstrates the severe lack of wood in this zone.


Rainfall varies from 400 to less than 150 mm, the maximum monthly rainfall is roughly 175 mm, drainage is calculated as nil, the erosivity factor is under 200, highest daily rainfall in a ten-year period is 80 mm, and the population density drops sharply to less than 10 per km˛.

The landscape is composed of dioritic hills followed by a broad, sloping, sandy, then loamy, pediment, terminating in the region of the pond. Small dunes form around clumps of grass and bushes on the sandy pediment. Some old Faidherbia albida and other thorny vegetation still survive on the loamy pediment, especially where the water table is not too far down. Soil is lithomorphic on the mountains and sandy on the dunes, with sub-arid, brown-red soils around the marshes. Traditional techniques entail flat-sowing millet on sand and sorghum on the clayey lowlands, and using the slopes as extensive pasture. Gardens are planted in the lowlands, with a certain amount of flood recession cropping all around the pond.


The main risk in the sandy zone is wind erosion along with degradation of vegetation from both overgrazing and the wind erosion. Rainsplash on the sloping loamy pediments results in very extensive runoff, which digs small gullies.


In this extremely fragile environment, it is dangerous to advise the development of an agropastoral system to match population growth. Development appears to be blocked today, since almost all the possible land is now being farmed. Fallow periods are disappearing, the soil is becoming exhausted, and the cost of inputs (mineral fertilizers and short-cycle varieties) is only economically viable in years when rainfall is abundant and well distributed. However, the following measures could be tested on an area such as that at Ségué in northern Yatenga:

• planting hedges or thorny fodder species in sandy areas (Balanites, Acacias albida, Acacias nilotica, etc.);

• microcatchment water-harvesting for small ridged fields on loamy pediments;

• agroforestry in the bottom lands (stone lines, hedges, forage and fruit trees);

• organizing the shores of ponds and marshlands for diversified intensive cropping (fodder for dairy production, cereals, vegetables and some fruit trees).

However, it is clear that agricultural production is restricted to the lowlands and that animal husbandry with short-distance nomadism is better adapted than cropping to this very fragile Sahelian environment.

FIGURE 64 Diagram showing improved use of a Sahelian landscape (R > 400 mm): example of an agropastoral system in which intensive farming is confined to the valley: valley farming

Water harvesting area and rangeland

Rainfed random crops under old trees

Intensive irrigated or falling-flood crops

dunes or sandy deposits

loamy pediments

edge of the valley or swampland


red-brown semi-arid soils

fairly fertile hydromorphic soils

Poor soils: deficient in N and P. poor in organic matter, risk of salinization

Fragile soils:

slaking and erosion crusts
permeable if covered by a sheet of sand
quickly becoming sealed on loams


rainfall impact on soil (r) scouring

splash erosion, degradation of organic matter and gullying

hydromorphism, surface salinity

wind erosion on sand


- Large area for water harvesting

- Supplementary irrigation from groundwater fed by runoff

- Extensive rangelands

- 1/2 moons or zaď for planting millet and shrubs

- Larges Acacia with roots down into groundwater

- Some millet cropping on the sandy deposits

- Millet-groundnut or cowpea rotation

Intensive irrigated fruit and household plots

- Harvesting runoff to form small ponds to water livestock

- If possible, thorny hedges: Acacia, Euphorbia balsamifera, or perennial grasses - Andropogon.

Fodder crops in and around swampland

- Stabilizing the sandy deposits with bushes so as to minimize the risks of damage to neighbouring crops from sheets of wind-blown sand

Variety of environmental conditions along a bioclimatic belt in West Africa, and range of suggested control methods (cf. Roose 1992)

Ecological zone Rainfall Case studied

Guinean forest 2500 to 1200 mm in 2 seasons (Abidjan)

Southern Sudanian 1400 to 1000 mm in 1 season (Korhogo)

Northern Sudanian 1000 to 700 mm Koutiala

Southern Sahelian 700 to 400 mm Ouahigouya

Northern Sahelian 400 to 150 mm Mare d'Oursi

Mean annual rainfall

2100 mm

1350 mm

900 mm

725 mm

535 mm

Monthly rainfall max.

700 mm

318 mm

250 mm

207 mm

177 mm

Daily rain 1/1 1/10 1/100

135-230-280 (mm)

76-119-169 (mm)

62-107-166 (mm)

55-101-146 (mm)

49-79-109 (mm)

Max. intensity 1/1 1/10

90-120 (mm/h)

75-106 (mm/h)

60-80 (mm/h)

59-78 (mm/h)

32-45 (mm/h)

Rain erosivity RUSA






PET (mm)

1250 mm

1660 mm

1750 mm

1905 mm

2000 mm

Calculated drainage

1200-800 mm

470-160 mm

180 to 10 mm

50 to 0 mm

0 mm

Diagnosis of risk:

- leaching, acidification

+ + + +

+ + +

+ +

+ +


-sheet erosion


+ + +

+ ++

+ + +

+ + (on pediments)

- gully erosion




+ + +

++ (on pediments)

- waterlogging

bottom lands

slopes and bottom lands

bottom lands

bottom lands

bottom lands

Soils on the slope

very desaturated ferralitic SC ± gravelly very acid

- ferralitic, desaturated ± gravelly
- or vertisol/brown soil on basic rock

- ferruginous leached SC ± gravelly
- or vertisol/brown soil on basic rock

- ferruginous leached SA ± gravelly
- or vertisol/brown soil on basic rock

- ferruginous, little leaching, sandy on dunes
- or brown-red sub-arid soil


Closed rainforest + Panicum, etc.

Tree savannah, Daniella, Parkia, Butyrospermum + Andropogon + various

Tree savannah, Parkia, Butyrospermum + thorn species + Andropogon + various

Shrub savannah with Combretum, Baobab, acacia + thorn species Andropogon + various Pennisetum

Steppe or bush baobab, acacia, Balanites, Ziziphus annual grasses

Farming systems

Cover farming Complete/Full/Total infiltration

Drainage farming during the 2 wettest months

Rainfed farming = total infiltration of rain

Runoff farming

Valley farming: concentration of water and crops in valleys

Population density (pop/km˛)

20 to 40

30 to 100

30 to 50

70 to > 100

10 inhab/km˛

Traditional techniques

- multicropped cassava + maize + herbs on small mounds
- coffee, cacao, oil palm, kola, under shade
- forest fallow

- yams on large mounds
- maize + various herbs on average ridges
- millet groundnut on degraded soil + ridges
- crops combined with useful trees
- drainage between plots

- flat-grown crops + 1 weeding + 1 mounding, sorghum/cotton or millet/ groundnut/cowpea
- passage of water from hills
- rain infiltration on fields
- low stone walls or stone lines

- sod seeding on the flat after burning, then 1 weeding and 1 mounding: sorghum or millet/groundnut/cowpea
- mulching, zaď, boli
- stone or grass lines
- levelling sandy dunes

- sod seeding on the flat + 1 weeding and loosening around roots
- millet on sand
- sorghum on pediment and clayey loamy bottom lands
- extensive grazing on slopes
- household plot on bottom lands
- flood recession crops on ponds

Treatment proposed

Land husbandry
- management of OM + NPK = f. of crops + lime if pH<4.5
- soil cover + close, early planting + multicropping + tree crops + cover plants
- grass banks or hedges on slopes
- drainage of bottom lands

SWC (1964-68)
Reforestation or ironstone
Buffer strips on slopes
Stabilization of gullies
Protection of rice fields

Land husbandry 1985-91
- rangeland improvement
- regeneration strips
- lines of stones or cotton stalks
- protection bunds uphill of block of crops
- hedges + trees around fields
- grassed spillways
- treatment of bottom lands

SPR of GERES 1960-65
- then SWC ORD + FEER
- Land husbandry CIRAD + CRPA 1986 = rangeland improvement + livestock ponds + gardens + stone lines + Andropogon + hedges around fields = treatment of gullies and roads + improvement of bottom lands

Land husbandry
- forage shrubs in 1/2-moons
- improvements to rangelands
- ponds for livestock
- runoff harvesting on pediment/hill
- filtering bunds on pediment or gully
- fodder crops on bottom lands


The above overview of this bioclimatic sequence indicates that development of farming techniques tailored to the water balance should go hand-in-hand with appropriate water management methods for erosion control (see Table 39). This makes it easier to understand one reason for the failure of the many SWC and SPR projects which have stubbornly applied the model developed by Bennett at another time, in a temperate climate, and under intensive mechanized farming.

It is also easy to understand traditional farmers who not only fail to maintain imposed erosion control schemes but actually destroy them when they come to realize that they are unsuited to their special farming conditions.

Analysis of both traditional strategies and the monthly water balance could provide a basis for future land use planning projects, which must focus on improving such strategies with the active involvement of farmers and herders.

This is a challenging, long-term research and development task, in which the human aspects are as important as the technical ones. Multidisciplinary teams will therefore be needed to monitor and evaluate such projects.


Chapter 10. Development of the Bamiléké bocage


Jean-Marie Fotsing, Head of Geography Department, University of Yaoundé, Cameroon

The situation
Diagnosis: relatively fragile environments
Effective traditional techniques
Some suggested improvements

The situation

Situated in Central Africa between 5° and 6° N. the Bamiléké uplands occupy 6196 km˛ to the south of the highlands of western Cameroon (Figure 65). With an average population of 168 per km˛ reaching 600 in some places, it is one of the few tropical regions supporting such a large population on traditional rainfed farming. Analysis shows that the farming techniques are relatively effective in maintaining fertility and controlling erosion. However, current changes in the region are leading to a simplification of techniques in areas long occupied and to an expansion of these same farming methods to recently developed areas. Heavy population pressure, increasing numbers of dwellings and contemporary social and economic demands may well have adverse effects on a fragile environment; even the relatively unaggressive rainfall tends increasingly to accumulate on the surface, and the ensuing runoff threatens farmed slopes. What is the answer? Is it possible to envisage a heavily populated, productive and stable mountain area? The partial success of the Western Province Rural Development Project - which included digging erosion control ditches, building bench terraces on the slopes, and applying mineral fertilizers - encourages consideration of solutions based essentially on local know-how in an environment with considerable agricultural potential.

Diagnosis: relatively fragile environments


The Bamiléké region is a high plateau at an average altitude of 1450 m. It can be divided into three main sections, ranging from 700 to 2740 m (Figure 65).

Up to 1100 m, the peripheral plains (Noun in the east and Mbo in the southwest) occupy nearly 20% of the area. The flat surface is relieved by small gentle hills (less than 12% slope).

FIGURE 65 Relief map showing rainfall distribution (cf. Suchel 1989)

Between 1100 and 1600 m, the uplands constitute the main relief pattern, accounting for more than 70% of the region, with two distinct types:

• the granito-gneissic plateau in the south, with polyconvex or half-orange landforms, and occasional granite outcrops;

• the basaltic plateau in the north, with more even landforms, in which the land between the rivers has flattened, rounded or elongated hillocks, separated by narrow valleys; slopes steeper than 25% and those between 12 and 25% are predominant.

Above 1600 m, the mountains (less than 15% of the area) exhibit a more rugged topography, with 75% of their area on slopes of over 25%. This category covers the small granite mountains rising to less than 2100 m in the south, and the volcanic Bambouto chain in the northwest which rises in steps to a maximum of 2740 m.


The climate is subequatorial monsoon in type, chiefly moist and cool, with one rainy season from mid-March to mid-November. Annual rainfall is everywhere over 1400 mm (Bangangté 1457, Bafang 1731, Bafoussam 1796, Santchou 1727, Dschang 1919, Baranka 2500), although it decreases considerably from west to east, and also from south to north due to altitude. The peak rainfall levels are in August and September; in Bafoussam, for example, they reach 90 to 11.6 mm in March, April and May, and 118 mm in August. However, hourly intensity is low (15 to 40 mm/h). Temperatures are kept down by the altitude (in Bafoussam maxima are between 23° and 27° C).

Soils can be divided into three groups (Champaud 1973, Segalen 1967):

• ferralitic soils derived from basalt are the most widespread, with very favourable physical and hydric properties - great depth, high porosity, friability without gravel, a high clay content, and surface permeability; hardened ferralitic soils with occasional outcrops of ironstone;

• relatively unevolved soils derived from basic soft volcanic rock (ash, lapilli), very rich in organic matter, nitrogen and exchangeable bases, and very permeable;

• hydromorphic soils - sandy and deficient on granite, peaty on basalt and alluvial deposits - are found in the marshy lowlands; they are not particularly fertile, but the presence of water, flat topography and high organic matter content makes for good farmland.

Soil texture is very varied, with silt content ranging from 10 to 30% and clay from 10 to 70%. However, whatever the soil make-up, local variations depend on the position in the toposequence. Generally speaking, soils are deeper, finer and more fertile on the lower slopes than on the higher reaches. The traditional farming techniques and organization of farmland reflect these local variations.


The Bamiléké country has been inhabited for a long time and is densely populated, with an average of 168 per km˛ (1987). This figure means very little, however: density everywhere in the basalt region is higher than 200, in some areas approaching or even exceeding 1000 (Ducret and Fotsing 1987), while outside the basalt region it rarely exceeds 150, with the lowest densities in the alluvial zones and in mountain areas.

Population pressure is accentuated by the fact that dwellings are scattered, and also by the inheritance system: one male inheriting the entire family landholding. Non-inheriting sons therefore become founders of new lineages and have to find land for themselves elsewhere. With an annual growth rate of 3.2%, there is no let-up in pressure on land, despite a massive exodus toward the towns.

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