Research Setting 2221 Description of Study Area

The research was conducted in the west-central part of Senegal that is known as the "Old Peanut Basin" (See Figure 22.1). The name goes back to the introduction of peanuts, or groundnuts, by the French colonial power at the end of the 19th century in an area initially overlapping with today's administrative regions of Diourbel, Louga, and Thiès (Pelissier and Laclavére, 1984). At present, the term "Peanut Basin" or "Bassin Arachidier" reflects a certain socioeconomic entity in Senegal (Stomal-Weigel, 1988). It is a gently undulating plain

Figure 22.1 Diagram showing the research area and villages (underlined) in the Old Peanut Basin of Senegal.

with soils that contain large amounts of aeolian material. The main soil types are luvic Areneols, ferric Luvisols, and chromic Vertisols (Food and Agriculture Organization-UN Educational, Scientific, and Cultural Organization, 1974). Farmers distinguish typically between two types of soil: dior and deck. Dior soils contain more than 95% sand and less than 0.2% organic carbon and are usually found on former dune slopes. Deck soils are hydromorphic with 85% to 90% sand, and organic carbon contents of 0.5% to 0.8% (Badiane et al., 2000).

Annual precipitation ranges from 350 to 700 mm. It is barely suitable for rainfed agriculture although 90% of all arable lands are used for cultivation (Centre de Suivi Ecologique [CSE], 2000). The main crops are millet (Pennise-tum typhoideum), groundnuts (Arachis hypogaea), sorghum (Sorghum bicolor), and cowpeas (Vigna unguiculata). The rainy season lasts from July to September or October. Spatial and temporal variation of rainfall are high, and episodic droughts and crop failures are common. The area under cultivation and crop yields also vary notably from year to year as indicated in Figure 22.2. The 1980-2001 mean millet yields were 527 kg ha-1, and mean yields for groundnuts, the major cash crop, were 665 kg ha-1 (Direction de l'Analyse, de la Prévision et des Statistiques/Division de Statistiques, Documentation et Information Agricole [DAPS/DSDIA], 2001).

The scope of agricultural intensification within farming systems varies depending on population pressure, ethnic group affiliation, and availability of and access to land (Pelis-sier, 1966; Copans, 1988; Stomal-Weigel, 1988; Lericollais et al., 1998). Today, population density in the Old Peanut Basin

120,000h

120,000h

196019651970197519801985199019952000 Years

Figure 22.2 Area under production (ha) and yields (kg ha-1) for millet, Département de Bambey, Région de Diourbel. (Data from DAPS/DSDIA.)

1,000 -- 900 .4- 800 ■ 700 ; 600 ' + 500 400 300 -- 200 -- 100 0

196019651970197519801985199019952000 Years i l d

Figure 22.2 Area under production (ha) and yields (kg ha-1) for millet, Département de Bambey, Région de Diourbel. (Data from DAPS/DSDIA.)

is higher than in any other agricultural zone in Senegal, ranging from 150 to 225 inhabitants km-2 (CSE, 2000). The two major ethnic groups are the Wolof and the Serer. Together they account for 88% of the population (CSE, 2000). Woody shrubs predominate and consist of Balanites aegyptica (sump) and Guiera senegalensis (nger). The most common tree species are Acacia raddiana (seing), Acacia nilotica (nebneb), Acacia seyal (surur), Adansonia digitata (gui), and Faidherbia albida (kad).

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