Main cropping systems

Since the spatial distribution and dynamics of land-use types is of prior concern in this study of land-use/cover change, it is necessary to obtain a valid definition of these land-use types.

The difficulty in defining the main land-use types is that many crops are grown in combi-nation with others, which leads to a high variety of land-use types if all combicombi-nations are considered. To reduce this variety in a reasonable way, different combinations of land-use types were tested for their relevance to the land-use model. To make sure that the model reflects the dynamics of land-use change in a reasonable way, those land-use types were cho-sen that were best reprecho-sented by the livelihood background of the farming households. This way, the following main land-use types could be identified for the rainy season: The mixed compound system, mixed cultures based on groundnuts, monocultures of groundnuts, rice, monocultures of cereals and a class consisting of the minor crops soybeans (Glycine max) and sweet potatoes (Ipomoea batatas). In the dry season, where the tomato is the by far most prevalent crop, only the two land-use types monoculture of tomatoes and a mixed culture based on tomatoes could be identified.

Cropping sytems in the rainy season

The compound farm system is a permanent mixed cropping system consisting mainly of early millet, late millet, guinea corn, cowpeas and leafy vegetables. Minor crops such as tobacco and okra, which are usually grown in the inner circle of the compound, were omitted in the analysis due to their low quantities. This system is mostly located around the compound buildings, and soil fertility is regenerated by techniques traditionally involving mainly house-hold refuse and manure from the livestock (Gyasi, 2004). This land-use type is the most widespread cultivation system, covering 48.2 % of the total cultivated area in the study area.

The monoculture system of groundnuts occupies about 7.8 % of the cultivated area.

Groundnuts (Arachis hypogaea) are less nutrient-demanding than the other staples grown in the area and can therefore be easily cultivated on gravelly or sandy-loamy soils, which are usually not suitable for other local staples. Furthermore, there is a tendency to cultivate groundnuts on distant plots, as this crop is less labor intensive than other local crops.

In Africa, the groundnut is considered a women’s crop (Kenny and Finn, 2004). This is also

Figure 4.2: Typical groundnut and millet fields in the Atankwidi catchment

substantiated by an analysis of household data, showing that the percentage of women within a household is highly correlated to the percentage of area with groundnuts. Groundnuts were originally grown by women to supplement their family diet with protein (Kenny and Finn, 2004). However, groundnut production can also be a way for women to earn cash income and participate in the economy. Among rainy season crops, the groundnut is the staple most often retailed, although, in general, the disposal rate of rainy-season food crops is quite low, due to the subsistence nature of rainfed cultivation.

The mixed culture based on groundnuts is, with 29.1 %, the second most widespread cultivation system in the study area. Within this system, groundnuts are often combined with bambara beans or cowpeas, and sometimes with late millet, which helps to enhance soil fertility. Another reason for combining groundnuts with beans on distant plots is that beans are not eaten by birds and therefore do not require supervision.

In 86.7 % of the cases, the rice-based system consists of a rice monoculture. The remaining 13.7 % of mixed cultures consist in most of the cases of a combination of guinea corn and rice, and sometimes of a combination with small amounts of early millet, late millet

Figure 4.3: Typical rice fields in the Atankwidi catchment

or okro. Until recently, most of the rice cultivated was African rice (Oryza glaberrima), which was gradually replaced by Asian rice (Oryza sativa) in most parts of the study area.

Rice production has increased during the last decades due to an improved access to tractors, which facilitates the field preparation on the heavy clayey-loamy soils that are usually suitable for rice cultivation. In total, rice fields cover about 6.7 % of the cultivated area.

The monoculture of cereals is, together with rice, the cultivation system with the greatest distance from the compound, with an average distance of 1 km. It consists of different combinations of Guinea corn (Sorghum guineense), early millet (Milium vernale), late millet (Pennisetum claucum) and sometimes maize (Zea mays). Guinea corn, which was originally adopted from a neighboring region, is increasingly cultivated in the study area, as it is more adapted to the reduced length of the rainy period, which is possibly a result of climate change.

The small quantities of maize, which usually need chemical fertilizers to grow well, are remnants of the times before the structural adjustment program, when fertilizer was locally subsidized by the government. Cereal monocultures are usually cultivated along the riverside, where the nutrient supply is sufficient, covering about 7.4 % of the total cultivated area.

The other cropping types, covering only 0.7 % of the cultivated area, comprise monoculture of soybeans and cultures based on sweet or Irish potatoes, usually mixed with red pepper. These two cultivation types had to be combined in one land-use type, since their occurrence turned out to be too low to allocate them to two separate classes.

Cropping systems in the dry season

As the tomato is the by far most prevalent crop in the dry season (90 % of all irrigated crops are tomatoes), the only meaningful classification of land-use types in this season was a sep-aration among monocultures of tomatoes and mixed cultures based on tomatoes. The major tomato varieties used are ’Petromech’ and ’No Name’, sometimes combined with onions, red pepper and leafy vegetables in a mixed culture system. These mixed systems amount to about 40 % of the irrigated area, the remaining 60 % being tomato monocultures. In general, irrigation is quite a young business in the study area. The irrigation farming in the study area only began around 16 years ago by using bucket irrigation. Nowadays, about 38 % of the farmers are involved in irrigation farming, with 35 % of them using motor pumps, and 65 % still practicing bucket irrigation. The choice of irrigation method does not seem to have an influence on the choice of land-use type.