Since the 1970s, research throughout West Africa showed that low soil organic matter and limited availability of plant nutrients, in particular phosphorus and nitrogen, are major bottlenecks to agricultural productivity, which is further hampered by substantial topsoil losses through wind and water erosion. A few widely recognized publications pointing to massive nutrient mining of the existing crop-livestock production systems triggered numerous studies on a wide array of management strategies and policies suited to improve soil fertility. Throughout Sudano-Sahelian West Africa, the application of crop residue mulch, animal manure, rockphosphates and soluble mineral fertilizers have been shown to enhance crop yields, whereby yield increases varied with the agro-ecological setting and the rates of amendments applied. In more humid areas of Western Africa, the intercropping of cereals with herbaceous or ligneous leguminous species, the installation of fodder banks for increased livestock and manure production, and composting of organic material also proved beneficial to crop production. However, there is evidence that the low adoption of improved management strategies and the lack of long-term investments in soil fertility can be ascribed to low product prices for agricultural commodities, immediate cash needs, risk aversion and labour shortage of small-scale farmers across the region. The wealth of knowledge gathered during several decades of on-station and on-farm experimentation calls for an integration of these data into a database to serve as input variables for models geared towards ex-ante assessment of the suitability of technologies and policies at the scale of farms, communities and regions. Several modelling approaches exist that can be exploited in this sense. Yet, they have to be improved in their ability to account for agro-ecological and socio-economic differences at various geographical scales and for residual effects of management options, thereby allowing scenario analysis and guiding further fundamental and participatory research, extension and political counselling.
Feeding experiments with pre-harvest tillers and leaves of 2 varieties of pearl-millet were conducted on a research station in semi-arid Mali. Tillers were harvested at 45 to 65 days after sowing (DAS) and fed green. Leaves were harvested at 65 to 85 DAS and fed to sheep or cattle green or after 8 months conservation as hay or as silage. Intake of organic (IOM) was higher for green leaves than for tillers, showing no difference for the 2 varieties used. In vivo digestible organic matter (DOM) was highest tillers in both varieties. Nutritive value of tillers and green leaves met the quality criteria for a maintenance diet of sheep. During conservation of millet leaves, the reduction in nutritional value was less with hay than with silage. Small amounts of silage offered as a supplement to rice straw helped to meet maintenance requirements for metabolizable energy. Conserved as hay, a quality forage was obtained which on an economic scale compensated for grain yielded losses when fed to selected animals.
In the pearl millet (Pennisetum glaucum) based agro-pastoral systems in the south-eastern part of Mali weeding is either done by hand or using animal (donkeys, cattle) traction. To feed the draught animals farmers are harvesting fodder. One of these comprise stripped millet leaves. To evaluate these millet production systems including draught animals, and defoliation, qualitative interviews were conducted in eight villages in the Seno-Bankass area (1991) and day-to-day activities were monitored in one village (1992). The existing defoliation practice was compared with results obtained from on-station defoliation trials. These showed that the farmers practice of leaving the upper leaves from stalks with grains in milk stage, and defoliating only plants on manured fields, results in an optimal balance between grain yield reduction and fodder quality of the harvested biomass. It is concluded that the use of animal traction for weeding increases efficiency on manured fields only. Furthermore, a reduction in millet grain yield through partial defoliation can be compensated in at least average rainfall years by the benefits of the obtained good quality fodder by either selling the fodder or feeding it to selected animals.
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