Influence of agricultural practices and ecological environment on the diversity of the fallows of forest origin (Highlands, Madagascar)

The present study relates to the fallow (kapoka) of forest origin in western edge of the forested “corridor” Ranomafana-Andringitra on the Malagasy Highlands. The objectives of this research were to characterize the evolution of the vegetation in the fallows and to describe the cultivation parameters and those related to the ecological environment in order to determine those which could infl uence the dynamics of succession. A synchronic approach was adopted: 14 fallow fields of different ages were retained. Formal investigations and pedological studies were carried out in the fields. The results showed that: (1) the fallow vegetation can be in a progressive evolution leading to a shrubby and wooded vegetation when intensity of exploitation, characterized by the cumulated duration of the cultivated period, mode of tillage, and the age of the fallow, is weak; on the other hand when intensity of exploitation is high the regressive evolution leading to a grassy formation of pseudo-steppic type occurs; (2) vegetation diversity within each field in fallow is low (from 3 to 41 species), whereas when scale is changed, total diversity for the 14 fields is much more important (107 species)La présente étude concerne les jachères (kapoka) d'origine forestière en lisière ouest du « corridor » forestier Ranomafana-Andringitra sur les Hautes-Terres malgaches. Les objectifs de cette recherche sont de caractériser l'évolution de la végétation dans les jachères et de décrire les paramètres culturaux et liés à la station, afin de déterminer ceux qui pourraient influencer la dynamique de succession. Une approche synchronique a été adoptée: 14 parcelles d'âges différents ont été retenues. Des enquêtes formelles et des études pédologiques ont été effectuées dans les parcelles. Il ressort des résultats que: (1) la végétation des jachères peut évoluer d'une manière progressive si l'intensité d'exploitation, caractérisée par la durée cumulée de la phase culture, le mode de préparation du sol, et l'âge de la jachère, est faible, sinon, c'est l'évolution régressive aboutissant à une formation herbeuse de type pseudo-steppe qui l'emporte; (2) la diversité végétale au sein de chaque parcelle en jachère est faible (de 3 à 41 espèces), alors que si l'on change d'échelle, la diversité totale pour les 14 parcelles est beaucoup plus importante (107 espèces)

Intensity cultivation induced effect on soil organic carbon dynamic in the western cotton area of Burkuna Faso

The soil organic carbon (SOC) dynamic is a key element of soil fertility in savannah ecosystems that form the key agricultural lands in sub-Saharan Africa. In the western part of Burkina Faso, the land use is mostly linked to cotton-based cropping systems. Use of mechanization, pesticides, and herbicides has induced modifications of the traditional shifting cultivation and increased the need for sustainable soil fertility management. The SOC dynamic was assessed based on a large typology of land cultivation intensity at Bondoukui. Thus, 102 farm plots were sampled at a soil depth of 0–15 cm, considering field–fallow successions, the cultivation phase duration, tillage intensity, and soil texture. Physical fractionation of SOC was carried out by separating the following particle size classes: 2,000–200, 200–50, 50–20, and 0–20 µm. The results exhibited an increase in SOC stock, and a lower depletion rate with increase in clay content. After a long-term fallow period, the land cultivation led to an annual loss of 31.5 g m?2 (2%) of its organic carbon during the first 20 years. The different fractions of SOC content were affected by this depletion depending on cultivation intensity. The coarse SOC fraction (2,000–200 µm) was the most depleted. The ploughing-in of organic matter (manure, crop residues) and the low frequency of the tillage system produced low soil carbon loss compared with annual ploughing. Human-induced disturbances (wildfire, overgrazing, fuel wood collection, decreasing fallow duration, increasing crop duration) in savannah land did not permit the SOC levels to reach those of the shifting cultivation system

Water, agriculture and poverty in the Niger River Basin.

In Fisher, M.; Cook, Simon (Eds.). Water, food and poverty in river basins: defining the limits. London, UK: Routledg

Conservation agriculture in Sub-Saharan Africa

Specific practices of conservation agriculture (CA) in sub-Saharan Africa are diverse and vary according to local farming conditions. However, despite more than two decades of investment in its development and dissemination, adoption of CA is low. Crop responses to CA are highly variable, and not always positive, which is an important hindrance for adoption, especially for resource-poor farmers who need immediate returns with their investments in CA in order to be able to feed their families. In contrast with commercial farms such as in Brazil, reduced costs with CA on smallholder farms in sub-Saharan Africa are not always observed. Another major challenge with the practice of CA is the use of crop residues for mulching since crop residues are a major source of feed for livestock, especially in semiarid regions, where biomass production is limited and livestock plays a crucial role in farming systems. Studies indicate that the three principles of CA, including mulching, are needed to increase crop yields compared with conventional tillage (CT)-based practices. Among the three principles of CA, mulching is certainly the one that is least observed in past and current cropping practices in Africa. CA has a potential to improve the soil water balance and increase soil fertility, and it is undoubtedly a cropping practice that can result in substantial benefits for certain farmers in Africa. The question is when and how it is the best approach for smallholder farmers in sub-Saharan Africa. In general, CA is more likely to be attractive for farmers with a strategy of intensification than for farmers who struggle to produce food for their family. The latter too often face multiple constraints that limit the possibilities to engage in technological innovations. Some farmers may not be interested in new technologies because they earn their income from off-farm activities. Good markets of input supply and sale of extra produce are a prerequisite condition for adoption of CA as they are for any other new agricultural technology that aims at intensification. In sub-Saharan Africa, there is certainly a need to better target CA to potential end users and adapt the CA practices to their local circumstances and specific farming contexts. (Résumé d'auteur