Multi Agents Model for carbone dynamic simulation at village area scale

Un système multi-agents (SMA) a été conçu et mis en œuvre en vue d’étudier la dynamique des ressources organiques et azotée d’un terroir africain. Les simulations réalisées ont permis de mesurer l’impact des modes de gestion sur les ressources dans le long terme. Trois types d’enquêtes ont été nécessaires pour collecter les données nécessaires. Un premier modèle à l’échelle de la parcelle a permis de simuler le stockage du carbone et de l’azote dans les sols et dans la biomasse végétale. Ensuite la définition des règles individuelles et collectives de décision et de gestion des exploitations agricoles et du terroir ont nécessité des enquêtes approfondies avec les principaux groupes utilisant le terroir. . Pour la conception informatique du modèle, le formalisme UML a été utilisé. La représentation statique et dynamique du modèle a été formalisée sur la plate forme de modélisation CORMAS. . La méthode développée est appelée MIROT Modélisation Intégrée de la dynamique des Ressources Organiques et analyse de viabilité de Terroirs agro-sylvo-pastoraux des savanes ouest africaines). Le modèle MIROT utilise un fond de carte du terroir avec des contraintes spatiales pour simuler le fonctionnement de celui-ci

Carbone des sols en Afrique

Les sols sont une ressource essentielle à préserver pour la production d’aliments, de fibres, de biomasse, pour la filtration de l’eau, la préservation de la biodiversité et le stockage du carbone. En tant que réservoirs de carbone, les sols sont par ailleurs appelés à jouer un rôle primordial dans la lutte contre l’augmentation de la concentration de gaz à effet de serre. Ils sont ainsi au centre des objectifs de développement durable (ODD) des Nations unies, notamment les ODD 2 « Faim zéro », 13 « Lutte contre le changement climatique », 15 « Vie terrestre », 12 « Consommation et production responsables » ou encore 1 « Pas de pauvreté ». Cet ouvrage présente un état des lieux des sols africains dans toute leur diversité, mais au-delà, il documente les capacités de stockage de carbone selon les types de sols et leurs usages en Afrique. Il propose également des recommandations autour de l’acquisition et de l’interprétation des données, ainsi que des options pour préserver, voire augmenter les stocks de carbone dans les sols. Tous les chercheurs et acteurs du développement impliqués dans les recherches sur le rôle du carbone des sols sont concernés par cette synthèse collective. Fruit d’une collaboration entre chercheurs africains et européens, ce livre insiste sur la nécessité de prendre en compte la grande variété des contextes agricoles et forestiers africains pour améliorer nos connaissances sur les capacités de stockage de carbone des sols et lutter contre le changement climatique

Soil properties and plant production after short-term fallows in Senegal

International audiencetrials of vegetation modification were carried out to test the hypothesis that the management of key plant groups such as trees, perennial grasses and legumes would improve soil chemical properties in short-term fallows. Soil properties and plant production during a 4-year fallow period and millet yields after clearing were recorded at two sites representing dry and subhumid climates in Senegal, West Africa. During the four years of fallow, soil organic matter did not vary significantly at either site. A decrease in amounts of Olsen P, calcium and potassium in soil (0-10 cm depth) by 42-50% occurred at one site due to an effect of perennial grasses. The highest millet yields were measured in plots on which the largest amounts of biomass had been burnt after clear-cutting. These results confirmed that short-term fallows do not replenish soil organic matter and nutrient contents. The introduction of planted species did not arrest the decline in soil quality

Carbon, nitrogen and phosphorus allocation in agro-ecosystems of a West African savanna I. The plant component under semi-permanent cultivation

International audienceOrganic matter (OM) is both a commodity and a means of production in low-input farming systems of sub-Saharan Africa. Since this resource is becoming increasingly scarce in West African savannas (WAS), there is a need to assess OM, carbon (C), nitrogen (N), and phosphorus (P) allocation in local ecosystems related to land management. Carbon, N and P storage under semi-permanent cultivation in savannas in southern Senegal was thus measured through a chronosequence including 25 groundnut (Arachis hypogaea L.) crops and plots left to fallow for 1-26 years. The amounts of C, N and P in cropped C they increased to 17.7 t C, 231 kg N and 19.6 kg P ha(-1) in fallow plots aged plots were 5.5 t C, 106 kg N and 5.9 kg P ha(-1), 1-9 years. A threshold was reached after 10 years of fallow. Beyond it biomass amounts remained steady. Older fallow plots stored 29 t C, 333 kg N and 33.8 ka P ha(-1). Highest increases in woody components were found within the very first year following crop abandonment, and were achieved at the expense of the herbaceous layer. Carbon and nutrient allocation to woody below-ground biomass occurred only later. Massive nutrient losses were expected to occur at clearing due to both burning and wood exportation. Because storage in woody and herbaceous biomass remained steady in fallows aged more then 10 years, young fallows were found to have the highest productivity for wood and forage. However, plant productivity relied on the high resprouting capacity of local tree species, and thus on the maintenance of long breaks of fallow needed for the maintenance of perennial rooting systems. One of the aims of programs to improve the management of fallows, or to replace them with agroforestry techniques, should thus be to preserve perennial rooting systems by any means that are possible in the cropping systems of the WAS. (C) 2002 Elsevier Science B.V All rights reserved

Organic Matter Knowledge and Management in Soils of the Tropics Related to Ecosystem Services

International audienc

Estimating tree biomass of sub-Saharan African forests : a review of available allometric equations

In response to the growing interest in estimating carbon stocks in forests, available allometric equations have been compiled for sub-Saharan Africa. Tree, sprout and stand volume and biomass equations were reviewed. The 850 equations-and 125 related references were incorporated into an open-access database on the Carboafrica website (http://www.carboafrica.net). The collected information provides a basic tool for the estimation of biomass and carbon stocks and other purposes, such as bioenergy and fodder supply assessment. A Tier-method approach was developed to illustrate the possible use of the equations. Current available biomass expansion factors that are used to convert a volume to the total aboveground biomass appear to be limited; incomplete species-specific allometric equations are preferred to generalised equations. The analysis of the database highlighted important gaps in available tools to assess forest carbon stocks and changes in these stocks. A quality control assessment revealed that 22% of the equations were misreported and recommendations were proposed to guide further research. Further statistical analyses, such as the Bayesian approach, would help to produce more accurate biomass estimates

West African mixed farming systems as meta-ecosystems : a source-sink modelling approach

Nutrient availability is a major limitation of the production of West African mixed farming systems. The fertility of these systems was traditionally sustained by fallowing, and nutrient transfers by livestock from savanna to croplands. However, demographic growth and socio-economic constraints require the agro-ecological intensification of these systems. To understand how agricultural practices and landscape management affect crop production, we built a meta-ecosystem model of nitrogen stocks and fluxes, and we examined different scenarios of fallow management with or without livestock. Our results suggest that crop production is highly dependent on the source-sink dynamics of nitrogen. Without livestock, maximum crop production is obtained for an intermediate duration of fallowing, highlighting a trade-off between space devoted to production (cropland) and space devoted to fertility restoration (fallow). In presence of livestock, crop production is maximum for a shorter duration of fallowing; it is markedly higher with than without livestock. This result highlights the positive roles of livestock and fallows as pumps (vectors) of nitrogen from savanna rangeland to cropland, and from fallow land to cropland, respectively. However, it also highlights the negative relationship between livestock presence and fallowing, suggesting that the optimal configuration of livestock and fallow management is highly context-dependent. Overall, we argue that the meta-ecosystem approach is particularly relevant for the study of agro-ecosystems characterized by high spatial heterogeneity. This work can be seen as a first step toward an alternative approach, integrating tools from theoretical ecology for the study of agro-ecosystems which functioning strongly depends on spatial organisation