International Science Foresight Workshop: Global Challenges and Research Gaps. The Royaumont process.

How scientists might better contribute to SDGs in the land sector? At the invitation of INRAE, a group of high-level international experts delivers a comprehensive and systemic approach

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

CaTMAS: a multi-agents model to simulate the dynamics of carbon resources of West African villages

International audienceCarbon is an important determinant of the sustainability of West African farming systems and of the atmospheric greenhouse effect. Given the complexity of C dynamics, various simulation models have been developed. Few include socioeconomic factors or handle system heterogeneity. This study pro- poses a generic, multi-agent model for the analysis of C dynamics at village level. It assumes that a better analysis of carbon dynamics at village level requires account to be taken of social, economic, physical and biological factors as well as of the actions of individuals and their interdependence. The Carbon of Territory Multi-Agent Simulator (CaTMAS) model is based on the Organization-Role-Entity-Aspect (OREA) meta-model and the Multi-Agent Systems (MAS) approach. OREA enables C dynamics to be studied from various points of view through the roles played by entities within organizations and also allows various entities to play the same role in various ways through the notion of aspects. The model was coupled with the Century model and a geographical information system to provide a realistic representation of C dynamics. CaTMAS provides not only a framework for the explicit description of the carbon dynamics of farming systems but can also be used to assess the viability of farming systems using various socioeconomic and biophysical scenarios. The model includes interactions between human activities and the environment. Simple simulations involving two cropping systems and focusing on the impact of population growth and different climate regimes on the C dynamics indicate that CaTMAS accounts realistically for the relationships between population, agriculture, climate and SOC dynamics. In simulation, population growth, which drives food demand, leads to agricultural expansion, land scarcity and decrease in fallow duration. These effects are accentuated by increasing temperature and decreasing rainfall which affect the SOC dynamics controlling soil fertility and thus crop production. Improvements to the model should make it possible to extend the scale of the simulation of C dynamics and include refinements such as the inclusion of the trading of carbon credits

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 III. Plant and soil components under continuous cultivation

International audienceCarbon (C) and associated nutrient budgets related to land use in agro-ecosystems in West African savannas (WAS) are a matter of both local (sustainability of farming systems) and global (C balance) concern. In a mixed-farming system in southern Senegal, patterns of C, nitrogen (N) and phosphorus (P) allocation in the plant-soil system (down to a 40 cm soil depth) were compared at harvest in 14 plots, six being under semi-permanent cultivation with groundnut (Arachis hypogaea L.), others being under continuous cultivation with millet (Pennisetum glaucum L.), maize (Zea mays L.) or rice (Oryza sativa L.). Carbon stored in the plant-soil system amounted to 25.0, 27.4, 34.9 and 71.9 t per ha, respectively, in groundnut, millet, maize and rice fields. Ninety percent of C and P (total in plant P-t, available P in soil (POD)) and 95% of N of the whole ecosystem were stored in the soil. The high C and nutrient amounts found in rice plots were attributed to the clayey texture of the soil and to seasonal flooding. The lower values for C, N and POD found in soils in the bush ring (groundnut crops) compared to those of the compound ring (millet and maize crops) stemmed from land management. Higher values for C, N and POD in soils in the compound ring were maintained under continuous cultivation thanks to higher organic and nutrient inputs originating from crop residue recycling, manuring and, in the maize plots, spreading of household wastes. In the compound ring, the amount of C stored seemed to depend as much on the amount of C input as on the chemical richness of organic inflow. The effect of land management (bush versus compound ring) on soil properties was generally restricted to the 0-20 cm layer (except for P, cations and pH), and the better soil status in the compound ring was linked to nutrient depletion of the bush ring. From the perspective of global change, the estimated potential of the WAS for C sequestration under continuous cultivation was found to be low. From a methodological point of view, soil carbon status may be considered as a relevant indicator for the fertility of agro-ecosystems in the WAS belt, provided that its biotic components are included, and that both the quality and dynamics of soil organic matter (assessment of seasonal variations, and C flows) and soil texture are characterised. (C) 2002 Elsevier Science B.V. All rights reserved

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

Les nématodes, reflet du fonctionnement biologique des sols en semis direct sous couverture végétale.

The nematofauna soil consists of plant parasitic nematodes (well known for the damage they cause to crops), as well as free-living nematodes which are for a large part microbivore. Because of the abundance and diversity of soil nematodes and of their biological characteristics, these organisms are good candidates to be use as bioindicators of soil conditions. The soil nematofauna was studied during 3 years in a long-term experiment with contrasting treatments (conventional tillage or notillage with or without permanent cover crops) in Madagascar (Antsirabé). The composition and structure of the nematofauna was clearly different between traitments according to tillage and cover crops. The structure of the nematofauna was stable over time for the period of study and was characteristic of the farming practices.La nématofaune des sols est constituée de nématodes phytoparasites, bien connus pour les dégâts qu’ils peuvent occasionner sur les cultures, ainsi que de nématodes libres dont une grande part est microbivore. Du fait de l’abondance et de la diversité des nématodes dans les sols ainsi que de leurs caractéristiques biologiques, ces organismes sont de bons candidats à leur utilisation comme bioindicateurs de l’état du sol. La nématofaune du sol a été étudiée 3 années successivement dans des systèmes SCV mis en place depuis plus de 10 ans à Madagascar (Antsirabé). La composition et la structure de la nématofaune est clairement différente en fonction du travail du sol et de la couverture végétale dans les systèmes étudiés. La structure de la nématofaune est stable au cours du temps pour la période d’étude et est caractéristique des pratiques culturales