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In November 2018, ITAB (Institute of Agriculture and Organic Food) and INRA (National Institute for Agronomic Research) organized a transdisciplinary seminar to bring together stakeholders to: i) share issues associated with soil management in Organic Farming (OF) systems, ii) collectively define the main research questions to be addressed; and iii) facilitate the construction of networks or projects. More than 150 participants attended the seminar, which was designed using the method of citizen facilitation of the community forum type (Town Hall Meeting) allowing all parties to express themselves and a live summary by experts. The seminar identified important knowledge gaps on soils in OF systems and research needs. The 20 questions resulting from these exchanges relate to: i) the overall functioning of soils, more particularly the major biogeochemical cycles Carbon, Nitrogen, Phosphorus (CNP) and biological interactions; ii) the long-term effects of agricultural practices more or less specific to OF systems; (iii) soil protection; and iv) soil diagnostic and management tools. Most of the issues identified are generic and require multidisciplinary research, especially when responding to systemic issues. The seminar identified needs in terms of device and research observatory that provide the references necessary to validate or adapt to OF systems the tools and methods of evaluation and soil management available for conventional systems. The main questions identified during the seminar are discussed and confronted with recent dynamics in terms of soil research and development., En noviembre de 2018, el ITAB (Instituto de Agricultura y Alimentos Orgánicos) y el INRA (Instituto Nacional de Investigaciones Agronómicas) organizaron un seminario transdisciplinario para reunir a las partes interesadas para: i) compartir problemas asociados con el manejo del suelo en Agricultura Orgánica (AO) sistemas, ii) definir colectivamente las principales preguntas de investigación que se abordarán; y iii) facilitar la construcción de redes o proyectos. Más de 150 participantes asistieron al seminario, que fue diseñado utilizando el método de facilitación ciudadana del tipo foro comunitario (Town Hall Meeting) que permite que todas las partes se expresen y un resumen en vivo por parte de expertos. Los resultados confirmaron las importantes lagunas de conocimiento sobre los suelos en los sistemas de AO y las necesidades de investigación. Las 20 preguntas resultantes de estos intercambios se relacionan con: i) el funcionamiento general de los suelos, más particularmente los principales ciclos biogeoquímicos Carbono, Nitrógeno, Fósforo (CNP) e interacciones biológicas; ii) los efectos a largo plazo de las prácticas agrícolas más o menos específicas de los sistemas de AO; iii) protección del suelo; y iv) herramientas de diagnóstico y manejo de suelos. La mayoría de los problemas identificados son genéricos y requieren una investigación multidisciplinaria, especialmente cuando se trata de responder a problemas sistémicos. El seminario identificó necesidades en cuanto a dispositivo y observatorio de investigación para obtener las referencias necesarias para validar o adaptar, en sistemas de AO, las herramientas y métodos de evaluación y manejo de suelos disponibles para sistemas convencionales. Las principales cuestiones dentificadas durante el seminario son discutidas y confrontadas con la dinámica reciente en términos de investigación y desarrollo de suelos., En novembre 2018, l'ITAB (Institut de l’agriculture et de l’alimentation biologiques) et l’INRA (Institut national de la recherche agronomique) ont organisé un séminaire transdisciplinaire pour : i) partager les enjeux associés à la gestion des sols dans les systèmes en Agriculture Biologique (AB), ii) définir collectivement les principales questions de recherche à traiter ; et iii) faciliter la construction de réseaux ou de projets. Plus de 150 participants ont assisté au séminaire qui a été conçu à partir de la méthode d’animation citoyenne de type forum communautaire (Town Hall Meeting), permettant à l’ensemble des parties de s’exprimer et à une synthèse en direct par des experts d’être réalisée. Les résultats identifient des manques importants de connaissances sur les sols dans les systèmes en AB et les besoins de recherche. Les 20 questions issues de ces échanges portent sur : i) le fonctionnement global des sols, plus particulièrement les grands cycles biogéochimiques Carbone, Azote, Phosphore (CNP), et les interactions biologiques ; ii) les effets à long terme des pratiques agricoles plus ou moins spécifiques aux systèmes en AB ; iii) la protection des sols ; et iv) les outils de diagnostic et de gestion des sols. La plupart des questions identifiées sont génériques et nécessitent des recherches multidisciplinaires, en particulier lorsqu’elles répondent à des enjeux systémiques. Le séminaire identifie des besoins en matière de dispositif et observatoire de recherche afin d’obtenir les références qui sont nécessaires pour valider ou adapter sur les systèmes en AB les outils et méthodes d’évaluation et de gestion des sols disponibles pour les systèmes agricoles conventionnels. Les principales questions identifiées lors du séminaire sont discutées et confrontées aux dynamiques récentes de la recherche et du développement sur les sols.

Inagroforestry systems, fine roots grow at several depths due to the mixture of trees and annual crops. The decomposition of fine roots contributes tosoil organic carbonstocks and may impactsoil fertility, particularly in poor soils, such as those encountered in sub-Sahelian regions. The aim of our study was to measure the decomposition rate of root litter from annual andperennialspecies according to soil depth and location under and far from trees in a sub-Sahelian agroforestry parkland. Soil characteristics under and far from the trees were analysed fromtopsoilto 200cm depth. Faidherbia tree,pearl milletand cowpea root litter samples were buried in litterbags for 15 months at 20, 40, 90 and 180cm depths. Rootlitter decompositionwas mainly impacted by soil moisture and soil depth. Faidherbia decomposed more slowly (36±12% remaining mass after 15 months) than cowpea and pearl millet roots (23±7% and 29±11% respectively). Pearl milletaboveground biomass, at harvesting time, was twice as high under (992gm−2) than far (433gm−2) from the tree, andbelowground biomass(0–200cm of depth) was 30.9gm−2and 19.6gm−2under and far from the tree, respectively. Faidherbia fine roots contributed slightly (p-value < 0.1) to higher stocks of C under the tree (7761±346gm−2) than far from it (5425±558gm−2) and from 0cm down to 200cm depth.

Made available in DSpace on 2021-06-25T10:27:16Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-07-01 While a recent study showed that significant amounts of the nitrogen (N) requirements of young Eucalyptus trees can be provided by nitrogen-fixing trees (NFTs) in mixed-species plantations through short-term belowground N transfer, the consequences of soil fertility on this facilitation process remain unknown. We assessed the effect of fertilization on the percentage of N derived from transfer (%NDFT) from Acacia mangium trees to Eucalyptus trees in mixed-species plantations. A complete randomized block design with two treatments (fertilized vs unfertilized) and three blocks was set up in mixed-species plantations of A. mangium and Eucalyptus in Brazil, with 50% of each species at 2.5 m × 2.5 m spacing. Collection of litterfall and forest floor made it possible to estimate the annual N release from forest floor decomposition between 46 and 58 months after planting, close to harvest age. 15N-NO3- was injected into the stem of one dominant Acacia tree in each plot, 58 months after planting. The x(15N) values of Acacia and Eucalyptus fine roots sampled within 1.8 m of the labelled A. mangium tree were determined at 7, 14, 30 and 60 days after labelling. The x(15N) values in wood, bark, branch and leaf samples were also determined for the 6 labelled Acacia trees and their two closest Eucalyptus neighbours, just before and 60 days after labelling. The amount of N released from forest floor decomposition was 31% higher in fertilized (F+) than in unfertilized (F-) plots. Sixty days after labelling, the aboveground compartments of Eucalyptus trees were significantly 15N enriched in both treatments. The x(15N) values of Acacia fine roots were higher than background values from 7 days after labelling onwards in F+ and 30 days after labelling in F-. The x(15N) values of Eucalyptus fine roots were higher than background values in both treatments, from 30 days after labelling onwards. Mean %NDFT values were 18.0% in F+ and 33.9% in F- over the first 60 days after labelling, and 22.8% in F+ and 67.7% in F- from 30 to 60 days after labelling. Fertilization decreased short-term transfer belowground of N from Acacia trees to Eucalyptus trees. Our study suggests that belowground facilitation processes providing N from NFTs to Eucalyptus trees in mixed-species plantations are more pronounced in low-fertility soils than in nutrient-supplied stands. USP ESALQ Forest Science Department Eco&Sols INRA CIRAD IRD Montpellier SupAgro University of Montpellier CIRAD UMR Eco&Sols UNESP School of Agriculture São Paulo State University ‘Julio de Mesquita Filho,’ Department of Forest Science and Wood UFES IPEF Instituto de Pesquisas e Estudos Florestais UNESP School of Agriculture São Paulo State University ‘Julio de Mesquita Filho,’

Alley cropping systems are composed of tree rows alternating with crop alleys. Their interest in providing ecosystem services is increasingly acknowledged. In particular, they could have a positive impact on nutrient accessibility, soil carbon content and could increase the biodiversity of soil invertebrates associated with the provision of ecosystem services (carbon and nutrient cycling, pest regulation, etc). However, few studies have taken into account the spatial heterogeneity of soil fertility and soil organisms within these systems. A key question, however, is whether soil functioning is impacted only below the tree row, or whether crop alleys benefit from the presence of the tree row. Moreover, the positive effects of alley cropping systems are often attributed to the tree. However, the tree row is not cultivated and not tilled, resulting in the development of predominantly herbaceous vegetation, either natural or seeded, forming an understory vegetation strip (UVS). This UVS could play a particularly important role in providing organic matter in the first few centimeters of the soil, and provide an interesting habitat for soil organisms. The objective of my PhD thesis is to determine the impact of the UVS on the spatial variation of soil fertility and some associated organisms (microorganisms and macrofauna), through various observations and an experimentation in situ.I studied in a first chapter the variations of soil fertility and soil organisms within the UVS (with the distance to the tree) and between UVS and crop alleys, in two young plots in South-West France. This study has shown on the one hand that the distance to the tree does not modify the properties of the UVS with sown UVS. On the other hand, it showed that young UVS can induce an increase in the C and available P contents in the first centimeters of soil under the UVS compared to the crop alley, but that their effect on the variation of soil microbial biomass and respiration and on the abundance of macrofauna is less clear. Soil organisms may even be negatively impacted by the proximity to the UVS. Secondly, I studied the variation of soil fertility and soil organisms with the distance from the UVS at different seasons within three shade treatments in a 22 year old market gardening plot in the South of France. This plot was sampled using a design that took into account the distance to the tree, but also the impact of herbaceous strips without trees. This study showed that the UVS has a strong impact on the abundance of soil macrofauna and the efficiency of microorganisms in the UVS independently of the presence and proximity to the tree, but that it induces little heterogeneity within the crop alley in its immediate vicinity. Moreover, the presence of trees has a greater impact on soil fertility than the UVS. Finally, there is a great variability in the response of soil organisms depending on the season, and the UVS can be a refuge for macrofauna in some seasons, while the distribution of macrofauna in the plot is more homogeneous in other seasons. In a final chapter, I studied the movement of earthworms near the UVS in a 23 year old plot near Montpellier. This study suggests that in spring, endogeic earthworms move more towards the UVS than towards the crop alley.; Les systèmes agroforestiers en allées cultivées sont composés d'une alternance de lignes d'arbres et d'allées cultivées. Leur intérêt dans la fourniture de services écosystémiques commence à être bien démontré. En particulier, ils auraient un impact positif sur l'accessibilité des nutriments, la teneur en carbone des sols et l'augmentation de la biodiversité des invertébrés du sol associés à la fourniture de services écosystémiques (cycle du carbone et des nutriments, régulation des ravageurs, etc). Cependant, peu d'études ont pris en compte l'hétérogénéité spatiale de la fertilité et des organismes du sol au sein de ces systèmes. Une question essentielle est pourtant de déterminer si le fonctionnement du sol est impacté seulement sous la ligne d'arbres, ou si les allées cultivées bénéficient de la présence de cette ligne d'arbres. De plus, les effets positifs des systèmes en allées cultivées sont souvent attribués à l'arbre. Cependant, la ligne d'arbres n'est pas cultivée et le sol n'y est pas travaillé, entraînant le développement d'une végétation majoritairement herbacée, naturelle ou semée, formant un linéaire sous arboré (LSA). Ce LSA pourrait jouer un rôle particulièrement important dans l'apport de matière organique dans les premiers centimètres du sol, et fournir un habitat intéressant pour les organismes du sol. L'objectif de mon projet de doctorat est de déterminer l'impact du LSA sur la variation spatiale de la fertilité du sol et de certains organismes associés (microorganismes et macrofaune), au travers de différentes observations et d'une expérimentation in situ.Pour cela, j'ai étudié dans un premier chapitre les variations de la fertilité et des organismes du sol au sein du LSA (avec la distance à l'arbre) et entre LSA et allée cultivée, dans deux jeunes parcelles en grandes cultures dans le Gers. Cette étude a montré d'une part que la distance à l'arbre ne modifie pas les propriétés de LSA semés. D'autre part, elle a montré que de jeunes LSA peuvent induire une augmentation de la teneur en C et en P disponible dans les premiers centimètres du sol sous le LSA en comparaison avec l'allée cultivée, mais que leur effet sur la variation de la biomasse et respiration des microorganismes du sol et sur l'abondance de la macrofaune est moins clair. Les organismes du sol peuvent même être négativement impactés par la proximité au LSA. Deuxièmement, j'ai étudié la variation de la fertilité et des organismes du sol en fonction de la distance au LSA à différentes saisons au sein de trois modalités d'ombrage, dans une parcelle de 22 ans cultivée en maraîchage dans le Gard. Cette parcelle a été échantillonnée selon un design permettant de prendre en compte la distance à l'arbre, mais également l'impact de bandes enherbées sans arbres. Cette étude a montré que le LSA impacte fortement l'abondance de la macrofaune du sol et l'efficience des microorganismes dans le LSA indépendamment de la présence et proximité à l'arbre, mais qu'il induit peu d'hétérogénéité au sein de l'allée cultivée dans sa proximité immédiate. De plus, la présence des arbres impacte davantage la fertilité du sol que le LSA. Enfin, il existe une grande variabilité de la réponse des organismes du sol en fonction de la saison, le LSA pouvant être un refuge pour la macrofaune a certaines saisons, alors que la distribution de la macrofaune dans la parcelle est plus homogène a d'autres saisons. J'ai étudié dans un dernier chapitre les mouvements de vers de terre à proximité du LSA dans une parcelle de 23 ans en grandes cultures près de Montpellier. Cette étude suggère qu'au printemps, les vers de terre endogés se déplacent davantage vers le LSA que vers l'allée cultivée.

International audience; Soil acidification and declining fertility are widespread in sub‐Saharan Africa. Nutrient depletion is mainly related to nutrient mining driven by biomass removal without replenishment of nutrients through use of fertilisers. Concomitant acidification is due to the high ash alkalinity of harvested biomass. We determined the nutrient content and ash alkalinity of biomass of the main crops produced in smallholder mixed crop–livestock farming systems in the Malagasy Highlands of Madagascar and calculated the soil acidification/alkalinisation occurring through biomass transfer. Samples of rice and forage were collected from 70 rice plots and 91 cultivated forage plots, and 70 manure samples were collected from farms. Nutrient exports induced by crop harvesting resulted in annual losses of 57 kg nitrogen (N), 6 kg (phosphorus) P and 33 kg potassium (K) ha–1 for rice (grain + straw), and 31–51 kg N, 8–9 kg P and 29–57 kg K ha–1 for each forage cut (with three cuts per year on average). The ash alkalinity of samples, calculated as the difference between cation and anion contents, was 49–100 cmolc kg–1 for forage crops, 31 cmolc kg–1 for rice straw, and only 4 cmolc kg–1 for rice grains. Biomass removal caused a loss of nutrients and an increase in soil acidity. Owing to low nutrient retention efficiency during the handling and storage of manure, the traditional input of manure at 5 t fresh matter ha–1 is insufficient to balance nutrient and alkalinity losses in Malagasy mixed crop–livestock farming systems. Maintaining productive and sustainable mixed crop–livestock farming systems requires greater attention to ensuring a nutrient balance at both plot and farm levels.

International audience; Tropical forests are generally considered to stand upon nutrient-poor soils, but soil nutrient concentrations and availabilities can vary greatly at local scale due to topographic effects on erosion and water drainage. In this study we physically and chemically characterised the soils of 12 study plots situated along a catena with a shallow slope in a tropical rainforest in French Guiana both during the wet and the dry season to evaluate seasonal differences. Soils along the catena were all Acrisols, but differed strongly in their water drainage flux. Over time, this differential drainage has led to differences in soil texture and mineral composition, affecting the adsorption of various nutrients, most importantly phosphorus. The more clayey soils situated on the slope of the catena had higher total concentrations of carbon, nitrogen, phosphorus and several micronutrients, while extractable nutrient concentrations were highest in the sandiest soils situated at the bottom of the catena. We found that carbon, nitrogen and extractable nutrients all varied seasonally, especially in the surface soil layer. These results are interesting because they show that, even at the local scale, small differences in topography can lead to large heterogeneity in nutrient concentrations, which can have large impacts on plant and microbial community organisation at the landscape level.

Forest-wood sector is a strategic sector for the mitigation of climate change, in particular through the production of fuelwood. However, the intensive harvesting of biomass can lead to a loss of forest soil fertility in the long term. The thesis work focuses on the sustainability of energy wood harvesting with (1) an environmental component, which concerns the assessment of nutrient returns by leaching during the pre-drying period, the characterization of exported biomass as well as the evaluation of dead wood on the ground (2) an economic component with an assessment of the economic impacts of a potential drop in productivity and their highlighting with the possible choices of cutting and silvicultural treatments.The Pre-drying operation of the trees proved to be unsatisfactory for an optimal return of nutrients contained in leaves and twigs. More than half of the nutrients remain exported from the forest after three months of pre-drying. The volumes of dead wood left on forests to maintain soil fertility and biodiversity were low (, La filière forêt-bois est un secteur stratégique pour l’atténuation des changements climatiques, notamment grâce à la production du bois-énergie. Toutefois, les récoltes intensives de biomasse peuvent induire à une perte de fertilité des sols forestiers sur le long terme. Le travail de thèse s’articule autour de la durabilité de la récolte de bois-énergie avec (1) un volet environnemental, qui concerne la quantification des retours d’éléments minéraux via la lixiviation pendant la phase de réessuyage, la caractérisation de la biomasse exportée ainsi que l’évaluation des bois morts au sol (2) un volet économique avec une évaluation des impacts économiques d’une potentielle baisse de productivité et leur mise en relief avec les choix possibles de coupe et de traitement sylvicoles.Le réessuyage des arbres s'est avéré insatisfaisant pour un retour optimal de nutriments contenus dans les feuilles et brindilles. Plus de la moitié de nutriments reste exportée de la forêt après trois mois de réessuyage. Les volumes de bois morts permettant de maintenir la fertilité des forêts et leur biodiversité étaient faibles (

International audience; A growing concern on the deleterious effects of chemical inputs to the environment has been on the rise from the excessive use of chemical inputs leading to soil and water pollution, destruction to fauna and microbial communities, reduced soil fertility and increased crop disease susceptibility. In the Great Mekong Region (GMR), a large majority of the population relies on agriculture and faces severe challenges including decline in soil fertility, increased pests and diseases, leading to lower ecosystem productivity. In this region, over-dependence on chemical fertilizers also continues to impact negatively on soil health and the wider ecosystem. Agroecological practices, and beneficial microorganisms in particular, offer an affordable and sustainable alternative to mineral inputs for improved plant nutrition and soil health for optimal crop performance and sustainable production. Biofertilizers are a key component in integrated nutrient management as well as for increased economic benefits from reduced expenditure on chemical fertilizers, holistically leading to sustainable agriculture. To cope with the need for biofertilizer adoption for sustainable agricultural production, the countries in the GMR are putting efforts in promoting development and use of biofertilizers and making them available to farmers at affordable costs. Despite these efforts, farmers continue to use chemical fertilizers at high rates with the hope of increased yields instead of taking advantage of microbial products capable of providing plant nutrients while restoring or improving soil health. This study explored the current agricultural practices in the six countries in the GMR (China, Vietnam, Myanmar, Thailand, Cambodia and Lao PDR), the critical need for sustainable agroecological practices with a special emphasis on biofertilizers. We highlighted the current status, distribution, adoption and gaps of biofertilizer production in the GMR, in order to obtain an insight on the nature of biofertilizers, efficacy and production standards, adoption or lack of biofertilizers in the GMR.

International audience; In European temperate forests, whole-tree harvesting increases nutrient exports and could compromise soil fertility in long term, especially when leaves, nutrient-rich compartments (leaves, fine and small wood) are exported. Pre-drying felled trees may allow leaves, twigs and branches to fall down or break during skidding, thereby remaining in the stand. However, the recommended pre-drying time is often based on expert estimates, and currently ranges from two to three months.In this study, we developed an experimental device to quantify nutrient leaching via rainfall (pH: 6.8 +/- 0.4) from fully developed leaves (collected in summer period) of four broadleaf species. We first set up an outdoor experiment under natural rainfall conditions to monitor the kinetics of nutrient leaching over around two and a half months. Second, we set up two controlled experiments under simulated rainfall conditions to investigate the effect of rainfall intensity and frequency on nutrient leaching.Foliar K was highly leached 60-79%, followed by Mg: 19-50%, P: 22-30% and only small proportions for Ca and N, < 16%. Nutrient leaching was positively correlated with rainfall amounts of < 30 mm but small rainfall amounts < 4 mm were more effective in leaching per unit (mm) than heavier rainfalls. More nutrients were leached out when the same rainfall amount was fractioned into small rainy events over several days.However, leaf leaching remains unsatisfactory because a large part of nutrients is still exported by foliage. Total nutrient exports by whole-tree harvest including foliage increased nutrient exports by 1.2-1.6 times compared to conventional harvesting. The exports by foliage are of equal importance as fine and small wood exports and thus leaving the foliage on the forest would increase significantly nutrient saving. We therefore recommend harvesting during the leafless period when possible and otherwise, letting all the leaves fall to the ground before skidding not only for nutrient returns but also because easily degradable organic matter is very important for soil biological activity.

Many forest ecosystems are developed on acidic and nutrient-poor soils and it is not yet clearly understood how forests sustain their growth with low nutrient resources. In forestry, the soil chemical fertility is commonly defined, following concepts inherited from agronomy, as the pool of plant-available nutrients in the soil at a given time compared to the nutritional requirement of the tree species. In this two-part study, Part 1 (Hansson et al., 2020) showed, through the compiled dataset of 49 forest ecosystems in France, Brazil and Republic of Congo, the limits of this definition of soil chemical fertility in forest ecosystem contexts. In this study (Part 2), we investigated the nutrient pools and fluxes between the different ecosystem compartments at 11 of the 49 sites in order to better characterize the role of the biogeochemical cycling of nutrients in the chemical fertility of forest ecosystems, and in particular the roles of the biological and geochemical components of biogeochemical cycling.\ud \ud The analysis of our dataset shows different types of biogeochemical functioning. When the geochemical component (inputs through mineral weathering and/or atmospheric inputs, capillary rise) is predominant, sufficient nutrients are provided to the plant-soil system to ensure tree nutrition and growth. Conversely, when the geochemical component of the cycle brings too few nutrients to the plant-soil system, the biological component (litterfall, plant internal cycling) becomes predominant in tree nutrition and growth. In the latter case, forest production may be high even when pools of nutrients in the soil reservoir are low because small but active nutrient fluxes may continuously replenish the soil reservoir or may directly ensure tree nutrition by bypassing the soil reservoir.\ud \ud This study highlights the necessity to include biogeochemical cycling and recycling fluxes in the definition and diagnosis methods of soil chemical fertility in forest ecosystems. We show that the chemical fertility is not only supported by the soil in forest ecosystem but by the sum of all the ecosystem’s compartments and fluxes between these pools.

With the development of agroecology, soil plays an important role in the design of sustainable agricultural practices. The soils are the place of many processes operated by living organisms interacting with one another. They also provide much needed services provided by agrosystems and enable their sustainability. In the context of the agroecological transition, it becomes urgent to promote these ecological processes, to intensify them by appropriate practices considering the socio-economic constraints, and finally, to be able to measure them. First, we recall the ecological theories of the terrestrial ecosystem functioning to improve our consideration of the soil in the agroecological transition. Then, we describe the need to improve our knowledge of the relationships between biodiversity, processes, aggregated functions and agrosystem services in a global context where biodiversity, including the soil one, is highly threatened. This theoretical approach is illustrated by four studies conducted in the tropics demonstrating the possibility to intensify the soil processes and to solve an agronomic dysfunction. Finally, we highlight the need to define soil indicators based on ecological processes for an appropriate measurement of this intensification. In conclusion, we propose a methodological framework to optimize the ecological functions of the soil for a sustainable supply of services provided by agrosystems., Avec le développement de l'agroécologie, le sol prend une place importante dans la réflexion sur la mise en place de pratiques agricoles durables. Le sol est le siège de nombreux pro-cessus opérés par des organismes vivants agissant de façon interactive. Ces processus sont indispensables pour la durabilité des services rendus par les agrosystèmes. Dans le cadre de la transition agroécologique, il devient alors nécessaire et urgent de promouvoir ces processus écologiques, de les intensifier par des pratiques adaptées et partagées avec d'autres contraintes socio-économiques, et enfin, de pouvoir les évaluer. Dans un premier temps, nous rappelons les théories écologiques du fonctionnement des écosystèmes pour améliorer notre prise en compte du sol dans la transition agroécologique. Puis, nous décrivons le besoin d'améliorer notre connaissance de la relation entre biodiversité, processus, fonctions agrégées et services rendus par les agrosystèmes dans un contexte mondial où la biodiversité, y compris celle du sol, est menacée. Cette approche théorique est illustrée par quatre études menées en zone tropicale démontrant la possibilité d'intensifier les processus du sol pour résoudre un dysfonctionnement agronomique, suite à un examen scientifique rigoureux du fonctionnement de l'agrosystème. Enfin, nous rappelons le besoin de définir des indicateurs fonctionnels des sols basés sur les processus écologiques pour une évaluation appropriée de cette intensification. En conclusion, nous proposons un cadre méthodologique permettant d'optimiser les fonctions écologiques du sol pour une fourniture durable des services rendus par les agrosystèmes.

International audience; Manipulating plant functional diversity to improve agroecosystem multifunctionality is a central challenge of agricultural systems world-wide. In cocoa agroforestry systems (cAFS), shade trees are used to supply many services to farmers, yet their impact on soil functioning and cocoa yields is likely to vary substantially among tree species. Here we compared the impact of five shade tree species (Canarium schweinfurthii (Canarium), Dacryodes edulis (Safou), Milicia excelsa (Iroko), Ceiba pentandra (Kapok tree), Albizia adianthifolia (Albizia)) and unshaded conditions on the functioning of poor sandy savanna soils within eight cocoa farms in Central Cameroon. We assessed the effects of plant functional traits, leaf litterfall and fine root biomass on a range of soil functions and on cocoa yield. Shade trees generally improved soil pH, NH4+, NO3- and Olsen P content, biomass production of bioassays and soil total C and N content, while leaving cocoa yields unchanged. However, these effects varied largely among species. Improvements of soil functions were low under the two fruit trees (Canarium and Dacryodes), medium under the legume tree Albizia and high under the two timber trees (Milicia and Ceiba). Low litter recalcitrance was most strongly associated with increases in soil fertility indicators such as N and P availability, whereas soil C and N content increased with litter Ca restitution. Synthesis and applications. We demonstrate that cocoa agroforest multifunctionality is substantially influenced by the functional traits of shade tree species. Shade tree species with the most dissimilar traits to cocoa (cocoa showing the lowest leaf litter quality) showed the largest improvement of soil functions. Therefore, selection of shade trees based on their functional traits appears as a promising practice to adequately manage soil functioning. In order to fully assess the beneficial role of shade trees in these agroecosystems. Future research will need to extend this approach to other below-ground traits and other aspects of multifunctionality such as long-term cocoa health and yield.

In Africa, cocoa yields are low, partly due to soil fertility constraints and poor management. While peoples’ knowledge, aspirations, and abilities are key factors explaining their behaviour, little is known about the rationales that underpin soil fertility management practices (SFMPs) of cocoa farmers. To address this gap, we conducted an exploratory survey in two contrasting regions in Cameroon where cocoa is an important crop: the humid forest and the forest-savannah transition zone. Some 30% of farmers in the transition zone as opposed to 13% in the humid forest expressed concerns about soil fertility. The most relevant soil fertility indicators for farmers were high cocoa yield, dark soil colour, ease of tillage, and floral composition. To enhance and maintain soil fertility, farmers used residues from weeding (100%), planting of trees (42%), mineral fertilisers (33%), compost (16%), and manure (13%). More farmers in the transition zone than the humid forest implemented SFMPs. Our findings suggest that soil fertility perceptions, access to inputs, local practices, and experience influence farmers’ use of SFMPs. The limited use of mineral fertilisers was explained by poor access whereas the use of organic fertilisers and tree planting were mostly constrained by lack of labour and knowledge. Farmers prioritised practices to increase yield and viewed SFMPs to be the least important management practices, although they believe high cocoa yield is an important indicator of soil fertility. To foster sustainable cocoa intensification, it is necessary to enhance farmers’ knowledge on SFMPs, increase access to inputs, and ensure returns on investment while considering farmers’ priorities and practices.

The multifunctional classification of grasslands in the Massif Central aims to characterise the diversity of grasslands and structure our knowledge about their processes and potential. The tool described here provides information to help livestock farmers transition towards more sustainable, grass-based production. The classification system currently covers 60 different grassland types, and the classification key is based on simple criteria such as field characteristics and farming practices. Here, we discuss 6 common and representative grassland types utilised in PDO cheese production in the Massif Central: we compared agronomic productivity (forage quantity and quality), environmental properties (species richness and the occurrence of rare species), and ecosystem services (carbon storage levels and cheese quality). The impact of farming practices was also analysed; the results can help inform discussions with farmers, to help them better match their practices with the production potential of their grasslands.; La richesse et la diversité des prairies du Massif central sont le résultat d’une longue histoire entre facteurs du milieu et pratiques des agriculteurs. La typologie multifonctionnelle des prairies du Massif central permet de caractériser la diversité des prairies et d’organiser les connaissances sur le fonctionnement et les potentiels agro-écologiques de ces surfaces. Cet outil contribue ainsi à accompagner la transition des systèmes d’élevage vers des modes de production plus durables et basés sur la ressource herbe. Les 60 types recensés actuellement sont organisés dans une clé basée sur des critères simples de milieux et de pratiques. Sur la base de 6 types emblématiques des zones AOP du Massif central, nous comparons les performances agronomiques (quantité et qualité de la production) et environnementales (richesse et rareté de la flore) de chacun, ainsi que les services rendus (stockage de carbone et qualité des fromages). L’analyse de l’impact des pratiques au regard des performances et services de chaque type constitue un support de discussion avec les éleveurs pour envisager les adaptations de leurs pratiques aux potentiels de production de leurs prairies.

Au coeur de l'Amazonie, des travaux archéologiques ont fait émerger les vestiges de cultures intensives et de sociétés structurées datant de l'époque précolombienne, faisant voler en éclats le mythe de la forêt vierge.

International audience; Cocoa agroforestry systems (cAFS) in Central Cameroon are established on lands which were either forest or savannah. The functioning and ecosystem services (ES) delivery of an agroecosystem can be influenced by past land-use. We hypothesised that savannah-derived cocoa agroforestry systems (S-cAFS) and forest-derived cocoa agroforestry systems (F-cAFS) would (i) progressively drift away from past land-use, and (ii) eventually converge and support comparable levels of ecosystem services. We selected 25 ecosystem attributes directly related to at least one of the following six ecosystem (dis)services (ES): species conservation, carbon storage, crop production, nutrient cycling, soil quality and soil pollution. We followed their temporal evolution in S- and F-cAFS along >70-year chronosequences. Our results showed that the attributes and services studied followed typical temporal trajectories in S- and F-cAFS while generally tending to reach comparable levels on the long run. However, the time needed to do so varied strongly and ranged from 20 to 30 years for perennial species diversity to more than 70 years for C storage or some components of soil quality. The results also demonstrated that S-cAFS could sustainably improve many of the studied attributes and ES. Regarding the attributes related to the cocoa stand, both S- and F-cAFS seemed influenced by their previous land-use up until 15 and 30 years, respectively, after their establishment. With respect to soil quality, nutrient cycling and carbon storage, only S-cAFS could be significantly distinguished from their past land-use, after 15 to 30 years.

Dans un hectare de sol cultivé, un entrelacs de racines abrite 1,5 tonnes de bactéries et 3,5 tonnes de champignons microscopiques. Sans compter les vers de terre, insectes, acariens… et toute une faune qui peut peser de 1 à 5 tonnes ! Cette biodiversité très riche fait la valeur de nos sols, participe à leur fertilité et contribue donc à la qualité de notre alimentation. Élément clé du bon fonctionnement de notre environnement, elle favorise la régulation du climat, le stockage du carbone, la qualité de l’eau… Interviews vidéos. Le sol est au carrefour du bon fonctionnement de notre agriculture, de notre alimentation et de notre environnement… S’il a longtemps été vu comme un support inerte, son patrimoine biologique est aujourd’hui apprécié pour tous les services qu’il rend aux communautés humaines. À l’Inra, il mobilise de nombreux chercheurs. Dans cette interview vidéo Pierre-Alain Maron, Inra Bourgogne Franche-Comté, Mickaël Hedde, Inra Occitanie-Montpellier et Antonio Bispo, Inra Val de Loire en livrent quelques enjeux qu’ils partageaient lors du Carrefour de l’Innovation agronomique sur la fertilité biologique des sols, le 18 octobre dernier.

(IF 3.95; Q1); International audience; The rapid expansion of perennial crops is a major threat to biodiversity in Southeast Asia. The biodiversity losses related to the conversion of forest lands to oil palm or rubber plantations (RP) are well documented by recent studies. However, the impact of the conversion from intensively managed annual crops to perennial crops on soil biodiversity has not yet been addressed. This study aims at assessing the impact on soil biodiversity of a) the short-term effect of land use conversion from cassava crop to RP, and b) the long-term effect of RP ageing. Soil biodiversity (bacterial, fungal and macrofaunal), microbial activities and pedoclimatic characteristics were measured over a chronosequence of 1–25 years old of RP compared to cassava fields, the former crop, in Thailand. The conversion from cassava to young RP (1–3 yr) had a significant effect on microbial biomass and activities and fungal composition, but did not impact the bacterial and macrofaunal diversity. This effect of land use conversion could be explained by the change in land management due to the cultivation of pineapple in the inter-row of the young RP. Canopy closure appeared to be the main driver of soil biota shifts, as most of the biotic parameters, composition, abundance and activities were significantly modified after 7 years of RP. The changes of composition in older rubber plantations originated from the dominance of Trichoderma (fungi), Firmicutes (bacteria), and earthworms. Old rubber plantations (23–25 yr) harboured the highest microbial and macrofaunal biomass; however, they were also characterised by a significant decrease in bacterial richness. The change in pedoclimatic conditions across the rubber chronosequence, i.e. increase in soil moisture, litter and organic carbon content, was a stronger driver of soil biota evolution than land use conversion. The macrofaunal composition was more resistant to land use conversion than the bacterial composition, whereas the microbial biomass was sensitive to land use conversion, but showed resilience after 20 years. However, bacterial, fungal and macrofaunal diversity, macrofaunal and microbial biomass and microbial activities were all sensitive to RP ageing.

International audience; Service crops are crops grown with the aim of providing non-marketed ecosystem services, i.e. differing from food, fiber and fuel production. Vineyard soils face various agronomic issues such as poor organic carbon levels, erosion, fertility losses, and numerous studies have highlighted the ability of service crops to address these issues. In addition to their ability to increase soil organic matter and fertility, and reduce runoff and erosion processes, service crops provide a large variety of ecosystem services in vineyards such as weed control, pest and disease regulation, water supply, water purification, improvement of field trafficability and maintenance of soil biodiversity. However, associating service crops with grapevines may also generate disservices and impair grape production: competition for soil resources with the grapevine is often highlighted to reject such association. Consequently, vinegrowers have to find a balance between services and disservices, depending on local soil and climate conditions, on their objectives of grape production and on the nature and temporality of the ecosystem services they expect during the grapevine cycle. This study proposes a review of the services and disservices provided by service crops in vineyards, and a framework for their management. Vinegrowers' production objectives and pedoclimatic constraints form the preliminary stage to consider before defining a strategy of service crop management. This strategy assembles management options such as the choice of species, its spatial distribution within the vineyard, the timing of its installation, maintenance and destruction. These management options, defined for both annual and long-term time scales, form action levers which may impact cropping system functioning. Finally, we underline the importance of implementing an adaptive strategy at the seasonal time scale. Such tactical management allows adapting the cropping system to observed climate and state of the biophysical system during the grapevine cycle, in order to provide targeted services and achieve satisfactory production objectives.

National audience; Plusieurs éléments généraux ressortent des observations. Tout d'abord, la structure du sol sous le cavaillon reste préservée des fortes dégradations et est favorable à l'enracinement de la vigne. Un second résultat générique est que la mécanisation des pratiques d'entretien des interrangs peut causer des changements de structure des sols irréversibles. Un troisième résultat est que des dégradations structurales des sols viticoles peuvent persister longtemps sous le cavaillon et au milieu des interrangs.

International audience; Soil bacterivorous nematodes are key plant mutualists that increase nutrient availability for plants either by enhancing the mineralization of organic compounds (the “mineralization pathway”) or by increasing plant lateral root branching following shifts in internal plant metabolism, and subsequently leading to a higher volume of soil prospected by the roots (the “hormonal pathway”). The effects of these organisms on the nutrition of plants growing in strongly nutrient-deficient ferrallitic soils, especially in soils with limited available inorganic phosphorus (P), are poorly known, as are the pathways involved. In our study, using Oryza sativa (Poaceae) and Acrobeloides sp. (Cephalobidae), we tested the “mineralization” and “hormonal” hypotheses in an acidic P-depleted Ferralsol from the Madagascar highlands. We assessed the effect of nematode inoculation on (i) inorganic P flow from soil to plant using the 32P labelling technique and (ii) plant root architecture using a rhizobox device. We showed that the ability of Acrobeloides sp. to enhance P uptake in plants is strongly limited in Ferralsols. However, when the soil pH was corrected with dolomite, Acrobeloides sp. increased plant P uptake probably through the “mineralization” pathway (higher microbial turnover). Indeed, the L-value increased by 49% in the presence of nematodes and dolomite, suggesting the production of unlabelled plant-available P, probably through a higher net P mineralization when the nematodes were inoculated. Using the rhizobox technique, we also observed increased root length in the presence of nematodes but the specific root length, the tip number and the root branching density did not increase in the presence of nematodes, suggesting that nematodes did not increase plant P uptake and growth in this soil as proposed by the “hormonal” hypothesis. From an ecological intensification perspective, to promote agro-ecological development in tropical regions, our results suggest that amending ferrallitic soils with P-rich organic matter and correcting soil pH with an appropriate amount of dolomite may constitute suitable agronomic actionable triggers to drive the mutualistic activity of bacterivorous nematodes.

Plant species may exert a strong influence on soil biological properties, but the linkages between plant and soil responses to severe drought remain unclear. We conducted an outdoor mesocosm experiment with five upland grass species and one Mediterranean drought-resistant grass cultivar to investigate the effects of root biomass and rhizosphere conditions on the drought responses of soil microbial biomass in the topsoil. In particular, we assessed whether variation in the drought resistance of microbial biomass could be linked to root biomass, soil inorganic nitrogen (N) or dissolved organic carbon (DOC). Experimental drought decreased microbial biomass but increased soil inorganic N and DOC across plant species. Root biomass responses to drought were less predictable, and varied depending on species. Microbial biomass resistance to drought showed a negative relationship with the drought resistance of root biomass across species, possibly via changes in rhizodeposition. Moreover, the drought resistance of microbial biomass showed a negative relationship with soil nutrient availability under droughted conditions. Our findings highlight the importance of root biomass as a predictor of soil microbial resistance to drought in grass-dominated systems, and suggest that trade-offs between plant and microbial processes could have significant implications for ecosystem function in a changing environment.

DOSSIER Sols forestiers, intégrer les dynamiques; En forêt, érosion rime avec prévention

Agromining aims to rehabilitate contaminated or natural metal-rich soils (ultramafic soils) by extracting metals of high economic importance, such as nickel (Ni), using hyperaccumulator plants and then to recover these metals for industrial purposes. Ultramafic soils are characterized by low fertility levels and this can limit yields of hyperaccumulators and metal phytoextraction. Here, we characterized the potential benefits for phytoextraction efficiency of co-cropping two plants: a Ni-hyperaccumulator (Alyssum murale; Brassicaceae) and a legume (Vicia sativa; Fabaceae). A field experiment with 3 replicates was set up in an ultramafic zone in North West Spain. Four treatments were tested: co-cropping (“Co”), fertilized mono-culture (“FMo”), non-fertilized mono-culture (“NFMo”) and bulk soil (“BS”). “FMo” and “Co” treatments increased the biomass yields of A. murale by 453% and 417% respectively, compared to “NFMo”. “Co” treatment generated 35% and 493% higher Ni-yields than “FMo” and “NFMo”, respectively. Most of the microbial analyses showed that introducing V. sativa (“Co” treatment) into the cropping system had beneficial effects. “Co” treatment significantly modified the phenotypical structure of bacterial communities and raise the relative abundance of the phylum Bacteroidetes and reduced that of Actinobacteria. In addition, non-metric multidimensional scaling analysis of the operational taxonomic units (OTUs) showed that “Co” was clearly separate from all other treatments. Thus, this study showed that co-cropping a hyperaccumulator with a legume in Ni-agromining systems not only improves plant biomass and Ni-yields, but also enhanced some soil microbial enzymatic activities. Ameliorating agromining by replacing fertilizers would combine eco-efficient or sustainable metal recovery with soil fertility/quality improvement.

International audience; The intensification and subsequent closing down of industrial activities during the last century has left behind large surfaces of derelict lands. Derelict soils have low fertility, can be contaminated, and many of them remain unused. However, with the increasing demand of soil surfaces, they might be considered as a resource, for example for non-food biomass production. The study of their physico-chemical properties and of their biodiversity and biological activity may provide indications for their potential re-use. The objective of our study was to investigate the quality of six derelict soils, considering abiotic, biotic, and functional parameters. We studied (i) the soil bacteria, fungi, meso- and macro-fauna and plant communities of six different derelict soils (two from coking plants, one from a settling pond, two constructed ones made from different substrates and remediated soil, and an inert waste storage one), and (ii) their decomposition function based on the decomposer trophic network, enzyme activities, mineralization activity, and organic pollutant degradation. Biodiversity levels in these soils were high, but all biotic parameters, except the mycorrhizal colonization level, discriminated them. Multivariate analysis showed that biotic parameters co-varied more with fertility proxies than with soil contamination parameters. Similarly, functional parameters significantly co-varied with abiotic parameters. Among functional parameters, macro-decomposer proportion, enzyme activity, average mineralization capacity, and microbial polycyclic aromatic hydrocarbon degraders were useful to discriminate the soils. We assessed their quality by combining abiotic, biotic, and functional parameters: the compost-amended constructed soil displayed the highest quality, while the settling pond soil and the contaminated constructed soil displayed the lowest. Although differences among the soils were highlighted, this study shows that derelict soils may provide a biodiversity ecosystem service and are functional for decomposition.

The application of agromining to abandoned ultramafic areas is a major challenge in the presence of potentially recoverable areas. Howerver, ultramafic soils are particular in terms of their fertility with high concentrations of metals and a near absence of organic matter. Nevertheless, this challenge was partly met by the application of chemical fertilizers and herbicides. Our challenge, through this PhD, was to develop a sustainable agro-ecosystem based on the introduction of a legume in association with the hyperaccumulating plant and then the reduction of any chemical input. Our results clearly confirmed that the introduction of a legume into these new cropping systems improved both the biomass production of Alyssum murale and the Ni yields in comparison to the fertilized and non-fertilized monoculture. Our work has also shown that the insertion of a legume into agromining cropping systems improves the structure of the soil due to stable and larger aggregates. In addition, higher levels of carbon and nitrogen and higher concentrations of organic matter were detected. These results led to an overall improvement of the soil structure, its fertility and its biofunctioning. Our results showed positive effects of these new cropping systems, both on the size of the bacterial communities and on the microbial enzymes involved in the soil biogeochemical cycles. In addition, the structure and diversity of bacterial communities were modified with the insertion of the legume, compared to the monoculture. Economically, the introduction of legume into cropping systems dedicated to Ni agromining involves a gain of money and time due to reduced application of mineral fertilizers as well as products of phytosanitary. Finally, all these benefits lead to the rehabilitation of ultramafic soils with the restoration of their physical, chemical and biological qualities while allowing these particular soils to offer many ecosystem services, L’application de l’agromine à des zones ultramafiques délaissées constitue un enjeu majeur à la vue des surfaces potentiellement valorisables. Par contre, les sols ultramafiques sont particuliers avec de fortes concentrations en métaux et une quasi absence de matière organique. Malgré tout, la mise en place de l’agromine a déjà donné de bons résultats, couplée avec l’application d’herbicides et une fertilisation minérale. Notre défi a été de développer une agromine durable par la mise en place d’agro-écosystèmes basés sur l’introduction d’une légumineuse en association avec une plante hyperaccumulatrice et la suppression de tout intrant chimique. Nos résultats ont confirmé clairement que l'introduction d'une légumineuse dans l’agromine a amélioré la production de biomasse de Alyssum murale et les rendements de nickel par rapport à sa monoculture fertilisée et non fertilisée. Nos travaux ont également montré que l'insertion d'une légumineuse dans l’agromine permet d’améliorer la structure du sol avec des agrégats plus stables. De plus, de meilleures teneurs en carbone, azote et en matière organique ont été détectées. L’ensemble de ces éléments conduit ainsi à une amélioration globale de la structure du sol, de sa fertilité et de son biofonctionnement. Corrélativement, nos résultats ont mis en évidence les effets positifs de ces nouvelles pratiques, à la fois sur la taille, la diversité et les acitivités liées aux cycles biogéochimiques des communautés bactériennes. D’un point de vue écononique, l’introduction de la légumineuse dans l’agromine implique un gain financier et de temps du fait de la réduction de l'application d’engrais et de produits phytosanitaires. Enfin, tous ces avantages conduisent à une réhabilitation des sols ultramafiques avec une restauration de leurs qualités physique, chimique et biologique, tout en permettant à ces sols particuliers d’offrir plusieurs services écosystémiques

The SEFerSol project aims at testing and assessing innovative cropping systems that enhance soil fertility of organic vegetable crops. Two cropping systems are tested compared to a system that is used as a reference regarding farmer’s practices. The innovative system “Max Green Manure” includes green manure as much as possible into the crop succession. This system is only fertilized with compost and soil tillage is superficial, permanent beds method is used. The innovative system “Soil conservation”, is fertilized according to a nitrogen balance, soil tillage is highly reduced or suppressed and soil is covered as frequently as possible. After two years of experimentation, the construction of a method to assess the results of the trial is needed. This multi-criteria assessment is based on the analysis of four criterions: soil fertility; impact on water quality; technical, economic and social results; self-sufficiency regarding inputs. The assessment consists in analyzing both statistical and dashboard methods. The dashboard method enables to interpret indicators by transforming them into a variation rate, relative to the “Reference” crop system. A second dashboard will be considered to interpret the results in another way, to contextualize them regarding regional references. First results show that two years of experimentation are not long enough to conclude on innovative systems performances. Soil fertility results are variable and mostly depend on the year of study. Cropping systems are probably in a transition phase. According to the results, innovative crop systems seem to reduce their impact on water quality. Both innovative systems seem to increase weeding time. The crop system “Soil conservation” also seems to increase working time because of manual mulching. Yields on “Max Green Manure” don’t seem to be different from the yields of the “reference” system, which make that crop system efficient. More results from the next years will reinforce SEFerSol data and confirm or invalidate conclusions of this initial analyze.; Le projet SEFerSol vise à concevoir, tester et évaluer des systèmes de cultures innovants, qui entretiennent la fertilité du sol en maraîchage biologique. Deux systèmes de cultures innovants sont testés, en comparaison à un système de référence qui représente les pratiques courantes des maraîchers en agriculture biologique d’Alsace. Le système innovant « Engrais vert max » est conduit sans fertilisation organique mais avec apport de compost, un maximum d’engrais verts insérés dans la succession culturale et un travail du sol superficiel en planche permanente. Le système innovant « Conservation du sol » est fertilisé selon un bilan azoté, le sol est couvert et non travaillé autant que possible. Après deux ans d’expérimentation, les porteurs du projet souhaitent construire une méthode d’évaluation adéquate aux objectifs de l’expérimentation et initier l’analyse des systèmes de cultures testés sur quatre critères : la fertilité du sol, l’impact sur la qualité de l’eau, les résultats technico-économiques et sociaux et l’autonomie vis-à-vis des intrants. La méthode d’évaluation proposée consiste à confronter les résultats d’analyses statistiques, avec une analyse par tableau de bord. Cette dernière analyse est plus sensible et permet d’exprimer un pourcentage de variation des systèmes de culture innovants vis-à-vis du système « Référence ». Face aux limites que peut présenter cette méthode, il est également envisagé de réaliser un tableau de bord basé sur des références régionales pour contextualiser les résultats sur les systèmes étudiés. Les premiers enseignements issus de l’analyse des résultats, révèlent que deux années d’expérimentation constituent une période trop courte pour conclure sur les systèmes de cultures innovants. Les résultats, notamment sur la fertilité du sol, sont variables et dépendent pour l’instant de l’année d’étude. Les systèmes de culture sont probablement en phase de transition. Des éléments permettent cependant de dire que la qualité de l’eau semble moins impactée sur les deux systèmes innovants. Les temps de travaux augmentent dû à la gestion des adventices sur « Engrais vert max » et « Conservation du sol » mais également dû à la pose manuelle de paillage sur ce dernier système. Le système « Engrais vert max » semble obtenir des rendements similaires au système « Référence » ce qui le rend particulièrement efficient. Les conclusions tirées de ces premières analyses sont à confirmer ou non dans la suite du projet SEFerSol.

La journée pour l'agroforesterie en france. Ministère de l'agriculture, le 1er février 2017; Les sols en agroforesterie, que sait-on? . Journée R&D pour l'Agroforesterie

The application of agromining to abandoned ultramafic areas is a major challenge in the presence of potentially recoverable areas. Howerver, ultramafic soils are particular in terms of their fertility with high concentrations of metals and a near absence of organic matter. Nevertheless, this challenge was partly met by the application of chemical fertilizers and herbicides. Our challenge, through this PhD, was to develop a sustainable agro-ecosystem based on the introduction of a legume in association with the hyperaccumulating plant and then the reduction of any chemical input. Our results clearly confirmed that the introduction of a legume into these new cropping systems improved both the biomass production of Alyssum murale and the Ni yields in comparison to the fertilized and non-fertilized monoculture. Our work has also shown that the insertion of a legume into agromining cropping systems improves the structure of the soil due to stable and larger aggregates. In addition, higher levels of carbon and nitrogen and higher concentrations of organic matter were detected. These results led to an overall improvement of the soil structure, its fertility and its biofunctioning. Our results showed positive effects of these new cropping systems, both on the size of the bacterial communities and on the microbial enzymes involved in the soil biogeochemical cycles. In addition, the structure and diversity of bacterial communities were modified with the insertion of the legume, compared to the monoculture. Economically, the introduction of legume into cropping systems dedicated to Ni agromining involves a gain of money and time due to reduced application of mineral fertilizers as well as products of phytosanitary. Finally, all these benefits lead to the rehabilitation of ultramafic soils with the restoration of their physical, chemical and biological qualities while allowing these particular soils to offer many ecosystem services, L’application de l’agromine à des zones ultramafiques délaissées constitue un enjeu majeur à la vue des surfaces potentiellement valorisables. Par contre, les sols ultramafiques sont particuliers avec de fortes concentrations en métaux et une quasi absence de matière organique. Malgré tout, la mise en place de l’agromine a déjà donné de bons résultats, couplée avec l’application d’herbicides et une fertilisation minérale. Notre défi a été de développer une agromine durable par la mise en place d’agro-écosystèmes basés sur l’introduction d’une légumineuse en association avec une plante hyperaccumulatrice et la suppression de tout intrant chimique. Nos résultats ont confirmé clairement que l'introduction d'une légumineuse dans l’agromine a amélioré la production de biomasse de Alyssum murale et les rendements de nickel par rapport à sa monoculture fertilisée et non fertilisée. Nos travaux ont également montré que l'insertion d'une légumineuse dans l’agromine permet d’améliorer la structure du sol avec des agrégats plus stables. De plus, de meilleures teneurs en carbone, azote et en matière organique ont été détectées. L’ensemble de ces éléments conduit ainsi à une amélioration globale de la structure du sol, de sa fertilité et de son biofonctionnement. Corrélativement, nos résultats ont mis en évidence les effets positifs de ces nouvelles pratiques, à la fois sur la taille, la diversité et les acitivités liées aux cycles biogéochimiques des communautés bactériennes. D’un point de vue écononique, l’introduction de la légumineuse dans l’agromine implique un gain financier et de temps du fait de la réduction de l'application d’engrais et de produits phytosanitaires. Enfin, tous ces avantages conduisent à une réhabilitation des sols ultramafiques avec une restauration de leurs qualités physique, chimique et biologique, tout en permettant à ces sols particuliers d’offrir plusieurs services écosystémiques

Key message Short-rotation forestry using eucalyptus in degraded oak forests in the semi-arid area of NW Morocco can be a useful strategy to avoid further degradation and carbon loss from this ecosystem, but it might be constrained by nutrient and water supply in the long term.[br/] Context Land degradation and deforestation of natural forests are serious issues worldwide, potentially leading to altered land use and carbon storage capacity.[br/] Aims Our objectives were to investigate if short-rotation plantations can restore carbon pools of degraded soils, without altering soil fertility.[br/] Methods Carbon and nutrient pools in above- and below-ground biomass and soils were assessed using stand inventories, harvested biomass values, allometric relationships and selective sampling for chemical analyses.[br/] Results Carbon pools in the total ecosystem were low in the degraded land and in croplands (6–13 Mg ha−1) and high in forests (66–94 in eucalyptus plantations; 86–126 in native forests). The soil nutrient status of eucalyptus stands was intermediate between degraded land and native forests and increased over time after eucalyptus introduction. All harvest scenarios for eucalyptus are likely to impoverish the soil but, for the moment, the soil nutrient status has not been affected.[br/] Conclusion Afforestation of degraded land with eucalyptus can be a useful restoration tool relative to carbon storage and soil fertility, provided that non-intensive forestry is applied.

In forest ecosystems, the specific influence of soil resources on stand productivity is difficult to assess because many other ecological variables also affect tree growth. In this study, we took advantage of a natural soil gradient, from shallow calcic soil to deep acidic soil, all with similar climate, atmospheric depositions, species composition and management, to determine the relationship between soil nutritive resources and the growth and mineral nutrition of a beech ( Fagus sylvatica ) mature forest of Northeastern France. Soil resources were assessed through the quantification of the stocks of available water and mineral nutrients (Ca, Mg, K and P 2 O 5 ). Beech stand growth and mineral nutrition were determined through the use of several indicators, i.e., standing aboveground biomass and annual biomass production, potential growth index (prediction of the height of dominant trees at 100 years) and foliar nutrient content. We observed a gradient of nutritive resources in soils as well as a gradient of stand growth on the study site: the current aboveground biomass was highest on the calci-brunisol which presented the highest water and nutrient stocks while it was lowest on the rendisol, characterized by a very low water holding capacity and a very low stock of available K. However, the growth of beech trees on the rendisol was equivalent to the highest growth classes of beech trees in France, and K nutrition was optimal. Observations on the study site suggest that, in favorable climate conditions, some biological adaptation processes, such as an efficient root colonization as well as an efficient nutrient cycling may allow to maintain stand growth and nutrition on soils with low water and nutrient reserves. The fertility of forest soils has thus to be assessed in a dynamic way by integrating nutrient fluxes as well as the adaptations of trees to environmental constraints. The biological processes become an increasingly important part in the conservation of soil fertility, notably in the perspective of global changes.

Introducing nitrogen-fixing species (NFS) in eucalypt plantations is a useful practice to compensate nitrogen loss at harvest, reduce fertilizer inputs, improve soil fertility and sustain forest productivity in low input systems.Nitrogen (N) and carbon (C) were evaluated in the active part of soil organic matter (SOM) i.e., the particulate organic matter (POM), which was obtained after soil (0-0.05 m) physical fractionation at the end of a first 7-year rotation (R1Y7) and at year 2 of a second rotation (R2Y2) in pure acacia (100A), pure eucalypt (100E) and mixed-species (50A50E) stands in an experimental plantation established on an Arenosol in the Congolese coastal plains. N concentration (in g kg(-1) of soil) was higher in coarse POM (cPOM, 4000-250 mu m) in 100A and 50A50E compared to 100E at 2YR2, while no difference was found in fine POM (fPOM, 250-50 gm) and in the organo-mineral fraction (OMF, < 50 mu m). N content in cPOM was more than 3 times higher at R2Y2 than at R1Y7. A slight increase was also observed in fPOM, while no difference was observed in OMF between R1Y7 and R2Y2. Lower C:N ratios in the two POM fractions in 100A and, to a lesser extent, in 50A50E compared to 100E suggests an improved soil N status after acacia trees have been introduced in eucalypt plantations.The lack of difference in N content of coarse POM between 100A and 50A50E at R1Y7, despite higher amount of N in the forest floor and N returning to the soil (harvest residues and litterfall) in 100A than in 50A50E, suggests a faster cycling of nitrogen under acacia than under eucalypt.

International audience; Palm oil is nowadays the first vegetable oil consumed worldwide. Given the world population growth and the increasing demand in fat for food and fuel, the increase in oil palm production is expected to continue. It is thus important to find ways of reducing the ecological impact of oil palm plantations at both the agroecosystem and the mill supply area levels, by improving agricultural practices and land uses. This is where agroecology can play a very critical role. The present article gathers short stories on agroecological practices currently taking place in oil palm plantations in South-East Asia. Such stories notably highlight the importance of the various palm co-products and how appropriate recycling strategies can allow for reducing external inputs to both the field and the mill. Besides limiting environmental impacts thanks to such savings, several co-products used as organic amendments can even help to maintain or enhance soil quality. Other stories explored agroecological practices developed for biological controls. Although integrated pest management has been applied in palm plantations for a long time, the underlying mechanisms are still not fully deciphered and practices still need to be improved. More knowledge is needed in order to better account for the holistic role of biodiversity and arbitrate trade-offs between practices and ecosystem services, at both plantation and landscape levels.; L'huile de palme est aujourd'hui la première huile végétale consommée au monde. Étant donné la croissance démographique mondiale et la demande accrue en corps gras pour l'alimentation et les biocarburants, l'augmentation de la production d'huile de palme devrait perdurer. Il est ainsi primordial de trouver des moyens de production permettant de réduire l'impact écologique des plantations de palmier à huile, à la fois à l'échelle de l'agroécosystème et celle du bassin d'approvisionnement de l'huilerie, en améliorant les pratiques et la gestion des usages des sols. Les principes de l'agroécologie peuvent aider à développer des solutions à ces diverses échelles. Cet article rassemble diverses histoires courtes illustrant des pratiques agroécologiques mises en place dans des plantations de palmier à huile en Asie du Sud-Est. Ces illustrations mettent en évidence l'importance des nombreux co-produits issus du palmier et leur rôle clé dans les stratégies de recyclage pour réduire le recours aux intrants externes pour la plantation comme pour l'huilerie. Au-delà de la réduction des impacts environnementaux du fait de ces économies d'intrants, certains co-produits restitués en plantation peuvent également permettre de maintenir, voire d'améliorer, la qualité des sols. D'autres histoires courtes parcourent quelques autres pratiques agroécologiques dans le domaine de la lutte intégrée. Bien que de nombreuses pratiques de contrôle biologique soient mises en œuvre dans des plantations de palmier à huile depuis de nombreuses années, les mécanismes sous-jacents ont été encore peu explorés et les pratiques peuvent être améliorées. De nouvelles connaissances sont nécessaires pour mieux caractériser et prendre en compte de manière holistique les enjeux et le rôle de la biodiversité et pouvoir arbitrer les compromis entre pratiques et services écosystémiques, aux échelles de la plantation et du paysage.

In terrestrial ecosystems, plant-available pools of magnesium and calcium are assumed to be stored in the soil as exchangeable cations adsorbed on the surface of mineral and/or organic particles. The pools of exchangeable magnesium and calcium are measured by ion-exchange soil extractions. These pools are sustained in the long term by the weathering of primary minerals in the soil and atmospheric inputs. This conceptual model is the base of input-output budgets from which soil acidification and the sustainability of soil chemical fertility is inferred. However, this model has been questioned by data from long-term forest ecosystem monitoring sites, particularly for calcium. Quantifying the contribution of atmospheric inputs, ion exchange and weathering of both primary, secondary and non-crystalline phases to tree nutrition in the short term is challenging. In this study, we developed and applied a novel isotopic dilution technique using the stable isotopes of magnesium and calcium to study the contribution of the different soil phases to soil solution chemistry in a very acidic soil. The labile pools of Mg and Ca in the soil (pools in equilibrium with the soil solution) were isotopically labeled by spraying a solution enriched in 26Mg and 44Ca on the soil. Labeled soil columns were then percolated with a dilute acid solution during a 3-month period and the isotopic dilution of the tracers was monitored in the leaching solution, in the exchangeable (2 sequential 1 mol L−1 ammonium acetate extractions) and non-crystalline (2 sequential soil digestions: oxalic acid followed by nitric acid) phases. Significant amounts of Mg and Ca isotope tracer were recovered in the non-crystalline soil phases. These phases represented from 5% to 25% and from 24% to 50%, respectively, of the Mg and Ca labile pools during the experiment. Our results show that non-crystalline phases act as both a source and a sink of calcium and magnesium in the soil, and contribute directly to soil solution chemistry on very short-term time scales. These phases are very abundant in acid soils and, in the present study, represent a substantial calcium pool (equivalent in size to the Ca exchangeable pool). The gradual isotopic dilution of Mg and Ca isotope ratios in the leaching solution during the experiment evidenced an input flux of Mg and Ca originating from a pool other than the labile pool. While the Mg input flux originated primarily from the weathering of primary minerals and secondarily from the non-crystalline phases, the Ca input flux originated primarily from the non-crystalline phases. Our results also show that the net calcium release flux from these phases may represent a significant source of calcium in forest ecosystems and actively contribute to compensating the depletion of Ca exchangeable pools in the soil. Non-crystalline phases therefore should be taken into account when computing input-output nutrient budgets and soil acid neutralizing capacity. (Resume d'auteur)

International audience; Organic fertilizer application is often touted as an economical and effective method to increase soil fertility. However, this amendment may increase dissolved organic carbon (DOC) runoff into downstream aquatic ecosystems and may consequently alter aquatic microbial community. We focused on understanding the effects of DOC runoff from soils amended with compost, vermicompost, or biochar on the aquatic microbial community of a tropical reservoir. Runoff collected from a series of rainfall simulations on soils amended with different organic fertilizers was incubated for 16 days in a series of 200 L mesocosms filled with water from a downstream reservoir. We applied 454 high throughput pyrosequencing for bacterial 16S rRNA genes to analyze microbial communities. After 16 days of incubation, the richness and evenness of the microbial communities present decreased in the mesocosms amended with any organic fertilizers, except for the evenness in the mesocosms amended with compost runoff. In contrast, they increased in the reservoir water control and soil-only amended mesocosms. Community structure was mainly affected by pH and DOC concentration. Compared to the autochthonous organic carbon produced during primary production, the addition of allochthonous DOC from these organic amendments seemed to exert a stronger effect on the communities over the period of incubation. While the Proteobacteria and Actinobacteria classes were positively associated with higher DOC concentration, the number of sequences representing key bacterial groups differed between mesocosms particularly between the biochar runoff addition and the compost or vermi-compost runoff additions. The genera of Propionibacterium spp. and Methylobacterium spp. were highly abundant in the compost runoff additions suggesting that they may represent sentinel species of complex organic carbon inputs. Overall, this work further underlines the importance of studying the off-site impacts of organic fertilizers as their impact on downstream aquatic systems is not negligible.

National audience

International audience; Understanding the environmental determinants of forests deciduousness i.e. proportion of deciduous trees in a forest stand, is of great importance when predicting the impact of ongoing global climate change on forests. In this study, we examine (i) how forest deciduousness varies in relation to rainfall and geology, and (ii) whether the influence of geology on deciduousness could be related to differences in soil fertility and water content between geological substrates.The study was conducted in mixed moist semi‐deciduous forests in the northern part of the Congo basin. We modelled the response of forest deciduousness to the severity of the dry season across four contrasting geological substrates (sandstone, alluvium, metamorphic and basic rocks). For this, we combined information on forest composition at genus level based on commercial forest inventories (62 624 0.5 ha plots scattered over 6 million of ha), leaf habit, and rainfall and geological maps. We further examined whether substrates differ in soil fertility and water‐holding capacity using soil data from 37 pits in an area that was, at the time, relatively unexplored.Forest deciduousness increased with the severity of the dry season, and this increase strongly varied with the geological substrate. Geology was found to be three times more important than the rainfall regime in explaining the total variation in deciduousness. The four substrates differed in soil properties, with higher fertility and water‐holding capacity on metamorphic and basic rocks than on sandstone and alluvium. The increase in forest deciduousness was stronger on the substrates that formed resource‐rich clay soils (metamorphic and basic rocks) than on substrates that formed resource‐poor sandy soils (sandstone and alluvium).Synthesis. We found evidence that tropical forest deciduousness is the result of both the competitive advantage of deciduous species in climates with high rainfall seasonality, and the persistence of evergreen species on resource‐poor soils. Our findings offer a clear illustration of well‐known theoretical leaf carbon economy models, explaining the patterns in the dominance of evergreen versus deciduous species. And, this large‐scale assessment of the interaction between climate and geology in determining forest deciduousness may help to improve future predictions of vegetation distribution under climate change scenarios. In central Africa, forest is likely to respond differently to variation in rainfall and/or evapotranspiration depending on the geological substrate.

Traditional yam-based cropping systems (shifting cultivation, slash-and-burn, and short fallow) often result in deforestation and soil nutrient depletion. The objective of this study was to determine the impact of yam-based systems with herbaceous legumes on dry matter (DM) production (tubers, shoots), nutrients removed and recycled, and the soil fertility changes. We compared smallholders’ traditional systems (1-year fallow ofAndropogon gayanus-yam rotation, maize-yam rotation) with yam-based systems integrated herbaceous legumes (Aeschynomene histrix/maize intercropping-yam rotation,Mucuna pruriens/maize intercropping-yam rotation). The experiment was conducted during the 2002 and 2004 cropping seasons with 32 farmers, eight in each site. For each of them, a randomized complete block design with four treatments and four replicates was carried out using a partial nested model with five factors: Year, Replicate, Farmer, Site, and Treatment. Analysis of variance (ANOVA) using the general linear model (GLM) procedure was applied to the dry matter (DM) production (tubers, shoots), nutrient contribution to the systems, and soil properties at depths 0–10 and 10–20 cm. DM removed and recycled, total N, P, and K recycled or removed, and soil chemical properties (SOM, N, P, K, and pH water) were significantly improved on yam-based systems with legumes in comparison with traditional systems.

The aim of the international "4 per 1 000" initiative is to support States and non-governmental actors in their efforts towards a better management of carbon (C) stocks in soils. These stocks depend on the inputs and outputs of C in soils. Stocks are the result of intercon¬nected mechanisms acting at fine spatial scales, leading to stabilisation/destabilisation of the C present in organic matter (OM). The need to federate research on these mechanisms and their effects on C stocks in a context of local and global changes (land uses, agricultural practices, climatic and soil conditions, etc.) led to the creation in 2015 of a group of french researchers, CarboSMS. This is the synthesis of the seminar dedicated to this issue. In the first part, we present recent advances in the understanding of soil C stabilisation mechanisms. Biotic mechanisms correspond to the effects of plants (main source of C through litter and root systems), microorganisms (fungi and bacteria) and ecosystem engineers (earthworms, termites, ants) on organic C stocks in soils. Abiotic processes are related to the physical structure of soils, to the organization of their porosity and to their mineral fraction : inclusion of the OM in aggregates, association with minerals, etc. These biotic and abiotic mechanisms take place concomitantly and interact. In the second part, we discuss the effects of agricultural practices on soil C stocks. By acting on biotic as well as abiotic mechanisms, land use and management specificities (choice of plant species and density, plant residue exports, amendments, fertilization, tillage, etc.) drive not only the spatial and temporal organic inputs into soils, but also the OM sensitivity to mineralisation. The complexity of the interactions between the different mechanisms and their effects on C stocks are evidenced by meta-analyses and long-term field studies. Organic C stabilisation mechanisms in soils are studied at fine spatial scales (mm-μm) under controlled conditions. The third part of this article addresses the issues of upscaling (up to the plot and to global scale) and validating the action of specific mechanisms in different soil and climatic contexts, before taking them into account in large scale models to improve predictions of the changes in soil C stocks. Finally, this literature review highlights some perspectives for future research aiming at preserving or even increasing C stocks. These perspectives focus on the mechanisms, the effects of agricultural practices on these mechanisms, and on predictive models of C stocks.; La iniciativa internacional "4 por 1 000" tiene como ambición sostener Estados y actores no gubernamentales en sus esfuerzos hacia una mejor gestión de los stocks de carbono (C) de los suelos. Estos stocks dependen de las entradas y salidas de C en los suelos. Los stocks son la consecuencia de mecanismos interconectados, que actúan a una escala espacial fina, que conducen al almacenaje o al desalmacenaje del C presente en las materias orgánicas (MO). Aparece necesario federar los investigadores sobre estos mecanismos y su acción sobre los stocks de C en un contexto de cambio local o global (uso de los suelos, prácticas agrícolas, condiciones climáticas o edáficas, etc.), lo que lleva a la creación del colectivo de investigadores CarboSMS. Este artículo es la síntesis del seminario dedicado a esta cuestión. La primera parte presenta los avances recientes sobre la compren¬sión de los mecanismos de estabilización. Los mecanismos bióticos corresponden a los efectos de las plantas (principal fuente de C, en particular a través de sus sistemas radiculares), de los microorganismos (hongos y bacterias) y de los ingenieros del ecosistema (lombrices, termitas, hormigas) sobre los stocks de C orgánico del suelo. Los procesos abióticos son ligados a la estructura física del suelo, a la organización de su porosidad y a su fracción mineral : inclusión de la MO en los agregados, asociación a los minerales, etc. Estos mecanismos bióticos y abióticos se desarrollan de manera concomitante y en interacción. La segunda parte discute de los efectos de las prácticas agrícolas sobre los stocks de C de los suelos. La elección de las especies vegetales y de su densidad de plantación, la intensidad de la extracción de los vegetales, la enmienda, la fertilización y el trabajo del suelo, etc. condicionan no solamente los aportes de MO al suelo en el tiempo y en el espacio, pero también la sensibilidad de estas MO a la mineralización, actuando sobre los mecanismos bióticos y abióticos. La complexidad de las interacciones entre los mecanismos y sus efectos en el tiempo sobre los stocks de C se constata por los meta-análisis y los estudios de terreno de larga duración. Se estudian los mecanismos de estabilización del C orgánico en los suelos a escala espacial fina (mm-μm), en condiciones especificas. La tercera parte de este artículo discuta proposiciones concretas para abordar las cuestiones del cambio de escala (hasta la parcela y al nivel global) y de la validación de la acción de un mecanismo en diferentes contextos pedo-climáticos antes de tomarlo en cuenta en los modelos a larga escala para mejorar las previsiones de evolución de los stocks de C de los suelos. En fin, en una óptica de preservar mejor los stocks de C, incluso de aumentarlos, esta revisión bibliográfica nos permite hacer proposi¬ciones para los ejes de investigaciones futuras sobre los mecanismos, los efectos de las prácticas agrícolas sobre estos mecanismos, y los modelos de predicción de los stocks de C.; L’initiative internationale "4 pour 1 000" a pour ambition de soutenir États et acteurs non gouvernementaux dans leurs efforts vers une meilleure gestion des stocks de carbone (C) des sols. Ces stocks dépendent des entrées et sorties de C dans les sols. Ils sont la consé¬quence de mécanismes interconnectés, agissant à une échelle spatiale fine, qui conduisent au stockage ou déstockage du C présent dans les matières organiques (MO). Il apparaît nécessaire de fédérer les recherches sur ces mécanismes et leur action sur les stocks de C dans un contexte de changement local ou global (usage des sols, pratiques agricoles, conditions climatiques ou édaphiques, etc.), ce qui a conduit à la création du collectif de chercheurs CarboSMS. Cet article est la synthèse d'un séminaire dédié à cet enjeu. La première partie présente les avancées récentes sur la compréhension des mécanismes de stabilisation. Les mécanismes biotiques correspondent aux effets des plantes (principale source de C, notamment à travers leurs systèmes racinaires), des micro-organismes (champignons et bactéries) et des ingénieurs de l’écosystème (vers de terre, termites, fourmis) sur les stocks de C organique du sol. Les processus abiotiques sont liés à la structure physique du sol, à l’organisation de sa porosité et à sa fraction minérale : inclusion de la MO dans les agrégats, association aux minéraux, etc. Ces mécanismes biotiques et abiotiques se déroulent de façon concomitante et en interaction. La deuxième partie discute des effets des pratiques agricoles sur les stocks de C des sols. Le choix des espèces végétales et de leur densité de plantation, l’intensité du prélèvement des végétaux, l’amendement, la fertilisation et le travail du sol, etc. conditionnent non seulement les apports de MO au sol dans le temps et l’espace, mais aussi la sensibilité de ces MO à la minéralisation, en agissant sur les mécanismes, biotiques comme abiotiques. La complexité des interactions entre les mécanismes et leurs effets dans le temps sur les stocks de C sont mis en évidence par les méta-analyses et les études de terrain de longue durée. Les mécanismes de stabilisation du C organique dans les sols sont étudiés à fine échelle spatiale (mm-μm), dans des conditions spéci¬fiques. La troisième partie de cet article discute de propositions concrètes pour aborder les questions du changement d’échelle (jusqu’à la parcelle et au niveau global) et de la validation de l’action d’un mécanisme dans différents contextes pédo-climatiques avant de le prendre en compte dans des modèles à large échelle pour améliorer les prévisions d’évolution des stocks de C des sols. Enfin, dans une optique de mieux préserver les stocks de C, voire de les augmenter, cette revue bibliographique nous permet de faire des propositions pour les axes de recherches futures sur les mécanismes, les effets des pratiques agricoles sur ces mécanismes, et les modèles de prédiction des stocks de C.

International audience; Soil acidity is a major constraint for crop production on highly weathered tropical soils characterized by high Al toxicity, low cation exchange capacity and low P availability to plants. To address these constraints, we compared the effects on crop production and soil properties of liming and adding biochar. Experiments were conducted under field conditions in an acidic soil in the Madagascar highlands using a two year rotation of maize intercropped with beans followed by rainfed upland rice over a period of six years. Five different levels of amendment were compared: 10 and 50 t ha−1 of eucalyptus charcoal residues (referred to as biochar), 1 and 3 t ha−1 of dolomite and a control (no amendment). They were combined with two types of soil management (conventional tillage and no tillage) and two fertilization levels. Soil characteristics were measured once after five years. Both biochar and dolomite amendment significantly improved yields of the maize and beans due to an increase in soil pH and a decrease in exchangeable aluminium. However, no significant effect was observed on the yield of upland rice. The incorporation of 50 t ha−1 of biochar was necessary to match the results obtained with 3 t ha−1 of dolomite. Amendment with dolomite was a more practical and cost-efficient option than amendment with biochar in our conditions. Long term trials are now needed to evaluate other types of biochar.

Oil palm is the most rapidly expanding tropical perennial crop. Its cultivation raises environmental concerns, notably related to the use of nitrogen (N) fertilisers and the associated pollution and greenhouse gas emissions. While numerous and diverse models exist to estimate N losses from agriculture, very few are currently available for tropical perennial crops. Moreover, there is a lack of critical analysis of their performance in the specific context of tropical perennial cropping systems. We assessed the capacity of 11 models and 29 sub-models to estimate N losses in a typical oil palm plantation over a 25-year growth cycle, through leaching and runoff, and emissions of NH3, N2, N2O, and NOx. Estimates of total N losses were very variable, ranging from 21 to 139 kg N ha−1 yr−1. On average, 31 % of the losses occurred during the first 3 years of the cycle. Nitrate leaching accounted for about 80 % of the losses. A comprehensive Morris sensitivity analysis showed the most influential variables to be soil clay content, rooting depth, and oil palm N uptake. We also compared model estimates with published field measurements. Many challenges remain in modelling processes related to the peculiarities of perennial tropical crop systems such as oil palm more accurately.

Sustainable wood production requires appropriate management of commercial forest plantations. Establishment of industrial eucalypt plantations on poor sandy soils leads to a high loss of nutrients including nitrogen (N) after wood harvesting. An ecological intensification of eucalypt plantations was tested with the replacement of half of the Eucalyptus urophylla × E. grandis by Acacia mangium in the eucalypt monoculture to sustain soil fertility through enhancement of the N biological cycle. A randomised block design was set up on ferralitic arenosol in the Congolese coastal plains to assess differences in soil N mineralisation, N fluxes in litterfall, and N stocks in forest floor litter and soil between pure acacia (100A), pure eucalypt (100E) and mixed-species treatments (50A50E). Soil N mineralisation was enhanced under acacia, reaching on average 0.17 and 0.15 mg kg−1 soil d−1 in 100A and 50A50E, respectively, compared with 0.09 mg kg−1 soil d−1 in 100E. Higher amounts of N returning to the soil through harvest residues and litterfall were observed under acacia than under eucalypt. However, N stock in mineral soil was not increased in 100A and exhibited a limited increase only in the top soil layer of 50A50E. Our results suggest a much faster N turnover under acacia than under eucalypt. Although A. mangium is an exotic N2-fixing tree in central Africa, it appears to be well adapted to the climatic and edaphic conditions of the Congo, showing an efficient growth strategy. Eucalypt trees could benefit from the increase in soil N availability in mixed-species stands.Keywords: ammonium, arenosol, Congo, ecological intensification, forest plantation, mixed species, N2 fixation, nitrate

Microbial species richness and assemblages across ultramafic ecosystems were investigated to assess the relationship between their distributional patterns and environmental traits. The structure of microorganism communities in the Koniambo massif, New Caledonia, was investigated using a metagenetic approach correlated with edaphic and floristic factors. Vegetation cover and soil properties significantly shaped the large phylogenetic distribution of operational taxonomic unit within microbial populations, with a mean per habitat of 3,477 (± 317) for bacteria and 712 (± 43) for fungi. Using variance partitioning, we showed that the effect of aboveground vegetation was the most significant descriptor for both bacterial and fungal communities. The floristic significant predictors explained 43% of the variation both for the bacterial and fungal community structures, while the edaphic significant predictors explained only 32% and 31% of these variations, respectively. These results confirm the previous hypothesis, that the distribution of microorganisms was more structured by the vegetation cover rather than the edaphic characteristics and that microbial diversity is not limited in ultramafic ecosystems.

Le recyclage des produits résiduaires organiques participe au développement durable des territoires. Il contribue à l'amélioration de la fertilité des sols, notamment via les apports en matière organique, et à une économie circulaire des nutriments (azote, phosphore et potassium principalement) à des échelles très variées. Il faut cependant veiller à la maîtrise des impacts environnementaux, notamment en raison de la difficulté à ajuster les pratiques de fertilisation et de la présence éventuelle de contaminants. L'impact du recyclage est global ; il peut se traduire par une substitution des engrais, préservant ainsi des ressources minières ou les sources d'énergie fossile. Comprendre les processus biogéochimiques impliqués dans le recyclage des produits résiduaires organiques, préciser les usages et proposer des solutions adaptées à différents contextes au Nord comme au Sud ont été les objectifs du travail pluridisciplinaire présenté dans cet ouvrage. Il s'appuie sur les résultats du projet "Intensification des systèmes de production agricole par le recyclage des déchets" (Isard), conduit de 2009 à 2013 avec le soutien financier de l'Agence nationale de la recherche française. Ainsi, de la plaine de Versailles à l'île de la Réunion, en France, et de la péninsule dakaroise, au Sénégal, à la zone périurbaine de Mahajunga, à Madagascar, anthropologues, sociologues, biogéochimistes, modélisateurs, technologues et agronomes se sont associés pour caractériser les déchets organiques et leurs usages, documenter l'intérêt de leur recyclage, mais aussi les risques inhérents à leur emploi. Cet ouvrage est destiné aux professionnels soucieux de pratiques agro-écologiques au Nord comme au Sud. De plus, les études de cas très approfondies intéresseront les scientifiques de diverses disciplines.

International audience; An increase in soil N availability by Acacia mangium in pure or mixed-species stands may reduce soil organic matter (SOM) mineralization compared to eucalypt stands. We measured the isotope composition (delta C-13) of coarse particulate organic matter (cPOM, 4-0.25 mm), of fine POM (fPOM, 0.25-0.05 mm) and of the remaining organo-mineral fraction (OMF

International audience; Background and aims. Positive below-ground interactions (facilitation) should be more pronounced when resources limit crop growth, according to the stress-gradient hypothesis. Our aim was to test this hypothesis for intercropped durum wheat and faba bean along a P-fertilizer gradient. Methods. A field experiment was conducted in a long-term P-fertilizer trial with three rates of P-fertilization (No, Low and High P). Microbial biomass was assessed by chloroform fumigation-extraction. Quantitative PCR was applied to evaluate the abundance of relevant microbial groups. Results. Phosphorus availability and microbial biomass systematically increased in the rhizosphere compared to bulk soil. P-fertilization resulted in higher abundance of targeted bacterial phyla, whole bacterial and fungal communities, and depressed mycorrhizal colonization of durum wheat, but not faba bean. Microbial biomass carbon significantly increased in the rhizosphere only in P-fertilized treatments, pointing to P limitation of microbial communities. Intercropping yielded a significant effect on rhizosphere microbial properties only at High P. Microbial biomass P increased in the rhizosphere of intercropped faba bean only at No P level, and was thus the sole finding supporting the stress-gradient hypothesis. Conclusions. P-fertilization was the main driver of microbial communities in this field trial, and P-fertilizer application modulated the species-specific effect in the intercrop. Plant performance did not validate the stress-gradient hypothesis as positive plant-plant interactions occurred regardless of the level of P-fertilization.

This book, coordinated by AllEnvi, is published on the occasion of the 22nd Conference of the Parties to the United Nations Framework Convention on Climate Change (COP22, Marrakech, 2016); Soil carbon as an indicator of Mediterranean soil quality

Erratum paru dans Agroforestry Systems = ISSN 0167-4366. - (2015)vol.89:n°1 p. 95-96. In Sudano-Sahelian agriculture, organic amendments are often limited by resource availability. Small branches (ramial wood, RW) represent an organic resource found in many landscapes but little is known about their effects. This field trial (2007-2009) studied the effects of RW or straw at low application rate (0.69 Mg C ha?1 year?1) on topsoil carbon (C), nitrogen (N) and available phosphorus (P, Pav), termite cast abundance, and sorghum yield. Straw and RW were chopped and either buried (StBu, WoBu) or mulched (StMu, WoMu). Mineral fertilizers were added to straw so that RW- and straw-amended plots received similar applications of C, N, P, and potassium. Another treatment had RW buried with additional N (WoBuN), and there was a control (Ctrl). Branches came from Piliostigma reticulatum, very common in the area. The treatments had little significant effect on topsoil and crop, owing to the low application rate and spatial variability. However, Pav was significantly lower with buried than mulched amendments in 2009, and decreased significantly over time in Ctrl and with buried amendments. Topsoil C also decreased significantly with time in WoMu. Significantly more termite casts were observed with RW. The sorghum yield averaged 0.87 Mg DM ha?1 in 2007 and then decreased. The treatments affected yield significantly in 2008 only: it was higher in WoBuN and StBu than in Ctrl. In 2009, the yield was mainly affected by initial topsoil Pav. These results suggest that RW stimulated biological activity, leading to P immobilization and C mineralization, but had little effect on yields.

L'avenir de l'Afrique de l'Ouest dépend de la capacité de son agriculture à assurer la sécurité alimentaire de sa population, qui devrait doubler en vingt ans, tout en faisant face aux risques nouveaux engendrés par le réchauffement climatique. En effet, les modifications de température et de précipitations déjà à l'oeuvre, et qui devraient s'amplifier, auront dans un futur proche des répercussions importantes sur la production agricole et sur les ressources en eau de cette partie du continent africain. L'adaptation des sociétés rurales aux risques climatiques est une des clés pour relever ce nouveau défi. Pour mieux en connaître le potentiel, les processus et les barrières, cet ouvrage analyse les évolutions récentes et en cours du climat et de l'environnement, et étudie comment les sociétés rurales les perçoivent et les intègrent : quels sont les impacts de ces changements, quelles vulnérabilités mais aussi quelles nouvelles opportunités entraînent-ils ? Comment les populations s'y adaptent-elles, et quelles innovations mettent-elles en oeuvre, alors que les effets induits par le climat interagissent avec les changements sociaux, politiques, économiques et techniques en cours sur le continent ? En associant des chercheurs français et africains (climatologues, agronomes, hydrologues, écologues, démographes, géographes, anthropologues, sociologues...) dans une approche interdisciplinaire, cet ouvrage apporte une contribution précieuse pour mieux anticiper les risques climatiques et évaluer les capacités des sociétés africaines à y faire face.

La fertilité des sols, notion centrale pour accroître la production des écosystèmes cultivés, est une réalité complexe : elle résulte de l'expression des composantes biologiques, physiques et chimiques des sols et de leurs interactions. Comprendre les mécanismes impliqués permet d'envisager les effets de modifications de pratiques ou de système de culture sur la fertilité. La fertilité est ici décrite comme la capacité des sols à fournir les éléments nutritifs nécessaires à l'alimentation des plantes. Le cycle de l'azote et ses relations avec la dynamique des matières organiques y joue un rôle central ; il est couplé au cycle du carbone par l'activité microbienne hétérotrophe qui minéralise (parfois très rapidement) les résidus de récolte. Les interactions entre processus chimiques, physiques et biologiques du sol sont décrites. Il est ainsi possible d'analyser l'influence de pratiques culturales comme la simplification ou la suppression du labour, l'insertion ou la destruction de prairies temporaires dans les rotations et d'envisager une agriculture reposant davantage sur le recyclage des matières organiques et le fonctionnement biologique du sol., In this study, soil fertility is defined as the ability of soils to furnish necessary nutrients to plants. It is a consequence of the biological, chemical, and physical properties of soils and their interactions. The nitrogen cycle and its relationship with soil organic matter dynamics play a key role; the nitrogen cycle is linked to the carbon cycle by the activity of soil bacteria. Here, we describe the interactions between various biological, chemical, and physical processes that take place in the soil. It is thus possible to examine the effects of cultivation practices, such as limiting or eliminating ploughing, including temporary pastures in rotations, and destroying temporary pastures as part of the rotation cycle. One can also envision an agricultural approach that promotes the recycling of organic matter and the soil's biological functions.