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Dans les bananeraies intensives conventionnelles, la fertilisation, essentiellement minérale, vise à satisfaire les besoins nutritionnels des bananiers mais ne permet pas d'assurer un stock de matière organique suffisant pour maintenir une fertilité des sols optimale. Or, l'utilisation de fertilisants organiques complexifie le raisonnement de la fertilisation puisque les nutriments apportés ne sont disponibles pour la plante qu'après minéralisation de la matière organique par les microorganismes du sol. L'objectif de l'étude est donc de concevoir des stratégies de fertilisation organique qui permettent de restaurer la fertilité sur plusieurs années, en s'appuyant sur un modèle de bilan humique, validé expérimentalement en condition réelles sous culture de banane plantain.

La faible productivité de l'agriculture en Afrique subsaharienne est due en grande partie à la dégradation de la fertilité des sols. Les agricultures familiales, pilier de la sécurité alimentaire de cette grande région, doivent relever le défi de la restauration et du maintien de la capacité productive des terres. Les pratiques endogènes des producteurs telles que les associations céréales-légumineuses, les jachères pâturées, les parcs arborés... ne permettent plus d'entretenir la fertilité sur des surfaces cultivées qui s'agrandissent, surtout lorsque les sols sont carencés. Durant quatre décennies, les décideurs et acteurs du secteur agricole ont privilégié la vulgarisation des engrais de synthèse. Mais l'utilisation des engrais minéraux demeure faible et bien en deçà de la moyenne de la consommation mondiale (15 kg/ha contre 135 kg/ha). Après avoir longuement promu l'utilisation de fumure organique, la recherche invite désormais à diversifier les sources de biomasse fertilisante via l'agroforesterie, les associations avec les légumineuses, l'agriculture de conservation. D'autres techniques de conservation de l'eau et du sol ont également été mises en avant. C'est bien la combinaison de différentes pratiques qui est à construire avec les agriculteurs pour chaque situation de production, en fonction des ressources disponibles localement, d'un apport raisonné d'engrais de synthèse et d'amendement, des savoirs paysans et scientifiques. Pour cela, il est nécessaire (i) de modifier les postures des chercheurs et des décideurs vis-à-vis des ruraux et (ii) de réviser les politiques publiques toujours focalisées sur l'usage des engrais minéraux, afin de fournir des services d'appui-conseil plus diversifiés, performants et intégrant les besoins de transitions agroécologiques indispensables aujourd'hui dans un contexte de changement climatique.

Ce fascicule, publié à l'occasion du Salon international de l'agriculture de Paris 2024, présente l'évolution des recherches sur la gestion de la fertilité des sols en Afrique subsaharienne, à partir d'un choix d'articles publiés au fil des ans par la revue Cahiers Agricultures.

Dicyandiamide decreased N2O emissions even under 40°C. Ammonia oxidizers and nirS were well adapted to 40°C in manured soils. Fungal nirK tolerated high temperature better in urea than manure treatment. Compared to nosZII, nosZI adapted to all temperature regardless of fertilization. nirS-denitrifier dominated N2O emissions at high temperature in fertilized soil. Heat waves associated with global warming and extreme climates would arouse serious consequences on nitrogen (N) cycle. However, the responses of the functional guilds to different temperatures, especially high temperature and the cascading effect on N2O emissions remain unclear. An incubation study was conducted to examine the effect of different temperatures (20°C, 30°C, and 40°C) and fertilizer types (urea and manure) on N2O-producers and N2O-reducers, as well as the efficacy of dicyandiamide (DCD) on N2O emissions in a vegetable soil. Results showed that ammonia oxidizers and nirS-type denitrifiers were well adapted to high temperature (40°C) with manure application, while the fungal nirK-denitrifiers had better tolerance with urea application. The nosZ clade I microbes had a strong adaptability to various temperatures regardless of fertilization type, while the growth of nosZ clade II group microbes in non-fertilized soil (control) were significantly inhibited at higher temperature. The N2O emissions were significantly decreased with increasing temperature and DCD application (up to 60%, even at 40°C). Under high temperature conditions, fungal denitrifiers play a significant role in N-limited soils (non-fertilized) while nirS-type denitrifiers was more important in fertilized soils in N2O emissions, which should be specially targeted when mitigating N2O emissions under global warming climate.

The distribution of plant communities in hot desert ecosystems is discontinuous and resembles the pattern of heterogeneous resource patches, known as “fertility islands”. Understanding the key factors that allow plants to establish in these conditions, as well as their associated microbial diversity, is crucial to the comprehension and preservation of these ecosystems. Saudi Arabia in the Arabian Peninsula, is one of the driest regions in the world, with a very low water regime and low soil nutrient contents. The establishment of ecosystems in these arid desert conditions is therefore subject to numerous constraints. Understanding the biotic and abiotic factors linked to the formation of fertility islands, from the perspective of soil composition and its associated microbiome, both in the soil and in the roots of associated plant community, is therefore a fundamental issue for the preservation of these ecosystems. In this study, we analyzed the soil composition between a fertility island and bare soil. The proportions of micro- and macro-elements important for plant nutrition, namely magnesium, phosphorus, potassium and iron were higher in the fertility island. We also observed that soil bacterial and fungal diversity increased in the fertility island. Key taxa such as Rhizobia and Glomeraceae which play important roles in ecosystem functioning were identified in both the fertility island soil and in the roots of the established plant community. These results confirm that plant establishment is linked to soil conditions, in line with the fertility island hypothesis, and that the microbial community in the fertility island differs both in diversity and in composition from that of the bare soil. Fertility islands soils and the roots of established plant community harbor a microbiome potentially crucial to ecosystem functioning, and are of major interest for conservation and agronomy programs.

Growing awareness of the environmental impact of intensive agriculture has prompted a quest for more sustainable approaches. The most promising alternatives include the application of organic waste products (OWPs), as well as biofertilizers containing local beneficial microorganisms (BMs) on cultivated soils. This study was designed to assess the effects of BMs on carbon and nitrogen mineralization of OWPs. A 28-day laboratory incubation experiment was conducted at 28 °C with a soil, three OWPs (poultry litter (PL), cow dung (CD), and sewage sludge (SS)), and three BMs (groundnut + millet from Saint-Louis (LGM), groundnut from the southern groundnut basin (BG), and rice from the southern groundnut basin (BR) in Senegal), alone and combined. The results showed that the C mineralization from OWP + BM + soil mixtures exceeded (range 13–41%) those measured for OWP + soil. The BM input induced an increase or reduction in OWP nitrogen mineralization, depending on the type of BM and OWP. However, the net mineral nitrogen (Nmin) obtained with the PL-LGM and SS-BG combinations was 13.6- and 1.7-fold higher than with PL and SS, respectively, at 28 days. The addition of BM seemed to lead to a decrease in the C: N ratio, an improvement in the availability of nitrogen, and an increase in microbial activity in the OWP + BM + soil mixture. Our results generated new information on the variation patterns of OWP carbon and nitrogen in OWP-BM-soil systems. This novel insight will be developed to guide the most appropriate choice of OWP-BM mixtures for improved fertilization in sustainable production systems.

Context: Crop productivity in sub-Saharan Africa cannot be substantially improved without simultaneously addressing short-term crop nutrient demand and long-term soil fertility. Integrated soil fertility management tackles both by the combined application of mineral fertilizers and organic resource inputs but few studies examined its' long-term effectiveness. Objective: To address this knowledge gap, this study analysed maize yield trends in four long-term (31–37 cropping seasons) field experiments in Kenya with contrasting soil textures and under different climates. Methods: All sites had two maize cropping seasons per year, received a base P and K fertilization and tested combinations of organic resource addition (1.2 and 4 t C ha-1 yr-1 ranging from farmyard manure, to high-quality Tithonia diversifolia and Calliandra calothyrsus material to low-quality saw dust), combined with (+N) and without (-N) mineral N fertilizer (120 kg N ha-1 season-1). General maize yield trends across sites and site specific trends were analyzed. Results: Across sites, the no-input control experienced significant average maize yield reductions of 50 kg ha-1 yr-1 over the study period. In contrast, the treatment with farmyard manure +N maintained yields at both 1.2 and 4 t C ha-1 yr-1. High initial yields following additions of Tithonia and Calliandra, reduced over time. Assessment by site showed site specificity of maize yields and yield trends. For example, the two climatically favorable sites in western Kenya experienced yield gains with high quality organic resources at 4 t C ha-1 yr-1, leading to yields of up to 8 t ha-1 per season, while sites in central Kenya experienced yield losses, leading to 3.5 t ha-1 per season. Yield site specificity for ± mineral N treatments was stonger than for organic resource treatments, e.g. the clayey site in central Kenya in the end showed no yield differences between ± N, except for the 1.2 t C ha-1 yr-1 farmyard manure treatment. Yet, farmyard ma

Arbuscular mycorrhizal fungi are major components of soil microbiota and mainly interact with other microorganisms in the rhizosphere. Mycorrhiza establishment impacts the plant physiology and some nutritional and physical properties of the rhizospheric soil. These effects alter the development of the root or mycorrhizas resulting from the activity of soil microorganisms. The rhizosphere of mycorrhizal plants (mycorrhizosphere), is inhabited by large microbial activities responsible for several key ecosystem processes. This review is focused on the microbial interactions between mycorrhizal fungi and components of rhizosphere microbiota and highlight the agronomic potentialities of the Mycorrhiza Helper Bacteria on mycorrhiza formation. The main conclusion is that this MHB effect in the rhizosphere of mycorrhizal plants, enhance plant fitness and soil quality and are of great interest to ensure sustainable agricultural development and ecosystem functioning.

Rubber tree plantations (Hevea brasiliensis) cover large areas in the tropics. In historical producing regions like South Thailand, rubber has been planted by smallholders for three successive rotations lasting a total of 75 years. Despite possible consequences on topsoil, the long-term impacts of repeated rubber plantations on soil quality remain unknown. This study aims to better understand how various factors linked to long-term rubber land use and land use change affect topsoil physico-chemical properties and soil organic carbon (SOC) thermal stability. We focus on the effects of three factors: i. deforestation (change from forest to first rubber plantation); ii. the age of the rubber stand (immature vs mature); and iii. Long-term rubber cultivation (first, second or third successive rotation) over a chronosequence in farmers plots. Our results show that soil was deeply degraded after deforestation to a rubber plantation. Long-term rubber cultivation is also detrimental for the soil and has a more negative impact on soil physico-chemical properties and carbon dynamics, than the age of the rubber stand (e.g. on average, decrease of 50% of SOC content between forest and third rotation). At the third rotation, after 50 years of rubber cultivation, the quality of the 0–10 cm soil layer was very low, with an increase in SOC thermal stability. At this stage, logging practices upset the sustainability of the system. These impacts could be limited by less destructive practices during planting.

La valorisation des travaux analytiques conduits par le CIRAD sur l'île de la Réunion au cours de la période 2005 à 2012 a permis de préciser les fournitures en azote associées à la minéralisation de l'azote organique en l'absence d'apport d'azote exogène (témoins 0N). Quatre contextes pédoclimatiques sont décrits en intégrant différentes altitudes et pluviométries. A l'échelle de l'année, le prélèvement d'azote par la prairie associé à la minéralisation de l'azote du sol dépasse les 200 kg N/ha/an. Sur le littoral, ce prélèvement varie de 200 à 380 kg N/ha/an. A 1 600 m d'altitude, il varie de 170 à 280 kg N/ha/an. Ces quantités d'azote disponibles pour le couvert doivent être prises en compte dans les prévisions de fertilisation en lien notamment avec les profils de croissance de l'herbe observés à La Réunion. La variabilité observée sur les différents sites renforce la nécessité de compléter ces données par de nouvelles références issues de sites complémentaires et de les intégrer dans un modèle de prévision.

Resorption is the active withdrawal of nutrients before leaf abscission. This mechanism represents an important strategy to maintain efficient nutrient cycling; however, resorption is poorly characterized in old-growth tropical forests growing in nutrient-poor soils. We investigated nutrient resorption from leaves in 39 tree species in two tropical forests on the Guiana Shield, French Guiana, to investigate whether resorption efficiencies varied with soil nutrient, seasonality, and species traits. The stocks of P in leaves, litter, and soil were low at both sites, indicating potential P limitation of the forests. Accordingly, mean resorption efficiencies were higher for P (35.9%) and potassium (K; 44.6%) than for nitrogen (N; 10.3%). K resorption was higher in the wet (70.2%) than in the dry (41.7%) season. P resorption increased slightly with decreasing total soil P; and N and P resorptions were positively related to their foliar concentrations. We conclude that nutrient resorption is a key plant nutrition strategy in these old-growth tropical forests, that trees with high foliar nutrient concentration reabsorb more nutrient, and that nutrients resorption in leaves, except P, are quite decoupled from nutrients in the soil. Seasonality and biochemical limitation played a role in the resorption of nutrients in leaves, but species-specific requirements obscured general tendencies at stand and ecosystem level.

Rubber trees are the main source of natural rubber (NR). The area occupied by rubber plantations rose from 3.9 million ha in 1961 to 12.5 million ha in 2018. Both the expansion of rubber plantations in marginal zones (prone to biotic and abiotic stress), and long-term rubber tree cultivation in traditional areas, raise questions about the sustainability of NR production in a context of climate change. Our study set out to gain insights into the biogeochemical cycles in rubber plantations, for a better matching of fertilizer inputs to the dynamics of nutrient demand throughout rubber tree growth. Nutrient accumulation in tree biomass is a major component of the biological cycle in tree plantations. We studied the dynamics of biomass and nutrient accumulation in two chronosequences covering the whole lifespan of a plantation in Ivory Coast managed on a sandy soil at the SAPH site, and one on a clayey soil at the SOGB site. In total, 56 trees were destructively sampled in 2-, 5-, 20- and roughly 40-year-old stands. While the use of allometric relationships is common for estimating nutrient stocks in planted forests, this study was the first to provide allometric equations predicting nutrient stocks in rubber tree components. Allometric models were applied to the inventory of 4 commercial stands, for each age at each site, to estimate stand biomass and nutrient stocks. The current annual increments of nutrient stocks in tree biomass peaked between 2 and 5 years after planting. They reached 80 kg ha-1 yr-1 for N, 14 kg ha-1 yr-1 for P and 34 kg ha-1 yr-1 for K at SAPH (53, 7, and 39 kg ha-1 yr-1 respectively at SOGB), which highlighted the importance of an appropriate fertilization schedule for young rubber trees. At the clear-cut age (38–40 years), the amounts of nutrients accumulated in tree biomass were 970 kg N ha-1, 188 kg P ha-1, 366 kg K ha-1, 941 kg Ca ha-1 and 255 kg Mg ha-1 on the sandy soil at SAPH (907,118, 629 1499, and 375 kg ha-1 respectively on the clayey

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

Conservation agriculture (CA) is one strategy with which both sustainability and productivity can be achieved by improving soil health. However, linkages between practices, soil health and cropping system performance remain poorly disentangled. We assessed the relationships between soil health and cropping system performance for three maize-based cropping systems in New Caledonia. Two CA systems, one with direct seeding into a mixed species dead mulch (CA-DM) and one into a stylo living mulch (CA-LM), were compared to a conventional tillage (CT) system. CA vs. CT experiment started in 2011, whereas the differentiation between CA-DM and CA-LM was initiated in 2017 only. In 2018, soil health was evaluated using Biofunctool®, a set of ten in-field tools that assess soil carbon transformation, structure maintenance and nutrient cycling functions. The performance of the three cropping systems were assessed by monitoring weeds, maize growth and yield components. Structural equation modelling (SEM) was used to disentangle the links between agricultural management, soil health and cropping system performance. Soil structure maintenance and nutrient cycling functions were higher under CA-DM and CA-LM than under CT, and carbon transformation function was higher under CA-DM than under CT and CA-LM. Overall, the soil health index (SHI) was 1.3-fold higher under CA systems than under CT. Cropping system management had both direct and indirect effects on soil functioning and crop productivity leading to a 1.3-fold higher yield under CA than under CT. The direct and indirect effects of CA systems on soil health had positive impacts on ecosystem services (i.e., productivity, weed regulation and soil ecosystem services). Such integrative approaches that account for the relationships and possible trade-offs between cropping system components enable a better understanding of the effects and the performance of practices, and support adaptive agricultural management.

Plant diversification through crop rotation or agroforestry is a promising way to improve sustainability of agroecosystems. Nonetheless, criteria to select the most suitable plant communities for agroecosystems diversification facing contrasting environmental constraints need to be refined. Here, we compared the impacts of 24 different plant communities on soil fertility across six tropical agroecosystems: either on highly weathered Ferralsols, with strong P limitation, or on partially weathered soils derived from volcanic material, with major N limitation. In each agroecosystem, we tested several plant communities for diversification, as compared to a matching low diversity management for their cropping system. Plant residue restitution, N, P and lignin contents were measured for each plant community. In parallel, the soil under each community was analyzed for organic C and N, inorganic N, Olsen P, soil pH and nematode community composition. Soil potential fertility was assessed with plant bioassays under greenhouse controlled climatic conditions. Overall, plant diversification had a positive effect on soil fertility across all sites, with contrasting effects depending on soil type and legumes presence in the community. Communities with legumes improved soil fertility indicators of volcanic soils, which was demonstrated through significantly higher plant biomass production in the bioassays (+18%) and soil inorganic N (+26%) compared to the low diversity management. Contrastingly, communities without legumes were the most beneficial in Ferralsols, with increases in plant biomass production in the bioassays (+39%), soil Olsen P (+46%), soil C (+26%), and pH (+5%). Piecewise structural equation models with Shipley's test revealed that plant diversification impacts on volcanic soil fertility were related to soil N availability, driven by litter N. Meanwhile, Ferralsols fertility was related to soil P availability, driven by litter P. These findings underline the import

Cet article est basé sur des données empiriques qui permettent de caractériser, pour chaque exploitation agricole, les pratiques de gestion de la fertilité effectivement utilisées sur les parcelles cultivées au cours de l'année agricole 2016/17. A partir des budgets de culture, établis pour toutes les parcelles, la part des charges de fertilisation est mise en relation avec les marges brutes dégagées par culture.

La dégradation des terres liée à l'intensification agricole, principalement due à la baisse de la fertilité des sols et à l'érosion, est devenue une problématique majeure en Nouvelle-Calédonie. Le contexte insulaire et les spécificités pédoclimatiques rendent en outre les enjeux d'autosuffisance alimentaire, de préservation des agroécosystèmes et de la biodiversité, d'autant plus prégnants. Les systèmes de culture (sdc) doivent donc évoluer en mobilisant les processus biologiques afin d'être viables, performants et durables. L'agriculture de conservation (AC) consiste en un ensemble de pratiques culturales basé sur trois principes : une réduction, voire une suppression du travail du sol, une couverture végétale du sol permanente et une diversification des espèces cultivées. L'AC peut répondre à ces problématiques en alliant durabilité et productivité, et en favorisant un certain nombre de services écosystémiques. A travers une démarche originale intégrant approches fonctionnelle et systémique, cette thèse vise à quantifier les relations entre pratiques, fonctions et services écosystémiques au sein de sdc complexes. Dans le contexte spécifique de la côte ouest de la Nouvelle-Calédonie, afin de savoir si l'AC pourrait maximiser la fourniture de services écosystémiques, trois questions sont apparues importantes à aborder : quels sont les impacts des pratiques de l'AC sur la santé du sol et les performances agronomiques de sdc ?, quels sont les effets de l'AC sur la biodiversité fonctionnelle (macrofaune) ?, et quelles sont les performances et l'efficience d'utilisation des ressources de sdc en AC notamment sous couvert végétal vivant ? Afin de répondre aux deux premières questions, une expérimentation système, initiée en 2011, a permis de comparer en 2018 trois sdc en production de maïs : un sdc en monoculture et en labour, représentant la pratique de référence de la région (CT), un sdc en AC sous couvert végétal mort (mélange de 4 espèces annuelles) (CA-DM), et un sdc

Les engrais azotés ont contribué de manière substantielle à la sécurité alimentaire et à la nutrition mondiales. Toutefois, l'azote qu'ils contiennent peut être accumulé en quantités excessives dans les écosystèmes ou dans l'atmosphère ; il entraîne alors des impacts environnementaux négatifs. Il existe souvent une grande disparité entre ce qui est fourni par la fertilisation et ce qui est utilisé par les cultures, ce qui entraîne de faibles rendements d'efficience de l'utilisation de l'azote (NUE) des engrais. Le recyclage des résidus organiques dans les agroécosystèmes pourrait être une alternative ou un complément prometteur aux engrais synthétiques, et un moyen de promouvoir une durabilité économique et agricole circulaire. L'objectif général de cette thèse de doctorat était dans un premier temps de dresser un bilan complet et dynamique des entrées et sorties d'azote dans un site expérimental fortement instrumenté cultivé en canne à sucre. Dans un second temps, il a s'agit d'étudier le devenir de l'azote apporté avec deux types d'engrais organiques (lisier de porc et boues d'épuration méthanisées chaulées séchées) dans ce système sol-plante en comparaison d'un apport d'engrais de référence (urée), pour la canne à sucre à la Réunion. L'évolution de la biomasse et de la minéralomasse de N a été mesurée au pas de temps mensuel au cours des 24 mois de l'étude dans les 4 traitements distincts (non fertilisé, urée, lisier de porc, boues de STEU). Les résultats a révélé que la part de l'azote de la plante contenu dans les racines pouvait être considérable et représenter jusqu'à 65 % et 104 % de l'azote mesurée dans la biomasse aérienne des traitements non-fertilisé et fertilisé. Un ensemble de méthodes peu destructives a été proposé afin d'estimer le NUE tout au long du cycle de croissance de la canne à sucre. Les contributions respectives de différentes sources de N pour la nutrition de la canne ont été déterminées à l'aide de microplacettes enrichis en 15N. Le pailli

Resorption is the active withdrawal of nutrients before leaf abscission. This mechanism represents an important strategy to maintain efficient nutrient cycling; however, resorption is poorly characterized in old-growth tropical forests growing in nutrient-poor soils. We investigated nutrient resorption from leaves in 39 tree species in two tropical forests on the Guiana Shield, French Guiana, to investigate whether resorption efficiencies varied with soil nutrient, seasonality, and species traits. The stocks of P in leaves, litter, and soil were low at both sites, indicating potential P limitation of the forests. Accordingly, mean resorption efficiencies were higher for P (35.9%) and potassium (K; 44.6%) than for nitrogen (N; 10.3%). K resorption was higher in the wet (70.2%) than in the dry (41.7%) season. P resorption increased slightly with decreasing total soil P; and N and P resorptions were positively related to their foliar concentrations. We conclude that nutrient resorption is a key plant nutrition strategy in these old-growth tropical forests, that trees with high foliar nutrient concentration reabsorb more nutrient, and that nutrients resorption in leaves, except P, are quite decoupled from nutrients in the soil. Seasonality and biochemical limitation played a role in the resorption of nutrients in leaves, but species-specific requirements obscured general tendencies at stand and ecosystem level.

Rubber trees are the main source of natural rubber (NR). The area occupied by rubber plantations rose from 3.9 million ha in 1961 to 12.5 million ha in 2018. Both the expansion of rubber plantations in marginal zones (prone to biotic and abiotic stress), and long-term rubber tree cultivation in traditional areas, raise questions about the sustainability of NR production in a context of climate change. Our study set out to gain insights into the biogeochemical cycles in rubber plantations, for a better matching of fertilizer inputs to the dynamics of nutrient demand throughout rubber tree growth. Nutrient accumulation in tree biomass is a major component of the biological cycle in tree plantations. We studied the dynamics of biomass and nutrient accumulation in two chronosequences covering the whole lifespan of a plantation in Ivory Coast managed on a sandy soil at the SAPH site, and one on a clayey soil at the SOGB site. In total, 56 trees were destructively sampled in 2-, 5-, 20- and roughly 40-year-old stands. While the use of allometric relationships is common for estimating nutrient stocks in planted forests, this study was the first to provide allometric equations predicting nutrient stocks in rubber tree components. Allometric models were applied to the inventory of 4 commercial stands, for each age at each site, to estimate stand biomass and nutrient stocks. The current annual increments of nutrient stocks in tree biomass peaked between 2 and 5 years after planting. They reached 80 kg ha-1 yr-1 for N, 14 kg ha-1 yr-1 for P and 34 kg ha-1 yr-1 for K at SAPH (53, 7, and 39 kg ha-1 yr-1 respectively at SOGB), which highlighted the importance of an appropriate fertilization schedule for young rubber trees. At the clear-cut age (38–40 years), the amounts of nutrients accumulated in tree biomass were 970 kg N ha-1, 188 kg P ha-1, 366 kg K ha-1, 941 kg Ca ha-1 and 255 kg Mg ha-1 on the sandy soil at SAPH (907,118, 629 1499, and 375 kg ha-1 respectively on the clayey

Litter-feeding soil animals are notoriously neglected in conceptual and mechanistic biogeochemical models. Yet, they may be a dominant factor in decomposition by converting large amounts of plant litter into faeces. Here, we assess how the chemical and physical changes occurring when litter is converted into faeces alter their fate during further decomposition with an experimental test including 36 combinations of phylogenetically distant detritivores and leaf litter of contrasting physicochemical characteristics. We show that, across litter and detritivore species, litter conversion into detritivore faeces enhanced organic matter lability and thereby accelerated carbon cycling. Notably, the positive conversion effect on faeces quality and decomposition increased with decreasing quality and decomposition of intact litter. This general pattern was consistent across detritivores as different as snails and woodlice, and reduced differences in quality and decomposition amongst litter species. Our data show that litter conversion into detritivore faeces has far-reaching consequences for the understanding and modelling of the terrestrial carbon cycle.

Intensive coffee production is accompanied by several environmental issues, including soil degradation, biodiversity loss, and pollution due to the wide use of agrochemical inputs and wastes generated by processing. In addition, climate change is expected to decrease the suitability of cultivated areas while potentially increasing the distribution and impact of pests and diseases. In this context, the coffee microbiota has been increasingly studied over the past decades in order to improve the sustainability of the coffee production. Therefore, coffee associated microorganisms have been isolated and characterized in order to highlight their useful characteristics and study their potential use as sustainable alternatives to agrochemical inputs. Indeed, several microorganisms (including bacteria and fungi) are able to display plant growth-promoting capacities and/or biocontrol abilities toward coffee pests and diseases. Despite that numerous studies emphasized the potential of coffee-associated microorganisms under controlled environments, the present review highlights the lack of confirmation of such beneficial effects under field conditions. Nowadays, next-generation sequencing technologies allow to study coffee associated microorganisms with a metabarcoding/metagenomic approach. This strategy, which does not require cultivating microorganisms, now provides a deeper insight in the coffee-associated microbial communities and their implication not only in the coffee plant fitness but also in the quality of the final product. The present review aims at (i) providing an extensive description of coffee microbiota diversity both at the farming and processing levels, (ii) identifying the “coffee core microbiota,” (iii) making an overview of microbiota ability to promote coffee plant growth and to control its pests and diseases, and (iv) highlighting the microbiota potential to improve coffee quality and waste management sustainability.

The symbiotic association (plant-soil-microorganisms) has an important role in nitrogen (N) and phosphorus (P) uptake. The main objective of this study is to assess the potential of fungal and rhizobial symbionts as well as the importance of plant-soil-microorganism interactions on microbial dynamics. The upland rice and the beans were cultivated in mono or in co-culture using the rhizospheric soil of the upland rice and beans collected on plots treated with different levels of organic and mineral fertilizers. What about saying: Microbial (fungal and rhizobial) inoculate were constituted by root fragments (rice or bean) collected from previous crop and coded as I1 (root fragments from rice), I2 (root fragments from bean) and I3 (mixed root fragments from rice and bean). The results showed that soils inoculated with I1 and I3, were characterized by high phosphatase activity. These two treatments enhance also the amount of nitrogen and phosphorus in the aerial part of upland rice intercropped with bean. These results suggest that the bean with its symbiont can be considered as ecological engineers that stimulate the biological functioning of soils and is beneficial for upland rice cultivation.

Many studies have shown that introducing N2-fixing trees (e.g. Acacia mangium) in eucalypt plantations can increase soil N availability as a result of biological N2 fixation and faster N cycling. Some studies have also shown improved eucalypt P nutrition. However, the effects of N2-fixing trees on P cycling in tropical soils remain poorly understood and site-dependent. Our study aimed to assess the effects of planting A. mangium trees in areas managed over several decades with eucalypt plantations on soil organic P (Po) forms and low molecular weight organic acids (LMWOAs). Soil samples were collected from two tropical sites, one in Brazil and one in the Congo. Five different treatments were sampled at each site: monospecific acacia, monospecific eucalypt, below acacias in mixed-species, below eucalypts in mixed-species as well as native vegetation. Po forms and LMWOAs were identified in sodium hydroxide soil extracts using ion chromatography and relationships between these data and available P were determined. At both sites, the concentrations of most Po forms and LMWOAs were different between native ecosystems and monospecific eucalypt and acacia plots. Also, patterns of Po and LMWOAs were clearly separated, with glucose-6-P found mainly under acacia and phytate and oxalate mainly under eucalypt. Despite the strongest changes occurred at site with a higher N2 fixation and root development, acacia introduction was able to change the profile of organic P and LMWOAs in <10 years. The variations between available Pi, Po and LMWOA forms showed that P cycling was dominated by different processes at each site, that are rather physicochemical (via Pi desorption after LMWOAs release) at Itatinga and biological (via organic P mineralization) at Kissoko. Specific patterns of Po and LMWOAs forms found in soil sampled under acacia or eucalypt would therefore explain the effect of acacia introduction in both sites.

La contrainte majeure évoquée par les exploitations agricoles des zones cotonnières est la baisse progressive de la capacité des sols cultivables à produire à cause de la mauvaise gestion de la fertilité. L'intégration agriculture-élevage en est une solution à travers l'amendement de la matière organique dont elle offre. L'objectif de l'étude était d'identifier les déterminants de l'adoption de la pratique de l'intégration agriculture-élevage au sein des exploitations agricoles. Une analyse des caractéristiques socio-économiques d'un échantillon constitué de 120 exploitations sélectionnées de façon aléatoire a été réalisée. Des statistiques ont été utilisées pour décrire les caractéristiques socio-économiques des unités de recherches enquêtées. Un modèle Probit Bivariée a été utilisé pour analyser les facteurs déterminants l'adoption de l'intégration agriculture-élevage. Les résultats ont révélé que la présence de légumineuse dans l'assolement, l'alphabétisation, la possession d'un moyen de transport, la proximité d'un point d'eau en saison sèche, le nombre de bovin, la possession de la radio, et le droit de propriété ont d'effet positif dans l'adoption des pratiques d'intégration agriculture-élevage. Par contre, la taille de l'exploitation a un effet négatif mais significatif. Il urge donc pour les institutions de recherche et les décideurs de prendre en compte ces facteurs, afin d'apporter de l'innovation pour une meilleure adoption de ces pratiques dans une perspective de gestion durable de la fertilité du sol.

Cet article est consacré à l'utilisation des fumures organiques et des engrais achetés par les exploitations agricoles familiales des Hautes de Madagascar. Quantités épandues, choix des cultures et des types de terres permettent de caractériser, en partie tout au moins, les stratégies de gestion de la fertilité des sols développées par les exploitants.

Litter-feeding soil animals are notoriously neglected in conceptual and mechanistic biogeochemical models. Yet, they may be a dominant factor in decomposition by converting large amounts of plant litter into faeces. Here, we assess how the chemical and physical changes occurring when litter is converted into faeces alter their fate during further decomposition with an experimental test including 36 combinations of phylogenetically distant detritivores and leaf litter of contrasting physicochemical characteristics. We show that, across litter and detritivore species, litter conversion into detritivore faeces enhanced organic matter lability and thereby accelerated carbon cycling. Notably, the positive conversion effect on faeces quality and decomposition increased with decreasing quality and decomposition of intact litter. This general pattern was consistent across detritivores as different as snails and woodlice, and reduced differences in quality and decomposition amongst litter species. Our data show that litter conversion into detritivore faeces has far-reaching consequences for the understanding and modelling of the terrestrial carbon cycle.

Intensive coffee production is accompanied by several environmental issues, including soil degradation, biodiversity loss, and pollution due to the wide use of agrochemical inputs and wastes generated by processing. In addition, climate change is expected to decrease the suitability of cultivated areas while potentially increasing the distribution and impact of pests and diseases. In this context, the coffee microbiota has been increasingly studied over the past decades in order to improve the sustainability of the coffee production. Therefore, coffee associated microorganisms have been isolated and characterized in order to highlight their useful characteristics and study their potential use as sustainable alternatives to agrochemical inputs. Indeed, several microorganisms (including bacteria and fungi) are able to display plant growth-promoting capacities and/or biocontrol abilities toward coffee pests and diseases. Despite that numerous studies emphasized the potential of coffee-associated microorganisms under controlled environments, the present review highlights the lack of confirmation of such beneficial effects under field conditions. Nowadays, next-generation sequencing technologies allow to study coffee associated microorganisms with a metabarcoding/metagenomic approach. This strategy, which does not require cultivating microorganisms, now provides a deeper insight in the coffee-associated microbial communities and their implication not only in the coffee plant fitness but also in the quality of the final product. The present review aims at (i) providing an extensive description of coffee microbiota diversity both at the farming and processing levels, (ii) identifying the “coffee core microbiota,” (iii) making an overview of microbiota ability to promote coffee plant growth and to control its pests and diseases, and (iv) highlighting the microbiota potential to improve coffee quality and waste management sustainability.

The symbiotic association (plant-soil-microorganisms) has an important role in nitrogen (N) and phosphorus (P) uptake. The main objective of this study is to assess the potential of fungal and rhizobial symbionts as well as the importance of plant-soil-microorganism interactions on microbial dynamics. The upland rice and the beans were cultivated in mono or in co-culture using the rhizospheric soil of the upland rice and beans collected on plots treated with different levels of organic and mineral fertilizers. What about saying: Microbial (fungal and rhizobial) inoculate were constituted by root fragments (rice or bean) collected from previous crop and coded as I1 (root fragments from rice), I2 (root fragments from bean) and I3 (mixed root fragments from rice and bean). The results showed that soils inoculated with I1 and I3, were characterized by high phosphatase activity. These two treatments enhance also the amount of nitrogen and phosphorus in the aerial part of upland rice intercropped with bean. These results suggest that the bean with its symbiont can be considered as ecological engineers that stimulate the biological functioning of soils and is beneficial for upland rice cultivation.

Cet article fait suite à celui publié dans le JAE n°8 et présente des résultats obtenus dans le cadre du projet de recherche SECuRE (Soil ECological function REstoration to enhance agrosystem services in rainfed rice cropping systems in agroecological transition), financé par la fondation Agropolis. La production et l'acquisition de fumures organiques par les exploitations agricoles sont caractérisées ici dans leur diversité. L'analyse des pratiques montre les logiques suivies. La variabilité observée est forte, notamment en terme de quantités disponibles, qui suggère une gamme de propositions adaptées de la part de la recherche et du développement, pour améliorer ces pratiques qui sont la clef de voute de la gestion de la fertilité des sols et de la durabilité des systèmes de culture.

The present study aimed to evaluate the correlations between productivity and eucalyptus drought (DR) response between soil attributes in two distinct climatic types in Brazil. For this, 24 experiments were installed in Brazil with four common clones in all the experiments to obtain strong edaphoclimatic contrasts, and, thus, to measure the productivity and the response to drought and to describe its relationship with the attributes of the soils. Two climatic groups were evaluated: Wet (precipitation rate: evapotranspiration between 1.0 to 2.5) and Sub-Humid (precipitation rate: evapotranspiration between 0.5 to 1.0). The attributes of the evaluated soils were: Sand, Silt, Clay, organic matter (O.M.), cation exchange capacity (CEC). For sites located in the wet climate class, CVWB correlated negatively with O.M. and clay, and positively with the sand. For DR, the correlations were observed for the Sub-Humid climate for the CEC and Sand variables, and for the Humid climate, no correlations were observed between the attributes of soils with DR.

This work showed for the first time that organic nutrient transformation techniques based on locally available materials (manure, green waste and advanced biochar) can increase fertilizing efficiency of the resulting substrate by a factor of three compared with other organic amendments without biochar. We used three different composting methods to investigate the techniques of organic nutrient transformations; i) conventional composting (composting process completed without turning the piles) ii) aerobic composting (composting process with manual turning of piles) and iii) bokashi composting (anaerobic lacto-fermentation). Composting was carried out in the absence (compost alone) and the presence of biochar (co-composted). Biochar was produced locally from an invasive forest shrub 'Eupatorium adenophorum'. A pot trial with maize grown in silty loam soil was carried out to investigate the agronomic effect produced using three above-mentioned composting methods that were compared with conventional mineral fertilizers (NPK). Significant effects of co-composted bokashi-biochar (60 t ha−1) were observed on maize growth, which increased biomass by 243% compared to mineral NPK, also showing better growth effects than conventional and aerobic composting amendments. Improved soil available nutrients (available P and other exchangeable base cations (K+, Ca2+ and Mg2+)) were probably the cause of the superior growth effect of co-composted bokashi-biochar.

Highly productive monoculture coffee (Coffea arabica L.) farms have rapidly expanded since the 1990s in Yunnan Province, China. In 2013, in order to initiate a large-scale transition towards more sustainable coffee growing practices, local government in southern Yunnan started distributing free shade tree seedlings to all coffee farmers in their jurisdictions. This study highlights the impact of three of these promoted shade tree species (Cinnamomum camphora, Bishofia javanica and Jacaranda mimosifolia) on soil fertility and coffee production only four years after their distribution to coffee farmers. Materials and methods Soil samples in the 0-20 cm soil layer were tested for chemical composition (soil organic matter, pH, total N, available P, exchangeable K, Ca and Mg), soil communities (free-living nematodes and microbial communities) and soil enzyme activities (β-glucodidase, N-acetyl-glucosaminidase and acid phosphatase) under shade trees (6 replicates per tree species) and in open areas (15 replicates), both in coffee rows and inter-rows, once during the rainy and once during the dry season. Additionally, we characterized root systems and soil water profiles to a depth of 1.2m, monitored litterfall for one year, as well as coffee production for two years. Major results We detected a clear positive impact of all three shade tree species on soil chemical, biological and biochemical fertility, despite the marked effect of 20 years of high mineral fertilizer inputs. In particular, we measured higher pH and soil organic matter; similar or higher soil enzyme activities throughout the year; more abundant fungi communities throughout the year; and more abundant microbial communities during the dry season below shade trees than in open areas. Furthermore, coffee trees shaded by B. javanica and J. mimosifolia yielded as much as open coffee trees. On the other hand, coffee trees shaded by C. camphora yielded less than open coffee trees, most likely as a result of high ro

Ce travail de thèse s'inscrit dans un contexte d'agriculture durable qui vise à consommer de moins en moins d'intrants tout en maintenant des niveaux de production de biomasse croissante, aussi bien en termes de quantité que de qualité. De tels niveaux ne peuvent être atteints qu'à la condition que les végétaux cultivés puissent se développer dans des conditions optimales, et notamment avoir accès aux éléments minéraux essentiels à leur croissance. De nombreux facteurs interviennent dans la mise à disposition des nutriments présents dans le sol pour les cultures comme le pH ou le potentiel d'oxydo-réduction (Eh). Plusieurs auteurs ont montré que les plantes fonctionnaient au sein d'une gamme interne Eh/pH bien spécifique et qu'elles ont la capacité de modifier ces paramètres dans la rhizosphère pour assurer l'homéostasie intracellulaire. Cette étude a pour objectif final de contribuer à la compréhension des effets du potentiel redox du sol sur la mobilité et la mise à disposition des nutriments pour la plante. La difficulté réside dans la nécessité de réaliser les mesures aussi bien pour le Eh que le pH, in situ dans le sol et en présence de plantes. Bien que connaître le Eh sol soit essentiel, sa mesure reste complexe en raison du manque de fiabilité des protocoles proposés, de l'hétérogénéité du système poral du sol et de la variabilité temporelle des conditions pédoclimatiques. Ainsi, le premier défi relevé par ces travaux a été d'ordre métrologique. Cette thèse propose des avancées pratiques sur la mesure du Eh dans les sols en utilisant des électrodes combinées. Le dispositif a été appliqué au suivi d'une culture en pots (1L) de tournesols placés pendant 70 jours dans différentes conditions pédoclimatiques. Cette campagne a notamment permis d'évaluer les relations existantes entre le couple Eh /pH du sol et la forme chimique disponible des principaux nutriments présents dans celui-ci (N, P, K, Ca, Mg, S, Fe, Mn, B, Zn, Cu et Mo). Les travaux ont ainsi montré qu

It is said that trees improve soil fertility. It might be due to biological interactions with micro-organisms and especially with arbuscular mycorrhizal fungi. Is-it the case with olive trees in south of France? The field experiments were conducted in South of France at INRA DiaScope experimental unit. Durum wheat was sown in 3 conditions: (AF) yearly pruned olive orchard, (AF+) never pruned olive orchard, (C) open field. Mycorrhizal analysis was performed on 6 durum wheat cvs. For each treatment and cv, 3 replicates of 90 root fragments were analyzed at the LSTM lab. All the root fragments coming from AFs treatments were colonized, while 96.4% for C. The intensity of AMF colonization, thus the % of the root fragment length being colonized, was significantly higher in AFs treatments (+51% compared to C), as the arbuscular abundance in the root system (+74% compared to C). A wide variability was observed among genotypes within the same treatment. The intensity of AMF colonization ranged from 11% to 57% in C, and from 55% to 74% in AF. The genotype showing the highest intensity of AMF colonization and arbuscular abundance in AF had the lowest values in C. AM fungi are known to be an essential component of sustainable agricultural ecosystems (Jeffries et al. 2003). Olive trees seem to play the role of permanent reservoir of AMF diversity, available to associated cereals. Arbuscular mycorrhizal (AM) fungi help the understorey crop to catch soil nutrients (Wahbi et al. 2016).

Basé sur des cas d'étude au Sénégal, ce chapitre dresse le bilan de 15 années de recherches sur le fonctionnement des sols d'agrosystèmes associant plantes cultivées (milarachide) et arbustes natifs au Sahel. Les travaux, publiés pour la plupart, ont montré que Guiera senegalensis et Piliostigma reticulatum redistribuent l'eau dans le sol, stimulent les microorganismes du sol et génèrent des îlots de fertilité au bénéfice de la culture associée. Ainsi, les rendements des cultures sont augmentés, y compris en absence de fertilisants : jusqu'à +137 % pour le mil en présence de P. reticulatum à Nioro-du-Rip. Cela justifie l'intérêt de maintenir ces arbustes dans les champs en appliquant une gestion agroécologique.

Agroforestry systems (AFs), where agricultural and livestock crops are associated with woody plants, are known as sustainable systems, that conserve biodiversity and improve the provision of ecosystem services without compromising productivity. This work focuses mainly on cacao AFs, which have been related to different ecosystem services in tropical regions. Especially, our study focuses on the ability of the cacao AFs to improve soil ecosystem services in the Colombian Amazon region. We focused on soil ecosystems ecosystem services in the Colombian Amazonia because: of the social importance of cacao production system in the study region, specifically within the post conflict context; the lack of knowledge on the capacity of cacao AFs to offer soil ecosystem services in the study zone and its capacity in restoring ecosystem services in degraded soils. Aim The objective of our work was to evaluate the soil quality in different cacao agroforestry systems in the Colombian Amazonia, and to compare these evaluated soil quality of soil quality in Forest and Pasture. Material and methods The study was conducted at the Macagual Amazon Research Center, located west of the Colombian Amazon. We evaluated soil quality in four types of AFs Cacao, presenting different establishment, composition and structural characteristics; but also in a plot of native forest composed of characteristic species of the area, and in a plot of pasture composed of grasses. In the different plot of each land use, we evaluated the diversity of macrofauna, the morphology of aggregate, the physical properties and the soil chemistry. We summarized these variables in a General Indicator of Soil Quality GISQ, characterizing soil quality in the different land uses. Major results and Conclusion It was found that the level of intensification among land uses (Bosque>AFs>Pasture) affects the decrease of the macrofauna populations, which was related to soil compaction (physical properties). Chemical fertility im

Trees are usually eliminated in field due their possible competition with crops for water and nutrients. Our work aimed to investigate how to manage S. senegal trees to optimize their association with crops. A field trial was conducted under natural conditions in a S. senegal plantation 10 years old. Investigations were conducted during two years to evaluate the effect of S. senegal trees management on gum arabic yield, associated cowpea yield, soil mycorrhizal fungi spores density and enzymes activities reflecting soil fertility such as fluorescein diacetate (FDA), acid phosphatase and dehydrogenase. Four treatments of pruning were applicated (control, shoots, roots, shoots and roots pruning) and tapped in november. Soil samples were collected during dry and wet seasons at 0-25 cm layer. Cowpeas were sown at the beginning of rainy season in rows 0.5 m apart. Results showed that shoots pruning significantly increased gum arabic while a negative effect of roots pruning was noted. The presence of S. senegal increased soil fertility and cowpea yield. Any significant effect of treatments was noted on pods yield during the first year. However, shoots pruning, shoot and roots pruning increased significantly pods yield during the second year. Shoots and roots pruning seemed to decrease FDA and spores density depending on the season. Our results showed that shoots and roots pruning increased the positive effect on soil fertility and the association of S. senegal with annual crops.

Conventional, intensively managed coffee monocultures are environmentally damaging. The use of shade trees and organic management are welcome options to reduce coffee physiological stress, reduce synthetic inputs and restore soil biological balance. However, whether the effects of shade trees on soil functioning would be similar for different coffee management practices should be investigated. Here, we measured soil total C and N, inorganic N, Olsen P, pH, biomass produced in bioassay, nematode and microarthropod communities under three shade types (unshaded coffee, shaded with Terminalia amazonia, and shaded with Erythrina poepiggiana) combined with two management practices (organic and conventional) in a 17- year old experimental coffee plantation in Turrialba (Costa Rica). Under conventional management, soil nutrient availability and fauna densities were higher under shade, regardless of the shade tree species (Fig 1). Under organic management, only Erythrina, a heavily pruned, N2-fixing species, had increased soil nutrient availability and fauna density, while Terminalia shade had a null or negative impact. Soil N availability was linked to bacteria-feeding nematodes while soil P availability was more linked to detritivorous microarthropods. Higher fertility was recorded in soil with balanced foodwebs. This study highlights the importance of the choice of shade tree species for soil fertility in low input systems, more so than in fertilized systems.

To produce charcoal and prevent the deforestation around Kinshasa (Gond et al., 2017), 7,700 ha of Acacia auriculiformis were planted on savannah ecosystems, in 1987 (Bateke Plateau, DR Congo). Since 1995, the plantation was managed using the rotational woodlot system alternating agricultural and charcoal production on the same area (Kimaro et al., 2007). The 7,700 ha produced a large amounts of charcoal, cassava and maize during many years (Bisiaux et al., 2009). However, farmers have observed for a while a decline in wood and crop productivity. The aim of this study was to compare chemical properties of soils in six acacia stands in two farms having undergone different agroforestry trajectories: - one 22-year-old acacia stand, never-harvested; 4 stands in their 2nd rotation after 1 cropping cycle; and 1 stand in its 3rd rotation after 2 cropping cycles - and soils in the native control savannah. Compared to the original savannah, all acacia stands showed an increase in soil C, N and N-NO3- contents, but a decline in soil pH and exchangeable cations, and an increase in exchangeable Al and CEC (Fig 1). To maintain the sustainability of the system, we recommend different practices in order to improve the nutrient balance and decrease the soil acidity. Such practices are the debarking of tree stems before carbonization, the restitution of small branches and charcoal residues to the soil, and the supply of natural rock phosphate (Dubiez et al., 2018).

Agroforestry systems have shown promising advantages in providing a number of key ecosystem services and many of them are directly linked with the soil compartment, such as fertility maintenance, carbon sequestration, erosion and landslide mitigation, fungi/bacteria-borne pest control, preservation of soil habitats etc. Today, managing a multifunctional agroforestry system has been a key quest for both researchers and practitioners. This is a challenging issue as it covers multiple disciplines stretching from biophysical to socio-economical domains. For this goal, this work will present a framework encompassing and highlighting some key issues on the multifunctionality of agroforestry systems, at both temperate and tropical conditions, with a focus on ecosystem services involving belowground functions. Bibliographical metrics based evidences will be presented showing the state-of-the-art and knowledge gaps in R & D on multifunctionality of worldwide agroforestry. Roadmap and emerging methodologies for optimisation of our management for promoting such multifunctionality are proposed and discussed.

Beninese smallholders associate food or cash crops with young oil palm stands to reduce field maintenance costs and gain income before the oil palm comes into production. However, little is known about the effects of these agroforestry systems on nutritional and growth status of the tree at end of its juvenile phase although it is well known that the tree production could be affected by the management in juvenile phase. We selected 15 plantations where the crop succession associated with the trees was mostly based on maize, cassava, tomato and pineapple respectively. Nutrient contents in soil and tree leaves, and the vegetative growth of the tree were examined at end of juvenile phase. We found that N and P nutrition of young palms was satisfactory but K nutrition was deficient in all systems especially in tomato and pineapple ones. There was a significant correlation between K contents in soil and palm tree leaves. In the pineapple- and tomato-based systems, the amount of K fertilizer did not compensate the exportations by the crop. We concluded that competition for K are particularly important in pineapple- and tomato-based systems although fertilizer inputs were the highest. Trade-offs between profitability of these associated crops and the productive performance of the tree could be sought. A better adaptation of mineral fertilization could help in satisfying these compromises.

Background: In the Sudanian region of North Cameroon, population growth has led to reduced fallow periods, soil fertility and trees (Peltier et al., 1993). Since 1984, CIRAD, Irad and Sodecoton have been testing techniques for planting tree legumes to restore soil fertility (Harmand et al., 2017). A 15-year-old A. senegal plot was harvested in 2011.It produced 1200 kg/ha of gum arabic for 8 years (750 €/ha) and 40 m3/ha of fuel-wood for 15 years (1100 €/ ha) (D'Andous et al., 2013). Aims: After A. senegal were harvested, we studied the evolution of chemical soil properties and the production of successive crops. Mat. & methods: On sandy ferruginous acidic soil, rainfall 1000 mm/year, the farmer planted successive crops of maize, cotton and groundnuts (2011-2013). In 2011 & 2015, the soil was analyzed (composite) on 2 plots of 12 x12 m after A. Senegal (Post=fallow = Pf) and on 2 control plots continuously cultivated (Cc). Results: Crop production was much higher for all 3 years and soil chemical properties (C, N, pH, CEC) were higher in Pf than in Cc (Table 1). Conclusion: Further studies are needed to determine for how long crop cultivation remains profitable (Dubiez et al. 2018). This will pave the way for farm and landscape management including plots planted with tree legumes, to improve biodiversity, carbon storage, wood energy production, food and cash crops of the territories, while limiting population migration and the destruction of the last Sudanese natural ecosystems.

In this study, soil organic P (Po) and low-molecular-weight organic acids (LMWOAs) were quantified under different land uses in order to investigate the effect of N2 fixing tree introduction on phosphorus cycle. Soils were collected from plantations of pure acacia (Ac), pure eucalyptus (Euc) or both species (50/50) and original savannahs (S) that were located in Brazil (low P, high N and high C soil) and in Congo (high P. low N and low C soil). Po and LMWOAs were identified in sodium hydroxide soil extracts with ion chromatography (IC). Phosphate monoesters as AMP and glucose-6-phosphate (G6P) were the main Po forms in both sites. Phytate, ATP and fructose-bisphosphate (FrucbisP) were also present as well as the mineral form of pyrophosphate (PrP). Malate, oxalate and malonate were the major components of LMWOA fraction in the two soils. Citrate was also present at low concentrations. lnterresingly, phytate concentrations were always decreased under acacia plantations. This could result from a better mineralisation or lower inputs into these soils. In mixed stands, the effect of acacia introduction on Po and LMWOAs composition is more pronounced in high P than in low P soil, due to a much better N, fixation. Our results highlight that the introduction of a legume tree is able to strongly modify the composition of Po and LMWOAs in soil even after a first short-time rotation, especially when the rate of N2 fixation is high.

Harvest residue management is a key issue for the sustainability of Eucalyptus plantations established on poor soils. Soil microbial communities contribute to soil fertility by the decomposition of the organic matter (OM), but little is known about the effect of whole-tree harvesting (WTH) in comparison to stem only harvesting (SOH) on soil microbial functional diversity in Eucalyptus plantations. We studied the effects of harvest residue management (branches. leaves. bark) of Eucalvptus grandis trees on soil enzymatic activities and community-level physiological profiles in a Brazilian plantation. We measured soil microbial enzymatic activities involved in OM decomposition and we compared the community level physiological profiles (CLPP ) of the soil microbes in WTH and SOH plots. WTH decreased enzyme activities and catabolic potential of the soil microbial community. Furthermore, these negative effects on soil functional diversity were mainly observed below the 0-5 cm layer (5- 10 and 10-20 cm), suggesting that WTH can be harmful to the soil health in these plantations.

Belowground interactions in mixed forest plantations remain poorly understood as that of short-tenn nitrogen (N) transfer from N-fixing trees to non-N-fixing trees (Non-NFT) depending on nutrient availability. We investigated in this facilitation process met the Stress Gradient Hypothesis. which predicts that under stressful environmental conditions competition decreases and facilitation increases. A 15N pulse-labelling study was conducted in a five-year-old mixture of 50% Eucalyptus grandis x E. urophylla and 50% Acacia mangium with the hypothesis of higher transfer from acacia when no fertilization was applied. A complete randomized block design was set up with three replicates of fertilized and non-fertilized mixture. In each treatment of each block, a labeled solution of potassium nitrate (98 atom% 15N-N03) was injected into the stem of an Acacia tree with the same basal area as the average of the stand. The x (15N) was monitored over two months in each labeled acacia and four neighboring eucalypts. For both species, young leaves and tine roots were sampled at 7.14 and 30 days after injection. After 60 days. the x (15N) was determined in the wood, bark, branches, total foliage and fine roots of the 6 labeled acacias and 12 eucalypts trees The preliminary results showed that complete absorption of the labeled solution occurred between 28 and 60 days after labeling depending on Acacia trees and treatments. The dynamics in the proportion of Eucalyptus N derived from transfer will give insights into how this process may promote N nutrition of non-NFTs growing in unfertile tropical soils.

Climate change and human pressures are changing the global distribution and extent of intermittent rivers and ephemeral streams (IRES), which comprise half of the global river network area. IRES are characterized by periods of flow cessation, during which channel substrates accumulate and undergo physico‐chemical changes (preconditioning), and periods of flow resumption, when these substrates are rewetted and release pulses of dissolved nutrients and organic matter (OM). However, there are no estimates of the amounts and quality of leached substances, nor is there information on the underlying environmental constraints operating at the global scale. We experimentally simulated, under standard laboratory conditions, rewetting of leaves, riverbed sediments, and epilithic biofilms collected during the dry phase across 205 IRES from five major climate zones. We determined the amounts and qualitative characteristics of the leached nutrients and OM, and estimated their areal fluxes from riverbeds. In addition, we evaluated the variance in leachate characteristics in relation to selected environmental variables and substrate characteristics. We found that sediments, due to their large quantities within riverbeds, contribute most to the overall flux of dissolved substances during rewetting events (56‐98%), and that flux rates distinctly differ among climate zones. Dissolved organic carbon, phenolics, and nitrate contributed most to the areal fluxes. The largest amounts of leached substances were found in the continental climate zone, coinciding with the lowest potential bioavailability of the leached organic matter. The opposite pattern was found in the arid zone. Environmental variables expected to be modified under climate change (i.e. potential evapotranspiration, aridity, dry period duration, land use) were correlated with the amount of leached substances, with the strongest relationship found for sediments. These results show that the role of IRES should be accounted f