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Many authors have expressed concerns about the evolution of soil fertility under cotton and cereal cultivation in southern Mali. Nevertheless, farmers have now cropped some of their fields for more than 30 years and still obtain fair yields. Our hypothesis is that the trees (mainly Vitellaria paradoxa) that farmers keep in their cropped fields help to maintain soil fertility. Consequently, we studied the relationships between the trees associated with crops and soil fertility on a sloped catena. On the lower section, 24 trees ha-1 cover 8% of the surface. They produce annually ~ 56.7kg of leaves per tree. Corresponding mineral recyclings, under the crown, are, per m2 and per year: 19 g N; 1 g P; 19 g K; 29 g Ca; 10 g Mg. The soil contains significantly more C and N under the crown of the trees than outside this area. V. paradoxa trees are less numerous on the middle section (3 ha-1) and on the top section (1.5 ha-1) of the catena than on the lower section, and consequently, their effect on the soil is decreasing from the lowlands to the uplands. On the lower section of the catena, the trees have an impact on the fertility of the whole field. Therefore, farmers intensify the cultivation in this section, which is the more favorable section of the catena.

Sodium affected rice (Oryza sativa L.)-cropped fields are very common. Due to their high exchangeable Na percentage, clay dispersion is one of the major risks for these soils when they are flooded. During flooding, Fe 2+ may become a major cation due to reductive dissolution of Fe oxides, but the flocculation effect of Fe 2+ is not known. In this paper, the effect of Fe 2+ on clay flocculation is studied by establishing critical coagulation concentration (CCC) curves of days extracted from a paddy soil of Northeast Thailand. The effect of Na-Fe 2+ and Na-Ca electrolytes on the CCC values is compared for sodium adsorption ratio (SAR) values ranging from 0 to 40 and total electrolyte concentration (TEC) ranging from 0.5 to 10 mmol L -1 . The extracted day is a mixture of kaolinite and smectite but only the smectite and some poorly ordered kaolinite could be dispersed. The CCC values largely reflected the behavior of smectite, in agreement with previous studies. The CCC values were equal for electrolytes with Fe 2+ or Ca 2+ cations, suggesting that Fe 2+ strongly adsorbs on smectite exchange sites and behaves similarly to Ca 2+ . The Fe 2+ concentration needed to flocculate the clays was at maximum 0.6 mmol L -1 for the most dispersive electrolytes, which is a common concentration in flooded rice fields. Reductive dissolution of Fe can protect sodic soils from clay dispersion upon flooded rice cropping.

Determinants of irrigated rice yield were studied in 45 rice fields in the Senegal River valley during 2 years in both wet and dry growing seasons. Grain yields were highly variable, ranging from 0 to 9.5 t ha −1 , with an average yield over years and seasons of 5 t ha −1 , indicating an average yield gap of about 4–5 t ha −1 between actual farmers’ yields and potential yields. Soil P and K status of farmers’ fields were mostly above critical limits and pH and electrical conductivity values were in the optimal range for irrigated rice. Average yield levels for three out of the four seasons were not significantly different. However, cold temperatures at the onset of the dry season induced slower development rate and lower above-ground biomass despite higher plant and tiller density at panicle initiation (PI). Analysis of growth cycle and spikelet sterility levels in the sample fields using the RIDEV simulation model showed that yield losses due to cold or heat stress around flowering could be neglected. Yield variability was, therefore, assumed to be mostly due to differences in crop management (other than choice of sowing and harvest dates) at the farmer level. Plant density in the dry season was significantly higher than in the wet season in both transplanted and direct-seeded fields, with farmers compensating for retarded growth at the onset of the dry season due to cold temperatures. Low transplanting density and the use of relatively old seedlings seriously affected plant and tiller densities determined at PI. Principal component analyses conducted with three variables, i.e. plant density, tiller density and rice—above-ground dry weight determined at PI and yield components at maturity allowed to determine the effect of crop management. Sub-optimal weed and N fertilizer management were major factors driving yield variability in farmers’ fields. Increasing the productivity of irrigated rice will require collective action at both field and scheme level.

Survival, biomass production, nutrient use and fertility of soil were examined in experimental stands of 10-year-old N-fixing indigenous Acacia nilotica (L.) Del. (eight provenances), A. senegal (L.) Willd. (one provenance), Acacia tortilis (Forsskal) Hayne (six provenances), Acacia raddiana syn A. tortilis (Forssk.) Hayne ssp. raddiana (Savi) Brenan (three provenances) and exotic N-fixing A. holosericea A. Cunn. ex G. Don (one provenance), A. cowleana Tate (one provenance), Acacia aneura F. Muell. ex Benth. (twelve provenances), Prosopis juliflora (Sw.) DC. (one naturalised provenance), Prosopis cineraria (L.) Druce (five provenances) and P. chilensis (Molina) Stuntz (two provenances) growing on a coastal site in semi-arid Senegal. Similar data were obtained for the non-N-fixing fast-growing exotic species Azadirachta indica Adr. Juss. and Eucalyptus camaldulensis Dehnh. of the same age that were growing on adjacent plots. P. juliflora produced more biomass than the other species and showed the greatest potential for use as a multipurpose tree. A. aneura showed the greatest potential for fodder production and despite its small stature, it ranked second for biomass among the N-fixing species. Of the indigenous species, A. nilotica was the most efficient user of non-renewable elements in biomass production. A. raddiana seemed profligate in its consumption of both N and P in wood production. E. camaldulensis was efficient in its use of N in wood but its wood contained large concentrations of P and K. A. aneura, P. juliflora and A. nilotica had the smallest concentrations of P in wood. A. raddiana and A. indica contained large concentrations of K in their wood in contrast to A. aneura and A. nilotica which were the most efficient users of K in wood production. There were few significant differences in fertility in soils beneath the differing tree species. Nevertheless, plots containing P. juliflora and P. cineraria tended to be the most fertile. Soil beneath A. indica was more fertile than soil beneath some N-fixing species. The extent of removal of plant nutrients in biomass suggests that without inputs of nutrient elements, harvest of wood and foliage is unlikely to be sustainable at the measured rate of production for more than two tree rotations of 10 years duration.

Measurement of recovery of fertilizer N and soil mineral N by maize must be improved in the western semiarid tropics for maximizing crop yield and reducing environmental pollution. The relevant variables for characterizing this N use are the N uptake by the plant from the applied fertilizer (NdfF) and that from the soil (NdfS). The direct measurement of these two variables requires the use of 15 N labeled fertilizer, a difficult and expensive technique. It would therefore be useful to have sensitive indicators for these variables. This study was conducted to measure the variability in the N use from soils. The experiments were carried out with maize at 24 sites in a 3000 ha area of village land with Luvisols located in the central zone of Burkina Faso. Each site had two treatments with two replicates: 0 and 80 kg N ha-' applied as urea labeled with 15 N. Statistical analysis of the results identified three groups of fields differing in soil fertility, each corresponding to a certain distance from the farmstead, and provided a relationship between the variables NdfF, NdfS, and easily measured indicators. The most pertinent indicators (r2 > 0.9) were: (a) for NdfS, the total N in plant without fertilizer (Nplt0) and the apparent crop recovery of N fertilizer (ACR %), and (b) for Nplt0, Nav (available N) as measured by the Waring Bremner test, exchangeable K, and (c) the clay content. The coefficients of determination improved when the regressions were calculated for each soil fertility group. These results have two important applications: (a) the possibility of estimating easily the part of N taken up by maize that comes, respectively, from the soil and the fertilizer; and (b) the identification of two factors limiting soil fertility, that is, the mineral N and exchangeable K + content of the soil before cropping. (Resume d'auteur)

The aim of the present work was to provide a synopsis of the scientific literature concerning the effects of different tree spe- cies on soil and to quantify the effect of common European temperate forest species on soil fertility. The scientific literature dealing with the tree species effect on soil has been reviewed. The composition of forest overstory has an impact on the chemical, physical and biolo- gical characteristics of soil. This impact was highest in the topsoil. Different tree species had significantly different effects on water ba- lance and microclimate. The physical characteristics of soils also were modified depending on the overstory species, probably through modifications of the soil fauna. The rates of organic matter mineralization and nitrification seem to be dependent on tree species. A coni- ferous species, Picea abies, had negative input-output budgets for some nutrients, such as Ca and Mg. This species promoted a higher soil acidification and a decrease in pH. Thus, it should not be planted in very poor soils in areas affected by acidic atmospheric deposi- tions. Nevertheless, the effect of the canopy species on soil fertility was rarely significant enough to promote forest decline. The impact of a tree species on soil fertility varied depending on the type of bedrock, climate and forest management. forest soils / tree species / fertility / sustainability / resiliency

This study was conducted to showcase a participatory method for assessing technical options in Southern Togo. The aim was to address farmers’ needs with respect to soil fertility problems in situations involving mixed crop-livestock farming systems. In collaboration with various stakeholders, the scientists thus assessed the potential for adopting a crop association involving maize for food (seed) and fodder (straw), i.e. a mixed function plant, and Mucuna pruriens, i.e. a long-cycle legume that is cropped to produce fodder and enhance soil fertility. The chemically fertilized crop association is here referred to as MME. Participatory action research (PAR) analytical tools were implemented in the four-phase method used. The first phase included an overall description of the entire study region to identify representative sites based on published information and exploratory interviews. In the second phase, the diversity of farmers was characterized through interviews with resource people at the selected sites. The third phase involved participatory selection of a range of technical options that included the MME association as well as local practices with features similar to this association, and alternative research proposals to enhance soil fertility and ensure the production of sufficient fodder to feed livestock. This selection was carried out by farmers chosen as being representative of their diversity. They were asked to rank—using notes, or pebbles because of the high illiteracy level—the different technical options presented during visits to the test plots or using visual aids. The fourth phase included an assessment of farmers’ comments on the perceived effects of the different options on agropastoral resource management (water, soil, biodiversity), their acceptability or cost-effectiveness relative to the labor cost. This method was applied in three villages in southern Togo. Six main farmer categories were identified in these villages: landowners, land tenants, members of farmers’ organizations, literate farmers, illiterate farmers, and women. In addition to MME, six options were selected, including the MME association with variants of local practices, such as the unfertilized maize and long cycle Mucuna association (MM), a fertilized maize and short cycle Mucuna association (MMCE), an unfertilized maize and short cycle Mucuna association (MMC), and a monocropped maize crop with massive fertilizer applications (ME). The two other options were proposed by researchers: maize cropped in fields surrounded by quickset hedges of fodder legumes that were harvested to feed livestock managed in stalls, with the dung subsequently spread in the fields (MHF), and strip intercropping of maize and Cajanus cajan. The MME association was the option that landowners, literate farmers and members of farmers’ organizations preferred. Women selected the MM association due to their scarce financial resources and land insecurity status. Land tenants and illiterate farmers favored MMCE as a second crop season is possible. An assessment of the different options revealed that most of the farmer categories considered that the MME association and the MHF option had the most positive impacts on agropastoral resources. MME and MMCE were considered as being the most socially acceptable associations, especially amongst landowners, as well as extension agents, consumers and merchants who had also been interviewed; this was followed by the MHF option. MM and MME turned out to be the most cost-effective associations whereas the two alternatives proposed by researchers were the least. This assessment method makes effective use of farmers’ expertise and is based on their perception of the impacts of technology. A positive perception is one of the factors influencing the adoption of a research proposal. Time and suitable tools are required when farmers are trained on the different options to ensure that this perception will not be biased by the quality of the information conveyed by researchers. Local variants of the options proposed by researchers can also be identified or adapted on the basis of this assessment. Development research initiatives should be focused on the processes involved in these participatory adaptations.

National audience

International audience; In order to meet growing demand for chocolate products, numerous initiatives have been launched over the last 10 years with a view to increasing cocoa production. These initiatives continue to promote the input-intensive model advocated since the 1960s, even though this model has reached its agronomic, socio-economic, and environmental limits. Hence the proposal to learn from agroforestry in order to develop the current model: introducing fruit and forest tree species into cocoa plantations contributes to the agro-ecological intensification of cocoa production, while improving flexibility and resilience, which are essential to smallholder farmers, who grow 95% of the world’s cocoa.; Para satisfacer el incremento en el consumo de productos con chocolate, se tomaron varias iniciativas en la última decena para aumentar la producción de cacao. Esas iniciativas siguen promoviendo el modelo intensivo en insumos recomendado desde los años 1960, aun si este modelo ha alcanzado sus límites agronómicos, socio-económicos y ambientales. A raíz de esto se elaboró la propuesta de inspirarse de la Agroforestería para influenciar la evolución del modelo actual: introducir árboles frutales y maderables en las plantaciones de cacao contribuye a la intensificación agroecológica del cultivo del cacao, aportando al mismo tiempo la flexibilidad y la resiliencia necesarias a los pequeños agricultores quienes producen el 95% del cacao en el mundo.; Pour satisfaire la consommation croissante de produits chocolatés, de nombreuses initiatives ont été lancées depuis une décennie afin d’augmenter la production de cacao. Ces initiatives continuent de promouvoir le modèle intensif en intrants préconisé depuis les années 1960, alors que ce modèle a atteint ses limites agronomiques, socio-économiques et environnementales. D’où la proposition de s’inspirer de l’agroforesterie pour faire évoluer le modèle actuel : introduire des arbres fruitiers et forestiers dans les cacaoyères contribue à l’intensification agroécologique de la cacaoculture, tout en apportant souplesse et résilience, nécessaires aux petits agriculteurs, qui produisent 95 % du cacao mondial.

International audience; In order to meet growing demand for chocolate products, numerous initiatives have been launched over the last 10 years with a view to increasing cocoa production. These initiatives continue to promote the input-intensive model advocated since the 1960s, even though this model has reached its agronomic, socio-economic, and environmental limits. Hence the proposal to learn from agroforestry in order to develop the current model: introducing fruit and forest tree species into cocoa plantations contributes to the agro-ecological intensification of cocoa production, while improving flexibility and resilience, which are essential to smallholder farmers, who grow 95% of the world’s cocoa.; Para satisfacer el incremento en el consumo de productos con chocolate, se tomaron varias iniciativas en la última decena para aumentar la producción de cacao. Esas iniciativas siguen promoviendo el modelo intensivo en insumos recomendado desde los años 1960, aun si este modelo ha alcanzado sus límites agronómicos, socio-económicos y ambientales. A raíz de esto se elaboró la propuesta de inspirarse de la Agroforestería para influenciar la evolución del modelo actual: introducir árboles frutales y maderables en las plantaciones de cacao contribuye a la intensificación agroecológica del cultivo del cacao, aportando al mismo tiempo la flexibilidad y la resiliencia necesarias a los pequeños agricultores quienes producen el 95% del cacao en el mundo.; Pour satisfaire la consommation croissante de produits chocolatés, de nombreuses initiatives ont été lancées depuis une décennie afin d’augmenter la production de cacao. Ces initiatives continuent de promouvoir le modèle intensif en intrants préconisé depuis les années 1960, alors que ce modèle a atteint ses limites agronomiques, socio-économiques et environnementales. D’où la proposition de s’inspirer de l’agroforesterie pour faire évoluer le modèle actuel : introduire des arbres fruitiers et forestiers dans les cacaoyères contribue à l’intensification agroécologique de la cacaoculture, tout en apportant souplesse et résilience, nécessaires aux petits agriculteurs, qui produisent 95 % du cacao mondial.

The maintenance of humus balance in cultivated soils is a guarantee of the sustainability of production systems. In West Africa, the advice regarding application of organic manure to fields remains unique and independent of the quality of organic manures available on farms. Some studies show that West African farms produce a diversity of organic manure. Should the advice for organic manure application be reformulated to reflect this diversity of farm-produced organic manure? We propose to analyze the diversity of organic manure produced on certain farms and estimate the optimal amount of organic fertilizer that should be applied to the fields to ensure the renewal of organic matter. The analysis distinguishes a great heterogeneity of farm-produced organic manure. Farm-produced manure with a high amendment value provides a reference for the quality of the manure, but this is also the case for farm-produced manure with an average quality and for farm-produced composts with a high or average amendment value. Depending on the quality of the manure, with these types of organic fertilizer, it would be necessary to apply between 2.4 and 5.1 t·ha-1 per year on sandy soils and 2.1 to 4.4 t·ha-1 per year for clay. Depending on the quality of the compost, it would be necessary to apply between 4.1 and 5.4 t·ha-1 per year for sandy soils and between 3.5 and 4.6 t·ha-1 per year for clay. Taking into account the heterogeneity of the quality of farm-produced organic manure, we can adapt the current technical advice to ensure a renewal of soil organic matter. However, the quantities of organic manure needed are beyond the current capacity of farms. It would be necessary to increase the amount of organic manure produced on farms, to improve its quality and to integrate other modes of soil fertility management at farm level., L’entretien du bilan humique des terres cultivées est un gage de durabilité des systèmes de production. En Afrique de l’Ouest, la recommandation d’application de fumure organique reste unique, quel que soit le type de sol, et indépendante de la qualité des fumures organiques disponibles dans les exploitations. Aujourd’hui, les paysans des savanes d’Afrique de l’Ouest produisent une diversité de types de fumures organiques, ce qui nous amène à caractériser cette diversité et à proposer de nouvelles recommandations pour assurer l’entretien du statut des sols agricoles dans cette région. L’analyse permet de distinguer une grande diversité de fumures organiques paysannes : des fumiers paysans à forte valeur d’amendement correspondant aux fumures organiques de référence, mais également des fumiers de qualité moyenne et des composts de valeur d’amendement forte et moyenne. Avec ces types d’amendement, il serait alors nécessaire d’appliquer, selon la qualité des fumiers, entre 2,4 et 5,1 t·ha-1 paran sur les sols sableux et 2,1 et 4,4 t·ha-1 par an pour les sols argileux et selon la qualité des composts entre 4,1 et 5,4 t·ha-1 par an pour les sols sableux et entre 3,5 et 4,6 t·ha-1 par an pour les sols argileux. Cependant, les quantités de fumure organique nécessaires dépassent les capacités actuelles de production des exploitations agropastorales de la région. Il est donc nécessaire que les producteurs combinent plusieurs voies d’amélioration de la gestion de la matière organique du sol : augmenter les quantités de fumures organiques produites, améliorer leur qualité et intégrer d’autres modes de gestion de la fertilité des sols cultivés à l’échelle des exploitations.

L'intensification écologique de la production en Afrique amène la recherche agronomique à observer autrement les systèmes agricoles. Dans le cadre d'une approche intégrée associant les approches disciplinaires de l'écologie du paysage, de l'agronomie et des sciences de l'action, la thèse questionne les logiques d'action à l'oeuvre dans les pratiques agricoles au niveau d'un territoire agricole et en propose une typologie. Sur le territoire de Kajulu (Ouest Kenya), caractérisé par une densité de population supérieure à 1100 hab km², les Luos perpétuent des règles coutumières quant à l'organisation de l'espace agricole et l'attribution des terres en fonction de l'âge et du sexe des individus au sein de l'exploitation. Dans ce contexte particulier, nous émettons l'hypothèse que l'accès à la terre et la structure spatiale des espaces cultivés sont des facteurs déterminant des logiques des logiques d'action à l'oeuvre au sein du territoire. Les logiques d'action qui nous intéressent sont celles de l'individu, sur les espaces agricoles dont il est gestionnaire, selon (i) les liens qu'il entretient avec les institutions de recherche, les marchés et les réseaux locaux d'échange de matières et de connaissances, et (ii) le contexte local de l'action auquel nous accédons par l'analyse du paysage et les savoirs qu'ont les agriculteurs de leurs parcelles et de leur environnement et qu'ils mettent en oeuvre dans leurs pratiques agricoles. L'analyse les données recueillies nous permet de discuter de la diversité des techniques culturales appliquées dans un espace hétérogène et densément peuplé, et notamment de la propension des agriculteurs à l'innovation.

International audience; The maintenance of humus balance in cultivated soils is a guarantee of the sustainability of production systems. In West Africa, the advice regarding application of organic manure to fields remains unique and independent of the quality of organic manures available on farms. Some studies show that West African farms produce a diversity of organic manure. Should the advice for organic manure application be reformulated to reflect this diversity of farm-produced organic manure? We propose to analyze the diversity of organic manure produced on certain farms and estimate the optimal amount of organic fertilizer that should be applied to the fields to ensure the renewal of organic matter. The analysis distinguishes a great heterogeneity of farm-produced organic manure. Farm-produced manure with a high amendment value provides a reference for the quality of the manure, but this is also the case for farm-produced manure with an average quality and for farm-produced composts with a high or average amendment value. Depending on the quality of the manure, with these types of organic fertilizer, it would be necessary to apply between 2.4 and 5.1 t·ha-1 per year on sandy soils and 2.1 to 4.4 t·ha-1 per year for clay. Depending on the quality of the compost, it would be necessary to apply between 4.1 and 5.4 t·ha-1 per year for sandy soils and between 3.5 and 4.6 t·ha-1 per year for clay. Taking into account the heterogeneity of the quality of farm-produced organic manure, we can adapt the current technical advice to ensure a renewal of soil organic matter. However, the quantities of organic manure needed are beyond the current capacity of farms. It would be necessary to increase the amount of organic manure produced on farms, to improve its quality and to integrate other modes of soil fertility management at farm level.; L’entretien du bilan humique des terres cultivées est un gage de durabilité des systèmes de production. En Afrique de l’Ouest, la recommandation d’application de fumure organique reste unique, quel que soit le type de sol, et indépendante de la qualité des fumures organiques disponibles dans les exploitations. Aujourd’hui, les paysans des savanes d’Afrique de l’Ouest produisent une diversité de types de fumures organiques, ce qui nous amène à caractériser cette diversité et à proposer de nouvelles recommandations pour assurer l’entretien du statut des sols agricoles dans cette région. L’analyse permet de distinguer une grande diversité de fumures organiques paysannes : des fumiers paysans à forte valeur d’amendement correspondant aux fumures organiques de référence, mais également des fumiers de qualité moyenne et des composts de valeur d’amendement forte et moyenne. Avec ces types d’amendement, il serait alors nécessaire d’appliquer, selon la qualité des fumiers, entre 2,4 et 5,1 t·ha-1 paran sur les sols sableux et 2,1 et 4,4 t·ha-1 par an pour les sols argileux et selon la qualité des composts entre 4,1 et 5,4 t·ha-1 par an pour les sols sableux et entre 3,5 et 4,6 t·ha-1 par an pour les sols argileux. Cependant, les quantités de fumure organique nécessaires dépassent les capacités actuelles de production des exploitations agropastorales de la région. Il est donc nécessaire que les producteurs combinent plusieurs voies d’amélioration de la gestion de la matière organique du sol : augmenter les quantités de fumures organiques produites, améliorer leur qualité et intégrer d’autres modes de gestion de la fertilité des sols cultivés à l’échelle des exploitations.

International audience; The maintenance of humus balance in cultivated soils is a guarantee of the sustainability of production systems. In West Africa, the advice regarding application of organic manure to fields remains unique and independent of the quality of organic manures available on farms. Some studies show that West African farms produce a diversity of organic manure. Should the advice for organic manure application be reformulated to reflect this diversity of farm-produced organic manure? We propose to analyze the diversity of organic manure produced on certain farms and estimate the optimal amount of organic fertilizer that should be applied to the fields to ensure the renewal of organic matter. The analysis distinguishes a great heterogeneity of farm-produced organic manure. Farm-produced manure with a high amendment value provides a reference for the quality of the manure, but this is also the case for farm-produced manure with an average quality and for farm-produced composts with a high or average amendment value. Depending on the quality of the manure, with these types of organic fertilizer, it would be necessary to apply between 2.4 and 5.1 t·ha-1 per year on sandy soils and 2.1 to 4.4 t·ha-1 per year for clay. Depending on the quality of the compost, it would be necessary to apply between 4.1 and 5.4 t·ha-1 per year for sandy soils and between 3.5 and 4.6 t·ha-1 per year for clay. Taking into account the heterogeneity of the quality of farm-produced organic manure, we can adapt the current technical advice to ensure a renewal of soil organic matter. However, the quantities of organic manure needed are beyond the current capacity of farms. It would be necessary to increase the amount of organic manure produced on farms, to improve its quality and to integrate other modes of soil fertility management at farm level.; L’entretien du bilan humique des terres cultivées est un gage de durabilité des systèmes de production. En Afrique de l’Ouest, la recommandation d’application de fumure organique reste unique, quel que soit le type de sol, et indépendante de la qualité des fumures organiques disponibles dans les exploitations. Aujourd’hui, les paysans des savanes d’Afrique de l’Ouest produisent une diversité de types de fumures organiques, ce qui nous amène à caractériser cette diversité et à proposer de nouvelles recommandations pour assurer l’entretien du statut des sols agricoles dans cette région. L’analyse permet de distinguer une grande diversité de fumures organiques paysannes : des fumiers paysans à forte valeur d’amendement correspondant aux fumures organiques de référence, mais également des fumiers de qualité moyenne et des composts de valeur d’amendement forte et moyenne. Avec ces types d’amendement, il serait alors nécessaire d’appliquer, selon la qualité des fumiers, entre 2,4 et 5,1 t·ha-1 paran sur les sols sableux et 2,1 et 4,4 t·ha-1 par an pour les sols argileux et selon la qualité des composts entre 4,1 et 5,4 t·ha-1 par an pour les sols sableux et entre 3,5 et 4,6 t·ha-1 par an pour les sols argileux. Cependant, les quantités de fumure organique nécessaires dépassent les capacités actuelles de production des exploitations agropastorales de la région. Il est donc nécessaire que les producteurs combinent plusieurs voies d’amélioration de la gestion de la matière organique du sol : augmenter les quantités de fumures organiques produites, améliorer leur qualité et intégrer d’autres modes de gestion de la fertilité des sols cultivés à l’échelle des exploitations.

In South America, factorial fertilisation trials were set up on oil palm estates managed by Palmeras de los Andes in Ecuador and Indupalma S.A. in Colombia to control fertilisation during the two oil palm crop cycles. These experiments were designed to determine the optimal leaf contents of N, P, K, Mg and Cl, in recent planting materials and to assess the impacts of the first crop cycle on the following cycle. In the two presented trials, nitrogen and chlorine treatments were found to have the greatest impact on production after 10 years of monitoring. The observed leaf N and Cl deficiencies resulted in a significant effect on the average bunch weight, but these differences did not lead to significant differences in yield. However, after 10 years of monitoring, it was found that the yield differences between the highest and the lowest nitrogen rates (N2-N0) and between the highest and the lowest chlorine rates (Cl2-Cl0), increased steadily until reaching a threshold at which some authors consider that supplementary fertilisation is required. In both experiments, soil mineral reserves had not been tapped during the first oil palm crop cycle, which had benefitted from mean rational fertiliser rates of 3 - 5 kg palm-1 yr-1. These reserves were sufficient to limit a yield decline in the non-fertilised treatments. We also noted that it took a long time for the differences in leaf mineral content and yields to become significant, thus confirming that these are long-term effects. Hence, in a suitably fertilised plantation, it is very unlikely that the effects of fertiliser applications during previous years could be reflected by inter-annual yield variations. However, there is no reason to consider that the depressive effect of poor climatic conditions, such as prolonged drought, could be overcome by increasing early fertilisation.

Pour satisfaire la consommation croissante de produits chocolatés, de nombreuses initiatives ont été lancées depuis une décennie afin d'augmenter la production de cacao. Ces initiatives continuent de promouvoir le modèle intensif en intrants préconisé depuis les années 1960, alors que ce modèle a atteint ses limites agronomiques, socio-économiques et environnementales. D'où la proposition de s'inspirer de l'agroforesterie pour faire évoluer le modèle actuel : introduire des arbres fruitiers et forestiers dans les cacaoyères contribue à l'intensification agroécologique de la cacaoculture, tout en apportant souplesse et résilience, nécessaires aux petits agriculteurs, qui produisent 95 % du cacao mondial.

Conservation agriculture (CA) constitutes a potential set of management practices to restore soil total N (STN), soil organic C (SOC) and its labile fractions (i.e., particulate organic C-POC, hotwater extractable organic C-HWEOC, permanganate oxidizable C-POXC), to increase soil enzyme activities and to enhance soil aggregation. After five years, CA averagely increased SOC stocks over CT at 0-5 cm by 10%, 20% and 18%, STN stock by 8%, 25% and 16% , POC stocks by 22%, 20% and 78%, HWEOC stocks by 61%, 55% and 53%, and POXC stocks by 23%, 21% and 32% for rice-, soybean- and cassava-based cropping systems (RcCS, SbCS and CsCS, respectively). In general, no noticeable changes in the subsoil layers were observed. When monitoring after three years, stocks of SOC fractions (i.e., mineral-associated organic C-MAOC, pyrophosphate extractable organic C-PEOC, chemically stabilized organic C-CSOC) were almost constant in each depth among land uses, except MAOC in SbCS and PEOC in CsCS at 0- 5 cm where CA showed significant effects. In contrast, ?-glucosidase activity was 18%, 28% and 49% greater in CA than in CT soils at 0-5 cm under RcCS, SbCS, CsCS, respectively, whereas arylsulfatase activity under CA was greater than CT by 36% in SbCS and 39% in CsCS. The proportions of large macroaggregates (8-19 mm) at 0-5 cm under CA averagely increased 23%, 39% and 53% in RcCS, SbCS and CsCS, respectively, and consequently increased soil aggregation indices (i.e., mean weight diameter-MWD, mean geometric diameter-MGD and aggregate stability index-ASI) compared with those under CT. On average, and across all aggregate size classes, CA accumulated SOC concentrations over CT by 11%, 7% and 6%, total N concentrations by 3%, 11% and 15% and POXC concentrations by 18%, 20% and 15% for RcCS, SbCS and CsCS, respectively, at 0-5 cm. These increases led to positive correlations between large macroaggregate-associated SOC and soil aggregation indices in 0-5 cm depth in the three cropping systems. The results of CP-MAS 13C NRM measurement showed that humic acid from soils under CT tended to have higher proportions of aliphatic C than under CT while in reverse for aromatic C. This supports the promotion of CMI under CA indicating greater lability of SOC. In conclusion, short-term CA practices in the three cropping systems increased the storage of STN, SOC and labile SOC pool and enhanced soil enzyme activities in the surface soils with potential effects in the subsoil layers through increased proportion of large macroaggregates and soil aggregation indices resulting from high and diversified biomass-C inputs and the absence of physical soil disruption.

In suboptimal conditions for coffee growth, the use of shade tree is usually considered beneficial to production. This study aimed to evaluate this benefit in the poorly documented East African smallholder Arabica coffee systems in optimal climatic but suboptimal management conditions. In a 4 year observational trial in 50 coffee farms, the association of shade trees and coffee generated an average 55 % cherry production increase. Neither delay in berry maturation nor buffer in alternate bearing patterns were observed, probably due to the low productivity of unfertilized coffee plants. Quality wise, the presence of shade trees did not result in an increase of larger green beans, but it reduced the proportion of altered and lighter cherries in 2009, a low production year. A shade species effect was detected through the positive influence of two non-leguminous shade trees, Persea americana and Ficus thonningii on production. The effect was correlated to greater canopy openness and increase in K soil content. In general, soil mineral content was not influenced by the presence of trees, but the legume species Inga oerstediana appeared responsible for a slight increase of total C and N soil content. It is concluded that in the small holder context of the Northern Lake Kivu region, the association of mature trees is beneficial to coffee production and can contribute to the improvement of producer’s income.

Permanent grasslands can provide a large diversity of ecosystem services. They are found in contrasted conditions in terms of management and climate in Europe. These conditions induce a wide variety of grassland types that differ in their vegetation and are expected to differ with respect to the provision of ecosystem services. Because ecosystem functioning in grassland has been shown to be linked to plant functional diversity criteria, we put forward that these functional diversity criteria can be used to evaluate the provision of ecosystem services. These criteria are influenced by the management and the climate. The overall objective of this PhD program is to assess the effects of management and climate on the plant functional diversity related to ecosystem services of permanent grasslands. The first step of the PhD program was to select 29 functional diversity criteria related to 8 ecosystem services (quantity of forage, forage quality, stability of the forage production, biodiversity conservation, pollination carbon sequestration, dryness resistance and nitrogen fertility). This selection was made using experts' interview and literature survey. The second step was to evaluate inaccuracies in the calculation of the 29 functional diversity criteria from functional trait databases and different sets of botanical surveys. The third step was to estimate the functional diversity criteria from management and climate data using "Random Forests" methodology. The results show that the climatic variables had generally more effect on the functional diversity than the management ones. Furthermore, for some climatic conditions, the management does not affect some functional diversity criteria. Among the 29 functional diversity criteria, only 8 have more than 40 % of their variance explained by the management and climate variables, Les prairies permanentes peuvent fournir une grande diversité de services écosystémiques. Elles se trouvent dans des conditions contrastées en termes de gestion et de climat en Europe. Cette diversité de conditions induit une grande variété de types de prairies différant par leur végétation et leur fourniture en services écosystémiques. Certains travaux suggèrent que le fonctionnement des écosystèmes prairiaux peut être directement relié à des critères de diversité fonctionnelle végétale. Ces critères, qui pourraient être utilisés pour évaluer les services écosystémiques, sont influencés par la gestion et le climat. L'objectif de ce doctorat est d'évaluer les effets de la gestion et du climat sur la diversité fonctionnelle végétale liée à des services écosystémiques des prairies permanentes. La première étape a consisté à sélectionner 29 critères de diversité fonctionnelles liés à 8 services écosystémiques (quantité de fourrage, qualité du fourrage, stabilité de la production de fourrage, conservation de la biodiversité, pollinisation, la séquestration du carbone, résistance à la sécheresse et fertilité azotée). Cette sélection a été faite à partir d'interviews d'experts et d'une revue de la littérature. La deuxième étape a consisté à évaluer différentes inexactitudes dans le calcul des 29 critères de diversité fonctionnelle à partir de bases de traits fonctionnels et différents jeux de relevés botaniques. La troisième étape a consisté à évaluer les critères de diversité fonctionnelle à partir des données de gestion et de climat, en utilisant notamment la technique mathématique des forêts de Breiman. Les résultats montrent que les variables climatiques ont généralement plus d'effet sur la diversité fonctionnelle que celles de gestion. En outre, pour certaines conditions climatiques, la gestion n'affecte pas certains critères de diversité fonctionnelle. Parmi les 29 critères de diversité fonctionnelle, seulement 8 critères avaient plus de 40% de leur variance expliquée par la gestion et le climat

Aims Tropical plantations are likely to supply a growing share of the increasing world demand for forest products. We aimed to gain insight into the role of the nitrogen (N) contained in harvest residues (HR) for tree growth and soil N stocks. Methods We used 15N-labeled harvest residues to (1) study the dynamic of N release throughout decomposition, (2) determine the vertical transport pathways of N from the forest floor to the upper soil layers, and (3) quantifying the contributions of HR to soil N stocks and the supply of N to young Eucalyptus trees. Results Almost all of the 15N initially contained in the HR was recovered 27 months after deposition, with 21 % remaining in HR, 38 % being transferred to the underlying O layer, 21 % being transferred to the 0-15 cm soil layer, and approximately 15 % accumulating in the tree biomass. Our results supported the presence of two pathways of N transfers from the O layer to the mineral soil: (1) the leaching of dissolved 15N from fresh litter during the first year after planting which actively contributed to Eucalyptus N nutrition and (2) the transport of particulate organic matter in percolating water which contributed to maintain N stocks in the first 15 cm of the soil. Approximately 40 % of the N content in 2-year-old Eucalyptus trees was derived from the labeled HR. Conclusions The sustainability of fast-growing Eucalyptus trees established on N-poor sandy tropical soils largely relies on organic residues, as an early source of mineral N for tree and as a source of organic N in the top soil.

International audience; 1. It is important to study how evolution impacts on plant functional traits and to determine how this subsequently determines ecosystem functioning. We tackle this general issue by studying the evolution of plant strategies that affect mineralization through the chemical quality of their own litter and their position on the leaf economic spectrum. This spectrum allows us to classify all plants on single axis ranging from resource-acquisitive to resource-conservative strategies. 2. We build a spatially explicit and individual-based simulation model: individual plants grow in the cells of a lattice and the limiting nutrient is recycled locally in these cells. Individual plants may die and produce seeds that are dispersed. Mutants with different mineralization strategies appear stochastically. A trade-off is implemented between the rate of nutrient loss from plants and litter mineralization. 3. In the spatial-explicit model, plant capacity to increase mineralization evolves and reaches an evolutionary equilibrium in most cases. The evolved mineralization decreases with plant longevity, seed dispersal efficiency, spatial homogenization of mineral nutrient availability and inputs of mineral nutrient to the ecosystem. 4. The evolved mineralization strategies neither maximize plant biomass, nor minimize the availability of mineral nutrient or the stock of dead organic matter. The evolutionary and ecological impacts of nutrient enrichment on the stock of organic matter are different. 5. Synthesis. Our results suggest that plant mineralization strategy may evolve provided that the mineral resource is not fully shared by all individuals. Such an evolution modifies soil capacity to store organic carbon thereby being relevant in the context of the current climate change and global nutrient enrichment. Indeed, our model shows that evolutionary feedbacks of plants to nutrient enrichment are likely to differ from purely ecological feedbacks.

Earthworm populations are important decomposers contributing to aggregate formation and nutrient cycling processes involving nitrogen cycles, phosphorus and carbon. They are known to influence soil fertility by participating to important processes in soil such as soil structure regulation and organic matter dynamics. Earthworms also modify the microbial communities through digestion, stimulation and dispersion in casts. Consequently, changes in the activities of earthworm communities, as a result of soil management practices, can also be used as indicators of soil fertility and quality. It is therefore important to understand how earthworm communities affect soil dynamics. This review adresses the current state of knowledge on earthworm’s impacts on soil structure and soil organic matter (carbon, nitrogen, and phosphorus) dynamics, with special emphasis on the effects of land management practices on earthworm communities., Les vers de terre sont des décomposeurs importants contribuant à la formation d’aggrégats et aux différents cycles d’éléments nutritifs tels que l’azote, le phosphore et le carbone. Ils sont connus pour leur influence sur la fertilité du sol en participant à la régulation de la structure du sol et à la dynamique de la matière organique. En ingérant d’importantes quantités de sol, les vers de terre modifient la communauté microbienne lors du passage à travers leur tube digestif. Par conséquent, les changements dans les activités de la communauté lombricienne, à la suite de pratiques de gestion des sols, peuvent également être utilisés comme indicateurs de la fertilité et de la qualité des sols. Il est important de comprendre comment les communautés lombriciennes affectent la dynamique des sols. Cette synthèse bibliographique porte sur l’état actuel des connaissances sur les impacts de vers de terre sur la structure des sols et la dynamique de la matière organique, en mettant l’accent sur les impacts des pratiques agricoles sur les communautés lombriciennes.

International audience; Background: Exogenous organic matter may be valuable amendments for degraded tropical soil in Northern Vietnam. Their effect on carbon storage and composition need to be evaluated. Method: The study investigates soil from mesocosms cultivated with maize and amended with four different kinds of amendments: only mineral fertilizers (control), buffalo manure, compost or vermiconnpost as well as biochar. Results: All organic amendments showed a positive effect on soil carbon storage and significantly influenced soil organic matter quality. The presence of biochar increased lignin-derived compounds abundance as well as both plant and microbial sugar content of soil amended with vermicompost but had no effect in the case of control soil. Conclusion: Synergistic effects between plants and different organic amendments influence carbon storage and soil organic matter composition.

International audience; The appearance of agriculture in urban areas improved the health-iness of the diet of people by enabling their consumption of fresh vegetables and fruits. This study assessed the level of fertility, and the impact of the cropping system and of the exploitation time on the physicochemical properties and the pseudo-total and EDTA-extractable metals contents of the vegetable soils of urban garden of in Libreville (Gabon). The results indicated a low fertility of the cultivated soils. The metal contents in the open field cultured soils were generally different from the soils cultured under shelters. Except Al that could be toxic for cultivated vegetables, the soil properties and metal element concentrations decreased significantly with time in the open field soil, while they did not vary in open shade cultured soils. The pseudo-total cadmium concentration was below the detection limit in all soils. Multivariate analysis showed that Al, Fe and Pb were of lithogenic origin, while Cu, Zn and Mn were of anthropogenic origin.

Background and aims The introduction of Acacia mangium in Eucalyptus urophylla x grandis stands improves wood production on poor sandy soils of coastal plains of the Congo. We assessed the impact of A. mangium plantations in pure stands and in mixture with eucalypt trees on the physico-chemical properties of the soil after one rotation. Methods Bulk densities, N, C, available P and pH were determined on soil sampled in the pure acacia (100A), pure eucalypt (100E) and mixed-species (50A:50E) stands. N and P were determined in aboveground litters and in leaves, bark and wood of trees. Results N and C concentrations were higher in 50A:50E than in 100A and 100E in the top soil layer. The pH was lower in 100A and higher in 100E than in 50A:50E. The available P was lower in 50A:50E than in 100A and 100E. Leaf N was lower in 50A:50E than in 100A for acacia, and higher than in 100E for eucalypt. Leaf P was similar for acacia but higher for eucalypt in 50A:50E than in 100E. In contrast to P, the amount of N in aboveground litterfall increased with the proportion of acacia in the stand. Conclusions The introduction of acacia trees in eucalypt plantations increased C and N contents of the soil but decreased the available P content in the mixed-species stand. This may be related to a higher uptake of P needed to maintain the N:P stoichiometry in eucalypt leaves.

Certains experts ont proposé des thèmes de recherche complémentaires dans le cadre de réponses à des appels d’offres divers. Deux réseaux de recherche sont également proposés dans les « conclusions et recommandations » du rapport. Utilisation d’indicateurs pour le suivi du cycle culture/jachère et des effets des aménagements L’identification et la mise au point d’outils pratiques et simples d’emploi, permettant de caractériser l’état des ressources et du fonctionnement des différents stades d...

Les contraintes majeures qui limitent la productivité des agroécosystèmes en milieu arides sont généralement attribuées aux carences minérales [plus particulièrement en phosphore (P) et en azote (N)], à un déficit en eau, aux processus d’érosion hydrique et éolienne, ainsi qu’à des perturbations dans le biofonctionnement du sol (faible diversité génétique et fonctionnelle de la microflore tellurique, etc.). Lorsque ces milieux ne sont pas soumis à une surexploitation, ils présentent une activité biologique élevée. Il a été ainsi suggéré que leur valorisation via des stratégies culturales adéquates pouvait réactiver les processus écologiques impliqués dans le maintien de la fertilité des sols et ainsi assurer une meilleure productivité de l’agro-écosystème. La plupart des plantes de ces régions arides (espèces sauvages ou cultivées) sont associées à des champignons mycorhiziens à arbuscules (CMA). Ces symbiotes fongiques sont reconnus comme étant des composantes microbiennes majeures dans le déroulement des principaux cycles biogéochimiques des sols (C, P et N) et en conséquence dans le développement des plantes en améliorant leur nutrition minérale mais aussi hydrique et leur état sanitaire. Paradoxalement, leur valorisation au sein d’itinéraires culturaux reste encore très limitée, voire inexistante. Ce chapitre a pour objectifs principaux de décrire le rôle des CMA dans le maintien et l’amélioration de la fertilité des sols et sur le développement des plantes tant au niveau de leur nutrition minérale, de leur résistance au stress hydrique que de l’état sanitaire des sols cultivés (ex. : lutte contre Striga spp.). Des stratégies d’ingénierie écologique seront ensuite proposées afin d’optimiser certaines techniques culturales (ex. : agroforesterie) dans le rôle de maintien du potentiel infectieux mycorhizogène des sols en relation avec une pleine expression des propriétés de la symbiose mycorhizienne sur les plantes cultivées, permettant ainsi d’atteindre des rendements culturaux compatibles avec les besoins des populations locales.

Les observations réalisées sur les interactions arbre/herbe dans le Sahel sénégalais (Ferlo, 280 mm de précipitations annuelles) montrent qu'Acacia raddiana augmente la richesse floristique, modifie le cycle phénologique et accroît la production et l'immobilisation minérale de la strate herbacée située sous son couvert. L'impact positif de l'arbre sur la strate herbacée est principalement dû à l'amélioration des disponibilités en eau et à l'augmentation de la fertilité du sol. Studies on tree and grass interactions in the Sahelian zone of Senegal (Ferlo, 280 mm of annual rainfall) show that Acacia raddiana increases the floristic richness, modifies the phenological cycle and improves the phytomass and the inorganic status of the understory herbaceous layer.These benefic effects are mainly due to the soil enrichment (water balance and fertility).

International audience; Budgets of mineral elements in small forested catchments in Galicia (NW Spain). In order to assess the sustainability of mineral supply to fast growing Eucalyptus globulus and Pinus pinaster stands in Galice (NW Spain), we calculated (input-output) nutrient budgets in three small catchments: the Castrove and Jabali catchments with eucalyptus on a base poor granite and the Arcos catchment with pine on granodiorite. In each catchment, the annual drainage output was lower than the rainwater input for Ca, Mg and K. This particularity is attributed to (a) the relative low content of Ca and Mg of the parent material, (b) the very low concentrations of NO3 and SO4 of drainage water in an area with very low level of atmospheric pollution, and (c) to the strong mineral uptake of fast growing stands. The present management of forests leads to negative budgets, both in the eucalyptus and pine catchments. But the traditional management of pine stands including the harvest of needles and branches was much more impoverishing than the present management of eucalyptus stands, where timber is the only harvested product. Various estimates of the weathering rate suggest that this flux is sufficient to compensate for the losses in the catchment on granodiorite but probably insufficient on granite. Since nitrogen deposition is extremely low, and forest fires are quite frequent, the symbiotic fixation of large amounts of nitrogen is needed in order to ensure the sustainability of forest growth.; Afin d'estimer la pérennité de l'alimentation minérale de plantations forestières de Pinus pinaster et Eucalyptus globulus de forte productivité en Galice, nous avons calculé des bilans (entrées-sorties) d'éléments minéraux dans trois petits bassins versants. Dans chacun de ces trois bassins, les sorties par drainage de Ca, Mg et K sont inférieures aux entrées par les pluies. Cette particularité est attribuée à la relative pauvreté en cations alcalino-terreux des roches mères, au très faible drainage de sulfate et nitrate lié à l'absence de pollution atmosphérique, et surtout à la forte immobilisation forestière qui tire directement profit des apports par les pluies. L'exploitation forestière actuelle des peuplements de pins et d'eucalyptus conduit à des bilans fortement négatifs de Ca, Mg et K, mais qui diffèrent peu entre ces peuplements. La différence majeure provient du mode d'exploitation, selon que les arbres sont ou non écorcés en forêt, et que la litière est exportée. La libération par altération minérale d'un flux relativement important de Ca et K est nécessaire pour compenser ces pertes. Les estimations du flux d'altération conduisent à penser que ce flux est suffisant dans le bassin versant sur granodiorite. Dans les bassins versants sur granite, ce flux est vraisemblablement insuffisant en ce qui concerne le Ca, mais des mesures complémentaires sont nécessaires pour pouvoir l'affirmer. Les bilans d'azote montrent qu'une forte fixation symbiotique est indispensable pour assurer la pérennité de la production forestière.

Soil nematode communities in the 0‐15 cm soil layer are used as indicators for describing the processes of fallow succession in the semi-arid zone of West Africa (Senegal). Abundance of plant feeding nematodes, non-plant feeding nematodes, plant parasite index (PPI), species richness and Shannon evenness of plant parasitic nematodes were measured at five stages of succession: fields, early (1‐3 years), intermediate (8‐10 years), old (18‐20 years) fallows, and forest stage. These nematological indexes were analyzed simultaneously by multivariate analysis to show the indicative properties of nematode communities. Overall, changes in abundance of nematode groups, PPI and diversity, show continuous trends from early fallow to mature stages of the succession; these trends parallel theoretical trends in secondary succession. In addition, soil nematode parameters were meaningful and expressed interactions of various uncontrolled factors with successional processes, such as environmental conditions or cropping history. During the 3 years of the survey, the structure of nematode communities, described by index analysis, showed little temporal change and supported the use of nematodes as stable indicators. ©2000 Elsevier Science B.V. All rights reserved.

Afin d'étudier l'influence de la jachère sur les nématodes phytoparasites et la fertilité du sol, la croissance du mil en serre a été comparée dans des sols stérilisés et naturellement infestés de la région de Thyssé-Kaymor au Sénégal. Ces sols sont ferrugineux et ont été collectés dans des parcelles voisines, l'une en jachère depuis 17 ans et l'autre cultivée depuis plusieurs années. Le peuplement de nématodes du sol cultivé est constitué principalement de deux espèces : un ectoparasite, #Tylenchorhynchus gladiolatus$ et un endoparasite, #Scutellonema cavenessi$. Le sol de la jachère est infesté par de nombreuses espèces, mais sous l'influence de la culture du mil, il évolue vers la situation simplifiée observée dans les sols cultivés, exception faite que dans nos conditions expérimentales, en pots, #Pratylenchus pseudopratensis$ remplace #S.cavenessi$. Que le sol soit ou non infesté de nématodes, la jachère précédente a un effet positif sur le développement du mil à chaque cycle. L'appauvrissement du sol, comme l'impact des nématodes, réduisent la croissance du mil. Les deux facteurs évoluent dans le même sens, c'est-à-dire une diminution du développment du mil au fur et à mesure que le nombre de cycles culturaux augmentent. Les symptômes d'épuisement du sol peuvent être rectifiés, soit en supprimant les nématodes, soit en pratiquant la jachère. (Résumé d'auteur)

The use of improved germplasm and management to increase rice production in rainfed lowland and upland systems is discussed. Understanding of the mechanisms conferring P efficiency, particularly external efficiency through root-induced changes in the rhizosphere, is reviewed together with evidence for genetic variation in P efficiency in upland and lowland rice germplasm. The following areas for improving resource and input management are considered: P management under alternately wet and dry soil conditions; P fertilizer formulations for banding in highly-weathered soils; cumulative responses to P fertilizer, including interactions with biological N fixation by legumes; amelioration of subsoil acidity, especially by leaching down the effects of surface-applied lime; and the management of soil spatial variability. Areas for future research are given.

National audience

The rapid expansion of oil palm cultivation in Southeast Asia raises environmental concerns, necessitating a critical evaluation of the impacts of this production system on ecological health. Oil palm growers in Indonesia are faced with the challenge of sustaining high yields to keep pace with the growing global demand for oil and fats, while reducing the environmental impacts of oil palm cultivation. Environmental impacts associated with the deforestation at the initial phase of an oil palm plantation establishment are well documented, however the impacts of mature oil palm plantation on water quality remain poorly investigated. Oil palm is a perennial crop (25-30 years) cultivated predominantly on weathered tropical soils, so high fertilizer input is necessary to sustain high yields, which is expected to endanger neighboring aquatic ecosystems when excess nutrients are carried out to waterways. In Indonesia, 39 % of oil palm planted area is owned by smallholder farmers, who rely on mineral fertilizers to support oil palm production, and 52 % are large private plantations operated by private industries. In addition to mineral fertilizers, industrial plantations also apply mill byproducts as organic fertilizers in the plots surroundings the mill (due to transportation costs). Soil characteristics and fertilizer management in oil palm plantations (i.e. mineral vs. organic fertilizer applications) were expected to alter the soil fertility status and nutrient loads to waterways. Due to the fact that oil palm plantations generally extend over thousands of contiguous hectares, crossing several watersheds and covering different soil types, the effect of fertilizer management on the soil response and nutrient loads to waterways requires landscape-scale studies accounting for soil variability and long-term fertilization sequences across the plantation. The first objective of the thesis was to (i) perform a literature review that provides an overview of the agricultural practices in oil palm plantations as well as hydrological processes involved in the nutrient transfers from those agroecosystems to waterways. Then I aimed to (ii) assess the effect of long term mineral and organic fertilizer sequences on the soil response, considering different soil types, (iii) characterize the dominant hydrological processes involved in the nutrient fluxes to waterways in oil palm plantations, and (iv) assess the effect of fertilizer management and soil characteristics on groundwater quality and nutrient fluxes to streams. The study area was located in the Petapahan area, Central Sumatra, Indonesia, which has a tropical humid climate (annual rainfall > 2000 mm) and weathered soils (Ferralsols). The study area was a landscape (100 km²) including a 4000 ha industrial plantation and a 1500 ha smallholder plantation using rational fertilizer programs. Low-fertility Ferralsols responded significantly to continuous applications of organic fertilizers, with greater improvement in loamy-sand uplands than in loamy-lowlands, compared to repeated applications of mineral fertilizers. I proposed that spatial fertilizer management at the landscape-scale should complement the current plotscale fertilizer management to get higher nutrient use efficiency and improve soil fertility in an oil palm plantation. One year (2009-2010) multi-site monitoring of stream water quality showed nutrient concentrations below Indonesian standards for water quality. In this case study, mature oil palm cultivation did not contribute to the eutrophication of aquatic ecosystems. This was ascribed to nutrient dilution in streams from the high rainfall as well as high nutrient demand by oil palm that was met with a rational fertilizer program. Assessment of nutrient fluxes from baseflow showed that loamy-sand uplands were more sensitive to nutrient losses than loamy lowlands, and organic fertilization helped to reduce nutrient losses to streams. The study also showed high dissolved organic matter content in streams, likely from natural sources. Oil palm agroecosystems in the study area are characterized by fast groundwater renewal indicating the potential for inputs to be quickly transported from soils to the streams. This may be of concern when unbalanced fertilizer management leads to over-application of nutrients or persistent agrochemicals like pesticides bind to dissolved organic matter, since they will be susceptible to contribute to nonpoint source pollution in streams., La rapide expansion de la culture du palmier à huile en Asie du Sud-Est soulève maintes interrogations sur ses impacts environnementaux. Les planteurs indonésiens doivent désormais assurer de hauts rendements pour répondre à une demande mondiale croissante d’huile de palme, tout en minimisant leurs impacts. Les impacts environnementaux associés à la déforestation lors de la phase initiale d’établissement d’une plantation sont déjà bien documentés. En revanche, les impacts d’une plantation mature sur la qualité de l’eau a été très peu étudiée. Le palmier à huile est une culture pérenne (25-30 ans) généralement cultivée sur des sols tropicaux peu fertiles d’où la nécessité de forts apports de fertilisants, apports susceptibles de menacer les écosystèmes aquatiques quand les nutriments en excès sont transportés vers les rivières. En Indonésie, les petits planteurs villageois détiennent 39 % des surfaces plantées en palmier à huile et n’utilisent que des fertilisants minéraux pour assurer leur production. Les industriels privés possèdent 52 % des surfaces, et appliquent, en plus des fertilisants minéraux, des fertilisants organiques issus des rejets de leurs usines. Ces fertilisants organiques sont généralement appliqués dans les parcelles à proximité de l’usine pour réduire les coûts de transport. Les caractéristiques du sol et la gestion de la fertilisation (i.e. fertilisants minéraux vs. organiques) des palmeraies sont susceptibles d’influer sur la fertilité du sol et sur les transferts de nutriments vers les rivières. Etant donné que les plantations s’étendent généralement sur plusieurs milliers d’hectares d’un seul tenant, couvrant plusieurs bassins versants et différents types de sol, l’effet de la gestion de la fertilisation sur la réponse du sol et les transferts de nutriments vers les rivières nécessite des études à l’échelle du paysage. Celles-ci doivent tenir compte tant de la variabilité du sol au sein de la plantation que de la variabilité des séquences de fertilisation pluriannuelles. Le premier objectif de cette étude est (i) de réaliser une revue de littérature sur les pratiques agricoles utilisées dans les palmeraies ainsi que sur les processus hydrologiques impliqués dans les transferts de nutriments dans ce type de contexte, (ii) d’évaluer l’effet de séquences pluriannuelles de fertilisation minérale et organique sur la réponse du sol, tenant compte de la variabilité des sols au sein de la plantation, (iii) de caractériser et quantifier les processus hydrologiques dominants impliqués dans le transfert de nutriments depuis la palmeraie vers les rivières, (iv) et enfin d’évaluer l’effet de la gestion de la fertilisation et des caractéristiques du sol sur la qualité des eaux souterraines et sur les flux de nutriments vers les rivières. La zone d’étude est située dans la région de Petapahan, dans le centre de Sumatra, en Indonésie. Le climat y est tropical humide (précipitations annuelles > 2000 mm) et les sols peu fertiles (Ferralsols). Il s’agit d’un paysage de 100 km² incluant une plantation villageoise de 1500 ha et une plantation industrielle de 4 000 ha, pratiquant une gestion raisonnée de la fertilisation. Cette étude a montré une amélioration significative des propriétés chimiques des sols suite à des applications continues de fertilisants organiques, avec une amélioration encore plus sensible sur les sols sablo-limoneux que sur les sols limoneux. Une gestion spatiale de la fertilisation à l’échelle de la plantation serait plus efficace et devrait compléter la gestion à la parcelle pour une meilleure stratégie d’application des fertilisants adaptée à la variabilité des sols sur les milliers d’hectares de la plantation. Le suivi multi-site sur un an de la qualité des eaux de surface dans le paysage a montré des niveaux de concentrations de nutriments en deçà des limites maximales recommandées par les standards indonésiens. Dans cette étude de cas, la culture d’une palmeraie mature ne semble pas avoir contribué à l’eutrophisation des cours d’eaux. Les raisons en seraient la dilution du système par la forte pluviosité locale, et la pratique d’une fertilisation raisonnée. L’évaluation des flux de nutriments a montré que les sols sablo-limoneux étaient plus sensibles que les sols limoneux aux pertes de nutriments et que la fertilisation organique pouvait réduire significativement ces pertes. De fortes teneur en matières organiques ont été observées dans les rivières, mais probablement dues à des causes naturelles. Le renouvellement rapide des eaux souterraines induit une grande réactivité du système aux intrants qui peuvent être rapidement drainés vers les cours d’eau. Des apports massifs de nutriments (fertilisation non raisonnée) ou des pesticides liés à la matière organique dissoute pourraient donc entraîner un risque de pollution en aval de l’agrosystème.

Pour évaluer les différents changements d’état ou les modifications de fonctionnement du milieu rural induits par les perturbations naturelles, et surtout par les interventions de l’homme, l’observateur a le plus souvent recours à la mesure ou à l’évaluation de simples paramètres, attributs et caractéristiques du système écologique étudié, mais aussi à l’utilisation d’indices complexes calculés à partir de paramètres élémentaires. Cet ensemble est désigné sous le vocable général d’indicateurs...

La fertilité des sols : concept de base. 4. Atelier REGEFOR : La gestion de la fertilité des sols forestiers est-elle à un tournant ?

National audience; Les paysans de l'Afrique subsaharienne doivent innover pour accroitre durablement la production agricole, pour contribuer à la sécurité alimentaire et pour s'adapter aux changements globaux (climatiques, démographiques, etc.). Mais force est de reconnaitre que la majorité des modèles de changement proposés par la recherche n'ont pas été adoptés par les paysans. L'une des raisons invoquée est leur manque d'implication active dans les processus de recherche. La Recherche Action en Partenariat (RAP) vise à remédier à cette insuffisance. Cette communication présente les principes et les dispositifs méthodologique de la RAP en s'appuyant sur le projet Fertipartenaires (Food/2007/144/075, 2008 à 2012). L'objectif du projet était de co-construire des innovations visant à relever la fertilité du sol en appliquant une démarche de RAP. La RAP s'appuie sur des plateformes d'innovations villageoises (Comité de Concertation Villageois, CCV) et se déroule en 4 phases (diagnostics, élaboration de solutions, actions, évaluation des résultats et impacts). Les CCV sont des associations de groupements paysans permettant d'enrôler les agriculteurs et éleveurs dans toutes les phases de la co-construction de l'innovation. La phase de diagnostic a permis de dresser un état des lieux des systèmes de production. La phase d'exploration des solutions a nécessité la mise en oeuvre de formations et de voyages à destination des membres des CCV. La phase de mise en oeuvre a permis d'expérimenter des innovations techniques (1 600 fosses fumières/compostières, 600 expérimentations de techniques culturales innovantes) et organisationnelle (1 charte foncière locale communale). La phase d'évaluation a permis d'estimer l'impact du projet sur les connaissances acquises, les changements de pratiques, leurs effets et leur diffusion. En favorisant l'échange et l'hybridation des connaissances entre paysans, acteurs de l'environnement des exploitations et chercheurs, la RAP renforce les capacités d'innovations et d'adaptation des acteurs face aux changements globaux.

International audience; A French programme, "Réseau de mesure de la qualité des sols: biodiversité des organismes" (RMQS BioDiv) was de-veloped in Brittany (27,000 km² in the western part of France) as an initial assessment of soil biodiversity on a regional scale in relation to land use and pedoclimatic parameters. The nematode community assemblages were compared among the land use categories. Crops were characterised by a high abundance of bacterial-feeders, particularly oppor-tunistic bacterial-feeders belonging to Rhabditidae. Meadows presented a higher total abundance of nematodes than did crops (20.6 ind·g −1 dry soil vs. 13.1 ind·g −1 dry soil), and they were mainly linked to the great abundance of plant-parasitic nematodes, particularly Meloidogyne, but with a very high heterogeneity between sampled plots. The nematodes were most abundant in forests (23.7 ind·g −1 dry soil) and presented the most structured community (SI = 82.2 in forests vs. 58.6 and 55.5 in crops and meadows, respectively). Forests had also the higher fungal component (fungal-feeders and facultative plant-feeders belonging to the Tylenchidae) leading to a significant higher part of the fungal decomposition pathway in forests than in crops. The ability of different taxonomic levels of nematode identifica-tion to discriminate among different cropping systems (i.e., continuous cropping system, crop with meadow in the rota-tion, meadow with crop in the rotation and permanent meadow) was also tested. The family level (48 families identified in these samples) was more efficient than the other taxonomic levels (86 taxa, 17 functional guilds and 6 trophic groups): best statistical significant discrimination for time spent in identification. The relation between the nematode ecological indices, the abundance of nematode trophic groups and the crop management practices were studied. The effects of fertilization, ploughing frequency, use of pesticides and management systems on ecological indices, particu-larly on the Maturity Indices, were observed.

National audience; The benefits of liming permanent grassland are controversial. A long-term trial (carried out on acid soil for 8 years, then on sown cocks foot for 4 years) provided information on the effect of liming (increased production, economic benefits) and on the ecological intensification of this type of grassland. Annual production for non-fertilized unlimed grassland was 1.1 t DM/ha. The positive effect of liming (+ 0,7 t DM/ha) was only true for non-fertilized land. The effect of NPKS fertilization (+ 4,0 t DM/ha) was much higher, which may be attributed to soil phosphorus levels. The effects of liming and fertilization were enhanced for sown cocks foot, where production reached 9 tons. In this case, liming and fertilization are economically beneficial and allow land to be used for intensive farming.; L'intérêt du chaulage dans les prairies permanentes est assez controversé. Un essai de longue durée (prairie permanente sur sol acide semée ensuite en dactyle) procure des informations sur l'effet du chaulage (gain de production, intérêt économique) et pour l'intensification écologique de ces milieux.La réponse au chaulage et à la fertilisation d'une prairie permanente suivie d'une prairie temporaire de dactyle a été étudiée pendant 8 + 4 ans. Laproduction annuelle de la prairie permanente non fertilisée non chaulée (pH 5) est de 1,1 t MS/ha. L'effet du chaulage (+ 0,7 t MS/ha) n'est significatif que sur les parcelles non fertilisées ; l'effet majeur de la fertilisation NPKS (+ 4,0 t MS/ha) est attribué à l'apport de P, limitant dans ce sol. Avec le dactyle (cv. Accord), les effets du chaulage (jusqu'à + 2,7 t MS/ha) et de la fertilisation (jusqu'à + 5,3 t MS/ha) sont supérieurs, la production du traitement fertilisé et chaulé atteignant 9 t MS/ha. Dans ce cas, la fertilisation et le chaulage sont justifiés économiquement et permettent d'utiliser cette parcelle dans un système plus intensif.

La capacité de nodulation des plantes de haricot est fonction de la présence de Rhizobia et de la fertilité des sols, et surtout fonction de la disponibilité en phosphore de ces sols. L’objectif principal de notre travail vise à étudier le potentiel de nodulation des haricots dans diverses parcelles agricoles afin de tester le lien éventuel entre cette disponibilité en phosphore du sol et la capacité de nodulation des variétés. Ce travail est mené en collaboration avec FOFIFA, IRD et PABRA/ECABREN. L’étude est concentrée dans la zone du Moyen Ouest du Vakinankaratra (Ankazomiriotra et Vinany), basée sur des réseaux de parcelles paysannes. Les matériels végétaux utilisés sont les variétés Goiano Precoce (variété tolérante sur tanety), utilisé comme témoin à long terme et Soafianarana pour témoins local. Les lignées contrastantes, RIL 115 et RIL 147 ont été testées. La fertilisation phosphate de Super triple phosphate est apporté avec 46% de P2O5. La quantité de P2O5 apporté est 50 kg/ha. L’expérimentation comprend 25 répétitions repartis dans le Moyen Ouest du Vakinankaratra. Une parcelle paysanne représente une répétition. Chacune de ces parcelles a reçu les quatre variétés de haricot avec deux niveaux de phosphore zéro et 50 kg/ha P2O5. De ce fait, le dispositif comporte huit traitements qui sont randomisés au hasard dans la parcelle et séparés par un canal pour éviter les contaminations entre traitements. Ainsi, les résultats permettent de classifier les parcelles en quatre typologies par rapport à la fixation symbiotique d’azote et selon les variétés. En effet, les résultats ont montré une faible réponse sur l’apport de phosphate. Ainsi, des analyses de corrélation entre le poids de nodosités et le poids de la biomasse aérienne n’ont pas montré un effet significatif.

Key words: crop production, intensification, extensification, farming systems, tradeoff analysis, maize, legume, manure, fertiliser, southern Africa Soil fertility decline and erratic rainfall are major constraints to crop productivity on smallholder farms in southern Africa. Crop production intensification along with efficient use of chemical fertiliser is required to produce more food per unit area of land, while rebuilding soil fertility. The objective of this thesis was to identify appropriate crop production intensification options that are suitable to the socio-economic and biophysical conditions of selected smallholder maize-based farming systems in southern Africa. Three sites that formed a gradient of intensity of crop and livestock production were selected for the study. Murehwa in Zimbabwe is characterised by the largest intensity followed by Ruaca and lastly Vunduzi both in central Mozambique. In all three sites, maize is a key staple and cash crop.A literature review, field methods based on participatory research, and modelling tools were combined in analysing potential crop production options across an agricultural intensification gradient. A meta-analysis on maize grain yieldunder rain-fed conditions revealed thatconservation agriculture required legume rotations and high nitrogen input use especially in the early years.Reduced tillage without mulch cover leads to lower yields than with conventional agriculture in low rainfall environments. Mulch cover in high rainfall areas leads to smaller yields than conventional tillage due to waterlogging, and improved yields under CA are likely on well drained soils. Crop productivity underconservation agriculture depends on the ability of farmers to achieve correct fertiliser application, timely weeding, and the availability of crop residues for mulching and systematic crop rotations which are currently lacking in southern Africa. Anadditive design of within-row intercropping was compared to a substitutive design with distinct alternating rows of maize and legume (local practice) under no-tillin the Ruaca and Vunduzi communities of central Mozambique. Intercropping increased productivity compared to the corresponding sole crops with land equivalent ratios (LER) of between 1.0 and 2.4. Maize yield loss was only 6-8% in within-row intercropping but 25-50% in the distinct-row option. Relay planting of maize and cowpea intercropping ensured cowpea yield when maize failed thus reduced the negative effects of dry spells. The residual benefits of maize-pigeonpea intercropping were large (5.6 t ha-1) whereas continuous maize (0.7 t ha-1) was severely infested by striga(Striga asiatica). The accumulation of biomass which provided mulch combined with no tillageincreased rainfall infiltration. Intensification through legume intercropping is a feasible option to increase crop productivity and farm income while reducing the risk of crop failureespecially where land limitation. Cattle manure in combination with chemical fertiliser that included N, P, Ca, Zn, Mn were evaluated for their potential to recover degraded soils and to support sustainable high crop productivity in Murehwa, Zimbabwe over nine years. The experiment was established on sandy and clay soils in two field types. Homefields were close to the homestead and relatively more fertile than the outfields due to previous preferential allocation of nutrients. Maize grain yields in sandy soils did not respond to the sole application of fertiliser N (remained less than 1 t ha-1); manure application had immediate and incremental benefits on crop yields in the sandy soils. A combination of 25 t ha-1 manure and 100 kg N gave the largest treatment yield of 9.3 t ha-1 on the homefield clay soils, 6.1 t ha-1 on clay outfield, 7.6 t ha-1 on sandy homefield and 3.4 t ha-1 in the eighth season. Despite the large manure applications of up to 25 t ha-1, crop productivity and soil organic carbon build-up in the outfield sandy soils was small highlighting the difficulty to recover the fertility of degraded soils. Manure can be used more efficiently if targeted to fields closest to homesteads but this exacerbates land degradation in the outfields and increases soil fertility gradients. The NUANCES-FARMSIM model for simulating crop and animal productivity in mixed crop-livestock farming systems was used to perform trade-off analysis with respect to crop residue management, animal and crop productivity in Murehwa, Zimbabwe. Retaining all maize residues in the field led to severe losses in animal productivity but significant gains in crop productivity in the long-term. Yield increased 4 to 5.6 t farm-1 for RG1, and from 2.8 to 3.5 t farm-1 for RG2. Body weight loss was on average 67 kg per animal per year for RG1 and 93 kg per animal per year for RG2. Retention of all crop residues reduced farm income by US37 and US38 per year for RG1 and RG2 respectively.Farmers who own cattle have no scope of retaining crop residues in the field as it results in significant loss of animal productivity. Non-livestock farmers (60% of the farmers) do not face trade-offs in crop residue allocation but have poor productivity compared to livestock owners and have a greater scope of retaining their crop residues if they invest in more labour to keep their residues during the dry season. This study has revealed that crop production intensification options developed without considering the biophysical conditions as well as socio-economic circumstances of farmers are nuisances. External ideas should be used to stimulate local innovations to push the envelope of crop production without creating new constraints on resource use.

Living organisms and their enzymes are responsible of most of the soil biotic interactions in agro-ecosystems. This study was to evaluate the impact of land use (cropping systems and farming practices) on the physical, chemical and biological properties of soil in Western Cameroon. We sampled soil (0-20 cm) in four different land use systems (extensive, intermediate, intensive and an undisturbed natural habitat). We also measured soil health indicators in each land use type. We observed that the total organic carbon (Corg) and P availability was significantly higher in agro-ecosystems as compared to undisturbed natural habitat. Similar trends were recorded for pH, electrical conductivity, and ?-glucosidase, dehydrogenases and acid phosphatase activities. We also recorded a significant variation in microbial biomass C (Cmic: 312.0 to 544.5 mg kg-1 dry soil) and microbial biomass N (Nmic: 5.40 to 25.31 mg kg-1 dry soil) with land use intensity. The Cmic/Corg ratios of soils were two-fold lower in agricultural lands with vegetables than the undisturbed control plot indicating a decrease in soil microorganisms. Regression analysis revealed a negative correlation (r = - 0.806, P < 0.01) between soil clay content and microbial biomass C, and a high Corg/N ratio suggesting a heterogeneous distribution of the population of microorganisms between soils and the immobilization of P, respectively. Our results suggest that the selected soil health indicators were sensitive to farming practices and cropping systems.

International audience; The isotopic exchange kinetic (IEK) method allows assessing the rate of orthophosphate ions (Pi) exchange between the solid phase and the solution of the soil with time. However, two challenges have to be tackled when using this technique in soils with a very low water extractable Pi concentration (C-P) and with a high sorbing capacity for Pi. The first is that current colorimetric methods do not allow quantifying Pi concentrations lower than 10 mu g P L-1. While the second challenge is that a significant fractionation between P isotopes may occur in the soil solution system in the presence of soils with high Pi sorption capacity. We assessed here: i) whether concentrating the blue phosphomolybdate complex (BPMC) in hexanol prior to its measurement would allow to lower the detection and quantification limits of Pi, ii) whether a significant isotopic fractionation between (32)Pi and (33)Pi could occur during IEK experiments conducted in the presence of high Pi sorbing substrates (e.g., pure goethite or Malagasy soils) and iii) whether the IEK method when used in conjunction with the hexanol concentration of the BPMC to measure C-P would detect changes in Pi isotopic exchangeability in a ferralsol cropped with upland rice following the input of manure or water soluble fertilizer. The detection and quantification limits of the BPMC concentrated by hexanol were 0.3 and 0.8 mu g P L-1, respectively, using a cell of 10 cm length for the colorimetric measurement. The IEK conducted on Pi amended goethite and on Malagasy soils with (32)Pi and (33)Pi did not show any systematic isotopic fractionation between both isotopes, suggesting that in these soils (31)Pi and (32)Pi or (33)Pi have a similar behavior during isotopic exchange. The analysis of the soils sampled in the field experiment showed a significant increase in the amount of Pi isotopically exchangeable after 1 min only after the application of water soluble P. This increase was paralleled by increases in rice yield and P export by grains demonstrating an increased P availability in this treatment. In conclusion, the IEK method can be used in low P and high Pi sorbing soils as the hexanol concentration method allows measuring very low C-P and as the different P isotopes have a similar behavior in the soil/solution system. The IEK experiments conducted in the presence of goethite, however, point out to the necessity of taking into account the dispersion of particles for a proper interpretation of the isotopic data.

The aim of the present study was to examine the interactions between an endogeic earthworm species, Metaphire posthuma , and purely mineral (control) or mineral plus organic (compost vs. vermicompost) amendments in terms of soil chemical properties and plant growth and yield. A one-year experiment was carried out in a greenhouse with a maize–tomato–maize cycle. Compost and vermicompost modified soil chemical properties leading to higher C and N, higher pH and CEC, and lower available P, NH 4 + and NO 3 − than in the control. Although no significant difference in plant growth was observed for the first maize planting, tomato and maize growth were then highest for the mineral and vermicompost treatments and lowest for compost. Overall plant yields were always highest in mineral fertilizer alone and lowest for the compost treatments. The application of vermicompost led to a similar yield as the control treatment for the first maize planting. However, its beneficial influence decreased during the experiment until it was similar to that of the compost treatment. The presence of earthworms reduced the C content in soil mixed with compost and vermicompost but only influenced plant growth and yield in the compost treatment. The effect of earthworms was initially null (i.e. for the first maize crop), positive (i.e. for tomato planting) and finally negative (i.e. for the second maize planting), thereby underpinning the complexity of the interactions between the quality of organic matter in soil, earthworm activity and plant growth.

Soil fertility decline is a major constraint to crop productivity on smallholder farms in Africa. The objective of this study was to evaluate the long-term (up to nine years) impacts of nutrient management strategies and their local feasibility on crop productivity, soil fertility status and rainfall infiltration on two contrasting soil types and different prior management regimes in Murehwa, Zimbabwe. The nutrient management strategies employed in the study were: a control with no fertiliser, amendments of 100 kg N ha −1 , 100 kg N + lime, three rates of manure application (5, 15 and 25 t ha −1 ) in combination with 100 kg N ha −1 , and three rates of P fertiliser (10, 30 and 50 kg P ha −1 ) in combination with 100 kg N, 20 kg Ca, 5 kg Zn and 10 kg Mn ha −1 . Maize grain yields in sandy soils did not respond to the sole application of 100 kg N ha −1 ; manure application had immediate and incremental benefits on crop yields on the sandy soils. A combination of 25 t ha −1 manure and 100 kg N gave the largest treatment yield of 9.3 t ha −1 on the homefield clay soils, 6.1 t ha −1 in the clay outfield, 7.6 t ha −1 in the homefield and 3.4 t ha −1 in the eighth season. Yields of the largest manure application on the sandy outfields were comparable to yields with 100 kg N in combination with 30 kg P, 20 kg Ca, 5 kg Zn and 10 kg Mn ha −1 in the homefields suggesting the need to target nutrients differently to different fields. Manure application improved rainfall infiltration in the clay soils from 21 to 31 mm h −1 but on the sandy soils the manure effect on infiltration was not significant. Despite the large manure applications, crop productivity and SOC build-up in the outfield sandy soils was small highlighting the difficulty to recover the fertility of degraded soils. The major cause of poor crop productivity on the degraded sandy soils despite the large additions of manure could not be ascertained. The current practice of allocating manure and fertiliser to fields closest to homesteads exacerbates land degradation in the sandy outfields and increases soil fertility gradients but results in the most harvest for the farm. On clay soils, manure may be targeted to outfields and mineral fertiliser to homefields to increase total crop productivity. Farmers who owned cattle in the study site can achieve high manure application rates on small plots, and manure application can be rotated according to crop sequences. Consistent application of manure in combination with mineral fertilisers can be an effective option to improve crop yield, SOC and moisture conservation under smallholder farming conditions. Combined manure and mineral fertiliser application can be adapted locally as a feasible entry point for ecological intensification in mixed crop–livestock systems.

African savannas developed an efficient strategy of nutrient uptake and control of nitrification making it possible to avoid large losses of nutrient by drainage. The conversion of native savanna into commercial forest plantations is an important global change driver that potentially impacts element cycles. Afforestation of native Congolese savannas by Eucalyptus started 30 years ago. Large amounts of nutrients are removed through biomass harvesting every 6-7 years. Losses of nutrients by deep drainage might be a serious threat for the sustainability of these plantations, established on sandy soils with high hydraulic conductivities. We compared the soil N-mineralisation, the nutrient fluxes and deep drainage beneath savanna and Eucalyptus plantation in Congo. Then, we discussed the strategy of nutrient recycling. The water fluxes at a depth of 400 cm were approximately 20% higher in the savanna than in Eucalyptus plantation. Although the nitrification rate and solution chemistry exhibited strong modifications during the first year following both savanna afforestation and the harvesting of the Eucalyptus stand, the losses of nutrients by deep drainage remained unexpectedly low. The largest fluxes of drainage at a depth of 6 m were found for NH4+-N, which reached a maximum of 0.4 g m(-2) yr(-1) in the second year following savanna afforestation and I g m(-2) yr(-1) in the first year after clear cutting. The deep drainage of NO3--N, Mg2+, Ca2+ and K+ did not exceed 0.2 g m(-2) yr(-1) in the savanna and at any stage of plantation development. These results are discussed regarding (i) the roots distribution in the soil of each ecosystem and (ii) the nutrient accumulation in biomass. The limited changes between the nutrient fluxes in both ecosystems were the result of fast root growth in the deep soil layers after planting, combined with an intense uptake of the tree roots to satisfy the large nutrient and water requirements for the development of tree crowns. Intense uptake and cycling of nutrients mitigated the risk due to clear cut and N fertilisation in this forest plantation. Nevertheless, forest managers must carefully fit fertilisation regimes to the nutrient requirements of new clone selected by breeding programmes and reduce as much as possible the delay between harvesting and re-planting to avoid high losses by deep drainage. Crown Copyright (C) 2013 Published by Elsevier B.V. All rights reserved.