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Soil phosphorus (P) loss from agricultural systems will limit food and feed production in the future. Here, we combine spatially distributed global soil erosion estimates (only considering sheet and rill erosion by water) with spatially distributed global P content for cropland soils to assess global soil P loss. The world’s soils are currently being depleted in P in spite of high chemical fertilizer input. Africa (not being able to afford the high costs of chemical fertilizer) as well as South America (due to non-efficient organic P management) and Eastern Europe (for a combination of the two previous reasons) have the highest P depletion rates. In a future world, with an assumed absolute shortage of mineral P fertilizer, agricultural soils worldwide will be depleted by between 4–19 kg ha−1 yr−1, with average losses of P due to erosion by water contributing over 50% of total P losses., Phosphorus is an essential nutrient critical for agriculture, but because it is non-renewable its future availability is threatened. Here the authors show that across the globe most nations have net losses of phosphorus, with soil erosion as the major route of loss in Europe, Africa and South America.

Ce numéro est constitué d’articles issus du colloque « Biodiversité et durabilité des agricultures » qui s’est tenu à Paris le 11 avril 2019.; The current economic, environmental and social context encourages a transition to agroecologicalpractices that limit the use of synthetic inputs and enhance planned biodiversity in agroecosystems.Such practices mobilize a number of ecosystem services provided by soil organisms. Thiscommunication presents the principal components of the soil biota and associated ecosystem services.The impacts of the main soil management practices (tillage, fertilization) and of alternative systems arethen described. In conclusion we stress the importance of soil biodiversity conservation foragroecosystem fertility and functioning, and suggest a few key improvements such as increasing plantdiversity in agricultural systems.; Notre contexte économique, environnemental et sociétal actuel nous incite à considérer, dans le cadrede la transition agroécologique, des pratiques agricoles limitant l’usage d’intrants de synthèse etfavorisant la biodiversité planifiée dans les agroécosystèmes. Ces pratiques mobilisent certains servicesécosystémiques réalisés par la biocénose du sol. Dans cette communication, nous présentons lesprincipales composantes de la biocénose du sol et certains services écosystémiques associés. Nousabordons ensuite les impacts des principales pratiques culturales (labour, fertilisation) et des modes degestion des terres alternatifs. Nous concluons sur l’importance de la préservation de la biodiversité dessols sur la fertilité des agroécosystèmes, et suggérons des pratiques clés d’amélioration telles quel’augmentation de la diversité végétale dans les systèmes de culture.

Notre contexte économique, environnemental et sociétal actuel nous incite à considérer, dans le cadre de la transition agroécologique, des pratiques agricoles limitant l’usage d’intrants de synthèse et favorisant la biodiversité planifiée dans les agroécosystèmes. Ces pratiques mobilisent certains services écosystémiques réalisés par la biocénose du sol. Dans cette communication, nous présentons les principales composantes de la biocénose du sol et certains services écosystémiques associés. Nous abordons ensuite les impacts des principales pratiques culturales (labour, fertilisation) et des modes de gestion des terres alternatifs. Nous concluons sur l’importance de la préservation de la biodiversité des sols sur la fertilité des agroécosystèmes, et suggérons des pratiques clés d’amélioration telles que l’augmentation de la diversité végétale dans les systèmes de culture., The current economic, environmental and social context encourages a transition to agroecological practices that limit the use of synthetic inputs and enhance planned biodiversity in agroecosystems. Such practices mobilize a number of ecosystem services provided by soil organisms. This communication presents the principal components of the soil biota and associated ecosystem services. The impacts of the main soil management practices (tillage, fertilization) and of alternative systems are then described. In conclusion we stress the importance of soil biodiversity conservation for agroecosystem fertility and functioning, and suggest a few key improvements such as increasing plant diversity in agricultural systems.

Agriculture brings with it a number of issues: agricultural production and food security, water and soil resource conservation, limiting the impact of farming on the quality of our environment (water, air, soil). In the context of global changes and the challenges they pose for agriculture sustainability, our ability to characterize how croplands function in terms of water, carbon and particle fluxes is crucial. Developments of agro-ecosystems modeling, including their interactions with the atmosphere and the anthropogenic factors are valuable tools for progress in this direction. Remote sensing, with the high variety of spectral ranges and the fine spatial and temporal resolution currently available, is a tool of great value for various applications in agriculture. The availability of robust inverse methods that allow surface biophysical variables to be assessed, combined with modeling approaches, makes it a high performance tool. The major contributions of remote sensing include: – its ability to cover large stretches of land and to provide information on the various land uses and practices generated by agriculture. These uses and practices are important to know, both for census purposes (agricultural statistics, agri-environmental monitoring, etc.) and for modeling the behavior of agro-hydrosystems; – providing frequent variables characterizing soil and vegetation properties that allows us to monitor the status of crops, their production potential, their irrigation requirements. This monitoring is a highly strategic issue, both for forecasting purposes, food security and good resource management; – the possibility, from the same information, of assessing the contribution of agricultural lands to net emissions of CO2 and other greenhouse gases (GHGs); this assessment is essential for proposing alternative agricultural scenarios for mitigating the contribution of croplands to climate change; – thanks to the fine spatial and temporal resolution of information, the possibility of providing a decision support for farming activities according to the intra-field variability (precision farming). This dimension represents an important lever for enabling agricultural systems to achieve better efficiency and economical use of inputs for an agriculture that respects the environment.

Many rubber smallholdings in Indonesia have developed into rubber agroforests as a result of the extensive management of the plantation. The resulting complex multi-species agroforests have a number of environmentally beneficial characteristics including a high level of natural biodiversity. Most environmental benefits would be significantly enhanced if these systems were not taken periodically through a new cycle of slash-and-burn, as normally happens when latex yield drops to uneconomic levels. This paper explores, from an agroecological perspective, the potential for such cyclical systems to be developed into permanent agroforests providing sustained latex yield over a longer time frame without a slash-and-burn intervention. Evidence is provided from direct observations, interviews with farmers and the results of specific agronomic experiments. Enrichment planting of seedling or grafted-clonal rubber plants into existing rubber agroforests resulted in low growth rates as a result of shading fr...

La production de coton biologique et equitable a demarre depuis 2004 au Mali dans un contexte de grave crise du systeme de production du coton conventionnel. Cette alternative a rencontre une forte adhesion, notamment aupres des femmes ; leurs nouvelles responsabilites en tant que productrices contribuent a une valorisation de leur statut social. Cependant, sans reduction des inegalites d’acces des femmes a la terre, a l’equipement agricole et a la main-d’œuvre, la durabilite de la filiere risque d’etre compromise.

A volcanic tuff rock known as cangahua (Ecuador) or tepetate (Mexico) is found throughout the Andes. Problems have arisen as the layers of light but fragile soil that once covered the tuff have been lost for both natural (environmental) reasons and because of over-cultivation. When the soil is gone, the tuff is impermeable and sterile. Now, a project in Ecuador has determined that the tuff itself can be reclaimed and is supporting a programme that sends bulldozers to the tuff regions to break up the rock and create a new fertile soil.

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.

The integrated soil–crop–atmosphere model Water and Agrochemicals in the Vadose Environment (WAVE) (Vanclooster et al., 1995) was evaluated for two contrasted sets of data. One was from the tropical climate and ferrallitic soil conditions that exist in Mare Island, in New Caledonia. The other was from a glacial terrace under the continental climate of La Cote Saint-Andre (Isere) in France. Water and NO 3 concentrations and fluxes were monitored during three consecutive years at instrumented sites with different surface covers (maize [ Zea mays L.] or bare soil) or amount of applied fertilizer. The comprehensive set of measurements allowed us to evaluate the prediction capabilities of the WAVE model. Several parameters were determined independently, while others were adjusted on the basis of simulations for the wettest year at Mare and an average hydrological year at La Cote Saint-Andre. A stepwise approach was used to calibrate these parameters by sequentially integrating each individual model component. A screening sensitivity analysis was performed to address the most critical parameters. The predictive ability of the model was evaluated by comparing simulated and measured states variables and water and NO 3 fluxes using two different years of data obtained at the same sites. For both sites, the model gave the best results for wet conditions, which actually posed the most critical problems in terms of groundwater pollution under our specific conditions. However, the model was used beyond its capacity as both soils had specificities for which the model was not designed. Overall, WAVE gave quite good predictions, but further studies are needed to fully evaluate WAVE with its crop growth model, SUCROS.

Vermicompost and biochar amendments are management practices which may contribute to sustainable agroecosystems by reducing dependence on inorganic fertilizers. However, little is known about their impacts on soil microorganisms and their transfer and evolution in connected aquatic systems. The aim of this study was to determine the influence of organic manure (buffalo manure, compost or vermicompost) and biochar amendments on bacterial and viral properties in soil and water. A three year experiment was carried out with terrestrial mesocosms which were used to test the effect of organic matter amendment on maize growth. In the last year of the experiment, runoff and infiltration waters from the terrestrial mesocosms were transferred to aquatic mesocosms. Organic fertilization improved soil properties (higher C, N content and pH H 2 O ) and as a consequence increased soil bacterial and viral abundance. Bacterial diversity (Shannon ‘H’ and richness ‘S’ indices calculated from DGGE fingerprint) was also enhanced after the continuous application of organic amendments. Compared with compost, vermicompost reduced viral abundance and S but similar H and bacterial abundance were observed. The pH H 2 O , C content and bacterial and viral abundance increased in the aquatic mesocosms following organic fertilization. As a consequence, bacterial and viral diversity also increased in the water, although no differences were found between compost and vermicompost. Biochar increased soil bacterial abundance for the mineral fertilizer treatment but did not influence bacterial and viral abundance in water. However, the combination of biochar and vermicompost led to an increase of viruses in soil and a reduction of bacteria in water. Similarity dendrograms from the DGGE banding patterns showed that the structure of bacterial communities was mainly influenced by the fertilizer treatments in soil but by the presence of biochar in water. In conclusion, this study demonstrated that the nature of the organic amendment has important consequences on both soil and water microbial abundance and diversity.

Les technosols construits sont une alternative au prélèvement de terre végétale en milieu naturel. La gestion durable de ces technosols suppose de comprendre l'évolution de leurs propriétés hydriques. Nous avons analysé les courbes de retrait de technosols dont la teneur en compost varie de 0 à 50%, en présence ou non de plantes et/ou de vers de terre. Les résultats montrent que ces organismes expliquent plus la variance (19%) des propriétés hydriques du sol que la dose de compost (14%). Le compost et les plantes jouent un rôle positif sur l'eau disponible présente à la fois dans la macroporosité et dans la microporosité, les vers de terre jouant un rôle positif uniquement sur cette dernière. L'effet conjoint des organismes et du compost explique davantage la variance ( 40%) que les effets simples de ces facteurs. En règle générale, l'effet simple du compost est inférieur à celui des plantes et des vers.

Busseola fusca (Lepidoptera: Noctuidae) is an important pest of maize and sorghum in sub-Saharan Africa. One century after its first description by Fuller in 1901, inaccurate information based on earlier reports are still propagated on its distribution (e.g., absent from the lower altitudes in East Africa) and host plant range (e.g., feeding on a large range of wild grass species). This review provides updated information on the biology, distribution and genetics of B. fusca with emphasis on insect-plant interactions. Related to this, new avenues of stem borer management are proposed.

In Northern Vietnam, organic fertilization programmes are being tested to restore soil fertility and reduce soil erosion. However, the amendment of organic matter in soil is also associated with the development of the invasive earthworm species Dichogaster bolaui. The objective of this study was to investigate the influence of organic matter amendment quality (compost vs. vermicompost) on D. bolaui. Our study confirmed D. bolaui development in organic patches in the field. However, we also observed that the flat-backed millipede Asiomorpha coarctata proliferated in these organic patches. Native to Asia, this millipede species is also considered as invasive in America. Both D. bolaui and A. coarctata more rapidly colonized compost than vermicompost patches. A laboratory experiment confirmed this trend and showed the limited development of D. bolaui in vermicompost. This is probably because of the decreased palatability of this substrate to soil fauna. In conclusion, any restoration practice that aims to increase the organic stocks in soils degraded by erosion should consider the quality of the organic amendment. In Northern Vietnam, vermicompost may be the preferred substrate for restoring soils while limiting the spread of D. bolaui. (C) 2014 Elsevier Masson SAS. All rights reserved.

The effects of a composted organic amendment and solarization on the organic matter (OM) of a sandy soil were determined by means of particle-size fractionation and analysis of carbon and nitrogen contents. After 2 years, total soil carbon increased under organic fertilization but did not significantly change with solarization. As a consequence of the climatic conditions in the greenhouse, the carbon concentrations (g/kg fraction) of the particle-size fractions were lower than those found for temperate soils and closer to those for tropical soils. The carbon amounts (g/kg soil) and carbon nitrogen ratios, which were highest in fractions greater than 200 micrometers reflected the short-term influence of the industrially processed organic amendment, rich in composted coarse plant debris. In contrast, the characteristics of the OM associated with each fraction were not significantly affected by solarization. In comparison with other coarse-textured temperate or tropical soils, carbon concentrations in fine silt (2-20 micrometers) and clay (0-2 micrometers) fractions were very low. This suggests a "greenhouse effect", together with a high rate of carbon mineralization affecting fine silt and clay fractions. (Résumé d'auteur)

A series of experiments was conducted where a range of injuries due to rice pests (pathogens, insects, and weeds) was manipulated simultaneously with a range of production factors (fertilizer input, water supply, crop establishment method, variety) in different seasons and years. These factors were chosen to represent lowland rice production situations characterized in surveys conducted in tropical Asia and their corresponding range of attainable yield. Experiments complemented one another in exploring the response surface of rice yields to yield-limiting and yield-reducing factors. The resulting experimental data base consisted of 445 individual plots and involved 11 manipulated injuries in a range of attainable yields of 2 to 11 t ha-1. A first, nonparametric, multivariate analysis led to a hierarchy of potential injuries, from marginally (e.g., bacterial leaf blight) to extremely harmful (e.g., rice tungro disease). A second, parametric, multivariate approach resulted in a multiple regression model involving factors generated by principal component analysis on injuries that adequately described the variation in actual yield. One major finding was that some (attainable yield × injury factors) interactions significantly contributed to the description of variation in actual yield, indicating that some injuries (or their combinations) had a stronger or weaker yield-reducing effect, depending on the level of attainable yield. For instance, yield losses due to sheath blight, weed infestation, and rice tungro disease tend to increase, remain stable, and decrease, respectively, with increasing attainable yields. Back-computations using the principal component regression model estimated yield losses caused by individual injuries, using the mean injury levels in a population of farmers' fields surveyed across tropical Asia. The results indicate that sheath blight, brown spot, and leaf blast are diseases that cause important losses (between 1 and 10%) regionally. Among the insect injuries, only white heads caused by stem borers appear of relevance (2.3% yield losses). These injuries, however, do not match in importance those caused by weeds, whether outgrowing the rice crop canopy (WA) or not (WB), both types of injuries causing about 20% yield losses when considered individually. When all mean injuries were combined into one mean injury profile occurring at a regional attainable yield of 5.5 t ha-1, a mean yield loss of 37.2% was estimated, indicating that injuries were less than additive in their yield-reducing effects. Scenario analyses were conducted in a set of (production situations × injury profiles) combinations characterized from surveys in farmers' fields in tropical Asia. Depending on the scenario chosen, losses ranging from 24 to 41% were found.

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.

Chapitre 6; International audience; Community and ecosystem ecology are paying increasing attention to evolutionary dynamics, offering a means of attaining a more comprehensive understanding of ecological networks and more efficient and sustainable agroecosystems. Here, we review how such approaches can be applied, and we provide theoretical models to illustrate how eco-evolutionary dynamics can profoundly change our understanding of agricultural issues. We show that community evolution models can be used in several contexts: (1) to improve the selection of agricultural organisms within the context of their ecological networks; (2) to predict and manage the consequences of agricultural disturbances on the ecology and evolution of ecological networks; and (3) to design agricultural landscapes that benefit from network eco-evolutionary dynamics, but without negative impacts. Manipulation of landscape structure simultaneously affects both community ecological dynamics (e.g., by modifying dispersal and its demographic effects) and co-evolution (e.g., by changing gene flows). Finally, we suggest that future theoretical developments in this field should consider appropriate co-evolutionary models and ecosystem services.

The amendment of vermicompost is a management practice that may contribute to sustainable agroecosystems by making them less dependent on inorganic fertilizers. However, little is known about the impact of this practice on soil biota and the flow of microbes to the water system. Using a 30-days laboratory experiment, we investigated the development of the peregrine earthworm species, Dichogaster bolaui , in presence of compost or vermicompost, and assessed its impact on the flow of bacteria and viruses to the water system. The dynamics of soil bacterial diversity (assessed by DGGE) and concentration in water together with their viral parasites were also assessed through an incubation of solution during 5 days (comparison between T 0 and T 5 ). This study highlights the rapid development of D. bolaui after compost amendment. However, the low quality of vermicompost and the absence of organic amendment in the control treatment allowed the survival but not the development of D. bolaui . Higher bacterial and viral abundances in compost and vermicompost substrates led to more important transfer of these communities from the soil to the water system in comparison with the untreated soil, but no difference was observed between compost and vermicompost treatments. In terms of abundance, the bacterial to virus ratio was rather stable in the soil solution but no such a relation was observed in the soil. A reduction of bacterial diversity (OTU) was measured at the end of the incubation period for all the treatments. However, higher number of OTU at T 5 for the compost treatment suggested a better adaptation and/or resistance of soil bacteria to the aquatic system, in comparison with the control treatment. Vermicompost treatment led to intermediate conclusions. The presence of D. bolaui significantly reduced bacterial abundance in the soil organic layer (both compost and vermicompost treatments) but it did not influence bacterial and viral abundance in water, suggesting independent processes. Earthworms buffered bacterial DGGE patterns after five days of incubation, probably through a facilitation of soil bacterial groups more able to resist in solution.

International audience; The aim of this study was to determine the influence of compost and vermicompost produced from buffalo manure on soil bacterial diversity and activity in the presence and absence of the endogeic earthworm Metaphire posthuma. This experiment was carried out for 15 months with a maize- tomato emaize cycle under greenhouse conditions in Northern Vietnam. It showed a positive influence of compost and vermicompost on soil microbial properties, with higher cultivable bacteria, higher bacterial and catabolic diversity (Shannon diversity 'H' and Richness 'S') indices and higher enzymatic activities than control soils which only received mineral fertilizers. Differences also occurred between compost and vermicompost with lower activity and diversity in the soil amended with vermicompost, probably because of its higher molecular stability. The presence of M. posthuma led to divergent dynamics of bacterial community in soils amended with compost and vermicompost. Earthworms negatively influenced soil microbial properties in composted soil (lower Average Well Color Development 'AWCD'), probably because of competition between bacteria and earthworms for organic resources and/or because of the consumption of microbes by earthworms. Conversely, the presence of earthworms increased bacterial diversity and activity with higher AWCD, and H and S indices for the vermicompost treatment, probably as a result of a stimulation of microorganisms that allow the degradation of stable organic matter and its further consumption by earthworms. In conclusion, this study clearly confirmed the different impacts of compost and vermicompost on bacterial activity and diversity and highlighted the importance considering the interaction of these organic substrates with local endogeic earthworms.

Low densities of #Pontoscolex corethrurus$ have been introduced into low-input cropping systems at Yurimaguas (Peru) to test their effects on soil fertility under field conditions for six succesive cropping cycles. Earthworm biomass was sustained at 40 g/m2 fw (ca. 3 g ash-free dry mass) on the average with peak values of 80 g at harvests 2 and 3 in treatments receiving an application of legume green manure. At the 6th harvest, earthworm biomass was significantly lower in the treatment with no organic input than in treatments with crop residues and legume green manure. Earthworm activities did not prevent C and nutrient stocks from being significantly depleted although P, K and Ca concentrations tended to be higher than in non-inoculated treatments at the 6th harvest. Plant production was significantly increased by 36% due to earthworm inoculation in a traditional low-input rotation (maize, rice, cowpea, rice, rice, rice) with variation between -43 and +78%, depending on the crop and climatic conditions. In a continuous maize culture that received fertilizers for the last three crops, grain production was increased by 2.45-fold on average, due to earthworm inoculation. These results demonstrate that the maintenance of active earthworm populations was favourable to crop production during the time scale of our experiments (3 y). Longer term experiments are required to test the sustainability of the positive effects observed. (Résumé d'auteur)

In the mountainous regions of Southeast Asia, smallholder farmers are both victims of and actors in the degradation of natural resources, as a result of their agricultural activities. Addressing sustainable development thus requires a good understanding of the agriculture-poverty-environment nexus – defined as the set of complex linkages between agriculture, poverty and the environment – and of the economic incentives that drive the natural resource use of smallholder farmers in vulnerable areas. The objective of this chapter is to improve our understanding of the extent and nature of these linkages across different settings in Southeast Asia – namely northern Vietnam and northern Thailand, and to derive policy recommendations that can contribute towards the enhancement of sustainable development in these regions. The chapter draws on empirical research conducted in northern Vietnam and northern Thailand between 2007 and 2011.

International audience; This work assesses the value of climate forecasts for millet growers in Niger. We quantify the potential value of three kinds of categorical forecasts assigning cumulated rainfall during the forthcoming rainy season by tercile (dry, normal or humid): (i) a realistic imperfect tercile forecast; (ii) a perfect tercile forecast and (iii) a perfect tercile forecast which includes a prediction of rainy season onset and offset dates. Eighteen management strategies are assessed. Corresponding yields are computed using the SARRA-H crop model then converted into utility by taking into account risk-aversion. Simulations over an historical 18-year period 1990-2007 show that benefit is lowest with imperfect tercile forecasts (+6.9 %), higher (+11%) with perfect tercile forecasts, and reaches +31% when enhanced adaptation strategies and additional climatic indices are available. These results show that improving existing forecast systems by including the prediction of onset and cessation of rainfall is of great value.

La pression demographique et les changements globaux menacent la durabilite des ressources naturelles dans la region sub-sahelienne de l'Afrique de l'Ouest. Les degradations et changements environnementaux peuvent etre attenues par l'adoption de pratiques agricoles adaptees qui permettent de restaurer durablement la productivite des sols degrades et d'assurer la securite alimentaire des populations rurales. A Ziga, village situe dans la region du Yatenga, un programme de recherche a ete conduit entre 1980 et 1987. Le but de cette recherche etait de decrire et d'analyser les pratiques de gestion de la matiere organique et de l'eau, d'apprehender leurs determinants, pour deduire leurs effets sur la durabilite des systemes agricoles. En 2005, des enquetes ont ete menees dans ce meme village, pour evaluer l'evolution des pratiques agricoles. Selon les resultats de ces enquetes, deux pratiques, appelees "zai" et "djengo", sont largement utilisees dans la production de cereales. Les caracteristiques du "zai" et du "djengo" ont ete evaluees et leurs effets sur les rendements des cultures de cereales mesures. Ces pratiques sont des systemes de culture caracterises par une concentration au niveau du systeme sol-plante de l'eau et des apports fertilisants sous forme organique ou minerale. La capture des eaux de ruissellement se fait au niveau de micro bassins creuses a la surface du sol dans lesquels sont apportes des matieres organiques et ou sont semees les graines de cereales. Elles sont associees a un controle des eaux de ruissellement et de l'erosion a l'echelle de la parcelle mais egalement a celle du petit bassin versant par l'intermediaire des cordons pierreux disposes le long des courbes de niveau. Alors que le zai se pratique sur des sols encroutes consideres comme degrades, le " djengo " base sur les memes principes est applique sur des sols a texture sableuse. Cette derniere pratique, qui porte le nom de l'outil utilise pour sa mise en oeuvre, une houe a long manche, n'avait pas ete decrite au cours des travaux anterieurs menes a Ziga. Les observations realisees ont revele une regeneration de la diversite de la strate arboree associee aux cultures. Les principales contraintes de ces pratiques sont la quantite de travail necessaire, la disponibilite du fumier. Cette etude a par ailleurs demontre la mise en oeuvre d'une veritable strategie d'intensification des systemes de production agricole dans cette region sahelienne. L'ensemble de ces pratiques associant des mesures de conservation des eaux et des sols du bassin versant au systeme sol-plante en passant par la parcelle cultivee permet aux agrosystemes d'entrer dans un cercle vertueux d'augmentation de la production agricole tout en preservant les proprietes environnementales du milieu. (Resume d'auteur)

Dans les milieux scientifiques, il est coutume de dire que le sol est une ressource naturelle non renouvelable : d’où des discours pessimistes sur l’avenir de la planète et de nombreux travaux sur la dégradation des sols. Or plusieurs expériences paysannes ou scientifiques montrent qu’en milieu tropical il est possible d’accélérer l’altération de certaines roches et de restaurer la capacité de production de sols dégradés par les cultures ou décapés par l’érosion. L’analyse de treize cas montre que pour restaurer rapidement la productivité de ces sols il faut respecter six règles : 1/prévoir une gestion adéquate des eaux de surface (cordons de pierres, haies, cuvettes) 2/rouvrir la macroporosité et la stabiliser (travail du sol et enfouissement de matières organiques), 3/revitaliser l’horizon de surface par l’apport de matières organiques fermentées, 4/nourrir les plantes, 5/adapter le pH du sol et 6/choisir des végétaux bien adaptés aux conditions locales mais non envahissants. Cet investissement (travail + fumure organique et minérale) n’est acceptable que si l’amélioration des revenus est sensible et les conditions socio-économiques (pression démographique et marché où écouler la surproduction) durables. Scientists commonly declare that soils are a not renewable resource and are pessimistic concerning the potential of soil restoration: therefore the studies concerning the degradation processes are abundant. Nevertheless, many farmers or scientists have shown that, in tropical areas, it is possible to accelerate the weathering of certain rocks like shale, argillite, marl, basalt. It seems possible to restore in a few years the productivity potential of degraded or eroded soils. In this paper, the author analyses 13 study cases showing that it is possible to restore rapidly the productivity of certain soils if six general rules are respected: 1/a good management of superficial waters, 2/opening the macro-porosity by deep tillage and stabilising the structure, 3/revitalising the upper horizon with 3t/ha of manure or compost, 4/regulate the pH between 5 & 8, 5/insure a good nutrition of cultivated plants and 6/select a good vegetative cover well adapted to local conditions but not invading the country. This investment (labour, organic + mineral fertilizers) is only acceptable if the net income is improved and the market durable.

El maíz es la planta principal del sistema agrícola tradicional mexicano llamado “milpa” y en el desarrollo de la agricultura moderna en México. Analizaremos la evolución del sistema de conocimientos del cultivo del maíz (“savoir-faire”: prácticas, conocimientos, representaciones) para comprender la forma de integración de innovaciones agrícolas a dicho cultivo. A partir de una investigación de antropología cualitativa en dos ejidos del sureste del estado de Veracruz documentamos las lógicas culturales y mercantiles. La producción del maíz es un fenómeno social total, componente constitutivo de las sociedades rurales mexicanas en toda su complejidad, pedestal de la evolución de los conocimientos locales agrícolas; los cuales se han adaptado a las transformaciones del entorno ecológico, económico y socio-político. El abandono masivo de variedades de maíz nativo –10% de la producción local hoy en día– y la valorización de variedades mejoradas son indicadores de la preponderancia de lógicas mercantiles sobre aquellas de consumo familiar. Encontramos que la conservación de maíces nativos depende de la estructura social, de sus formas de adaptación al modelo agrícola comercial, y en particular de la resiliencia de las prácticas de la agricultura de autoconsumo e intercambio de productos a nivel de las redes sociales., Maize is the main plant of “milpa”, a Mexican traditional agricultural system. It played a key role in the development of both, the “traditional” and the modern agriculture in Mexico. This article analyzes the evolution of knowledge around this crop, to understand the ways that agricultural innovations are integrated in household agriculture. Our anthropological research in two ejidos in the southeast of Veracruz documents cultural and market logics that guide agricultural practices linked to the maize crop. The production of the maize is considered a total social phenomenon because it is related in complex ways to all components of rural Mexican societies. The abandonment of native maize varieties –today, only 10% of local production– and the emphasis on hybrid varieties are indicators of the supremacy of the market logics over those of household consumption. We find that the conservation of native varieties depends on the social structure, on the ways in which rural communities adapt to a commercial agricultural model, and in particular on the resilience of social relations and social networks related to agricultural practices and exchange of products.

The effects of various levels of cow manure (equivalent to 0–50 kg nitrogen/ha.) or ground limestone (equivalent to 0–5 tons calcium/ha.) on the expression of resistance of cassava, Manihot esculenta Crantz to the cassava mealybug, Phenacoccus manihoti Mat. Ferr., were investigated under semi-controlled conditions in the laboratory. The study was made on two varieties of cassava, Moudouma and MM79, characterized by different levels of resistance in terms of antibiosis and tolerance. The antibiotic component was evaluated by determining the intrinsic capacity for increase rc and tolerance by quantifying morphological and physiological modifications in the growth of plants induced by 2 months infestation by 100 mealybugs. The antibiotic resistance of the two varieties was reduced by both fertilizers. However, the reduction was only significant at levels of 10 and 20 kg N/ha. and 1 and 1.51 Ca/ha. for Moudouma and MM79 respectively. In both varieties, tolerance was increased by the addition of nitrogen and not modified by the addition of lime. The integration of these results into traditional cassava crops systems has also been discussed.

National audience; La gestion raisonnée du phosphore dans les zones d’élevage en situation d’excédent phosphaté par rapport aux besoins des cultures, sera ici traitée par le développement de trois thèmatiques complémentaires : la gestion des cycles des éléments nutritifs, la gestion de la fertilité des sols, l’activité biologique des sols et la nutrition. L’objectif étant de tendre vers une agriculture durable, économe des ressources naturelles et de mettre en oeuvre la fertilisation raisonnée des cultures.

In tropical regions, crop yields generally decrease with time, partly due to a decline in the levels of exchangeable bases linked to acidification of the upper layers of the soil. Nitrogen, calcium and magnesium balances were studied on an oxisol in southern Togo under continuous maize cropping with mineral fertilization and crop residue return, by measuring inputs and outputs. The balance was near equilibrium for nitrogen (urea dressing, 120 kg N ha−1 y−1) and negative for calcium and magnesium. Leaching represented between 29% and 85% of the total output for nitrogen and accounted for practically all the calcium and magnesium outputs. In the upper horizons, nitrate, calcium and magnesium contents in the soil solution were correlated. This was interpreted as an exchange between the calcium and magnesium ions adsorbed on the soil and the protons released by the transformation of ammonium into nitrate. The nutrient content of the soil solution increased in the case of no potassium fertilization, probably because of a lower nitrogen immobilization by microorganisms, the crop residue yield being reduced by the induced deficiency. An insufficient potassium fertilization increases leaching losses of calcium, magnesium and nitrogen. In the deeper horizons, the nitrate content of the soil solution was not correlated with the calcium and magnesium contents. Nitrogen was probably taken up by roots and some calcium and magnesium ions exchanged during their transport through the soil.

In New Caledonia, soils developed on ultramafic rocks (5. 500 km2) are constituted of more than 65 % iron oxi-hydroxide. They present very low contents in nitrogen and phosphor (only 1/10 to 1/100 of average contents); besides their Ca / Mg ratio is unbalanced and they contain very high heavy metals concentrations (nickel, manganese, cobalt, chromium). Nowadays the nickel open mines which exploit such soils must consider both economic interests and ecological preoccupations, as these soils are associated to particularly original and diversified ecosystems. Within these, several endemic pioneer plant species have been identified. Among them, some Costularia (Cyperaceae) are recommended in revegetation programmes of mining sites, after their exploitation. Ecological restoration requires a multidisciplinary approach integrating soil sciences, physiological and microbiological data of ultramafic scrubland ecosystems. Analysis of soils / plant’s relations along a topo-sequence, including various types of scrubland, clearly shows there is a direct relationship between the concentrations of soil available elements and the variety and organization of the vegetation, in particular for the herbaceous stratum. This work, coupled with the creation of an experimental Cyperaceae seed orchard, in association with SIRAS Pacifique Company, indicates that the growth of Costularia comosa answers positively the nitrogenous and phosphated fertilization. The experiment also underlines the fact that vigour, growth speed, rate of mycorhization and fruiting of plants are stimulated by moderate doses of these elements. Other assays enabled to improve our knowledge of the role of the microorganisms associated to Costularia roots. Thus, we shows that nine pioneer species of Cyperaceae, studied in situ, develop arbuscular mycorhizal symbioses. An experiment of controlled mycorhization on Costularia comosa shows that mycorhization by Glomus etunicatum is functional, with an increase of the plants’ biomass of 2,8 times compared to the control. Furthermore, such a mycorhization of C. Comosa reduces the nickel concentration in the plant, suggesting the mycorhize acts as a barrier towards nickel. In this study, we also present a description of the aerobic, heterotrophic and nickel resistant bacterial populations isolated from roots of two Costularia species associated to ultramafic scrublands. The density of these bacterial populations is low and Protéobactéria dominate. Some of the isolated strains present a tolerance to 15 mM of soluble nickel and the capacity to solubilize phosphates. The progresses in both our knowledge of Cyperaceae mineral nutrition and the role of associated microorganisms brought by this study, allow to envisage the implementation of productive seed orchards and the use of the microorganisms associated to Costularia, in the technical routes for optimised ecological restoration plans., En Nouvelle-Calédonie, les sols développés sur roches ultramafiques (5. 500 km2) sont constitués à plus de 65% d’oxy-hydroxyde de fer, ils présentent des teneurs très faibles en azote et en phosphore (1/10 à 1/100 des teneurs moyennes), de surcroît ils sont déséquilibrés pour le rapport Ca/Mg et contiennent des concentrations très élevées en métaux lourds (nickel, manganèse, cobalt, chrome). L’exploitation à ciel ouvert du nickel sur ces sols associés à des écosystèmes particulièrement originaux et diversifiés doit prendre en considération à la fois les intérêts économiques et les préoccupations écologiques. Des espèces endémiques pionnières des sols ultramafiques ou cicatricielles des sites miniers dégradés ont été identifiées. Parmi ces espèces, plusieurs espèces de Costularia (Cyperaceae) sont préconisées pour la revégétalisation des sites miniers après exploitation. Les itinéraires techniques de restauration écologique des sites miniers requièrent une approche pluridisciplinaire intégrant des données pédologiques, physiologiques et microbiologiques des écosystèmes des maquis miniers. L’analyse des relations sols/plantes sur une toposéquence comprenant différents types de maquis a permis de mettre en évidence une relation directe entre les concentrations du sol en éléments disponibles et la diversité et l’organisation des espèces, notamment pour ce qui concerne la structuration de la strate herbacée. Ce travail couplé à la mise en place par la société SIRAS Pacifique d’un champ semencier expérimental de Cyperaceae a permis de montrer que la croissance de Costularia comosa répond positivement à la fertilisation azotée et phosphatée. L’expérimentation a permis également de souligner que la vigueur, la vitesse de développement, le taux de mycorhization et la fructification des plants sont stimulés par des doses modérées de ces éléments. D’autres travaux réalisés ont apporté un approfondissement de nos connaissances sur le rôle des microorganismes associés aux racines des Costularia. Ainsi, nous avons montré que neuf espèces pionnières de Cyperaceae étudiées in situ, développent des symbioses mycorhiziennes arbusculaires. Une expérience de mycorhization contrôlée de Costularia comosa a permis de montrer que la mycorhization par Glomus etunicatum est fonctionnelle, avec une augmentation de la biomasse des plants 2,8 fois supérieure au témoin. De plus, la mycorhization réduit la concentration en nickel dans la plante, suggérant un rôle barrière du champignon mycorhizien vis-à-vis du nickel. Dans cette étude, nous présentons également une description des populations bactériennes aérobies, hétérotrophes et résistantes au nickel, isolées des racines de deux espèces de Costularia inféodées aux maquis. Ces populations bactériennes sont de faible densité et dominées par les Protéobactéries. Certaines des souches isolées présentent une tolérance à 15 mM de nickel soluble et la capacité de solubiliser les phosphates. L’avancement apporté dans les connaissances concernant la nutrition minérale des Cyperaceae et le rôle des microorganismes qui leur sont associés permet d’envisager la mise en place en routine de champs semenciers productifs et l’utilisation des microorganismes associés aux Costularia dans les itinéraires techniques de restauration écologique pour en améliorer la réussite.