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Vietnam is the world's 1st and 2nd largest exporter of black pepper and coffee robusta, respectively. However, due to intensive management practices, soil health has gradually reduced, resulting in production of both commodities being seriously affected by Soil Borne Pests and Diseases (SBPDs). About 300,000 ha of coffee plantations must be renewed, but all attempts to replant them have failed due to high populations of SBPD (mainly attributed to nematodes) in severely degraded soils. During the early years after its introduction, black pepper yields have exceeded the Vietnamese government's expectations even in areas with poor soils. However, farmers now observe a decrease in pepper yield. Pathogenic oomycetes including Phytophthora capsici and P. tropicalis were previously considered to be the only agents responsible for reduced pepper yields in the region. In the frame of the V-Scope project funded by the Australian Centre for International Agricultural Research (ACIAR), our team investigate SBPDs responsible for destruction of plantations of both black pepper and coffee in 3 Provinces 20 (Gai Lai, Dak Lak and Dak Nong). Our results show that in addition to Phytophthora, other groups such as Pythium, Phytopythium and Fusarium are also causing damages in black pepper plantations. Nematodes (Meloidogyne and Pratylenchus) were also found to affect both commodities and analysis of secondary data suggests that the populations of nematodes may be increased when coffee trees are intercropped with jackfruit and black pepper. Moreover, by using quantitative PCR, we found that Phytophthora and Fusarium were also present in black pepper plantations showing no symptoms, suggesting complex interactions between soil health, pathogen presence and plant damages. Overall, understanding the complex relationship between agricultural management practices and the consortium of SBPDs is crucial to restore soil health, control the SBPD populations and improve yields of coffee and pepper.

International funding agencies had put a lot of effort for financially supporting projects aiming the production of highperforming hybrids of Australian Acacias in Vietnam. The main consequence is the significant surface of forests covered by these hybrids across the country (mainly in Northern and Central Vietnam). These hybrids are widely used by the local populations because businesses related to this production were developed with significant incomes for the people dealing with it. Meanwhile, all these plantations contribute to the effort of soil restoration as these trees can symbiotically fix atmospheric nitrogen with a soil bacteria called rhizobia and released a part of it to the soil. But the current production of seedlings is not satisfying. Among all the difficulties we listed, we noticed that many private nurseries used unknown or mixed hybrid material; sometime seedlings are produced with seeds collected on hybrids; and instead of promoting effective bio-inoculants (such as rhizobia and mycorrhiza), the nurseries use massive amounts of chemical inputs killing all the beneficial living organisms contained in the soil. The main consequence of this is the low rate of survival of the seedlings after plantation in the field and the limited growth of the trees because there cannot take advantage of the nutrients supplied by the lacking symbiotic partners. The presentation is about describing the current situation and after what needs to be done for sustaining an effective production of vigorous and healthy seedlings of Australian Acacia including the selected hybrids. In addition of using a well-known plant material, we will make a big focus on the formulation and the development of effective bio-inoculants working for Acacia mangium only and for hybrids Acacia mangium x Acacia auriculiformis only as the literature shows that their symbiotic requirements are different. This is a real innovation in Vietnam where decades of projects were funded aiming to introduce new Acacia materials and hybrids in the country, to run clonal selection tests and to set up units in charge of producing by tissue culture micropropagation plantlets of the selected plant material. All these activities were undertaken without paying attention of the symbiotic partners of these Acacia trees. Currently, we pay the price of this absence and we consider it is time to move on with such bio-inoculant's approach with the overall objective to sustain these plantations in Vietnam and then to improve the livelihoods of smallholders financially depending of the wood production.

Intensive tea cultivation has caused serious soil health degradation globally, including severe soil acidification, metal toxicity, nutrient leaching and imbalance. Conducted accross 20 different tea plantations from 2019-2021, this project examined the impacts of agroecological management practices (mulch and organic fertilizer applications) on tea soil health indicators, yield and quality, and net income of tea farmers in Northern Vietnam. We showed that agroecological practices enhanced soil physicochemical properties by significantly increasing soil OM content and reducing soil acidity. Soil biological properties, including arbuscular mycorrhizal fungi colonization, soil macro and mesofauna abundance, richness and diversity were also significantly higher in agroecological tea soil and root samples than in conventionally managed tea plots. Despite lower tea yield and yield components, agroecological tea management adopters earned around USD 9200 ha/ year more than the non-adopters. To further counter soil acidification and consequently enhance soil health and crop productivity, lime was applied at a rate of 1.5 tons/ha in 6 agroecological tea plantations. Nine months after application, liming significantly increased soil pH by 0.6 units on average. A significant increase of soil macrofauna abundance and diversity were also observed in lime treatments (average of 122 and 89 individuals/m² in lime and control plots, respectively). Additional analyses will be conducted on soil microbial communities, tea quality indicators and soil nematodes populations. Our results provide a better understanding of the effects of management practices on soil health and tea productivity and can be used to promote sustainable tea management practices, while increasing farmers' income.

Sustainability Science, 17 (6), ISSN:1862-4065, ISSN:1862-4057

Tea is one of the most important cash crops in Vietnam. The continual use of conventional tea cultivation strategies in the country has led to numerous issues that are reducing tea yield and quality, and ultimately profitability for tea growers. Key issues affecting production include soil health degradation and environmental pollution with serious consequences on human health. In recent years, there has been a rapid conversion from conventional tea management practices and annual croplands to agroecological tea cultivation methods. This is driven by an increasing interest in high tea quality and awareness of the harmful effects of agrochemicals on human health and the environment. To date, the sustainability of this conversion regarding soil health properties has been poorly understood. Therefore, this study was conducted to investigate impact of agroecological tea management and land conversion practices on soil health indicators in northern Vietnam. Our research results demonstrated that agroecological management practices significantly increased soil organic matter, soil pH and AMF colonization compared to conventional management. While with conventional management, soil total nitrogen was significantly higher compared to agroecological tea plantation soils, this could be explained by intensive applications of nitrogen-based fertilizers in conventionally managed tea plantations. Soil macro and microfauna diversity was significantly greater in agroecologically managed tea gardens than in conventional tea plantations. Interestingly, for both management practices, the highest AMF intensity (M%) was only 48.7%, suggesting that there is room for options to improve AMF root colonization of tea plants with a benefit on soil health and plant growth. As for AMF, our result highlights the possibilities for enhancing soil fauna diversity by management practices for improving soil conditions such as soil acidity. Effects of field lime applications on soil pH and soil health parameters are currently being investigated. Based on the outcomes of these trials, additional management practices such as biochar application will also be investigated. The overall objective is to sustain a high-quality tea production while improving soil diversity and soil health, with overall outcomes towards achieving long-term economically and environmentally sustainable tea production for Vietnam.

JNGG 2020, 10èmes Journées Nationales de Géotechnique et de Géologie de l'Ingénieur , Lyon, FRANCE, 02-/11/2020 - 03/11/2020; En septembre 2011, deux digues expérimentales ont été construites sur le site du CER de Rouen. L'une a été construite en utilisant un sol limoneux de classe GTR A1, la seconde est constituée du même limon traité à 2,5% de chaux vive. Le présent article fait état de la méthodologie déployée pour l'évaluation des caractéristiques des matériaux 7 ans après le chantier de construction, en environnement réel, y compris les difficultés rencontrées pour procéder à cette évaluation.

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

Industrial agriculture has allowed food safety through the crop homogenization and the massive use of pesticides and chemicalfertilizers. This intensive agriculture has positively influenced the crop productivity but has also negatively affected the environment with direct consequences on soil health and productivity. The importance of the micro and macro organisms in the sustainability of soil fertility is widely recognized. Soil fauna represents 23% of the global fauna and contributes to most of the ecosystem services such as porosity, soil aggregation, control of the microbial activity and plant protection against pests and diseases. To mitigate the collateral effects of intensive agriculture on soil productivity in South East Asia, agro-ecological practices are currently promoted, including the use of legumes in intercropping systems. We studied the effect of the intercropping system cassava-cowpea (Vigna unguiculata L.) on the soil biotic compartment in Yen Bai province, a mountainous region in the North of Vietnam. Intercropping resulted in the increase of macro fauna richness and evenness. Intercropping system also significantly enhanced both diversity and abundance of soil micro fauna. The high throughput sequencing analysis of the microbial community showed that bacterial communities' abundance and richness were significantly higher in intercropping system than in mono-cropping fields. However, intercropping did not significantly affect the fungal communities and the soil parameters including pH and organic matter. Our results highlight the importance of the promotion of agro ecological practices such as legume intercropping systems in the Highlands in Northern Vietnam where the sustainability of the ecosystem is very fragile.

Cassava and maize are widely grown in the Northern mountainous regions of Vietnam. By applying huge amount of mineral fertilizers and promoting monocropping, the farmers have hugely contributed to soil degradation with as direct consequence to the decline of crop yield by unsustainable management practices. Legume-based intercropping system, one of the most widespread agroecology practices, have been widely promoted by scientists and the local authorities in Northern Vietnam because of their numerous advantages: better use of land, economic benefit, diminishing soil erosion, and also gradually increasing soil N content through biological nitrogen fixation as well as mulching legume residues. Nevertheless, the upland farmers have no idea about the use of commercial rhizobial inoculants and their potentials. This study aimed at assessing the needs to promote such rhizobial inoculants in the 2 districts in Yen Bai province of Vietnam, where cowpea is intercropped with cassava and maize. Our results showed that the natural nodulation of cowpea was really low at different soil characteristics and slope categories. There are indigenous rhizobial strains in the soils but it is not sufficient for them to form effective symbiosis with cowpea. Unfortunately, there is no valid commercial inoculant product on the markets in Vietnam until now, it is imperative to develop effective rhizobial inoculants for grain legumes for Vietnam, as well as in the whole South East Asia. There are markets for private companies willing to open new business on such activities. The presence of commercial inoculants on the markets would help in sense of agroecology to improving soil health and building sustaining agricultural systems in this zone.

With Myanmar, Vietnam is one of the biggest producers of grain legume in South East Asia. Unfortunately, farmers don't know anything about rhizobial inoculants and keep applying high rates (sometime more than 1 tonnes of NPK per ha) of mineral fertilizers for growing legumes and other associated crops. In Northern Vietnam, the soil erosion issue is very important because basically there are ills with almost no vegetation and when it rains, the water runs off and the soil become highly degraded. The promotion of the intercropping system is relevant because the legume release part of the atmospheric nitrogen they fixed in symbiosis with rhizobia and it contributes to maintain yields to a certain level. However, the absence of rhizobial inoculants and the systematic utilization of mineral fertilizers reduce the potential of the biological nitrogen fixation. Our study was aiming to point out this in 2 districts of the Yen Bai province in Norther Vietnam where the local authorities try to promote as much as they can agro-ecological practices such as intercropping. Basically, our results showed the nodulation of cowpea intercropped with maize or cassava remained limited whatever the soil characteristics and the landscape. There are native rhizobial strains available within the soils, but their numbers need to be increased, their genetic diversity has to be assessed and their effectiveness has to be measured. It becomes urgent to move on with new initiatives involving the private sector aiming to elaborate effective commercial rhizobial inoculants for grain legumes for Vietnam but also in the whole South East Asia to sustain legume and crop production through an environmental-friendly management. This is definitively the way forward and the market exists because of the huge demand, it is matter to make the inoculants available on the markets.

Extensive interactions of plant roots with soil microorganisms affect plant nutrition either directly by influencing mineral nutrient availability or indirectly through enhanced uptake efficiency via plant root growth promotion. Beneficial microbial interactions with roots may be either endophytic or associative and can be symbiotic, mutualistic, or incidental in nature. The increased understanding of the role of root – or rhizosphere –associated with microbes in the nutrition and/or yield of agricultural crops in particular has resulted in promotion of their use in agricultural production as alternatives or supplements to mineral or organic fertilizers. Despite this, there is an obvious lack of market penetration of microbial inoculants. This review specifically focuses on microbial inoculants, collectively termed biofertilizers, used to improve nutrition and yields of grain, legume, oil, tuber, and other crops. A vast number of commercial biofertilizers are available worldwide; however, the quality and efficacy of many of them are not proven or tested. In the absence of efficacious biofertilizers of good and consistent quality, the dependence on the use of mineral fertilizers is not likely to decrease. Thus the availability of high-quality biofertilizers must be priority particularly in countries where crop plant production plays a key role in the economy and food security.

Une couche de collage est épandue sur le support des couches bitumineuses afin d'assurer une répartition optimale des charges sur l'ensemble du corps de chaussée. Cependant, le trafic de chantier la détériore immanquablement. Aussi, une solution consiste à protéger la couche de collage par un lait de chaux stabilisé dilué. Avec une expérience accumulée de plus de 5 ans et plus de 25 millions de m2 traités, l'arrachement des couches de collage par le trafic de chantier est ainsi évité, garantissant une bonne durabilité des infrastructures, limitant les salissures aux abords des chantiers et facilitant le nettoyage des engins.Le principe de ce procédé, ses moyens d'implémentations et ses conséquences surl'adhésion inter-couches sont détaillées dans le présent article.

Les ions orthophosphates (Pi) représentent les seules formes de phosphore (P) utilisable par les cultures. Dans les sols, ils sont généralement présents à de faibles concentrations dans la solution, en raison des nombreux processus géochimiques contraignant leur mobilité et disponibilité. Les plantes et les micro-organismes associés, au travers de relations rhizosphériques, symbiotiques et par la prédation des populations microbiennes, modifient considérablement la quantité de P que la plante est capable d’acquérir tout au long de sa croissance (biodisponibilité). Cette revue décrit les différents processus (modifications des racines, rôle du pH, des anions organiques, des enzymes, de la microfaune et de la macrofaune) qui peuvent modifier la biodisponibilité du P dans la rhizosphère. Des pistes pour mieux valoriser le potentiel intrinsèque des végétaux et de l’écologie des organismes du sol et optimiser l’acquisition de P des cultures à partir du sol sont proposées., Orthophosphate ions (Pi) are the only forms of phosphorus (P) available to plants. In soils, they are generally present at low concentrations because of a number of geochemical processes that restrict their solubility and mobility. Plants, due to their own properties and those of their associated microorganisms via rhizosphere or symbiotic relationships, as well as soil fauna, are able to change the amount of P taken up by roots, defined as P bioavailability. This review describes the different processes (root changes, role of pH, organic anions, enzymes, microfauna and macrofauna) that affect P bioavailability in the rhizosphere. It also discusses how plant properties and soil ecology could be better used to optimize plant P acquisition from the soil.

Commercial agricultural inoculants are increasingly being produced and sold in the market worldwide, and are claimed to have a major impact on increasing crop productivity. The main objective of this research was to characterize and assess the microbial content of biofertilizers obtained from different countries in order to verify whether they fulfill the claims of the manufacturers. The proliferation of the underperforming inoculants can thereafter be prevented, and value can be added to effective products. The microorganisms contained in the commercial inoculants were isolated, purified, and identified by partial sequencing of the 16S rDNA. Results showed that the majority (about 64%) of the products contained one or several strains of contaminants and only 37% of the products could be considered as pure. Forty percent of the tested products did not contain any of the claimed strains but only contaminants and several potential human pathogens were found. Rhizobial products were generally of better quality than the other PGPR-based products. Results highlight the need for better quality control systems to ensure efficacious products reach the end users. (Texte intégral)

The perennial plantations of rubber trees (Hevea brasilensis Muell. Arg.), oil palm trees (Elaeis guineensis) and coffee trees (Coffea L.) are economically important in South-East Asia. Despite some initiatives promot-ing organic farming, mineral fertilisers are predominately used for growing these crops, with huge economic and environmental consequences. It is well known that for many agricultural and horticultural systems, a healthy soil microbial community leads to healthier plants and increased yields. That can be explained by the extensive interactions between plant roots and soil micro-organisms that further affect plant nutrition either directly by influencing mineral nutrient availability, or indirectly through root-growth promotion enhancing uptake efficiency. The increased understanding of the roles of root- or rhizosphere-associated microbes in plant nutrition and/or crop yields has resulted in their promotion for use in agricultural production as alterna-tives or supplements to mineral and/or organic fertilisers. However, little information is available concerning perennial plantations. Moreover, there is an obvious lack of promotion of beneficial soil micro-organisms to farmers, associated with a lack of market penetration of microbial inoculants for limiting the use of mineral fertilisers. Our presentation describes how the soil micro-organisms could efficiently be used for improving and sustaining the production of perennial plantations in South-East Asia. Several examples will be given to illustrate the way forward and an example of oil palm plantations will be emphasised. (Texte intégral)

Rubber tree (Hevea brasiliensis) is a crop of major socio-economic importance in Southern Asia as it represents a substantial source of income for small landholders. In Thailand (1/3 of world latex production) rubber tree plantations are currently greatly expanding in adverse eco-climatic zones, especially in Isan provinces (North East Thailand), where soils have sandy texture, low fertility and are prone to erosion and leaching of applied fertilizers. A major potential for increased production in these conditions relies on the important roles of rhizosphere microbial communities in supporting soil fertility and plant nutrition. A chronosequence of 3, 6 and 16 year-old plantations was identified and cassava fields were used as no-rubber controls for comparison. Soils from each treatment were characterized for texture and chemistry. Using 454 sequencing, total bacterial and fungal communities as well as Arbuscular Mycorrhizal Fungi (AMF) community were analyzed. Because they are known to contribute to plant P and N nutrition by increasing mineral nutrient availability or by enhancing plant nutrient uptake, root-interacting P-solubilizing bacteria (PSB) and free-living N fixing bacteria were assessed after culturing on selective media. Nematodes populations were characterized, as there are good soil fertility indicators. Functional traits were also analyzed by both qPCR and Ecoplates (Biolog) methods. Results showed significant differences between rubber and cassava associated communities but didn't reveal a strong impact of the age of the plantations on the different communities. For instance, the AMF community in cassava roots was twice as rich as in rubber tree samples but was not affected by the age of rubber trees. Concerning nematodes, their total populations decreased with the age of the plantations, and are significantly higher in the cassava fields than in the rubber plantations. The indices suggest a progressive lost of the soil fertility with the age of the plantations. To conclude, the improved understanding of the diversity of root-associated microbes and the soil nematodes will contribute to the development of alternative sustainable practices to improve and sustain soil fertility in perennial plant plantations such as rubber plantations. (Texte intégral)

Rubber tree (Hevea brasiliensis) is a crop of major importance for smallholders in Southern Asia because it produces latex, a substantial source of income for farmers. Rubber tree can grow on very poor soils (sandy soils, low fertility, subject to erosion and leaching of applied fertilizers), which are unsuitable for other commonly cultivated cash crops. It covers 2.7 million ha across Thailand, but its establishment in areas with very poor soils, especially in Northeast Thailand, represents a major potential for increased production. The important roles of rhizosphere microbial communities in supporting soil fertility and plant nutrition has been widely recognized. In particular, root -interacting P-solubilizing bacteria (PSB) and arbuscular mycorrhizal fungi (AMF) contribute to plant P nutrition by increasing mineral nutrient availability and by enhancing plant nutrient uptake. The diversity of AMF in roots and of PSB in rhizosphere soil was assessed along a chronosequence of rubber tree plantations (3, 6 and 16 year-old) and compared to cassava fields. AMF diversity was assessed by 454 sequencing of SSU 18S rDNA. PSB strains were characterized after culturing on selective media. AMF communities in cassava roots were twice as rich as in rubber tree samples. AMF diversity was not affected by the age of rubber trees, but was related to the soil P content. The improved understanding of the diversity of root-or rhizosphere-associated microbes will contribute to the development of alternative sustainable practices to improve and sustain soil fertility. (Texte intégral)

Rubber tree (Hevea brasiliensis) is a crop of major socio-economic importance in Southern Asia as it represents a substantial source of income for small land holders. In Thailand (1/3 of world latex production) rubber tree plantations are currently greatly expanding in adverse eco-climatic zones, especially in Isan provinces, where soils have sandy texture, low fertility and are prone to erosion and leaching of applied fertilizers. A major potential for increased production in these conditions relies on the important roles of rhizosphere microbial communities in supporting soil fertility and plant nutrition. A chronosequence of 3, 6 and 16 year-old plantations was identified and cassava fields were used as no-rubber controls for comparison. Soils from each treatment were characterized for texture and chemistry. Using 454 sequencing, total bacterial and fungal communities as well as arbuscular mycorrhizal fungi (AMF) community were analyzed. Because they are known to contribute to plant P and N nutrition by increasing mineral nutrient availability or by enhancing plant nutrient uptake, root-interacting P-solubilizing bacteria (PSB) and free living N fixing bacteria were assessed after culturing on selective media. Nematodes populations were characterized as there are good soil fertility indicators. Functional traits were also analyzed by both qPCR and Ecoplates (Biolog) methods. Results showed significant differences between rubber and cassava associated communities but didn't reveal a strong impact of the age of the plantations on the different communities. For instance, the AMF community in cassava roots was twice as rich as in rubber tree samples but was not affected by the age of rubber trees. The improved understanding of the diversity of root-associated microbes will contribute to the development of alternative sustainable practices to improve and sustain soil fertility.

Not only phosphorus (P) bio available in soil is very low but phosphate fertilizing efficiency is also low. Consequently, annual world P demand increases predicting phosphorus stock end in the coming 125 years. In addition to that, the high cost of chemical fertilizers obliges most Sub Sahara African smallholder farmers to do not use fertilizers which ultimately results in poor yields. In this paper, we present opportunities and challenges of using bio fertilizers as sustainable way of alleviating soil P deficiency effects in Kenya and Senegal. In Kenya where soil P deficiency has been identified as the biggest challenge of crop productivity increases, we share results on the use of commercialized arbuscular mycorrhizal inoculants to replenish soil P. While in Senegal known having huge quantities of P rock deposit and important quantities of feed stock material that can be charred (biochar), we present results on the capacities of biochar to improve P availability for plant cultivated in sandy soil. Results from both countries show that current expectations on the use of bio fertilizers are numerous and justified. However challenges on sustainable agriculture through the use of the called bio fertilizers especially mycorrhizal inoculants and biochar are still ahead. (Texte intégral)

Not only phosphorus (P) bioavailable in soil is very low but phosphate fertilizing efficiency is also low. Consequently, annual world P demand increases predicting phosphorus stock end in the coming 125 years. In addition to that, the high cost of chemical fertilizers obliges most Sub Sahara African smallholder farmers to do not use fertilizers which ultimately results in poor yields. In this paper, we present opportunities and challenges of using bio fertilizers as sustainable way of alleviating soil P deficiency effects in Kenya and Senegal. In Kenya where soil P deficiency has been identified as the biggest challenge of crop productivity increases, we share results on the use of commercialized arbuscular mycorrhizal inoculants to replenish soil P. While in Senegal known having huge quantities of P rock deposit and important quantities of feed stock material that can be charred (biochar), we present results on the capacities of biochar to improve P availability for plant cultivated in sandy soil. Results from both countries show that curre nt expectations on the use of bio fertilizers are numerous and justified. However challenges on sustainable agriculture through the use of the called bio fertilizers especially mycorrhizal inoculants and biochar are still ahead. (Texte intégral)

Although soils generally contain a large amount of total P, only a small proportion is immediately available for plant uptake making it a major constraint on crop production in many tropical countries. Free - living bacteria and fungi can mobilize o rthophosphate from either organic or inorganic P sources such as Phosphate Rock (PR). These phosphate - solubilizing microorganisms (PSM) are characterized by their capacity to solubilize precipitated forms of P, the main P ingredient in PR and could be good bio - fertilizers for improving phosphorus plant nutrition. The present study examined phosphate solubilising bacteria (PSB) isolated from cassava, groundnut , rubber tree, sunchoke , rice, rice - soybean, rice - soybean - corn and rice - chili fields and vermicast o f earthworm varieties in Northeast of Thailand, where soils are mainly sandy and P - deficient. PSB isolates were tested by using different P sources [Tri - calcium Phosphate (Ca 3 (PO 4 ) 2 ), Ferric Phosphate (FePO 4 ) and Aluminium Phosphate (AlPO 4 )] on specific cu lture media (National Botanical Research Institute Phosphate Growth Medium, NBRIP). Our results showed that five of the PSB isolates from economic crops and vermicast of earthworm varieties solubilised a significantly (P  0.01) higher amount of AlPO 4 and FePO 4 over the uninoculated control. The highest activity of solubilization was achieved for AlPO 4 followed by FePO 4 which are the main forms of insoluble phosphates in acidic sandy soils. We found that PSB isolated from vermicast of earthworm varieties Ph eretima posthuma and Eudrilus eugeniae were able to solubilize both AlPO 4 and FePO 4 at relatively high rates (up to 1,918.49 mgP/l ), in contrast, PSB isolated from cassava, rice - soybean and groundnut field soil tended to have lower solubilisation rates for FePO 4 . None of the isolates tested were able to solubilize CaPO 4 . Finally, IAA production was observed only in PSB isolated of E. eugeniae vermicast and rice - soybean field soil. These results highlight variability of specific PSB isolates from different r hizospheres and vermicast of earthworm varieties and provide essential information for the management of soil fertility.

Rubber tree (Hevea brasiliensis) is a crop of major importance for smallholders in Southern Asia because it produces latex, a substantial source of income for farmers. Rubber tree can grow on very poor soils (sandy soils, low fertility, subject to erosion and leaching of applied fertilizers), which are unsuitable for other commonly cultivated cash crops. It covers 2.7 million ha across Thailand, but its establishment in areas with very poor soils, especially in Northeast Thailand, represents a major potential for increased production. The important roles of rhizosphere microbial communities in supporting soil fertility and plant nutrition has been widely recognized. In particular, root -interacting P-solubilizing bacteria (PSB) and arbuscular mycorrhizal fungi (AMF) contribute to plant P nutrition by increasing mineral nutrient availability and by enhancing plant nutrient uptake. The diversity of AMF in roots and of PSB in rhizosphere soil was assessed along a chronosequence of rubber tree plantations (3, 6 and 16 year-old) and compared to cassava fields. AMF diversity was assessed by 454 sequencing of SSU 18S rDNA. PSB strains were characterized after culturing on selective media. AMF communities in cassava roots were twice as rich as in rubber tree samples. AMF diversity was not affected by the age of rubber trees, but was related to the soil P content. The improved understanding of the diversity of root-or rhizosphere-associated microbes will contribute to the development of alternative sustainable practices to improve and sustain soil fertility. (Texte intégral)

International audience; This paper describes the SOTREDI project, “Soil TREatment for Dikes”, undertaken by Lhoist Group, a lime producer, since 2005. This project was led in partnership with research centres and universities, and presents some potential applications. The objective was to demonstrate that soil treatment with lime, besides enhancing the materials workability, confers high levels of mechanical properties, low permeability values, and is likely to reduce piping and internal erosion hazards, and to significantly increase the erosion resistance against overtopping and overflowing. This paper is a first step toward the application of lime-treated soils in earthen hydraulic structures (namely canals, dams, dikes and levees).

Several types of associative microbes inhabit in the rhizosphere of legumes. These include plant growth promoting rhizobateria (PGPR) with a prominent place taken by N2-fixing bacteria (symbiotic and N-free fixing) and mycorrhizal fungi. Associations with these microbes play important role in the nutrition, development and yields of legumes. Whereas symbiosis with N2-fixing bacteria can mitigate the need for N fertilizer applications in soils where P availability is not a serious constraint, mycorrhizal symbiosis often can provide a more efficient mechanism for P uptake from the soil by plant roots. Stimulation of mycorrhizal symbiosis has the potential to improve yields and sustainability of agricultural production in the short term. However, it will require replenishment of soil P resources on a long run. Phosphate solubilising bacteria (PSB) possess the ability to solubilise insoluble inorganic P sources. Given the variety of functions, different microorganisms can synergistically interact with respect to improving legume yields. This appears particularly important in tropical soils, in Africa and Asia where yields remain very low and socio-economic constraints limit applications of expensive mineral fertilisers. Use of microbial inoculants tailored to local soil conditions thus present an alternative to sustainably improve yields and empower farmers in the short term. This paper aims to review results of several field inoculation trials using commercial inoculants and to raise some important issues such as product quality, role of plant genotype in the efficiency of microbial inoculations, formulation of commercial microbial inoculants including mycorrhizal fungi, and prospects to optimize crop responses to inoculation under field conditions. (Texte intégral)

Microbial interactions in the plant rhizosphere play important roles in the overall development of legumes. Legumes are able to establish beneficial symbiotic relationships with two types of soil-borne microorganisms: N2-fixing bacteria and mycorrhizal fungi (mainly arbuscular mycorrhizal or AM) which result can result in enhanced legume nutrition and health. Plant growth promoting rhizobacteria (PGPR) generally include all root-associated bacteria that enhance plant growth. Among PGPR, plant associated N2-fixing bacteria are considered as an alternative to inorganic N fertilizer for promoting plant growth and yield. Phosphate solubilising bacteria (PSB) are also included in PGPR group and possess the ability to solubilise insoluble inorganic P compounds. To benefit from these beneficial rhizosphere interactions in the field, farmers have to apply commercial microbial inoculants containing several kinds of bacterial and/or fungi, often along with expensive chemical fertilizers. This paper aims to review of the results obtained in the field with such microbial commercial inoculants and to highlight the effects of microbial quality of the commercial products, the role of the plant variety on the efficiency of the microbial inoculation and the formulation of the microbial inoculants (including AM on the likelihood of success of those inoculations in field conditions. (Texte intégral)

Soils comprise structured biological assemblages and microbial communities must adapt to physical environment and biological constraints. Rhizospheric bacteria called rhizobia interact with roots of legumes to form nodules and perform atmospheric nitrogen fixation. Both plant and bacteria signals contributing to nodule establishment have been shown to play a major role in the specificity of the legume-Rhizobium interaction. The present study aimed to assess if several factors such as cropping systems, N fertilization and application of crop residues affect this specificity. Promiscuous soybean (TGx 1740-2F) was planted in Meru South district (Kenya) every season from March 2007 and three factors were considered: (i) cropping (system monolegume (ML) i.e soybean, association (AS) i.e soybean and maize grown simultaneously or rotation (RO) i.e maize and soybean grown alternately), (ii) Nitrogen fertilization 60 kg.ha-1 (+N or –N) and (iii) maize residues application (+R or –R). Nodulation was assessed and nodules collected during the long rainy season 2008 and the short rainy season 2009. After surface sterilization DNA was extracted and Inter Genic Spacer (IGS) region amplified by Polymerase Chain Reaction (PCR). PCR products were then restricted to obtain Restriction Fragment Length Polymorphism (RFLP) profiles. Results showed that nodulation was not significantly affected by the different factors except N fertilization, regardless the season. Nodule occupancy revealed only 3 main profiles representing 93.6% and 92.5% of all the RFLP profiles obtained from 2008 and 2009 nodules respectively. This suggested a low diversity of native rhizobial strains capable to nodulate the promiscuous variety. The cropping system, N and R application didn't increase the diversity of the rhizobia but results indicated an effect on the distribution of the 3 profiles within the nodules of the plants. Within same treatments, significant differences were found between the two seasons in term of strains occupying the nodules and this may be explained by the shorter rainfall received in 2008 compared to 2009. Results suggest that cropping systems and both N and crop residues applications affect more specifically plant growth and grain yields than the diversity of the native rhizobia nodulating promiscuous soybean variety TGx 1740-2F. (Texte intégral)

Low effectiveness of native strains remains a limitation to soybean productivity in sub-Saharan Africa, while commercial rhizobial inoculants are widely and successfully used for soybean production in Latin America. The inoculants may become expensive to farmers who want to purchase them especially if the inoculation has to be repeated every season. To assess the competitiveness of effective rhizobial strains and their persistency in the field for two cropping seasons, it's very important to assist poor farmers targeted by the COMPRO project funded by BMGF with appropriated technologies. Field experiments were set up for two seasons (one with inoculation and the following one without) to evaluate the response of three promiscuous soybean varieties (a non-promiscuous and two promiscuous) to commercial rhizobial inoculants in a Nitisol (no soybean growing history) and a Ferralsol (with soybean growing history) in Central and Western Kenya respectively. High nodulation was observed in the Ferralsol while nodule occupancy showed indigenous strains occupied < 90 % of the nodules for all the varieties whatever the rhizobial inoculants. The Nitisol showed nodule occupancy variation depending on variety and inoculants. Legumefix was having the highest grain increases, showed competitiveness and hence better grain yield, nodule occupancy and biological nitrogen fixation.

A range of soybean commercial inoculants were tested under greenhouse and field conditions in different locations in Kenya. One rhizobial (Legumefix) and one mycorrhizal (Rhizatech) inoculants were selected according to the promising results obtained. The efficiency of these 2 products (single or combined inoculation) was assessed in 150 farms in 3 mandate areas in Kenya presenting different soil characteristics and environmental conditions. Both biomass and grain yields were measured and nodules occupancy of the rhizobial strain was assessed by ELISA using specific monoclonal antibodies. Application of the rhizobial inoculant, alone or in combination with the mycorrhizal product significantly increased the yields in all mandate areas (about 75% of the farms). However, the co-inoculation didn't perform significantly better than the rhizobial product alone. Controls plots gave poor results, as well as the mycorrhizal product, though that was not expected given the good performances observed under greenhouse conditions. Nodule occupancy analysis showed that a high number of nodules occupied by the inoculated strain did not obviously lead to an increase of soybean production. Soil factors (pH, P, C, N…) seemed to affect the inoculant efficiency whether the strain is occupying the nodules or not. Our statistic analysis showed that soil pH significantly affected nodulation and yield, though the effect was variable depending on the region. P content also positively correlated with nodulation and yields. This study provided relevant information on field efficiency of rhizobial inoculants on soybean yield in Kenya and showed that the competitiveness of rhizobial strains might not be the main factor explaining the effect (or lack of) of legumes inoculation in the field. (Texte intégral)

There is a proliferation of commercial bioinoculant products appearing on the market that claim major impact in increasing crop productivity without any scientific assessments about their effectiveness in the field. TSBF-CIAT has been mandated by Bill and Melinda Gate Foundation to scientifically evaluate and select effective commercial products for improving and sustaining crop yields in selected agro ecological zones in 3 African countries. Our results on about 120 products showed that many private companies commercialize a mix of non-defined microorganisms and thus do not ensure the quality of their inoculants. This may explain their lack of impact on the plant growth even under controlled greenhouse conditions. Generally, high level of contamination was observed as pure products represented only 33% of the products, 41% of the products contained all the expected strains and 52% of the products contain none or part of the expected contaminants. We assessed under greenhouse conditions the possible effect of the formulation of effective rhizobial inoculants on both soybean growth and nodulation. Our results showed that there was no effect and the association of the rhizobia with a Bacillus strain didn't induce any significant stimulation of soybean growth. However, through field demonstration trials combining rhizobia with mycorrhiza and P solubilizing bacteria, our results suggested some relevant positive interactions on soybean yield. In Kenya, we tested one rhizobial inoculant in 3 mandates areas (about 50 farms in each) and our results demonstrated a significant effect of the inoculation on soybean yield. The next step will consist of making such effective inoculants cheap and available on the local markets. Administrative issues shall be sorted out for each country as the national regulations are not similar and of course the quality control issue shall be taken into account to ensure the viability of the inoculants to farmers who purchase them. (Texte intégral)

Biological communities differ over time and in space, and in the forest these communities often vary according to forest cover, tree species and deforested areas cultivated during many years. These land-uses can have significant impacts on soil conditions and microbial communities are likely to respond to these changes. However, such responses are poorly characterized as few studies have examined how specific changes in edaphic do, or do not, influence the composition of soil bacterial and fungal communities across land-use types. The present study aimed to determine whether forest vegetation has a greater influence on both soil characteristics and soil fungal community structure based on denaturing gradient gel electrophoresis (DGGE) analysis of 30 top soil (0-10 cm) samples harvested in May 2006 in the Mau Mount, in Kedowa areas (Kenya). Five different land-uses were investigated: the natural forest; a 41-years old Pinus canariensis plantation installed after the clearance of the forest, a rotation: natural forest-cypress (Cupressus lusitanica) plantation (within 34 years)-crops (within 3 years)- natural vegetation since 2002, a rotation: natural forest- Pinus canariensis plantation (within 34 years)-crops (3 years)-natural vegetation since 2002 and finally a cypress (Cupressus lusitanica) plantation. Our results showed that natural forest had significantly higher organic C content, total N content and P available content. Total microbial biomass is also significantly higher in the soil of natural forest than in soil of Pinus canariensis plantation and natural regeneration of the previous forest plantation. In despite of such huge soil characteristic differences fungal DGGE analysis using 28S rRNA genes was strongly related to the land-use with specific clusters significantly differing each other. By running a Pearson correlation analysis of the corresponding Shannon index values, our results indicated that only total P, Mn and Fe contents showed a positive and significant (p

Numerous studies have been conducted focusing on the effectiveness of plant growth promoting (PGP) rhizobacteria with different PGP functions. Various commercial biofertilizers are available with promises of yield improvement and crop growth enhancement, but no studies have confirmed their effectiveness. This study seeks to evaluate the co-inoculation effects of commercial bioinoculants such as Phosphorus Solubilizing Bacteria -PSB (Myco Tea, Soluble Maxx, Symbion P and Symbion VAM), Arbuscular Mycorrhizae Fungi -AMF (Rhizatech) and rhizobial inoculants (LegumeFix and 1495MAR) on soybean growth. No phosphorus (P) was applied to the treatments but a positive control with optimal P concentration was included. Statistically significant (P≤ 0.001) positive effect upon co-inoculation of PSB bioinoculants and rhizobial strains was observed on shoot dry biomass when Soluble Maxx and Myco Tea were applied alone or co-inoculated with Bradyrhizobium. Interaction between Soluble Maxx and Bradyrhizobium produced the highest shoot biomass, with an increase of 66% (with LegumeFix) and 42% (with 1495MAR) above non-inoculated controls. These results indicated positive interaction between Bradyrhizobium and effective PSB commercial products suggesting that co-inoculation renders the biofertilizers more competitive in rhizosphere. Field studies are ongoing to confirm the effectiveness of these products in different agro-ecological zones. (Texte intégral)

Mycorrhizal technologies are being developed around the world as a suitable answer to crops yields increases, lowering farmers cost inputs and modern agriculture improvement. But, many studies already pointed out products incapability to improve plants yield or, attributed increases to added ingredients. In the frame of the COMPRO project funded by Bill and Melinda Gates Foundation, we evaluated under greenhouse conditions 13 commercial Arbuscular Mycorrhizal Fungi (AMF) products on soybean using a sandy and a clay soil and two sources of Phosphorus before assessing the most promising products in different agro-ecological zones of Kenya. Results from greenhouse indicated 11 products significantly increasing plants roots colonization by mycorrhizae in both soils. However, any product was able to improve plants growth in the clay soil and only 2 products did it in the sandy soil. Assessment of most promising products from greenhouse trials in subsequent field trials in 3 agro-ecological zones of Kenya showed still good roots colonization but, any significant effects on yield compared to control and usual fertilizers. Preliminary tests under local soil context must be conducted before large-scale use of commercial AMF bio-inoculants and synergetic effects with other soil microorganisms should be looked for.

Cereal- legume rotation has been promoted as a strategy to increase crop yields in subsistence farms of sub Saharan Africa, and is believe d to promote changes in the rhizosphere that enhance early plant growth. This study investigates the effect of cereal-legume rotation (maize (Mz)–soybean (SB); common bean (CB)-SB-Mz; SB-Mz) in combination with different rates and types of phosphate (P) fertilizers: Minjingu phosphate rock (MPR) and Trip le super phosphate (TSP) on crop yields and total microbial diversity in a Kenyan Ferralsol. Soil sampling for analysis of microbial diversity was done in the third season of rotation, at three weeks af ter crop emergence. The microbial communities from the rhizospheric soil were genera ted using denaturing gradient gel electrophoresis (DGGE). Shannon Weaver index of diversity was used to determine the microbial diversity. Results showed significant increases in crop yields with a significant interaction (P ≤ 0.05) between fertilizer addition and rotation regime during the three seasons. The highest maize yields were realized following a CB-SB-Mz rotation with a 150% increase (3 t /ha above the control), in plots with 50 kg P/ha MPR, while Mz-CB and SB-Mz rotation had si milar maize yields regardless of the fertilizer applied. Crop rotation and applica tion of P fertilizers had a highly significant interaction (P=0.001) and a positive impact on both total bacterial and fungal community. Significant increases in total community bacteria were noted in Mz-CB rotation system (1.48), followed by the SB-Mz (1.44) and CB-SB-Mz systems (1.42), while the total fungal diversity was significantly lower in the Mz-CB rotation (0.93), but higher in the SB-Mz system (1. 12). Overall interactions between crop rotation and P fertilizers affected the total diversity of bacterial and fungal communities in the bulk soil but crop rotation was more important in determining the total microbial diversity than the fertilizers! . There seems to be no significant correlation between the crop yields and the total microbial diversity, probably because soil sampling was done earlier in the season. Further work is required to monitor the changes of the total community structure within and at the end of the cropping season.

Limited information is available on reduced cowpea and green gram yields in Kenya. Declining soil fertility or presence of ineffective indigenous rhizobia? In regards to this, soils were collected from Western province (Bondo, Bungoma) to Eastern (Isiolo), Central (Meru) and at the Coast (Kilifi) to trap indigenous rhizobia nodulating both legumes under greenhouse condition. Highest nodule fresh weights of 4.63 and 3.32 g plant-1 for cowpea and green gram were observed in soil from Isiolo site A and Kilifi site A respectively suggesting significant populations of indigenous strains in such soils. Lowest nodule fresh weights of 2.17 and 0.72 g plant-1 were observed in soil from Bungoma site B for cowpea and green gram respectively. Genetic diversity of indigenous strains nodulating both legumes was assayed using PCR-RFLP of the 16S-23S rDNA IGS and 19 IGS groups were identified with I and II predominating for both legumes. A second greenhouse experiment was set up to evaluate if commercial inoculants significantly improve cowpea and green gram yields in soils with significant populations of native rhizobia. Rhizobial inoculation did not significantly (p

In Kenya soybean is grown under different soil management systems. Scarce information is found on the effect of cropping systems, N and crop residue application on the diversity of total soil microbial communities. The objective of this study was to evaluate the response of total soil microbial communities to different soybean cropping systems, N and crop residue incorporation. Four cropping systems each per main plot were compared; mono-legume (ML), mono-cereal (MC), association (AS) and rotation (RO). N and crop residue were randomly applied in a split pattern. Soil samples were collected at (0-10 cm) depth from each sub-plot after three years and at time zero for comparison. Soil microbial DNA was analyzed using Polymerase Chain Reaction–Denaturing Gradient Gel Electrophoresis method based on 16S/18S rDNA to assess the composition of both bacterial and fungal communities. After 3 years, diversity of total bacterial communities after cropping was significantly lower compared to diversity at time zero. AS plots had significantly lower diversity of total bacterial communities compared to the other cropping systems. Crop residue applications had no significant effect on diversity of total bacterial communities. On the other hand, plots having received crop residues had significantly higher diversity of total fungal communities compared to those which did not receive crop residues. Additionally, diversity of total fungal communities was significantly lower under MC and ML systems compared to RO system at (P < 0.05), and compared to AS system at (P < 0.001). MC and ML plots were significantly different in fungal communities' diversity at (P < 0.001). Higher diversity of total bacterial communities than to tal fungal communities was observed both at time zero and after cropping. We noticed the absence of signifi cant differences in diversity due to N application on both total bacterial and fungal communities. This could be because amounts of total N (%) and total C (%) were moderate at time zero (0.22 and 2.39) respectively. Addition of mineral N to these soils may therefore not influence total diversity of microbial communities. This study was useful to get a better understanding on the impact of factors such as cropping systems, crop residue applications and N fertilization on total microbial diversity. The next step would be to investigate functional activities linked up with N cycle such as nitrification by using specific primers or quantitative PC. (Texte intégral)

The major setback in successfully obtaining an effective inoculant is overcoming difficulties in formulating a viable and user-friendly final product as the live nature of the active ingredient underscores the importance of formulation in maintaining the microbial cells in a competent state. Co-cultures of rhizobia and PGPR (Plant Growth Promoting Rhizobacteria) are also known to influence the efficacy of the symbiotic bacteria on plant biological nitrogen fixation. A greenhouse experiment was set to assess the formulation effect of one strain i.e. Bradyrhizobium japonicum, 532c (granules, liquid and broth) and to determine the efficiency of co-inoculation of Bacillus subtilis with two strains of Bradyrhizobium japonicum (532c and RCR 3407). The objectives were evaluated on 2 soybean (Glycine max L.) varieties: Nyala, a non-promiscuous variety and TGx1740-2F, a promiscuous test variety. A non sterile soil from Central Kenya (Chuka) classified as a Nitisol was used. Nodule occupancy was determined by PCR-RFLP. Most of the inoculants showed increased nodulation and biomass yields as compared to the un-inoculated controls with a higher response seen in the promiscuous TGx1740-2F variety as compared to the non-promiscuous variety. The liquid and granule-based inoculants had higher biomass yields suggesting an impact of formulation on the effectiveness of the inoculants. The co-inoculants also gave higher yields but showed no significant differences to the rhizobial inoculants alone. Nodule occupancy was 100 % for all the rhizobial inoculants as well as the co-inoculants emphasizing the infectivity and high competitiveness of 532c and RCR 3407 strains even in the presence of indigenous strains (80-113 cell/g of soil). These inoculants, though not initially made for SSA countries, showed promising increased yields in a Kenyan soil containing significant populations of native rhizobia nodulating soybean, signifying a possibility of their adoption in increasing soil fertility and crop yields in the poor SSA soils. (Texte intégral)

Soil is the habitat of an array of microorganisms in all three taxonomic domains. Because many species of soil microorganisms are still unknown or non-described, the assessment of microbial diversity, especially the symbiotic bacteria and fungi is not feasible undertaking. In designing field sampling to collect symbiotic microorganisms, the challenge is to select a subset of the soil biota that adequately reflects the anticipated taxonomic spectrum, and which at the same time includes all the symbiotic microorganisms considered important. Designing a successful, practical sampling scheme is an art. In this chapter, we tried to provide a guideline to make it correctly ensuring the representative of all the indigenous symbiotic bacteria and fungi naturally present in the soils of sampled sites. As the majority of the microorganisms, including the symbiotic ones, are found in the upper 20cm of the soil profile, the main investigations have to be done on topsoil even if it doesn't mean that microorganisms are not naturally present in deeper layers. Once the samples have been harvested, it is important to be cautious and store them nicely for further microbial analysis. Otherwise the risk to lose them or to get only contaminants after streaking is pretty high. This chapter describes some protocols and methodologies with practical and simple recommendations easily repeatable by people who have interest to make such laboratory work. We tried to raise the main steps ensuring the success of the establishment of the collection of symbiotic bacteria and fungi coming from all around the world.

Smallholder farmers in sub-Saharan Africa are confronted by low crop production due to phosphorus deficiency and a limited investment capacity in P inputs. Alternative P fertilizer types are being commercialized which aim at improved P use efficiency through specialized formulations. These products include, amongst others, leaf sprays, seed coatings and conditioners with humic acids. We evaluated these products in pot trials under greenhouse conditions and in multi-locational participatory field trials with farmer groups in three distinct agro-ecological zones in Kenya. The products were applied in conjunction with TSP fertilizer at half the recommended economic rate, as the P supplied through these products was insufficient to attain adequate crop yields. P response was assessed by including treatments without P addition, and TSP applied at half and full recommended rate. In the pot trial, none of the products significantly (P