Associative Diazotrophs Research Articles

Microbes in Agriculture: Prospects and Constraints to Their Wider Adoption and Utilization in Nutrient-Poor Environments

Microbes such as bacteria and fungi play important roles in nutrient cycling in soils, often leading to the bioavailability of metabolically important mineral elements such as nitrogen (N), phosphorus (P), iron (Fe), and zinc (Zn). Examples of microbes with beneficial traits for plant growth promotion include mycorrhizal fungi, associative diazotrophs, and the N2-fixing rhizobia belonging to the α, β and γ class of Proteobacteria. Mycorrhizal fungi generally contribute to increasing the surface area of soil-root interface for optimum nutrient uptake by plants. However, when transformed into bacteroids inside root nodules, rhizobia also convert N2 gas in air into ammonia for use by the bacteria and their host plant. Thus, nodulated legumes can meet a high proportion of their N requirements from N2 fixation. The percentage of legume N derived from atmospheric N2 fixation varies with crop species and genotype, with reported values ranging from 50–97%, 24–67%, 66–86% 27–92%, 50–92%, and 40–75% for soybean (Gycine max), groundnut (Arachis hypogea), mung bean (Vigna radiata), pigeon pea (Cajanus cajan), cowpea (Vigna unguiculata), and Kersting’s groundnut (Macrotyloma geocarpum), respectively. This suggests that N2-fixing legumes require little or no N fertilizer for growth and grain yield when grown under field conditions. Even cereals and other species obtain a substantial proportion of their N nutrition from associative and endophytic N2-fixing bacteria. For example, about 12–33% of maize N requirement can be obtained from their association with Pseudomonas, Hebaspirillum, Azospirillum, and Brevundioronas, while cucumber can obtain 12.9–20.9% from its interaction with Paenebacillus beijingensis BJ-18. Exploiting the plant growth-promoting traits of soil microbes for increased crop productivity without any negative impact on the environment is the basis of green agriculture which is done through the use of biofertilizers. Either alone or in combination with other synergistic rhizobacteria, rhizobia and arbuscular mycorrhizal (AM) fungi have been widely used in agriculture, often increasing crop yields but with occasional failures due to the use of poor-quality inoculants, and wrong application techniques. This review explores the literature regarding the plant growth-promoting traits of soil microbes, and also highlights the bottle-necks in tapping this potential for sustainable agriculture.

Nitrogen Fixation, Carbohydrate Contents, and Bacterial Microbiota in Unelongated Stem of Manure Compost-Applied Rice at Panicle Initiation

In rice, symbiotic N2 fixation via nodule bacteroids does not take place naturally. Although N2 fixation by endophytic and associative diazotrophs has been reported in rice, the main organs and seasonal regulation for the N2 fixation have not been elucidated. In this study, seasonal changes in nitrogenase (acetylene reduction) activity and carbohydrate contents in elongated culm (EC), unelongated stem (US), and crown root (CR) were investigated in manure compost (MC)- and chemical fertilizer (CF)-applied rice. Nitrogenase activity increased after rooting (June) and reached the highest activity in US of MC-applied rice at panicle initiation (August). The sucrose content in EC continued to increase after rooting regardless of the applied materials, whereas the glucose content in US increased after rooting only in CF-applied rice, suggesting higher consumption of glucose in US of MC-applied rice. There were significant differences among bacterial microbiota in EC, US, and CR at panicle initiation. In addition, Clostridia class anaerobes were more abundant in US of MC-applied rice than in EC and CR of MC-applied rice. Such difference was not observed in US of CF-applied rice. These results suggest the suitability of US of MC-applied rice at panicle initiation as a site of N2 fixation under anaerobic conditions.

BIOLOGICAL ACTIVITY OF RHISOSPHERE OF GRAIN FORAGE CROPS IN CASE OF APPLICATION OF BACTERIAL PRODUCTS

The studies were carried out in field experiments of Federal State Budgetary Scientific Institution "Omsk Agrarian Research Center" in the southern forest-steppe of Western Siberia. The aim of the research is to study the effect of application of biological products of associative diazotrophs on biological properties of the rhizosphere of grain forage crops of varieties of Omsk selection. The tests were carried out on varieties of spring barley for grain forage and brewing purposes bred at Omsk agrarian scientific centre (FSBSI "SibSRIA"): Omsky 95, Sasha, Omsky hulless 1, Omsky 90, Omsky 91, Omsky 101 and oats for cereal purposes - Siberian Hercules. Preparations of complex action produced at All-Russian Research Institute of Agricultural Microbiology (FSBSI All-Russian Research Institute of Agricultural Microbiology:, St. Petersburg, Pushkin) Rizoagrin (Agrobacterium radiobacter), Azorizin (Azospirillum), Mizorin (Arthrobacter mysorens), Flavobacterin (Flavobacterium) were used for inoculation of seeds. The soil of the experimental plot is meadow-black soil, medium-thick, medium-humus, heavy loamy with a humus content of 6.5%, water pH - 6.5. It was found that the microflora population of the rhizosphere of agricultural crops reacted dubiously to application of biological products and depended on genotypic characteristics of the varieties. The greatest positive effect of seed inoculation on the total number of microorganisms was noted in the rhizosphere of barley variety Omsky 95, the increase was 35% when the seeds were treated with Azorizin, with Rizoagrin -70% in relation to the control. The inoculation of oat seeds of Siberian Hercules variety with the bioproduct Flavobacterin contributed to an increase of the total number of microorganisms in the rhizosphere up to 27% compared to the control. The processes of nitrogen immobilization (Kimmob.>1) prevailed in the soil under crops of grain forage crops in the years of the research. The highest coefficient of organic matter (potentially mineralizing) transformation was noted in the rhizosphere of grain-forage barley Omsk hulless 1 when seeds were treated with Rizoagrin - 148 units (109 units in the control) and in the rhizosphere of cereal oat Siberian Hercules when seeds were treated with Mizorin - 91.5 units . (55.8 units in the control).

Altitudinal niches of symbiotic, associative and free-living diazotrophs driven by soil moisture and temperature in the alpine meadow on the Tibetan Plateau

Legume-associated symbiotic diazotrophs contribute more to nitrogen (N) fixation than non-symbiotic diazotrophs in many terrestrial ecosystems. However, the percentage of legume biomass is low in alpine meadows on the Tibetan Plateau. Therefore, non-symbiotic diazotrophs may play important roles in N fixation in alpine meadow soils. Moreover, Tibetan alpine meadows are fragile and sensitive to global climate change, and the investigating of the key factor driving soil diazotrophic community still entails several challenges. To address these issues, we investigated diazotrophic spatial distribution and diversity along the elevational gradient between 3200 and 4200 m in the alpine meadow using amplicon sequencing of nifH gene. The result clearly showed that soil moisture and temperature were key factors driving soil diazotrophic community structures. Both altitude and soil depth significantly differentiated diazotrophic community composition. Alpha diversity indices of diazotrophic communities showed unimodal distribution along elevation gradient, strongly affected by soil moisture. Altitudinal niches were occupied by different diazotrophs. Soils at lower elevations were dominated by symbiotic diazotrophs and associative diazotrophs related to high biomass of plant hosts, while those at higher elevations were dominated by free-living psychrophiles such as Polaromonas. Furthermore, high moisture stimulated free-living anaerobes at middle elevations, such as Geobacter and Anaeromyxobacter, while suppressed legumes and symbiotic Mezorhizobium. Soil temperature not only directly affected temperature-sensitive diazotrophs, but also indirectly affected them through plants and soil properties such as pH and ammonium content. Our results suggest that climate change may strongly affect biological nitrogen fixation (BNF), and free-living diazotrophs may play important roles in BNF of alpine meadow system on the Tibetan Plateau.

Improved Stability of Engineered Ammonia Production in the Plant-Symbiont Azospirillum brasilense.

Bioavailable nitrogen is the limiting nutrient for most agricultural food production. Associative diazotrophs can colonize crop roots and fix their own bioavailable nitrogen from the atmosphere. Wild-type (WT) associative diazotrophs, however, do not release fixed nitrogen in culture and are not known to directly transfer fixed nitrogen resources to plants. Efforts to engineer diazotrophs for plant nitrogen provision as an alternative to chemical fertilization have yielded several strains that transiently release ammonia. However, these strains suffer from selection pressure for nonproducers, which rapidly deplete ammonia accumulating in culture, likely limiting their potential for plant growth promotion (PGP). Here we report engineered Azospirillum brasilense strains with significantly extend ammonia production lifetimes of up to 32 days in culture. Our approach relies on multicopy genetic redundancy of a unidirectional adenylyltransferase (uAT) as a posttranslational mechanism to induce ammonia release via glutamine synthetase deactivation. Testing our multicopy stable strains with the model monocot Setaria viridis in hydroponic monoassociation reveals improvement in plant growth promotion compared to single copy strains. In contrast, inoculation of Zea mays in nitrogen-poor, nonsterile soil does not lead to increased PGP relative to WT, suggesting strain health, resource competition, or colonization capacity in soil may also be limiting factors. In this context, we show that while engineered strains fix more nitrogen per cell compared to WT strains, the expression strength of multiple uAT copies needs to be carefully balanced to maximize ammonia production rates and avoid excessive fitness defects caused by excessive glutamine synthetase shutdown.

INFLUENCE OF RISOAGRINE SEED INOCULATION ON RHIZOAGRINE MICROFLORA AND WINTER WHEAT YIELDS IN WESTERN SIBERIA FOREST-STEPPE

The researchers conduct the field stationary experiment with the use of mineral fertilizers and straw in the grain and steam crop rotation with the withdrawal field of alfalfa and study the number of microflora in the rhizosphere of winter wheat of the new variety Priirtyshskaya after treatment of seeds with biospecimen of complex effect - risoagrine. The highest number of useful crop groups of microorganisms was observed in the variant with inoculation of crop seeds by risoagrine on the basis of applying mineral fertilizers, as well as in combination of inoculation techniques, application of mineral fertilizers and straw (N15P23 + straw + inoculation), respectively, 444 and 355 million UU/yr with 217 million UU/yr in the control group. In the variant with inoculation of winter wheat seeds by mineral fertilizers (N15P23 + inoculation), the number ofoligonitrophils and bacteria, mineralizing mineral phosphates, increased by 2.2 times, nitrifiers - by 60%, microorganisms that utilize organic nitrogen compounds on MPA - by 39, consuming mineral nitrogen on CAA - by 73% compared to the control group. The celluloseolytic soil activity under winter wheat sowing in variants N15P23 + inoculation and N15P23 + straw + inoculation increased to 66.5-67.0%, exceeded the control group by 1.7 times. The highest increase in the crop’s grains was observed in the combination of mineral, organic (straw) and bacterial (rizoagrine) fertilizers - 40.3% in comparison with the control group. Additional nitrogen removal by winter wheat crop due to the activity of associative diazotrophs varied from 6 to 16.5 kg/ha. Correlative relations of high (r=0.84-0.91) and average (r=0.62-0.72) degree of microorganisms in the rhizosphere were observed among the indicators of crop yield and number of microorganisms. The closest correlation took place between the value of winter wheat grain yield and the number of bacteria growing on MPA, including ammonifiers, and the yield and number of nitrifying bacteria.

Edaphic correlates of feedstock‐associated diazotroph communities

AbstractMiscanthus × giganteus and Panicum virgatum are potential promising bioenergy feedstock crops suitable for the temperate zone. The energy efficiency and sustainability of bioenergy production could be improved by reducing their fertilizer inputs – particularly energy intensive nitrogen fertilizers. Miscanthus is known to benefit from nitrogen fixation by associative diazotrophs. However, because the effects of edaphic‐, management‐, and plant‐related factors on feedstock‐associated diazotroph communities have not yet been characterized, it is not currently possible to optimize the nitrogen contribution to feedstock crops from associated diazotroph communities. To address this critical knowledge gap, we characterized the bacterial and diazotroph communities in the rhizosphere and endophytic compartments of both species at eight research sites across Illinois. We also quantified the nifH gene abundance in the rhizosphere soil as well as a range of soil chemistry parameters at these sites. Multivariate statistical analyses revealed that diazotroph and bacterial communities in the rhizosphere varied primarily among sites, with very small differences between host species. Conversely, diazotroph and bacterial communities in the endophytic compartments differed significantly between plant species, but did not vary substantially among sites. Finally, nifH gene abundance in the rhizospheres of both species varied substantially from site to site and was positively correlated with soil iron concentration as well as soil ammonium concentration, and negatively correlated with abundance of other soil nutrients including calcium, total nitrogen, and nitrates. These results indicate the potential edaphic drivers of associative diazotroph communities in feedstock rhizospheres and suggest that manipulating bioavailable iron content in the soil is a potential direction for investigating the optimization of these communities to improve their nitrogen contribution to crops.

ECONOMIC AND ENERGETIC EFFICIENCY OF COMPLEX BACTERIZATION IN SOYBEAN CULTIVATION

The results of efficiency studies by major economic and energetic parameters of pretreatment of soybean with inoculants based on rhizobia Bradyrhizobium japonicum and associative diazotrophs Azospirillum brasilense are provided. It was established that the highest levels of the studied parameters are achieved using mixed cultures of nitrogen fixing microorganisms. The high economic and energetic efficiency was also observed during inoculation of soybean with rhizobia pure culture. However, no significant positive impact of A. brasilense applied separately was found in terms of studied parameters.

Agrobacterium tumefaciens as associative nitrogen-fixing bacteria

From the root surface of vegetable plants growing in the soils of North Vietnam, 227 pure bacterial cultures are isolated on nitrogen-free media. All the cultures show nitrogen-fixing ability and positive effect on plant growth in model experiments, while none of them cause the formation of root nodules or tumors. Based on the gene sequencing of the 16S rRNA, our determination of the phylogenic position of the most active isolated strains reveals their affiliation with the family Rhizobiaceae of the phylum Alpharoteobacteria and that they are closest to the type strain of the genus Agrobacterium—A. tumefaciens. The physiology and morphological features also indicate the affiliation of these organisms with A. tumefaciens. Thus, our isolated strain of this plant pathogen bacterium appears as associative diazotrophs, which also have a positive effect on the growth of cultural plants.

Lipopolysaccharides in diazotrophic bacteria.

Biological nitrogen fixation (BNF) is a process in which the atmospheric nitrogen (N2) is transformed into ammonia (NH3) by a select group of nitrogen-fixing organisms, or diazotrophic bacteria. In order to furnish the biologically useful nitrogen to plants, these bacteria must be in constant molecular communication with their host plants. Some of these molecular plant-microbe interactions are very specific, resulting in a symbiotic relationship between the diazotroph and the host. Others are found between associative diazotrophs and plants, resulting in plant infection and colonization of internal tissues. Independent of the type of ecological interaction, glycans, and glycoconjugates produced by these bacteria play an important role in the molecular communication prior and during colonization. Even though exopolysaccharides (EPS) and lipochitooligosaccharides (LCO) produced by diazotrophic bacteria and released onto the environment have their importance in the microbe-plant interaction, it is the lipopolysaccharides (LPS), anchored on the external membrane of these bacteria, that mediates the direct contact of the diazotroph with the host cells. These molecules are extremely variable among the several species of nitrogen fixing-bacteria, and there are evidences of the mechanisms of infection being closely related to their structure.

Diversity Analysis of Diazotrophic Bacteria Associated with the Roots of Tea (Camellia sinensis (L.) O. Kuntze)

The diversity elucidation by amplified ribosomal DNA restriction analysis and 16S rDNA sequencing of 96 associative diazotrophs, isolated from the feeder roots of tea on enriched nitrogen-free semisolid media, revealed the predominance of Gram-positive over Gram-negative bacteria within the Kangra valley in Himachal Pradesh, India. The Gram-positive bacteria observed belong to two taxonomic groupings; Firmicutes, including the genera Bacillus and Paenibacillus; and Actinobacteria, represented by the genus Microbacterium. The Gram-negative bacteria included alpha-Proteobacteria genera Brevundimonas, Rhizobium, and Mesorhizobium; gamma-Proteobacteria genera Pseudomonas and Stenotrophomonas; and beta-Proteobacteria genera Azospira, Burkholderia, Delftia, Herbaspirillum and Ralstonia. The low level of similarity of two isolates, with the type strains Paenibacillus xinjiangensis and Mesorhizobium albiziae, suggests the possibility of raising species novum. The bacterial strains of different phylogenetic groups exhibited distinct carbon-source utilization patterns and fatty acid methyl ester profiles. The strains differed in their nitrogenase activities with relatively high activity seen in the Gramnegative strains exhibiting the highest similarity to Azospira oryzae, Delftia lacustris and Herbaspirillum huttiense.

REGULATION OF GROWTH ACTIVITY OF POPULATION OF INDUSTRIAL BRADYRHIZOBIUM JAPONICUM STRAINS IN VITRO

The results of researches on optimization of soya rhizobium cultivation process through choosing optimum environments are shown in the article. It also represents growth activity of Bradyrhizobium japonicum population influenced by products of symbiotic and associative diazotroph metabolism in vitro. The highest growth activity of these microorganisms is shown when their cultivation in the medium with sterile bacterial suspensions with exo- and endo- metabolites of Azospirillum brasilense.

Production of biofertilizers using baker's yeast effluent and their application to wheat and barley grown in north Sinai deserts

Effluent from the baker's yeast industry was experimented on as a culture medium for the growth and biomass production of diazotrophs. The effluent supported good growth of Azotobacter chroococcum, Enterobacter agglomerans and Klebsiella pneuomoniae, Azospirillum brasilense, Bacillus polymyxa and Pseudomonas putida and strongly proposed for biofertilizers production of associative diazotrophs. Slurry preparations containing natural polymers, e.g. Arabic gum (5%), pero-dextrin (20%), starch granules (10%) or gelatine (20%) were impregnated with cells of tested diazotrophs. With storage, entrapped cells of B. polymyxa were viable up to 160 days, while gradual decreases in Azospirillum numbers were recorded. Pero-dextrin, a by-product of the starch industry, was selected as the appropriate biocarrier accommodating diazotroph cells and maintaining prolonged survival rates and nitrogenase activity. Cell cultures of A. brasilense, A. chroococcum, B. polymyxa, E. agglomerans and P. putida were equally mixed and entrapped into pero-dextrin slurry biofertilizer formulation named as “BIOGRAMINA”. Tested diazotrophs successfully survived (ca. 108 cfu ml−1) in such formulation up to 6 months at both ambient and cold temperatures. The response of wheat and barley to “BIOGRAMINA” in the presence or absence of N fertilizers was evaluated in greenhouse and field trials. Highest total biological yields were recorded for inoculated plants simultaneously supplemented with rational N fertilizer dose.

Production of rhizobia biofertilizers using baker's yeast effluent and their application to Leucaena leucocephala

Industrial baker's yeast effluent (BYE) was experimented on as a culture medium for growth and biomass production of six fast-growing rhizobia strains. Diluting the effluent with distilled water was necessary to maximize bacterial biomass production. The addition of phosphate buffer, ammonium chloride or trace-elements did not improve the final biomass yield of tested micro-organisms. Rhizobial growth and biomass on the effluent were comparable to traditional yeast extract mannitol medium (YEM). The Rhizobium spp. biomass, produced using either YEM or BYE, was evaluated as inoculum for Leucaena leucocephala (Lam.) de Wit in a pot experiment. No significant differences were reported in respect of legume nodule and growth parameters. Simultaneous inoculation with rhizobia and a group of associative diazotrophs supported better nodulation and nitrogenase activity.

History on the biological nitrogen fixation research in graminaceous plants: special emphasis on the Brazilian experience

This review covers the history on Biological Nitrogen Fixation (BNF) in Graminaceous plants grown in Brazil, and describes research progress made over the last 40 years, most of which was coordinated by Johanna Döbereiner. One notable accomplishment during this period was the discovery of several nitrogen-fixing bacteria such as the rhizospheric (Beijerinckia fluminensis and Azotobacter paspali), associative (Azospirillum lipoferum, A. brasilense, A. amazonense) and the endophytic (Herbaspirillum seropedicae, H. rubrisubalbicans, Gluconacetobacter diazotrophicus, Burkholderia brasilensis and B. tropica). The role of these diazotrophs in association with grasses, mainly with cereal plants, has been studied and a lot of progress has been achieved in the ecological, physiological, biochemical, and genetic aspects. The mechanisms of colonization and infection of the plant tissues are better understood, and the BNF contribution to the soil/plant system has been determined. Inoculation studies with diazotrophs showed that endophytic bacteria have a much higher BNF contribution potential than associative diazotrophs. In addition, it was found that the plant genotype influences the plant/bacteria association. Recent data suggest that more studies should be conducted on the endophytic association to strengthen the BNF potential. The ongoing genome sequencing programs: RIOGENE (Gluconacetobacter diazotrophicus) and GENOPAR (Herbaspirillum seropedicae) reflect the commitment to the BNF study in Brazil and should allow the country to continue in the forefront of research related to the BNF process in Graminaceous plants.

Rhizosheath of sinai desert plants is a potential repository for associative diazotrophs

Among 42 plant species representing the flora of north Sinai, two possessed sand grain sheath encasing the roots. They are Panicum turgidum Forssk. and Stipagrostis scoparia (Trin.and Rupr.) deWinter. Rhizosheaths, compared to surrounding free sand, accommodated higher population density of microorganisms including associative diazotrophs. Isolates secured belonged to the species of Bacillus circulans, Paenib. macerans ( Bacillus macerans), Enterobacter agglomerans, Agrobacterium radiobacter and Chryseomonas luteola ( Pseudomonos luteola). The rhizosheath potentiality in re-vegetating sand dunes and arid lands, through nitrogen fixation, plant–water relationship and root continuity for nutrient uptake, are discussed.

Complement of integrated fertilizer management and integrated pest management concepts to ameliorate faba bean growth and yield

Twenty-one microbial preparations recommended for controlling pathogenic fungal strains causing root rot and wilt diseases of faba bean were investigated for antibiosis against several symbiotic and associative diazotrophs adopting a modified agar-plate-inhibition-zone assay. Rhizobium and Bradyrhizobium exhibited a somewhat similar susceptibility to biocontrol agents while associative diazotrophs showed variable responses. Azotobacter, compared to others, was severely inhibited by such bio-candidates. The members of the biofertilizer formulation ‘Biofertan’ did bear mixed cultivation with the majority of biocontrol agents. Among those, Bacillus subtilis was deemed the pioneer. In pot experiments, almost all the antagonists significantly restricted the severity of root rot and wilt diseases besides modifying faba bean seedling stand and improving plant development. This was very obvious with shoot biomass increases of > 50%. Moreover, the bioagents successfully recovered the legume establishment, seriously injured due to pathogenic fungal infection. Simultaneous inoculation with Rhizobium and biocontrol agents provided more growth stimulation compared to either when introduced individually. Field-grown faba beans were inoculated with the diazotroph and representatives of biocontrol strains by two different methods, seed coating and over-head soil. Growth parameters determined were the highest when the legume plant was seed-coated by Rhizobium simultaneously over-head soil inoculated with the bacterial bioagents; this was reported with Bacillus subtilis and Pseudomonas aerugenosa. The significance of combined application of biofertilizer and bioagent to ensure cheap, clean and safe farm products is discussed.

Plant Growth-Promoting Effects of Diazotrophs in the Rhizosphere

Because of their ability to transform atmospheric N2 into ammonia that can be used by the plant, researchers were originally very optimistic about the potential of associative diazotrophic bacteria to promote the growth of many cereals and grasses. However, multiple inoculation experiments during recent decades failed to show a substantial contribution of Biological Nitrogen Fixation (BNF) to plant growth in most cases. It is now clear that associative diazotrophs exert their positive effects on plant growth directly or indirectly through (a combination of) different mechanisms. Apart from fixing N2, diazotrophs can affect plant growth directly by the synthesis of phytohormones and vitamins, inhibition of plant ethylene synthesis, improved nutrient uptake, enhanced stress resistance, solubilization of inorganic phosphate and mineralization of organic phosphate. Indirectly, diazotrophs are able to decrease or prevent the deleterious effects of pathogenic microorganisms, mostly through the synthesis of antibiotics and/or fungicidal compounds, through competition for nutrients (for instance, by siderophore production) or by the induction of systemic resistance to pathogens. In addition, they can affect the plant indirectly by interacting with other beneficial microorganisms, for example, Azospirillum increasing nodulation of legumes by rhizobia. The further elucidation of the different mechanisms involved will help to make associative diazotrophs a valuable partner in future agriculture.

Response of Triticum aestivum to an Associative Diazotroph Inoculum under Varying Levels of Nitrogen Fertilizer

Response of Triticum aestivum to an Associative Diazotroph Inoculum under Varying Levels of Nitrogen Fertilizer

Intercropping of sesbania (Sesbania sesban) and leucaena (Leucaena leucocephala) with five annual grasses under semi-arid conditions as affected by inoculation with specific rhizobia and associative diazotrophs

La culture intercalaire de legumineuses et de non-legumineuses est consideree comme un moyen pour ameliorer quantitativement et qualitativement la production de fourrage. Dans des conditions semi-arides dans le desert, la plantation intercalaire de leucaena et sesbania entre les graminees annuelles est evaluee a partir d'une serie d'essais au champ. Un inoculum constitue par le rhizobium specifique pour les legumineuses et d'un complexe de bacteries fixatrices d'azote (diazotrophes) associees aux non-legumineuses a ete applique en presence et en absence de fertilisation azotee. L'inoculation specifique par le Rhizobium a ete indispensable pour ameliorer la croissance des legumineuses qui s'est etendue aux non-legumineuses voisines. Les diazotrophes associees ont ameliore la biomasse et le rendement en azote des non-legumineuses en particulier en presence d'une fertilisation azotee moderee pour l'orge d'hiver et le ray-grass et avec une dose d'azote elevee (300 kg.ha -1 ) pour l'orge d'ete et l'herbe du Soudan (Sorghum sudanense). La culture intercalaire a ameliore la productivite des non-legumineuses en particulier celle de l'orge associee au sesbania et le transfert d'azote calcule des legumineuses aux non-legumineuses est compris entre 20 et 70 kg.ha -1 .