Abstract: Sugarcane is an important Brazilian commodity, being usually cultivated in soils with low natural fertility. This study aimed to isolate diazotrophic endophytes from sugarcane tissues and evaluate the morphological and physiological characteristics of their colonies as well as their plant growth-promoting (PGP) traits in select diazotrophic endophytic bacteria. Fifty-six bacterial isolates were identified in the sugarcane tissues, and these isolates presented distinct morphological and physiological traits. A total of thirty-five bacterial isolates were biochemically evaluated. Overall, Bacillus was the dominant genus. Isolates of Methylobacterium spp. and Brevibacillus agri were present only in leaves, while Herbaspirillum seropedicae occurred only in stems. Except to IPA-CF45A, all isolates were nitrogenase positive. All endophytes exhibit production of indol 3-acetic acid. Over 50% of endophytes solubilize phosphate, release N-acyl homoserine lactones, and present the activity of 1-aminocyclopropane-1-carboxylic acid deaminase, catalase, lipase and protease. The network analysis showed that isolates belonged to Burkholderia, Herbaspirillum, and Methylobacterium interact with Bacillus. Bacterial endophytes exhibited distinct morphological, physiological, and PGP traits that are useful for sustainable agriculture, highlighting the isolates IPA-CC33, IPA-CF65, IPA-CC9 and IPA-CF27. Further studies on the effects of these diazotrophic endophytes and their potential for providing microbial inoculants for improving sugarcane fields will provide valuable information to maintain the sustainability and environment quality.

ABSTRACT The inoculation of rhizobia in lima bean can increase its yield and contribute to smallholder farms. In this study, the potential of rhizobia in increasing the lima bean yield was evaluated in two regions from Piaui and Ceará states. The experiments were conducted in field comparing three rhizobia strains (UFPI32, UFPI38, UFPI59), one strain of reference to Phaseolus vulgaris (CIAT899) and two controls (with and without nitrogen). The parameters of nodulation, N accumulation and yield varied between treatments and locations. The nodule biomasses were higher in UFPI59 and UFPI32 (Piauí), and CIAT899 and UFPI32 (Ceará). The highest values of nodule size were found in treatments UFPI59 in both locations. Lima bean presented highest values of leaf N in UFPI59 and CIAT899. The highest values of grain yield were found in the treatment UFPI59 as compared to CIAT899 and the controls. The results confirmed the potential of UFPI59 in promoting nodulation, N accumulation, plant growth and yield of lima bean in both locations.

Resumen La diversidad de aislamientos rizobianos en el Bosque Seco Tropical de Brasil (BST) (Caatinga) ha sido ampliamente estudiada debido a la gran importancia de encontrar nuevas especies de bacterias con capacidad para fijar nitrógeno en leguminosas arbóreas, entre ellas, Mmosa tenuiflora (Willd.) Poir., Piptadenia stipulacea (Benth.) Ducke y Mimosa caesalpiniifolia Benth. El bioma del BST es importante en Brasil, por tanto, el conocimiento de comunidades microbianas que hacen simbiosis con plantas autóctonas ayuda en la comprensión de la interacción planta-microorganismos, así como en la optimización de procesos biológicos que pueden mejorar el sistema de cultivo en un área como ésta, rica en diversidad y que ha sido poco estudiada. Este estudio se realizó en tres municipios del Sertáo de Pernambuco y Paraíba, con las especies antes citadas. Para el efecto, se realizaron las mediciones siguientes: aislamiento de rizobios y su caracterización fenotípica y molecular con el uso de marcadores de fingerprint como BOX, REP, ERIC y BOX-PCR; y confirmación de los aislamientos, utilizando la técnica de amplificación por dúplex-PCR con los genes niJH y nodC. Los resultados mostraron que dada la variación encontrada en la amplificación de los genes niJH y nodC, la técnica duplex-PCR puede mostrar resultados falsos positivos, ya que estos genes tienen un polimorfismo muy grande. La falta de conocimiento de los aislamientos que hacen simbiosis con estas plantas ayuda, aún más, a concluir que esta técnica de autenticación todavía no puede ser aplicada a todos los aislados nodulantes de leguminosas. En cuanto a los análisis realizados con marcadores de fingerprint (huellas digitales), se observó que todos eran muy eficientes en la capacidad de distinguir especies y que cuanto mayor es el número de marcadores utilizados, más seguro es el conocimiento sobre la taxonomía y diversidad de rizobios.

Abstract The diversity of rhizobial isolates in tropical dry forests (TDF) has been studied due to the great importance of finding new species of bacteria capable of fixing nitrogen in tree legumes. In the Brazilian TDF (caatinga), Leguminosae is the most important family of plants, so the knowledge of microbial communities that make symbioses with native plants can help in the understanding of the interaction plant-microorganisms, as well as in the optimization of biological processes that can improve the cultivation system in an area so rich and understudied. In this study was determined the characteristics of rhizobia isolated from nodules of Mimosa tenuiflora (Willd.) Poir., Piptadenia stipulacea (Benth.) Ducke and Mimosa caesalpiniifolia Benth, grown in soils collected under caatinga vegetation. The phenotypic and molecular characterization of the isolates, with use of fingerprint markers such as BOX, REP, ERIC and BOX-PCR were performed. Amplification technique by duplex PCR with the niJH and nodC genes was used for the authentication of isolates. The results showed that given the variation found in the amplification of the niJH and nodC genes, the duplex PCR technique can show false-positive results, as these genes have a very large polymorphism. The lack of knowledge of isolates that make symbioses with these plants further help to conclude that this authentication technique cannot yet be applied to all legume-nodulating isolates. Regarding the analyses made with fingerprint markers, it was observed that all were very efficient in the ability to distinguish species and that the greater the number of markers used, the safer the knowledge on the taxonomy and diversity of rhizobia.

Abstract Erythrina velutina ("mulungu") is a legume tree from Caatinga that associates with rhizobia but the diversity and symbiotic ability of "mulungu" rhizobia are poorly understood. The aim of this study was to characterize "mulungu" rhizobia from Caatinga. Bacteria were obteined from Serra Talhada and Caruaru in Caatinga under natural regeneration. The bacteria were evaluated to the amplification of nifH and nodC and to metabolic characteristics. Ten selected bacteria identified by 16S rRNA sequences. They were tested in vitro to NaCl and temperature tolerance, auxin production and calcium phosphate solubilization. The symbiotic ability were assessed in an greenhouse experiment. A total of 32 bacteria were obtained and 17 amplified both symbiotic genes. The bacteria showed a high variable metabolic profile. Bradyrhizobium (6), Rhizobium (3) and Paraburkholderia (1) were identified, differing from their geographic origin. The isolates grew up to 45 °C to 0.51 mol L-1 of NaCl. Bacteria which produced more auxin in the medium with l-tryptophan and two Rhizobium and one Bradyrhizobium were phosphate solubilizers. All bacteria nodulated and ESA 90 (Rhizobium sp.) plus ESA 96 (Paraburkholderia sp.) were more efficient symbiotically. Diverse and efficient rhizobia inhabit the soils of Caatinga dry forests, with the bacterial differentiation by the sampling sites.

To improve yield and nutrient absorption, the addition of fertilizers to provide nutrients in adequate quantities is recommended. An alternative substitution for soluble fertilizer is the use of Acidithiobacillus bacteria to produce rock biofertilizer that is then mixed with organic matter inoculated with diazotrophic bacteria (Beijerinckia indica) for N enrichment. This study evaluates the effectiveness of biofertilizer on nutrient uptake and its interaction with sugarcane filter cake in field-grown sugarcane on an Ultisol in the Brazilian rainforest region. The experiment used two NPK fertilizer treatments (biofertilizer and soluble fertilizer) applied at three rates (50, 100 and 150% of the recommended rate [RR]) and a control treatment of earthworm compost (20 t ha-1). The fertilizer treatments were applied with and without filter cake, in four replicates. Total C and N, available P and K, and exchangeable Ca and Mg in plants (upper shoots, leaves and stems) as well as soil samples were analyzed. The biofertilizer showed similar responses as did the soluble fertilizer in nutrient uptake in the different parts of sugarcane and in the soil samples. The effects of biofertilizer were enhanced by the interaction of the fertilizer treatments with sugarcane filter cake. We concluded that the biofertilizer enriched in N by inoculation with B. indica may be a viable alternative for the replacement of soluble fertilizers in sugarcane.

ABSTRACT The deployment of soluble fertilizers has been one of the most commonly applied agricultural practices in the bid to increase crop yield. However, the production of soluble fertilizers has a considerable economic cost and consumes a substantial amount of energy. In general, soil organic matter provides the nutrients needed for plant growth in organic agriculture. However, these nutrients are not sufficient if the best yield is to be obtained. The aim of our field experiment was to evaluate the effectiveness of phosphate and potassic sources (rocks, bio-fertilizers and soluble fertilizers) based on several sugarcane characteristics and soil attributes. Our experiment was conducted over two consecutive years, and we assessed the effect of using sugarcane filter mud cake (SFMC). In addition, we mixed the phosphate and potassic sources with earthworm compost enriched in N by inoculation with diazotrophic bacteria (OM) and applied at 50, 100 and 150 % of the recommended dosage rate (RDR). The PK biofertilizer with OM enriched in N positively affected sugarcane height, yield, and industrial characteristics. The application of SFMC greatly increased available P and K in the soil and plant characteristics with residual effect in the two consecutive harvests. We conclude that the biofertilizer has the potential to increase sugarcane characteristics and may represent an alternative to soluble fertilizers.

O objetivo deste trabalho foi estimar as quantidades de N fixadas em feijão-caupi em sistema tradicional e em feijão-caupi e gliricídia em sistema agroflorestal, sob condições semiáridas do Nordeste brasileiro. O experimento foi conduzido em blocos ao acaso, em arranjo em parcelas subdivididas, com quatro repetições, no semiárido da Paraíba. As parcelas consistiram dos sistemas agroflorestal e tradicional (sem árvores), e as subparcelas, dos três cultivos entre as linhas das árvores, no sistema agroflorestal. Para estimar a fixação de N, amostras das plantas foram coletadas no quarto ciclo de crescimento das espécies perenes e no quarto ciclo de cultivo das espécies anuais. No sistema agroflorestal com capim-buffel e palma forrageira, a gliricídia fixa simbioticamente altas proporções de N (>50%) e adiciona quantidades maiores de N (40 kg ha-1 nas folhas) que no sistema tradicional (11 kg ha-1 nos grãos e 18 kg ha-1 na palhada). No sistema agroflorestal com milho e feijão-caupi, a gliricídia não fixa N e a adição de N é limitada à fixação no feijão-caupi (2,7 kg ha-1), que é menor que no sistema tradicional em razão da sua baixa produção de biomassa.

The objective of this work was to estimate the amounts of N fixed by cowpea in a traditional system and by cowpea and gliricidia in an agroforestry system in the Brazilian Northeast semiarid. The experiment was carried out in a randomized complete block design, in a split-plot arrangement, with four replicates, in the semiarid region of the state of Paraíba, Brazil. Plots consisted of agroforestry and traditional systems (no trees), and split-plots of the three crops planted between the tree rows in the agroforestry system. To estimate N fixation, plant samples were collected in the fourth growth cycle of the perennial species and in the fourth planting cycle of the annual species. In the agroforestry system with buffel grass and prickly-pear cactus, gliricidia plants symbiotically fix high proportions of N (>50%) and contribute with higher N amounts (40 kg ha-1 in leaves) than in the traditional system (11 kg ha-1 in grain and 18 kg ha-1 in straw). In the agroforestry system with maize and cowpea, gliricidia plants do not fix nitrogen, and N input is limited to the fixation by cowpea (2.7 kg ha-1), which is lower than in the traditional system due to its lower biomass production.

Solos salinos sódicos necessitam aplicação de condicionadores como gesso e matéria orgânica. Vários compostos foram avaliados como condicionadores para solos sódicos; entretanto, frequentemente estes materiais não promovem satisfatória redução no pH. Pesquisa recente demonstrou efeitos efetivos da aplicação da mistura de gesso e enxofre inoculado com Acidithiobacillus em solos sódicos com alto pH e sódio solúvel, todavia, os efeitos na planta não foram avaliados. O trabalho procurou verificar os efeitos de biofertilizantes de rochas (BPK), na nodulação, produção de biomassa e absorção de nutrientes em caupi comparado com fertilizantes minerais após adição dos condicionadores. Biofertilizantes (BPK) e fertilizantes minerais PK foram aplicados em diferentes doses, e as plantas inoculadas com rizóbios efetivos. Tratamento controle sem fertilização com PK foi incluído. Os resultados indicaram efeito do gesso e enxofre com Acidithiobacillus na redução do pH e sódio trocável. O biofertilizante de rochas (BPK) aumentou a nodulação, a biomassa e a absorção de nutrientes. Os rizóbios nativos do solo favoreceram o crescimento do caupi, apresentando resultados similares quando comparado com plantas inoculadas com rizóbios efetivos. O biofertilizante de rochas (BPK) mostrou ser alternativa para fertilizantes minerais com P e K em solos sódicos, após adição de gesso e enxofre inoculado com Acidithiobacillus.

Sodic soils require application of amendments as gypsum and organic matter. Many types of compost have been tested in sodic soils reclamation; however, these materials often do not provide satisfactory pH reduction. A recent study reported effective effects applying mixture of gypsum and sulfur inoculated with Acidithiobacillus in sodic soils with high pH and exchangeable sodium, though the effects on plant parameters were not evaluated. The present study was conducted to verify the effects of BPK rock biofertilizers on nodulation, biomass yield and nutrient uptake in cowpea compared with mineral fertilizer after sodic soil amendment. The BPK biofertilizers and PK mineral fertilizer were applied at different rates, and plants were inoculated with effective rhizobia strains. A control that did not receive PK fertilization was included. The results indicated that gypsum and sulfur with Acidithiobacillus reduced the soil's pH and the amount of soil exchangeable sodium. BPK rock biofertilizer increased cowpea nodulation, biomass yield and nutrient uptake. The native rhizobia in the soil exhibited effectiveness in cowpea growth; displaying similar results compared with the rhizobia inoculated plants. BPK biofertilizers may be used as alternative to mineral PK fertilizers in sodic soils after the application of gypsum and sulfur inoculated with Acidithiobacillus.

A fixação biológica de nitrogênio foi avaliada em jureminha (Desmanthus pernambucanus), orelha-de-onça (Macroptilium martii) e feijão-de-rolinha (Macroptilium lathyroides) cultivados em solos do semiárido da Paraíba, em vasos sem e com esterco bovino. Foram determinados o número e a biomassa de nódulos, os teores e as proporções de nitrogênio (N) fixado (percentual de nitrogênio da planta derivado do ar-%Ndda), pelo método da abundância natural, utilizando-se o capim-buffel como planta controle. As leguminosas tiveram nodulação abundante, nos três solos e na ausência ou presença de esterco, salvo quando cultivadas em Neossolo Flúvico sem adubação. A adubação com esterco aumentou o número e a biomassa de nódulos. A fixação biológica de nitrogênio foi alta nas três espécies, nos três solos: na maioria das plantas, os valores superaram 50%, chegando a 85%. Esses dados permitem estimar a capacidade de fixação das espécies no campo em 10 a 30 kg ha-1 de N, considerando as densidades de plantio e produtividade usuais. As menores %Ndda e quantidades fixadas foram encontradas nas plantas cultivadas em Neossolo Regolítico e aumentaram com a adição de esterco. Entre as espécies testadas, a fixação biológica de nitrogênio foi menos importante para D. pernambucanus. Nenhum dos parâmetros de nodulação avaliados (número, biomassa e biomassa/nódulo) explicou as proporções nem as quantidades de nitrogênio fixadas pelas plantas.

The biological nitrogen fixation (BNF) of Desmanthus pernambucanus (pigeon bundleflower), Macroptilium martii and M. lathyroides (wild bushbean), grown in soils from the semiarid region of Paraíba, manured or not, was evaluated in a pot experiment. Nodule number and biomass, N content and the proportions of fixed N (%Ndfa) were estimated, using the natural abundance methodology and buffel grass as a reference plant. The legume plants nodulated abundantly in all three soils, manured or not, except when grown in Fluvic Neosol without manure. The number and biomass of the nodules increased with manure. The BNF was high in all three species and soils: in most of the plants resulting in %Ndfa above 50% and reaching 85%. Using these data, a rough estimate of the fixation capacity of these species in the field indicates amounts of 10 to 30 kg ha-1 of N, taking planting and yielding usual densities. The lowest %Ndfa and fixed quantities were obtained in plants growing in the Regolithic Neosol and they increased with manure application. Among the species, BNF was least important to D. pernambucanus. Neither the proportion nor the fixed quantities were explained by any of the nodule variables measured (number, biomass or biomass/nodule).

Pesquisas sobre a biodiversidade microbiológica de solos salinos envolvem a busca por genótipos tolerantes a esse tipo de estresse ambiental. Dados genotípicos correlacionados às características morfológicas, fisiológicas e bioquímicas de bactérias fornecem informações importantes para sua identificação e agrupamento. Este trabalho objetivou caracterizar rizóbios provenientes de solos salinos, do Agreste e Sertão de Pernambuco, utilizando jacatupé (Pachyrhizus erosus L. Urban) como planta-isca. Os testes foram efetuados em meio YMA e as características culturais observadas em 24 isolados foram as seguintes: mudança de pH, tempo de crescimento, transparência, forma, borda, produção de exopolissacarídeo das colônias e resistência à salinidade. Os testes moleculares utilizando análise por PCR (reação em cadeia da polimerase) por meio de seqüências repetitivas de DNA amplificadas com o primer BOX envolveram 13 isolados. Os resultados revelaram alta diversidade fenotípica e genotípica entre os isolados nativos. As características culturais e genéticas desses isolados foram comparados com 19 estirpes de referência. Os isolados NFB746 e NFB747 tiveram alta semelhança entre si e também com as estirpes Rhizobium sp. NGR234 (BR2406) e Mesorhizobium ciceri USDA3383 (BR521). O isolado NFB742, possivelmente, era da mesma espécie de M. ciceri (BR521). Com relação ao isolado NFB741, a semelhança com as bactérias Rhizobium tropici IIA CFN299T (BR10016) e Sinorhizobium terangue USDA4894 (BR527) foi de 87%. Os demais isolados, praticamente, formaram grupos independentes quando comparados com as estirpes de referência. Os resultados foram de grande relevância para diagnosticar novas espécies de rizóbios nativos altamente tolerantes a estresses ambientais.

Investigation on microbiological biodiversity in the saline soils involves searching for tolerant genotypes to this type of emvironmental stress. Genotypic data associated to morphologic, physiological and biochemical characteristics of bacteria provide important information regarding its identification and clusters. The objective of this work was to characterize indigenous rhizobial strains of saline soils in the Wasteland and Hinterland of Pernambuco State, using yam bean (Pachyrhizus erosus L. Urban) as plant-tramp. Assays had been performed in YMA media and the observed cultivation characteristics of twenty-four isolates had been: change of pH, time of growth, transparency, form, edge, production of exopolysaccharides of the colonies and resistance to salinity. DNA amplification by the PCR technique of the repetitive sequence BOX indicated a high level of genetic and fenotipic diversity between the thirteen indigenous isolates. Comparing cultivation and genetic characteristics of these isolates with nineteen reference strains, indicated that isolates NFB746 and NFB747 had presented high similarity between then and also with the Rhizobium sp. NGR234 (BR2406) and Mesorhizobium ciceri USDA3383 (BR521).The isolated NFB742 possibly belongs to of the same species of the M. ciceri BR521. In relation to the isolated NFB741, the similarity with the Rhizobium tropici IIA CFN299T (BR10016) and Sinorhizobium terangue USDA4894 (BR527) was of 87%. All others isolates had clustered in comparative independent groups when comared to reference lineages. These results are important for diagnosis of new species of native rhizobia in areas where the use of FBN can improve and rehabilitate saline soil using the rizobia-leguminous interaction.

A produção de biofertilizantes é um processo prático e econômico que reduz o consumo de energia e a sua aplicação visa aumentar o fósforo (P) disponível no solo. Biofertilizantes fosfatados (B5, B10, B15, B20) produzidos em laboratório usando fosfato natural (FN) e enxofre em diferentes concentrações (5; 10; 15 e 20%), inoculado com Acidithiobacillus (S*) e enxofre (20%) sem Acidithiobacillus (S), com incubação por 30, 45 e 60 dias, foi utilizado em um experimento em vasos com solo da Zona da Mata de Pernambuco (Argissolo Amarelo), com baixo nível de P disponível, cultivado com jacatupé (Pachyrhizus erosus), por dois períodos consecutivos. Os tratamentos fosfatados foram: fosfato natural (FN); biofertilizantes (B5, B10, B15, B20), com Acidithiobacillus (FN+S*) e B20, sem Acidithiobacillus (FN+S); superfosfato triplo (ST); e um controle sem fósforo (P0). As plantas foram inoculadas com a mistura das estirpes de rizóbio NFB 747 e 748, e sem inoculação. Nos ensaios em laboratório analisou-se o pH e o P extraído dos biofertilizantes, em cada período de incubação, e nos experimentos em vasos com solo determinou-se a biomassa seca, o N e o P total acumulado da parte aérea, o pH e o P extraído do solo. O P disponível foi mais elevado para os biofertilizantes com Acidithiobacillus (FN+S*) e para o superfosfato triplo. A fertilização fosfatada, condicionou resposta positiva dos biofertilizantes (FN+S*) e do superfosfato triplo. Os rizóbios nativos foram tão eficientes quanto os do inoculante. Após os dois cultivos o P disponível foi maior com os biofertilizantes B15 e B20 com Acidithiobacillus.

The production of mineral fertilizers is a expensive process, since it requires high energy consumption, and cannot be produced by small farmers. Laboratory assays were conducted to produce P-biofertilizers from natural phosphate (B5, B10, B15, B20), applying sulphur at different rates (5; 10; 15 and 20%) inoculated with Acidithiobacillus (S*) and testing increasing periods of incubation. A greenhouse experiment was carried out to evaluate the effect of the biofertilizers in a soil with low available P (Typic Fragiudult) from the "Zona da Mata" of Pernambuco State, grown with yam bean (Pachyrhizus erosus) in two consecutive harvests. The treatments were: Natural Phosphate (NP); biofertilizers produced in laboratory (B5, B10, B15, B20) with sulphur and Acidithiobacillus (NP+S*); natural phosphate with sulphur (20%) without Acidithiobacillus (NP+S); triple super phosphate (TSP) and a control without phosphorus. Plants were inoculated with a mixture of rhizobia strains (NFB 747 and NFB 748) or did not receive rhizobia inoculation. In bioassays pH and available P in the biofertilizers were analyzed. In the greenhouse experiment shoot dry matter, total N and total P in shoots, soil pH and available P were determined. Higher rates of available P were obtained in biofertilizers with sulphur and Acidithiobacillus (NP+S*) and in triple super phosphate (TSP), and biofertilizers with sulphur and Acidithiobacillus (FN+S*) and triple super phosphate (TSP) increased plant parameters. Native rhizobia were as effective as the strains applied in inoculation. After the two harvests soil presented lower pH values and higher rates of available P when the biofertilizers B15 and B20 with sulphur and Acidithiobacillus were applied.

Com o objetivo de avaliar o efeito da fertilização com fósforo, potássio e magnésio na fixação do N2 em jacatupé (Pachyrhizus erosus (L.) Urban) cultivado em um Latossolo Amarelo distrófico álico da Zona da Mata de Pernambuco, foi conduzido um experimento inoculando as sementes com a estirpe de Bradyrhizobium sp. NFB 450. Foram aplicadas quatro fórmulas de adubação com potássio e magnésio, na proporção (K2O:MgO) 2:1, em quantidades crescentes (0:0, 40:20, 60:30 e 80:40 kg ha-1 de K2O e MgO, respectivamente) e cinco níveis de fósforo (0, 20, 40, 60 e 80 kg ha-1 de P2O5, na forma de superfosfato triplo). A produção máxima foi obtida quando aplicou-se 64 kg ha-1 de P2O5. Observou-se efeito significativo para os níveis de K2O-MgO, quando em comparação com o tratamento sem K e Mg; entretanto, com o aumento da aplicação verificou-se diminuição da produção de matéria seca e do N total, e aumento do P total acumulado na parte aérea. O jacatupé respondeu a níveis baixos da fertilização com P, K e Mg, e mostrou-se efetivo na fixação do N2, com grande potencial na produção de biomassa.

In order to evaluate the effects of phosphorus, potassium and magnesium application on the nutrient absorption and yield of yam bean (Pachyrhizus erosus (L.) Urban), in a Yellow Latosol of the Zona da Mata of Pernambuco State, Brazil, an experiment was carried out using the strain of Bradyrhizobium sp. NFB 450, isolated from yam bean and selected for efficient N2 fixation in previous experiments. Potassium and magnesium were applied in the proportion of 2:1 (K2O:MgO) in increasing levels (0:0, 40:20, 60:30 and 80:40 kg ha-1 of K2O and MgO, respectively), and crescent levels of phosphorus (0, 20, 40, 60 and 80 kg ha-1 of P2O5) were added in the form of triple superphosphate. Maximum dry matter production, total N and total P accumulated were obtained when applying 64 kg ha-1 of P2O5. A significant effect of K2O:MgO levels was observed in relation to the treatment without K and Mg application; nevertheless, higher levels of K2O:MgO decreased dry matter and total N, and increased total P accumulation. Yam bean responded to low levels of P, K and Mg fertilizer, and showed ability in N2 fixation, with great potential for biomass production.