ABSTRACT Silvopastoral systems based on tree legumes intercropped with forage grasses can harbor a high diversity of rhizobia, and these bacteria are good indicators of soil quality in several management systems. The objective of this work was to evaluate the morphophysiological, genetic and symbiotic diversity of cowpea [Vigna unguiculata (L.) Walp] rhizobia from soils under silvopastoral systems based on shrub-tree legumes. The experiment was performed in a randomized block design with three treatments and three replications, consisting of signalgrass (Urochloa decumbens Stapf.) intercropped with sabia (Mimosa caesalpiniaefolia); signalgrass intercropped with gliricidia (Gliricidia sepium) and single signalgrass. The samples were collected in the legume row (0 meter) and 4 and 8 meters away. Later, cowpea was used as a trap plant to capture the rhizobia. All strains were phenotypically characterized, authenticated, and genetically identified. Phenotypical characterization of the 431 isolates showed high diversity forming 69 groups at 100% similarity, of which 60 were able to nodulate cowpea during the authentication, and 36 presented relative efficiency superior or equal to the recommended bacteria for the crop. Most of the sequenced strains belonged to Bradyrhizobium (67%) and Methylobacterium (9%). Leifsonia (9%), Cohnella (6%), Rhizobium (3%), Burkholderia (3%), and Paenibacillus (3%) were also represented. Soils under silvopastoral systems harbor efficient rhizobia populations in cowpea with a high genetic diversity, which can be recommended for agronomic efficiency assays.

ABSTRACT Some forage species, such as pangolão grass (Digitaria eriantha Steud. cv. Survenola), are resilient in tropical semi arid regions. A possible reason for this is the presence of endophytic and rhizospheric microorganisms. Thus, this study evaluated the diversity of associative bacteria in pangolão grass. Bacteria associated with the roots, culm, leaves, and rhizospheric soil were isolated and characterized in three municipalities of Pernambuco, Brazil. An initial phenotypic characterization was followed by a genotypic assessment by based repetitive extragenic palindromic-polymerase chain reaction (BOX-PCR) and partial sequencing of the 16S rRNA gene. We obtained 325 phenotypically-characterized isolates grouped into 243 strains with 100% similarity by BOX-PCR. The most diverse sampling environment was Araripina, and all factors affected bacterial diversity. There were 135 groups with 90% similarity, that were represented by a single strain each for sequencing. Among the sequenced strains, 118 showed 96.84–99.9% similarity with previously described strains, whereas 17 could not be identified. The following 18 genera were identified from three phyla, five classes, seven orders, and 13 families: Achromobacter, Agrobacterium, Bacillus, Burkholderia, Curtobacterium, Enterobacter, Herbaspirillum, Kosakonia, Ochrobactrum, Paenibacillus, Pantoea, Priestia, Pseudomonas, Rhizobium, Serratia, Shinella, Stenotrophomonas, and Variovorax. The diversity of endophytic and rhizospheric bacteria may contribute to the resilience of pangolão, as various strains of these genera have been described as plant growth promoters. This is the first evaluation of pangolão bacterial diversity under tropical semi arid conditions. Since several of the genera include strains known to promote plant growth, we propose further research to evaluate this on crops.

RESUMO O feijão-caupi (Vigna unguiculata L. Walp) é econômica e socialmente importante nas regiões Norte e Nordeste do Brasil e estabelece simbiose com bactérias fixadoras de nitrogênio. Foi avaliada a compatibilidade simbiótica e eficiência de isolados rizobianos de solos do semiárido de Pernambuco e determinada sua estabilidade simbiótica com as cultivares IPA-206, BR 17-Gurguéia e BRS Novaera, selecionadas para diferentes ambientes. O experimento foi em casa-de-vegetação, avaliando um fatorial 3 × 28 (cultivares selecionadas para diferentes ambientes × inoculação com a estirpe atualmente recomendada, ausência de inoculação com e sem adição de nitrogênio mineral ou inoculação com 25 estirpes de solos do semiárido), em blocos casualizados com quatro repetições. Foram avaliados: número de nódulos, matérias secas da parte aérea, raiz e nódulos, matéria seca de nódulos por número de nódulos, nitrogênio acumulado na parte aérea pela matéria seca de nódulos, teor e acúmulo de nitrogênio na parte aérea, eficiência relativa com base no acúmulo de nitrogênio e eficiência relativa à estirpe recomendada baseada na matéria seca da parte aérea. No geral, as cultivares responderam diferentemente às diferentes linhagens e potencial de fixação biológica de nitrogênio da cultivar. As linhagens G7.85 e BR 3262 apresentaram potencial para fixação biológica de nitrogênio. A confirmação da BR 3262 foi adequada para inoculação do feijão caupi em diferentes cultivares.

ABSTRACT Cowpeas (Vigna unguiculata L. Walp) are an economically and socially important legume in northern and north-eastern Brazil and can establish effective symbiosis with nitrogen-fixing bacteria. We evaluated the symbiotic compatibility and efficiency of rhizobial strains from Pernambuco semi-arid soils and determined their symbiotic stability on the IPA-206, BR 17-Gurguéia, and BRS Novaera cultivars, selected for different environments. The experiment was conducted in a greenhouse to evaluate a 3 × 28 factorial arrangement (cultivars selected for different environments × inoculation with the currently recommended strain, uninoculated plants with or without mineral nitrogen, and 25 rhizobial strains from semi-arid soils) in a randomized block design with four replicates. We determined nodule number, shoot and root dry matter, nodule dry matter by nodule number, nitrogen accumulated in the shoot by nodule dry matter, nitrogen content and accumulation in the shoot, relative efficiency of the recommended strain based on nitrogen accumulation, and shoot dry matter. Overall, the cultivars responded differently to different strains and cultivar biological nitrogen fixation potential. Strains G7.85 and BR 3262 showed potential for biological nitrogen fixation. BR 3262 was confirmed to be adequate for inoculation of different cowpea cultivars.

ABSTRACT Biochar is a material produced by the pyrolysis of agro-industrial waste, which has become one of the most promising management tools to improve soil quality. The aim was to determine the effects of incorporating biochar from different coffee wastes in sandy soil, cropped with maize, on soil chemical and microbial attributes. The experiment followed a factorial design 2 × 3 + 1 with two types of biochar, including coffee ground (CG) or coffee husk (CH) in 3 doses (4, 8, and 16 t·ha-1) and a control fertilized solely with bovine manure (3 t·ha-1). The variables analyzed were soil organic carbon, chemical attributes, microbial biomass (C, N and P), soil basal respiration and microbial gene abundance (16S rRNA, 18S rRNA and nifH gene). Most chemical attributes were strongly increased by CH application, while CG at 8 t·ha-1 increased the soil C:N ratio (3.5 times), P (2.1 times) and K+ (7.9 times) and at 4 t·ha-1 increased the C content, microbial biomass C and N (3, 2.1 and 1.6 times, respectively). The application of CG biochar at 16 t·ha-1 showed trend to increase the abundance of bacteria, fungi and diazotrophic genes (11, 10 and 2%, respectively). Contribution of both coffee biochar types, but mainly CH, was more effective than the soil that received organic manure alone. Biochar from coffee wastes is a promising tool to improve sandy soil quality.

ABSTRACT Legume green manure is a popular practice for sustainable agriculture in tropical environments. The use of grain, forage and purely green manure legumes in a subhumid tropical area in Northeast Brazil was investigated to determine the total C and N contents and estimate C-microbial biomass, soil basal respiration, microbial and metabolic quotients, before and after green manures and after the following corn. It was hypothesized that, although all legumes would increase microbial biomass and activity, there would be different effects in function of the main economic usage of the legume. The experimental design evaluated the soil before and after harvest of seven legumes: (i) purely green manures – sunn hemp (Crotalaria juncea L.) and velvet bean (Stizolobium aterrimum Piper & Tracy); (ii) forage – Campo Grande stylo (a physical mixture of 80% of Stylosanthes captata Vog. and 20% of Stylosanthes macrocephala) and calopo (Calopogonium mucunoides Dev.) and (iii) grain – common bean (Phaseolus vulgaris L.), cowpea (Vigna unguiculata L.) and peanut (Arachis hypogaea L.), followed by corn crop. After corn harvest, soils had the same total C and N contents before legume seeding, but C-microbial biomass was significantly higher in soils with grain and purely green manures, which produced higher shoot and root dry mass. Soil basal respiration decreased after corn harvest for all legumes comparing to control treatments, but metabolic stress increased in soils with forage species. Despite this, microbial quotient indicated an efficiency of the microorganisms in degrading the residual organic matter of all green manures used in corn.

BACKGROUND: Statins are used as cholesterol-lowering drugs and may also have direct antimicrobial effects. OBJECTIVE: To evaluate synergic interactions between simvastatin and both amphotericin B and fluconazole, against environmental strains of Cryptococcus neoformans isolated from captive birds’ droppings. DESIGNAND SETTING: Experimental study conducted at Federal University of Piauí, Parnaíba, in collaboration with Federal University of Triângulo Mineiro, Uberaba, Brazil. METHODS: Statin susceptibility tests of Cryptococcus neoformans samples were performed as prescribed in standards. Interactions of simvastatin with amphotericin and fluconazole were evaluated using the checkerboard microdilution method. Presence of these interactions was quantitatively detected through determining the fractional inhibitory concentration index (FICI). RESULTS: Isolates of Cryptococcus neoformans were obtained from 30 of the 206 samples of dry bird excreta (14.5%) that were collected from pet shops and houses. Ten isolates were selected for susceptibility tests. All of them were susceptible to amphotericin and fluconazole. All presented minimum inhibitory concentration (MIC) > 128 µg/ml and, thus, were resistant in vitro to simvastatin. An in vitro synergic effect was shown through combined testing of amphotericin B and simvastatin, such that six isolates (60%) presented FICI < 0.500. Two isolates showed considerable reductions in MIC, from 1 µg/ml to 0.250 µg/ml. No synergic effect was observed through combining fluconazole and simvastatin. CONCLUSION: These results demonstrate that simvastatin should be considered to be a therapeutic alternative, capable of potentiating the action of amphotericin B. However, further studies are necessary to clarify the real effect of simvastatin as an antifungal agent.

Legumes used as green manure provide essential chemical elements to the soil through their biomass decomposition. However, nutrient availability may be significantly affected by herbicide application such as glyphosate. Thus, we evaluated the decomposition and nutrients release from the shoot dry phytomass and the root system of Crotalaria spectabilis with and without glyphosate application. After 90 days of C. spectabilis cultivation, the shoot and the root system were collected to determine the remaining phytomass. The analysis of variance for the remaining dry mass indicated the two-way interaction between herbicide and age was significant (P <0.0001). For most elements being released, the two-way interaction was significant. The remaining dry mass that received herbicide presented greater mineralization and faster reduction for most of the elements, resulting in the considerable nitrogen and phosphorus loss compared to the material without the herbicide, concluding that their decomposition was affected by the glyphosate application.

Las legumbres utilizadas como abono verde proporcionan elementos químicos esenciales al suelo a través de la descomposición de su biomasa. Sin embargo, la disponibilidad de nutrientes puede verse significativamente afectada por la aplicación de herbicidas, como el glifosato. En este trabajo se evaluó la descomposición y liberación de nutrientes de la fitomasa seca de parte aérea y sistema radicular de Crotalaria spectabilis con y sin aplicación de glifosato. C. spectabilis fue cultivada por 90 dias, luego se colectó y separó el material en parte aérea y sistema radicular para determinar la fitomasa remanente. El análisis de varianza de la masa seca remanente indicó la doble interacción entre herbicida y edad que fue significativa (P <0.0001). Para la mayoría de los elementos liberados, la interacción doble fue significativa. La masa seca remanente que recibió herbicida presentó una mayor mineralización y una reducción más rápida para la mayoría de los elementos, dando como resultado una pérdida considerable de nitrógeno y fósforo en comparación con el material sin herbicida, permitiendo concluir que su descomposición se vio afectada por la aplicación de glifosato.

Abstract In forage crops such as cactus morphological characteristics respond to management practices such as fertilization. An evaluation was done to determine if organic matter (OM) fertilization (0, 10,000, 20,000 and 30,000 kg OM ha-1 yr-1 bovine manure), mineral fertilization (0, 120, 240 and 360 kg N ha-1 yr-1, using urea) and cut frequency (annual and biennial) influenced cladode length, width and perimeter, and Cladode Area Index (CAI) values in Nopalea cochinillifera Salm Dyck cv. Miúda, and how these variables related to productivity. The experimental design was random blocks, using a sub-sub-plot arrangement with four replicates. Fertilization with 30,000 kg OM ha-1 year-1 increased cladode width by 9.8 % and length by 17.8 % compared to the control. Cladode perimeter increased proportionally to OM fertilization level. At the optimum fertilization level (25,970 kg ha-1) the CAI value was 68.29 % higher than the control. Mineral fertilization only affected cladode perimeter at 120 kg ha-1 and only with an annual cut; however, at this fertilization level the CAI value was higher with a biennial cut. Organic matter fertilization increased cladode width and length, and CAI values in N. cochenillifera cv. Miúda, while mineral fertilization had only a minimal effect. Biennial cutting frequency results in higher CAI values. Correlations were high between the evaluated variables and dry matter production, highlighting the utility of morphological variables in evaluating productivity.

Resumen Las características morfológicas de las plantas forrajeras como el nopal, son influenciadas de acuerdo al manejo recibido, prácticas como la fertilización son importantes; debido a lo anterior el objetivo de esta investigación fue evaluar el efecto de la fertilización con materia orgánica (MO) (0, 10,000, 20,000 y 30,000 kg MO ha-1 año-1 con estiércol bovino) o mineral (0, 120, 240 y 360 kg de N ha-1 año-1 utilizando urea) y la frecuencia de corte (anual y bianual) en la longitud, ancho, perímetro, e Índice del Área de Cladodio (IAC) en cladodios de nopal forrajero cv. Miúda (Nopalea cochenillifera Salm Dyck), y su relación con la productividad. El diseño experimental fue de bloques al azar, con el arreglo de parcelas sub-sub-divididas con cuatro repeticiones. La fertilización con 30,000 kg MO ha-1 año-1 incrementó el ancho y longitud de cladodio de 9.8 a 17.8 % respecto al tratamiento testigo. El perímetro de cladodio se incrementó proporcionalmente cuando aumentó la MO. El IAC fue 68.29 % mayor (con 25 970 kg ha-1) respecto al tratamiento testigo. La fertilización mineral sólo afectó el perímetro de cladodio en el corte anual con dosis de 120 kg ha-1 y el IAC fue mayor en el corte bianual. Se concluyó que la fertilización con MO aumentó el ancho, longitud e IAC en cladodios de nopal forrajero cv Miúda (Nopalea cochenillifera Salm Dyck), mientras que la fertilización mineral tuvo bajo impacto en el ancho, longitud e IAC, el corte bianual favorece el IAC. Se presentó una alta correlación entre las variables evaluadas y la producción de materia seca.

RESUMO: Existem poucos estudos sobre a diversidade microbiana em solos de mamona no ambiente semiárido tropical. Os produtos de mamona têm sido amplamente utilizados em todo o mundo e justificam a importância comercial da ricinocultura no semiárido nordestino brasileiro. Como não há qualquer tipo de fertilização, ou manutenção de resíduos da cultura nos solos de mamona do presente estudo, presume-se que a comunidade de diazotróficas forneça o nitrogênio (N) nesses solos. Avaliou-se a estrutura e diversidade de comunidades de diazotróficas em solos de mamona do semiárido tropical em: i-Mamona com 50 anos de cultivo, consorciada com milho (CB-50); ii-Mamona com 10 anos de cultivo sem consórcio (CB-10) e iii-solo sob vegetação de Caatinga preservada (CAA). Realizou-se avaliação de redução do acetileno a etileno (ARA) e o perfil do gene nifH foi separado por eletroforese em gel de poliacrilamida com gradiente desnaturante (DGGE). A diversidade de diazotróficas foi estimada pelos índices de Shannon (H’) e Simpson (D). Com base na manutenção dos estoques de nitrogênio no solo e da biomassa microbiana ao longo do tempo, a atividade dos diazotróficos de vida livre foi determinante na entrada de N nesses solos. O gene nifH esteve presente e seus perfis agruparam os tratamentos CB-50 com CAA, reforçando a fixação de N pelos diazotróficos, os quais apresentaram maior diversidade nos solos cultivados, mesmo após a mudança de uso da terra para o plantio de mamona.

ABSTRACT: There are few studies of microbial diversity in castor bean soils in tropical semiarid environmental. Castor bean products have been widely used around the world justifying the commercial importance of ricinoculture in Brazil’ northeastern semiarid. There is no fertilization or maintenance of litter on the soils from the present study, so we hypothesized that the free-living diazotrophs microorganisms drive the nitrogen (N) input into these soils. We evaluated the communities’ structure and diversity of diazotrophs in tropical semiarid soils with i-Castor bean 50 years of cultivation intercropping with maize (CB-50); ii-Only Castor bean 10 years of cultivation (CB-10) and iii-soil under Caatinga vegetation (CAA). Nitrogenase enzyme activity was performed by the acetylene reduction assay (ARA) and the community profile of nifH gene was separated by denaturing gradient gel polyacrylamide electrophoresis (DGGE). Diazotrophs diversity was estimated by the Shannon (H’) and Simpson (D) indexes. Based on the maintenance of soil N stocks and N-microbial biomass over time, the activity of free-living diazotrophs was determinant in the N-input into these soils. The nifH gene was present and its profiles grouped the CB-50 with CAA treatments, so it reinforced the N-fixing by diazotrophs, which presented a greater diversity in the cultivated soils, even after the land use change for the castor bean implementation.

ABSTRACT The objective was to evaluate the effect of three stocking rates (2, 3.9, and 5.8 animal units ha−1) and three fertilization levels (0, 150, and 300 kg N ha−1 yr−1) on herbage mass and nutritive value of elephantgrass (Pennisetum purpureum Schum.) cv. IRI-381. The experiment was conducted from May to August of 2009 and 2010 in Itambé, PE, Brazil, during the rainy season. Treatments were allocated in a split-plot arrangement in a completely randomized block design. The variables measured included leaf mass (pre- and post-grazing), botanical composition, soil cover, leaf area index, light interception, leaf angle, and concentrations of dry matter, organic matter, N, and in vitro digestible dry matter. When fertilized with 300 kg N ha−1 yr−1, leaf mass reached 18,560 kg ha−1. Leaf area index decreased with increasing stocking rate. The relationship between sward height and light interception was R2 = 0.0126. Increased stocking rate resulted in greater contribution of signalgrass [Brachiaria decumbens (Stapf.) R.D. Webster] in the botanical composition, with a contribution up to 29% in 2010. Elephantgrass nutritive value is directly affected by the fertilization levels and stocking rate, with highest nutrient concentrations observed with 2 AU ha−1 and 300 kg N ha−1 yr−1.

Abstract Soil and water salinity are considered the main limiting factors of plant production. This work aimed to evaluate the influences of irrigation frequency and soil salinity on the development of cactus pear cv. Miúda (Nopalea cochenillifera Salm Dyck). The experiment was conducted in factorial arrangement of four salinity levels: 0.3 (control), 0.5 (low), 1.5 (medium) and 3.6 (high salinity) (ds m-1), associated with four irrigation frequencies (each 7, 14, 21 and 28 days) and two soil textures (sandy and sandy loam) in a randomized block design with four replicates. One cladode was planted in each polyethylene pot containing 10 kg of soil. The soil texture influenced some of the morphological characteristics of the cactus pear, so that plants grown in sandy loam soil yielded higher number of cladodes (9.47) and higher productivity (62.1 g plant-1). The sandy soil produced plants with fewer cladodes (4.50). Irrigation water with a salinity level of 3.6 ds m-1 and an irrigation frequency of 7 days showed higher soil electrical conductivity (48.65 dS m-1) and plants with a higher damage (5.0) and lower productivity (32.51 g plant-1), indicating a low tolerance of the cv. Miúda to salt stress.

Resumo: O objetivo deste trabalho foi caracterizar morfologicamente genótipos de capim-elefante (Pennisetum purpureum) e estimar as proporções de tecido de suas lâminas foliares, sob pastejo. Duas variedades altas (Elefante B e IRI-381) e três baixas (Mott, Taiwan A-146 2.37 e Taiwan A-146 2.114) foram avaliadas sob pastejo intermitente de ovelhas quanto às seguintes variáveis morfológicas: altura de planta, comprimento de entrenós e razão entre lâminas foliares e colmos. Além disso, foram estimadas as proporções dos seguintes tecidos da lâmina foliar: esclerênquima, epidermes adaxial e abaxial, células buliformes, feixes vasculares, floema, bainha vascular, xilema e mesófilo. As variedades baixas foram 28,6% menores do que as altas e apresentaram maiores razões entre lâminas foliares e colmos; Mott e Taiwan A-146 2.114 tiveram os menores entrenós de 3,9 e 4,7 cm, respectivamente, ao longo de dez ciclos de pastejo. Os clones diferiram quanto às proporções de tecidos da sua lâmina foliar, exceto para epiderme abaxial, floema e xilema. As diferenças nas características morfológicas indicam que os clones baixos Mott e Taiwan A-146 2.114 são melhores adaptados ao pastejo por ovelhas e, portanto, podem ser recomendados para o melhoramento de pastagens.

Abstract: The objective of this work was to characterize morphologically elephant grass (Pennisetum purpureum) genotypes and to estimate their proportions of leaf blade tissues under grazing. Two tall varieties (Elephant B and IRI-381) and three short ones (Mott, Taiwan A-146 2.37, and Taiwan A-146 2.114) were evaluated under intermittent sheep grazing as to the following morphological characteristics: plant height, internode length, and leaf blade/culm ratio. Moreover, the proportions of the following leaf blade tissues were estimated: sclerenchyma, adaxial and abaxial epidermis, bulliform cells, vascular bundles, phloem, vascular sheath, xylem, and mesophyll. The short varieties were 28.6% shorter than the tall ones and showed higher leaf blade/culm ratio; Mott and Taiwan A-146 2.114 had the shortest internodes of 3.9 and 4.7 cm, respectively, over ten grazing cycles. The clones differed regarding their proportions of leaf blade tissues, except for abaxial epidermis, phloem, and xylem. The differences in morphological characteristics indicate that the short clones Mott and Taiwan A-146 2.114 are better adapted to sheep grazing, and, therefore, may be recommended for the improvement of pastures.

Objetivou-se avaliar características morfológicas de clones de Panicum maximum durante o período de rebrota após a interrupção da irrigação. Os clones de Panicum foram coletados em Sergipe e em três locais de Pernambuco ("São Bento do Una", "Itambé" e "São João da Coroa Grande"), além das cultivares 'Mombaça', 'Tanzânia' e 'Massai'. Os tratamentos consistiram de sete clones submetidos a 7, 14, 21 ou 28 dias de suspensão da irrigação. O delineamento utilizado foi o inteiramente casualizado em arranjo fatorial 7 × 4 com quatro repetições. Foram avaliados o número de perfilhos, altura da planta, comprimento da lâmina foliar, número de folhas verdes por perfilho e número de folhas mortas por perfilho. O fator clone afetou significativamente o número de perfilhos por vaso e o número de folhas mortas por perfilho (P≤0,05). O clone de Sergipe produziu mais perfilhos (8.39) que os demais após 28 dias de interrupção da irrigação, enquanto a cultivar 'Mombaça' apresentou mais folhas mortas (5.39) após 7 dias sem irrigação. Em geral, a interrupção da irrigação por 28 dias resultou em plantas mais altas com lâminas foliares maiores e com número superior de folhas verdes por perfilho.

This study aimed to evaluate the morphological characteristics of Panicum maximum clones during the regrowth period following cessation of irrigation. Panicum clones were collected in Sergipe and in three Pernambuco locations (‘São Bento do Una’, ‘Itambé’ and ‘São João da Coroa Grande’), in addition to ‘Mombaça’, ‘Tanzânia’ and ‘Massai’ cultivars. The treatments consisted of seven clones, which were subjected to either 7, 14, 21 or 28 days of water suspension. The experimental design was completely randomized in a factorial 7 × 4 design, with four replicates. The morphological characteristics evaluated included the number of tillers, plant height, leaf blade length, number of green leaves per tiller and number of dead leaves per tiller. The clone factor significantly affected the number of tillers per pot and the number of dead leaves per tiller (P ≤ 0.05). The clone from Sergipe produced a greater number of tillers (8.39) than the other clones following 28 days of water suspension, while the ‘Mombaça’ cultivar had a greater number of dead leaves (5.39) after 7 days of water suspension. In general, the 28-day cessation of irrigation period resulted in taller plants with larger leaf blades and a greater number of green leaves per tiller.

RESUMO O consórcio de leguminosas arbóreas com gramíneas forrageiras em sistema silvipastoril pode evitar a degradação das pastagens e recuperá-las. Neste sistema, o fornecimento de nitrogênio (N) ocorre através da simbiose entre leguminosas e bactérias. No entanto, a qualidade das pastagens permite a ação de bactérias diazotróficas de vida livre, que possuem o gene nifH que codifica a enzima nitrogenase. Além disso, na etapa da nitrificação, as bactérias amônio oxidantes (AOB) são avaliadas por regiões específicas do 16S rRNA de AOB. Assim, investigamos a influência da introdução das leguminosas arbóreas no sistema silvipastoril na estrutura da comunidade, na diversidade e na abundância de bactérias totais, bactérias diazotróficas e bactérias amônio oxidantes por DGGE (Eletroforese em Gel com Gradiente Desnaturante) e qPCR (PCR quantitativa em tempo real). O experimento teve nove parcelas de um hectare com Sabiá (Mimosa caesalpinifolia), Gliricídia (Gliricidia sepium) e Braquiária solteira (Brachiaria decumbens), em delineamento em blocos ao acaso com três tratamentos: I-Braquiária em consórcio com Sabiá; II-Braquiária em consórcio com Gliricídia e III - Braquiária solteira, com três repetições. A estrutura das comunidades de bactérias totais e bactérias amônio oxidantes foi influenciada pela introdução das leguminosas arbóreas, possivelmente por meio da modificação dos atributos químicos do solo. Bactérias totais, bactérias amônio oxidantes e bactérias diazotróficas foram mais abundantes nos solos sob leguminosas, que proporcionaram melhores condições para o crescimento microbiano quando comparado à braquiária solteira. O manejo silvipastoril com leguminosas arbóreas melhora a qualidade biológica do solo, favorecendo a comunidade bacteriana ligada ao ciclo do N.

ABSTRACT Intercropping tree legumes with forage grasses in a silvopastoral system can avoid pasture degradation benefiting the soil. In such a system, nitrogen (N) is supplied by symbiosis between legumes and bacteria. However, the pasture quality determines the action of free-living nitrogen-fixing bacteria, which possess nifH genes, which encode nitrogenase enzyme. Ammonium-oxidizing bacteria (AOB), involved in the nitrification step, can be evaluated by specific regions of the 16S rRNA corresponding to AOB. Thus, we investigated the influence of the introduction of tree legumes into a silvopastoral system on the community structure and abundance of total bacteria, diazotrophic bacteria and ammonium-oxidizing bacteria by DGGE (denaturing gradient gel electrophoresis) and real-time qPCR (quantitative PCR). The experiment involved nine plots of one hectare each, planted with sabia (Mimosa caesalpinifolia), a Gliricidia species (Gliricidia sepium), and a Brachiaria species (Brachiaria decumbens) in a randomized block design, forming three treatments: I-Brachiaria intercropped with sabia; II-Brachiaria intercropped with Gliricidia and III-Brachiaria only, with three replicates. The structures of the total bacterial and ammonium-oxidizing bacterial communities were influenced by tree legume introduction, possibly through modification of the soil chemical attributes. The copy numbers of total bacteria, ammonium-oxidizing bacteria and diazotrophic bacteria were higher in soils planted with legumes, which provided better conditions for microbial growth compared to planting with the Brachiaria species alone. Silvopastoral management with tree legumes improves the biological quality of soil, favouring the bacterial community linked to N-cycling.

Resumo: O objetivo deste trabalho foi estimar a repetibilidade (r) e o número de amostragens necessárias para mensurar o valor nutricional de quatro gramíneas forrageiras tropicais numa região semiárida. As gramíneas avaliadas foram Urochloa mosambicensis, Cenchrus ciliares, Digitaria pentzii e Megathyrsus maximus. As avaliações ocorreram sob duas condições de manejo da forragem: diferimento e pastejo. Amostras de forragem coletadas por pastejo simulado foram analisadas para matéria seca (MS), proteína bruta (PB), fibra em detergente neutro (FDN), fibra em detergente ácido (FDA), lignina e digestibilidade in vitro da MS (DIVMS). Para a análise de r e número de amostragens necessárias, utilizaram-se quatro métodos: análise de variância, componentes principais da matriz de covariância (CPCOV) e de correlação (CPCOR), e análise estrutural (AECOR). As espécies foram comparadas pela probabilidade da diferença, tendo-se utilizado o teste t. Para o método CPCOV, observa-se maior coeficiente de r, portanto, menor número de amostragens necessárias. A lignina é a característica que apresenta o maior número de amostragens necessárias. Em termos qualitativos, D. pentzii e M. maximus mostram melhores características entre as espécies forrageiras avaliadas.

Abstract: The objective of this work was to estimate the repeatability (r) and the number of samples required to measure the nutritional value of four warm-season forage grasses growing in a semiarid region. The grasses evaluated were Urochloa mosambicensis, Cenchrus ciliaris, Digitaria pentzii, and Megathyrsus maximus. Evaluations occurred under two forage management conditions: stockpiling and grazing. Hand-plucked forage samples were analyzed for dry matter (DM), crude protein (CP), neutral detergent fiber (NDF), acid detergent fiber (ADF), lignin, and in vitro DM digestibility (IVDMD). Four methods were used to estimate r and the number of samples required: analysis of variance, method of principal components based on the covariance (PCCOV) and the correlation (PCCOR) matrices, and structural analysis (EVCOR). Species were compared by the probability of the difference using the t-test. The method PCCOV presents the highest coefficient of repeatability and, therefore, a lower number of samples required. Lignin is the trait that have the highest number of samples required. In terms of qualitative traits, D. pentzii and M. maximus show the best forage qualities among the species evaluated.