HREM studies of intergrowths in Sr2[Srn-1TinO3n+1] Ruddlesden-Popper phases synthesized by mechanochemical activation

A mechanochemical activation route has been applied in order to obtain the <i>n</i>=1–4 and ∞ members of the Sr<sub>2</sub>[Sr<sub>n</sub><sub>−1</sub>Ti<sub>n</sub>O<sub>3n+1</sub>] Ruddlesden– Popper series from different (<i>n</i>+1)SrO:nTiO<sub>2</sub> mixtures. The mechanosynthesis of SrTiO<sub>3</sub> and Sr<sub>2</sub>TiO<sub>4</sub> was observed during the milling process from the initial stoichiometric mixture, but in the cases of the <i>n</i>=2–4 members, a subsequent thermal treatment was needed. The synthesis protocol of Sr<sub>3</sub>Ti<sub>2</sub>O<sub>7</sub> has been greatly improved and this compound can be isolated as a single, crystalline phase after annealing at 800°C. In the case of Sr<sub>4</sub>Ti<sub>3</sub>O<sub>10</sub> and Sr<sub>5</sub>Ti<sub>4</sub>O<sub>13</sub>, the formation temperature was also decreased, but members with <i>n</i>=3 and 4 could not be isolated. Detailed investigations using electron microscopy methods (TEM, HREM and SAED) were carried out in the samples corresponding to <i>n</i>=2–4. Although a single ordered Sr<sub>3</sub>Ti<sub>2</sub>O<sub>7</sub> structure is dominant in the sample corresponding to <i>n</i>=2, a few intergrowths of other Ruddlesden–Popper phases were observed. In the cases of <i>n</i>=3 and 4, the intergrowths of Ruddlesden–Popper phases are more frequent than in the <i>n</i>=2 composition and are randomly distributed in the sample. The more frequent occurrence of such stacking faults, with increasing <i>n</i> value, leads to a somewhat disordered layer stacking sequence

Oportunidades e ameaças à contribuição da fixação biológica de nitrogênio em leguminosas no Brasil.

A fixação biológica de nitrogênio (FBN) é o mais bem sucedido exemplo de aplicação biotecnológica na agricultura, principalmente na cultura da soja, que consome cerca de 95% dos inoculantes produzidos no Brasil. A FBN pode ser expandida para várias outras espécies leguminosas, tanto para culturas destinadas à produção de grãos, quanto espécies forrageiras, arbóreas ou adubos verdes, contribuindo para a sustentabilidade dos sistemas de produção. Entretanto, algumas práticas como o uso de fertilizantes nitrogenados e inoculação inadequada das sementes têm colocado em risco a plena eficiência dessa técnica

Indicadores microbiológicos da qualidade do solo.

Ciclos biogeoquímicos. Atividade e diversidade microbiana do solo. Enzimas do solo. Como interpretar resultados de atributos microbiológicos e bioquímicos do solo

Phylogenetic analysis of nodulation and nitrogen fixation genes of a brazilian collection of Bradyrhizobium strains.

The genus Bradyrhizobium encompasses a variety of bacteria that can live in symbiotic and endophytic associations with legumes and non-legumes, and are characterized by physiological and symbiotic versatility and broad geographical distribution. In studies with Bradyrhizobium strains the comparison of phylogenies of nodulation and housekeeping genes has indicated a monophyletic origin of nodulation genes and diffusion by vertical and horizontal gene transfer, the last one probably influenced by the host plants. In previous studies with the strains analyzed in this study we have shown high diversity in the 16S rRNA, ITS rRNA, atpD, glnII, dnaK and recA housekeeping genes (Menna et al., 2006, 2009). However, despite indications of great genetic variability within the Bradyrhizobium genus, little is known about the phylogeny of the nodulation and nitrogen fixation genes. In this study the nodulation genes nodY/K, nodA and nodZ and the nitrogen fixation gene nifH of forty Bradyrhizobium strains were sequenced and analyzed. The great majority of the strains are from tropical regions and were isolated from members of the three subfamilies and nine tribes of the family Leguminosae (=Fabaceae). In all phylogenetic trees a high level of genetic diversity was observed and several clusters were correlated with the subfamilies of the host plants. One example was with the symbionts of Glycine max and Acacia sp., classified in the subfamilies Papilionoideae and Mimosoideae, respectively. In the phylogenetic trees built with nodY/K and nodA the symbionts of Acacia sp. were clustered in an isolated group, and no amplification was obtained for the nodZ gene. A successful amplification of nifH gene was obtained with all strains, and the resulting phylogenetic tree had similar clusters in comparison to the trees build with the nodulation genes (nodY/K, nodA and nodZ). The strains which failed in the amplification for some nodulation genes occupied an isolated position in the nifH tree. The comparison of all trees has shown no correlation between housekeeping and nod and nifH genes. The results pointed out the high diversity of nodulation and nitrogen fixation genes of tropical Bradyrhizobium strains and in several clusters high correlation between nod and nif genes and the host plants was observed. Partially financed by: CNPq (577933/2008-6; 558455/2008-5; 470162/2009-0

Análise quantitativa das bactérias fixadoras de nitrogênio presentes em inoculantes comerciais para soja.

A Fixação biológica de nitrogênio (FBN) é um processo de grande importância para a cultura da soja, uma vez que a simbiose com bactérias específicas consegue suprir o nitrogênio necessário para um bom desenvolvimento da planta e, consequentemente, para um aumento na produtividade e na produção. O Brasil investe na FBN que, atualmente, é um processo amplamente adotado por agricultores, sendo os inoculantes um dos responsáveis pelo Brasil ocupar o segundo lugar na produção mundial de soja. Assim, a legislação brasileira precisa manter rigoroso controle da qualidade desses insumos. Portanto, visto a importância dos inoculantes para a soja, o presente trabalho analisou a concentração de células viáveis/g ou mL de alguns desses produtos vendidos comercialmente, a fim de verificar qual a situação atual dos produtos que chegam aos agricultores. Os inoculantes foram analisados pelo método de espalhamento e contagem em placas de Petri. Doze produtos foram testados e apresentaram uma concentração acima da exigida por lei, que é 1x109 células viáveis/g ou mL, bem como ausência de contaminantes na diluição 105. Existe a percepção, portanto, de que os fabricantes estão atentos em manter a qualidade dos produtos, levando segurança para agricultor

Soybean seed co-inoculation with Bradyrhizobium spp. and Azospirillum brasilense: a new biotechnological tool to improve yield and sustainability.

Legume nodulation by rhizobia can supply crops with nitrogen and reduce environmental impacts caused by chemical fertilization. The soybean crop in Brazil is an impressive example of how biological N2 fixation can be employed with a plant species of high economic value. However, the development of more productive cultivars, along with the increasing global climatic changes demand agricultural practices to become more productive and yet more environmentally friendly. Plant growth-promoting rhizobacteria (PGPR) are highly beneficial to agriculture worldwide, acting in plant nutrition, protection, and growth stimulation. Azospirillum is, certainly, the most employed PGPR in the world, but little is known about its interaction with rhizobia, when both are applied to legume seeds. We have evaluated the co-inoculation of bradyrhizobia and azospirilla on soybean seeds under different soil and climate conditions in Brazil. Our results demonstrated that co-inoculation is efficient and beneficial to the crop, and promotes yield increases without adding any chemical N fertilizers even in soils where established populations of soybean bradyrhizobia exist. The strategy of co-inoculation thus represents a new biotechnological tool to improve soybean yield without adding any chemical N fertilizers, thus contributing to current practices of sustainability in agriculture

A importância do controle de qualidade dos inoculantes.

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A pesquisa em fixação biológica do nitrogênio na Embrapa Soja: passado, presente e perspectivas futuras.

O passado. O presente. Pensado em sistemas agrícolas. Economia em fertilizantes e divisas. O futuro