A fixação biológica de N2, associada às plantas forrageiras é importante no ciclo do nitrogênio (N), pois bactérias podem contribuir no suprimento de parte do N necessário às plantas, reduzindo os danos ambientais. Amostras de raízes foram coletadas de três gramíneas: Andropogon, Capim Tanzânia e Capim Buffel. Para bactérias isoladas em meio seletivo procederam-se: Quantificação, caracterização fenotípicas, e posteriormente purificadas e armazenadas. A densidade de bactérias foi influenciada pelos nichos radiculares e gramíneas forrageiras, sendo o capim Andropogon e Buffel que apresentaram maiores densidades de microorganismos.

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Organic carbon is a sensible indicator to evaluate the environmental quality of the soil. The objective of this study was to evaluate the organic carbon content of the soil in a toposequence in Serra do Teixeira, municipality of Teixeira, PB. Soil samples were collected in the upper third (UT), upper middle third (UMT), lower middle third (LMT) and lower third (LT) on three depths (0-5, 5-10 and 10-20 cm), with five replicates for each depth, resulting in a total of 60 samples. The organic carbon was evaluated using the methodology of Walkey-Black. Physical and chemical soil analysis were also carried out. The highest mean of carbon content was found in the first 5 cm (19.83 g dm-3), significantly differing from the other depths. It was also observed that the mean content of soil organic carbon on LMT was significantly higher than the other thirds, with 19.39 g dm-3. It is concluded that the highest contents of organic carbon are found on the most superficial layer of the soil. The organic carbon content variations found along the toposequence indicates influence of the relief and the anthropic action.

Allelopathy has been conceptualized as the direct or indirect effect of a plant onto another one through secondary metabolites, or allelochemicals spread in the environment, with the power to interfere in seed germination and increase or inhibit the development of neighboring plants. The objective of this study was to analyze the possible allelopathic effects of aqueous extracts of Tephrosia cinerea in the germination of lettuce (Lactuca sativa L.) seeds. The experiment has been carried out at the Laboratório de Nutrição Mineral de Plantas (Laboratory of Plant Mineral Nutrition)/UAEF/UFCG in Patos (state of Paraíba). We collected T. cinerea organisms, having separated the stem, leaves, roots fractions and the aerial part of the plant + roots, having prepared the extract at 20%. The experimental delineation that we adopted was entirely casualized, with five treatments and four repetitions (without extract, leaf extract, root extract, stem extract, aerial part extract + roots). The seeding was held in aluminum trays, with autoclaved sand as the substrate, setting 25 seed per tray. The calculation of the number of germinated seeds was made in a dailybasis, and, after a week of seeding, the next step was the deactivation, with the evaluations being performed regarding the length of the radicle and of the hypocotyl, as well as the height of the seedlings. The data collected in this research allows us to conclude that: the extracts obtained from T. cinerea plants has a negative impact on the germination of lettuce seedlings. Now, when it comes to the height of lettuce seedlings, it is affected by the use of leaf, stem and aerial part extracts + T. cinerea roots. It is crucial to make efforts in order to determine the existing constituents in the several parts of T. cinerea plants.

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