Influence of Molybdenum doses in inoculation and mineral fertilization in cowpea beans

In some leguminous plants, associations with nitrogen-fixing microorganisms allow their nutrition with nitrogen (N) from the atmosphere. This process is known as Biological Nitrogen Fixation (BNF), where through nitrogenase enzymes, N2 is converted to an available form. This process can replace in part, or in total, nitrogen fertilizers. Cowpea bean is a legume species that is recognized for its high capacity to carry out BNF. In the last decades, studies have encouraged small farmers from north and northeast Brazil to use inoculants with rhizobia species since the results of researches have demonstrated that inoculation is an interesting strategy to improve cowpea production. Considering the specific function of molybdenum (Mo) in the N assimilation, different doses of Mo were tested in this study in order to find doses that could improve and enhance BNF. Therefore, this study aimed to compare nitrogen fertilization and BNF in the N assimilation by plants with different Mo doses. Inoculation was performed with the strains UFLA 03-84 and INPA 03-11B. Doses of Mo were applied in seeds and each pot contained five seeds. Thirty-five days after germination, the plants were analyzed for shoot dry matter and fresh matter, N contents and accumulation, as well as the Soil-Plant Analysis Development (SPAD) Index and nodulation in inoculated plants. The different doses of Mo and also the nodulation treatments did not show significant differences in the contents of N. Plants with N fertilization had significant higher shoot dry matter and root dry matter production, in addition to higher N foliar contents and N accumulation. Therefore, BNF was not as efficient as nitrogen fertilization in the evaluated experimental conditions using cowpea beans

Remoção de arsenito e arsenato de água contaminada a partir da precipitação de (hidr)óxidos de alumínio, Fe ferroso e Fe férrico

Arsenic is a metalloid commonly found in mining sites and can be mobilized in water following acid mine drainage. Due to severe consequences of As contamination, the World Health Organization (WHO) recommended 10 µg L -1 as a threshold concentration for As in drinking water. To face As toxicity, several methods to remove it from water have been considered, including co-precipitation with Fe and Al (hydr)oxides. Such compounds have been considered a good alternative to remove As from contaminated water due to strong bindings between them. However, not only the water needs to be efficiently clean, but also the waste generated must be safe to disposal. In this study three Fe:Al molar ratio (100:0, 80:20 and 60:40) were used to synthesize ferrous and ferric (hydr)oxides by precipitation in water containing high concentrations (50 and 500 mg L -1 ) of As (III) and As (V). Mineralogical phases detected by XRD were goethite, lepidocrocite, magnetite, maghemite, gibbsite and bayerite for precipitates from Fe (II) and ferrihydrite, hematite and gibbsite for synthesis with Fe (III). BCR extractants were used in order to evaluate As remobilization from precipitates, including acid soluble, reducible and oxidizable phases. Arsenic associated to Al and adsorbed phases were also assessed by extractions with NH 4 F and KH 2 PO 4 , respectively. Arsenic adsorbed to iron (hydr)oxides represented the major phase among all other extracted phases. It was found that the method was highly efficient for all treatments (> 93 %) in the beginning of the experiment, but efficiency was somewhat lower for treatments in which lepidocrocite and gibbsite were identified in the precipitated phases. In spite of the high efficiency, however, the threshold for drinking water was not attained to the higher concentration of As (III and V). At this high concentration, even the required threshold for effluent discharge was not attained for arsenite in some treatments. In general, the sludges resulting from treatments were considered safe for disposal, except for treatments with arsenite, which were considered hazardous by leaching test. In general, the presence of Al increased the efficiency as well as the stability of the sludge resulting from treatments with Fe (II), but was unfavorable for treatments with Fe (III). In summary, precipitation of Fe (III) in the absence of Al was more efficient to remove As, therefore, treatments in which precipitation of hematite is favored are the most effective to treat As contaminated water ensuring a safe sludge disposal.Arsênio é um metaloide comumente encontrado em áreas de mineração e por isso pode ser solubilizado em água pela formação de drenagem ácida. Devido às severas consequências da contaminação por arsênio, a Organização Mundial de Saúde (OMS) recomendou como sua concentração limite em água potável o valor de 10 µg L -1 . A elevada toxicidade do As requer o desenvolvimento de métodos para remoção de As solúvel, incluindo a co-precipitação com (hidr)óxidos de Fe e Al. Esses compostos têm sido considerados uma boa alternativa para remoção de As de águas contaminadas devido às fortes ligações entre eles. Além da qualidade da água, há também a necessidade de avaliar a estabilidade do rejeito formado para fins de deposição. Nesse estudo, três relações molares Fe:Al (100:0, 80:20, 60:40) foram usadas para sintetizar hidróxidos de Fe ferroso e férrico a partir da precipitação em água com altas concentrações (50 e 500 mg L -1 ) de As (III) e As (V). As fases mineralógicas identificadas pela difratometria de Raios-X nos tratamentos com Fe (II) foram: goethite, lepidocrocita, magnetite, maghemita, gibbsita e bayerita e para os tratamentos com Fe (III) foram: ferridrita, hematita e gibbsita. Os extratores BCR foram usados para avaliar a remobilização do As presente no precipitado, incluindo as fases solúveis em ácido, reduzíveis e oxidáveis. Arsênio associado com Al e as fases adsorvidas foram avaliadas pela extração com NH 4 F e KH 2 PO 4 , respectivamente. Arsênio adsorvido aos (hidr)óxidos representa a maior fase extraída entre todas as outras. A remoção de As pelos precipitados foi altamente eficiente ( > 93%) no início do experimento, mas a eficiência foi ligeiramente menor para tratamentos onde foram identificados lepidocrocita e gibbsita. Apesar da alta eficiência, a concentração limite para água potável não foi satisfeita nas maiores concentrações iniciais de As (III e V). A essa concentração, nem mesmo o limite de concentração de As para descarte de efluentes foi satisfeito em alguns tratamentos. Em geral, o lodo resultante dos tratamentos foi considerado seguro para deposição, com exceção dos tratamentos com arsenito, que foi considerado perigoso pelo teste de lixiviação. Em geral, a presença do Al aumentou a eficiência de remoção assim como a estabilidade do lodo gerado dos tratamentos com Fe (II), mas foi desfavorável para os tratamentos com Fe (III). Resumindo, a precipitação de Fe (III) na ausência de Al foi mais eficiente para a remoção de As e portanto, os tratamentos que favoreceram a precipitação de hematita foram considerados os mais eficientes para o tratamento de água contaminada com As e para disposição segura do rejeito

Physiological effects of mercury-contaminated Oxisols on common bean and oat

The heavy metal mercury (Hg) is one of the most complex and toxic pollutants. When present in soils, it may impair plant growth, but the intensity of damage depends on the physical-chemical properties of the soil such as pH, clay, and organic matter content, which in turn affects Hg sorption and bioavailability. Understanding Hg potential damage to staple food crops is of paramount relevance. Here, we evaluated the physiological effects of Hg in Phaseolus vulgaris (common bean) and Avena sativa (oat) cultivated in two Oxisols with contrasting properties: Rhodic Acrudox (RA) and Typic Hapludox (TH). We performed four independent experiments (one per species/soil combination) that lasted 30 days each. Treatments were composed by HgCl2 concentrations in soils (0 to 80 mg kg−1 Hg). At the end of the experiment, we determined the impact of Hg on photosynthesis, nutritional status, and oxidative stress. Cultivation in TH contaminated with Hg resulted in oxidative stress in common bean and decreased photosynthesis/P accumulation in oat. No deleterious effects on physiological variables were detected in both species when cultivated in the RA soil. In general, we conclude that the lower Hg sorption in the TH soil resulted in toxicity-like responses, while acclimation-like responses were observed in plants cultivated in RA, reinforcing soil physical-chemical properties as key features driving Hg toxicity in Oxisols