RESUMO
A set of attributes endows the soils with distinctive characteristics and astute understanding is required in order to formulate suitable strategies for soil management. The aim of this study was to physically, chemically and mineralogically characterize samples of the main soil classes in Minas Gerais, Brazil, determine the point of zero salt effect (PZSE) and the point of zero charge (PZC), and ascertain the correlation between these factors and soil attributes. The soils evaluated presented different textural classes ranging from loamy sand (Entisol) to very clayey (some Oxisols and Ultisols). The soils differed substantially in terms of fertility, presenting a range from dystrophic (low fertility, base saturation < 50 %) to eutrophic character (fertility, base saturation >= 50 %), even within the same soil class, such as the Oxisols, which suggests the concurrence of the parent material. Highly weathered soils are predominant in Minas Gerais and these soils are composed predominantly of kaolinite, gibbsite, goethite and hematite. Traces of hydroxy-Al interlayered vermiculite and illite were also found in the Oxisols, Ultisols and Inceptisols. A correlation between the PZSE and the PZC in the A horizon was observed. A high degree of correlation was observed between the PZC and the exchangeable aluminum and the ratio of iron obtained by ammonium oxalate and dithionite-citrate (Feo/Fed) in both the A and B horizons of soil classes. The results obtained reinforce the importance of knowledge of soil attributes to the adoption of practices such as the management of phosphate fertilization in clayey soils and liming in soils rich in aluminum.(AU)
Assuntos
Solo/química , Solos Argilosos/análise , Minerais/análiseRESUMO
A set of attributes endows the soils with distinctive characteristics and astute understanding is required in order to formulate suitable strategies for soil management. The aim of this study was to physically, chemically and mineralogically characterize samples of the main soil classes in Minas Gerais, Brazil, determine the point of zero salt effect (PZSE) and the point of zero charge (PZC), and ascertain the correlation between these factors and soil attributes. The soils evaluated presented different textural classes ranging from loamy sand (Entisol) to very clayey (some Oxisols and Ultisols). The soils differed substantially in terms of fertility, presenting a range from dystrophic (low fertility, base saturation = 50 %), even within the same soil class, such as the Oxisols, which suggests the concurrence of the parent material. Highly weathered soils are predominant in Minas Gerais and these soils are composed predominantly of kaolinite, gibbsite, goethite and hematite. Traces of hydroxy-Al interlayered vermiculite and illite were also found in the Oxisols, Ultisols and Inceptisols. A correlation between the PZSE and the PZC in the A horizon was observed. A high degree of correlation was observed between the PZC and the exchangeable aluminum and the ratio of iron obtained by ammonium oxalate and dithionite-citrate (Feo/Fed) in both the A and B horizons of soil classes. The results obtained reinforce the importance of knowledge of soil attributes to the adoption of practices such as the management of phosphate fertilization in clayey soils and liming in soils rich in aluminum.
Assuntos
Minerais/análise , Solo/química , Solos Argilosos/análiseRESUMO
Animal production is a leading economic activity in Brazil and antibiotics are widely used. However, the occurrence, behavior, and impacts of antibiotics in Brazilian soils are still poorly known. We evaluated the sorption behavior of four fluoroquinolones (norfloxacin, ciprofloxacin, danofloxacin, and enrofloxacin) and five sulfonamides (sulfadiazine, sulfachloropyridazine, sulfamethoxazole, sulfadimidine, and sulfathiazole) in 13 Brazilian soils with contrasting physical, chemical, and mineralogical properties. Fluoroquinolone sorption was very high (Kd≥544 L kg(-1)) whereas sulfonamide sorption ranged from low to high (Kd=0.7-70.1 L kg(-1)), consistent with previous reports in the literature. Soil texture and cation exchange capacity were the soil attributes that most affected sorption. Cation exchange was the most important sorption mechanism for the fluoroquinolones in highly weathered tropical soils, although cation bridging and ion pairing could not be ruled out. Hydrophobic partition played an important role in the sorption of the sulfonamides, but sorption was also affected by non-hydrophobic interactions with organic and/or mineral surfaces. Sorption for both compound classes tended to be higher in soils with high Al and Fe oxihydroxide contents, but they were not correlated with Kd values. No direct effect of soil pH was seen. The fluoroquinolones are not expected to leach even in worst-case scenarios (soils rich in sand and poor in organic carbon), whereas soil attributes dictate leaching potential for the sulfonamides.