No abstract

Mehlich-1 soil extract is currently used in Rio Grande do Sul (RS) and Santa Catarina (SC) States, in Brazil, to evaluate soil phosphorus available to plants and Mehlich-1 is sensitive to soil buffering capacity. This limitation is overcome partly by soil separation into buffering classes based on soil clay content. However, soil clay content has some technical and operational limitations, such as the underestimation of soil clay levels in soils under no-till. The aim of this study was to evaluate the remaining phosphorus (P-rem) compared to soil clay content as an index of the buffering capacity in soils of RS. The relationship between P-rem and soil clay content was assessed using 200 soil samples from a wide range of locations across the state. In 20 representative soil types, P-rem, soil clay content, P maximum adsorption capacity, total and pedogenic Fe contents, amount of P 2 O 5 needed to increase soil P in 1 mg kg -1 extracted by Mehlich-1 and -3 methods and P capacity factor were determined. Furthermore, a pot experiment was carried out with plants to determine soil P content extracted by Mehlich-1 and -3 at the maximum technical efficiency (MET) and the maximum absorption efficiency (MEA). Correlation analyses were performed between P-rem and soil clay content and, with the attributes of soils involving the P buffering capacity. The relationship between P-rem and soil clay content was described as a decreasing exponential function; however, the adjustment was not adequate to propose critical levels for P-rem. The P-rem index was superior to soil clay index in practically all relationships with the attributes related to the soil buffering capacity of the soils. In some cases, the indexes were similar; however, P-rem was not lower than the soil clay content in any case. The P-rem is a more reliable index to represent soil buffering capacity than the soil clay content in soils from RS, and P-rem might be used to implement soil classes for Mehlich-1 and Mehlich-3 determinations of soil P.

Phytoremediation consists of biological techniques for heavy metal remediation, which include exploring the genetic package of vegetable species to remove heavy metals from the environment. The goals of this study were to investigate heavy metal and bioaugmentation effects on growth and nutrient uptake by Mucuna deeringiana; to determine the metal translocation factor and bioconcentration factor and provide insight for using native bacteria to enhance heavy metal accumulation. The experiment was conducted under greenhouse conditions using a 2 × 4 factorial scheme with highly and slightly contaminated soil samples and inoculating M. deeringiana with three highly lead (Pb)-resistant bacteria Kluyvera intermedia (Ki), Klebsiella oxytoca (Ko), and Citrobacter murliniae (Cm) isolated from the rhizosphere of native plants identified as Senecio brasiliensis (Spreng.) Less., Senecio leptolobus DC., and Baccharis trimera (Less) DC., respectively. The increased heavy metal concentrations in soil samples do not decrease the root dry mass of M. deeringiana, concerning the number and dry weight of nodules. The shoot dry mass is reduced by the increasing concentration of heavy metals in soil associated with Kluyvera intermedia and Klebsiella oxytoca bacteria. The number of nodules is affected by heavy metals associated with Citrobacter murliniae bacteria. The bacteria K. intermedia, C. murliniae, and K. oxytoca increase the lead and cadmium available in the soil and enhanced metal uptake by Mucuna deeringiana. The M. deeringiana specie has characteristics that make it hyperaccumulate copper and zinc. The translocation and bioconcentration factors for M. deeringiana characterize it as a promising candidate to phytostabilize multi-metal contaminated soils.

-The objective of this work was to evaluate remaining P compared with soil clay content as a P buffer index to classify P extracted by the Mehlich-1 (M1) and Mehlich-3 (M3) methods in soils from the state of Rio Grande do Sul, Brazil. The experiment was carried out in a completely randomized design with five P 2 O 5 rates (0, 50, 100, 200, and 400 mg kg -1 ) and two sucessive corn crops, and three replicates, in 20 representative soils of the state. P extracted by M1 and M3 before crop planting was adjusted to P contents in biomass, considering soil buffer capacity. The division of soils into different buffering classes, based on soil clay or remaining P, improved the capacity of estimating soil available P of both methods. However, there was no difference among the correlation coefficients obtained by classifying soils according to the evaluated indexes (remaining P or soil clay) for both M1 and M3 methods. Remaining P is a viable alternative to replace soil clay content to classify soil P extracted with the M1 and M3 methods.Index terms: clay content, phosphate buffer capacity, phosphate fertilization, phosphorus adsorption, soil test. Fósforo remanescente para determinar a disponibilidade de fósforo em solos do Rio Grande do SulResumo -O objetivo deste trabalho foi avaliar o P remanescente comparado ao teor de argila como índice tampão para classificar o P extraído pelos métodos de Mehlich-1 (M1) e Mehlich-3 (M3), em solos do Rio Grande do Sul. O experimento foi realizado em delineamento inteiramente casualisado, com cinco doses de P 2 O 5 (0, 50, 100, 200 e 400 mg kg -1 ), dois cultivos sucessivos de milho, e três repetições, em 20 solos representativos do Estado. O P extraído pelos métodos M1 e M3, antes dos cultivos, foi ajustado aos conteúdos de P na biomassa, tendo-se considerado a capacidade tampão do solo. A divisão dos solos em classes de tamponamento, de acordo com o teor de argila ou com o P remanescente, melhorou a capacidade preditiva do P disponível para ambos os métodos. Todavia, não houve diferença entre os coeficientes de correlação obtidos pela classificação dos solos de acordo com os índices avaliados (P remanescente ou teor de argila), tanto para o método M1 como para o M3. A análise do P-rem é uma alternativa viável para substituir o teor de argila na classificação do P extraído pelos métodos M1 e M3.Termos de indexação: teor de argila, fator capacidade de fósforo, adubação fosfatada, adsorção de fósforo, análise de solo.