Heavy‐metal cations can be introduced into agricultural soils by application of fertilizers, liming materials, sewage sludge, composts, and other industrial and urban waste materials. Therefore, heavy‐metal adsorption reactions, in a competitive system, are important to determine heavy‐metal availability to plants and their mobility throughout the soil. This study was conducted to evaluate the selectivity sequence and estimate the competitive adsorption of several heavy metals in seven soils with different chemical and mineralogical characteristics. Distribution coefficients (Kd), which represent the sorption affinity of metals for the solid phase, were obtained for each soil and heavy‐metal cation. On the basis of these Kd, the selectivity sequence was evaluated. The most common sequences were Cr > Pb > Cu > Cd > Zn > Ni and Pb > Cr > Cu > Cd > Ni > Zn. Chromium, Pb, and Cu were the heavy‐metal cations most strongly adsorbed by all soils, whereas Cd, Ni, and Zn were the least adsorbed, in the competitive situation. Selectivity sequences related to valence for the trivalent Cr. For metals of the same valence, sequences did not exactly follow the order of electronegativity. For individual elements, the Misono softness parameter and hydrolysis properties of the heavy‐metal cations may have influenced the sequences. Correlation analysis showed that soil characteristics that may have affected the heavy‐metals adsorption, represented by the distribution coefficients, were pH and cation‐exchange capacity (CEC) for Cd and Cr; organic carbon, clay, and gibbsite contents for Cu; pH and CEC for Ni and Pb.

In terrestrial ecosystems of Maritime Antarctica (King George Island), the transference of primary marine production to the land promoted by penguins (Pygoscelis adeliae) and other birds, appears to influence soil formation and chemical weathering to a greater extent than formerly predicted. This paper summarizes the results of pedological investigations on the vicinity of the American Pieter J. Lenie Field Station (62°10′ S, 58°28′ W), discussing soil formation processes related to vegetation succession in the studied area. Soil organic matter (SOM) accumulation and associated phosphatization are marked soil‐forming processes in ice‐free areas once colonized by penguins. Also there is a high correlation between soil development and vegetation patterns. Nutrient supply in these cryogenic soils is affected by low pH following nitrification and high contents of P, K, Ca, and Mg due to seabirds' inputs. Lithic Umbriturbels and Glacic Haploturbels are the most common ornithogenic soils, followed by Lithic Fibristels and Psammentic Aquiturbels. In all soils phosphatization and ornithogenesis occurs in varying degrees. However, the recent Gelisols order of Soil Taxonomy does not consider the influence of ornithogenesis or phosphatization in its framework, so that a more detailed classification of such soils is not possible.

Resumo -O objetivo deste trabalho foi verificar a influência de diferentes manejos no carbono orgânico e na estabilidade de agregados em um Latossolo Vermelho. Os seguintes tratamentos foram avaliados: PDs -plantio direto, por quatro anos, com a sucessão milho (silagem)/soja; PDg -plantio direto, por quatro anos, com a sucessão milho/milho/milho/soja; PDtf -três anos contínuos, com tifton (feno), e no quarto ano, soja sob plantio direto; SC -sistema convencional com soja, nos últimos quatro anos; e MN -mata nativa. A estabilidade de agregados foi expressa pelos índices: diâmetro médio ponderado, diâmetro médio geométrico, porcentagem de agregados maiores que 2,0 mm estáveis em água e índice de estabilidade de agregados. Em todos os tratamentos, houve diminuição da estabilidade de agregados com o aumento da profundidade. Os tratamentos cultivados tiveram seus índices de agregação reduzidos em relação à mata nativa. O sistema convencional apresentou os menores índices de agregação. O uso da gramínea perene tifton foi o tratamento que promoveu a melhor recuperação da estabilidade de agregados em água. Correlações significativas e positivas foram obtidas entre carbono orgânico total e os índices de estabilidade estudados.Termos para indexação: solos tropicais, cerrado, plantio direto, agregação. Organic carbon and aggregate stability of a Red Latossol under different managementsAbstract -The objective of this work was to verify the influence of different managements on organic carbon and on aggregate stability of a Red Latossol (Typic Haplorthox). The following treatments were appraised: PDsno tillage for four years with successions corn (silage)/soybean; PDg -no tillage for four years with the successions corn/corn/corn/soybean; PDtf -three years with tifton (hay) and soybean in the fourth year; SC -conventional cultivation with soybean in the last four years; and MN -native forest. The aggregate stability was expressed by the indexes: mean weight diameter, mean geometric diameter, percentage of stable aggregates >2.0 mm, and stable aggregates index. The aggregate stability in all the treatments decreased with depth. Indexes in cultivated treatments reduced in relation to native forest ones. The conventional system presented the worse indexes. Perennial grass tifton was the best treatment to recover aggregate stability. Significant positive correlations were obtained between total organic carbon and the studied aggregate stability indexes.

RESUMOEm muitos casos, a substituição da vegetação nativa por sistemas agrícolas resulta em decréscimo nos conteúdos de C e N nos diferentes compartimentos da matéria orgânica do solo. Para testar se as práticas de manejo que priorizam o aporte de resíduos orgânicos promovem aumento dos compartimentos da matéria orgânica mais sensíveis ao manejo, este estudo se propôs estudar áreas de uma propriedade que utiliza um sistema de produção de acerola em larga escala, sob manejo orgânico, e uma área sob cultivo convencional de cenoura e beterraba em rotação com milho, pertencentes à Fazenda Amway Nutrilite do Brasil e à Associação de Horticultores do Pivot Central, respectivamente, ambas localizadas na região da Chapada da Ibiapaba, Ceará. Selecionou-se, também, uma área de pastagem localizada no interior da primeira propriedade amostrada, bem como áreas sob mata nativa, próximas às áreas de cultivo. Amostras de um Neossolo Quartzarênico foram coletadas nas profundidades de 0-5 e 5-15 cm e foram determinados os teores de C orgânico total, de C e N microbiano (Cmic e Nmic) e da matéria orgânica leve (Cmol e Nmol), além do C mineralizável obtido por respirometria. O acúmulo médio nos estoques de Nmic nas áreas sob manejo orgânico em relação à mata nativa foi de 11,7 kg ha -1 , o que representou um incremento de 585 % de Nmic nas áreas de cultivo. Já na pastagem, ocorreu acúmulo de 211 kg ha -1 no estoque de Cmic em relação à mata nativa em subsuperfície, representando um incremento de 514,6 %. Por outro lado, os

Soil CO 2 emission is an important part of the terrestrial carbon cycling and is influenced by several factors, such as type and distribution of vegetation. In this work we evaluated the spatial variability of soil CO 2 emission in terrestrial ecosystems of maritime Antarctica, under two contrasting vegetation covers: 1) grass areas of Deschampsia antarctica Desv., and 2) moss carpets of Sanionia uncinata (Hedw.) Loeske. Highest mean emission was obtained for the Deschampsia (4.13 mmol m -2 s -1 ) developed on organic-rich soil with a strong penguin influence. The overall results indicate that soil temperature is not directly related to the spatial pattern of soil CO 2 emission at the sites studied. Emission adjusted models were Gaussian and exponential with ranges varying from 1.3 to 2.8 m, depending on the studied site and vegetation cover.