ABSTRACT Plinthite and petroplinthite occur frequently in Brazilian soils, but there is little information on the behavior of these materials. The aim of the present study was to assess the effect of different drying periods on the hardening and stability of plinthic materials of soils in the floodplain of the Araguaia River and the João Leite stream in Goiás. Soil samples were collected, with the aid of 0.10 m high and 0.15 m diameter PVC cylinders, directly from the plinthic horizons of five profiles of Plintossolos Argilúvicos (Plinthosols). Plinthite and soil matrix subsamples were obtained from these samples. Homogeneous petroplinthite samples were collected from the concretionary horizon of a Plintossolo Pétrico (Plinthosol) profile, and these were separated into subsamples with the aid of a rock hammer. All subsamples were dried in two manners: air drying and drying in a forced ventilation oven for 10, 20, 40, 80, and 160 days. Compressive strength and degree of stability were assessed. The results show a considerable variety of responses to the compressive force applied to the plinthite and petroplinthite samples in the same horizon and among the different profiles examined.

ABSTRACT Although ferruginous materials occur frequently in soils of tropical regions, information about the reversal of the hardening process of these materials is scarce. This study assessed the influence of different chemical treatments and periods of immersion on the reversibility of the hardening process of plinthite and petroplinthite in soils of the Araguaia River plain. Soil samples were collected from the plinthic horizons in 0.10 m high and 0.15 m diameter PVC cylinders and divided into subsamples with a rock hammer. Homogeneous petroplinthite samples were also collected and broken into subsamples with a rock hammer. The plinthite and petroplinthite subsamples were subjected to five immersion treatments: distilled water, calcium carbonate solution, sodium hydroxide solution, sodium hydroxide solution + sodium hexametaphosphate, and acidic solution. The subsamples were immersed for 20, 40, 80, and 160 days. The dispersion and stability degrees and compressive strength in these subsamples were assessed. The wet aggregate stability test indicated no impact on the structural stability of plinthite and petroplinthite subsamples subjected to the treatment with different chemical agents, demonstrating the non-reversibility of the hardening process of these materials of the Araguaia River floodplain, under the studied conditions.

O planejamento e o manejo ambiental são atividades que visam o controle e adequação do uso das terras com a finalidade de maximizar a produtividade agrícola por meio de um sistema de exploração capaz de sustentar as atividades humanas com um mínimo de distúrbios nos processos físicos, ecológicos e sociais. Para garantir o uso racional dos recursos naturais devem-se considerar as classes de solo bem como suas características físicas e químicas e os atributos morfométricos da bacia hidrográfica onde estão inseridos, pois esses indicam a intensidade de cultivo e o manejo a ser aplicado ao solo para que não haja exaustão da capacidade produtiva em decorrência da erosão. O objetivo desse trabalho foi avaliar os atributos morfométricos em relação à distribuição dos solos na paisagem e sugerir o potencial de uso da terra com base no coeficiente de rugosidade na bacia hidrográfica do alto rio Meia Ponte, Goiás. Dentre as variáveis necessárias ao planejamento de bacia, a análise dos atributos morfométricos associada às características dos solos e relevo revelou-se de grande importância por fornecer a definição de sua potencialidade. Quanto ao uso dos solos, com os resultados obtidos a partir do cruzamento do levantamento dos solos, declividade média e do coeficiente de rugosidade, verificou-se que o uso potencial da bacia é a agricultura e a pecuária, desde que mantida as demais áreas para a preservação da vegetação natural e de reflorestamento.

Planning and environmental management are necessary to manage land use and to assess the suitability of land in order to maximize agricultural productivity by designing an operating system capable of sustaining human activities with minimal disruption to physical, ecological and social processes. In order to ensure the rational use of natural resources with regard to various types of soil, the physical, chemical, and morphometric characteristics of the watershed must be evaluated in order to determine the proper intensity of cultivation and soil management to avoid the loss of productive capacity due to erosion. The aim of this study was to evaluate morphometric attributes in relation to the distribution of soils in the landscape and to suggest potential alternative land uses based upon the roughness coefficient in the watershed of the upper Meia Ponte river, Goiás. Among the variables necessary to watershed planning, morphometric analysis of soil characteristics and topography has proven to be of great importance in defining its potential and characteristics with respect to water dynamics. This analysis allowed us to infer that runoff in Inceptisols and Ultisols soil classes is greater than in Oxisols. Based upon the analysis of the morphometric data, soil, and roughness coefficient, it was possible to conclude that the optimal use of the basin is for agriculture and cattle grazing, provided that the areas of natural vegetation and reforestation are preserved.

O conhecimento das propriedades físicas do solo, incluindo os teores de argila, é de suma importância para a agricultura. Solos aparentemente iguais podem apresentar comportamento diferente devido a características intrínsecas, determinadas pela atuação de processos de formação diferentes e pela natureza de seu material formador. Este trabalho objetivou avaliar pré-tratamentos, métodos de dispersão e agentes químicos dispersantes, isoladamente ou de forma combinada, na determinação dos teores de argila de algumas classes de solos selecionadas com base na sua natureza mineralógica. Foram selecionados cinco (mas estão citados apenas 4) solos de natureza mineralógica contrastante: Latossolos Acriférricos (oxídicos), Argissolo e Nitossolo (cauliníticos) e Chernossolo (esmectítico). Foram utilizados tratamentos distintos: substâncias químicas como dispersantes, (hidróxido de sódio, hidróxido de lítio e hexametafosfato); pré-tratamentos com ditionito, oxalato de amônio e água oxigenada, para eliminação de matéria orgânica; como ações mecânicas, foi testado o uso de areia grossa como abrasivo e do ultrassom. Os resultados permitiram a conclusão de que: há a necessidade de que sejam dados tratamentos diferenciados na determinação de argila, levando-se em consideração a natureza mineralógica do solo; o hidróxido de lítio não é eficiente para dispersar solos eletropositivos com baixa CTC, mas muito eficiente na dispersão de solos eletronegativos com elevada CTC; o uso de areia grossa como abrasivo aumentou os níveis de argila em todos os tratamentos em que aconteceu a dispersão para todos os solos, com e sem o uso de dispersante químico; e a utilização de areia grossa não tem eficácia igual em todas as classes de solo.

Knowledge of the soil physical properties, including the clay content, is of utmost importance for agriculture. The behavior of apparently similar soils can differ in intrinsic characteristics determined by different formation processes and nature of the parent material. The purpose of this study was to assess the efficacy of separate or combined pre-treatments, dispersion methods and chemical dispersant agents to determine clay in some soil classes, selected according to their mineralogy. Two Brazilian Oxisols, two Alfisols and one Mollisol with contrasting mineralogy were selected. Different treatments were applied: chemical substances as dispersants (lithium hydroxide, sodium hydroxide, and hexametaphosphate); pre-treatment with dithionite, ammonium oxalate, and hydrogen peroxide to eliminate organic matter; and coarse sand as abrasive and ultrasound, to test their mechanical action. The conclusion was drawn that different treatments must be applied to determine clay, in view of the soil mineralogy. Lithium hydroxide was not efficient to disperse low-CEC electropositive soils and very efficient in dispersing high-CEC electronegative soils. The use of coarse sand as an abrasive increased the clay content of all soils and in all treatments in which dispersion occurred, with or without the use of chemical dispersants. The efficiency of coarse sand is not the same for all soil classes.

Solos concrecionários (Plintossolo Pétrico concrecionário) nas Regiões Central e Norte do Brasil são muito comuns, ocorrendo em áreas baixas e nas bordas das chapadas, constituindo geralmente solos distróficos,pobres em nutrientes. A ocorrência de solo concrecionário eutrófico no município de Ouro Verde de Goiás, em área de borda de chapada motivou esta pesquisa, desenvolvida com a finalidade de verificar a relação eutrofia/solo/material litológico subjacente, provável fonte das bases trocáveis. As relações pedológicas e geoquímicas do solo com as concreções e a rocha de origem foram pesquisadas por meio de determinações da constituição química total dos elementos maiores, utilizando ICP-AES (espectrometria de emissão atômica por plasma acoplado indutivamente), análise mineralógica da fração argila por DRX, análise mineralógica da fração areia, além da caracterização analítica de rotina em pedologia. Os resultados analíticos de amostras de rocha, concreções ferruginosas e TFSA, as relações moleculares Ki e Kr e bases/R2O3 e a relação Zr/Ti são abordados e discutidos. Ocorrências mais significativas quanto a alguns elementos móveis são creditadas ao conteúdo elevado de matéria orgânica no horizonte superficial do solo, ao acúmulo residual de quartzo e à contribuição de material externo nos horizontes superiores . A relação solo/material litológico subjacente indica para o perfil de origem a partir de um metatonalito, atribuindo-se ao material petroplíntico presente na porção superior do solo, origem relacionada à desagregação e arraste de materiais relacionados à Superfície de Aplanamento Sul-Americana.

The occurrence of concretionary soils in the Central and Northern Brazil is very common. They are found in low areas and on plateau edges, usually constituting dystrophic soils,poor in nutrients. The finding of an eutrophicc concretionary soil in the edge of a plateau in Ouro Verde de Goiás stimulated this research, which had the purpose of verifying the relationship between the soil eutrophic conditions and the underlying lithologic material, the probable source of the exchangeable bases. The pedologic and geochemical relationships of the soil with concretions and parent rock were investigated by determining the total major element content by ICP-AES (inductively coupled plasma - atomic emission spectrometry), mineralogical analysis of the clay fraction by DRX, mineralogical analysis of sand fractions, besides standard analysis procedures used in pedology studies. The analytical results of rock samples, concretions and soil, the molecular relationships Ki and Kr, basic cations/R2O3 and the Zr/Ti relationship were described and discussed. The higher contents of some soluble elements were ascribed to the high organic matter content in the surface horizon, to the residual accumulation of quartz, and the contribution of external. The relationship soil/parent material indicated that the profile was originated from a metatonalite and the concretionary horizons in the upper part of the soil were originated by soil disaggregation and transport of material related to the South American Plain Surface.