M. R. Coelho

Caracterização e gênese de perfis plínticos desenvolvidos de arenito do Grupo Bauru: I - química

Plintita e petroplintita sao feicoes de ocorrencia comum nos solos desenvolvidos de arenitos do Grupo Bauru, Formacao Adamantina, nas regioes norte e oeste do estado de Sao Paulo. Com o objetivo de avaliar os atributos quimicos, bem como os processos pedogeneticos envolvidos na formacao desses materiais e dos perfis onde ocorrem, foram estudados dois solos da baixa meia encosta de uma vertente representativa da paisagem local, constituida por feicoes plinticas, petroplinticas e mosqueados. O estudo foi realizado na Estacao Experimental de Agronomia de Pindorama do Instituto Agronomico de Campinas (IAC), regiao norte do estado de Sao Paulo. Com base nas analises pedologicas de rotina, dissolucoes seletivas e fluorescencia de raios-X, constatou-se a origem predominantemente oxidica das glebulas estudadas, nao associadas a compostos orgânicos, com baixos teores de manganes e maiores conteudos de ferro pouco cristalino nas plintitas, comparativamente as petroplintitas. A segregacao e precipitacao de ferro em massa, os mecanismos de eluviacao-iluviacao das argilas e compostos de ferro, a ferrolise, bem como a degradacao dos horizontes petroplinticos, liberando ferro para a formacao da plintitas sotopostas, correspondem aos principais processos pedogeneticos atuantes nos perfis estudados, os quais influenciam sobremaneira os atributos quimicos dos horizontes saproliticos dos perfis plinticos.

Caracterização e gênese de perfis plínticos desenvolvidos de arenito do Grupo Bauru: II - mineralogia

In northern and western landscapes of Sao Paulo State, plinthite and petroplinthite are features observed commonly above the cretaceous Adamantina Formation sandstones (Bauru Group). Two representative soil profiles with plinthic, petroplinthic and mottling features were selected in the local landscape to evaluate the mineralogical characteristics and to study their formation. The study was carried out at the foot of a mountainside in the Experimental Station Pindorama of the Agronomic Institute Campinas (IAC), in the north of Sao Paulo State, Brazil. Scanning microscopy and pontual microanalysis of selected glaebules, as well as the mineralogical analyses of the ironfree clay fraction and the iron oxides of all studied soil profiles were carried out. It was concluded that the main clay fraction minerals of the nodules and the soil are kaolinite, hematite, and goethite. Mica, gibbsite, and anatase also contribute to the mineralogy of the clay fraction of these glaebules, being similar in composition to the surrounding soil material of the profiles. The silt and sand fraction of the nodules is composed by quartz, potassium feldspars, traces of sodium feldspars, and ilmenite. The constant presence of weatherable minerals in the petroplinthic glaebules clearly indicates that the formation of these features was related to iron segregation in the saprolite. This phenomenon, associated with low levels of aluminum in the structure of the glaebules iron oxides suggests their formation under hydromorphic conditions. The hydromorphic environment is probably related to the solubilization and mobilization of ferrous iron that was removed from the upper landscape and precipitated into the vadose zone, where oxidative conditions were favorable for iron segregation and precipitation.

Relação solo-relevo-substrato geológico nas restingas da planície costeira do estado de São Paulo

Atributos morfologicos de 28 pedons, descritos e amostrados em cronossequencias, e datacoes absolutas por luminescencia (TL e LOE) e 14C foram utilizados para elucidar os principais fatores envolvidos na formacao e evolucao dos Espodossolos nos depositos marinhos quaternarios da planicie costeira do Estado de Sao Paulo. Os solos estudados localizam-se nos municipios de Bertioga (Baixada Santista), Cananeia e Ilha Comprida (Litoral Sul). Essa abordagem, pouco comum nos estudos dos ambientes de planicie costeira brasileiros, possibilitou as seguintes interpretacoes: (a) o relevo, a dinâmica hidrica e o tempo (incluindo as variacoes do nivel relativo do mar) sao os principais condicionantes da diferenciacao espacial dos Espodossolos nos terracos marinhos; (b) os Espodossolos mais antigos e bem drenados, devido as condicoes de relevo e rebaixamento do nivel do lencol freatico, apresentam grande variabilidade e diversidade de seus horizontes e atributos morfologicos, diferindo daqueles mal drenados (antigos ou jovens), em que os horizontes sao mais homogeneos; (c) os Espodossolos mais antigos, quando bem drenados, mostram-se em avancado estadio de degradacao, enquanto os mal drenados encontram-se bem preservados, indicando que a sua genese e permanencia na paisagem estao ligadas ao relevo, que, por sua vez, controla a dinâmica hidrica; (d) os Espodossolos mais evoluidos e antigos, dotados de horizontes cimentados (orstein), podem ser considerados indicadores pedolitoestratigraficos dos depositos marinhos pleistocenicos da Formacao Cananeia; e (e) a genese do horizonte orstein se deu em condicoes topograficas e hidrologicas preteritas diferentes das atuais, indicando se tratar de solos poligeneticos ou paleossolos.

Validation of the near infrared spectroscopy method for determining soil organic carbon by employing a proficiency assay for fertility laboratories

Current research indicates that near infrared (NIR) spectroscopy is the most promising alternative technique for the determination of soil organic carbon (SOC) in laboratories worldwide and that it may serve as a total or partial replacement for the traditional wet chemistry methods. In this research, NIR spectroscopy was developed and validated as a method for the determination of SOC aiming to promote the use of NIR technology in the soil laboratories of Brazil as a routine analysis method. To this end, multivariate calibration models were constructed from a large number of soil samples (1490 samples) that encompassed the variability of Brazilian soils. These models were validated by submitting the concentrations of soil organic matter (SOM) as determined by NIR spectroscopy to the proficiency assay for fertility laboratories, which is coordinated by the Brazilian Agricultural Research Corporation (Embrapa Soils). The proposed methodology using NIR spectroscopy received the excellence index of quality, which gives a certificate seal issued by the interlaboratory programme. Therefore, the robustness of the NIR method was proved in a conclusive way by a proficiency test programme dedicated to evaluating the reference method for SOM determination employed by over a hundred soil laboratories in Brazil.

Seletividade do pirofosfato de sódio e de cloretos não tamponados (CuCl2 e LaCl3) como extratores de alumínio associado à matéria orgânica em solos de restinga do estado de São Paulo

Aluminum in complexes with soil organic matter is usually determined by selective extraction techniques. A common extractant for this Al form is sodium pyrophosphate. Due to its lack of selectivity for some soil samples, unbuffered Al extractants, such as CuCl2 and LaCl3, have been recommended. The selectivity of sodium pyrophosphate (Alp) and of unbuffered Cu (AlCu) and La (AlLa) chlorides to extract aluminum bound to soil organic matter (Al-humus) was evaluated in soil samples from 31 pedons (Spodosols and Quartzipsamments) representative of the sandy coastal plains of the state of Sao Paulo. The results were compared with those obtained by ammonium oxalate and KCl and the extraction capacity and selectivity of the reagents interpreted as commonly used in the literature. Pyrophosphate was not totally selective for some samples containing inorganic aluminum. CuCl2 and LaCl3, in turn, were more selective for Al-humus in the same samples and their order of extractability was: Alp>AlCu>AlLa . Based on the different extraction capacities and the relations between the reagents used the analytic evidences were converged in order to analyze and interpret parameters such as Al saturation in the soil organic matter and stability of C-metal interactions. The stability of the interaction C-metal and humus Al saturation of all horizons studied was greater in the Bs, Bhs and Bsm spodic horizons. Based on the results it was concluded that all reagents studied can be used as Al extractants since they allow establishing relations and interpretations that may help understanding the complex chemistry of Al-humus on the studied Restinga soil. These extractors are therefore adequate and promising to study and understand processes involved in the genesis of tropical Spodosols derived from sandy coastal plain sediments.

Soil Organic Carbon Determination Using NIRS: Evaluation of Dichromate Oxidation and Dry Combustion Analysis as Reference Methods in Multivariate Calibration

Dichromate oxidation and dry combustion analysis were evaluated as reference methods to determine organic carbon in Brazilian soils using near infrared spectroscopy (NIRS) as an alternative. The main objective of this study was to evaluate which of the reference methods could provide a calibration model with higher predictive ability. A total of 161 soil samples obtained from horizons in full profiles (Parque Estadual da Mata Seca, Minas Gerais State, Brazil) were used. Models were mean centered and built from partial least squares. The dichromate oxidation method presented a lower accuracy when compared to dry combustion analysis as reference for NIRS. Figures of merit such as sensitivity, analytical sensitivity, detection and quantification limits, adjust and linearity presented results very similar. A paired t-test was applied to the figures of merit results and with 95% confidence did not show significant differences between the two methods used as reference for NIRS. The non-parametric Mann Whitney test showed that the samples provided with the partial least squares (PLS) model when the reference method was the dichromate oxidation or dry combustion analysis come from the same population, indicating that the reference methods employed for multivariate calibration from NIRS provide the same results practically.

Avaliação de cloretos não tamponados como extratores de alumínio associado à matéria orgânica em solos da planície costeira do estado de São Paulo

Pirofosfato de sodio e o extrator mais utilizado para a determinacao do Al complexado a materia orgânica do solo (MOS). Devido a sua falta de seletividade para algumas amostras de solos, extratores nao tamponados de Cl tem sido recomendados em substituicao ao pirofosfato. Com o objetivo de avaliar a eficacia dos cloretos nao tamponados de Cu (CuCl2), lantânio (LaCl3) e potassio (KCl) como extratores de Al unido a MOS, analisaram-se amostras de 31 perfis de solos representativos das areas sob vegetacao de restinga do litoral paulista. Os resultados foram comparados aqueles obtidos com pirofosfato de sodio. O CuCl2, mais forte que o LaCl3 e KCl e menos eficaz que o pirofosfato, extraiu parte do Al de compostos inorgânicos amorfos e de complexos Al-humus bastante estaveis; estes ultimos possivelmente nao sao reativos em termos de acidez do solo e troca ionica. Ao contrario, KCl e LaCl3 removeram somente as formas reativas do elemento associadas ao C orgânico do solo (Corg). No entanto, o Al extraido por LaCl3 (AlLa) foi que melhor se correlacionou com o Corg e com a CTC, indicando que AlLa esta relacionado ao principal componente responsavel pelo desenvolvimento de cargas nos solos estudados. Os extratores permitiram analisar o grau de interacao da MOS com o Al e a influencia do pH do solo na interacao. Os complexos Al-humus mais estaveis foram observados nos horizontes bem drenados Bs, Bhs e C, em que o LaCl3 e, sobretudo, o KCl mostraram as mais baixas eficacias entre todas as amostras analisadas. O Al mais labil unido a MOS foi encontrado nos horizontes superficiais do tipo A. De maneira geral, os horizontes estudados apresentaram a seguinte sequencia de estabilidade da interacao Al-humus: A < Bh < C < Bhm < Bs/Bhs/Bsm. Esses ultimos, juntamente com alguns poucos horizontes C, sao os unicos horizontes de subsuperficie bem drenados, indicando que o hidromorfismo nos horizontes Bh e a ciclagem da serapilheira nos horizontes A favorecem a manutencao de especies de aluminio mais labeis nos solos estudados.