Adierson Gilvani Ebeling

ANÁLISE DOS COMPONENTES PRINCIPAIS E MÉTODOS MULTICRITÉRIO ORDINAIS NO ESTUDO DE ORGANOSSOLOS E SOLOS AFINS

One important property of Organosols (Histosols) (and soils with high content of organic carbon) to predict use potential and degradation risks is the degree of subsidence (loss of mass and volume). In Organosols the subsidence risks vary according to the soil attributes, mainly the nature of organic matter and deposition environment. In this paper we studied 19 soil profiles from different parts of the country, collected and described according to procedures recommended by the SBCS (Brazilian Soil Science Society); the analytical methods proposed by EMBRAPA-Solos were used to characterize the soils. The principal component analysis was used to cluster the profiles based on morphological, physical, chemical and environmental attributes and proved adequate to group the soils under study based on the profile attributes and the grouping was well related to their taxonomy. The soil profiles were ranked by the ordinal multicriteria methods of Border, Condorcet and Copeland based on the subsidence risk. Results indicated a correlation between the methods (with exception of the Condorcet approach, unsuitable to rank the alternatives) and the minimum residue, which is the classical parameter for the evaluation of subsidence, indicating efficacy to rank/classify the soil profiles in relation to subsidence risk. The quantitative approaches used are promising as evaluation tools in soil science studies.

Organic carbon determination in histosols and soil horizons with high organic matter content from Brazil

Soil taxonomy systems distinguish mineral soils from organic soils based on the amount of soil organic carbon. Procedures adopted in soil surveys for organic carbon measurement are therefore of major importance to classify the soils, and to correlate their properties with data from other studies. To evaluate different methods for measuring organic carbon and organic matter content in Histosols and soils with histic horizons, from different regions of Brazil, 53 soil samples were comparatively analyzed by the methods of Walkley & Black (modified), Embrapa, Yeomans & Bremner, modified Yeomans & Bremner, muffle furnace, and CHN. The modified Walkley & Black (C-W & B md) and the combustion of organic matter in the muffle furnace (OM-Muffle) were the most suitable for the samples with high organic carbon content. Based on regression analysis data, the OM-muffle may be estimated from C-W & B md by applying a factor that ranges from 2.00 to 2.19 with 95% of probability. The factor 2.10, the average value, is suggested to convert results obtained by these methods.

Atributos químicos, carbono orgânico e substâncias húmicas em Organossolos háplicos de várias regiões do Brasil

The dynamics and properties of soil organic matter (SOM) in mineral soils have been studied for many years. However, under tropical conditions, few studies involve organic soils, the characterization of humic substances (HS), or their relationship with chemical properties related to the agricultural potential of Histosols. The objectives of this study were to characterize chemical properties of Histosols in different Brazilian regions; to quantify soil organic carbon and carbon in the SOM fractions; and to evaluate possible relationships between organic carbon content and soil chemical properties in each environment. The chemical properties were measured and carbon was quantified in the soil samples and the SOM fractions (fulvic acid - C-FAF, humic acid - C-HAF, humin - C-HUM). The ratios C-HAF/C-FAF, C-EA/C-HUM, where C-EA (carbon of the alkaline extract) is equal to the sum of C-FAF+C-HAF, were also evaluated. The acidity of the Histosols was high, base saturation below 50 %, and the cation exchange capacity (CEC) high, although the Ca and Mg levels and sum of bases were high in most profiles. The humic fractions were significantly correlated with different soil properties, such as C-HAF and also C-HUM with N, H+, and CEC. The C-HUM and C-HAF predominated over C-FAF. The C-HAF/C-FAF ratio was reduced in the surface layer of Histosols under intense agricultural use or frequent vegetation burning; the SOM, C-HUM and C-HAF contents were also reduced. The chemical properties and C content in the humic substances reflected the transformation degree of SOM and the changes caused by agricultural use, indicating the vulnerability of Histosols.

Humic Substance Fractions and Attributes of Histosols and Related High‐Organic‐Matter Soils from Brazil

Abstract Knowledge of the distribution of soil organic matter (SOM) fractions is important in managing soils toward a sustainable agricultural system in a tropical environment. However, data on Histosols is limited. This study developed 19 profiles of Histosols and soils with high organic-matter content from different regions of Brazil. Soil organic matter was fractionated into fulvic acids (FAF), humic acids (HAF), and humin (HUM). The ratios HAF/FAF and AE (alkaline extract)/HUM were calculated. The objectives were to evaluate the method for SOM fractionating in Histosols and related soils and to correlate the distribution of organic fractions with other soil attributes. The humic fractions presented significant correlations with other soil attributes, the best being the correlation between FAF and nutrient level. The HAF and HUM presented high correlation with cationic exchange capacity, active acidity (H+) and pH. Humin and the alkaline extract absorbance measured at 380 nm and 465 nm and presented good correlation with total organic carbon.

Substâncias húmicas e relação com atributos edáficos

Este trabalho teve como objetivo caracterizar a distribuicao das substâncias humicas (acidos fulvicos livres, acidos humicos, acidos fulvicos e humina) e atributos edaficos em perfis de solos de diferentes regioes do Brasil, que foram objeto de estudos de reunioes de correlacao e levantamentos de solos realizados pela Embrapa e outras instituicoes. As amostras foram selecionadas e fracionadas seguindo conceitos da IHSS. A fracao humina apresentou os maiores valores de C em todos os perfis, seguida pelos acidos fulvicos livres. Nos perfis em ambientes com altitudes elevadas o clima (Cwa, Cfb, Cwb) favoreceu a formacao dos acidos fulvicos livres. Quanto as propriedades quimicas, em ambos os horizontes foram verificados coeficientes de correlacao positiva entre o hidrogenio e o conteudo de carbono orgânico, r=0,58* e r=0,83**, para os horizontes A e B, respectivamente. Dentre as substâncias humicas a de melhor correlacao com o conteudo de carbono orgânico foi a fracao humina, com r=0,89** e r=0,91** para os horizontes A e B, respectivamente. Foi observada correlacao positiva (p<0,05) entre a areia grossa e os C-FAF, C-FAH, C-HUM e a relacao C-EA:C-HUM, nos horizontes A, indicando que a textura mais arenosa de alguns horizontes superficiais favorece a formacao destas substâncias humicas. O teor de C nos horizontes superficiais e subsuperficiais e a distribuicao das substâncias humicas variaram com a pedogenese e a altitude.

COMPARISON OF H/AL STOICHIOMETRY OF MINERAL AND ORGANIC SOILS IN BRAZIL

Exchangeable Al has been used as a criterion for the calculation of lime requirement in several Brazilian States. However, the laboratory method with extraction by a 1 mol L-1 KCl solution followed by indirect alkaline titration is not accurate for some Brazilian soils, mainly in the case of soils with high organic matter content. The objective of this study was therefore to evaluate the stoichiometry of H+/Al3+ in KCl soil extracts. The results suggested that organically complexed Al is the main contributor to exchangeable acidity in soils enriched with organic matter. Liming recommendations for organic soils based exclusively on exchangeable Al determined by the NaOH titration method should therefore be revised.

Atributos físicos e matéria orgânica de organossolos háplicos em distintos ambientes no Brasil

Histosols are formed under geomorphic and climate conditions that allow the accumulation of organic material, and their drainage for agriculture leads to the subsidence process and changes in the content of soil organic matter (SOM), with implications in the sustainability of these soils. The objective of this study was to evaluate some physical properties of Histosols and their relationship to SOM content and degree of decomposition in soils formed under hydromorphic conditions in the states of Rio de Janeiro (Aw tropical Atlantic), Maranhao (Awh tropical), and Parana (Cfb subtropical), with different usages. The methods recommended by the Brazilian Soil Classification System (SiBCS) were applied for characterization of the eight profiles, totaling 30 horizons; the organic matter content was quantified using a muffle furnace. The physical properties, soil bulk density (BD), organic matter density (OMD), percentage of mineral material (MM), and minimum residue (MR), reflected the content and transformation degree of the organic matter. The BD values varied from 0.09 to 0.93 Mg m-3, with an average of 0.44 Mg m-3 and OMD varied from 0.02 to 0.66 Mg m-3, with an average of 0.28 Mg m-3. A directly proportional relationship between BD and the properties MM and MR was observed. In the classification of the decomposition degree, the organic materials were identified mainly as hemic and sapric. Since different classes were obtained according to the method applied, it is recommended the combined usage of the pyrophosphate index and the content of rubbed fibers, defining the classes according to a range of values. In the Histosols with less anthropic alteration, in the State of Rio de Janeiro (profiles RJ02 and RJ08), the levels of organic matter were highest and the values of BD, OMD, and MM lowest. Thus, these properties are relevant to indicate the potential of subsidence and degradation in Histosols, an important soil class with regard to carbon storage and preservation of aquifers.