Revisiting the definitions of the sombric horizon in soil taxonomy and world reference base for soil resources

Bockheim, James G.

doi:10.1016/j.geoderma.2011.11.017

Cited by 7 publications

(7 citation statements)

References 13 publications

(25 reference statements)

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“…Bockheim (2012) concluded that only twelve out of thirty soil profiles reported in the literature as sombric horizons were in accordance with the definition of sombric horizon by Soil Taxonomy and WRB systems. In the thirty soil profiles studied, however, the author did not considere sombric horizons those where the requirement of an increase in carbon content was not satisfied.…”

Section: Hypothesis For the Sombric Horizon Formationmentioning

confidence: 88%

“…In many cases, the presence of high exchangeable Al extracted with the 1 M KCl solution is used as a parameter to discard the hypothesis of the sombric horizon (Bockheim, 2012); however, this is not a safe criterion, once Al can derive from dissolution of mineral fraction.…”

Section: Distinction Between Sombric and Spodic Horizonsmentioning

confidence: 99%

“…Several authors report the occurrence of the sombric horizon in soils; however, in many cases, its characteristics do not allow its definition or there are insufficient analytical data for an accurate identification. Bockheim (2012) analyzed 30 soil profiles with the occurrence of the sombric horizon and observed that only 12 profiles met the requirements established in Soil Taxonomy and WRB for the classification of the sombric horizon.…”

Section: Introductionmentioning

confidence: 99%

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Sombric horizon: five decades without evolution

Almeida

Neto

Vidal‐Torrado

2015

Sci. agric. (Piracicaba, Braz.)

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The sombric horizon is a diagnostic subsurface horizon defined in the soil classification system of the United States (Soil Taxonomy) and FAO (WRB), used to classify the soil at different categorical levels. The sombric horizon has a soil color darker than the overlying surface(s) horizon(s), and must show illuvial humus accumulation features, though they are not associated with aluminum (Al), as in the spodic horizon, nor associated with sodium (Na), as in the natric horizon. There are also criteria to distinguish it from buried A horizons. However, since the first references and proposed concept of the sombric horizon in African soils made by Sys and co-workers in the 1960s, and adopted by the Soil Taxonomy edition of 1975, few modifications have been made to its definition. Moreover, the pedogenic process involved in illuvial humus accumulation in these horizons remains inadequately clarified, making the distinction between the sombric and spodic or buried A horizon difficult and unclear. This review reports the historical evolution of the sombric horizon concept, its definition and inconsistencies under different soil classification systems, and the current hypothesis, together with its fragilities, proposed to explain the soil illuvial humus accumulation. Although it is recognized that further research is necessary, alternative criteria are proposed for the definition of the sombric horizon in the Brazilian System of Soil Classification.

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Section: Hypothesis For the Sombric Horizon Formationmentioning

confidence: 88%

Section: Distinction Between Sombric and Spodic Horizonsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Sombric horizon: five decades without evolution

Almeida

Neto

Vidal‐Torrado

2015

Sci. agric. (Piracicaba, Braz.)

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“…Sombric and sombric-like horizons are found in well-drained landscape positions with high soil moisture, on high plateaus and/or mountains in tropical and subtropical regions, and several theories exist as to their formation (Almeida et al, 2009;Bockheim, 2012;Almeida et al, 2015). Except for Faivre (1990), sombric horizons described in the literature lack evidence of OM illuviation, and are therefore frequently referred to as sombric-like horizons (De Craene and Laruelle, 1955;Sys et al, 1961;Gouveia et al, 2002;Caner et al, 2003;Almeida et al, 2009;Velasco-Molina et al, 2010).…”

Section: Introductionmentioning

confidence: 99%

Sombric-like horizon and xanthization in polychrome subtropical soils from Southern Brazil: implications for soil classification

Chiapini

Oliveira

Schellekens

et al. 2021

Sci. agric. (Piracicaba, Braz.)

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The occurrence of dark subsurface horizons rich in organic matter (OM) associated with polychrome in the B horizon (yellowish over reddish hue) is common in soils from Southern Brazil. The formation of these horizons and the combination with such morphological attributes has not been properly documented, and neither has the cause effect relationship. Four soil profiles with such sombric-like horizons with a yellowish color at the upper part of the B horizon over red subsoil were studied in Southern Brazil. Results from micromorphology, extractable sesquioxide minerals, clay mineralogy and isomorphic substitution of Fe by Al in iron minerals showed that melanization, xanthization, bioturbation, moderate shrinking/swelling and moderate ferralitization were the most evident pedogenetic processes in role. Xanthization is closely related to the sombric-like horizon formation. In the studied area the findings demonstrated that no clay and OM illuviation had taken place. Therefore, the classification of these soils was revisited, so as to take into account the processes that underlie their genesis with emphasis on xanthization, clay illuviation and soil aggregation. The results suggest that the sombric horizon may need redefinition, unless profiles can be found in which illuviation of clay and/or OM can be proven.

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“…Apesar de o horizonte sômbrico ser diagnóstico nos sistemas de classificação de solos da Soil Taxonomy e da FAO, esse horizonte foi criado a partir de dados limitados e sua pedogênese ainda é pouco compreendida (Bockheim, 2012). A origem iluvial do húmus é apontada pela maioria dos autores como o principal processo pedogenético responsável pela formação do horizonte sômbrico; porém, ainda há muitas dúvidas sobre os mecanismos responsáveis pela sua gênese (Frankart, 1983;Smith, 1986;Mutwewingabo, 1989;Caner et al, 2003).…”

Section: Comissão 12 -Levantamento E Classificação Do Solo Introduçãounclassified

Caracterização e classificação de solos com horizontes subsuperficiais escuros derivados de rochas graníticas no Escudo sul-rio-grandense

Botelho¹,

Pinto²,

Lima³

et al. 2014

Rev. Bras. Ciênc. Solo

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RESUMOHorizontes subsuperficiais escuros com características morfológicas similares aos solos com caráter sômbrico são encontrados nas áreas mais elevadas da porção leste do Escudo sul-rio-grandense, desenvolvidos nos horizontes A2, AB (ou AC) e BA de Argissolos, Luvissolos e Neossolos Regolíticos, respectivamente. Os mecanismos responsáveis pela sua gênese são ainda pouco compreendidos, apesar de a maioria dos autores concordar com a origem iluvial do húmus e de constituir horizonte diagnóstico. Os objetivos deste trabalho foram caracterizar e analisar o enquadramento de nove perfis de solos com horizontes subsuperficiais escuros do Escudo sul-rio-grandense nos critérios do SiBCS, WRB e Soil Taxonomy, sendo sete deles com características morfológicas de sômbrico. A observação de campo (continuidade lateral na paisagem) e a morfologia (ausência de horizonte E, cores mais escuras que os horizontes sobrejacentes e presença de cutans) apóiam o caráter sômbrico para a maioria dos perfis estudados, com a inserção do caráter sômbrico em nível de subgrupo nas classes de Argissolos Bruno-Acinzentados, Amarelos e Vermelho-Amarelos, bem como em Luvissolos e Neossolos Regolíticos, além da inclusão de eutrófico no nível de grande grupo na classe dos Argissolos Bruno-Acinzentados. Os dados sugeriram a revisão da definição de dessaturação na determinação do caráter sômbrico (distrófico) no SiBCS, com a adoção do valor V de 65 %, adequando essa à definição do Soil Taxonomy e WRB, bem como uma investigação mais aprofundada quanto à não associação do húmus com Al; e a consideração da retirada da capacidade de troca de cátions da matéria orgânica no cálculo da atividade da argila, para os horizontes subsuperficiais escuros.Termos de indexação: pedologia, caráter sômbrico, morfologia do solo.

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Revisiting the definitions of the sombric horizon in soil taxonomy and world reference base for soil resources

Cited by 7 publications

References 13 publications

Sombric horizon: five decades without evolution

Sombric horizon: five decades without evolution

Sombric-like horizon and xanthization in polychrome subtropical soils from Southern Brazil: implications for soil classification

Caracterização e classificação de solos com horizontes subsuperficiais escuros derivados de rochas graníticas no Escudo sul-rio-grandense

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