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.

Solos reconstruídos após mineração de carvão têm suas propriedades físicas, químicas e biológicas alteradas. Nesse sentido, este trabalho foi desenvolvido com o objetivo de avaliar efeitos da aplicação de corretivos, da adubação e da revegetação nas propriedades físicas de um solo reconstruído após mineração a céu aberto. O experimento foi conduzido na Mina do Apertado, em Lauro Müller, SC, entre 2001 e 2005, sobre um solo minerado em 1991 e reconstruído em 1995. O delineamento experimental foi de blocos ao acaso, com três repetições. Os tratamentos foram: (1) testemunha; (2) "dregs" (resíduo alcalino); (3) calcário; (4) calcário + Brachiaria brizantha; (5) calcário + Brachiaria brizantha + cama de aviário. Em todos os tratamentos, foram transplantadas mudas de Pinus taeda e de Eucalyptus saligna em subparcelas. O calcário dolomítico e o "dregs" foram incorporados a 10 cm de profundidade. Toda a área recebeu adubação nitrogenada, potássica e fosfatada conforme recomendação técnica. As amostras de solo foram coletadas em fevereiro de 2005, nas camadas de 0 a 5 e 5 a 10 cm, avaliando-se os seus atributos físicos. Os tratamentos não alteraram a densidade de partículas, densidade do solo, porosidade total, macro e microporosidade do solo. O calcário elevou o pH, dispersou a argila e reduziu a estabilidade de agregados, enquanto o "dregs" aumentou o pH sem dispersar a argila. A adubação orgânica e o uso de Brachiaria brizantha aumentaram a estabilidade dos agregados e a água prontamente disponível, favorecendo a recuperação da qualidade física do solo degradado.

The physical, chemical and biological properties of soils of reconstructed areas after coal mining are altered. This study aimed to evaluate liming, mineral and organic fertilizers and revegetation effects on the physical properties of a reconstructed soil after open-pit mining. The experiment was carried out in a former mine in Lauro Müller County - SC, in southern Brazil, from 2001 to 2005. The site was mined in 1991 and reconstructed in 1995. A randomized complete block design was used, with three replications. The treatments consisted of: (1) Control; (2) "dregs" (alkaline residue); (3) Lime; (4) Lime + Brachiaria brizantha; (5) Lime + Brachiaria brizantha + poultry litter. Pinus taeda and Eucalyptus saligna seedlings were transplanted to subplots of all treatments. Dolomitic limestone and dregs were incorporated in the soil at a depth of 10 cm. Nitrogen, potassium and phosphorous fertilizers were added on the soil surface of all plots according to the official recommendation. Soil samples were collected in February 2005 (from the layers 0-5 and 5-10 cm), and their physical and chemical properties evaluated. The treatments had no effects on soil bulk density, particle density, total porosity, macroporosity and microporosity. Liming increased pH, caused clay dispersion and reduced aggregates stability in water, while dregs increased pH without dispersing clay. Poultry litter and Brachiaria brizantha increased the aggregate stability and volumetric water content, thus favoring the recovery of soil physical quality in degraded areas.