ABSTRACT The diagnostic anthropic A horizon in the Brazilian Soil Classification System (SiBCS) and the Pretic horizon in the World Reference Base for Soil Resources (WRB) comprise the surface mineral genetic horizons of soils formed under strong influence of original indigenous communities for a long time, notably in Brazil those known as Terras Pretas de Índio (TPI) or Amazonian Dark Earths (ADE). The surface horizons of these soils in Brazil are characterized by ceramic artifacts, charcoal, dark colors, and higher levels of carbon, calcium, magnesium, and phosphorus than the adjacent soils. This study aimed to propose additional quantitative criteria for the anthropic A horizon in the SiBCS and contribute to the Pretic horizon and Pretic Anthrosols in the WRB. A database of many studies on these soils was compiled, including morphological, physical, and chemical diagnostic characteristics of horizons classified as anthropic (Au) in anthropized soils. The following data was used to identify and differentiate these horizons: thickness, color (value and chroma), pH(H 2 O), calcium (Ca 2+ ), magnesium (Mg 2+ ), sum of bases (SB), cation exchange capacity (CEC), base saturation (V), available phosphorus (P – Mehlich-1 extractant), and organic carbon (C org ). For SiBCS, it is suggested to define the diagnostic anthropic A horizon based on a limit of organic carbon content (C org ) greater than or equal to 6.0 g kg -1 and a color with value ≤4 and chroma ≤3; to create the “anthropic character” for surface mineral diagnostic horizons with expressive anthropic modifications that do not meet the quantitative criteria of thickness, color, P, and C org for the diagnostic anthropic A horizon; and to define a criteria of “anthric properties”, to be used in soils in which the surface mineral diagnostic horizons show recent and significant modifications due to agricultural and/or other activities, meeting a P content (Mehlich-1 extractant) ≥30 mg kg -1 and V ≥50 %, abrupt transition from the surface horizon to the subsequent one, and/or absence of transitional horizons AB and/or BA. In the WRB system, it is proposed that the Pretic horizon should maintain the P content (Mehlich-1 extractant) ≥30 mg kg -1 , and in the Pretic Anthrosols class, to reduce the combined thickness of Pretic sub horizons to ≥0.30 m (0.30 m) within 1.00 m (1.00 m) of the mineral soil surface.
Cordeiro et al. (Thu,) studied this question.