The representative elementary area (REA) in studies of quantitative soil micromorphology

Abstract

A fundamental question to be answered for studies in quantitative micromorphology at varying scales is: What is the minimum area on a soil thin section or block that is required to represent the pedofeature of interest based on its distribution in soil space? This paper investigates the necessity of establishing a representative elementary area (REA) in the study of pedofeatures for quantitative analysis of pedofeatures. It also proposes a means by which an absolute REA may be determined. This was achieved by suggesting that the REA for voids on 3.5×4.7 cm soil thin sections is attained at the area where the measurements made on a parameter in three successive areas of measurements do not change ±10% relative to the next greater area of measurement. Using this method, the REA for void pedofeatures in the size range of 50 to 2000 μm on 3.5×4.7 cm thin sections from silt loam agricultural soils of southern Ontario was investigated. The REA was achieved for total void area between 50 and 500 μm in diameter in 99% (97 of 98) of the thin sections, whereas for total perimeter 97% (95 of 98) of the sections achieved the REA. The average REA between 50 and 500 μm in diameter for total void area and perimeter was 5.09 and 5.00 cm 2, respectively. The average REA between 500 and 2000 μm for total void area and perimeter was 6.73 and 4.95 cm 2, respectively. It is suggested that the REA determination should be performed in every quantitative soil micromorphological study in order that the parameter of interest is an adequate representation of that feature in soil space.