Soil Classification System Based on Soil Pore Structure

SPSCS (Soil Pore space-Structural Classification System) has been proposed for the classification of pore structure of soils. This system is based on the clustering of similar soil air content curves determined on the soil sampling scale. These curves express the volume of air in non-hydrated pores of different sizes and represent the soil pore structure.

SPSCS considers two hierarchic categorical levels of classification: Order and Suborder.

The Order level combines soil samples with similar soil volumetric fractions corresponding to their pore sizes in relation to the total pore space available. The following three fractions of pore size are used: macrospace fractions (large pores), mesospace (intermediate-sized pores) and microspace (small pores), defined in a standardized way.

As these fractions add up 100%, they allow representing a given soil sample in a ternary diagram, herein called a structural triangle (figure below). The sides contain the macrospace, mesospace and microspace fraction scales, from 0 to 1 (or 0 to 100%).

Based on this triangle, nine Orders (from A to I) are proposed.

Structural triangle with the identification of Brazilian soil samples

The Suborders represent groups of soils with similar total pore space. Four Suborders are used (from 1 to 4), each corresponding to the following value intervals, respectively: 0 - 0.20 cm³ cm⁻³, 0.20 - 0.40 cm³ cm⁻³, 0.40 - 0.60 cm³ cm⁻³, > 0.60 cm³ cm⁻³.

The nine Orders (from A to I) and the four Suborders (from 1 to 4) proposed provide 36 possible structural soil classes in SPSCS which group soils with similar air content curves.

SPSCS was implemented in an extensive and diverse database containing approximately 3,000 soil samples from tropical and temperate environments. The classification of the Brazilian soil samples within the Orders of the system is indicated in the structural triangle. SPSCS has been proven to be a method suitable to and useful in the characterization of soil pore structure.

A full description of the SPSCS methodology and an application study of this system to the 3,000 samples of international soils mentioned above will be presented in a CPRM institutional report to be published.

See also