Technique for preparation thin sections of structural soil aggregates of certain size fractions

Abstract

Morphological properties of poil aggregate aer developed in the process of pedogenesis and reflect the complex of structure formation processes. The peds' size, shape, and internal structure are peculiar to each corresponding soil type and genetic horizon. The technique proposed allows preparing thin sections on every sizes of structural units and, in contrast to known methods, it provides not only a ped immobilization in the mass of fixing material, but also pore space saturation with natural resin. It is also possible to prepare the sections with marking of large aggregates orientation in space; it requires application of gypsum marks on the aggregate surface in the process of their sampling from the soil profile. The technique modified consists of following stages: selection of aggregates with required fractions; preparation of sections with separate aggregates larger than 5 mm; preparation of sections with aggregations smaller than 5 mm. In preparation of aggregates larger than 5 mm, a technique similar to that of preparing large soil block samples is used because it makes possible to process each soil aggregate separately. Another approach is required for processing of structural units up to 5 mm in size because it is impossible to prepare a section of individual issue with this size. The problem is solved when the units are saturated and processed not separately, but as a whole block sample which include a mass with peds of separate fraction. For this purpose, it is required to prepare cups comprised of walls from thick paper and a gypsum bottom. For preparation the caps use a gypsum in the form of fine white powder rapidly solidified in addition of water in a certain proportion and forms a firm bottom of the paper сup. Cut out a square of 4×4 cm in size and a strip from thick paper and glue them together to gain a tube of 5 cm in height and 1.5–2 cm in diameter (i.e. 10×5 cm). Apply on the paper squares a prepared gypsum mass sufficient to retention of the paper tube until gypsum hardening.  Fill a fraction of aggregates into the prepared cup in one-third of its height and cover it with prepared fixing substance with solvent. Saturation is carried out in accordance with the standard technique of section preparing using natural resins (Gagarina, 2004). After complete saturation, paper cups with a mass of aggregates in them turn into monoliths that should be processed in the same way as large soil samples. As a result of all operations, significant number of structural soil aggregates with same sizes may be found within the section plane.