Saturday, 15 July 2006

Mapping of Micromorphometric Types of Pore Space in Loamy Soils.

Elena B. Skvortsova and Polina V. Koroleva. V.V. Dokuchaev Soil Science Inst, Pyzhevskii Per. 7, Moscow, Russia

Modern micromorphological studies are not limited to the solution of traditional problems of the genesis and diagnostics of soils. Owing to the development of computer-based technologies, the quantitative micromorphology (micromorphometry) becomes an important component of geographic information and cartographic systems. An original system of digitized maps of the micromorphometric structure of soil pore space (SPS) has been developed at the Dokuchaev Soil Science Inst. The system is based on a digitized soil map (1:1 M scale) covering the areas in Kaluga, Moscow, Orel, and Tula oblasts of central Russia. The soil cover of the region consists of Soddy-Podzolic and Gray Forest Soils and Podzolized and Leached Chernozems (according to the classification system of 1977). Schematic maps of SPS structure were compiled for loamy and clayey soils developed from mantle loams and moraine deposits. Soils of the sandy and loamy sandy texture, as well as alluvial soils, were not used for the micromorphometric mapping because of their specific microfabric (mainly inherited from the parent material) and the relatively low areas within the studied region. The maps were compiled on the basis of the micromorphometric database on SPS structure as studied in vertically oriented thin sections from the depths of 0, 30, 60, 90, 130, and 150 cm. The samples for thin section preparation were taken from key soil pits within the investigated region and beyond it, in similar soil and lithologic conditions. The method of pedogenetic extrapolation was used to develop the attribute database for the entire region. The thin sections were studied using image analyzers Majiscan-2 (Joyce Loebl Co) and DiaMorph (DiaMorph Co). Pore size, shape, and orientation were measured and quantitatively characterized. The discriminant analysis was used for automated diagnostics of the SPS structure within the framework of the earlier suggested 8 types of SPS typical of the loamy soils on the Russian Plain (figure). The schematic maps of SPS show that it has its own "geography" (distribution in different soil types) at particular depths. It does not coincide with the geography of soils shown on the basic soil map. At none of the depths, the areas of particular types of SPS coincide with the initial soil areas. The number of mapping areas distinguished on the maps of SPS for all the depths does not exceed 70% of the number of initial soil areas. The reason for this lies in the polygenetic nature of particular micromorphometric types of SPS; these types are not strictly confined to the particular pedogenetic units shown on the soil map. The maximum degree of similarity between the two maps is seen for the depth of 30 cm, where different pedogenic types of SPS are most fully represented. The analysis of the system of SPS maps shows that natural pedogenesis results in the increasing diversity of SPS types in the soil profiles as compared with the parent materials. This is proved by the values of Shannon's index of diversity calculated for the deep and upper soil layers. At the depth of 150 cm, SPS is relatively homogenous in different soil types and the index has minimum values. It increases in the upper soil horizons. However, in the uppermost surface horizons it decreases again, which attests to some convergence in the character of SPS formation (and, hence, soil structuring) in the topsoil within the studied territory.

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