[pp.63-70]

Classification of the Size Distribution of Soil Aggregates in Arid and Semi-arid Regions in East Asia

Tomoo OKAYASU and Kazuhiko TAKEUCHI （The University of Tokyo）

Abstract:
Broad-scale evaluation of wind erosion requires details of the spatial distributions of the primary factors controlling wind erosion, such as soil characteristics, vegetation cover and soil water conditions. Soil aggregates are one of the factors, and their size distribution have usually been mapped by assuming a one-to-one relationship with soil texture class. We dry-sieved 31 soil samples from arid and semi-arid regions in East Asia. Cluster analysis showed that the size distribution of aggregates varied even within a single soil texture class, mainly because of the difference in soil types, indicating that the above assumption does not hold in this region. Azonal aeolian sediments have typical well-sorted forms of size distributions, but zonal steppe soils show various patterns of size distribution. Parent material can be a good indicator to use to classify the size distributions of aggregates in steppe soils, loess materials and soils formed on newer (Quaternary and Cretaceous) igneous rock (finer soils), on sedimentary materials (coarser soils), and on ancient geological layers (complex, coarse particle size composition). Soil maps and geological maps of this region are readily available, so the mapping of soil aggregates in relation to these thematic maps should be efficient and practical.

Key Word:
dry sieving, cluster analysis, wind erosion, China, Mongolia

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