A New Soil Material Classification for Tropical Asian Paddy Soils

Abstract

An attempt was made to reclassify Tropical Asian paddy soils with respect to their material characteristics, based on data including those of various total trace element status. Data pertaining to contents of both macro and microelements and mechanical composition for 482 samples were processed. By factor analysis, six factors were extracted, each of which appears to represent a different aspect of soil material characteristics. The scores of the six factors were computed and used for numerical classification by means of numerical taxonomy. Based on the dendrogram, seven classes, I-VII, were set up. Of these, two classes (I and III), containing 188 samples, were evaluated to have low capabilities as soil material; two other classes (II and IV), containing 138 samples, to be intermediate; and the remaining three classes (V, VI, and VII), accounting for 156 samples, to have high capabilities. To facilitate objective placement of a new sample into one of the seven classes, discriminant functions were derived for each pair of classes. Compared with the previously established material classification for Tropical Asian paddy soils, the new classification set up in the present study involves more information about different aspects of soil material characteristics, as represented by the six factors, and particularly about the trace element status. By country, Indonesia (Java), Philippines, and Burma appear to have paddy soils with better soil materials. In contrast, the paddy soils of Cambodia, East and West Malaysia, and Thailand have generally poor materials. Bangladesh, India, Sri Lanka, and Vietnam soils have developed on materials of moderate quality.