Paddy Soils in Tropical Asia: Part 4, Soil Material Classification

Abstract

In view of the importance of soil material characteristics in determining paddy soil capability, a method of classification for soil materials is proposed. Special attention was paid to make it as practically applicable as possible because of the great need for such a method of ready applicability, especially in the alluvial soil areas of tropical Asia. An X-ray fluorescence spectrographic method for the total chemical analysis of soil materials was proved satisfactory for routine use in terms of accuracy and time. The total chemical nature of soil material was described in terms of nine major elements (Si, Fe, Al, Ca, Mg, Mn, Ti, K, P) analyzed. Total chemical composition and mechanical composition data were subjected to data processing. To avoid redundance in information, 3 mutually independent principal components were extracted, which appear to represent different aspects of soil material features. From the 3 principal component scores taxonomic distance was computed as a similarity coefficient for use in numerical taxonomy. By means of numerical taxonomy 10 soil material classes were set up, each of which was characterized in terms of texture, base status, mineral composition, etc. In order to facilitate objective placement of a new sample in one of the classes, discriminant functions were derived for all pairs of the 10 material classes. The 10 soil material classes appear to represent the major varieties of paddy soil materials in tropical Asia. Since the correlation between the soil fertility rating and the soil material composition has been confirmed, the use of the 10 material classes as the basis of "soil family" separation in soil surveys would improve homogeneity of the lower taxonomic units ("soil series") and make their interpretation easier and more correct in relation to soil capability assessment.