Paddy Soils in Tropical Asia: Part 3. Correlation and Regression Analyses of the Soil Data

Abstract

Correlation coefficients between all pairs of 29 variables that had been described previously in relation to fertility and material characteristics were computed for the same 410 tropical Asian paddy soil samples. Chemical characters related to base status are highly correlated not only with each other but also with such character groups as textural composition, clay mineralogy, and total chemical composition. Characters related to organic matter status are not highly correlated with any of the other character groups, though their mutual correlations are high. The same holds for characters related to phosphorus status. Multiple regression of CEC on the contents of different clay mineral species and organic matter was studied. The 14 A minerals alone explained more than 80% of the variance of CEC. The 7 A and 10 A minerals also contributed significantly, but the contribution of organic matter to CEC turned out to be insignificant. Hayashi's theory of quantification (No. 1) was adopted to assess the contributions of such qualitative variables as climate, relief, and texture to organic matter status of the soil. Climate was proved to be most relevant to the reserve of mineralizable nitrogen, while local relief contributed most to TC and TN. Effect of texture on accumulation of organic matter was clearer under a drier climatic condition.