A method of capability evaluation for upland soils

Abstract

Abstract Soil tilth is a concept defined in relation to plant growth and tillage efficiency. It is mainly determined by soil structure and consistency, both of which have been defined rather vaguely and represented by many indices, such as degree of aggregation, dispersion ratio, Atterberg's and Yoneda's consistency constants, etc. This study aims at extracting a compound character (or characters) that can be used as a quantitative measure of soil tilth, and further predicting the quantified tilth index from the characters observed in the field. In the present study, factor analysis (FA) was applied to a set of to variates, that are thought to be related to either or both of soil structure and consistency. Two basically lame factors were Consistently extracted for any strata of the samples; one is highly correlated with humus, bulk density (BD), porosity (PORE), plastic limit (PL), and dispersion ratio (DR) and the other with soil texture, clay and sand, and cohesive forces, ultimate breaking strength (UBS) and natural reaking strength (NBS). The first factor is closely related to structure and therefore named as “structure index.” The second factor seems to represent important part of soil consistency and is called “consistency index.” hese two indices are mutually independent and are more exactly definable than the ordinary concepts of structure and consistency. Moreover. they have definite advantage over individual variates that have been used as indices of these two physical characteristics. because they are cOmpound characters extracted from these individual variates. In the second part of this study we will derive a numerical measure of soil tilth based on these two indices.