The “Catena‐Drainage Profile” Key‐Form as a Frame of Reference in Soil Classification

» HE main point in this paper is a suggestion that i. detailed "keys" for soils of different regions, each with limited range in climatic. conditions, might be combined without essential changes, especially in catena groupings, into a "classfication" embracing all soils of the world. Numerous "broad" soil classification schemes (i, 7, 8) already published have much in common, and differ chiefly in the viewpoints of the authors and details of arrangements, which is also true in this case. This paper is actually a continuation of a previous paper (4) and acquaintance with the ideas and terminology presented therein is a necessary background. Some points basic for further discussion are as follows . 1. The assumed viewpoint is that of a soil surveyor who reports observations in light of a working theory that soils may be regarded as functions of formative factors, chiefly climate, parent materials, native vegetation, age, drainage, and topography. 2. The primary data include (a) observed profile characteristics, vertical differences in which indicate "horizons", and (b) limited variations in horizons parallel to the land surface which show the extent, 'locations, and patterns of individual areas of a soil species (types) or identify two areas of the same species. 3. Similarities in profiles of two soil species in all characteristics except for textural differences (within moderate range) serve in grouping them within a soil genus (series). 4. Profiles of soil genera with characteristics which are apparently related to homologous factors of climate, parent materials, vegetation, and age, but which run the gamut of hydrologic sequence, serve in grouping those genera in a "SIMPLE TAXONOMIC CATENA". 5. The general similarities between soil genera in comparable steps of the hydrologic sequence of different catenas serve in grouping those genera under "MAJOR DRAINAGE PROFILES", designated by Roman numerals as "I profiles", "II profiles", etc. 6. The "CATENA-DRAINAGE PROFILE KEY-FORM" is simply a tabular arrangement with (a) vertical columns containing general descriptive headings, with names of soil genera classed under each drainage profile, and (b) horizontal lines, or tiers of boxes, with generalized descriptions and names of component genera of a given catena all on the same line. 7. In such keys, the SIMPLE CATENAS may be arranged in sequence with those most alike close together, and those more unlike farther apart. The order of criteria for such arrangement may be varied. 8. In the Indiana Soil Key(5), SIMPLE CATENAS are arranged in small groups according to gradations due .to the native vegetation, in larger groups according to gradations in parent material factors, and in still broader groups related to age. It happens that no soil genera of the state are separated from each other on basis of differences interpreted as due to differences in climate. In other words, the climatic complex is, from a soil formation standpoint, practically a constant factor and requires no special section in the keying device. Such an arrangement (2, 3, 6) for soils'of limited climatic conditions may be called a "MONO-CLIMATIC, CATENADRAINAGE PROFILE, KEY-FORM".