Diagnostic materials

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Elwin Smith
6 years ago
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1 Diagnostic materials It appeared appropriate to define diagnostic soil materials. These diagnostic soil materials are intended to reflect the original parent materials, in which pedogenetic processes have not yet been so active that they have left a significant mark. They comprise anthropogeomorphic, calcaric, fluvic, gypsiric, organic, sulfidic and tephric soil material. The fluvic, calcareous and calcaric, and gypsiferous properties of the Revised Legend (FAO, 1988) are redefined under fluvic, calcaric and gypsiric soil material.

2 Anthropogeomorphic soil material General description. Anthropogeomorphic soil material (from Gr. anthropos, human) refers to unconsolidated mineral or organic material resulting largely from land fills, mine spoil, urban fill, garbage dumps, dredgings, etc., produced by human activities. It has, however, not been subject to a sufficiently long period of time to find significant expression of pedogenetic processes. Descriptions of some anthropogeomorphic soil materials are given in Table 1. TABLE 1: Some anthropogeomorphic soil materials Aric Garbic Reductic Spolic Mineral soil material which has, in one or more layers between 25 and 100 cm from the soil surface, 3 percent or more (by volume) fragments of diagnostic horizons which are not arranged in any discernible order. Organic waste material; land fill containing dominantly organic waste products. Waste products producing gaseous emissions (e.g. methane, carbon dioxide) resulting in aerobic conditions in the material. Earthy material resulting from industrial activities (mine spoil, river dredgings, highway constructions, etc.). Urbic Earthy material containing building rubble and artifacts (cultural debris > 35 percent by volume).

3 Calcaric soil material Definition. Calcaric soil material (from En. calcareous) shows strong effervescence with 10 percent HCl in most of the fine earth. It applies to material which contains more than 2 percent calcium carbonate equivalent.

4 Fluvic soil material General description. Fluvic soil material (from L. fluvius, river) refers to fluviatile, marine and lacustrine sediments, which receive fresh material at regular intervals, or have received it in the recent past 1. Diagnostic criteria. Fluvic soil material is soil material which shows stratification in at least 25 percent of the soil volume over a specified depth; stratification may also be evident from an organic carbon content decreasing irregularly with depth, or remaining above 0.2 percent to a depth of 100 cm. Thin strata of sand may have less organic carbon if the finer sediments below, exclusive of buried A-horizons, meet the latter requirement. Field identification. Fluvic soil material shows stratification. Alternating darker coloured soil layers may reflect an irregular decrease in organic carbon content with depth. 1. Recent past covers the period during which the soil has been protected from flooding, e.g. by empoldering, embanking, canalization or artificial drainage, and during which time soil formation has not resulted in the development of any diagnostic subsurface horizon apart from a salic or sulfuric horizon.

5 Gypsiric soil material Definition. Gypsiric soil material (from L. gypsum) is mineral soil material which contains 5 percent or more gypsum (by volume).

6 Organic soil material General description. Organic soil material consists of organic debris which accumulates at the surface under either wet or dry conditions and in which the mineral component does not significantly influence the soil properties. Diagnostic criteria. Organic soil material must have one of the two following: 1. if saturated with water for long periods (unless artificially drained), and excluding live roots: - 18 percent organic carbon (30 percent organic matter) or more if the mineral fraction comprises 60 percent or more clay; or - 12 percent organic carbon (20 percent organic matter) or more if the mineral fraction has no clay; or - a proportional lower limit of organic carbon content between 12 and 18 percent if the clay content of the mineral fraction is between 0 and 60 percent; or 2. if never saturated with water for more than a few days, 20 percent or more organic carbon.

7 Sulfidic soil material General description. Sulfidic soil material (from E. sulphide) is waterlogged deposit containing sulphur, mostly in the form of sulphides, and only moderate amounts of calcium carbonate. Diagnostic criteria. Sulfidic soil material must have: percent or more sulphur (dry weight) and less than three times as much calcium carbonate equivalent as sulphur; and 2. a soil-ph (H2O) of more than 3.5. Field identification. Deposits containing sulphides often show in moist or wet condition a golden shine, the colour of pyrite. Forced oxidation with a 30 percent hydrogen peroxide solution lowers the ph by 0.5 unit or more. Oxidation also gives rise to the smell of rotten eggs.

8 Tephric soil material 1 General description. Tephric soil material (from Gr. tephra, pile ash) consists either of tephra, i.e. unconsolidated, non or only slightly weathered primary pyroclastic products of volcanic eruptions (including ash, cinders, lapilli, pumice, pumice-like vesicular pyroclastics, blocks or volcanic bombs), or of tephric deposits, i.e. tephra which has been reworked and mixed with material from other sources. This includes tephric loess, tephric blown sand and volcanogenic alluvium. Diagnostic criteria. Tephric soil material must have: percent or more tephra; and 2. less than 0.4 percent Al + ½Fe, both extractable in acid oxalate (ph 3). Relationships with some diagnostic horizons. The low amount of acid oxalate extractable aluminium and iron sets tephric soil material apart from vitric horizons. 1. Description and diagnostic criteria are adapted from Hewitt (1992).

ANDOSOLS and ARENOSOLS

ANDOSOLS and ARENOSOLS Otto Spaargaren ISRIC World Soil Information Wageningen The Netherlands Definition of Andosols (WRB 2001) Soils having 1. an andic or a vitric horizon starting within 25 cm from