Evidence of wustenquartz, which was a commonly used identifier of parna in the 1960s and 1970s, is only apparent with any certainty in the Merungle Loam
soil horizons. At Merungle Hill, wustenquartz is evident throughout the profile, with a greater abundance in the A horizon.
This can be explained by the fact that the air temperature and precipitation differed between the plots due to the differences in their microhabitat topography: soil type, texture, composition of chemical elements, which influenced the changes of soil moisture content and properties of
soil horizons.
As leaves drop and decompose at the soil surface, organic matter and nutrients are resup-plied to the upper
soil horizons, creating islands of fertility and enhanced soil quality.
Eluvial soils are
soil horizons that have lost material through this process.
Five master
soil horizons are used to describe and characterize soil profiles: O, A, E, B, and C (Figure 2-30).
In the dry interpluvial periods, the reduction of the plant cover favored accelerated soil erosion (rexistasis) and was generally accompanied by crust formation linked to the destruction of the upper
soil horizons. The gradual in situ accumulation of iron oxides, due to annual oscillations in the level of the water table over considerable periods of time and the later disappearance of the poor seasonal drainage, forms ferruginous crusts known as laterites or plinthites (also see p.
- Figures 1A-F and 2 depict the mean differences in percentage germination between seeds treated with [A.sub.1]
soil horizon extracts and water-treated seeds.
The mean thickness of the
soil horizons increased from 17.0 cm in the A horizon to 29.5 and 48.9 cm in the B and C horizons respectively (Table 1).
Therefore, the formation of humus
soil horizon (H) in time (t) may be represented as follows:
Soil horizon thickness was regionalised by Moore et al.
Clay and sand mineralogy in 4
soil horizons for a selected well-drained and imperfectly drained soil profiles were investigated.
They form mainly in
soil horizons that have abundant organic matter and relatively dense concentrations of roots spread through the soil.