- Soil can be defined as the weathered material that accumulates at the earth's surface.
- It consists of weathered parent rock (which supplies mineral particles) and organic matter from the overlying vegetation (which decays to form humus).
- It is the most common medium for plant growth.
Soils are influenced by five factors:
1. Parent material.
2. Climate.
3. Relief.
4. Vegetation.
5. Time.
It is important to consider all these factors when attempting to explain where, why and how many different variations in soils type can occur.
How geology affects soil type
- Parent material is a passive factor in the formation of the soils above them. It is subjected to weathering, supplying minerals and nutrients to the overlying soils.
- The sandstones, shales, mudstones and coals of the Dark Peak consist of mainly of quartz and feldspars, which are high in silica (silicon dioxide, SiO2) producing acidic conditions in the overlying soils (as opposed to alkali soils found in the Limestone areas of the White Peak).
- The soils over the Millstone Grit are therefore termed non-calcareous or calcifuge (lime intolerant) and siliceous (silica rich).
Siliceous soils characteristics:
1. Acidic.
2. Low in soluble mineral salts.
3. Peaty (and the characteristics associated with this).
4. Water retentive
Mineral soils with at most a thin layer of peat are more closely related to their underlying geology than the thicker blanket peats as discussed in the peat themes pages..
This is because the soils are physically closer to the parent rock, and are therefore more affected by it.
Soil pH & rock type
Millstone grits which normally have a thinner covering of blanket peat have very acidic soils which commonly range from pH 3.5 to 5.8.
Coalshales and sandstones produce slightly less acidic soils which dominate the pH 4.0 - 6.0 region.
pH affects soil fertility in unexpected ways:
Extremely acidic soils stimulate the production of humic acid which can cause some minerals (e.g. aluminium and manganese) to become toxic.
pH also effects nutrient availability to vegetation:
- Low pH soils in the Dark Peak have a low nitrate concentration (as nitrogen fixing bacteria cannot tolerate the acidic conditions).
- They also have low levels of soluble phosphates which are essential to many plants' development.
- Therefore, these soils will have a limited vegetation diversity as only a few moorland species are adapted to survive these conditions.
Soils over the Mudstones:
- Soils here are mostly of Brown Earth characteristics.
- The exact nature of soils varies according to slope, aspect, agricultural interference, rainfall etc.
- Soils can contain clay subsoils which act as an impermeable basal layer.
- This causes reduced infiltration through the soils, which in turn causes water logging and overland flow in periods of heavy rainfall. This effect can also form gleys in some areas.
See how soil conditions effect the vegetation of the area.