Soils are: ‘natural bodies whose properties are due to the combined effects of climate and livinf matter acting on parent material, as conditioned by relief over a period of time.’
Soil formation begins with the weathering of rock to give a framework of large and small particles called regolith.
Weathering is carried out by mechanical, biological and chemical means.
The relative proportions of three sizes of particle: Sand, Silt and Clay determine the texture of the soil.
Texture is important as it determines the volume of pore spaces. These determine the soil’s ability to retain air and water, and how quickly the water drains through the soil.
Soil formation is completed by the production of humus: through the action of bacteria and fungi on dead vegetation. This layer returns nutrients to the soil, and helps retain water in sandy soils which would otherwise drain quickly.
Soils are therefore controlled by 5 pedogenic (soil forming) factors:
1. Parent material (nature and mineral content)
2. Organic content
3. Topography (slopes and drainage)
4. Climate (rainfall and evaporation)
5. Time
Soil is stratified: horizontal layering. The layers build upwards from the parent material (C horizon), through sub-soil layers (B horizon) to the organically enriched topsoil (A horizon). The succession of layers is known as the profile.
UPLAND SOILS
Most important factor in development of Lake District
soil profiles is the downward movement of water. This removes
soluble substances from the upper horizons in a process called leaching,
and deposits them lower down in the profile.
Leaching is more pronounced where rainfall exceeds evaporation, such as the high Fells.
It is often the alkaline compounds which are most soluble, and leaching therefore tends to make the soil more acidic. This promotes the solvent action of rainwater and increases the losses. In areas of very high rainfall such as the High Fells of the Lake District these heavily leached soils are known as rankers. Many are immature soils formed on glacial till deposited during the last stages of the last glaciation, and are characteristically stony and shallow. The more intensely leached have a pale band, often sandy, beneath a darker horizon of slowly decaying vegetation. This pale band has had all the nutrients washed out of it, and the nutrients can be found in a darker red or yellow iron-rich layer in the sub-soil (the so-called ‘iron pan’)
These soils are called Podsols.
If the soil is subject to poor drainage as a result of local relief or geology, the podsol may be overlain by a layer of acid peat. These soils are known as peaty podsols.
Seasonal saturation of the soil may occur in areas of very high rainfall and poor drainage. If soils are alternately saturated and dried, a process called gleying occurs. Water becomes de-oxygenated and bacterial action is slowed down in the anaerobic conditions. Iron within the soil is reduced and imparts a blue-grey tinge to the soil. Where there are cracks or macropores in the soil, oxygenated water oxidises the iron giving red or yellow mottled patches. These peaty gley podsols are common in the high fells.
On the limestone in the southern part of the Lake District, the soils tend to be well drained and drier. There are 3 main types of soil here:
Brown Earths develop on free-draining areas where thicker deposits of parent material occur. These soils are subject to less intensive leaching. Being lower and warmer, there is more decay of organic matter, and a deeper humus layer. This creates a deep topsoil. Horizon boundaries are indistinct. The soil is light and easily worked. Develops beneath woodlands.
In some areas on open upland areas e.g Hampsfell or Whitbarrow, there are deposits of fine, red windblown loess, formed from material deflated from glacial sand deposits in areas such as Morecambe Bay. This is normally thin and acidic.
On grassland where till is enriched by humus, and the soil is freely draining, a thin crumbly dark-brown soil may form. This tends to be associated with chalk or limestone and is called a rendzina.
LOWLAND SOILS
The soils of lowland Cumbria derive from 4 main sources:
Glacial Till (covering the lower valley slopes, and large coastal lowlands such as the Furness peninsula)
Glacial Head (solifluction deposits at the base of steeper slopes)
Alluvial deposits (on the floors of the valleys, the result of infilling)
Marine Sediments (particularly around Morecambe Bay)
Most extensive till soils are found on Furness and Cartmel peninsula, resulting from deposition by decaying ice from valley glaciers of Windermere and Coniston areas. It is a reddish-brown till. The relief is undulating with drumlins and hillocks tending from N - S. Soils forming here are mainly brown-earths with a characteristic red-brown colour and a fine texture, although they are often stony. Permeable nature allows free-drainage. Soils have a red-brown A horizon blending into stony and coarser B and C horizons. Depth varies considerably. Under woodland and grassland they are browner than under bracken.
In the infilled hollows between drumlins, gley and peaty gley soils form.
Where there is waterlogging gleyed brown earths can develop.
Soils on the head deposits are mainly brown earths.
Alluvial soils give rise to gleys due to seasonal flooding.
