There are an infinite number of soil types . Pedology is the branch of science associated with soils. The process of origin of soil is known as pedogenesis.
Soil is a very broad term. It has different meanings in different fields. For an agriculturist soil is simply the upper layer supporting life.
For a Geologist, it is a surface layer of rock waste produced due to the physical and chemical processes of weathering along with organic processes.
The essential constituents in soil are solid matter, soil liquids and air.
The term solid matter incorporates both the inorganic constituents which are derived from rocks and minerals as well as the organic constituents.
Soils are characterised by porous nature. The pores between the particles can be completely or partially filled by air or water or both.
2. Triangular diagram
Various classification schemes are available. The triangular diagram of soil classification gives a broad idea about the textural variations of different soil types.
|Triangular diagram of soil textural classification|
For determining the textural class of soil sample following steps needs to be followed:
- Determine the percentage of sand in the sample and plot a line along the bottom line of the triangular diagram.
- Determine the clay percentage and plot a line.
- The two lines will intersect and the point of intersection indicates the percent of silt.
3. Soil types
Broadly speaking there are six soil types.
- Sandy soil
- Clayey soil
- Silt soil
- Loamy soil
- Chalk soil
- Peat soil
Sandy soil is rich in silica content. Therefore the parent rock for derivation should be rich in silica content. Sandy soil is derived from granite, quartzite and sandstone.
- Derived from acidic rocks thus has acidic pH and low in nutrients.
- Light in colour and thus also known as “light soil”.
- Drains water quickly, dries out in summer and suffers from deficiency of minerals because of the escape with rain water.
Sandy soil is generally not very productive because of quick water drainage. For stimulating productivity, organic matter can be supplemented. It also improves water holding capacity of the soil.
Shrubs and bulbs such as Tulips, tree mallow, Sun roses, Hibiscus, Carrots, Potatoes, Strawberries etc. can be grown.
Clay soil must have been derived from minerals such as feldspars, micas and aluminium silicate minerals.
- It is highly rich in nutrients thus it is also known as “heavy soil”.
- The water drains slowly through them and thus such soil will take longer time to warm up.
- Fairly rich in potash and poor in phosphates.
- Mud cracks are formed during the summer season. Such soil gets swell during wet conditions and shrinks during the dry conditions.
Mudcracks- clay soil
Clay soils require infrequent dressings of lime for maintaining the pH conditions.
Perennials and shrubs such as Aster, Bergamot, Flowering quince, fruit trees and ornamental trees can be grown.
The size of silt is between sand and clay. Silt soil is derived from minerals such as quartz and feldspars.
- Comparatively good soil for the plants.
- The main advantage of this soil is its capacity to retain moisture.
- It is light in colour and has a high fertility rate.
The particles of silt soil are fine and are vulnerable for washing away with rain. Adding organic matter can form stable clumps out of the soil.
Shrubs, climbers, grasses and Perennials such as Mahonia, New Zealand flux etc. can be grown.
Peat soils are derived from the accumulation of organic debris which gets partially decomposed or remains undecomposed.
- Peat soils are characterized by high water table and can retain large amounts of moisture.
- Such soils have an absence of oxygen and thus reducing conditions .
- Such soils have low fertility and high acidity.
As the soil is rich in organic matter, it is often imported into the garden to provide an optimum soil base for planting.
Plants like legumes, root crops and salad crops should be grown.
Chalk soils are derived from carbonate terrain and thus from carbonate rocks such as limestone, dolomite or marble.
The terrain having carbonate deposits shows a unique topography which is collectively known as “Karst topography”.
- Chalk soils are having alkaline pH due to the presence of lime or CaCO3.
- Chalk soil cannot support big trees. However grass like small plants are able to survive.
- It can be light or heavy.
- If the soil has a presence of clumps of CaCO3, the soil can’t be acidified.
Chalk soil is of less agricultural importance as it does not support ericaceous plants.
Plants like Lilac, Weigela, Madonna lilies, pinks, spinach beets, sweet corn and cabbage can be grown.
Bonus tip to identify chalk soil:
Chalk soil is identified by the table like flat topography and the low life profile it supports.
Loam soil is considered as gardeners best friend as well as also it is regarded as “Agricultural soil”.
- Loam soil is a combination of sand, silt and clay.
- Such a combination will abolish the negative impacts of each soil type.
- Loam soil is fertile and has good drainage facilities.
- Depending on the prominent constituent it can be either sandy loam or clay loam.
In Spite of having a high fertility rate still it requires certain practices to maintain its fertility.
It requires practices like crop rotating, addition of organic matter, green manure and compost.
Most vegetable crops, berry crops, black bamboo and Wisteria can be grown.
4.Soil types based on climatic conditions:
Pedalfer: the name itself gives ideas about the mineral content. Pedalfer contains aluminium and iron.
Deciduous trees produce such soils. It requires 65 cm rainfall. The soil is very fertile.
Pedocal: the soil is rich in calcium content. It forms in drier temperate forests. The soil requires less than 65 cm rainfall.
As the soil is rich in calcium content, it undergoes chemical weathering and water dissolves the soluble minerals.
Laterite: the soil requires hot and wet conditions for the formation. Lateritic soil forms due to the residual weathering. The soil is rich in least soluble minerals like Al and Fe oxides.