In this article, I will discuss the main types of soil, the meaning of soil, and its properties. The soil is a natural renewable resource, that can be sustained by proper management. Most of man’s needs come from the soil. It is therefore essential for agriculturists to understand the types and properties of the soil so that they can protect, conserve and improve this most valuable resource.
Soil is originated from rocks; rocks are continuously disintegrating (breaking into smaller pieces) and decomposing (changing into substances) to form soil. Substances from rocks make up the mineral matter in the soil.
The soil is formed by a process described as weathering. Weathering refers to the wearing away of rocks. This produces small fragments and particles which help to make up the soil. Factors that bring about weathering are:
- the roots of plants.
There are three stages of soil:
- Soil Solid
- Soil with air in the pores
- Soil with water in the pores
Soil Solid: The soil solids are made up of (i) inorganic (ii) organic matter. The inorganic matter makes up the mineral materials in the soil. These supply some nutrients to the plants.
Soil Air: Soil air is necessary for the development of healthy roots and soil organisms.
Soil Water: Soil water is necessary for the movement of nutrients from the soil into the plants. The soil is the place from which the land plants obtain water. Some soil nutrients are Nitrogen, Magnesium, Phosphorous, Manganese, Potassium, Sulphur, Calcium, etc.
What is Soil
The soil is the loose material on the earth’s surface which is made up of mineral material which comes from, weathered down rocks, organic material which comes from the excreta and remains of a living organism and decayed leaves of plants, soil air, and soil water.
Composition of the soil: Inadequately drained soil, liquid and gas occupy the pore spaces between soil particles. Soil is made up of 50% solid, 25% liquid, and 25% gas.
Types of soil
Soils are classified according to the size of the soil particles (international system). Also, Soils vary in color. The common colors of soils are red, yellow, brown, grey, and black. The brown, yellow, and red indicate the iron compounds present. In well-drained soils with iron the color is red. In poorly drained soils with iron the color is yellow or brown. The dark-colored soils have organic matter. Black soils have a mixture of limestone and humus, while grey soil is most times waterlogged.
Soil is classified into four types:
- Sandy soil.
- Silt Soil.
- Clay Soil.
- Loamy Soil.
|Types of soil||Sizes (mm)|
|Clay||Less than 0.002|
|Sandy||2.0 – 0.2|
|Loamy||0.2 – 0.02|
|Silt||0.02 – 0.002|
|Stone and Gravel||More than 2.0|
Clay soil is said to have a fine texture because of the fineness of the particles. The clay particles are plastic and very sticky when wet. Clay soils retain water and plant nutrients. The particles are tightly held together. However, water is easily retained in clay soils thus they are easily waterlogged during the heavy rainy seasons. Clay soil will feel smooth between the fingers.
Sandy soil is said to be coarse. The sand particles are gritty while the silt particles are smooth and powdery. Sandy soils are well-drained since the particles are loosely held. These soils cannot retain much water; thus, they are poor in plant nutrients. Strong winds can easily blow sandy soil particles away. Sandy soils need organic matter, fertilizer, and water regularly to maintain water and nutrients in the soil and promote plant growth. Sandy soil will feel gritty between the fingers.
Loamy soils is one of the common types of soil, they have a good crumb or granular structure and are favorable agricultural soils. They are fertile since the shape and size of the pore spaces are suitable for the retention of adequate air, water, and plant nutrients. It is a mixture of sand, clay, and silt. It contains more moisture, nutrients and humus compared to sandy soil and better drainage compared to clay and silt soil. It has the right water holding capacity needed for the growth of plants.
Silty soil is slippery when wet, not grainy or rocky. They have medium water holding capacity and their permeability is low to moderate. Silt is made up of rock and mineral particles that are larger than clay but smaller than sand.