Types of Soil: Characteristics and Importance


Types of Soil: Characteristics and Importance

We will deals mainly with various types of soil. You will recollect that agricultural practices without appropriate soil requirements will give poor rewards to farmers. Proper soil composition with efficient management will definitely lead to bumper harvest. This is because the soil itself is the basis of farming.

A soil type is a taxonomic unit in soil science. All soils that share a certain set of well-defined properties form a distinctive soil type. Soil type is a technical term of soil classification, the science that deals with the systematic categorization of soils. Every soil of the world belongs to a certain soil type.

Definition of Soil

Soil can be defined as the loose material covering the surface of the earth which supports life and is the basis of farming. Soil is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. 

The soil itself is a natural body consisting of layers or horizons of minerals which differ in their characteristic, physical, chemical and mineralogical components. This is but the merit component of the soil. The active component comprises of some micro-organisms that belong to the families of soil flora (plants) and fauna (animals). Together with the soil is, therefore, a natural medium for the growth of crops.

Physical Characteristics of the Soil

The most important physical characteristics of the soil are soil texture and soil structure. Let us consider this, briefly.

1. Soil texture: This is the relative proportion of various fraction or particle sizes in a given soil. For instance, the basic particles of the soil are sand, silt and clay. The division of soil particle into these fractions is based on the size or diameter of the particle.

For example, soil particle is said to be:

a. Sand- if the diameter is between .002.02mm.

b. Silt -if the diameter is between .0 – 0.002mm

c. clay- if the diameter is less than 0.002mm.

2. Soil structure: If soil particles are left on their own without binding them together then farming will be impossible. Soil structure, therefore, explains the binding together of soil particles into soil aggregates. It is in the form of these aggregates that soil can support good growth of crops.

Importance of Soil Structure to Farmers

It is important that you understand the structure of the soil because of the following reasons:

1. Soil structure determines the physical properties of the soil- e.g. water and air content, as well as type and sizes of the pore in the soil.

2. It also influences the chemical properties, e.g. mineral composition, non-content, the level of exchangeable cat ion etc.

3. Soil structure also influences the rate of leaching and other processes of the translocation of soil articles e.g. erosion. This affects the amount of nutrient available for crop growth.

4. Soil activities also influence the biological activities in a given soil, for instance, the activities of soil micro-organisms that help in the decomposition of organic matters.


Major Components of the Soil

Here, we are going to consider the major components of the soil.

1. Inorganic matter- This include sand, clay silt, gravel, etc., which is about 45% of the total volume of the soil. It contains nutrients like nitrogen, calcium, magnesium, iron, etc., and holds water in the soil. It serves as anchor for plants and it is the home for soil organisms which may improve the growth of plants. It can also hold air for plants, as well as helping in moderating soil temperature; but the porosity of the soil can be affected by its mineral content.

2. Organic matter- Organic materials which are made up of plant and animals are about 5% of the total volume of the soil. It may be decayed plant and animal products leading to the formation of humus; it is a rich source of plant nutrients. The total number of soil micro-organism- like bacteria, fungi, can be increased, while the texture and structure of the soil can be improved. Water holding ability of the soil can also be improved and the PH of the hydrogen ion concentration can be moderated. It prevents soil erosion.

3. Soil air- This is the amount of gases found inside the soil. The amount of air is inversely proportional to the amount of water in the- soil which is about 25% of the total volume of the soil. It is essential for respiration of soil micro-organisms, and helps in the absorption of plant nutrients. It is very essential for root development; and it is needed for respiration of the root. It is also required for seed germination and needed in nitrogen and carbon cycles.

Oxygen is necessary for growth and development, while carbon dioxide and sulphur react with water to form weak acids which aid weathering of rocks.

4. Soil water- this is the amount of water in the soil, and that is available to plant; and it is about 25% (in volume) in the soil. Soil nutrients are dissolved by water and this aids root absorption. It is essential for plant metabolism e.g. transpiration, photosynthesis, translocation. It is also influenced by the physical properties of the soil.

The water under the influence of gravity is called gravitational water. It is essential in the tillage and improvement of soil structure.

However, you should please take note of the following:

a. Avoid tampering with soil pores, ploughing should be done only when the soil is moist, but not wet.

b. Only minimum pulverisation (harrowing) is permitted and to avoid the reduction of medium and large pores and increasing small pores.

c. Ploughing in succulent thrash/plants should be encouraged to aid microbial activities and encourage aeration.

Available water to plant

Available water to any growing crop plant depends on:

1. - The structure and texture of the soil

2. - The humus contents of the soil

3. - The composition of ions or cat ions in the soil

4. - The amount of silt in the soil, especially in the tropical region.


Chemical Characteristics of the Soil

The types of minerals present in the soil confer on the oil some distinct chemical characteristics. For instance, if hydrogen ions (H+ ) and aluminum ions (A13 ) + predominate in a soil, the soil is bound to be acidic; but if it is hydroxyl ion (OH) that is common, the soil is alkaline or basic.

When both hydrogen ions (H+ ) and hydroxyl ions (OH) are of equal proportion, the soil is neutral. An instrument known as the PH scale is used to measure the chemical reaction of the soil-whether the soil is acidic, alkaline or neutral.

Soil PH affects the nutrients available to plants. Some crops are tolerant to acidic soils- e.g. oil palm, but majority of crops plants will perform best under slightly acidic to neutral conditions.


Types and Properties of Soil

There are three major types of soil properties, sandy, clay, and loamy.

Let us take a look at these.

1. Sandy soil:  It is made up of quartz; the range in diameter is between 2.00mm and 0.02mm, and it is coarse grained and gritty. Sandy soil is well drained, loose and highly aerated, with low capillary actions and high percolation feature. Leaching is high, with low plant nutrients. Therefore, sandy soil does not support the growth of plants because there is little or no nutrients required by plants for good growth.  

2. Clay soil:  Clay has very good chemical properties but poor physical properties. It is rich in nutrients, but because of its adhesive nature, the nutrients are not readily available to plants. The high water holding capacity makes percolation low and leaching may not be possible. Capillary is very high when wet. The particles are tightly bound together with little poor spaces; while the colour is usually brown.

3. Loamy Soil: This is a soil that combines the three panicles of sand, silt and clay in suitable proportion and therefore is the best soil type for cropping. It is very rich in plant nutrients and has loose particles. It can withstand moderate period of drought, because percolation is low and capillary is high. The lumps of loam fell apart easily and so they are friable. Loams are classified as heavy, light or medium, according to the proportion of clay present.

Its water-holding capacity is very high, while erosion and water-logging are not usually possible. Loam can also contain decayed organic matter or humus. The colour varies from brown to dark brown or even black.


Special categories of soil

These are the soil particles which cannot easily fit into the above three particles, but they are a combination of one or two, or all the above soil particles. They arc silt, silt-loam, clay-loam, medium and heavy clay and silt-clay.

Conclusion on Types of Soil: Characteristics and Importance

We really highlighted to you the various types of soil with their characteristics which range from soil texture to soil structure.

We have exposed you to the characteristics of each soil; it has also highlighted the importance of soil to successful farming. The point has been affirmed that if soil is fertile and managed properly, yield will be bountiful.

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