Soil science

SOIL SCIENCE

Soil is the loose part of the earth’s crust that can support plant growth.

Importance of soil

 It serves as habitat for some living organisms

 It provides the nutrients requirement of plants

 It supports plants growth

Factors that influence the formation of soil

·         Topography of the land

·         Climate

·         Living organisms

·         Time

·         Human influence

·         Parent rock materials

  

COMPONENTS OF SOIL

Mineral components (it consists of salt, silt and clay)

Soil water

Soil air

Organic matter

Soil Living organisms

PHYSICAL PROPERTIES OF SOIL

Soil Texture: This refers to the degree of coarseness or the fineness of the soil particles

Soil Structure: This refers to the way in which the different soil particles are arranged. It gives the physical appearance of the soil.

Water Holding Capacity: This is the measure of the ability of soil to retain water. It determines drainage through the soil.

Characteristics	Sand	Clay	Loam
Particle size	Large	Small	Intermediate
Texture	Coarse- feels gritty when wet	Fine- feels sticky when wet	Intermediate
Air Space	Large	Small	Intermediate
Water Retaining Capacity	Low	High	Intermediate
Porosity	High	Low	Intermediate

SOIL PROFILE

This refers to the vertical cross-section of the soil which shows all the layers of the soil particles.

Characteristics of each layer/ horizon

1.      Topsoil/Horizon A

It is rich in organic matter and microbes

It is dark in colour

Nutrients here can be leached to the sub-soil

It is usually less thick than sub-soil

2.      Sub-soil/ Horizon B

It contains less organic matter and microbes

Relatively thicker and less dark than the top-soil

It is usually reddish-brown in colour

Nutrients leached are deposited here

3.      Horizon C

It contains no organic matter and microbes

It contains weathered materials

Soil minerals occur in this layer

4.      Horizon D

It contains rocks which have not undergone weathering

It contains no organic matter and microbes

IMPORTANCE OF SOIL PROFILE

·         It helps to determine the nutrient content of a soil

·         It helps to determine the soil type of a particular land

·         It helps the farmer to determine the crop suitable for a particular land

·         It helps to determine the susceptibility of a land to soil erosion

·         It enables the farmer to know the type of implement to use.

SOIL FERTILITY AND SOIL PRODUCTIVITY

A fertile soil is one that can provide adequate conditions and nutrients for effective growth of plant.

Features of a fertile soil:

It is rich in soil nutrients and organic matter

It must contain useful soil organisms

It must have a good water holding capacity

It must have a suitable Ph

The texture must be loamy

SOIL FERTILITY

This refers to the ability of soil to provide physical conditions and nutrients required for effective growth of a plant.

SOIL PRODUCTIVITY

This refers to the ability of soil to provide desired yield in the cultivation of a given plant when properly managed.

LOSS OF SOIL FERTILITY

The following are some of the ways through which a soil can lose its fertility:

Crop removal

Leaching

Erosion

Bushfires

Overgrazing by cattle and other farm animals

Poor farming and tillage methods

Surface mining and quarrying

MAINTENACE OF SOIL FERTILITY

In order to avoid soil losing its fertility, the farmer can undertake or carry out any of the following to preserve the fertility of the soil.

Growing of cover crops

Practicing crop rotation

Application of organic and inorganic fertilizers

Adding lime top the soil

Practicing fallow cropping

Strip cropping: This refers to the planting of crops along the contours of slope

Terracing: This refers to leveling of hilly areas in the form of steps.

Practicing mixed farming and mixed cropping

PLANT NUTRIENTS

These are substances that plants require in various quantities in order to grow. There are two types of nutrients. These are macronutrients and micronutrients.

a.       Macronutrients: These are the nutrients required in large amount for proper growth of the plant. Example Nitrogen (N), Potassium (K), Phosphorus (P), Calcium (Ca), Magnesium (Mg) and Sulphur (S).

b.      Micronutrients: These are the nutrients required in small amounts to support the growth of the plant. Example Boron (B), Manganese (Mn), Chlorine (Cl), Zinc (Zn), Copper (Cu) and Iron (Fe).

SOME ESSENTIAL NUTRIENTS FOR PLANT GROWTH

Nutrients	Functions	Deficiency
Nitrogen	Formation of proteins and chlorophyll	-          Small sized plants -          Poor development -          Yellowing of leaves
Phosphorus	Formation of energy compounds and acts as a buffer in the cell sap	-          Poor root development -          Small sized plants -          Mottling (colours of different shades)
Potassium	Formation of cell membranes and regulates certain metabolic processes in the cell	-          Red leaf coloration -          Weak plants -          Poor growth
Magnesium	Formation of chlorophyll	Yellowing of leaves
Iron	Formation of chlorophyll	Yellowing of leaves
Sulphur	Formation of protein	Slender stems and yellowing of leaves
Calcium	Formation of cell walls	-          Stunted growth -          Poor roots development