MINISTRY OF AGRICULTURE, LIVESTOCK AND FISHERIES
STATE DEPARTMENT OF LIVESTOCK
DIRECTORATE OF VETERINARY SERVICES
ANIMAL HEALTH AND INDUSTRY TRAINING INSTITUTE
NDOMBA
CERTIFICATE IN ANIMAL HEALTH AND PRODUCTION
(LECTURE NOTES 2022)
COURSE CODE: 0811 451 08/A COURSE TITLE: SOIL SCIENCE
LH –30; PH – 15; TH – 45 CF= 2.5 LECTURER: MR. KARUGA J. M
Objective
This subject is intended to provide the trainee with knowledge on basic properties and characteristics of the soil as an important
base for both crop and livestock production.
Julius M Karuga- Director Curriculum Development & Human Resource Management
,1.0 Soil Origin 6 hrs
By the end of the topic the trainee should be able to:
a) Define soil.
It a natural material composed of weathered rock minerals and organic matter on
the uppermost layer of the earths crust
b) Explain the process of soil formation:-
i) List the broad categories of soil forming rocks
IGNEOUS ROCK: They are rock made from molten material (magma or lava). This material is exuded at
high temperature from the interior region of earths crust to the surface where it cools and solidifies. Major
igneous rocks include: silicate materials such as micas , feldspars and quartz
METAMORPHIC ROCK: These rocks may be derived from metamorphic or existing sedimentary or
igneous through the action of intense heat and pressure and a number of chemical changes within the earths
crust. When metamorphosis take place limestone is changed into marble, sandstone into quartzite and
igneous rocks into schists and gneisses.
SEDIMENTARY ROCK: These are formed from weathered material of other rocks. The sediments are
transported and deposited at the bottom of prehistoric seas, lakes and lower slopes of the landscape. The
materials become cemented and hardened into rocks e.g. Quartz into sandstone, while limestone is a product
of transformed and cemented accumulation of shells of see animals and the fine textured clay sediments form
a arrange of clay soils.
ii) Define weathering
It is the breakdown and disintegration of solid rock into tiny particles by physical, chemical and biological
means.
iii) Differentiate between Physical/ mechanical and chemical weathering
iv) State the physical, chemical and biological agents of weathering
Physical weathering: it involves the splitting of rocks into small fragments without any change in chemical
composition.
Agents of physical weathering include: wind, water, temperature, moving ice and glaciers
a) Wind: strong winds carry materials which hit against each other making the surfaces of the materials to
break off into small fragments. They can also crumble rock surfaces especially where they are already
weakened by chemical or biological means.
b) Water: as rain drops hit the ground they have some force which erodes the surfaces. Running water of
rivers wash the rock particles which hit against each other causing further crumbling. They also have an
abrasive effect on the surfaces.
c) Moving ice and glaciers: Rocks are split by movement of huge blocks of ice and by freezing and thawing
of water in cracks in the rocks.
d) Temperature: Extreme heat and cold can cause changes in the structure of the rocks that leads to splitting
and crumbling e.g. exfoliation in deserts causing rocks to flake off.
Chemical weathering: It involves a change in chemical composition and thus the original structure of the rocks.
Agents of chemical weathering
Solution: Water dissolves any soluble mineral in the rocks and the removal of minerals weaken the rock structure so
that it crumbles easily
Hydrolysis: weak acids react with minerals in the rock and dissolves out e.g.
H2O +CO2 H2CO3
H2CO3 + Ca2CO3 Ca (HCO3)2
Julius M Karuga- Director Curriculum Development & Human Resource Management
, Hydration: Water acts on minerals to form crystals which contain water. The crystals weakens the rock structure
Oxidation: The atmospheric oxygen and free oxygen contained in rain water converts the rock minerals to oxides.
These oxides usually take up more space and thus help break up the rocks. The red and brown colour of many
tropical soils is a diagnostic feature.
Carbonation: This is a process by which the carbonate and hydrogen carbonate ions combines with rock minerals.
Carbonation is particularly important in limestone regions where carbonates are dissolved. And in the process
potassium, magnesium and lime found in these rocks are released.
Biological weathering:
Agents of biological weathering include: Plants and animals
a) Animals: Heavy animals exert pressure and set up vibrations on the rocks causing them to disintegrate. This effect is
also produced by a variety of human activity e.g. mining and quarrying
b) Plants: Bacteria and fungi initiating breakdown of plants tissue on the soil surface within the soil. Roots of growing
vegetation force their way into cracks on the rocks and exert pressure which eventually split the rocks.
v) Explain the factors that influence soil formation
Parent material: The rock material influences the physical properties and chemical constituents of then
soil. The rock material defines the soil properties such as colour, texture, structure and the nutritive value of
the soil e.g. the granite and sandstone give rise to coarse sand soils while the basalt give rise to fine grained
alkaline clayey soil.
Climate: Factors such as rainfall, temperature , wind and sunshine affects the weathering process and the
movement of rock particles e.g. increase in temperature increases the rate of chemical reactions and the
activity of the micro organisms in soil forming process e.g. the decomposition . Wind will act as transport
agent and carries weathered material.
Topography:
The slope of the land affects the depth and distribution of soil and nutrients within it which it tends to wash down the slope
forming rich alluvial soils in the valleys.
Topography influences the movement of products of weathering consisting of soluble substances and solid soil particles
Time: Time required for the formation of a soil from a particular parent material varies greatly depending
on the conditions. Where the soil forming process have taken a long period , deep mature soil can be found
if other factors favour the development.
Vegetation:
it contributes organic matter for the soil in the form of fallen leaves, fruits, flowers, roots and dead plants.
Closely intermeshed root system of the grasses hold the soil surface together to prevent damage by wind and rain
LIVING ORGANISMS: BOITA/BIOSPHERE
Lichen are the first plants to colonize bare rocks and as weathering proceeds, plants and hollow spaces appear, and seeds of
other plants will take root and start growing. This assist the process of weathering and breakdown rock surfaces into finer
particles.
Animals such as ants and termites are of great significance in tropical areas for their maintenance of suitable physical and
chemical condition in the soil for plant growth.
c) Define soil profile
It is the vertical cross section through the soil showing various soil layers which differ in colour, texture and structure
d) Describe soil profile
Julius M Karuga- Director Curriculum Development & Human Resource Management
STATE DEPARTMENT OF LIVESTOCK
DIRECTORATE OF VETERINARY SERVICES
ANIMAL HEALTH AND INDUSTRY TRAINING INSTITUTE
NDOMBA
CERTIFICATE IN ANIMAL HEALTH AND PRODUCTION
(LECTURE NOTES 2022)
COURSE CODE: 0811 451 08/A COURSE TITLE: SOIL SCIENCE
LH –30; PH – 15; TH – 45 CF= 2.5 LECTURER: MR. KARUGA J. M
Objective
This subject is intended to provide the trainee with knowledge on basic properties and characteristics of the soil as an important
base for both crop and livestock production.
Julius M Karuga- Director Curriculum Development & Human Resource Management
,1.0 Soil Origin 6 hrs
By the end of the topic the trainee should be able to:
a) Define soil.
It a natural material composed of weathered rock minerals and organic matter on
the uppermost layer of the earths crust
b) Explain the process of soil formation:-
i) List the broad categories of soil forming rocks
IGNEOUS ROCK: They are rock made from molten material (magma or lava). This material is exuded at
high temperature from the interior region of earths crust to the surface where it cools and solidifies. Major
igneous rocks include: silicate materials such as micas , feldspars and quartz
METAMORPHIC ROCK: These rocks may be derived from metamorphic or existing sedimentary or
igneous through the action of intense heat and pressure and a number of chemical changes within the earths
crust. When metamorphosis take place limestone is changed into marble, sandstone into quartzite and
igneous rocks into schists and gneisses.
SEDIMENTARY ROCK: These are formed from weathered material of other rocks. The sediments are
transported and deposited at the bottom of prehistoric seas, lakes and lower slopes of the landscape. The
materials become cemented and hardened into rocks e.g. Quartz into sandstone, while limestone is a product
of transformed and cemented accumulation of shells of see animals and the fine textured clay sediments form
a arrange of clay soils.
ii) Define weathering
It is the breakdown and disintegration of solid rock into tiny particles by physical, chemical and biological
means.
iii) Differentiate between Physical/ mechanical and chemical weathering
iv) State the physical, chemical and biological agents of weathering
Physical weathering: it involves the splitting of rocks into small fragments without any change in chemical
composition.
Agents of physical weathering include: wind, water, temperature, moving ice and glaciers
a) Wind: strong winds carry materials which hit against each other making the surfaces of the materials to
break off into small fragments. They can also crumble rock surfaces especially where they are already
weakened by chemical or biological means.
b) Water: as rain drops hit the ground they have some force which erodes the surfaces. Running water of
rivers wash the rock particles which hit against each other causing further crumbling. They also have an
abrasive effect on the surfaces.
c) Moving ice and glaciers: Rocks are split by movement of huge blocks of ice and by freezing and thawing
of water in cracks in the rocks.
d) Temperature: Extreme heat and cold can cause changes in the structure of the rocks that leads to splitting
and crumbling e.g. exfoliation in deserts causing rocks to flake off.
Chemical weathering: It involves a change in chemical composition and thus the original structure of the rocks.
Agents of chemical weathering
Solution: Water dissolves any soluble mineral in the rocks and the removal of minerals weaken the rock structure so
that it crumbles easily
Hydrolysis: weak acids react with minerals in the rock and dissolves out e.g.
H2O +CO2 H2CO3
H2CO3 + Ca2CO3 Ca (HCO3)2
Julius M Karuga- Director Curriculum Development & Human Resource Management
, Hydration: Water acts on minerals to form crystals which contain water. The crystals weakens the rock structure
Oxidation: The atmospheric oxygen and free oxygen contained in rain water converts the rock minerals to oxides.
These oxides usually take up more space and thus help break up the rocks. The red and brown colour of many
tropical soils is a diagnostic feature.
Carbonation: This is a process by which the carbonate and hydrogen carbonate ions combines with rock minerals.
Carbonation is particularly important in limestone regions where carbonates are dissolved. And in the process
potassium, magnesium and lime found in these rocks are released.
Biological weathering:
Agents of biological weathering include: Plants and animals
a) Animals: Heavy animals exert pressure and set up vibrations on the rocks causing them to disintegrate. This effect is
also produced by a variety of human activity e.g. mining and quarrying
b) Plants: Bacteria and fungi initiating breakdown of plants tissue on the soil surface within the soil. Roots of growing
vegetation force their way into cracks on the rocks and exert pressure which eventually split the rocks.
v) Explain the factors that influence soil formation
Parent material: The rock material influences the physical properties and chemical constituents of then
soil. The rock material defines the soil properties such as colour, texture, structure and the nutritive value of
the soil e.g. the granite and sandstone give rise to coarse sand soils while the basalt give rise to fine grained
alkaline clayey soil.
Climate: Factors such as rainfall, temperature , wind and sunshine affects the weathering process and the
movement of rock particles e.g. increase in temperature increases the rate of chemical reactions and the
activity of the micro organisms in soil forming process e.g. the decomposition . Wind will act as transport
agent and carries weathered material.
Topography:
The slope of the land affects the depth and distribution of soil and nutrients within it which it tends to wash down the slope
forming rich alluvial soils in the valleys.
Topography influences the movement of products of weathering consisting of soluble substances and solid soil particles
Time: Time required for the formation of a soil from a particular parent material varies greatly depending
on the conditions. Where the soil forming process have taken a long period , deep mature soil can be found
if other factors favour the development.
Vegetation:
it contributes organic matter for the soil in the form of fallen leaves, fruits, flowers, roots and dead plants.
Closely intermeshed root system of the grasses hold the soil surface together to prevent damage by wind and rain
LIVING ORGANISMS: BOITA/BIOSPHERE
Lichen are the first plants to colonize bare rocks and as weathering proceeds, plants and hollow spaces appear, and seeds of
other plants will take root and start growing. This assist the process of weathering and breakdown rock surfaces into finer
particles.
Animals such as ants and termites are of great significance in tropical areas for their maintenance of suitable physical and
chemical condition in the soil for plant growth.
c) Define soil profile
It is the vertical cross section through the soil showing various soil layers which differ in colour, texture and structure
d) Describe soil profile
Julius M Karuga- Director Curriculum Development & Human Resource Management
