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Factors Infuencing Agriculture

Factors Infuencing Agriculture
As noted in previous lesson, agriculture has become a common human activity that requires scientific research and discoveries for sustainability. This is because of many factors influencing agricultural production.

The four main factors influencing agricultural production include;

  • Human factors
  • Biotic factors
  • Climatic factors
  • Edaphic(soil) factors

Human factors that influence agricultural production. 


Good and efficient road infrastructure improved accessability
to the remote areas


The improvement of technology in communication has improved farmers access to important information from the research stations and the market.


Good transport to and from the farm is important in efficient farming

Market forces 

The price of agricultural goods in the market are dictated by the amount of goods available (supply) and the amount of goods required by the consumers (demand).

Cultural and Religious beliefs

These are customary and Religious values which restrict farmers in adopting certain practices or producing certain enterprises.


Keeping large herds of low quality animals under extensive system as a sign of prestige.

Factors Infuencing Kenyan Economy

This lesson will cover both human and biotic factors


1. Human factors: These are factors in human beings, created or made which influence the way they carry out farming activities.

2. Biotic factors: These are living organisms which affect the quality and quantity of agricultural products.

3. Level of education: It is necessary of equip the farmers with correct knowledge which will allow them to carry out farming practices

4. Technology: This is use of applied sciences such as engineering to improve agricultural productivity.

5. Health:This is the state of being physically, mentally, economically and socially well or fit.

6. H.I.V: Human Immuno Deficiency Virus. 

AIDS: Acquired Immunedeficiecy Syndrome

7. Economy: Proper use of a countries wealth to generate more wealth

8. Liberalization : Making the market free for all the willing buyers and sellers.

9. Communication: A way of passing important information

10. Markrt Forces: -The tendency to sell and buy commodities in the market which is influenced by the consumers desire and ability to buy or sell.

11. Government Policy-These are guidelines or statements of ideal proposed by the government that influence the way of doing things.

12. Cultural Beliefs - Customary values of a particular group that control their way of life.

13. Religious Beliefs-A particular system of faith that controls ones life.

14. Pests:-A destructive organism

Biological control of Aphids Mealy Bugs feeding on Aphids

15. Decomposers: Organisms which causes decay.

16. Pathogens: These are disease causing micro-organisms

17 . Parasites: An organism which depends on another without benefiting it.

18. Predators: These are organisms that kill others and feed on them e.g. wild cat

19. Pollinators: Are organisms which transfer pollen grains from one flower to another

20. Nitrogen Fixing Bacteria: These are micro-organisms in the soil which convert atmosphere nitrogen into nitrates which are available for use by the crops.

Project Work

1. Organize a visit to a nearby farm and identify the human factors which;

  • Improve Agricultural production
  • Lower agricultural Production

2. Organize a practical where the learners will;

  • Observe the effects of various pests and parasites within the school farm

  • List and collect storage pests in a school food store.

Human and Biotic Factors

Lesson Objective

By the end of this lesson you should be able to;

(i) explain human factors influencing agriculture

(ii) explain biotic factors influencing agriculture.

Human factors

Packing of tea leaves for export

Availability of ready market for agricultural produce
controls human factors for production

Biotic factors

Pest and parasite
affect quality and quantity of
agricultural produce

Climatic factors

weather pattern affects distribution and production of crops and animals.

Rainfall,Temperature, Wind and Light can be controled by human to improve agricultural production

Edaphic factors

Good soil management can improve agricultural production

Factors Influencing Agricultural Production

Human factors include all those aspects of human beings that lead either to increased or decreased agricultural production. They may influence agriculture either directly or indirectly.
For example, availability of ready market for agricultural produce enables the farmers to gain from their work. This improves the overall activities performance in farming.

The above factors influencing agricultural production can be classified into the following categories;

Factors which improve production

  • Good health of the farmer
  • Availability of money
  • High taxation on imported agricultural produce
  • Availability of ready market for agricultural produce
  • Availability of storage facilities
  • Liberalized market

Factors which lower production

  • Restrictive cultural and religious beliefs

  • Poor road network

1. Level of education and technology

This is translated as the ability of a producer who is a farmer to apply appropriate methods and techniques in production using available resources for example

Farmer weighing livestock food to ensure efficiency

Farming techniques

Mechanized harvesting of wheat

Good education level makes a farmer able to understand and translate technical language in farming.


A healthy nation is a productive nation

The following are some of the diseases that contribute to lowering agricultural productivity

  • Malaria,
  • Tuberculosis,
  • Typhoid,
  • Pneumonia and HIV/AIDS

Effects of HIV/AIDS on farming

  • Loss of skilled labour
  • Time spent caring for the infected
  • Money spent on treatment 

Healthy workers are productive

How does HIV/AIDS affect farming in your area?

Human Factors

They are factors in human beings or the way human beings do things.
The following is a list of human factors that influence agricultural production.

  • Levels of education and technology

  • Health of the farmers

  • State of economic development

  • Transport and communication network

  • Government policy on agricultural input and produce taxation
  • Availability of storage facilities

  • Cultural and religious beliefs.

  • Local and International market forces

Agriculture is a foreign exchange earner

he capital earned from economic activities such as farming is used to raise economic growth in the country.

Good Communication Network

Good and efficient infrastructure is important for the smooth flow of farm produce from the farm to the consumer.

Improving rural roads through tarmacking

The improvement of technology in communication has improved farmers access to important information from the research stations and other fellow farmers

Government policy

he government of Kenya, through different ministries formulates guidelines to be followed by producers of different products. After the guidelines and proposals are legislated they become policies

Biotic factors Influencing Agricultural Production

These are living organisms that affect agricultural production.

Biotic factors influencing agriculture can be divided into the following classes.
Crop pests:
stalk borer damaging maize in the field

Livestock parasites:
suck blood and transmit diseases to animals


Causes diseases in livestock and crops thereby lowering quality of produce.Increase cost of production when control measures are implemented.Introduce toxic substances into agricultural products thereby lowering the quality of the produce.Can cause death to crops and animals.

Fungal infection

Fungi can damage maize when drying among other crops


Eagle can eat chiken, rabbits among other livestock.
Eagle can aso eat insects and pests for example rats, moles and birds which destroy crops.

Bee pollinating maize flower. Pollination in crop production increases yields and viability of seeds.

Nitrogen fixing Bacteria

Nitrogen fixing bacteria are found in root nodules of leguminous plants. Improve crop production through increasing soil nitrogen content which crops require for proper growth.

Effects of Biotic Factors on Agricultural Production

1. Pests

  • Feed on crops thereby lowering quantity of agricultural produce.
  • Feed on grains thereby affecting viability of the seeds
  • Act as disease vectors
  • Lower palatability of crop produce
  • Increase cost of production when control methods are applied
  • Create entry points for disease causing organisms

2. Parasites

  • Irritate livestock
  • Causes anemia in livestock
  • Some block alimentary canal
  • Lower rate of production in livestock
  • Increase cost of production when controlled
  • Some lower quality of hides and skins
  • Some absorb food meant for the livestock thereby lowering the level of production.
  • Some for example ticks transmit disease causing organisms.

3. Decomposers

  • Cause rotting of organic matter there by releasing nutrients for crop growth
  • Help in improving soil structure through incorporating organic matter into the soil.

Factors Influencing Agriculture.

The following are maps of Kenya showing land potential (crops & livestock distribution in Kenya)

Scroll the mouse on the map to see the average temperature of the area

Amount of rainfall (precipitation) received in different areas of Kenya determines types of crops to be grown in different parts of the country

Land potential is based on research developments done by famers and Kenya Agricultural Research Insititutes (KARI)centers

Factors Influencing Agriculture


Rainfall Intensity: This is the amount of rainfall in an area in a given period of time

Rainfall reliability: This is the timeliness and dependency of rainfall in crop production.

Rainfall amount (quantity): This is the amount of rainfall received in an area over a specific period of time.

Rainfall distribution: This refers to the number of times rainfall is experienced in an area.

Topography:This refers to the features of a place.

Evapotranspiration: This is the process by which water which is lost by the plant through transpiration is evaporated from the surface of the leaves.

Light intensity: This is the strength in which light hits the surface of the earth.

Light duration: This is the period of time the plants are exposed to light.

Photoperiodism: This is the response of plants toward light duration.

Long-day plants: These are plants which require more that 12 hours of lighting to flower and produce fruits or seeds.

Short-day plants: These are plants which require less than 12 hours of lighting to flower and produce e.g Rice, tobacco

Day-Neutral plants: These are plants which produce flowers regardless of the duration of lighting they have been exposed to e.g Beans, Sorghum

Light wavelength: This refers to the type or quality of light. A wavelength is the distance between two corresponding points of a light wave.

Accountability: A principle through which individuals, organisations and the community are responsible for their actions and may be required to explain them to others.

Afforestation: The process of planting trees and/or seeds in areas not previously forested.

Agroforestry: Combines agriculture and forestry technologies to create more integrated, diverse, productive, profitable, healthy and sustainable land use systems.

Agropastoralism : A livelihood that is based on land use that incorporates both settled crop agriculture and the tending of animals that are moved from place to place.

AIDS : Acquired Immuno-Deficiency Syndrome (AIDS) is a disease characterized by the destruction of the human immune system. Although there are treatments to hinder the progress of AIDS, there is no known cure or vaccine. UNAIDS and the World Health Organization (WHO) estimate that AIDS has killed more than 25 million people since it was first recognized on December 1, 1981, making it one of the most destructive pandemics in recorded history. In 2005 alone, AIDS claimed between an estimated 2.8 and 3.6 million people, of which more than 570,000 were children.

Algae: A simple, photosynthetic plant usually inhabiting moist or aquatic environments.

Allochthonous: Material introduced into rivers from terrestrial environments. Examples include leaves or branches from trees that fall into a river.

Ambient environmental standards: Standards used to set limits to which levels of environmental resources may be permitted to fall.

A flowering plant.

Arid (Aridity)
An arid environment has a high precipitation deficit, receiving much less precipitation annually than would satisfy the climatological demand for evaporation and transpiration. This is mainly due to the high temperatures and few storms bringing rainfall. Regions are classified as arid if their aridity index falls between 0.05 and 0.20.

A river basin includes the river channel and surrounding drainage area that is, the land and tributaries that drain precipitation falling within this area to the river.

A tropical disease spread by parasitic worms living in fresh water, hosted by snails, that can cause rash or itchy skin, fever, chills, muscle aches, and possible damage to the liver, intestines, lungs, and bladder. Also known as schistosomiasis.

Refers to the variety of life on earth. The most widely accepted definition of biodiversity is found in Article 2 of the Convention on Biological Diversity: Biological diversity means the variability among living organisms from all sources including, inter alia, terrestrial, marine and other aquatic ecosystems and the ecological complexes of which they are part; this includes diversity within species, between species and of ecosystems.

A thin layer of biotaincluding algae, fungi, bacteria, and other invertebratesthat forms on river substrate.

A process in which concentrations of certain compounds found in tissues of organisms increase in successive levels of the food chain.

The mass of all living and dead organic matter in an ecosystem. In certain contexts, the term biomass may also refer only to the mass of living organisms in an environment.

The biological and physical components of the environment .

Capacity building
Activities undertaken to develop certain skills or competence, or for upgrading performance ability.

An animal that feeds on other animals.

Carrying capacity
The extent to which an ecosystem or resource can withstand pressure from external forces such as degradation, climate variability, development and internal use.

Cascade interaction
Occurs when one group of organisms indirectly affects another group by feeding on the animals that would have eaten them.

The long - term average of weather in a particular region.

Cold Cloud Duration (CCD)
Provides an estimate of rainfall by counting the number of hours that cold precipitation clouds (-40 C) are present over a given area for a fixed period of time.

Consume fine to very fine organic particles suspended in the water (filtering collectors or filter-feeders) or deposited on the stream bed (collector-gatherers).

Common pool resource
A resource from which it is not feasible to exclude users, and for which consumption is subtractive. Incentives to improve individual welfare by overusing common pool resources can lead to depletion of the resource for all. An example of a common pool resource is a common grazing pasture or an unregulated lake fishery.

Common property resources
Renewable natural resources with the characteristics of a common pool resource (i.e., subtractive consumption, difficult to exclude users) but to which access is controlled in some manner, typically by the group or unit that manages the resource.

Convective rainfall
The formation of precipitation due to surface heating of the air at the ground surface. With sufficient heating, the mass of air becomes warmer and lighter than the air in the surrounding environment, and begins to rise, expand and cool. Saturation occurs after sufficient cooling, and leads to precipitation.

Convention on Biological Diversity (CBD)
An agreement signed by 150 world leaders at the 1992 Earth Summit in Rio de Janeiro. The goals of the CBD include the conservation of biodiversity, the sustainable use of its components, and the fair and equitable sharing of the benefits from genetic resources.

Critically endangered
Facing an extremely high risk of extinction in the wild.

Cultural Diversity
A result of cultural adaptations and livelihoods that are created through linkages between languages, social systems, customs knowledge systems, local histories and interaction with the environment.

A large and diverse group of bacteria capable of photosynthesis. Also known as blue-green algae.

A range of 10-years time-period.

The conversion of forested area to non-forested area through the removal of trees.

A reduction in the biological productivity of an area of land.

A form of government where the population of a society or country controls the government through a process where ministers and leaders are elected through free and fair elections.

Aquatic animals that consume fine particles of organic matter found on and within the bottom sediments.

The increase of desert-like conditions caused by degradation on arid, semi-arid and subhumid lands.

Organisms that consume dead organic matter.

Dead organic matter; the particulate remains of dead plants and animals.

Earth Observation (EO)
EO is the study of Earth and its changing environment by observing the atmosphere, oceans, and land through remote sensing technologies.

The scientific study of: 1) the interactions or relationships between organisms and their environment, 2) the interactions that determine the distribution and abundance of organisms. 

An interacting ecological unit comprising the biotic community and abiotic environment within a defined area.

Ecosystem diversity
Refers to the variety of identifiable ecosystems in which organisms live.

Ecosystem Goods & Services
Benefits derived from ecosystems. Goods provided by ecosystems are usually more tangible benefits such as food products, fuel wood, drinking water or timber. Ecosystem services are usually enabling benefits that people obtain from ecosystems and include provisioning services; regulating services; supporting services; and cultural services.

Ecosystem health
A concept that uses a systematic approach to the preventative, diagnostic, and prognostic aspects of ecosystem management, and to the understanding of relationships between ecosystem health and human health. It seeks to understand and optimize the intrinsic capacity of an ecosystem for self-renewal while meeting reasonable human goals. It encompasses the role of societal values, attitudes and goals in shaping our conception of health at human and ecosystem scales (University of Western Ontarios Ecosystem Health group).

Ecosystem services
The goods (tangible resources) and services (functions) provided by an ecosystem.

Ecosystem services
The goods (tangible resources) and services (functions) provided by an ecosystem.

Groups and communities of organisms (animals, plants, insects and micro-organisms) that form one functioning unit. It also includes all of the non-living physical and chemical factors of the environment that maintain its existence, linked together through nutrient cycling and energy flow.

An area of transition or overlap between two habitat types.

An outflow of liquid waste released from a facility such as a sewage treatment plant or industrial operation.

Facing a very high risk of extinction in the wild.

Occurring naturally in only one specific area.

Environmental Education and Awareness (EE&A)
A process designed to increase public awareness and understanding of the community of interest and the common ecospace that the Nile River creates.
Environmental Effects Monitoring - The repetitive and systematic measurement of environmental components to test specific hypotheses regarding the effects of human activity on the environment.

Environmental Impact Assessment
A procedure that examines the possible environmental consequences of implementing a project, program, or policy.

Environmental management
The management of human interaction with and impact on the natural environment. Environmental management is concerned with the links between the natural world and human social, cultural, and economic systems.

Environmental management plan
A plan outlining the means of achieving environmental objectives and goals.

Environmental Mitigation Compliance Monitoring
Monitoring conducted to determine whether specified environmental mitigation measures are being implemented properly and are having the intended effect. 

Environmental monitoring
The collection of systematic, geo-referenced observations of the environment to detect changes over time and space.

Equatorial Lakes Plateau
An elevated plateau bounded by two branches of the Rift Valley.

The equity dimension of governance seeks to ensure that development is inclusive, that all people benefit from well-functioning political and economic institutions and political, economic and social processes .

The wearing away, detachment, and movement of surface materials by forces of wind, water, or ice.

The accumulation of nutrients in a waterbody that results in excessive growth of organisms and depletion of oxygen.

The conversion of a liquid substance to a gaseous state.

The loss of water to the atmosphere via the combined effects of evaporation and transpiration.

Factors Influencing Agriculture

Factors Influencing Agriculture.

Lesson Objective:

By the end of the lesson, you should be able
to explain how climatic factors influence agriculture.

Apart from human and biotic factors, climate is another factor influencing agriculture.
Climate refers to the weather conditions of a place when observed for a longer time (35 - 40 years)

Climatic factors include;

  • Rainfall
  • Temperature
  • Wind
  • Light

Weather Changes

We all have experiences with weather change in our daily life. As the weather changes different conditions are experienced as illustrated blow.

Sunny condition

The sun provides light energy for photosynthesis in plants.

Rainy conditions

The rain is a source of water which is important for all life process e.g. photosynthesis, translocation.

Cloudy condition

Rain bearing clouds provide rain for crop growth and development

Windy conditions

Strong winds destroy farm structures and cause lodging in crops.

The weather conditions when observed for a longer time (35 - 40 years) are referred to as climatic factors,

Effects of rainfall on agriculture

The four aspects of rainfall which affect agricultural production include:-

Rainfall Amount

Rainfall amount refers to quantity of rainfall received in a given area for a period of one year. Rainfall amount is measured using a rain gauge in millimeters per annum. The amount of rainfall determines the crops grown in an area.

Rain Gauge

Rainfall distribution
This refers to the spread of rainfall over the year. Rainfall distribution is

very poor in Kenya and therefore irrigation is necessary to supplement the short supply.

Rainfall reliability
This refers to the certainity with which a given amount of rain is expected in a given place in the year.

Kenya has an unreliable rainfall pattern.

Rainfall unreliability affects timing in land preparation, planting and harvesting.

Rainfall Intensity

This refers to the strength with which rain falls, it is therefore measured in terms of amount per hour.
Rainfall of low intensity is preferred as it improves water infiltration into the soil and causes less soil erosion.

List of effects of rainfall on agriculture

Causes of soil erosion

Excess rainfall can cause soil erosion

Deficiency of moisture

Poor rainfall distribution results to wilting of crops


Excess rainfall can result to crop failure due to flooding.

Effects of Temperature on Agriculture

Temperature is the coldness or hotness of a place.

Temperature is measured in degrees celcius using a thermometer.

Temperature is influenced by altitude and topography.

Temperature decreases with increase in altitude, such that for every 300 meters rise in altitude above sea level temperature decreases by1.7-2.2 degrees celcius.
Each crop has a temperature range within which it can grow referred to as the cardinal range of temperature.
For crops to grow well and produce high yields, they require a narrow temperature range within the cardinal range referred to as optimum range of temperature

Effects of temperature on agriculture

  • Livestock feed more at lower temperature
  • Quality of some crop produce is affected by temperature
  • High temperatures cause wilting in crops at low moisture
  • At lower temperature, there is higher incidence of diseases
  • Germination and growth rates are influenced by temperature

Temperature has alot of effect on hydrological cycle

Effects of altitude on agriculture
Kenya is divided into three ecological zones which include;

  • Low altitude zone o - 1500 meters above sea level
  • Medium altitude zone 1500 - 2500 meters above sea level
  • High altitude zone above 2500 meters above sea level

Crops perform differently when grown in each of these ecological zones and therefore each crop has its most suitable zone for maximum performance as illustrated below.

Merino sheep suitable for high altitude ecological zone: above 2100m above sea level

Sorghum suitable for Low altitude ecological zone: 900 - 1500m above sea level

Zebu cattle suitable for semi arid to Low altitude ecological zone: 900 - 1500m above sea level

Bananas suitable for wet medium altitude ecological zone: 1500 - 2100m above sea level

Tea suitable for wet high altitude ecological zone: above 2100m above sea level 

Effects of Wind on Agriculture

Wind refers to air in motion.

Below is a list of effects of strong wind on agricultural production.

  • Blowing and bringing rain bearing clouds
  • Destruction of farm structures
  • Strong wind may course lodging in weak plants.
  • Wind erosion on bare land
  • Increases rate of moisture evaporation
  • Increase spread of pests and diseases

Soil erosion coursed by wind.

Wind erosion is common on flat bare land

Positive effect of wind in farming

  • Seed dispersal
  • cooling effect on plants and animals
  • Helps in pollination of crops

Pollination in crops.

Cross pollination in maize by wind

Excess evapotranspiration result in wilting of plants

Wind carry away
evaporated water from the crops

Blowing away rain bearing clouds;

Cloud movement by wind affects amount of rainfall in a given place

Wind has alot of effect on hydrological cycle

Effects of Light on Agricultural Production

Light is the source of energy which plants require for photosynthesis.

During photosynthesis, plants manufacture food using water and carbon dioxide in the presence of sunlight and chlorophyll. As illustrated below:

Apects of light that influence agriculture
i) Light intensity

This is the strength with which light hits the surface of the earth.

ii) Light duration

This is the period of time the plants are exposed to light recorded using a campbell sunshine recorder

a) Photoperiodism

This is the response of plants toward light duration.

Long day plants

These are plants which require more that 12 hours of lighting to flower and produce fruits or seeds eg, some wheat varieties

Short day plants

These are plants which require less than 12 hours of lighting to flower and produce e.g Maize

Day neutral plants

These are plants which produce flowers regardless of the duration of lighting they have been exposed to e.g Tobacco.

iii) Light wavelength:

This refers to the type or quality of light.  A wavelength is the distance between two corresponding points of a light wave.

Project Work

1. Organize a visit for the:

(i) Learners to visit 20 local farmers and record the type of crops the farmers are growing and type of livestock reared.

ii)Draw a map of Kenya showing land potential (crops & livestock distribution in Kenya)

2. Organized a visit to the nearest Meteorological Department and

(a) Observe and list instrument used for measuring

(i) Speed of wind

(ii) Amount of rainfall

(iii) Relative humidity

(iv) Temperature

(v) Light intensity

(b) Collect data on amount of rainfall and temperature for the district for the last 35 years


Marking Scheme

1. (i) In the students reports for visit 2, the following should be noted:

- Type and cash crops grown in the area covered.

- Type of livestock kept

- Reasons for keeping the type of livestock mentioned.

(ii) In the students reports for soil sample analysis the following should be noted.

- The feel of the soil

- The consistence of the soil

- Size of particles

- Behavior in the soil when wet.

iii)A map of Kenya showing land potential

(2) After the visit the learners should write a report which should include the following points:

(i) Time period strong winds are expected within the day and which months of the year.

(ii) Reliability of the rainfall for agricultural production

(iii) Where frost is experienced in Kenya

(iv) Shortest and longest days in Kenya

Definition of soil
Soil is the natural material on the upper most layer of the earths crust which supports plant growth.

Soil is made up of five components

  • Mineral matter (inorganic constituents)
  • Organic matter (humus)
  • Living organisms
  • Water (moisture)
  • Air (gases)

Importance of soil

  • Provides anchorage to plants
  • Provides plants with water
  • Contain oxygen necessary for respiration
  • Supports micro-organisms that aid decomposition

Types of soils.

Sandy soil

This soil is coarse and is made of large particles. It cannot stick together even when wet.

Clay soil

This soil is smooth and it is made of small particles.
When wet it can be molded into different shapes.

Loam soil

Contain average of 30 - 50% Sand, 50 - 70% Silt & Clay, 0.4% Organic matter.


(i) Wind

The force of wind carries along smaller pieces of rock which hit against the surface of parent rock causing it to disintegrate.

(ii) Chemical

Rain water dissolves carbon (iv) dioxide in the atmosphere forming carbonic acid which dissolves limestone in the parent rock causing it to disintegrate. 

This is chemical weathering.

(iii) Water

Moving water or ice has a grinding effect against the surface of the parent rock. This causes the rock to disintegrate into smaller particles. 

This is physical weathering.

(iv) Termites

These are living organisms which burrow through the soil breaking and mixing the particles. This is biological weathering.

(v) Mans Activities

Mans activities such as mining, earth moving, mechanized cultivation etc. break the rock into smaller particles. This is biological weathering.

Edaphic Factors Influencing Agriculture

Lesson objectives:

By the end of the lesson you should be able to

(i) give the definition of soil,

(ii) describe the process of soil formation,

(iii) describe the soil profile ,

(iv) classify soil by its characteristics.

Edaphic Factors Influencing Agriculture

Soil (edaphic) factors influencing agriculture include

Soil formation influenced by soil profile
at sloping landscape

The carrying away of soil particles down the slope resulting to high fertility zones.

Soil profile can influence vegetation and crops to be grown in a given area

The following are factors influencing soil formation.

(i) High rate of weathering of the parent rock.

(ii) Low temperature

(iii) Sloping landscape

(iv) Impermeable parent rock

(v) Destruction of soil by burning

Burning during land preparation can destroy soil microorganisms and humus

Factors which Increase soil Formation

(i) High rate of weathering of the parent rock

(ii) Sloping landscape

Factors which reduce soil formation

(i) Low temperature

(ii) Impermeable parent rock.

(iii) Destruction of soil by burning.

Soil Formation
Soil formation takes place during a process called weathering
There are three forms of weathering:

  • Physical weathering,
  • Biological weathering,
  • Chemical weathering

Physical weathering

This involves the disintegration of rocks into smaller fragments by physical weathering agents

Agents of physical weathering include;


The force of wind carries along small pieces of soil which hit against the surface of parent rock causing it to disintegrate into smaller soil particles.


Moving water or rain has a grinding effect against the surface of the parent rock. This causes the rock to disintegrate into smaller soil particles. 

Man's activities

Man's activities such as mining, earth moving machines, mechanized cultivation etc. break the rock into smaller particles. 

Factors influencing soil formation

Biotic factors

The amount of nutrient in the soil depend on the presence of living organisms in the environment.

Biological weathering
This involves the action of living organisms, such as animals and plant materials (roots, leaves, stem)

The roots force their way through the rock crevice coursing them to split.
Upon decomposition of plant materials a weak acid called humic acid is formed, which reacts with rocks weakening them.

Soil Profile
Soil profile refers to the vertical arrangement of different layers of the soil from

the top surface to the bedrock.
These layers are also called horizons

Layers of the soil profile
Superficial layer -Consist of dry decaying and decayed organic matter

Top soil - Well aerated, darker, contains active organism and has most of the plant roots.

Sub soil - Compact, less aerated and has an impermeable layer called hard pan.

Weathered rock - Has rocks being broken down and has no humus

Parent rock - Has intact rocks and ponds of water

Physical properties of soil

These properties are recognised by seeing or feeling as explained below

Clay: - This soil is smooth and it is made of small particles.
When wet it can be moulded into different shapes.

Sandy: This soil is coarse and is made of large particles.
It cannot stick together even when wet.

By feeling the two types of soil, clay and sandy when wet, you will tell that soil is made up of particles which have different sizes and are arranged in different ways to stick together or to remain loose.

The particles that make soil are:

  • Clay particles,
  • Sand particles,
  • Silt particles,
  • Organic matter.

Soil Structure
Soil structure refers to the physical appearance of the soil according to

the way the individual soil particles are arranged packed or aggregatated.

 It is a term used to describe the overall arrangement or grouping of soil particles or aggregates.
The soil structure type is determined by general shape aggregate. 

Soil structure type is determined by general shape of aggregate.

 Soil structure class is determined by the size of the aggregate and

The soil structure grade is dependent up the stability or cohesiveness of the aggregates.
Type of soil structure is influenced by climate, living organism, topography, parent material and time.
Clay particles and humus influence soil structure by the way they cement or

build up the different particles into bigger and more stable aggregates.
Secretions from plant roots may influence soil structure.

Types of Soil Structure

There are many types of soil structure. The most common include:

This is an elementary structure which forms no aggregates meaning that particles are not cemented together.
It is relatively non- porous with small or spherical particles mostly found in the topsoil or sandy soil, arid climates and alkaline soils.

This soil consists of small, soft porous aggregate of irregular shape. 
The type of structure does not closely fit together and such soils and water will pass through the pores quickly.
However, a good structure should not only have enough pore spaces for water and air to enter, but should also be able to retain sufficient water in the soil for plant roots to use.

Granular Structure

This is the type of soil structure made of friable rounded aggregates of irregular shape called granules. This structure can be found in the topsoil horizon of cultivated soils and in the sub-soil horizons of soils under grass or bush. Granular structure is the only arrangement influenced by practical methods of tillage and trampling

These soils structures have aggregates arranged in vertical, cylindrical columns or pillars. The pillars vary in length and may reach a diameter of 15cm or more. When the tops of the pillars are rounded the structures is referred to as columnar but the pillars have flat, level tops the structural pattern is prismatic.
The columnar structures are found in middle horizons of soils with poor drainage while prismatic structures are common from the middle to the lower horizons of fine textural soils.

Platy Structure

platy structures is mostly found in top horizon of soil in the forest and in clayey soils.Usually in layers on top of each other as illustrated in the diagram.

Blocky Structure

This structure resembles the blocks used in construction. The aggregates easily fit together along vertical edges with their dimensions more or less equal.

Influence of Soil Structure on Crop Production

The soil structure influences the pore space in the soil. When the particles are closely packed together, the soil has very few pore spaces. The amount of air and water present in soil depend on the pore space available. This implies that soils with closely packed particles are poorly aerated and drained. Most crops do well in well aerated and drained soil except a few such as rice, which do well in water logged soil. Soil with good structure ensure a balance between soil air and water are good for crop production.The soil structure should allow free circulation of air by having enough pore spaces which can be occupied by air as in granular or crumby structures.

In such soil the plant roots and micro-organisms can get the oxygen they need and carbon IV dioxide is expelled easily. The soil structure influences the water holding capacity of soil. A good soil structure should hold enough water for plants use. Using heavy machinery on wet soil destroys the structure, thus decreasing permeability and aeration. This may result into high incidence of surface run off and erosion. NB: Soil structure can be used to classify soil. It refers to the general arrangements of the soil particles or aggregates. Depending on the aggregation, soil could have granular,crumby, prismatic, blocky or platy structures.

Soil Texture

The term soil texture refers to the relative proportions of the various sizes of mineral particles in a sample of soil. These mineral particles include:

  • gravel,
  • sand,
  • slit and clay.

    It is also defined as the coarseness or fineness of the soil when felt between the fingers.

     The texture of soil determines its ability to absorb and retain water and soil nutrients.

Soil Particles And Their Sizes.

Particle Size (Diameter) in MM

  • Stones (Gravel) Above 2.0 mm
  • Fine sand between 0.02mm and 0.20mm
  • Silt between 0.002mm and 0.02mm
  • Clay below 0.002mm

Soil Classification
Soil can be classified according to their physical characteristics such as:

  • Colour
  • Texture
  • Structure

The colour of the soil will depend on the mineral composition of the parent rock. If soil was formed from a rock containing a lot of iron compounds, it tends to be brownish, yellow reddish or orange in colour. Dark grey, grey brown or black coloured soils are so due to the presence of humus and other substances in the soil such as peat and more or less decomposed plant residues.
Soil colour influences soil temperature. Dark soil absorbs and retains more heat than light coloured soil. High temperature affects the activity of soil micro-organisms. 
Soil micro-organisms will be more active in high temperature and under such conditions decay of organic matter is faster than in the low temperature.

Soil Textural Classes
Soil can also be classified according to soil texture which refers to their proportion of particle sizes.

Loamy Soil

  • They contain 30% - 50% Sand
  • 50% - 70% Silt and clay
  • 0.4% Organic matter

Clayey Loams Contains

  • 20 %- 50% Sand
  • 20 %-60% Silt and clay
  • 0.1 %- 6% Organic matter
    They are finely textured and poorly drained and have a high water holding capacity

Sandy Soil Contains
50% - 80% Sand
20% - 50% Silt and clay
0.1% - 3% Organic matter

Very well drained

Coarse textured and moderately fitile

Low water holding capacity

Prone to erosion

Less stable structure on the surface

Easy to cultivate and can be improved by addition of organic manure

Silty Loams Contains

20% - 30% Sand
70% - 80% Silt & Clay
0.1% - 4% Organic matter

Fine texture

Well drained

Good water holding capacity

Moderately fertile and aerated

Chemical Properties of Soil
Soil pH is the degree of acidity or alkalinity level of soil solution. 

A pH scale is used to estimate the degree of acidity and alkalinity. The scale runs from 1 to 14 with neutral pH at the midpoint. The lower numbers present acidic conditions. Numbers above 7 represent alkaline conditions. 

The degree of acidity depends on the concentration of hydrogen ions in the soil solution. A high concentration of hydrogen ions makes the soil acidic.In pH scale the numbers are negative logarithms or powers. For example at pH 4 the amount of hydrogen ion concentration is

There are alkalis in the soil solution which neutralize the acids.

These are metals in solution form. During heavy rains these alkalis are leached and are replaced by hydrogen ion. Higher rainfall regions have high soil acidity. Plants also exhaust the alkali content of the soil by using them as nutrients.

Influence of Soil pH on Mineral Availability, on Plant Growth and Production

Soil pH affects availability of various nutrients.

 Low pH makes phosphorous and molybdenum less available.

 High pH makes manganese, potassium, iron, boron and Zinc less available.

Very acidic or alkaline conditions affect activities of micro organisms particularly nitrogen fixing bacteria. Hence acidic soils contain very low level of nitrates. The activities of most beneficial micro-organisms are at their optimum at pH 5.5-7.8

Different crop species react to pH in a different manner. For each crop species there is an optimal range of soil pH for example coffee does well at pH5.3 -6.0

Modifying Soil pH
In lowering acidity or increasing soil pH the following can be done:

  • Application of lime. This is a basic compound which raises soil pH after some time.
  • Application of a basic fertilizer.

In raising acidity or lowering soil pH the following can be done:

  • Application of an acidic fertilizer such as sulphate of ammonia.

  • Application of sulphur.

Experiment to find the percentage of soil water content

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