FACTORS INFLUENCING AGRICULTURE (24 LESSONS)
By the end of the topic, the learner should be able to:
topic/ sub-topics guidelines
Levels of education and technology
Health - HIV/AIDS and health in general
Economy (include liberalization)
Transport and communication
Market forces (local and international)
Cultural and religious beliefs
Definition of soil
i) Soil structure
Chemical properties of soil
Introduction TO FACTORS INFLUENCING AGRICULTURE
Agricultural production is influenced by external factors:
These are human characteristics which affect the way decisions are made and operations carried out.
Level of education and technology:
These are living organisms which affect agricultural production.
Climatic Factors (weather elements).
Climate - weather conditions of a place observed and recorded for a period of 30-40 years.
Important Aspects of Rainfall:
Rainfall reliability; - This is the dependency on the timing of the onset of the rains.
Amount of rainfall; - Quantity of rain that falls in a given area within a given year.
Rainfall distribution; - The number of wet months in a year.
Rainfall intensity; - Amount of rainfall that falls in an area within a period of 1 hour.
This is the degree of hotness or coldness of a place measured in degrees Celsius.
Cardinal range of temperature is the temperature required by plant to grow and thrive well.
Optimum range of temperatures - the best temperature for the best performance of plants.
Effects of Temperatures on Crop Production:
Wind is moving air.
Good effects of wind include:
This is the amount of water vapour in the air
Provide radiant energy harnessed by green plant for photosynthesis.
Important aspects of light:
The strength with which light is harnessed by chlorophyll for photosynthesis.
This is the period during which light is available to plants per day.
This is the distance between two - successive crests of a wavelength.
Edaphic Factors Influencing Agriculture
These are soil factors.
Soil is the natural material that covers the surface of the earth,
Made of weathered rock particles and decomposed animal and plant tissues, and on which plants grow.
Importance of Soil
Soil is formed through weathering process.
Weathering is the breakdown and alteration of the parent rock near the surface of the earth to a stable substance.
Weathering process is a combination of disintegration (breakdown) and synthesis (build up) process.
Weathering process is continuous.
Types of Weathering
Physical Agents of Weathering
Include wind, water, moving ice and temperature.
Wind - carry materials which hit against each other to break into fragments.
Water - intensity of rainfall causes breakdown of rock.
Moving ice - has grinding effects which tear off rock particles.
Extreme temperature cause rocks to expand and contract suddenly peeling off their surface.
Affects the chemical composition and structure of the rock.
Involves processes such as;
The process by which soluble minerals in the rocks absorb water and expand weakening the rock thus leading to disintegration.
The process whereby water dissolves soluble minerals in the rock weakening it.
The reaction of rock minerals with oxygen to form oxides which break easily.
The process whereby carbonic acids formed when rainwater dissolves carbon dioxide,
It reacts with calcium carbonates in limestone causing it to disintegrate.
Factors influencing soil formation
It is the vertical arrangement of different layers of soil from the ground surface to the bedrock.
These layers are also referred to as horizons.
The layers show differences in their contents and physical properties such as colour, texture and structure.
The layers include: organic matter region, top soil, sub-soil, weathered rocks and parent material.
Organic Matter Region
First layer of the soil found on the surface.
Made up of leaves and other plant remains at various stages of decomposition.
Some soil organisms may also be found here.
Has a dark colour due to the presence of humus.
Is rich in plant nutrients and well aerated.
It is a zone of maximum leaching (zone of eluviation)
It is compact and less aerated.
It is a zone of accumulation of leached material (zone of aluviation) from the top layers.
Deep rooted crops have their roots growing up to this region.
Hard pans normally form in this layer
It is also called substratum.
Rocks at various stages of disintegration are found in this zone.
Most of the materials found in this zone originate from the parent rock.
It exists as a solid mass which is un-weathered.
It is the source of the inorganic composition of the soil.
The water table is on the surface of this rock.
Soils Formed in Situ and Soils Deposited
Soil formed in the same place and remains there is said to be in situ. However, soil can be formed due to deposition of soil particles carried from its original site of formation to another area which is usually in the lower areas of slopes. Such soils are said to have been formed through deposition.
This is the distance between top soil layer and the bottom soil layer in a profile.
It dictates root penetration and growth
Deep soils are more suitable for crop growth since they contain more nutrients.
Have a larger surface are for root expansion.
Deep soils facilitate good drainage and aeration.
Formed from the parent materials.
Found in the pore spaces of the soil.
Found in the large spaces (macro-pores) in the soil particles.
Held by gravitation forces.
When the pores are saturated, the soil is said to be waterlogged.
It moves and may cause leaching.
Water found in thin films on the soil particles.
Held by strong adhesive forces between water and soil particles.
Does not move and hence not available for plant use.
Occupy micro-pores in the soil particles.
Held by cohesive forces between water molecules.
Moves through capillary action
Available to plants for use.
This is the arrangement of soil particles in a soil horizon.
Types of Soil Structure
Importance of Soil Structure on Crop Production
Soil Structure Influences
It refers to the relative proportion of the various sizes of the mineral particles of soil.
Importance of Soil Texture on Crop Production;
Influences soil fertility
This depends on the, mineral composition of the parent rock and the organic matter content.
Soils containing a lot of iron are brownish, yellowing and reddish in colour.
Soils with a lot of silica are white.
Soils with a lot of humus are dark or grey.
This refers to the acidity or alkalinity of the soil solution/the concentration of hydrogen ions in the soil solution.
Soil pH is determined by the concentration of hydrogen ions (H+) or the hydroxyl ions (OH) in the soil solution.
Influence of Soil pH Crop Growth
It determines the type of crop to be grown in a particular area.
Most crops are affected by either very acidic or very basic soil PH.
Soil pH affects the choice of fertilizers and the availability of nutrients to crops.
At low PH the concentration of available iron and aluminium in the soil solution may increase to toxic levels, which is harmful to plants.
Very acidic or low pH inhibit the activity of soil micro-organisms.
FACTORS INFLUENCING AGRICULTURE QUESTIONS ON TOPIC
1. State two roles of humus in the soil that are beneficial to crops
2. a) outline five activities that may be undertaken in organic farming
3. List four effects of temperature on crop growth
4. State four ways by which wind affects the growth of crops
5. Name two factors related to light that affect crop production and distribution in Kenya
6. Describe the environmental conditions that may lead to low crop yields
7. List three environmental factors that affect crop distribution in Kenya
8. State one physical characteristic used in classifying soil
9. Outline four advantages of organic farming
10. The diagrams below show an experiment carried out by a form 1 class. Study them carefully and answer questions that follow:
(a) What was the aim of the experiment?
(b) What was the observation that form 1 students made at the end of the experiment in flasks D and E?
(c) Give the reason for the observation made in flask D
12. Briefly explain how sub-soil as a horizon in a soil profile can affect soil productivity
13. (a) What are the three aspects of light that are important to a farmer?
(b) Mention three ways through which relative humidity affect crop production
14. The diagram labeled E and F below illustrates some type of soil structure. Study the diagrams carefully and answer the questions that follow:
(a) Identify the types of soil structure illustrated in diagrams E and F
(b) Identify the parts labeled (i) and (ii) in diagram F
(c) Outline the influence of physical characteristics of soil on its properties
15. State three physical characteristics of soil
16. Study the diagram below and answer the questions that follow
a) State merits of horizon A
b) State distinct features of horizon B
c) What does the term transition zone refer to in soil profile
i) Name horizon C and state its importance
17. Outline two ways temperature affects crop production
18. List four ways by which biological agents can enhance the process of soil formation
19. List four environmental factors that affect crop production in Kenya
20. Explain the role played by topography in soil formation
22. Mention two importance of parent’s material in soil profile
23. Mention four ways of modifying soil temperature in crop production
24. a) Mention two factors that affect selectivity of herbicides b) Name two farming practice that cause water pollution
25. Give four factors that influence soil formation
26. State three properties of soil that is influenced by soil texture
27. Name any three agents of biological weathering
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