Agriculture Form 1 – Factors Influencing Agriculture

Introduction

Agricultural production is influenced by external factors:

• Human factors
• Biotic factors
• Climatic factors
• Edaphic factors.

Human Factors

These are human characteristics which affect the way decisions are made and operations carried out.

• Level of education and technology:
• Skills
• Technological ad van cements .

• Human health/HIV-AIDS:
  • These affect the strength, the vigour, vision and the determination

    to work.

• HIV/AIDS is the biggest threat to human health today and has long

  lasting effects on agriculture, such as;

• Shortage of farm labour.
• Loss of family support.
• Low living standards leading to despondency and hopelessness.
• Increased criminal activities.
• More time spent by the Government and NGO’s in Carring for the sick.

• Economy;
  • Stability in the countries‘ economy affect agricultural production.
  • Government Policy:
    • These are governmental laws which have been enacted to protect farmers, land and livestock.

They include:

• Food policy
• Policies on control of livestock parasites and diseases.
• Policies on marketing of both local and export products and others.

• Transport and communication:
• For agricultural goods to move from the farm to the consumers.
• Cultural practices and religious beliefs:
  
  • These activities hinder important changes in a society that may bring agricultural development.
• Market forces:
  • Demand and supply forces which affect prices of commodities in a free market.

Biotic Factors

These are living organisms which affect agricultural production.

• Pests – Destructive organisms which destroy crops.
• Parasites – These are invertebrates which live in or on other living organisms.
  • Decomposers – Organisms which act on plants and animal tissues to form manure.
• Pathogens – Micro-organisms which cause diseases.
• Predators – Animals that kill and feed on other animals.
• Pollinators – They transfer pollen grains from the stamens to the pistil of a flower.
• Nitrogen fixing bacteria -They are micro-organisms which convert atmospheric nitrogen to nitrates ready for use by the plants.

Climatic Factors(weather elements).

• Rainfall,
• Temperature,
• Wind,
• Relative humidity
• Light.

Weather
– Atmospheric conditions of a place at a given time period.

Climate – weather conditions of a place observed and recorded for a period of 30-40 years.

Rainfall

Supplies Water:

• Which is necessary for the life process in plants and animals.
• Which makes the plant turgid hence provides support.
• Acts as a solvent for plant nutrients.
• Cools the plant during transpiration.
• Which is used as a raw material in photosynthesis.

When plants lack enough water they respond in different ways as follows:

• By closing the stomata to restrict water loss.
• Hastens maturity.
• Some will roll their leaves.

Other plants have developed permanent adaptation to water stress such as:

• Growing needle like leaves.
• Develop fleshy leaves for water storage.
• Develop long roots.
• Wilting and death in extreme conditions.

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.

Temperature

• 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:

Low temperatures:

• Slow the growth rate of crops due to slowed photosynthesis and respiration.
• High incidences of disease infection.
• Improves quality of crops such as tea and pyrethrum.

High Temperatures

• Increase evaporation rate leading to
• Wilting.
• Hastens the maturity of crops.
• Increase disease and pest infection.
• Improves quality of crops such as pineapples, oranges and pawpaws.

Wind

Wind is moving air.

Good effects of wind include:

• Seed dispersal
• Cooling of land
• Pollination in crops
• Brings rain bearing clouds

Negative effects of wind:

• Increases the rate of evaporation of water.
• Causes lodging of cereals and distorts perennial crops.
• Increases evapo-transpiration.
• Spreads diseases and pests.
• Destroys farm structures.

Relative humidity

• The amount of water vapour in the air
• Affects the rate of evapo-transpiration.
• Forms dew which supplies soil with moisture under dry conditions.
• High humidity induce rooting in cuttings.
• Increases disease multiplication and spread.

Light

• Provide radiant energy harnessed by green plant for photosynthesis.
  

Important aspects of light:

• Light intensity
  • The strength with which light is harnessed by chlorophyll for photosynthesis.
• Light duration
• The period during which light is available to plants per day.
• Plant response to light duration is known as photoperiodism.
  
  • Short-day plants – require less than 12 hours of daylight to flower and seed.
  • Long-day plants – require more than 12 hours of daylight to flower and seed.
  • Day-neutral plants require 12 hours of daylight to flower and seed.
• Light wavelength;
  
• This is the distance between two – successive crests of a wavelength.
• It dictates the difference between natural and artificial light.
• Chlorophyll absorbs certain wavelengths of light.

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

• Provides anchorage to the plants by holding their roots firmly.
• Provides plants with mineral salts/ nutrients which are necessary for their growth.
• Provide the plants with water.
• Contains oxygen necessary for respiration of the plants and soil micro-organisms.

Soil Formation:

• 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 weathering
• Chemical weathering
• Biological weathering

Agents 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.

Chemical Weathering

• Affects the chemical composition and structure of the rock.
• Involves processes such as
  • Hydrolysis,
  • Hydration,
  • Carbonation
  • Oxidation.
• Hydration;
  • The process by which soluble minerals in the rocks absorb water and expand weakening the rock thus leading to disintegration.
• Hydrolysis;
  • The process whereby water dissolves soluble minerals in the rock weakening it.

• Oxidation
  • The reaction of rock minerals with oxygen to form oxides which break easily.

• Carbonation
  • The process whereby carbonic acids formed when rain water dissolves carbon dioxide,
  • It reacts with calcium carbonates in limestone causing it to disintegrate.

Biological Weathering

This involves the action of living organisms, plants and animals on the rocks.

• Burrowing animals, for example, termites and moles bring soil particles to the surface exposing them to other agents of weathering.

• Big animals like, elephants, buffaloes, camels and cattle exert a lot of pressure on the rocks as they step on them due to their heavy weights causing the rocks to disintegrate.

• Earthworms take part in the decomposition of plant matter with the soil particles.

• Man’s activities like, mining and quarrying expose rocks to the surface during excavation. These activities breakdown large rocks into smaller rock particles.

• Plant roots force their way through the cracks in the rocks thus widening and splitting them.

• Humic acids formed when plant tissues decompose react with the rocks weakening them further.
  • Plant remains-decompose adding humus into the soil.

Factors influencing soil formation

• Climate- (rainfall, temperature and wind)
• Biotic factors – living organisms.

• Parent material– Nature and properties of the original rock from which the soil is formed.

• Time – length of time during which the soil forming processes have taken place.

• Topography – influences the movement of disintegrated materials.

• 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.

Top Soil

• 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 eluviations)

Sub-Soil

• 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

Weathered Rocks

• 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.

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.

Soil Depth

• 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.

Soil Constituents

• Organic Matter
  – Dead and decaying plants and animal remains
• Living Organisms
  – Soil organisms and plant roots.
  • Micro-organisms (bacteria, protozoa and fungi)
  • Invertebrates -termites,
  • Earthworms and molluscs.
  • Higher animals – rodents and others.
• Inorganic or Mineral Matter
  
  • Formed from the parent materials.
  • Supply plant nutrients
  • Form the skeleton and framework of the soil.
• Air
  
  • Found in the pore spaces of the soil.
  • Used for root and organism respiration
  • Used for germination of seeds.
  • Helps in decomposition of organic matter.
  • Regulates soil temperature.
  • Regulates the movement of water through capillary action.

• Water
  
  • Dissolves mineral salts
  • Maintain turgidity in plants.
  • Used for germination of seeds
  • Used by soil organisms.
  • Regulate soil temperature
  • Dictates the amount of air in the soil.

Water in the soil exists in three forms namely:

• Superfluous/Gravitational Water
  
  • 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.

• Hygroscopic Water
  
  • 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.

• Capillary Water
  
  • Occupy micro-pores in the soil particles.
  • Held by cohesive forces between water molecules.
  • Moves through capillary action
  • Available to plants for use.

Soil Structure

• This is the arrangement of soil particles in a soil horizon.
• Types of Soil Structure –
  
• Single-grained
• Crumby
• Granular
• Prismatic
• Columnar
• Platy
• Blocky

Importance of Soil Structure on Crop Production

Soil Structure Influences

• Soil aeration
• Soil drainage and water holding capacity.
• Plants root penetrability and anchorage.
• Microbial activities in the soil.
• Circulation of gases in the soil.

Farming practices which improve the soil structure are:

• Application of inorganic manure into the soil.
• Tilling the land at the right moisture content.
• Crop rotation.
• Minimum tillage.
• Cover cropping.
• Mulching.

Soil Texture

• 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
• Affects the organic matter content
• Influences the drainage of the soil.
• Influences soil aeration.
• Influences water holding capacity.
• Influences the capillarity or movement of water in the soil.

Soil Textural Classes

Sandy Soils

• Made up largely of sand particles.
• Have large pore spaces hence poor in water retention.
• Easy to till (light soils).
• Freely draining.
• Low fertility due to leaching of minerals.
• Easily erodible.

Clayey Soils

• Made up largely of clayey particles.
• Have small pore spaces hence good in moisture retention.
• Difficult to till (heavy soils).
• Poorly ‘drained.
• Expand when wet, crack when dry.
• High capillary.
• Rich in plant nutrients.

Loam Soils

• About equal amounts of sand and clay.
• Moderately good in both moisture and air retention.
• Fertile soils.

Soil Colour

• 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.

Soil pH

• 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.
• A pH of less than 7 means that the soil is acidic.
• A pH of more than 7 means that the soil is alkaline.
• As the hydroxyl ions (OH) in the soil increase the soil becomes more alkaline.

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.