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