Environmental Factors – SS1 Horticulture and Crop Production Lesson Note (Second Term)

Environmental factors are the conditions around a plant that affect how it grows, flowers and bears fruit.

Behavioural objectives

By the end of the lesson, students should be able to:

1. name the five main environmental factors that affect plants;
2. explain how light and temperature affect plant growth;
3. describe the effects of the amount and distribution of rainfall on crops;
4. state the good and bad effects of wind, and of high and low humidity;
5. list ways in which horticulturists manage environmental factors.

What are the five main environmental factors?

The five main environmental factors are light, temperature, rainfall, wind and humidity.

• Light: the energy plants use to make food.
• Temperature: the degree of heat or cold around the plant.
• Rainfall: the main source of water for crops grown in the field.
• Wind: air in motion.
• Humidity: the amount of water vapour in the air.

Why do they matter?

• Plants are living things and react to the conditions around them.
• If one factor is out of balance, tomatoes may grow poorly and flowers may fail to bloom.
• Horticulturists cannot change the weather, but they can reduce its harmful effects.

How does light affect plants?

Light is the energy that green plants use to make food by photosynthesis.

Light and photosynthesis

• Photosynthesis: the process by which green plants make food from carbon dioxide and water, using light energy.
• Too little light: the plant becomes pale, thin and weak, and may die.
• Etiolation: a plant grown in very poor light grows tall and thin as it stretches towards light.

Duration of light (photoperiodism)

Photoperiodism is the response of a plant to the length of day and night.

Intensity of light

Light intensity is how bright the light is.

• Sun-loving crops: peppers grow best in direct, bright sun.
• Shade-loving plants: ferns and young cocoa seedlings prefer shade.

How does temperature affect plants?

Temperature is the degree of heat in the air and soil, and it controls how fast a plant grows.

• High temperature: makes plants lose water (transpire) faster, so they may wilt if the soil is dry.
• Low temperature: slows growth.
• Crop choice: Irish potatoes grow well in cool parts of Nigeria such as Jos, but not in the heat of Lagos.
• Seed germination: seeds sprout properly only within a suitable temperature range.
• Flowering and ripening: temperature affects when plants flower and how quickly fruits ripen.

How does rainfall affect plants?

Rainfall is the water that falls from the sky, and it is the main water source for most Nigerian farmers.

• Water as carrier: water carries dissolved nutrients from the soil into the plant.
• Water for food making: water is needed for photosynthesis and keeps plant cells firm.

Amount of rainfall

• High-water crops: rice needs a lot of water.
• Moderate-water crops: horticultural crops such as carrots need a steady, moderate supply.

Distribution of rainfall

Distribution is how evenly the rain is spread through the season.

• The amount of rain and how often it falls both matter.
• Heavy rain for one week followed by a dry month makes plants suffer.

Too much or too little rain

• Too much rain: washes away soil (erosion).
• Waterlogging: too much water drowns roots so they cannot breathe.
• Too little rain: plants wilt, dry up and die unless irrigation is used.

How does wind affect plants?

Wind is moving air, and it has both good and bad effects on plants.

Good effects of wind

• Pollination: wind carries pollen from one flower to another so that fruits and seeds can form.
• Cooling: wind cools plants on a hot day.

Bad effects of wind

• Breakage: strong wind breaks the stems of tall plants such as maize.
• Flower and fruit loss: strong wind blows flowers off fruit trees.
• Drying: wind makes soil lose water faster.

How does humidity affect plants?

Humidity is the amount of water vapour in the air.

• High humidity: the air holds a lot of water vapour, as in Southern Nigeria, and feels heavy.
• Low humidity: the air is dry, as in the Harmattan.

How can horticulturists manage environmental factors?

Horticulturists manage environmental factors by reducing their harmful effects on crops.

What should a farmer check before planting?

1. Look at the sky and the season to judge light and rainfall.
2. Feel the wind to judge whether a windbreak is needed.
3. Touch the soil to see whether it is wet or dry.
4. Choose crops that suit the local conditions.

Evaluation

1. Name the five main environmental factors that affect plant growth.
2. What is photosynthesis, and why do plants need light for it?
3. State two problems caused by too much rain.
4. Give one good effect and one bad effect of wind on plants.
5. Name one way of managing each of these: too much light, strong wind, high temperature.

Assignment

Choose any two environmental factors from the lesson. For each one, explain how it affects plants and state one way a horticulturist can manage it.