Advanced Greenhouse Technology – SS3 Horticulture and Crop Production Lesson Note (First Term)

Advanced greenhouse technology is the use of climate control, fertigation and automated sensors to give crops exactly what they need, exactly when they need it.

Behavioural objectives

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

1. state why the environment inside a greenhouse is controlled;
2. describe how temperature, humidity, light and carbon dioxide are managed in a greenhouse;
3. define fertigation and give its advantages;
4. describe the parts of a fertigation system;
5. explain the work of EC sensors, pH sensors and the controller.

Why is the environment inside a greenhouse controlled?

The environment is controlled so that crops grow in ideal conditions whatever the weather outside.

• Weather risks in open farming: too much heat makes plants wither, and too much rain makes roots rot.
• Year-round growing: crops can be grown in the dry season or the cold harmattan.
• Faster growth: plants stay in their comfort zone and do not stop growing to protect themselves.
• Bigger harvests: yield per square metre is higher than in the open field.
• Better quality: fruits such as tomato and cucumber are cleaner and more uniform.

Think of a greenhouse as a “smart home” for plants.

How is the climate controlled in a greenhouse?

Four main climate factors are managed in a greenhouse: temperature, humidity, light and carbon dioxide.

Plants are very sensitive to their surroundings. If the air is too dry or too hot, the plant stops growing to protect itself.

1. How is temperature managed?

Temperature is managed by cooling the greenhouse when it is too hot and heating it when it is too cold.

• Cooling: many tropical greenhouses get too hot, so evaporative cooling pads and fans are used.
• Heating: in cooler or high-altitude areas, heaters or thermal blankets keep plants warm at night.

How does an evaporative cooling pad system work?

1. Water runs through a cardboard pad on one side of the greenhouse.
2. Fans on the opposite side pull air through the wet pad.
3. Water evaporates from the pad and takes heat from the air.
4. Cooler air enters the greenhouse and lowers the temperature by several degrees.

2. How is humidity managed?

Humidity is the amount of moisture in the air, and it is managed by letting moisture out or adding it.

• High humidity: fungi and diseases spread quickly, so roof vents are opened to let moisture out (ventilation).
• Low humidity: plants lose water too fast, so misters or foggers spray a fine mist into the air.

3. How is light controlled?

Light is controlled because plants need sunlight for photosynthesis, but too much direct sun can “sunburn” the leaves.

• Shade nets: black or green netting that blocks a percentage of the sun.
• LED grow lights: these extend the “daylight” hours, especially for high-value flowers or vegetables.

4. Why is carbon dioxide (CO₂) enriched?

Carbon dioxide enrichment means adding extra CO₂ to greenhouse air to speed up photosynthesis.

• Reason: plants take in CO₂ for photosynthesis.
• Problem: in a closed greenhouse, plants can use up the CO₂ quickly.
• Solution: advanced systems inject extra CO₂ into the air to speed up growth.

What is fertigation?

Fertigation is the delivery of dissolved fertiliser to crops through the irrigation water.

• Origin of the word: it combines “fertilisation” and “irrigation”.
• Method: nutrients are dissolved in water and delivered directly to the roots, instead of throwing handfuls of fertiliser on the soil.

What are the advantages of fertigation?

1. Efficiency: the plant is fed immediately, and very little fertiliser is wasted in the soil.
2. Accuracy: the nutrient formula can change for young plants and for plants already producing fruit.
3. Labour saving: the system does the work automatically.
4. Water saving: drip delivery keeps roots moist but not soaked, so less water is used.

What are the parts of a fertigation system?

A fertigation system has three main parts: the mixing tank, the injector (venturi) and the drip emitters.

• The mixing tank: large tanks where concentrated nutrients (nitrogen, phosphorus, potassium and micronutrients) are mixed.
• The injector or venturi: a device that sucks a precise amount of fertiliser into the main water line.
• Drip emitters: small plastic nozzles at the base of each plant that release water drop by drop.

How does fertigation flow from tank to plant?

1. Concentrated nutrients are mixed in the tank.
2. The injector draws a measured amount into the main water line.
3. The nutrient solution travels along the pipes.
4. Drip emitters release it drop by drop at the base of each plant.

How are greenhouses monitored and automated?

Greenhouses are monitored by sensors that act as the “eyes and ears” of the farmer, and a controller that acts on their readings.

What is an EC sensor?

• Full name: electrical conductivity sensor.
• Use: it shows the strength of the nutrient solution.
• Warning: a very high reading means the mix is too strong.

What is a pH sensor?

• Use: it measures how acidic or alkaline the water is.
• Preferred range: plants usually like a slightly acidic environment, around pH 5.5 to 6.5.
• Effect of wrong pH: the plant cannot “eat” the food, even if it is right there.

What is the controller?

• Role: the “brain” of the greenhouse, a computer that reads data from the sensors.
• Actions: it automatically turns on the pumps or opens the windows.

What practical management tips should a greenhouse farmer follow?

A good greenhouse farmer observes the crop daily, even with high-tech sensors.

• Clogged drippers: minerals or algae can block the water holes, so check them often.
• Leaf colour: yellowing leaves often mean the pH is off or a specific nutrient is missing.
• Air flow: make sure there are no “dead zones” where air does not move, because pests hide there.
• Sustainable use of resources: greenhouse technology produces more food using less water and land.

Evaluation

1. Why do farmers control the environment inside a greenhouse?
2. Name the four main climate factors managed in a greenhouse.
3. Describe how an evaporative cooling pad system cools a greenhouse.
4. Define fertigation and state three advantages of using it.
5. What does an EC sensor measure, and what can happen if the EC is too high?

Assignment

List the three main parts of a fertigation system and state the function of each. Then explain the roles of the pH sensor and the controller in an automated greenhouse.