Learn how to manage a commercial greenhouse!
Learn about different greenhouse designs and how to manage the greenhouse environment to propagate and grow marketable plants efficiently.
Learn how to:
- Choose the right greenhouse for your situation
- Improve greenhouse efficiency and function
- Automate your greenhouse
Course Duration - 100 hours
Course Structure and Content
There are nine lessons in this course:
1. Types of Greenhouses
- Greenhouse Designs for Commercial Nursery Production
- Greenhouse Construction Methods and Materials
- What Type of Greenhouse is Appropriate for Your Nursery?
- Siting Greenhouses
- Greenhouse Benching
- What Can You Grow?
- Environmental Control in Greenhouses
- Computerised Environmental Control
2. Growing Systems and Equipment
- How to Grow Plants
- Measuring Conditions Inside a Greenhouse
- Environmental Control Systems
- Getting Plants to Flower Out of Season
3. Pest and Disease Management in Greenhouses
- How to Stop Pests and Diseases Entering the Greenhouse
- Detecting and Controlling Pests and Diseases in the Greenhouse
- Common Greenhouse Diseases
- Disease Control
4. Temperature Control in a Greenhouse
- Heating Systems
- Ventilation Systems
5. Water Management
- Greenhouse Irrigation
- Soil and Water
- When to Irrigate
- The Nursery Irrigation Program
- Plants and Water
- Equipment and Methods
- Maintenance of Watering System
6. Nutrition Management
- Irrigation and Nutrition Control
- Liquid Feed Systems
7. Managing Light
- Importance of Lighting in a Greenhouse
- Artificial Lighting
- Measuring Light
- Controlling Light in the Greenhouse
- Photoperiod Manipulation
- Growth Rooms
- Efficient Lighting Control
8. Managing Gasses
- Carbon Dioxide Enrichment
- Pollutant Gases
- Temperature Control Systems (Ventilation)
9. Automation and Robotic Application for Greenhouse Production
- Automation in Vegetable Nurseries
Lesson Aims
- Compare different types of greenhouses to better match the plants to be grown inside the greenhouse to be built.
- Explain the equipment and measuring devices (manual and automated) used inside a greenhouse to help grow plants more effectively.
- Explain options for reducing the impact of pests and diseases on plants grown inside greenhouses.
- Detect and control the temperature within an optimal growing range for plants being grown in a greenhouse.
- Control water in a greenhouse, including irrigation and humidity.
- Control nutrient levels in a greenhouse at optimal levels for plant growth and health
- Explain how light levels can be maintained in a greenhouse for optimal plant production.
- Explain how to best manage the air characteristics inside a greenhouse.
MEASURING CONDITIONS INSIDE A GREENHOUSE
Managing a modern greenhouse requires the use of measuring devices which monitor the greenhouse conditions. Simple, manually operated measuring systems might be used, such as a thermometer, barometer, EC meter or pH meter (or chemical test kit). Commercial operations, however, increasingly will use automated sensors.
Weather Sensors
Wind Speed and Direction Sensors
The most common method to measure wind speed is with cup anemometers. Wind causes the cups to rotate around a vertical shaft and the number of rotations within a specified time interval is measured to determine the wind speed. Many greenhouse environment control computers have a “storm surge” protection feature. When the wind speed exceeds a threshold, the ridge vents are closed so that they are not damaged by high winds.
Precipitation Sensors
Rain sensors are commonly used to close or limit roof vents when it is raining. The sensors are mounted on the weather station to measure the precipitation. Simple rain grids indicate the presence or absence of the precipitation. Heated rain grids enable snow sensing and differentiation between dew and rain.
Climate Sensors
Temperature and Humidity Sensors
Temperature sensors in a greenhouse are exposed to the airstream and measure dry bulb temperature. The wet bulb temperature on the other hand is the temperature at which air is fully saturated (relative humidity, RH, is equal to 100%). It is used as an indication of the amount of moisture in the air.
You should locate thermostats near the centre of the greenhouse for good temperature control. Also, enclose the thermostat in an aspirated box, or shade it, so that it indicates the air temperature correctly. If the sun is permitted to shine directly on the thermostat, it will read a higher temperature than the air surrounding it. With the use of an aspirated unit, the temperature range may be only plus or minus 2 or 3 degrees off the desired setting.
Light Intensity Sensors
The light sensor is made using an LDR (light dependent resistor). The resistance of the LDR varies according to intensity of light falling on the surface. When the torch is turned on, the resistance of the LDR falls, allowing current to pass through it.
The sensors are placed under the shading system at a height approximately 30 cm above the plants on each side of the greenhouse. Light measurements help optimise growth and can be used to automate supplemental light levels in greenhouses and guide positioning of lights in indoor growth facilities. There are two common ways to measure light: (1) Photosynthetically active radiation (PAR) and (2) Global radiation, often referred to as the energy unit.
PAR Sensor
PAR or quantum sensors measure Photosynthetically Active Radiation (PAR) in the 400 to 700 nm wave band. In commercial greenhouses, they can be used to compare the PAR values at various points in the plant canopy, and under screens, and to check the PAR uniformity and intensity when deploying new lighting systems.
Pyrometer
A pyrometer is used to measure global radiation which is the most common light measurement for greenhouse control because it measures the entire spectrum of energy producing light. The common unit of measurement is watts per square metre per second (W/m2).
Water Sensors
Sensors such as tensiometers, electric resistance blocks and dielectric sensors are used to determine either the water availability (soil moisture) or actual water content in the substrate.
Tensiometers
Tensiometers are simple instruments consisting of a plastic (typically) tube, a porous ceramic cup at one end, and a vacuum gauge at the other. Nowadays, gauges are substituted by pressure transducers which give precise readings and allow continuous monitoring.
Electric Resistance Block Sensors
Electric resistance block sensors are also known as gypsum block sensors. The principle of operation is that the resistance of an electrode-embedded porous block is proportional to its water content. Thus, the wetter a block is, the lower the resistance measured across two embedded electrodes.
Dielectric Sensors
Dielectric sensors measure the soil dielectric constant, an important electrical property that is highly dependent on substrate moisture content. The substrate dielectric constant can be considered as the substrate’s ability to transmit electricity and it increases with the increase of substrate water content. One advantage of this type of sensor is it gives an almost instantaneous reading.
Nutrition Sensing
pH Sensors
pH sensors measure hydrogen ion activity and produce a voltage. The sensor operates based on the principle that an electric potential develops when two liquids of different pH levels come into contact on opposite sides of a thin glass membrane. The thin glass membrane can facilitate ion exchange. As the ions exchange, they create a voltage that is measured by the measurement electrode. This voltage is converted into a corresponding pH level.
EC Sensors
EC sensors measure the ability of materials to conduct an electrical charge. They are composed of two electrodes, which when they detect a voltage give a reading. Based on the distances between the electrodes the resistance can be calculated. They are most useful for measuring the resistance of nutrient solutions since they contain positively and negatively charged ions from salts. Greater conductance indicates greater nutrient solution strength. Therefore, an EC sensor can help to allow plants to absorb essential fertile nutrients for maximum plant growth.
