Importance of Temperature Control
Temperature plays a crucial role in the physiological processes of plants, including photosynthesis, respiration, translocation, ion uptake, transpiration, pigment formation, and reproduction. The biochemical processes in plants can double with every 10 degrees Celsius rise in temperature. However, if the soil is cold, water and ion uptake, as well as root growth, will be reduced. Therefore, the temperature in a greenhouse is dependent on the types of plants being grown, as different species require different temperature ranges for optimal growth.
Optimal Temperature Ranges
Optimal temperature refers to the best temperature at which plants can grow under specific climatic conditions. This range varies for different species and is influenced by factors such as day and night cycles, seasonal changes, location, and growth stages (e.g., germination, rooting, fruiting). For instance, the temperature requirements for tomatoes at various growth stages are as follows:
- Seed Germination: Minimum 11°C, Maximum 34°C, Suitable Range 16-29°C
- Seedling Growth: Minimum 18°C, Maximum 32°C, Suitable Range 21-24°C
- Fruit Set Day Temperature: Minimum 18°C, Maximum 30°C, Suitable Range 20-24°C
- Fruit Development at Night: Minimum 10°C, Maximum 30°C, Suitable Range 15-17°C
These examples illustrate that each biological process has a minimum and maximum temperature limit, as well as a suitable range where optimal activity occurs.
Methods of Temperature Control in Greenhouses
Temperature in a greenhouse can be controlled by either increasing or decreasing it, depending on the plants' requirements. There are two main types of methods for temperature control:
- Active Methods: These require continuous involvement and adjustment.
- Passive Methods: These do not require continuous adjustment once set up.
Active Methods to Increase Temperature
- Use of Heaters with Fans: A heater combined with a fan circulates hot air inside the greenhouse, effectively raising the temperature.
- Use of Boilers: Black-painted metal pipes are laid down in the greenhouse, and hot water from a boiler flows through these pipes, releasing heat by radiation to increase the greenhouse temperature.
Active Methods to Decrease Temperature
- Minimization of Direct Beam Radiation: Screens can be used to control the entry of direct sunlight, thereby reducing temperature increases.
- Evaporative Cooling Systems: This includes:
- Fan and Pad System: A cooling pad is installed on one side, and water is circulated over it. A fan on the opposite side pulls air through the pads, cooling it before it enters the greenhouse.
- Fog Systems: Fine mist is sprayed throughout the greenhouse, providing uniform cooling compared to the pad and fan system.
- Use of Gani Cloth: Covering the roof with thick cloth and spraying water over it allows for evaporative cooling, reducing heat inside the greenhouse.
Passive Methods of Temperature Control
- Water Storage: Water tanks are placed on the north side of the greenhouse to store excess heat during the day and release it at night.
- Latent Heat Storage Materials: Materials like hydrated calcium chloride can absorb heat during the day and release it at night, helping to maintain temperature stability.
- Buried Pipe Ground Storage: Plastic or aluminum pipes buried underground circulate air, transferring heat from the air to the ground during the day and releasing it at night.
- Rock Bed Storage: A rock bed made of gravel is placed below the greenhouse floor to absorb heat during the day and release it at night.
- North Wall Storage: A black-painted brick wall on the north side absorbs heat during the day and releases it at night, helping to regulate temperature fluctuations.
Conclusion
In summary, controlling temperature in a greenhouse is vital for the healthy growth of plants. Various methods, both active and passive, can be employed to maintain optimal temperature ranges, ensuring that plants thrive under the best possible conditions. Understanding these systems is essential for effective greenhouse management and maximizing plant productivity.
