Environmental Control: Temperature, Humidity and Ventilation
This domain tests your ability to read temperature, humidity and airflow together and choose a control action. The exam favours VPD reasoning over isolated humidity numbers.
Target ranges and controls
- Most greenhouse vegetables grow well at 20–28°C by day and 15–18°C at night; avoid sustained above 32°C.
- Relative humidity of 60–70% is a working range; VPD around 0.5–1.2 kPa supports transpiration.
- Ventilation removes hot air and adds CO2; fan-and-pad cooling can lower air temperature by roughly 5–8°C in dry heat.
- Fogging raises humidity and cools slightly; shading cuts incoming radiation by 30–50% in summer.
- Heating is rarely needed in Maharashtra but may protect seedlings in winter nights.
Worked example
At 2 pm the house reads 38°C and 40% RH. Reasoning: VPD is high, so the crop is stressed and stomata may close. Immediate actions: open ridge and side vents, apply 35% shade, start fogging in pulses, and check that the pad system is not recirculating warm water. Do not spray water on foliage at high temperature without ventilation, because leaf scorch and disease risk rise.
Traps that cost marks
- Reading RH alone and missing that high temperature makes VPD too high.
- Closing vents to keep humidity up while temperature climbs.
- Running foggers continuously and creating leaf wetness.
- Using shade as the only cooling method and reducing photosynthesis too much.