Lesson 2: Relative humidity RH and plant growth

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Module 4 Weather and Plant Growth
Virtual Academy for the Semi Arid Tropics
Modules
Lessons

Lesson 2 Relative humidity (RH) and plant growth
After completing this Lesson, you will be able
to answer 1. Why RH is important for crop
plants? 2. What is photosynthesis? 3. How RH
is important for crops? 4. What happens if RH
is low? 5. How high RH affects plant growth?
Course on Crop-Weather Relationships
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Lesson 2 Relative humidity (RH) and plant growth

• Why RH is important for crop plants?
• Most plants prefer a relative humidity range of
  40 to 80
• High humidity in the air lowers the intensity and
  the quality of solar radiation.
• Low intensity and poor quality of solar radiation
  in turn reduces photosynthesis in crop plants.
• Reduced photosynthesis leads to low crop yields.
• High air humidity favors many plant diseases and
  insect pests. It increases the growth of shoots
  and leaves at the expense of yield of crops.

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Lesson 2 Relative humidity (RH) and plant growth

• How RH is important for crop plants?
• RH together with air-temperature and the solar
  radiation intensity, affects the rate at which
  water is evaporated from the leaves of the
  plants.
• If the evaporative demand is too high, that is,
  if the roots and duct system of the plant cannot
  deliver water to the leaves, the plant responds
  by partially or totally closing its stomata.
• At higher RH percentages, the stomata have
  problems getting rid of excess water.

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Lesson 2 Relative humidity (RH) and plant growth

• How RH is important for crop plants?
• At a lower RH, the stoma keep releasing water
  until the plant dries out.
• At that moment, the stomata close.
• Then, the intake of carbon-di-oxide stagnates,
  and plant growth is impaired.

Dots represent water vapor
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Module 4 Weather and Plant Growth
Virtual Academy for the Semi Arid Tropics
Modules
Lessons

This concludes Lesson 2- Relative humidity and
plant growth - in this Module.
Next Lesson is about Sunshine and plant
growth. Click Lessons button to select Lesson 3
Course on Crop-Weather Relationships