1. Why and how the following weather elements are important and influence the growth and development of crop plants and yield? a. Rainfall b. Relative Humidity c. Sunshine d. Air-Temperature e. Wind velocity After successful completion of 5 Lessons in this Module, you have learned to answer: Virtual Academy for the Semi Arid Tropics Course on Crop-Weather Relationships Module IV: Weather and Plant Growth

2. Lesson 1: Rainfall and plant growth Lesson 2: Relative humidity and plant growth Lesson 3: Sunshine and plant growth Lesson 4: Air-Temperature and plant growth Lesson 5: Wind and plant growth The 5 Lessons in this Module are: Virtual Academy for the Semi Arid Tropics Course on Crop-Weather Relationships Module IV: Weather and Plant Growth

3. Virtual Academy for the Semi Arid Tropics Lesson 2: Relative humidity (RH) and plant growth Course on Crop-Weather Relationships Module IV: Weather and Plant Growth After successful completion of 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?

4. Virtual Academy for the Semi Arid Tropics Lesson 2: Relative humidity (RH) and plant growth Course on Crop-Weather Relationships Module IV: Weather 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.photosynthesis 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.

5. Virtual Academy for the Semi Arid Tropics Lesson 2: Relative humidity (RH) and plant growth Course on Crop-Weather Relationships Module IV: Weather 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.stomata At higher RH percentages, the stomata have problems getting rid of excess water.

6. Virtual Academy for the Semi Arid Tropics Lesson 2: Relative humidity (RH) and plant growth Course on Crop-Weather Relationships Module IV: Weather 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

7. This concludes Lesson 2- Relative Humidity and plant growth - in this Module. Next Lesson is about Sunshine and plant growth. Select Lesson 3 from Module IV contents Virtual Academy for the Semi Arid Tropics Course on Crop-Weather Relationships Module IV: Weather and Plant Growth

8. One of the major differences between plants and animals is plants' ability to manufacture their own food. This process is called photosynthesis. Photosynthesis To produce food, a plant requires energy from the sun, carbon dioxide from the air, and water from the soil. During photosynthesis, it splits carbon dioxide into carbon and oxygen, adds water, and forms carbohydrates (starches and sugars). After producing carbohydrates, a plant either uses them as energy, stores them, or builds them into complex energy compounds such as oils and proteins.

9. Stoma (plural: stomates, stomata) – Tiny openings in the epidermis that allow water, oxygen, and carbon dioxide to pass into and out of a plant. Stomata Cross section of leaf