Light

1. Light Plant Science Chapter #8

2. What is light? • energy that travels in wavelengths • short wavelengths = high energy (blue) • long wavelengths = low energy (red) • ultraviolet = invisible

3. What is meant by light quality? • amount of light of different colors • plants absorb red & blue, reflect green • smoke filters blue, sun looks red • glass & plastic filter light

4. What is meant by light quantity? • amount of light energy recieved • measured in foot candles • summer day = 10,000 • living room = 20 • crops need 100-10,000 • if not enough light, grow tall (leggy, weak stems) • weed control reduces competition for light • planting rate & row spacing • some plants need shade (tobacco), burlap, lathes, screens

5. What is light duration? • length of day • Long Day Plants >13 hours • Short Day Plants <12 hours • Day Neutral Plants = no response

6. How does temperature influence crop selection? • Warm Season Crops - soil temp >70 degrees (corn) • Cool Season Crops - soil temp <70 degrees (wheat)

7. What are the Cardinal Temperatures? • minimum, maximum, optimal temperatures for a crop • wheat min=40 max=90 (when flowering) • crops generally don't grow in areas where average 24 hour temperature <50 or >130

8. What is the Frost Free Period? • the time from the last killing frost until the first killing frost of summer • at least 90 days • plant spring wheat when average soil temperature is 37 degrees

9. How does snow cover affect the temperature of the soil? • snow cover insulates, keeps warm

10. How can we keep a crop from freezing? (orchards etc.) • heaters, smudge pots, irrigation, fans

11. What is Vernalization? • some plants need periodic exposure to cold to regulate life cycle • cherries, winter wheat, sugar beet

12. What is Bolting? • sugar beets are exposed to cold during the first year, which triggers the plant to flower instead of develop roots