Light

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Light

• Plant Science
• Chapter 8

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What is light?

• energy that travels in wavelengths
• short wavelengths high energy (blue)
• long wavelengths low energy (red)
• ultraviolet invisible

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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

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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

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What is light duration?

• length of day
• Long Day Plants gt13 hours
• Short Day Plants lt12 hours
• Day Neutral Plants no response

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How does temperature influence crop selection?

• Warm Season Crops - soil temp gt70 degrees (corn)
• Cool Season Crops - soil temp lt70 degrees (wheat)

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What are the Cardinal Temperatures?

• minimum, maximum, optimal temperatures for a crop
• wheat min40 max90 (when flowering)
• crops generally don't grow in areas where average
  24 hour temperature lt50 or gt130

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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

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How does snow cover affect the temperature of the
soil?

• snow cover insulates, keeps warm

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How can we keep a crop from freezing? (orchards
etc.)

• heaters, smudge pots, irrigation, fans

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What is Vernalization?

• some plants need periodic exposure to cold to
  regulate life cycle
• cherries, winter wheat, sugar beet

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What is Bolting?

• sugar beets are exposed to cold during the first
  year, which triggers the plant to flower instead
  of develop roots

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