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VII. TEMPERATURE IMPORTANCE

VII. TEMPERATURE IMPORTANCE. A. Greenhouse Crops affects plant growth rate important for crop timing involved in flower bud initiation controls crop quality a significant operating cost. Photosynthesis. Respiration. Optimizing light, temperature and CO 2. Temp 85; CO2 1300 ppm.

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VII. TEMPERATURE IMPORTANCE

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  1. VII. TEMPERATURE IMPORTANCE A. Greenhouse Crops • affects plant growth rate • important for crop timing • involved in flower bud initiation • controls crop quality • a significant operating cost

  2. Photosynthesis Respiration Optimizing light, temperature and CO2 Temp 85; CO2 1300 ppm Temp 70; CO2 1300 ppm Carbohydrate produced Carbohydrate metabolized Temp 70 & 85; CO2 340 ppm Light intensity increase Temperature increase Photosynthesis Carbohydrateproduced Light intensity & Carbon dioxide significantly above optimum & constant Temperature increase

  3. Optimum Linear range

  4. Factors affecting compensation pt light intensity Leaf location CO2 Compensation point Photosynthesis Apparent photosynthesis Carbohydrate metabolized or produced Respiration Temperature increase

  5. Plant growth 1. Optimum Day temperature depends on • light intensity • CO2 • Species • Stage of growth • Quality needed

  6. 2. Night temperature depends on • Day conditions (carbohydrate end of day) • Quality needed • Type of growth • Rooting • Propagation Warm roots, cool shoot • Breaks Cool temperatures promote breaks • Energy costs

  7. 3. Optimum temperature • Quality vs quantity a. young plant • Higher temperatures • Most leaves exposed to light • Photo. area = Resp. area • higher temp initially, gradually lowered b. old plant • Lower temperatures • Top leaves; high rate photo • Lower leaves; low rate photo • intensifies color • improves keeping quality

  8. 4. Grower objectives • Best possible quality • Greatest quantity • Shortest time • Greatest profit

  9. 5. Practical control 1) Thermostats (cooler months) • Night (adjusted for day environment) • Cloudy day +0-5° • Sunny day 10-15° 2) Thermostats (warmer months) • lose control: low as possible • Day: Ambient outside • Night: Ambient outside 3) Computers

  10. C. Flowering • Bud initiation • Phytochrome temp range • Bud development D. Transpiration • Lower - reduces stress

  11. E. DIF height control 1. Night/Day relationship • DIF = Day temperature - Night temperature • Ex. D N Ave. DIF • Temp* • 70 60 65 +10 • 65 65 65 0 • 60 70 65 -10 • *assumes day length = night length

  12. 2. DIF - Management a. • Change in +DIF towards -DIF • Either decrease day temp. or Increase night temp. • Effects internode length • Benefits • less growth regulators • less cost for regulators • less labor

  13. Disadvantage • Energy cost? • Management skills b. Flowering time • Same if average daily temp. same • D N Ave. DIF • 70 60 65 +10 • 65 65 65 0 • 60 70 65 -10

  14. Height control of greenhouse crop with DIF

  15. c. Additional information • Species dependent • Flowering may be inhibited • Ex. Poinsettia above 73° • Chlorosis at greater -DIF • Downward curling of leaves at greater-dif • Alternatives Lower temp. 2 hr after sunrise

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