heat - a quantitative measure of the amount of heat energy;
                     - it is a measure of the quantity or amount of heat energy.

MEASURES OF HEAT (HEAT ENERGY)
calorie (cal) - amount of heat (heat energy) required to raised 1 g of water by 1 ^oC.
kilocalorie (kcal) - 1,000 calories 
British Thermal Unit (BTU) - amount of heat required to raise 1 lb. of water by 1 ^oF 
specific heat - amount of heat (# calories) needed to raise 1 g of a substance by 1 oC.
                              (water = 1.0)
heat of fusion - amount of heat (# calories) needed to change 1 g of a substance from solid to
                         liquid at its melting/freezing point. (water = 80 cal/g)
heat of vaporization - amount of heat (# calories) needed to change 1 g of a substance from
                                   liquid to gas at its boiling/condensation point. (water = 540 cal/g) 

WAYS TO TRANSFER HEAT (HEAT ENERGY)
There are 3 ways in which heat (heat energy) can be moved
1) conduction- flow of heat energy through a medium from molecule to molecule.
2) convection - mass movement of heat energy. 
3) radiation- flow of energy as electromagnetic waves, with no transferring medium; when 
                     radiation is absorbed it may be converted to heat energy.

How the Greenhouse Effect Happens
The greenhouse effectgets its name from the  heat build-up characteristic in greenhouses during the day.  Solar radiation from the sun is composed of relatively short wavelength radiation, with about 10% being ultraviolet (UV), about 40% being visible and about 50% being short wavelength near infrared (IR).  This radiation is absorbed by the objects of the earth or inside the greenhouse and the radiant energy is converted into heat energy and the objects increase in temperature.  The objects will then begin cooling themselves by conduction, convection and radiation.  The radiation emitted (re-radiated) is long  wavelength IR.  The atmosphere and greenhouse glass are opaque to the long wavelength IR.  In the atmosphere, carbon dioxide gas and water vapor absorb the long wavelength IR, which is then radiated back down, thus trapping the long wavelength IR in the earth's atmospheric environment.  In the greenhouse, the glass bounces the long wavelength IR back down.  This trapped long wavelength IR is absorbed by objects, which causes further heating, and the cycle continues.  Thus, the earth and greenhouse act as solar collectors. 

Carbon Dioxide Emissions and Global Warming
The increased carbon dioxide emissions from burning fossil fuels (and  to a lesser degree massive forest and oil field fires) have caused the level of carbon dioxide in the atmosphere to increase from about 300 ppm to 350 ppm over the last century.  This is "fueling" speculation of global warming due to an enhanced greenhouse effect.  Is it real?  Time will tell!
 

TERMINOLOGY USED TO DESCRIBE CLIMATE OVER SMALL AREAS
1) macroclimate- the climate or weather conditions of a relatively large area, usually 24-50 miles.
2) local climate - the climate or weather conditions of a smaller localized area; ex. a valley,
                            stand of trees, open field, sides of a hill, etc.
3) microclimate - the climate or weather conditions of a very small area, ex. inside vs. outside
                            a canopy, upper vs. lower leaf surface, etc.
.
GLOBAL CLIMATIC ZONES - (determined by position of the earth relative to the sun)
1) Tropical Climatic Zone
    The area between the 23 1/2^o latitude N and S of equator.
    Between the Tropic of Cancer (off S. tip of Fla. and middle of Mexico) & Tropic of Capricorn
    Warm, rarely if ever freezes
2) Temperate Climatic Zone
    The area between the 23 1/2^o and 66 1/2^o latitude N & S.
    Between Tropic of Cancer and Arctic Circle, and Tropic of Capricorn and Antarctic Circle.
    Has hot and cold seasons
    a)sub-tropical - often used to describe the southern most area of Temperate Climatic Zone 
        (ex. South Florida and Rio Grande Valley), but it is not an official climatic zone.
3) Arctic Climatic Zone
   The area between the 66 1/2^o N latitude and the N. Pole and the 66 1/2^o S latitude & the S. Pole.
   North of Arctic Circle, and south of Antarctic circle.
    Always cold and frozen

Seasons: Caused by the unique tilt of earth and orientation to sun
summer solstice - June 21 or 22, when earth's axis is tilted 23 1/2^o towards sun.
    Warmer due to:
    a) sun's rays concentrated over smaller area
    b) sun's rays travel through thinner layer of atmosphere
    c) days longer
winter solstice - Dec. 21 or 22, when earth's axis is tilted 23 1/2^o away from sun
    Colder due to:
    a) sun's rays spread over larger area
    b) sun's rays pass obliquely through thicker layer of atmosphere
    c) shorter days
vernal or spring equinox - March 20 or 21, when earth's axis is oriented oblique to,
    but neither towards nor away from, the sun
autumnal or fall equinox - Sept. 22 or 23, when earth's axis is oriented oblique to,
    but neither towards nor away from, the sun

• At the summer solstice, the earth's axis is orientated 23 1/2 degrees towards the sun, thus the sun's rays strike the earth at a 90 degree angle at the Tropic of Cancer. 
• At the winter solstice, the situation is reversed, i.e. the earth's axis is orientated 23 1/2 degrees away from sun, thus the sun's rays strike the earth at a 90 degree angle at the Tropic of Capricorn. 
• At the the autumnal and vernal equinox, the earth's axis is neither orientated away from nor towards the sun (I made up the term obliquely parallel to describe this, or sometimes I call it cock-eyed parallel), thus the sun's rays strike the earth at a 90 degree angle at the equator.  

MINIMUM CARDINAL TEMPERATURE
a) growth: 40-50 ^oF (5-6 ^oC) for most species
b)survival
    1)tender or chilling sensitive: 32 to 45 ^oF (0 to 7 ^oC)
    2) semi-hardy plants: 15 to 29 ^oF (-9 to -2 ^oC)
    3) hardy plants: less than 0 ^oF (-18 ^oC)

OPTIMUM TEMPERATURE
a) cool-season plants: grow best at 65-75 ^oF (18-24 ^oC)
    1) in southern U.S.: grow as fall-winter crops.
    2) in northern U.S.: grow in late spring, summer, early fall
b) warm season plants: grow best at 78-90 ^oF (24-32 ^oC)
    1) in southern U.S.: grow in late spring and summer, early fall
    2) in northern U.S.: grow in summer, but for some warm season crops the growing season
        may be too short to get good yield.

MAXIMUM CARDINAL TEMPERATURE
a) growth: 90-96 ^oF (32-36 ^oC), most species
b) survival: 130 ^oF (54 ^oC), most species.

METHODS USED TO DECREASE HIGH TEMPERATURES
A) Soil temperatures
    1)mulch - insulates and blocks out light
B) Air temperatures
    1)Decrease light intensity (decrease both visible and infrared if possible)
        a) lath covering over nursery drops
        b) shade cloth or saran over nursery crops or greenhouses
        c) shading compound or white wash painted on greenhouse roof
        d) colored solution flowing through a double-layered greenhouse roof (primarily decreases IR)
    2)Evaporative cooling (relies on heat of vaporization)
        a) spray foliage and physical structures during mid-afternoon
        b) fine mist or fog injected into a greenhouse
        c) fan-and-pad cooling system in a greenhouse

TWO TYPES OF FREEZES BASED ON HOW THEY OCCUR
1) Radiational Freeze or Frost - temperature drops due to radiational cooling which results
                                                  in a temperature inversion; occurs on calm, clear nights (see 
                                                  diagram next page).

• radiational cooling - loss of heat by long wavelength infrared (IR) radiation. 
• temperature inversion - a warm air mass above a cold air mass. 
• dew point - the temperature at which air reaches 100% relative humidity.  

 

 
 
 
 
 

2 Types of Radiational Freezes
a) white frost - occurs when the temperature drops below both the current dew point (dew 
                       forms) and below freezing (dew freezes).
b) black frost - occurs when the temperature drops below freezing, but remains above 
                       the current dew point.

Sensitive Plants:

• tropical plants 
• tropical fruits  
• summer annuals and bedding plants  
• chilling sensitive vegetables 

 

more sensitive vs. more resistant
young tissue vs. old mature tissue
growing tissue vs. dormant tissue
flower buds vs. vegetative buds
roots vs. shoots

HOW TO PREVENT ADVECTIVE FREEZE DAMAGE
1) Plant selection - the ideal method, because then no other method is needed
2) Radiational freeze methods - some are moderately effective for mild, short freezes.
    a) Insulate: mulch, foam, hot caps (NOT fog or smoke)
    b) Increase air temperature: irrigation, oil burners or smudge pots if mild and little wind
    c) CANNOT USE: fog, smoke or eliminate temperature inversion
3) Site selection - avoid north side of hills, buildings, etc.; avoid low areas, valleys, etc.
4) Delay development in spring - avoids damage to new spring growth and flower buds 
                                                    from late spring frost.
5) Harden-off or cold acclimation in fall: is a normal part of dormancy and preparation of
                                                                the plant for for winter.
    Naturally triggered by:
    a) short days
    b) cool temperatures
    c) cold temperatures

  Allow to occur naturally by observing the following:
    1)Do not encourage growth:
         a) decrease fertilization
         b) decrease watering
         c) avoid pruning
    2)Avoid stress
         a) insect, disease or physical damage
         b) poor nutrition and nutrient deficiencies
         c) too heavy fruit load

TWO TYPES OF DORMANCY
1) Quiescence - dormancy imposed by external or environmental conditions

What triggers?
a) Unfavorable environmental conditions
b) External factor, such as hard seed coat
What causes?
Unfavorable environment; too dry, cold, hot, etc.
How to overcome?
Remove unfavorable environment

What triggers?
Environment:
a) short days (SD)
b) decreasing temperatures
What causes?
Internal physiology is unfavorable:
a) low level of growth promoters (e.g. auxin or gibberellic acid), and/or
b) high level of growth inhibitors (e.g. ABA)
How to overcome?
Give period of cold between 32-45 ^oF (0-7 ^oC), which satisfies the chilling requirement.
• chilling requirement - the number of hours of cold between 32-45 ^oF (0-7 ^oC) 

                                    required to satisfy rest.

VEGETATIVE AND FLOWER BUD DORMANCY
Cold is required for some trees and shrubs to flower and/or start vegetative growth in the spring, especially temperate trees, shrubs and other perennial plants that are native to the Temperate Climatic Zone.

• chilling requirement - the number of hours of cold temperatures between 32-45 ^oF  

                                   (0-7 ^oC) required to overcome rest (physiological dormancy).
• flower buds - usually have a shorter chilling requirement 
• vegetative buds - usually have a longer chilling requirement 

• cold storage or bulb chilling - a period of cold to satisfy chilling requirement of bulbs to 

                                                overcome flower bud rest (physiological dormancy).
• usually 6-12 weeks at 35-45 ^oC (0-7 ^oC) in a cooler or refrigerator. 

SEED REST OR EMBRYO REST
Cold is required for some seeds to germinate, especially seeds of trees and shrubs which are native to the Temperate  Climatic Zone.

• stratification - moist, cold (32-45 ^oF, 0-7 ^oC) storage  for 6-12 weeks required to 

                       overcome embryo rest (physiological dormancy).

LIFE CYCLE
1st year - grow vegetatively as rosettes or bulbs in late summer-fall
winter - are vernalized by cold of winter to trigger flower inception
2nd year - in spring flower forms and develops, called bolting

GROWTH HABITS
rosettes - radish, carrot, turnip, mustard, kale, bluebonnet, Indian paint brush
heads - cabbage
bulbs - onion

DEFINITIONS
vernalization - a cold treatment (32-45 ^oF for 4-12 weeks) required to trigger or initiate
                         flower formation in biennials.
bolting - flower formation and seed stalk elongation in biennials.
de-vernalization- exposure (1 day to 1 week) to high temperatures (90-95 ^oF) immediately 
                              after vernalization, which erases the vernalization treatment.
site of perception - growing point (apex) of stems.