A.  Temperature Units: ^oF, ^oC, Kelvin (K)
 

             F = 9/5 ^oC + 32
             C = 5/9 (^oF - 32)
                Precise temperature measurements are made by using thermocouples or thermistors
 
 

Table 1. Temperature Conversion Table

To convert a temperature in either Celsius or Fahrenheit to the other scale, find that temperature in the center column, and then find the equivalent temperature in the other scale in either the Celsius column to the left or in the Fahrenheit column to the right.

On the Celsius scale the temperature of melting ice is 0^oand tile temperature of boiling water is 100^oat normal atmospheric pressure. On the Fahrenheit scale the equivalent temperatures are 32^o and 212^o respectively. The formula for converting Celsius to Fahrenheit is 'F = % ^oC + 32, and the formula for converting Fahrenheit to Celsius is ^oC = -5/9(^oF - 32).
 

oC	oC or oF	oF		oC	oC or oF	oF		oC	oC or oF	oF
-73.33	-100	-148.0		-6.67	20	68.0		15.6	60	140.0
-75.56	-95	-139.0		-6.11	21	69.8		16.1	61	141.8
-67.78	-90	-130.0		-5.56	22	71.6		16.7	62	143.6
-65.00	-85	-121.0		-5.00	23	73.4		17.2	63	145.4
-62.22	-80	-112.0		-4.44	24	75.2		17.8	64	147.2
-59.45	-75	-103.0		-3.89	25	77.0		18.3	65	149.0
-56.67	-70	-94.0		-3.33	26	78.8		18.9	66	150.8
-53.89	-65	-85.0		-2.78	27	80.6		19.4	67	152.6
-51.11	-60	-85.0		-2.78	27	80.6		19.4	67	152.6
-48.34	-55	-67.0		-1.67	29	84.2		20.6	69	156.2
-45.56	-50	-58.0		-1.11	30	86.0		21.1	70	158.0
-42.78	-45	-49.0		-0.56	31	8708		21.7	71	15
-40.0	-40	-40.0		0	32	89.6		22.2	72	161.6
-37.23	-35	-31.0						22.8	75	163.4
-34.44	-30	-22.0		0.56	33	91.4		23.3	74	165.2
-31.67	-25	-13.0		1.11	34	93.2		23.9	75	167.0
-28.89	-20	-4.0		16.7	35	95.0		24.4	76	168.8
-26.12	-15	5.0		2.22	36	96.8		25.0	77	170.6
-23.33	-10	14.0		2.78	37	98.6		25.6	78	172.4
-20.56	-5	23.0		3.33	38	100.4		26.4	79	174.2
-17.8	0	32.0		3.89	39	102.2		26.7	80	176.0
				4.44	40	104.0		27.2	81	177.8
-17.2	1	33.8		5.00	41	105.8		27.8	82	179.6
-16.7	2	35.6		5.56	42	108.6		28.3	83	181.4
-16.1	3	37.4		6.11	43	109.4		28.9	84	183.2
-15.6	4	39.2		6.67	44	111.2		29.4	85	185.0
-15.0	5	41.0		7.22	45	113.0		30.0	86	186.8
-14.4	6	42.87		7.78	46	114.8		30.6	87	188.6
-13.9	7	44.6		8.33	47	116.6		31.1	88	190.4
-13.3	8	46.4		8.89	48	118.4		31.7	89	192.2
-12.8	9	48.2		9.44	49	120.2		32.2	90	194.0
-12.2	10	50.0		10.0	50	122.0		32.8	91	195.8
-11.7	11	51.8		10.6	51	123.8		33.3	92	197.6
-11.1	12	53.6		11.1	52	125.6		33.9	93	199.4
-10.6	13	55.4		11.7	53	127.4		34.4	94	201.2
-10.0	14	57.2		12.2	54	129.2		35.0	95	203.0
-9.44	15	59.0		12.8	55	131.0		35.6	96	204.8
-8.89	16	60.8		13.3	56	132.8		36.1	97	206.6
-8.33	17	62.6		13.9	57	134.6		36.7	98	208.4
-7.78	18	64.4		14.4	58	136.4		3702	99	210.2

            a.   cal = calorie
                      = Amount of heat required to raise the temp of 1g water by 1C (specifically from 15 ^oC to 16 ^oC)
                           (1 kcal = 1000 cal)

            b.  BTU = British Thermal Unit
                         =  Amount of heat required to raise the temp of 1 lb water by 1^oF  (specifically from 62 F to 63F)
                              (1 BTU = 252 cal)

     C.  Heat Absorption and Release by Water

                    Solid          ^heat       >  Liquid        ^heat*         >   Gas
                    (Ice)                          (water)                            (vapor)

                    Vapor      ^{- heat}         > Water          ^{- heat**}       > Ice
 

               *Heat of vaporization =  970 BTU/lb
                     When water evaporated, heat energy (979 btu/lb) is absorbed from the surrounding.
                                This phenomenon is utilized in the evaporative cooling system in greenhouse production.

               **Heat of Fusion
                            When water freezes, it releases heat to the surrounding.
                                This phenomenon is widely applied in horticulture
                                    - Sprinking of water on the trees to form ice in a citrus orchard
 

     D.   Dry-Bulb and Wet-Bulb Temperatures

2. Movement of HeatEnergy

    A. Convection - Transfer of heat from one place to another by air or water movement

    C. Radiation - Emission of heat energy from a surface of metal to air

3. Biological Effects of Temperature

    A.  Q₁₀ - Change in rate of chemical reaction brought about by a 10 ^oC temperature rise
                   The rate of reaction doubles every time temp rises 10 ^oC
                            - To reduce the rate of respiration, fruits and vegetables are stored in the refrigerator.

    B. High temperature damage
                    Desiccation injury due to excessive water loss
                    Heat tolerance by production of heat-shock proteins

    C. Low temperature damage
 

When cell saps (protoplasm) or intercelluar water freeezes, ice crystals are formed.  These ice crystals rupture cell walls, making the cell contents leak out and killing the plant. The tissues of cold tolerant plants like evergreens do not form ice crystals, keeping cell walls intact.

           Supercooling- presence of water in liquid or non-crystalline state below the freezing point by osmotic adjustment
                                    Example -  pine needles

    D.  Hardening

           Cold acclimation - plants acclimate themselves
        Cold acclimatization - we acclimatize plants
        Increase in the concentration of carbohydrates (sugars) as osmoticum

    E. Cryogenic Storage
            Storage in liquid N (-196 ^oC, -320 ^oF) - pollen, seed, meristem

4. Dewpoint and Frost

    A. Dewpoint

                Temperature at which RH reaches 100%
                Condensation (dew) of water vapor at temp dew point, 32F

    B. Frost

            White Frost -  Frozen dew occurs when air temp is dew point 32F and when humidity is high
            Black Frost -  freezing of tissue appearing 'dark' occurs when humidity is low (at above dew point, below 32F)

   C. Causes of Frost

            Radiation frost -  formed by rapid radiation of heat to air  (clear day, 32F by weather forecast)
            Air-mass freeze -  by cold air mass with temp below 32F  (most winter cold damage)

5. Thermal Belt and Temperature Inversion

    A. Thermal belt

        A relatively warm microclimate formed by cold air drainage, usually on a slope
            good site for orchard

        South-facing vs. north-facing

    B.  Frost pocket

        Usually formed by temperature inversion in low areas of a valley site for cold drainage

            use wind machine to mix air

6. Temperature Controls

    A. Cultural practices

            Mulching - use of crop residue or organic materials
                            use of plastics (clear vs. opaque)

    B. Frost control

        1)  by Escape

                - Wait seedling transplanting until it is frost-free (mid May in Fargo?)
                - Delay blooming - variety selection, evaporative cooling
                - Use of INA bacteria? (strawberry in California)
                        genetically engineered or mutant ice-nucleating active bacteria

        2) by Reduction of heat loss

                    Hotcaps
                    Plastic tunnels
                    Cold frames - for seedling culture

        3) by addition of heat

             Smudging - burning of fuel in orchard
             Water sprinkling (heat of fusion released) to form ice on plant
                                Florida orchards

7. Plant Growing Structures

        CEA- Controlled Environment Agriculture (Read page 285 text)
                (Greenhouse Production)

        a. Cold frames - inexpensive, mostly for seedling culture, bulb-forcing

        b. Hotbeds -seedling culture
                        Heat source - composting, electrical, hot water

        c. Cloches and plastic tunnels - extensively used in Europe and Japan

        d. Greenhouses - more than 85% used for floriculture (US)
                                over 65% used for vegetables in Europe

        e. Shade houses - for hardening plants for transplanting
                                    (mostly for nursery crops)