Chap 10. Temperature  Temperature and Heat Units  Thermal Properties of Water  Movement of Heat Energy  Biological Influence of Temperature  Dew Point and Frost  Thermal Belt and Temperature Inversion  Temperature Control for Crop Protection  Controlled Environment Agriculture (CEA)

Heat of Vaporization  Heat is absorbed from surrounding when water evaporates  Heat of vaporization = 970 BTU per lb of water evaporated  Greenhouse cooling by the pad-and-fan evaporative system

Pad-and-fan evaporative cooling system Evaporative pad on one side wall and fans mounted on the other side wall Flow of cooled air from pad area to fan area ( one air exchange/min) Maximum distance from pad to fan = 200 feet Temperature differential (∆T) between pad and fan areas is usually 7 o F Greenhouse air can be cooled down to the wet-bulb temperature Cool-cell padExhaust fans mounted on the side wall

Psychrometric Chart Illustrates the thermal properties of air Dry-bulb temperature Air temperature of sensible heat measured by dry-bulb thermometer Wet-bulb temperature Temperature of an aspirated thermometer measured with the bulb encased in a water saturated wick Measure the room temperature Dry-bulb temp: ________ o F Wet-bulb temp: ________ o F

Greenhouse Cooling with High-Pressure Fogging System Use high-pressure (1000 psi) to generate fog (size µ diam) Use stainless steel pipe to prevent corrosion problem Use low-salinity de-ionized water to prevent clogging of nozzles More efficient in cooling the ambient air where it is needed Less disease and algae problem, compared to misting system Cost of installation high High-pressure fogging Summer cooling of greenhouse with fogging system

Heat of Fusion  Heat is released to surrounding when water freezes  Heat of fusion is used to protect citrus fruits from freezing

Heat of fusion from ice formation protects citrus crops exposed to freezing temperature in Florida

Overhead water sprinkling on citrus crops in Florida to save them from freezing

Transfer of Heat Energy

Temperature Influence in Biological System

Cell Damage by Low Temperature  Ice crystals rupture cell walls  Intracellular or intercellular event  Leakage of cell contents  Readily occurs in tender plants  Influence of “extensin” on cell wall Ice crystals Cell wall ruptures Extensin (rupture-resistant)

Cryogenic Storage  Liquid nitrogen (-196 o C, -320 o F)  Permanent storage of pollen, seed, meristems

Thermal Belt Normal Condition Temperature Inversion cold warmcold warm warm slope  Good site for locating an orchard  Usually on a sloped hill side  North-facing slope is better the south-facing slope

Peach orchard located on a thermal belt, Western Slope, Colorado

Fruit growing area in Oregon

Grape orchards (vinyards) in Napa Valley, California Frost damage in vinyards is not as severe in other orchards because flowering of grapes occurs after shoot emergence

Windmills and helicopters are used to mix the air to prevent frost damage on fruit crops during temperature inversion Prevention of frost damage by movement

Use of Plastic Mulch

Strawberry Production in California

Frost Damage on Strawberry Plants in California A. Freezing of leaves is often initiated by the presence of ice nucleating active (INA) bacteria that secrete proteins that act as primers for ice crystal formation B. Crop failure often results from freezing of flower parts that are delicate and fragile. Stigmas and anthers are easily damaged by light freeze and become incapable of pollination and fertilization. AB NormalDamaged

Ice Nucleating Active (INA) Bacteria on Strawberries  INA bacteria secrete protein on the leaf  Protein serves as a primer for ice crystal formation  Mutant INA bacteria secrete defective proteins (ice-)  Mutant proteins are incapable of forming Ice crystals Wild type INA bacteria Mutant type INA bacteria defective protein Ice crystals formed on the leaf → frost damage No ice crystals formed on the leaf → no frost damage

Smudging in a fruit orchard to prevent frost injury

Plant Growing Structures Controlled Environment Agriculture (CEA)  Cold Frames  Hotbeds  Cloches and Plastic Tunnels  Greenhouses  Shade and Lath Houses

Cold Frame

Cloches or Hotbeds

Use of Hotcaps for Vegetable Production

Standard Peak Greenhouses

Gutter-connected Standard Peak Greenhouses

Construction of a Modern Greenhouse

Quonset House

Air Inflated plastic greenhouses

Air Inflated Greenhouse with no internal support structure

Geodesic Dome Greenhouse