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 oF• Greenhouse air can be cooled down to the wet-bulb temperature

Cool-cell pad Exhaust 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: ________oF Wet-bulb temp: ________oF

Greenhouse Cooling with High-Pressure Fogging System

• Use high-pressure (1000 psi) to generate fog (size 25-40 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 oC, -320 oF)

Permanent storage of pollen, seed, meristems

Thermal Belt

Normal Condition Temperature Inversion

coldwarm cold

warm

warm slope

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.

A B

Normal Damaged

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