Frost Protection - UTL Repository

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F R O S T P R O T E C T I O N : F U N D A M E N T A L S , P R A C T I C E A N D E C O N O M I C S 8] [ cleared (i.e. 21–25 December 1990 and 23–25 December 1998), the subzero temperature resulted from radiation losses rather than advection of cold air. Major frosts occur in Mediterranean climates, but they tend to be more common in the eastern part of continents where cold continental air masses occasionally advect from arctic regions into subtropical areas. Some of the best examples are in the Florida, USA, citrus growing region. Attaway (1997) describes the first “major impact” frost, which occurred in 1835, by citing John Lee Williams’ account of the frost, which stated that “the northwest wind blew for 10 days and the temperature fell as low as -13.9 °C. Even the local river froze and all kinds of fruit trees were killed to the ground as far south as 28 °N latitude.” Clearly, there is a big difference when trying to protect against subzero temperatures in windy conditions without an inversion than to protect against a relatively mild radiation frost. The saving grace is that major frost events tend to be sporadic, whereas radiation frost events occur often. CLASSIFICATION OF PROTECTION METHODS <strong>Frost</strong> protection techniques are often separated into indirect and direct methods (Bagdonas, Georg and Gerber, 1978), or passive and active methods (Kalma et al., 1992). Passive methods are those that act in preventive terms, normally for a long period of time and whose action becomes particularly beneficial when freezing conditions occur. Active methods are temporary and they are energy or labour intensive, or both. Passive methods relate to biological and ecological techniques, including practices carried out before a frost night to reduce the potential for damage. Active methods are physically based and energy intensive. They require effort on the day preceding or during the night of the frost event. Active protection includes heaters, sprinklers and wind machines, which are used during the frost night to replace natural energy losses. A classification of methods is presented in Table 1.2. GEOGRAPHICAL ASSESSMENT OF FROST DAMAGE TO CROPS <strong>Frost</strong> damage can occur in almost any location, outside of tropical zones, where the temperature dips below the melting point of water (0 °C). The amount of injury depends on the crop’s sensitivity to freezing at the time of the event and the length of time the temperature is below the “critical damage” temperature (T c ). For example, Argentina, Australia, Canada, Finland, France, Greece, Israel, Japan, Jordan, New Zealand, Portugal, Switzerland, United States of America and Zambia have developed minimum temperature forecasting techniques (Bagdonas, Georg and Gerber, 1978) to aid frost protection. Of course, many other countries in temperate and arid climates and at high elevations also have problems with frost damage.
INTRODUCTION TABLE 1.2 Categories and sub-categories for methods of frost protection CATEGORY Passive Active SUB- CATEGORY Biological (avoidance or resistance) Ecological Covers and Radiation Water Heaters Wind machines Combinations PROTECTION METHOD Induction of resistance to freezing without modifying plant genetics Treatment of the seeds with chemicals Plant selection and genetic improvement Selecting species for timing of phenological development Selecting planting dates for annual crops after the probability of freezing lessens in the spring Growth regulators and other chemical substances Site selection for cropping Modification of the landscape and microclimate Controlling nutritional status Soil management Cover crop (weed) control and mulches Organic materials Covers without supports Covers with supports Over-plant sprinklers Under-plant sprinklers Microsprinklers Surface irrigation Artificial fog Solid fuel Liquid fuel Propane Horizontal Vertical Helicopters Fans and heaters Fans and water 9
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Page 3 and 4: FOREWORD Agrometeorology deals with
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Page 11 and 12: LIST OF PRINCIPAL SYMBOLS Roman Alp
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Page 17 and 18: INTRODUCTION Freeze and frost defin
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] F R O S T P R O T E C T I O N : F
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CHAPTER 4 FROST DAMAGE: PHYSIOLOGY
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FROST DAMAGE: PHYSIOLOGY AND CRITIC
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CHAPTER 5 FROST FORECASTING AND MON
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FROST FORECASTING AND MONITORING st
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CHAPTER 6 PASSIVE PROTECTION METHOD
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PASSIVE PROTECTION METHODS enhance
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PASSIVE PROTECTION METHODS use an
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PASSIVE PROTECTION METHODS FIGURE 6
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PASSIVE PROTECTION METHODS After st
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PASSIVE PROTECTION METHODS of miner
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PASSIVE PROTECTION METHODS FIGURE 6
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PASSIVE PROTECTION METHODS CANOPY T
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PASSIVE PROTECTION METHODS damage h
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PASSIVE PROTECTION METHODS of culm
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PASSIVE PROTECTION METHODS AVOIDING
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PASSIVE PROTECTION METHODS TABLE 6.
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PASSIVE PROTECTION METHODS Organic
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PASSIVE PROTECTION METHODS Fucik (1
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PASSIVE PROTECTION METHODS Many com
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] Once started, the sprinklers shou
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CHAPTER 8 APPROPRIATE TECHNOLOGIES
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APPROPRIATE TECHNOLOGIES frost prot
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APPROPRIATE TECHNOLOGIES fashion. O
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APPROPRIATE TECHNOLOGIES CROP COUNT
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APPROPRIATE TECHNOLOGIES CROP COUNT
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APPROPRIATE TECHNOLOGIES other crop
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APPENDIX 2 CONSTANTS Specific heat
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- FAO ENVIRONMENT AND NATURAL RESOU
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