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Executive summary

This publication reviews the physical, chemical and biological factors involved in frost damage to agricultural and horticultural plants, and presents common methods of frost protection. In addition, computer analysis tools are provided to help growers design and manage various frost protection methods, investigate the risk of freezing temperatures and to analyse the economics of frost protection methods relative to risk, in order to decide on the costs and benefits of various protection methods.

Although the World Meteorological Organization (WMO) has published information on frost protection in the past, this is the first FAO publication specifically written on frost protection, and it greatly expands on the old WMO publication. It synthesizes and simplifies complex, technical information from the literature to provide understandable guidelines to reduce losses due to frost damage -losses that can be economically devastating for growers and their local communities.

Typical weather during freezing conditions is discussed, and computer tools are provided to predict minimum temperatures and temperature trends during radiation frost nights. In addition, the publication presents information on how environmental factors (soil conditions, clouds, fog, plant canopies, etc.) affect energy balance and how these factors affect temperature trends.

The publication discusses what happens to plant tissue when freezing temperatures occur, and it presents information on the sensitivity of plants to frost damage. The biological factors that affect freezing are presented (including growth stage, cell solute content and ice-nucleating bacteria), and the possible management methods to manipulate those factors are discussed (choice of rootstocks and varieties, water application, soil fertility, bacteria control, etc.).

The main methods of passive frost protection (no-tillage, wetting dry soils, removing litter and cover crops, etc.) are thoroughly discussed to provide growers with the most cost-effective methods of frost protection. A discussion of active frost protection (liquid- and solid-fuel heaters, surface irrigation, sprinklers and wind machines) is presented to indicate how the methods work and how to manage them - alone or in combination - for optimal protection.

Finally, a thorough discussion of the risks and economics of various protection methods is provided, together with computer applications to help simplify computations. The text and the accompanying Excel-based software applications should help growers and consultants to make wise decisions on the cost-effectiveness of alternative protection methods, depending on the local risk of frost and other factors.

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