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October 2005

Frost protection: fundamentals, practice and economics

Environment and Natural Resources Series No. 10, FAO, Rome, 2005. 2 vols. + CD-ROM

Richard L. Snyder, University of California, Atmospheric Science Department of Land, Air and Water Resources, Davis, California, USA
J. Paulo de Melo-Abreu, Technical University of Lisbon, Instituto Superior de Agronomia, Departamento de Ciencias do Ambiente, Lisboa, Portugal
Scott Matulich, Washington State University, Department of Agricultural and Resource Economics, Washington State University, Pullman, USA

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 icenucleating 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 costeffective 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.

A thorough discussion of the risks and economics of various protection methods is provided in volume 2, 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. This volume reviews concepts of probability and risk of frost damage and uses that information to help readers make economic decisions about frost protection. Computer application programs are included with the book to help simplify complex calculations. The application programs are written in Microsoft Excel and sample calculations are presented in the text.

The TempRisk.xls application computes the probability of temperature falling below critical temperatures and then, determines the certainty that such an event will happen at least once over a defined number of years. This application is useful to determine the probability and risk of frost damage occurring when the damage sensitivity is fixed during the period of interest.

The FriskS.xls application calculates probability that a particular date will experience the last frost in the spring, the first frost in the autumn and the length of the growing season between the spring and autumn dates. The user inputs the critical damage temperature and the probabilities are computed. In addition, the certainty that an event with the computed probability will occur at least once over a selected period of years is displayed. The FriskS.xls application is useful to help people decide the physical risk of early planting or late harvest of field and row crops.

The DEST.xls application program is used to compute the risk of frost damage specific to a tree or vine crop that has changing sensitivity to frost during critical phenological stages. The program uses climate data and critical temperatures associated with 90% (T90) and 10% (T10) damage, which are input corresponding to specific phenological dates. It analyses the data between the first and last dates with sensitive phenological stages and produces tables of (1) yearly percentage frost damage for an unprotected crop and for 11 protection methods, (2) yearly yield for the unprotected crop and the 11 protection methods, (3) means and standard deviations of percentage fruit losses and crop yields and damages over years of record and (4) the mean and standard deviation of the number of frost events and the duration of the frost events. Thinning is taken into account in the fruit loss and yield calculations. If more than one damaging temperature occurs in a season, the percentage damage is applied to the potential yield after reduction due to the earlier event(s). It is similar to the FriskS.xls application, which uses one critical temperature to determine probability and risk, but it integrates over several phenological stages having different frost sensitivity.

Finally, the FrostEcon.xls program is provided to help users determine the economic risk of frost damage protection as well as the cost effectiveness of various methods of frost protection. This is an elaborate program that combines probability and risk with cost and revenue information on various protection methods to determine which if any frost protection method should be adopted. The text contains illustrative examples and the FrostEcon.xls application will help growers and consultants to make wise decisions when considering the adoption of frost protection.

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