CHAPTER 8 - APPROPIATE TECHNOLOGIES

Introduction

Passive protection is widely practiced in all countries with frost problems. In reality, passive methods are often more beneficial and cost-effective than active methods. These methods include:

• choosing sites for planting that are less prone to frost;

• planting deciduous tree and vine varieties that bloom later in the spring;

• planting annual crops after the probability of frost has diminished in the spring;

• planting deciduous crops on slopes facing away from the sun;

• planting citrus trees on slopes facing the sun;

• avoiding planting on organic soils;

• maintaining high soil water content to obtain the highest possible thermal diffusivity; and

• minimizing or removing cover crops (e.g. grasses and weeds) between rows in tree and vine crops.

In all countries, removing obstacles to cold air drainage and using topography and obstacles to influence the flow of cold air around crops provide protection and should be practised. If passive methods are inadequate to provide protection, then active methods may be needed.

Growers have and continue to use solid-fuel and liquid-fuel heaters to combat frost on a worldwide basis; however, cost and availability of fuel has become an increasing problem over time. Today, the use of stack heaters is generally restricted to high value crops in wealthy countries or countries with low-cost fuel sources. In some areas of South America, oil is burned in small open pots and many countries burn solid fuels. Because of the cost, wind machines and helicopters are mostly used on high value crops (e.g. citrus and wine grapes). Over-plant and under-plant sprinklers are used on a wide variety of tree, vine and row crops in many countries; however, the method is more cost-effective in arid climates where the benefits from irrigation partially pay for the expense of protecting against frost.

What active methods are used for frost protection depends on a combination of weather and economic factors. Most active frost protection methods are more effective when there is a temperature inversion present. In windy locations, advection rather than radiation frosts are more likely and many protection methods provide limited protection. The branches of some tree crops are damaged by ice loading when over-plant sprinklers are used, so generally under-plant sprinklers are used for citrus and deciduous tree crops with weak scaffold branches. A common trend in California is to change from trickle-drip irrigation to micro sprinklers. This change is partly to increase the volume of soil wetted by the irrigation system, which typically improves management and production, but it also provides a frost protection method that does not exist with drip irrigation. Therefore, when installing an irrigation system for a new or existing crop, using micro sprinklers rather than trickle-drip irrigation is desirable. Surface irrigation (i.e. furrow or flood) is commonly used for frost protection in locations with adequate and inexpensive water supplies. The main concerns are to apply sufficient water to provide the required heat, to ensure that the water reaches the end of the field before the temperature falls to damaging levels, and to keep the water as warm as possible (e.g. by heating or by not recirculating water).

Common protection methods

Frost protection methods used around the world were discussed by Bagdonas, Georg and Gerber (1978); however, changes in economics, pollution laws, etc., have influenced the methods currently used. A recent survey by the present authors provides some information on current protection methods and why the technology is changing. Results of the survey are shown in Table 8.1 and general conclusions are discussed here.

Because there are many publications on protection methods from Europe and North America, information from those locations is well known and the practices used have been reported in earlier chapters. However, less information on grower practices is available from other parts of the world. In March 2003, a survey questionnaire was distributed to weather services, educational institutions and government agencies around the world, with emphasis on countries not mentioned in the preceding chapters, to assess current frost protection practices. There were numerous responses to the survey from a range of countries. While some of the information collected was expected, there were some surprises.

Passive methods

It is well known that growers, regardless of the location, will attempt to minimize damage by practicing low-cost passive methods. Although the survey questionnaire did not specifically ask for information on passive methods of frost protection, some feedback was received. For example, the following passive protection methods were mentioned in the responses:

1 Site selection of frost-free sites (e.g. upper hill slopes are better).

2 Late planting to avoid sensitive stages during frost periods

3 Selecting tolerant varieties

4 Planting in protected environments (e.g. greenhouses) and transplanting after the weather warms up.

5 Creating physical barriers (e.g. walls and bushes) to control cold air drainage.

6 Covering row crops with plastic tunnels.

7 Spraying copper compounds to control INA bacteria concentrations

8 Spraying NINA bacteria on crops to compete with INA bacteria

Site selection is clearly an important practice everywhere in the world regardless of the income level of the local farmers. Many guidelines on passive methods are given in Chapter 6. Growers with limited resources can manage their soil water content, cover crops, mound soil around young tree trunks, etc., at relatively low cost. Perhaps one of the most effective low-cost technologies is to use fences, hay bales, etc., to control air drainage around sensitive crops. Removing obstacles that cause ponding of cold air is usually also cost-effective. Also, selecting varieties that are frost tolerant, and planting after the probability of damage has decreased in the spring, are simple but also cost-effective practices. Removing grasses and weeds from orchards and vineyards and avoiding planting of winter cereal crops adjacent to frost-sensitive crops is also good management.

Active methods

In the Americas from Mexico through South America, there seems to be wide usage of heaters for frost protection. Heaters are not commonly used alone in Europe or in North America, mainly because of the cost of fuel relative to the value of the crops. It is the most common method of frost protection in Mexico. The widespread usage in Mexico is probably related to the lower cost for fuel oil. Liquid fuels were also used until recently in Argentina, but the respondents noted that growers moved from using liquid-fuel to solid-fuel heaters in about 2001. Since Argentina is not a major oil producer like Mexico, it is likely that the change from liquid to solid fuels was related to rising oil prices in the early 2000s. Information on the type of liquid-fuel heaters and their management is unknown, but the pollution effects on the environment resulting from liquid-fuel heaters should be a concern. Proper management of the liquid-fuel heaters can reduce pollution effects and guidelines are given in Chapter 7. Solid-fuel heaters are used more widely than liquid-fuel heaters. In addition to Argentina, Uruguay, Turkey and Zimbabwe reported use of solid-fuel heaters (including coke, charcoal, wood, tyres and cow dung) on a wide range of crops. Environmentally friendly paraffin wax products are being studied as a solid fuel for frost protection in Argentina.

Flood irrigation for protection was reported from Mexico and Argentina, but not from the other locations. Over-plant sprinklers were used for protection of bananas in Cyprus and for blueberries, citrus and stonefruit orchards in Argentina. Over-plant sprinklers were also used over buddlings, cucurbits, flowers and potatoes in Zimbabwe. In Greece, over-plant microsprinklers are being used over kiwifruit. Under-plant techniques - both conventional and microsprinklers - are used for frost protection of citrus in Greece. No other locations mentioned the use of under-plant sprinklers. The respondent from Turkey identified the use of artificial foggers for frost protection on cherries, olives and peaches, and foggers are also used on banana trees in Cyprus. Sprinklers are sometimes used for frost protection of annual crops in the Jordan Rift Valley and mountainous regions.

Conventional (i.e. horizontal blowing) wind machines are being used for protection of apples in Mexico and citrus (mainly sweet oranges and mandarins) in the Argolic plain of Greece. Although field tests on downward-blowing fans demonstrated poor performance and the literature on upward-blowing vertical wind machines is limited, vertical-blowing wind machines were identified as being used in both Greece on citrus and in Uruguay. Helicopters have been used for frost protection of stonefruit orchards in Argentina, and there are plans to used helicopters for grapevines in Uruguay.

Most active protection methods are somewhat energy intensive, and therefore the technologies may or may not be appropriate, depending on local availability and costs. For example, use of heaters is cost-effective if there is a reliable, low cost source of fuel. However, heaters are generally polluting, so only efficient heaters with little smoke should be used. Recent research has shown that heating irrigation water for application by under-plant sprinklers is less polluting than using heaters directly, and it provides a method of distributing heat more evenly through an orchard or vineyard. Wind machines are commonly used for protection of high value crops in wealthier countries, but the costs are often too high for subsistence farmers. The use of flooding and furrow irrigation is an option in most parts of the world if low-cost water is available in a timely fashion. One of the problems with surface irrigation is that one must often have a forecast of freezing temperatures a few days in advance of the frost night in order to be able to order water from the local water district.

The control of INA bacteria was identified as a protection method in several countries. For small plantings and infrequent frost events, this could be a cost-effective protection method in many locations and research on the control of INA bacteria continues.

Appropriate technology summary

It seems that a wide range of simple to sophisticated frost protection technologies are used around the world. The main determining factors depend on local availability and costs. For example, liquid-fuel heaters are widely used in Mexico because low-cost fuel is available. It is not widely used where costs are higher. Of course, even within a country, protection methods vary depending on the size and wealth of the farming operation as well as government support. Each protection method must be considered on its own merits and an economic evaluation should be performed to determine whether or not the method is cost-effective. Of course this also requires the availability of climate data and the computer facilities to analyse the data. For locations with inadequate funding, lack of critical supplies and equipment could hinder the usage of some methods. For example, either a good forecast from the weather service or a thermometer is the minimum requirement for the efficient use of sprinklers or wind machines. For sprinklers, a wet-bulb thermometer or a measure of the dew-point temperature will improve management of the system. Similarly, it is difficult to practice frost protection with heaters or wind machines without some fruit frost shelters and thermometers as a minimum.

TABLE 8.1
Frost protection practices reported by crop type from several countries and estimate percentage of the crop that is protected

Frost protection survey respondent comments

Argentina (NE of Buenos Aires)

Until 2001, liquid-fuel heaters were the main method used to protect stonefruit orchards. After 2001, because of increased oil prices, solid-fuel heaters became the main method for frost protection, especially burning wood. About 80 percent of the area is protected by heaters. In the Buenos Aires region, citrus plantings are insignificant.

Greece

In Greece, there is only minor active frost protection for fruit trees, although, over the years, spring frost damage is often high. Due to overproduction and low prices, few farmers are willing to invest in frost protection. Typically, growers use 80-120 litre h^-1 microsprinkler applications for tree irrigation.

There is no appreciable area with vegetables or other cultivated plants that are protected from frosts with active methods. Low or high plastic tunnels are used for the protection of many early-planted vegetables, and in a small area (< 5 percent of the total) early summer squash is being protected with drip irrigation in low tunnels.

Frost protection in citrus crops is mostly practised in Arta plain, which is the most northern part of Greece with citrus production (about 15 percent of the total area occupied by Citrus crops in Greece). Peach is grown almost exclusively in the northern parts of Greece (Macedonia), where late frost in spring is common and, therefore, frost protection is justified.

The basic protection of sweet oranges and mandarins in the Argolic plain is accomplished using windmills (air mixers) installed in the orchards. Open field vegetable crops often suffer frost damage.

Jordan

In the Jordan rift valley, frost rarely occurs. However, when it occurs, farmers usually protect their annual plants using heaters or by operating sprinklers. Plastic tunnels are used to protect early-planted summer crops. In mountainous areas, farmers protect vegetable crops by not planting during frost-prone periods, or by using plastic tunnels. They also use sprinklers or heaters. For tree crops, they use heaters.

Mexico (Chihuahua)

The State of Chihuahua is perhaps the coldest State in Mexico. Fruit crops with high profitability are typically protected against late spring frost damage. Most other crops are not protected. For example, avocado growers in Michoacan State, have applied NINA bacteria to reduce the INA bacteria, with good protection results. Some pear and small-fruit growers in Michoacan and Chihuahua States have also achieved good results by applying NINA bacteria. Because Mexico is considered a petroleum-rich country and the federal government subsidizes the oil price, the number one frost control method in Chihuahua State and probably in Mexico is liquid-fuel heaters (oil, petroleum, etc.). However, this frost protection method is a big source of pollution for the atmosphere, soil, water and humans.

Zimbabwe

In general, most frost protection is for sensitive horticultural crops, which are grown in the Zimbabwean winter. It is important for farmers in frost-risk areas in Zimbabwe to listen to the weather forecasts and to take precautions. Most growers already know the tentative dates that frost is common in their own areas. However, the meteorological service offers helpful frost prediction and forecasting information. Those methods that involve a lot of investment and require electricity are mainly practiced on large commercial farms. Small farmers practice less expensive protection methods. Flowers and buds are protected at different stages from cuttings/seedlings newly budded or grafted fruit trees in the nurseries, and also in the field. Winter wheat is sensitive to frost damage at flowering.