GUIDE BOOK

COOLINGHOW TO AVOID CROPS AND ANIMALS FROM BEING AFFECTED BY HIGH TEMPERATURES

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TABLE OF CONTENTS

COOLING 1

■■ Netafim’s solutions 3

COOLING PROTECTION IN OPEN FIELDS 4

■■ Damage Mechanisms for Sun Burn 5

■■ Cooling Mechanisms 6

■■ Evaporative Cooling for Color 8

■■ Evaporative Cooling for Sun Burn Reduction 8

■■ Evaporative Cooling for Larger Fruit Size 9

■■ Other Considerations 9

■■ Specific Concerns (not inclusive) 9

■■ System Selection and Design Criteria 10

General Considerations 10

Water Quantity 10

Water Quality 10

Irrigation Scheduling 12

Application Rates 13

■■ Mechanics of cooling 14

Controls 15

Summary 16

■■ Case Study 1: Fruit color improvement of 'Delicious' apples in Spain 18

■■ Case Study 2: Fruit growth rates and quality of 'Jonee' and 'Golden Smith' apples in Spain 19

■■ Case Study 3: Evaporative cooling of Fuji apples 20

■■ Case Study 4: Codling moth damage in USA 21

■■ Case study 5: Grape response to cooling in California 22

■■ Case study 6: Improving grapevine bud-break and yields in Israel 24

■■ Case study 7 : Fruit color and firmness in 'Sensation Red Bartlett' pear in Oregon 26

■■ Case study 8: Cooling in strawberry production in USA 27

■■ Case study 9: Photosynthesis and heat stress 29

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■■ Case study 10: Cooling of Ginger in South Africa 30

■■ Case Study 11: Cooling protection in greenhouses 33

■■ Case study 12: Leaf temperature in greenhouses 35

■■ Case Study 13: Intermittent application of water to an externally mounted greenhouse shade cloth to modify cooling performance 37

■■ Case Study 14: Cooling Protection of Livestock 38

■■ Case Study 15: Cooling Italian dairy cows 40

■■ Case Study 16: Dairy cattle heat stress 42

■■ Case Study 17: Cooling pigs 42

■■ Case Study 18: Cooling Poultry Houses 43

NETAFIM™ PRODUCTS 45

SuperNet™ 45

GyroNet™ 45

CoolNet Pro™ 45

FIGURES

Figure 1: The airflow required to maintain the desired conditions (70%c-27°C) in relation to the temperature and

humidity of the surrounding environment 34

Figure 2: Rate of water evaporation required to maintain the desired conditions (70%C-27°C) in relation to the surrounding

environment’s temperature and humidity ratio 34

II

COOLINGThere are some areas of the world in which the agricultural crops require assistance and cooling, espe cially during hot days, in order to prevent them from being subjected to unnecessary stress. In other areas, the color of fruit can be improved by cooling the trees during the correct time period.

It is possible to extend the shelf life of some types of fruit by cooling them while they are still on the trees. And by using correct and supervised cooling, we can increase the flower fruit set during periods of very hot weather. In other regions, we can aid and improve the yield of fruit crops by cooling during the autumn and winter months, and then adding cold units to the same trees or cooling the same crops at the end of the winter months in order to cause early blossoming.

In addition to employing cooling in open fields, an additional—perhaps primary—use of cooling is in vari ous types of greenhouses. The principle of a green house is that the farmer can control its internal climate and thereby provide the plants with optimal growth conditions. Therefore, a system that will have a cool ing effect on the internal temperature on hot days is almost indispensable for every greenhouse.

Another use of a cooling system inside a green house is, perhaps surprisingly, in cold countries where the greenhouse is especially built with few ventila tion openings to conserve internal heat. As a result of this design, on the few days that are very hot, there is insufficient air flow to cool the interior. An efficient cooling system can solve the problem. Further, in these same cold countries, the crops are usu ally already inside the greenhouse by the first days of spring, but the heating system still needs to be oper ated in order to ensure the correct conditions. The windows must not be opened, and inside the build ing, the relative humidity drops beneath the desired levels. At this time, operating a suitable cooling system improves these crops.

What is possible to do to improve agricultural crops is also possible to do with livestock, including all types of poultry, cows, and pigs. A suitable system can cool their micro-environment and improve production.

The different methods of cooling based on sprinkler-spraying products are as follows:

CONVECTIVE COOLING This method wets the plant. The drops absorb heat from the plant, and are then evaporated by the air movement, thus cooling the plant. This is the very phenomenon that we experience when we get out of the sea or a swimming pool and stand, wet, in the wind.

HYDRO COOLING Based on the principle that the relatively large drops of water reach the plant. Energy in the form of heat passes from the hot body to the body with the lower temperature, that is, from the plant to the drops of water, and then the drops drip to the ground. With this method, it is very important that the drops do drip off the plant.

EVAPORATIVE COOLING With this method, a controlled number of very small drops are sprayed into the air and absorbed into the atmosphere. The physical change of water from its liquid state to a gas state absorbs energy from the environment (560 calories for every gram of water) thereby cool ing the micro-climate.

Of all the methods, evaporative cooling is considered the most effective cooling method for crops, but it is important to note that it should only be used in suitable conditions and in the correct way.

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At this point, the difference between FOG and MIST should be clarified. The officially recognized def inition throughout the world for fog is that it com prises drops of an average size of 5-10 micron. Fog systems are used in some parts of the world in cotton and tobacco barns, and also in greenhouses where the farmer has decided to make a heavy investment. These are relatively expensive systems that require pressures of 70-120 bar and a water transportation system made from metal. The pipes and connectors of this transportation system are also made of metal, and have very small nozzles.

Mist can be worked with in a number of different ways. The finest mist that it is possible to obtain with regular spraying systems that work with pressures of from 3-5 bar, comprise drops of an average size between 60-100 microns. Mist performs good and effective evaporative cooling, as long as it is used in a manner that suits both the crop and the area (such as short periods of operation, height of sprinkler posi tioning, surrounding air movement, etc.).

With all of the methods described above, special attention must be paid to the quality of the water used. The greater the salt deposits in the water, the greater the chances of salt stains on the leaves or fruit. The cooling method has to suit the water quality and/or deal with the salt deposits before the water enters the sprinkler system.

In this issue, we present to you, by way of a number of articles, the physical principles, the possible uses, the applications of the methods on different crops, and the various solutions that are in use throughout the world. A very large number of articles on this subject may be found in professional literature and by way of the internet; we have chosen a small number of them by way of introduction in this particular issue, and will continue to widen and add to the information in future issues.

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NETAFIm’S SOLuTIONS Our sprinkler-spraying product range offers an extremely wide variety of products that will meet all cooling requirements by applying the various methods to the different crops, in accordance with their specific needs. All the products presented herein are in use all over the world, and fulfill the agricultural requirements in the most successful and professional manner possible.

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COOLING PrOTECTIONIN OPEN FIELdSBy Robert G. Evans, Agricultural Engineer at Washington State University-Prosser

Apple growers in the arid areas of the Pacific North west (PNW) are rapidly adopting the use of overtree evaporative cooling (EC) as a feasible, chemical-free technique to reduce sun burn (also called sun scald) and/or enhance color development on “red” or “red-striped” fruit. Much of this interest is due to the emergence of new varieties, new training systems that open canopies to greater light intensities, and the loss of daminozide (Alar) to delay fruit maturity. However, significant problems are arising with long-term orchard health, general orchard management, mineral depositions on fruit, and general EC system design and operation.

Overtree EC applies water above the crop. As this water evaporates, it directly cools the leaves, fruit and the orchard air depending on local climatic conditions and the rate water is applied. Avoiding excessive leaf and fruit temperatures during the hottest part of the day can greatly reduce the incidence of sun burn. Orchardists have found use of EC just prior to sundown and sometimes around sunrise has improved color development on red apples (especially early varieties) before harvest. If done properly, EC may generally increase harvested fruit size due to reduced water stress levels and improved management of soil water status throughout the season.

Almost every type of commercially available sprin kler and microsprinkler is being utilized in the PNW for EC with applications ranging from 30 l/m/ac (8 gpm/ac - 1.25 l/sec/ha) to over 303 l/m/ac (80 gpm/ac - 12.5 l/sec/ha) with varying degrees of effectiveness. Problems occur as a result of one or a combination of the following: a) existing irrigation systems are used which were not designed to meet hydraulic and operational requirements of EC; b) there is an inadequate supply of water for both irrigation and cooling, EC water application rates are too low and soils may become too dry; c) water applications cannot be cycled to maximize evaporative efficiency and avoid excessive water use; and d) poor water quality causing deposits on fruit and/or leaf burn from salt accumulations.

In some areas and years, orchardists may use EC for 35-75 days and even more per season. Consequently, EC potentially impacts several major areas of total orchard management including pest and disease control, fruit maturity, fruit storage characteristics, fruit color development, seasonal irrigation water requirements and irrigation scheduling. In addition, expensive investments in treatment facilities in the orchards and packing sheds due to poor water quality (primarily calcium carbonates and silicates) may be necessary to remove surface deposits on fruit. Scientifically-based irrigation scheduling programs with actual measure ments of soil and/or plant parameters are desirable. All of these factors increase system installation and operating costs which must be recovered through improved fruit grade.

Limited past research on EC of apples has been associated only with improving red color development ranging from about 3.9 l/sec/ha (90 l/m/ac 25 gpm/ac, continuous applications) to around 10.9 l/sec/ha/ (265 l/m/ac, 70 gpm/ac) pulsed on 15 minute cycles (Unrath, 1972a, 1972b; Unrath and Sneed, 1974; Griffin, 1974). The studies were successful at improving red color development on ‘Red Delicious’ apples.

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Skin color and appearance are some of the most important commercial attributes of fresh pack apples, Comice pears as well as many vegetable crops such as peppers and tomatoes. Sun burn (discoloration or burning of fruit surface exposed to direct sun, also often referred to as “sun scald”) has become a serious economic problem in PNW orchards. The surface blemished fruit cannot be sold for fresh market consumption which receives the highest prices. Almost all apples can burn regardless of color. Some red varieties may color over burned areas so the damage may not be visually evident, but these apples often have storage problems due to the internal damage. The mechanisms and the causes of sun burn are not well understood and much work remains to be done by plant physiologists on this subject. Data on the threshold conditions where the burn begins to occur are not available for any variety, but it is well known that there are big differences between varieties in their susceptibility to sun burn. Satisfactory criteria for evaluating these conditions and the long-term horticultural impacts of EC techniques are not known. Available information on the design, management and operation of overtree EC systems for sun burn reduction is mostly anecdotal grower experiences. Innovative orchardists are learning by trial-and-error about EC under the low humidity and hot summer temperatures typical of many PNW fruit growing districts. Consequently, a research project was initiated by WSU and the Washington State Tree Fruit Research Commission in 1991 to develop knowledge on design and operation of EC systems for apples where the primary emphasis is on reducing the temperature of exposed fruit tissue (skin) to reduce sun burn.

dAmAGE mEChANISmS FOr SuN BurN A narrow range of ultraviolet (UV) light contributes to red color development in apples (Arakawa, 1988). Experiments with UV-inhibiting plastic films have indicated that radiant heating in conjunction with certain bands of ultraviolet light may contribute to sun burn damage (Andrews, 1993). Certain antioxidants (e.g. ascorbate) applied to the fruit surface have also been effective in reducing sun burn by UV radiation (Patterson and Moore, 1983). The contribution of heat and UV light is probably interdependent. Evaporative cooling may be affecting the entire burn process by reducing radiant heating of exposed fruit.

Data on the threshold conditions where burn begins to occur are not available for any variety, how ever, it is well known that there are big differences between varieties in their susceptibility to sun burn. Some of the more tender varieties are ‘Jonagold’, ‘Braeburn’, ‘Golden Supreme’, ‘Ginger Gold’ and ‘Fuji’.

Some data indicate that sun burn is a progressive phenomenon and accumulates over time. Some varieties may become more susceptible as they begin to approach maturity. Darker (e.g. red) fruit also tend to absorb heat faster than green fruit which may be tied to the perceived increase in sensitivity to sun burn as season progresses. There is also some evidence that exposed fruit may be “conditioned” early in the season to withstand some burn damage later in the season.

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COOLING mEChANISmS There are basically three ways water reduces crop temperatures. In order of increasing effectiveness, they are:

1. CONVECTIVE COOLING, evaporate water in air (undertree or overtree) and use the circulation (convection) of the cooled air to reduce fruit temperatures.

2. HYDRO COOLING, apply water to the leaves and fruit, using the “cool” water to extract the sensible heat from the plant organs and carry it away via “runoff”.

3. EVAPORATIVE COOLING, apply water to the leaves and fruit and directly extract heat by sensible to latent heat transfer.

All water-based orchard cooling techniques will use one or more of the mechanisms. The relative contribution of each will depend on climatic conditions, water application rates, application uniformity and system operation. It can be shown that the most effective of these cooling modes will be evaporation of water from the fruit surface followed by removal of the water vapor by mass air movement (Merva, et al. 1979; Barfield et al., 1974; Barfield et al, 1990; Chesness, et al., 1979; Hamer, 1986).

Evaporation of water requires large amounts of heat (910 BTU/lb of water at 86F [2.43 MJ/kg of water @ 30C]). The heat comes directly from solar radiation and/or anything else that is in contact with the evaporating water including air and vegetation. Direct evaporative cooling has its primary emphasis on operating the system to maximize “evaporative efficiency” while minimizing the total application of water.

For sun burn protection, it is desirable to reduce fruit temperature for protection during the warmest parts of the day. To cool fruit, we must first counteract the all sources of incoming heat energy “loads” that cause the exposed fruits’ temperatures to rise. Evaporative cooling relies on the fact that the evaporation of water takes heat and it will take the energy it needs from the air and fruit. If the amount of heat extracted is greater than the total incoming heat energy, the temperature of the fruit will decrease. If the amount of heat extracted is less than the incoming energy, fruit temperature will increase. The most effective fruit temperature reductions occur when the water directly evaporates from the surface of the fruit.

This heat “load” on fruit that is exposed to the sun has two principal components:

1. DIRECT RADIATIVE heating from the sun

2. ADVECTIVE HEATING from hot air originating from outside the block moving through the orchard.

Taking a simple physical chemistry approach, we can make some calculations to give us the relative magnitude of the amount of water required for effective overtree evaporative cooling of exposed fruit. Assuming that we want to cool apples under conditions where the incoming solar radiation has an intensity of 800 W/m2 (a reasonable number for the middle of a hot summer day), and that we have an air temperature of 350ºC (95ºF). To equal (neutralize) the energy from the incoming solar radiation would require the complete evaporation of about 21 US gal/min/ac above the tree canopy (assuming: 8.36 lbm/US gallon of water, 1040 Btu/lbm is the latent heat of vaporiza tion, 8695 Btu to evaporate 1 US gallon of water, and 1 W/m2 = 0.3170 Btu/hr/ft2). However, there is also an advective (wind) component that is typically at least equal to the solar radiative heating during periods of high air temperatures, low humidities and low wind speeds. This means that at least 151 l/m/ac (40 gpm/ac) would have to be continuously applied over the tree during this period to just equal the incoming both radiative and advective heat energy and maintain the exposed fruit surface at ambient temperatures (in this case 95F) under these assumed conditions.

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Cooling the exposed fruit below ambient temperature would require the application of additional water. These calculations are supported by field data measuring actual exposed fruit temperatures on hot summer days in south central Washington of cooled and uncooled fruit. Higher wind speeds and/or higher air tempera tures would increase the amount of water required for effective evaporative cooling.

Overtree sprinkler/microsprinkler systems that apply water in very fine droplets (fogging or misting) and/or at low application rates (<114 l/m/ac, <30 gpm/ac) tend to evaporate most if not all the applied water before it reaches the fruit. The tree/fruit temperatures are essentially reduced by convection of cooled air. These systems are generally not cycled, but are on continuously for several hours. Cooling is usually initiated and turned-off based on arbitrary threshold air or fruit temperatures. These systems usually require a duplicate water application system for irrigation due to the low application rates, poor uniformities and lack of adequate water reaching the soil surface. Soil water management is a major concern. There is a much greater risk of problems with deposition of minerals on fruit and leaves than with higher application rate systems. Low pH water should always be used with these systems.

Undertree sprinkler systems cool the air below the plant canopy and must also rely on convection to cool the fruit. Use of this process for heat transfer is inefficient. Undertree sprinkling for cooling often results in excessive amounts of water applied to the orchard floor due to typically long on-times and daily use over extended periods. Cycling of these systems is possible but may not be feasible due to low cooling benefits.

Systems that primarily rely on hydro-cooling generally apply substantially greater than 151 l/m/ac (40 gpm/ac) on a continuous basis over the total area being cooled once the “critical” air or fruit temperatures (as determined by the grower) are reached. Some evaporation occurs, but much of the heat transfer is by constant runoff of free water from the plant. This technique is quite effective in reducing fruit temperature but it is also extremely inefficient in its use of water and often results in seriously waterlogged soils. These conditions can seriously affect the long-term health of the orchard, blister spot, bitterpit and scab may increase, trees may have less physical stability, soil-borne diseases may increase, runoff from the field may occur, and nutrients / chemicals may be leached from the soil profile into the groundwater. Fruit may be softer at harvest. Consequently, heavy reliance on this practice is not recommended for orchard cooling even on very sandy soils without drainage problems.

Direct evaporative cooling has its primary empha sis on operating the system to maximize “evaporative efficiency” while minimizing the total application of water. These systems apply water at average rates at least equal to 114 l/m/ac (30 gpm/ac). The management of these systems requires pulsing the water on and off so that free water is continually evaporating. Much of the following discussion is directed towards this type of EC for the PNW.

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EvAPOrATIvE COOLING FOr COLOr Some orchardists are utilizing EC primarily for earlier color development on early red and red-striped apples. There is probably limited benefit using EC for improved color on late apples (e.g. harvested towards the end of September and later) in most years in the PNW.

Threshold temperatures and color responses vary widely between different varieties of apple. Color pig ment development (i.e., idaein) generally occurs in the temperature range from 5ºC (41ºF) to about 30ºC (86ºF) (optimum approaches 21ºC, 70ºF) and the amount of coloring will be in direct proportion to the amount of time that fruit is in this range. Consequently, midday EC will have minor coloring benefits.

To try for improved early color, these growers are applying water over the fruit and canopy starting 4 to 6 weeks before expected harvest date. Depending on application rate and uniformity, it is believed that optimum benefits will occur by starting EC about 30 minutes before and continuing about 20 to 40 minutes after sundown or until fruit and ambient air temperatures are similar. Some of these growers are also applying water again at sunup for about a 1 hour period to extend the lower fruit temperature periods. However, there are no data from controlled experiments to support the benefits of early morning sprinkling. Because of the need to cool fruit rapidly at dusk for color enhancement, basically all overtree water application systems will have some benefit regardless of the application rate. Even very low volume systems will be able to rapidly cool orchard temperatures once the incoming radiative loads (e.g. daily peak of 600-800 Watts/m2) from the sun are absent (solar radiation is only a part of energy balance). This type of operation will probably have little effect on either delaying or enhancing fruit maturity levels.

No firm recommendations can be made on the timing or the temperature thresholds for most effective EC for color.

However, EC for color should probably be discontinued in the morning when average fruit flesh temperatures rise above the 21ºC (70ºF) range due to considerations of water conservation and general orchard health.

EvAPOrATIvE COOLING FOr SuN BurN rEduCTION Sun burn will be reduced by EC during the hottest parts of the day. EC will often be required from midmorning until sundown (at which time come color benefits may accrue). The purpose is to maintain the temperature of the cells just under the skin of exposed fruit below heat burn damage levels by evaporating applied water. However, it should be noted that some burn may occur on hot days even under high application rates. Fruit maturity may be delayed with daytime EC. It should be pointed out that in south central Washington that at least 5.0 l/sec/ha (76 l/m/ac, 20 gpm/ac) is required to meet radiation loads and at least another 5.0 l/sec/ha (76 l/m/ac, 20 gpm/ac) is required to meet advective energy inputs in order to control fruit temperatures when the water is applied directly to the fruit.

The requirements of EC for reducing sun burn are the most restrictive in terms of water application rates, system design and orchard management. The systems must be able to meet requirements dictated by the extreme PNW climatic conditions. Application rates should at least equal peak evaporative demands of about 151-170 l/m/ac (40-45 gpm/ac) for minimal sun burn damage (total area actually covered; e.g., tree canopy and cover crop) on a continuous basis. If EC is cycled based on time (e.g. 20 minutes on, 20-40 minutes off), applications should be in the range of 227-265 l/m/ac (60-70 gpm/ac). At lower rates fruit temperatures can continue to increase during periods with high solar radiation loads. “Targeted” EC which wets only the canopy could potentially apply less on a total area basis. Cycles should not have less than 15 minute on-times.

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Overtree irrigation of susceptible varieties (e.g., Jonagold, Fuji, etc) during daytime hours are not recommended until you want to start EC for the rest of the season. Since daytime irrigations also cool, it apparently predisposes fruit for burning, much like late season branch shifts that expose new fruit that quickly burn. Once you start cooling – you have to continue for the rest of the season. EC for sun burn is usually not required before mid-July on most varieties.

Cooling at night for sun burn reduction with either overtree or undertree systems is not effective. Fruit temperatures are usually below damaging levels and there is no solar radiation load to counteract. Night applications of water should be limited to irrigations and/or at dawn and dusk for some possible color development.

EvAPOrATIvE COOLING FOr LArGEr FruIT SIzE Growers using EC must do an exceptional job of managing the soil water (irrigation scheduling) to maintain optimal growing conditions. Most increases in fruit size under EC will be primarily due to improved water management and, to a lesser degree, to reduced heat stresses. Fruit sizes will frequently vary across any block. However, improved water management under high frequency water applications may reduce many effects of soil type, depth and nutrient status variability on sizing.

Theoretically, fruit size may be increased by utilizing EC to reduce plant water stress due to high temperatures and maintain plant organs closer to their optimum photosynthesis range (16ºC, 60ºF to about 80ºF). Photosynthesis will begin to decrease above and below this range. However, the actual number of hours that photosynthesis would be greatly reduced are rela tively small and water management is likely the most dominant factor.

Fruit sizes may be reduced if growers are not adequately monitoring soil water status. EC (vs.. hydro-cooling) cannot provide crop irrigation requirements and soils can become quite dry at increasing soil depths causing excessive moisture stress in the tree. Waterlogged conditions under “hydro-cooled” systems may also reduce fruit size. It is remotely possible that fruit size could also be reduced due to: a) disease/pest pressures due to potentially reduced efficacy of spray programs; and, b) poor water quality reducing photosynthetic efficiency due to mineral precipitates and/or specific ion toxicities.

OThEr CONSIdErATIONS EC for sun burn reduction has been shown to delay maturity. This tends to result in firmer fruit with lower sugars which may be a benefit for controlled atmosphere (CA) storage. It may also be used to lengthen harvest intervals by manipulating fruit maturity. Another potential side benefit is that fruit in wetted bins, which were watered in the field prior to harvest, tend to have less desiccation in storage.

SPECIFIC CONCErNS (NOT INCLuSIvE) Growers must prevent primary apple scab infections prior to initiation of any EC for the season. The same is true for Fireblight where infections must be prevented and/or removed from the orchard before use of EC. Control of codling moth in the first generation may be critical because of the risk of washing off pesticides by EC during the second codling moth generation.

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SySTEm SELECTION ANd dESIGN CrITErIA Systems for EC should be engineered from the very beginning of orchard planning. It is often expensive and very difficult to retrofit existing irrigation systems for EC. Many growers are installing two systems: 1) overtree sprinkler for cooling; and 2) undertree sprinkler for irrigation and frost protection. The average application rates for EC are usually much too low for overtree frost protection. This dual system approach is preferable, but is more expensive. There is no perfect EC-irrigation system.

GENERAL CONSIDERATIONS

The most dominant considerations will be the overall economics (cost, available capital, anticipated returns, etc), water supply (quantity, quality and seasonal availability) and personal preference. Other general factors will include: available labor (cost/ quantity/quality); soils (depths, types, variations, saline/sodic); field size, shape and topography; and climatic factors. Cultural considerations will include: variety and spacing; trellising/training systems; specific spray programs; pruning programs/practices; fertilizer requirements; tillage practices; cover crop / soil erosion problems; soil compaction; harvesting; existing pressure from fire blight and apple scab. Crop factors that should be specifically considered with respect to EC are fruit quality, mineral deposition and disease control.

Design factors will include: desired uniformity of application; potential average application rates; level of automation (control systems); chemigation and fertigation; larger pipe sizes and pressure controls; pump selections (efficiency, power costs, etc); soil or crop limitations; and reuse of any runoff water.

WATER QUANTITY

Reliable and adequate long-term water supplies are critical for EC programs. There will generally be a 25% to 40% or more increase in seasonal water requirements through a properly designed and operated EC system. EC for sun burn reduction is not a water conservation measure.

By intent, EC is specifically designed to have very high water losses to evaporation. There may be a slight reduction in actual total crop water use compared to a non-cooled block, but the use of EC will definitely require more total water over the season.

Most growers do not have adequate water sup plies for both cooling and irrigation under typical canal delivery systems. Consequently, many are buying “extra” water, drilling wells and/or building large ponds for holding supplemental water and/or unused allocations. Storage ponds can also be used to supply water for overtree or undertree sprinkling for frost protection in the spring. Ponds should be lined to reduce the potential for contamination of ground water.

WATER QUALITY

Water quality is one of the most significant problems facing successful EC. High evaporation rates with over-tree EC can leave excessive surface deposits of calcium carbonates, silicates and other salts on the fruit depending on the chemical composition of the applied water. Mineral deposition tends to be more significant at lower application rates (<114 l/m/ac, <30 gpm/ac) because less is washed from the fruit during EC. Even with acid treatment, growers may still need to operate low application rate systems 1-2 nights each week to try to wash off deposits for 4-6 hours using with low pH water.

The problem of mineral deposition must be considered from two perspectives:

1. the amount and types of salts present

2. the potential for mineral precipitation and the solubility of the compounds.

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If the amount of total salts in the water is too high (i.e. conductivity > 2 dS/m2) it is not economical to treat the water (i.e., reverse osmosis) and the water should not be used for overtree applications. However, the only exception is that if the vast majority of the salt is sodium bicarbonate (high pH water) it is some times possible to treat the water by reducing pH and use it for overtree cooling. Water for overtree appli cations should be treated anytime bicarbonates and carbonates are present. Water from deep wells in central Washington should always be acidified whether for irrigation or cooling.

Water sources in arid areas commonly have pH values of 7.0 or greater. When ground and surface waters have a pH of 7.5 or higher, the potential for calcium carbonate precipitation is high. The treatment and use of chemicals requires an in-depth understanding of water and soil chemistry and an idea of what is desired. The first step in determining treatment needs is to have a chemical analyses made of the water supply (pH, electrical conductivity, Ca++, Mg++, Na+, CO3--, HCO3-). These analyses can be used to determine, among other needed information, the “lime deposition potential” (LDP). The LDP is estimated as the least concentration of either (CO3--milli-equivalents per liter [meq/L] + HCO3-meq/L) or Ca++ meq/L. Halverson and Dow (1975) suggested that a LDP below 2.0 was not a problem for over crop irrigation (but it is for EC). However, LDPs above 2 (100 ppm CaCO3) should be cause for concern and probable treatment. An LDP above 4 (200 ppm CaCO3) should be used for over crop irrigation with caution and only with pH reducing treatments. However, experience has shown that LDPs as low as 1.0 have caused serious mineral deposition problems with evaporative cooling applications.

If combined levels of calcium and magnesium are higher than 50 ppm, calcium phosphates could pre cipitate and magnesium could form with ammonium to create a magnesium-ammonium phosphate precip itate. The key to prevent such phenomenon is lowering the pH level of the water.

Calcium carbonate (lime) precipitates can be readily controlled by maintaining the pH of the applied water at about 6.5-6.6 (a swimming pool pH tester can be used to monitor) by the careful injection of an acidifying agent (e.g., technical grade sulfuric acid or N-pHuric) or a sulfur burner. The use of “spent acids” from smelting or other industrial applications is not recommended. Acidification only addresses the carbonate/bicarbonate problem, it may do very little for problems due to other salts and precipitates.

Yet, one has to watch the soil buffering capacity and crop sensitivity to toxicity of various elements if pH is lowered too far. Sulfuric acid is commonly used and is the least expensive, but this is a dangerous compound to handle. Another compound that some use is N-pHuric® which is a mixture of urea and sulfuric acid that is easy to handle, but may apply nitrogen in excess of plant needs over the season. Likewise, the amount of acidity required to lower pHc of water to acceptable levels from phosphoric acid alone usually exceeds the crop’s requirement for P.

However, with any acidifying agent, it is necessary to develop a water buffering curve to predict how much acid to inject. This can also be established by trial-and-error through direct measurement of the pH of the water and slightly incrementing acid injection rates upward (wait 30-45 minutes then measure) until a pH of about 6.6 or less is reached. Use a simple, inexpensive portable pH meter to monitor pH of the applied water throughout the season since the chemical characteristics of the water can vary over the year, and adjust injection rates accordingly.

Acids are congruent or incongruent depending upon whether or not they disassociate completely in water or form other compounds. Sulfuric acid (H2SO4) is a congruent acid that disassociates in water (H2O), Phosphoric is incongruent meaning it does not donate all its protons to water at the same time, therefore it has to be injected on a quantitative basis not qualitative, such as pH.

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Certain chelating agents are often used to reduce calcium deposits on fruit because of safety concerns over strong acids, but they are considerably more expensive and less effective than acids. Polymers such as polyphosphates, organo-phosphates, polymalaic acids and others are also being investigated for carbonate solubility effectiveness. They are less expensive than sulfur burners, do not persist in the environment, approved by the EPA, and are safer to handle than an acid. Dosages as low as 1 -2 ppm may increase carbonate solubility. Chelates or polymers do not affect water pH, do not reduce the amount of deposits and require frequent washing to remove deposits and avoid possible” salt burning” of leaves. Some believe that the high electrical charge of the polymer molecule keeps potential precipitates in solution and if a compound such as carbonate crystallizes in a polymer environment, the crystal shape does not have sharp corners to give rise to stacking and combining. Rather, the crystals have rounded corners and do stack together at all and wash off easily. These materials are not needed when acidifying agents are used to lower water pH to acceptable levels.

Finally, chlorination may be required for iron and sulfide problems or to eliminate microbial problems. This requires a measured value of least 1.0 ppm of free residual chlorine at the ends of the lines. The free residual is the amount of chlorine that is left after the injected chlorine has reacted with all the sulfides, iron, algae or bacteria. Sufficient quantities must be injected into the system to meet the required reactions to still leave 1.0 ppm residual chlorine. Constant, automated, chlorination is often recommended. Chlorination is most effective when water pH is less than 6.5.

Injection equipment (pumps, tubing, etc) must be able to withstand the specific chemicals being injected (e.g., PVC pipe cannot be used with concen trated sulfuric acid). The injection pump supplier should have the necessary information for you to purchase and install the correct materials. Positive displacement chemical injection pumps are recommended.

All chemicals and/or chemical mixtures should also be checked to avoid phytotoxic effects as well as for compatibility to prevent precipitations and maximize efficacy. Except for acids, chemicals should usually be injected upstream of any filters or screens. Injection locations should always provide for adequate mixing. With the exception of chlorine treatments for microirrigation, the hydraulic systems must be flushed of the chemicals before turning off the water. Special chemigation safety devices are required for all chemical injection systems under federal/state laws and regulations. There can be no reverse flows, system drainage or back siphoning.

IRRIGATION SCHEDULING

EC is not a one-for-one substitute for irrigation. EC reduces the actual water use of the tree on the order of only 15%-20% depending on climatic conditions. Irrigations must be in addition to EC, usually at night. Improved water management including some form of scientific irrigation scheduling is absolutely required.

Under all forms of high-frequency irrigation, the real questions concerning irrigation management are not only when to irrigate but also how much to apply and how to accurately evaluate the water status of the tree. Extensive and frequent soil water measurements should be made across the block with appropriate soil water monitoring equipment. These readings should be used to schedule directly and/or to make adjust ments to available reference evapotranspiration (crop water use) estimates from WSU Public Agricultural Weather System (PAWS) and other sources.

An irrigation scheduling program becomes absolutely essential when a grower is attempting to minimize seasonal water use while maximizing EC. This goal requires cycling applications based on plant measurements. Implementation of a “cycled” EC or continuous applications below about 114 l/m/ac (30 gpm/ac) should always include a scientifically-based irrigation scheduling program.

Continuous applications above 114-151 l/m/ac (30-40 gpm/ac) may have excessive soil water for extended periods (hydro-cooling) and proper water management can be very difficult if not impossible when EC water applications exceed plant water use requirements.

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Substantial and detrimental soil water deficits may develop under EC systems, but may not be readily evident because of the luxurious appearance of cover crops, particularly at higher application rates under pulsed systems. Estimating actual irrigation needs by traditional methods under these conditions can be difficult. Past irrigation scheduling practices such as calendar scheduling or fixed rotations (e.g. every 10 days) will usually not be appropriate under EC due to variable effects on plant water use.

Daily records on flow rates, pressures and total water applications across the system should be kept for maintenance as well as evaluation of system operation for future improvement. Information on proper irrigation scheduling techniques and use of PAWS data can be obtained from the county offices of WSU Cooperative Extension.

APPLICATION RATES

There is a compromise between relative levels of sun burn protection and water application rates. Average application rates below about 151 l/m/ac (40 gpm/ac) may not minimize sun burn on extremely hot days. Consequently, at lower rates, the decision must be made to either accept increased burn damage over the entire block on extreme days or to cool smaller blocks of more valuable fruit at higher application rates. If the decision is to use EC on a smaller area, the piping and pumping system must be designed to handle the increased local flows at required pressures.

Recent research at WSU-Prosser shows that higher application rates (151 l/m/ac, 40 gpm/ac) work better than lower rates in reducing fruit temperatures. Rapid wetting of the fruit and then letting the water evaporate directly from the surface is effective in reducing fruit temperatures and for water conservation.

Recommendation: Greater than 151 l/m/ac (40 gpm/ac) for automatic cycling based on fruit temperature, water quantity not limiting on a continuous basis for the entire block. Application rates should be 227-265 l/m/ac (60-70 gpm/ac) if cycling based on time clocks with at least one 20 minute cycle per hour. All EC should be started and stopped based on fruit temperatures and low pH water used every time. Frequent night time applications with low pH water may be required to wash off inorganic deposits (e.g., 2-4X/wk).

Droplet sizes should be large enough to penetrate the canopy and wet all crop surfaces. Some type of control system is required to pulse or “cycle” the water applications based either on time sequences (e.g. 15 minutes on, 30 off as water cycles between three blocks) or on fruit temperatures (core or skin).

Systems in windy areas need to be designed for higher application rates and shorter intervals between pulses. Droplet sizes need to be larger and sprinkler spacing must be closer to provide the necessary appli cation uniformity and penetration of the canopy.

Cycling based on temperature measurements from exposed fruit will require higher flow rates and/or water storage capacities in the event that all blocks turn on at the same time because of timing and/or when evaporation rates exceed the average application rate (system operates continuously) across the orchard. As a general rule for sun burn reduction, it is better to divide a block into two 151 l/m/ac (40 gpm/ac) (or 3 at 227 l/m/ac, 60 gpm) cooling sets (cycled) than to have one 20 gpm block that would be on continuously. Hydro-cooling should always be minimized.

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mEChANICS OF COOLING Resolution of the above considerations will deter mine the hydraulic design. This will be dictated by the proposed use of the system which requires the great est amounts of water at any one time (usually EC for sun burn reduction in windy areas and/or frost protec-tion). There is little question that proper design of a EC system will be more expensive than a straight irri gation system because of increased pipe sizes, pres sure control measures, larger pumps, expanded valving needs, control/automation costs, and possible stor-age ponds. The entire system should be designed by a competent hydraulic engineer familiar with irrigation systems.

It may be necessary that mainlines, submains, pumps and motors be sized so that entire blocks can be sprinkled at one time, depending on the control criteria. Sizing of sprinkler laterals is usually not differ ent for cooling or irrigation unless different heads are used for each use. Looped hydraulic systems where water feeds into laterals from both ends may have large hydraulic benefits, but can be costly.

Separate undertree sprinkler or trickle systems are often installed for irrigation, or, if the same system is to be used for both cooling and irrigation, a smaller pump is often installed for irrigation purposes and the block watered in smaller sets at night. Low applica tion rate EC systems may have to be operated at night in order to maintain the cover crop. Daytime EC appli cation rates greater than 114 l/m/ac (30 gpm/ac) would probably be sufficient for cover crops during most of the season. Drip/trickle systems could be utilized for irrigation with some potential water supply savings, but would have no frost protection benefits.

Pulsed (cycled) systems at higher flow rates (114 l/m/ac, 30 gpm/ac) are preferred for their cooling effi ciency in reducing sun burn. However, pulsed systems at any flow rate generally present numerous design challenges, particularly with respect to pipe sizing and pressure controls. These systems will operate for short periods (e.g. 10 to 45 minutes) several times each day. Water will drain from the highest elevations in the block through the lowest sprinkler heads every time the system is turned off causing severe waterlogging of soils in low areas. In addition, the shorter the pulse time, the more rapidly the piping system must fill in order to have a uniform application of water over the block. Thus, two major design objectives with these systems are:

a. to avoid excessive drainage from the sprinkler heads at lower elevations b. to rapidly fill a system (block) with water.

Most of these concerns can be generally solved by following the design considerations below:

1. Break the blocks under each solenoid valve into several smaller, equal elevation subblocks with individual, spring-loaded check valves to prevent drainage from higher elevations. This also provides for more rapid filling since the entire system does not have to be recharged for each pulse.

2. After the initial fill, the entire system for a block should be designed to fill in 5% or less of the total pulse on-time (e.g. a 15 min pulse should fill in less that 40 seconds), usually by the use of mechanical check valves and/or other water elevation controls.

3. The application of water to the canopy must be much more uniform than required for irrigation so that no area receives less than the designated amount and to maximize the evaporative surface. A sprinkler water application uniformity coefficient (UCC) of not less than 80% is often specified and a design UCC of 90% is recommended for windy areas. Generally, this requires that sprinkler radius of throw equal sprinkler spacing along the lateral and not less than about 70% of the spacing between laterals.

4. Solenoid valves should have manual over-rides and should be of the highest quality as they must dependably open and close several thousand times over their useful life. Solenoid and other control valves should be slow closing to avoid water hammer problems.

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5. Each solenoid and each subblock under a solenoid valve should have manual isolation valving so that the entire system does not have to shut down to fix local problems in small blocks.

6. Pressure control valving may be required for fully automated systems. They will also be necessary if the same system is used for both irrigation and cooling because piping is oversized for irrigation and eleva tion effects are often significant. Zone pressure control valves such as pressure regulation valves (down stream pressure is controlled depending on flow) or pressure sustaining valves (upstream pressure is con stant regardless of flow; some valves may do both) should be considered under these conditions.

7. Numerous pressure taps should be placed throughout the entire pipe system for maintenance and trouble shooting particularly on low volume and/or low pressure microsprinkle and misting systems.

8. Flow variations from individual sprinkler heads should not vary more than 10% due to pressure. Con stant flow nozzles may reduce flow variations, but may have substantial variations in droplet sizes affecting their susceptibility to wind.

9. Continuous bleed air relief, vacuum relief (to prevent syphoning), and pressure relief valves should be installed in appropriate locations (e.g. ends of mains and submains, high points, etc). Gate valves should be installed to isolate them for maintenance.

10. Totalizing and rate-of-flow measurement should be installed for the entire system to make sure the entire system is operating correctly and to assist in irri gation scheduling efforts. It is advantageous to have a flow meter on each block being cooled.

11. Foggers, misters and many microsprinklers require good filtration and additional water treatment (e.g. chlorine) to reduce the incidence of plugging.

12. Flush valves and drains should be installed for winter maintenance. Provisions should also be made to drain lines above each check valve, solenoid valves (and bonnets), and any low points.

13. Chemical injection for pH control (e.g. acid, sulfur burners, etc) is generally required for groundwater supplies and is often needed with canal (river) water. All chemicals should be injected before the fil ters for microsprinkle systems. Backflow prevention devices are required under Washington state laws and regulations for all chemical injection systems.

Selection of a particular sprinkler/microsprinkler head should be dictated by the design requirements for uniformity, spacing, application rates and costs. Equipment selection is often a matter of personal pref erence, but a competent designer should be able to accommodate any operational quirks of a particular device.

CONTROLS

Evaporative cooling will necessitate good control. Automation is usually required to pulse or “cycle” the water applications based either on time sequences or on fruit temperatures. New advances in irrigation equipment and microprocessor controls make it possible to specifically manage each area of an orchard.

Microprocessor controls can potentially reduce labor, monitor climatic conditions and initiate some action such as frost protection or cycled cooling. When properly designed and used, automation will lead to more efficient cooling, improved soil water management and reduced leaching of nutrients and chemicals to groundwater.

Some EC systems are cycled based on air temperatures, fruit temperatures and/or time while others are operated on a continuous basis (usually based on air temperatures) during the hot parts of the day. Available information shows that starting EC based on air temperatures is a very poor procedure. Research has shown that fruit can warm much more quickly (e.g., -90C to -7C (15F to 20F warmer) and cool off more slowly than ambient air temperatures. It is recommended that initiation and cycling of all EC should be based on fruit core, skin temperatures, or other alternative measurements (e.g. “simulated” fruit) that reflect actual fruit conditions.

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Sensors to measure fruit core or skin temperatures can be used to either manually control a system or by automated controls. These devices are usually inexpensive thermocouples (TC) or infrared sensors. Thermocouples are easy to make and a simple meter to manually read the TCs can be purchased for $80-150. Thermocouples may be used about 2 weeks in a fruit and then switched to another fruit. The TCs should be sanitized between fruit by soaking them in household bleach (Clorox) for about 2 minutes to kill potential “rot” pathogens.

The simplest control systems will utilize clocks to initiate preset sequences of timed cycles. They can be started either manually or automatically, but should be based on fruit temperature rather than air. This type of control is often used where water supplies are limited. It is recommended that minimum on times should be about 10-15 minutes and each block should have water applied at least once an hour.

Fixed time control sequences are, in effect, designed from some maximum evaporative condition. Above this rate the grower is willing to accept some sun burn damage (average application rate is too low), and below which there may be excess water applied.

Computer automated systems are required for fruit temperature based control of EC. Each block should be able to operate independently and apply water when ever the fruit temperatures rise above target levels.

Temperature probes can be inserted into exposed fruit or into “plaster-of-Paris” (fake) fruit that have almost the same thermal characteristics as real fruit. The exposed fruit (or fake fruit) may be on the tree or picked (replaced weekly) and placed in a fully exposed position above the canopy for control. Control sensors above the canopy will tend to have slightly higher tem peratures than those within the canopy. The micro processor monitors the temperatures and initiates a cycle for a given block when a pre-specified target is reached. The computer would turn the cycle off when the turn-off target is achieved. As evaporative demand increases and fruit temperatures rise, computer controls based on fruit temperatures will result in a decrease between the time interval between cycles until, depending on the average application rate, the system may be on continuously in an attempt to maintain targeted fruit temperatures.

Typical core temperatures for control are: 91-92F turn on, turn-off at about 90Fº or just as the core temperatures start to decrease. Research indicates that continuous applications around 151-170 l/m/ac (40-45 gpm/ac) are sufficient to hold core temperatures in this range during extremely hot, clear sky, sunny radiative conditions.

Currently, the most significant problem with computerized control systems is that even though the controls, feedback and communications technology are commercially available, they are not currently “user-friendly”. There is a real need for simple control systems that start and stop EC cycles by monitoring current fruit conditions allowing control set-points to be easily changed.

SUMMARY

The configuration that presents the least design and operational problems is to have two systems: one for irrigation, one for cooling. The design and operation of an overtree EC system should be aimed at maximizing the direct evaporation of the applied water to the fruit and leaves. These conditions are met by pulsing water applications based on plant measurements. Some form of computerized automation is usually required.

Figure 1 presents an estimation of the relative effectiveness of the various water application systems used for EC in the PNW. Application rates should generally be in excess of 114 l/m/ac (30 gpm/ac) for reducing sun burn. Color development may be enhanced with all over-tree water applications at dusk and perhaps dawn, but minimal color benefits will be achieved by daytime EC.

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Evaporation of water takes very large amounts of heat, and, for EC in orchards, this heat can come from the absorption of incoming radiation from the sun, from the air and directly from the fruit and leaves. Therefore, cycling or intermittent water applications to maximize evaporation directly from the fruit and leaves is greatly preferred in reducing sun burn. The EC process can be optimized in areas with low humidities and high daytime temperatures common to many fruit growing regions in the PNW by the use of fruit temperature-based control of pulse initiation and duration. Hydro cooling should be minimized, not only because it is less efficient but also because orchard soils may become saturated over extended periods leading to disease, excessive deep percolation and other problems.

Management of EC systems by pulsing water applications on and off so free water is continually evaporating reduces hydro-cooling and conserves water. Rapid wetting followed by water evaporation directly from the fruit surface was effective in controlling fruit temperatures at the higher application rates. Droplet sizes should be large enough to penetrate the canopy and wet all crop surfaces for effective evaporative cooling. Whenever lime precipitates (calcium carbonates) are in the water, acidifying agents should be injected every time that the overtree EC systems is used.

Scientific irrigation scheduling is required to manage EC and irrigations. Higher levels of control that irrigate each zone according to individual, specific requirements are generally more water use efficient with less runoff and deep percolation.

EC is not a water conservation measure and will require extra water. Total seasonal water application amounts will be from 25% to 40% greater than historical irrigation requirements since the cooling is a very “inefficient” use of water and, by design, much is lost to the atmosphere. Microirrigation (drip, trickle) methods may be a viable alternative for irrigation since the cover crop could be maintained with most EC systems. Size increases compared to previous years and/or adjacent un-cooled blocks for EC fruit is often indicative of a past history of inadequate water management practices.

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CASE STudy 1

FruIT COLOr ImPrOvEmENT OF 'dELICIOuS' APPLES IN SPAIN Hortscience 1207-1208, 2000

The influence of supplemental sprinkler irrigation on fruit color of ‘Oregon Spur Delicious’ (Trumdor) apples (Malus xdomestica Borkh) was evaluated in the area of Lleida (NE Spain) over a 3-year period. Cooling irrigation was applied for 2 hours daily for 25-30 days preceding the harvest. Three treatments were evaluated

1. Control without overtree sprinkler irrigation. 2. Sprinkler irrigation applied at midday. 3. Sprinkler irrigation applied at sunset.

Fruit color was significantly affected by the cool ing irrigation and also by the weather of the particular year. Increased red color and higher anthocyanin content resulted from sprinkler irrigation, especially when applied at sunset.

Chromaticity values just before starting the treatments, were essentially the same in all treatments. In 1992 and 1994 color parameters indicated that irrigation applied at sunset hastened and intensified fruit color. Midday cooling gave values intermediate between those for the control and sunset cooling. Treatments applied in 1993 were less effective, probably because of lower temperatures than in 1992 and 1994. Treatment x fruit side interaction was in general not significant. Thus, evaporative cooling increased fruit color equally on both sides.

Mean anthocyanin content increased continuously on both sides of the fruit in the last 2 weeks before harvest. In late August and at harvest, anthocyanin content was significantly higher in fruit that were cooled at sunset than in the control, whereas cooling at midday was less effective. Both cooling treatments improved red pigmentation significantly, in accordance with results reported by several researchers with ‘Deli cious’ strains using continuous or pulsed overtree sprinkler irrigation in warm regions.

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CASE STudy 2

FruIT GrOwTh rATES ANd quALITy OF 'JONEE' ANd 'GOLdEN SmITh' APPLES IN SPAINActa Horticulturae 228, 1988

The sprinklers were started when the air temperature was 32°C and had a precipitation rate of 3 mm per hour. This increased the relative humidity of the atmosphere for 2 to 3 hours and reduced the atmosphere temperature by 3 or 4°C while the watering took place.

This microclimate had an important effect on the yield and quality of the fruit. The microclimate and the position of the fruit on the tree influenced the levels of soluble solids, firmness, acidity and skin colour, but storage life was not influenced consistently by irrigation.

The highest fruits on the tree were found to contain the most soluble solids and acidity, but no difference in levels of internal ethylene was noted between apples from cooled trees and the controls.

It is clear that the fruits from cooled, irrigated trees, whether at the top or at the bottom of the tree, when compared with non-cooled, irrigated trees, had: 1) bigger size, 2) higher soluble solids, 3) perhaps higher titratable acidity, 4) similar firmness, 5) similar internal ethylene content, and 6) equal storage life. This sug gests refreshing irrigation does not advance maturity at harvest nor in cool storage, but may give bigger and better fruits.

The refreshing microclimate had an important effect on the fruit size and highly significant increases in yield have been demonstrated for other varieties of apples (Recasens, 1984). Increased crop yield is attributed to improved conditions for plant growth and to a reduction of such stress-induced problems as fruit dehydratation. This dehydratation-induced turgor loss can severely wilt stomate guard cells when evapora tive demand is extreme. During these periods (particularly in the mid-day hours) stomatal apertures are reduced or nearly closed and resistance to water loss and C02 influx are then greatly increased.

Evaporative cooling on wetted surfaces typically results in leaf temperature reductions of about 2.0 to 2.5 times the attained air temperature reduction (Chesness et al., 1979). Tree cooling with sprinkled water also causes near immediate reduction of plant water potential. Thus after cooling-irrigation periods, trees may tolerate more warm, dry air.

Only about a half of the sprinkler water amount was available for the tree roots, because the evaporative capacity of the atmosphere was high when the sprinkling took place.

The tendency of fruits at the top of the trees to be higher in soluble solids, with more skin color at harvest, and a bigger size, suggests they took advantage of higher photosynthesis activity of leaves near the fruit at the top of the tree, using higher light intensity.

Refreshing irrigation systems operating in high temperatures and in dry air, can be used to obtain a good quality of fruit (Recasens,1985). Refreshing irrigation systems open up the possibility of greatly increased sophistication in the irrigation of apples in hot countries. The quality of the apples will vary according to the water status of the tree which can be controlled using this system.

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CASE STudy 3

EvAPOrATIvE COOLING OF FuJI APPLES Good Fruit Grower, 1997

Fruit size and color are among the most important attributes determining the profitability of Fuji apples. Thousands of acres of this valuable variety have been planted in high density orchards in Washington State over the past five years. The grower’s investment can become nearly worthless when fruit are small or sunburned. Optimum fruit size is achieved by judicious thinning, both with chemicals and by hand.

To prevent sunburn, fruit must be cooled or protected from the direct rays of eastern Washington’s hot summer sun. Some protection can be afforded by shading the fruit during the hottest time of the day, either by planning for the orientation of the tree rows at planting, by canopy management, with artificial shade covers, or by “bagging” the fruit for the season.

Still, the most widely used method for protecting fruit from sunburn is evaporative cooling (EC) with overtree sprinklers or mist systems. EC is very effective in preventing sunburn if the system is designed and managed properly.

As many growers know, however, evaporative cooling is a compromise. First, EC requires copious quantities of water that either must be available on demand for the entire orchard or cycled between blocks so that no block is without EC for more than about an hour on a hot summer day.

CONCLUSIONS

Evaporative cooling can protect Fuji apples from sunburn injury. To prevent some of the adverse effects of EC (e.g., mineral deposits), however, the system must be properly designed, constructed, and operated. When proper design and operational criteria are not met, EC systems may cause more problems than they solve. One of the most important design criteria is sprinkler application rate. Based on our research at Pepperbridge Farm, the 60 gpm per acre rate resulted in superior packouts than the lower rates. This may be due to this rate’s higher EC efficiency or because it washed more mineral deposits from the fruits.

It is also important to be aware that EC of Fuji apples may only provide marginal benefits in commercial packouts when appropriate canopy management is practiced. I think this was partly responsible for the better packouts of uncooked fruit at Pepper-bridge Farm in 1994.

Even though the summer of 1994 was very hot, the canopy of this fourthleaf V-trellis orchard had been managed attentively with summer pruning, irrigation, and nitrogen management, so that only a small portion of the crop was subjected to the intense light and temperature stresses associated with sunburn. When the orchard canopy is so managed, the EC system may Of by provide protection for the small portion of the crop that is vulnerable to sunburn. Under these conditions, the marginal costs of EC may exceed the marginal benefits. EC is not the “magic bullet” for producing high quality Fuji apples, it is only one potential component of successful sunburn management.

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CASE STudy 4

COdLING mOTh dAmAGE IN uSA By Geraldine Warner, Good Fruit Grower, 1997.

Apple growers who have been using evaporative cooling to improve fruit color or reduce sunburn have often been getting a bonus in the form of better con trol of codling moth.

Dr. Alan Knight, entomologist with the U. S. Depart ment of Agriculture in Yakima, has been investigating reports that codling moth is less of a problem in cooled orchards, despite the fact that pesticide resi dues are washed off the trees.

It has long been known that codling moth is better adapted to dry climates than humid ones, and is not well adapted to being exposed to water. This is the reason codling moth is not a concern in the apple-growing regions of the eastern United States, whereas it is the number-one pest in the West.

Knight began his experiments two years ago on potted trees, and last year set up tests on small num bers of Red Delicious trees in a research orchard in which l00 percent of the fruit is typically injured by codling moth. He can now confirm that control is improved in cooled orchards.

In his experiments, the moth was controlled with mating disruption and two applications of an experi mental insect growth regulator during the first gen eration. During the second generation, there was no control other than the pheromone dispensers.In July and August, the trees were cooled from l0:00 a.m. to l :00 a.m. the next morning. Three differ ent types of systems were used: fogging, where water was applied at l0 gallons per acre per minute; cooling with microsprinklers at higher rates on a l 5-minute cycle, and continuous cooling with microsprinklers.

Knight concluded that as well as making the fruit redder, the cooling dramatically reduced damage from codling moth. The more water was applied, the less damage there was. With the continuous, high-rate application through microsprinklers, damage was reduced by 97 percent compared with uncooled trees. The cycled cooling gave an 84 percent reduction and the fogging a 70 percent.

Under the continuous cooling treatment, there were fewer male moths caught in traps and lower sur vival rates of eggs and young larvae. Only half as many eggs were laid as on the uncooled trees.

“Apparently, water is affecting all those factors,” Knight said. “It’s affecting all the stages of codling moth. I think we established in our experiments that the water has a major impact on the moth’s behavior and reproductive potential in the orchard. “

During the coming season, Knight will assess the effect of standard evaporative cooling practices on the moth with the goal of figuring out how growers might modify their systems or timing for the best effect on codling moth, while still improving the quality of the fruit.

Codling moth adults are active at dusk, and eggs are laid during the night, last season’s study showed. Knight said it may be that growers could get better codling moth control if, instead of turning their cool ing systems off at dusk, they leave them on during the night.

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However, cooling can only help control codling moth and is not feasible as a stand-alone method. Growers would not want to cool their orchards during the moth’s first generation because of the risk of set ting up conditions for the development of scab.

Cooling during the second generation apparently has no detrimental effect on the pheromone dispens ers in the orchard. In fact, the lower temperature in the orchard, compared with an uncooled orchard, may help prolong the life of the dispensers because less pheromone is emitted and wasted, Knight said.

The bad news is that leafrollers, which often become a primary pest in orchards where pesticides are not used for codling moth, seem unaffected by the cooling.

CASE STudy 5

GrAPE rESPONSE TO COOLING IN CALIFOrNIAViticult Vol.26, No. 4, 1975 By F. K. Aljibury, Robert Brewer, Peter Christensen, and A. N. Kasimatis. Respectively Irrigation Area Specialist and Associate Horticulturist, Cooperative Extension, University of California, Parlier, California 93648; Fresno CounW Farrn Advisor. Fresno, California 93702; and Agriculturist, Viticulture & Enology, Cooperative Extension, University of California, Davis, California 95616 ‘Chardonnay,”Semillon,’ and ‘Chenin bland vines, grown in a large vineyard east of Reedley, California, were sprinkled sequentially during the daytime for a specific period when the berries reached the veraison stage and when air temperature exceeded 32ºC. Sequential cooling continued until harvest. Air, leaf, fruit, and soil temperatures were measured and were usually 5-10ºC lower on cooled vines during the peak temperature periods than the uncooled treatments.

All cooled treatments increased the fresh weights of the berries in all varieties. Cooling also increased the shoot growth of all three varieties. Although in most cases the cooled treatments produced more acid berries with lower pH, these values were low and not statistically significant. Cooling definitely delayed fruit maturity by 2-3 weeks and reduced the levels of total soluble solids.

Cooled treatments of these varieties showed limited benefits under field conditions of the San Joaquin Valley, which must be considered in relation to the investments made in permanent sprinklers for cooling objectives.

Increased demand for California varietal wines has encouraged many Central Valley growers to experi ment with varieties not normally grown in this region. In these warm interior valleys of California, considerable interest developed in using overhead sprinklers to cool vineyards in hope of modifying the microenvironment and producing acceptable wine quality. Experience has indicated that most California wines of highest quality are produced from grapes grown in cooler regions. Studies made previously (1,9,10) showed that most premium-quality grapes ripened at cool day temperatures (20-25ºC) had considerably higher acidity, lower pH, and better wine properties than did fruits ripened at warm day temperatures (30-38ºC). Enological studies in California have gener ally indicated that, for a given climatic region, musts with high acidity and low pH produce wines superior to those from musts with lower acidity and higher pH, provided fruit sugar and maturity are adequate.

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Water, because of its unique energy-exchange properties, is an efficient and economical tool for microclimate modification. As water changes from one phase to another, it absorbs or releases heat energy. When a liter of water applied by sprinklers evaporates, 560 Kcal of heat energy is absorbed from the surround ing environment, with cooling resulting. Furthermore, the evaporation of water increases the water content or relative humidity of otherwise dry air. Lowering the temperature and increasing the relative humidity of the surrounding air greatly reduces transpirational stress on plants.

RESULTS

This area of the San Joaquin Valley received high levels of incoming radiation during July and August, Is resulting in daily maximum air temperatures exceeding 35ºC, dropping below 25ºC in the afternoon. Temperatures above 37.8ºC may cause sunburn damage, dehydration of exposed fruit, and some reduction of shoot growth rate. High temperatures are also known to decrease acid, increase pH, and affect the color development of grapes. Sprinkling lowered the temperature of the air, leaf, and clusters, while the checkplot temperature continued to rise above 32ºC. Leaf temperature was at a maximum about 2:00 P.M. Sprinkling dropped the leaf temperature 11ºC in ’Chenin blanc’ and 16.5ºC in ‘Semillon’. The deviation in leaf response to cooling might be attributed to differences of varietal leaf characteristics, the type of leaf canopy, leaf orientation to the sun, or leaf wetting with the sprinkler.

The cluster temperature showed the effect of cooling on average berry temperature during August 5-16, 1971. The cooled vines produced significantly (0.05 level) greater vegetative growth. To what degree this can be attributed to reduced plant moisture demands or direct cooling effects is open to question. The soil moisture data clearly indicate a reduced evapotranspirational demand in the cooled plots.

The cooled vines produced larger berries. The same factors influencing vine shoot growth may be involved.

The three varieties in the cooled plots showed lower fruit sugar than the uncooled checks. This delay in maturity due to cooling was consistent each year. The sprinkler-cooled fruit tended to have slightly higher total acids and slightly lower pH at harvest, though the differences were not statistically significant.

The effect of crop cooling with sprinklers on the relative humidity of the treated plots some days increased the relative humidity more than 10% during the hottest hours.

At night, the relative humidities of the sprinkled and unsprinkled areas tended to be equal.

Occurrence of bunch rot was higher in the cooled plots.

DISCUSSION

Cooling grapevines when air temperature-exceeded 32ºC increased the fresh weights of the berries over those of fruit from uncooled vines. It appears that high fruit and vine temperatures (over 32ºC) of these vines grown in this area reduces the final size of grape berries. High temperatures during this cooled stage are believed to reduce the number of cells per berry and reduce cell elongation. The cooled berries had less total soluble solids than fruit from the uncooled treatments. Cooling reduced leaf and berry temperatures 5-10ºC below those of the uncooled. This lower temperature may have slowed photosynthesis or the movement of sugars from leaves to fruit below that of uncooked fruit. It is further believed that the increased shoot elongation of the cooled vines may have diverted part of the photosynthate from the fruit.

23

Cooling

The primary objective of this cooling experiment was to determine the effect of cooling on the total acidity, the reduced pH, and the wine quality of the treated berries without greatly affecting fruit sugar or maturity. Although the cooled vines produced ber ries with a bit higher titratable acids and lower pH, these values were not significantly different from those for the untreated vines. These same varieties, when grown in the California coastal grape areas, are significantly higher in total acidity and significantly lower in pH than those produced east of Reedley, with or without cooling. It remains to be determined whether cooling of varieties more adapted to the climatic conditions of the San Joaquin Valley could produce berries with higher weight, total acidity, and wine characteristics, reducing the pH of the berry juice without reducing the sugar content or delaying maturity.

An undesirable effect of sprinkler cooling was the increased incidence of bunch rot. Additional experience and study would be necessary to determine whether this could be minimized by avoiding wetted fruit through the night and by fungicide treatments.

CAsE sTuDY 6

ImPrOvING GrAPEvINE Bud-BrEAk ANd yIELdS IN ISrAELBy G. Nir. G. Spieler The effect of evaporative cooling on budbreak and yield of Vitis vinifera L. (Perlette and Thompson Seedless) wines grown is the southern Jordan Valley in Israel was investigated. Overhead microsprinklers were operated from 0600 to 1830 hr dairy daring the autumn and winter months either alone or in com bination with cyanamide sprays after pruning. Evap orative cooling decreased the temperature of beds exposed to direct sunlight from 30° to 16°C and that of shaded buds from 25° to 13°C. Exaporative cooling induced an early uniform budbreak. However when evaporative cooling was combined with cyanamide spray, its effect was evident only during the initial phase of bud emergence. In 1985 cyanamide spray and evaporative cooling alone increased yield of ‘Perlette’ by 6% and 6% to 24%, respectively and by 17% to 46% then both treatments were combined. In 1986 prolonged evaporative cooling increased the yield of ‘Perlette’ by 25% but, in combination with cyanamide. by only 11.6% over the unwetted cyanamide-treated control. In both years, evaporative cooling with or without cyanamide advanced fruit maturation.

In many warm areas grapevines suffer from insufficient chilling needed to induce full and uniform bud-break. The problem is most severe in early maturing cultivars grown in regions where scary and clear days prevail during autumn and winter. In these regions, the days are hot and temperatures of the buds exposed to the sun exceed considerably those or the air. The detrimental effect of high day temperatures during autumn and winter on budbreak has been demonstrated in peaches. A negation by high day temperatures of the chilling acquired during the colder night period was shown.

In recent years, cyanamide has been used to improve Budbreak of grapevines and of some other deciduous species. This chemical sometimes can substitute for chilling, although in extreme cases it is only partly effective. In situations where early maturation is forced by means of very early pruning and poly ethylene covers, or complete budbreak of canepruned cultivars is desired, the effect of cyanamide is not satisfactory.

The objective of this study was to evaluate evaporative cooling to counteract the effect of high day temperatures for improved budbreak of grapes. Aspects of early and uniform budbreak were studied using evap orative cooling alone and in combination with cyanamide treatments.

24

Cooling

DISCUSSION

It was demonstrated previously that evaporative cooling decreased peach and nectarine bud tempera tures by 3° to 5°C. The low humidity prevailing is the southern Jordan Valley was conducive to high rates of evaporation, which explains the marked effect of wet ting on bud temperatures in this study. The large dif ferences in temperature between shaded and exposed buds may explain the uneven budbreak in such a warm region. Evaporative cooling -reduces these dif ferences, thus improving synchronization of budbreak. The pronounced effect of evaporative cooling operating only during the warmer daytime hours is in agree ment with the previous studies showing the adverse effect of high day temperatures on the accumulation of chilling units needed to overcome dormancy.

The wetting of the wines advanced the time of budbreak, as determined by the rate of bud opening following pruning. The difference in the rate of bud-break between wetting and control was more pro nounced and lasted longer when cyanamide was not supplied than when it was. When evaporative cooling was combined with cyanamide spray, budbreak also accured early, but the differences persisted for only about a week at the initial phase of bud emergence. During that stage, the effects of evaporative cooling and cyanamide appeared to be additative. About one week after initial budbreak, the effect of cyanamide was fully expressed and evaporative cooling did not contribute any more to percent budbreak, which then was essentially complete.

Early pruning (in December) combined with cyan amide spray, has been found to advance budbreak, but the final percentage of open buds is low and bud growth is non-uniform.

Early opening of a few buds increases the polarity and competition between shoots on the vine. The early effect of evaporative cooling on budbreak when used alone or in combination with cyanamide resulted in highly uniform budbreak and shoot growth.

When evaporative cooling was continued after prun ing on ‘Perlette’ vines, budbreak was slightly delayed and the young leaves that emerged were somewhat stressed. This effect of evaporative cooling has been used to delay bud opening of peaches and plums in the Golan Heights, (A. Pales, unpublished data) where the bloom is usually damaged by spring frosts.

Prolonged wetting, which did not extend past the time of pruning, was nest effective in breaking the dormancy of grapevine buds, but, when cyanamide was sprayed on vines of this treatment, there was a slight decrease and delay of budbreak. These results indicate that buds on vines of the prolonged wetted treatment were already nondormant at the time of the cyanamide spray, thus becoming very susceptible to phytotoxicity of cyanamide.

Cyanamide also is a herbicide, which is probably the reason for the ineffectiveness of cyanamide treatments or even damage occurring sometimes in cool areas, where natural chilling is sufficient to break dormancy.

Thus, it may be necessary to reduce concentrations of cyanamide when the material is applied after prolonged wetting to avoid phytotoxicity. The evaporative cooling improved percent and uniformity of budbreak also in long, pruned ‘Thompsin-Seedless‘, although in l986 only the prolonged wetted treatment was effective.

In spite of an improvement in budbreak of ‘Thompsin-Seedless‘, evaporative cooling did not increase yields in this cultivar. The reason for this is unclear.

Complete budbreak of the grapevine is a prerequisite for achieving maximum yield, whereas advancing the time of budbreak is essential for early maturation.

25

Cooling

Attempts to achieve both objectives by use of a cyanamide spray and early pruning were rarely successful, since earliness is associated with incomplete budbreak and vice versa. The use of evaporative cooling in combination with cyanamide enabled the achievement of both objectives.

Evaporative cooling alone improved yield and earliness of ‘Perlette’ only in 1987 in the prolonged wetted treatment, whereas cyanamide alone (which caused earliness in both years) failed to increase yield in 1985. The combination of the two treatments, however, successfully advanced harvest date and increased yield of ‘Perlette’ in both seasons.

Evaporative cooling consumed large volumes of water (91 m3/ha/day). The water applied evaporated from the grape canopy and from the top 2 to 5 cm of the soil without contributing to the water reservoir in the soil. Shutting off the system (using the thermostats) whenever air or bud temperatures are low during autumn and winter could improve efficiency in terms of water consumption.

The economic value of evaporative cooling is yet to be established, but well-designed system may be used with slight modifications also for irrigating the vineyard, using the same microjets but lowered to ground level. The overhead microjets also can be used to overcome frost hazards and for improving fruit quality (e.g., size, sugar content, and color) by reducing supra-optimal temperatures (35°C) during fruit development provided that the water contains only small amounts of salts.

CAsE sTuDY 7

FruIT COLOr ANd FIrmNESS IN 'SENSATION rEd BArTLETT' PEAr IN OrEGON By Dusssi/Sugar/Azarenko/Righetti HortTechnology Jan-March 1997

Over-tree sprinkler irrigation cooling treatments were applied to ‘Sensation Red Bartlett’ pear trees during the final 30 days of fruit maturity in 1992 and 1993 when orchard air temperatures were >29°C. Fruit from cooled trees were more red and less yellow than fruit from noncooled trees, resulting in lower hue values by the middle of the harvestable maturity period in both years of study. In 1992, cooled fruit had a greater portion of the fruit surface covered with red blush than fruit that were not cooled. Fruit firmness decreased more rapidly in fruit from cooled trees than in fruit from noncooled trees, indicating advanced matturity. Accordingly, cooled fruit should be harvested earlier than noncooled fruit to maintain postharvest quality. Differences between cooled and noncooled fruit with respect to hue, surface blush, and rate of firmness loss were more pronounced in a warm season requiring frequent cooling than in a cooler season.

RESULTS AND DISCUSSION

In 1992, cooling was applied on 15 of the 30 final days of fruit maturity; while in 1993, temperatures high enough to require cooling occurred only on 7 d. The average difference in maximum temperature between cooled and noncooled trees was 9.9 °F (5.5 °C) in 1992 and 6.8 °F (3.8 °C) in 1993.

Sun-exposed fruit surfaces in both treatments had higher a* values (more red) and lower b* values (less yellow) than the shaded surfaces, resulting in lower-hue values. Cooled fruit had lower hue values (more red and less yellow) than control fruit at 133 and 139 DAFB on both surfaces in 1992 and at 148 DAFB on shaded surfaces in 1993. Sun-exposed and shaded surfaces in both treatments gained in hue value as fruit matured, which reflects the “fading” observed by growers. Cooled fruit tended to increase in hue value as fruit matured less than the control fruit, indicating that cooling can reduce this effect.

26

Cooling

The percentage of blush was higher in cooled fruit than in noncooled fruit in 1992, but the difference in blush was not significant in 1993. This improved blush is consistent with results in apple where over-tree irri gation produced fruit with greater surface coloration and red surface area than fruit which received under-tree or no irrigation (Unrath, 1972).

Over time, firmness of fruit from cooled trees decreased faster than fruit firmness in noncooled trees. Promoting maturity by cooling with over-tree irrigation also was noted by Lombardetal. (1966) in ‘Bartlett’ but not in ‘d’Anjou’ pears. Since cooled ‘Bartlett’ pears matured earlier, they suggested earlier harvest for opti mum keeping quality. Cool temperature treatments also have induced premature ripening on the tree in ‘Bartlett’ pears (Wang et al., 1971), while this response is not seen in other pear cultivars grown in the United States (D.S., personal observation). Unrath (1972) reported that in ‘Red Delicious’ apple trees receiving over-tree sprinkler irrigation, harvest was completed 1 week earlier than in those with under-tree or no irriga tion.

Anthocyanin synthesis in apple is promoted by low temperatures, whether applied during a light or dark period and in poorly exposed skin areas as well as in sun-exposed surfaces (Creasy, 1968). The greater red color (lower hue values) on the exposed surfaces of cooled fruit in this study may have resulted from the direct effects of cooling and from the indirect effects of cooling in advancing fruit maturity. Anthocyanin accumulation in apples approaching maturity may be more directly related to the ripening process than to a fall in temperature (Faragher, 1983; Arakawa, 1991).

Fruit color in ‘Sensation Red Bartlett’ pear appears to respond to temperature similarly to other anthocyanin-containing fruit. Cool temperatures promoted red skin color and a decline of fruit firmness. Modifying red pear fruit color by over-tree sprinkler irrigation has potential value to producers, provided that the earlier-fruit maturity is managed appropriately.

CASE STudy 8

COOLING IN STrAwBErry PrOduCTION IN uSA By Heinemann/Stombaugh/Demchak/Morrow, The Pennsylvania State University

Irrigation is used for many purposes in strawberry production. Aside from alleviating water stress, water is applied for frost protection during bloom and for evaporative cooling to alleviate heat stress during the bearing season. Currently, the determination of when to apply water is largely dependent on the percep tions and convenience of the individual grower. While research has been conducted in automating irrigation for frost protection of apple, peach and citrus little work has been done on strawberry, and still less on the use of such a system for evaporative cooling. High ambient air temperatures probably play a critical role in inhibiting vegetative growth and fruit development in warm climates. The mechanism of this growth inhibition is probably through heat induced photosynthetic activity reduction. In Louisiana, using overhead irrigation to cool plants during the hottest part of the afternoon reduced leaf temperatures by more than 12°C (Chesness and Braud, 1970). In Iowa, runner production, dry matter accumulation, and truss numbers were increased in sprinkler irrigated vs.. non-sprinkler irrigated day-neutral strawberry (Fear and Nonnecke, 1989). Goulart and Gardner (1987), and Goulart et al. (1992) found that an automated system was feasible for both control and monitoring of temperature in strawberry, and found that fruit size was increased when plants were sprinkled as compared to applying water to the soil surface.

27

Cooling

EVAPORATIVE COOLING

Treatment differences were much more apparent in 1991, a particularly warm season than in 1990. Marketable yield from mini-sprinkler treated plants was higher than that of the control, while yields of the trickle irrigation and minisprinkler + iprodione treatments were similar to that of the control. Total yield, however, was highest for the mini-sprinkler treated plants, significantly greater than of the control or mini-sprinkler + iprodionetreated plants. Unmarketable yield, due primarily to gray mold infection, was higher on the mini-sprinkler treated plots than in the control plots.

Mini-sprinkler-treated fruit were consistently cooler on hot days (15 and 27 June). On cool days, however, temperatures were very similar to those in control plots. Trickle-treated plots were most often Intermediate in canopy temperature. Trickle-irrigated and control fruit temperatures were more likely to be similar. Control fruit temperatures far exceeded ambient temperatures, reaching 40ºC (104ºF) routinely on hot days.

EVAPORATIVE COOLING AND FUNGICIDE INjECTION

While marketable, cull, and total yield for the minisprinkler-treated plots was greater than for the control plots, there was no difference in fruit size among treatments, though the high degree of variability which may have masked differences. The more perplexing result, however, was that the minisprinkler + injected iprodione-treated plots had lower total yields, similar to the control plot. This decrease in yield was accompanied by an increase in plant dry mass in the injected treatment as compared with the control, suggesting that the iprodione may have had a growth regulator like effect which diverted the plants’ resources from reproductive to vegetative production. While there is some anecdotal suggestion of this, the authors are unaware of any other documented cases of yield reduction due to injected iprodione. Regarding yield, it should also be noted that the increase in yield due to evaporative cooling was no greater than the increase in yield due to increased water application, as the yields of trickle-irrigated and mini-sprinkler-only treated plants was statistically the same.

The physiological indices of plant stress in this experiment were water potential and related parameters, and A and GS. Under low stress (low PAR), the water potential of watered plants was lower (less negative) than non-watered plants, regardless of application method, indicating that even under non-stressful conditions, the effects of the long-term water deficit persisted. Under high stress conditions, mini-sprin kler treated plants had less negative water potential that the control, with the trickle treated plants being intermediate. The control plants had a more negative osmotic potential than the mini-sprinkler + iprodione treated plants, however they also had a significantly lower turgor pressure, suggesting that osmoregulation was not enough to compensate for stress under high stress conditions. Assimilation rates differed only under high stress conditions, with plants receiving water (either via mini-sprinklers or trickle irrigation) having higher A and high GS rates than non-watered control plants. This suggests that the process of photosynthesis is extremely robust, operating at similar rates in watered and unwatered plants when less stressful conditions permit, even when plant water potentials are more negative.

CONCLUSIONS

The multi-purpose automated irrigation system worked well in preventing frost injury, and reduced water usage by 20-75%, depending on the particular frost event. It offers great potential for grower use. The evaporative cooling system also performed well, however, benefits of the use of evaporative cooling in temperate climates are unclear. While plant stress indicators suggest that the evaporatively cooled plants were less stressed than control plants, the trickle irrigated plants consistently yielded as well as the evaporatively cooled plants, indicating that the application of water was more significant than the cooling effects associated with mini-sprinkler application. It should also be noted, cooling may be magnified over time. Further, the climate in Pennsylvania is not exceptionally hot, even though the 1991 season was particularly hot and dry. It is likely that differences among treatments would be more pronounced in warmer and/or drier climates. There appeared to be a growth regulator-like response exhibited by plants that received iprodione by injection into their cooling system. Certainly, since one of the manifestations of this response was reduced yield, growers should use injected iprodione with caution.

28

Cooling

CASE STudy 9

PhOTOSyNThESIS ANd hEAT STrESS By Allan/Jager, South Africa, Acta Horticulturae 102, 1979

The rate of net photosynthesis in the subtropical macadamia was at a maximum at temperatures from about 16 to 25°C, but decreased above 26°C and would have reached zero at 41-43°C. When both young and mature leaves were present on the trees the rate of net photosynthesis was slightly higher than in trees with mature leaves only. At 26°C the rate of net photosynthesis decreased as radiant flux density decreased below 600 We and especially below 300 Wm-2.

In the tropical papaw the rate of net photosynthesis started to decrease above 30°C and was still about half the maximum at 41°C. In this plant net photosynthesis also decreased most rapidly below a radiant nux density of 300 Wm-2 .

Since these orchard trees are often exposed, during the heat of the day, to temperature levels that are obviously adverse for net photosynthesis, the effects of evaporative cooling of orchard trees through intermittent sprinkling, when conditions warrant it, are being studied.

ALLEVIATION OF HEAT STRESS

It is clear that subtropical plant such as the macadamia must often be exposed during the heat of the day in summer in South Africa to temperatures that are detrimental to maximum net photosynthesis. In addition, due to a lag in the rate of water absorption by plant roots compared to the rate of loss by transpiration through the leaves, temporary plant water stress can still occur during the heat of the day, even when abundant soil moisture is present. Without the cooling effect of transpiration, leaf temperatures can rise 10°C more than air temperature which can have a detrimental effect on net photosynthesis and plant growth.

Any technique that lowers plant and air temperature and increases relative humidity in the immediate plant atmosphere during periods of intense transpiration, should be helpful in preventing the development of high plant water deficits and in achieving a normal water balance within the plant (Gerakis & Carolus, 1970).

The technique of mist propagation of leafy cuttings has revolutionized the propagation of many plant species (Hartmann & Kester, 1975). The mist spray maintains a film of water on the leaves, increases the relative humidity and lowers both air and leaf temperatures through the cooling effect of evaporating water. Wet leaves can be 6 to 8°C cooler than dry leaves. Intermittent applications of mist reduce the quantity of water applied.

An extension of this concept of evaporative cooling through mist sprays to field or orchard situations has given beneficial results with various vegetable and fruit crops (Allan, 1976).

A major problem in evaporative cooling experiments has been the excessive quantities of water that have been applied. A low application rate (1.2 mm/h.) is necessary (a) to avoid the danger of over-irrigation and poor drainage, and (b) to conserve water. An even coverage of the whole area is also necessary to obtain maximum cooling of all plant parts and the water must be of good quality. The ideal system would be to have intermittent sprinkling of several blocks in sequence, when temperatures exceed optimum levels, but with the system switching off late in the afternoon to enable the plants to dry off before sunset and so reduce disease incidence.

29

Cooling

A suitable controller will be necessary to activate the sprinklers intermittently, when temperatures are too high for maximum net photosynthesis. An electronic controller that will not only cause intermittent sprinkling when required, but will also modulate the ‘OFF’ time depending on relative humidity and light intensity, is still undergoing trials. Meanwhile an experiment has been started near Komatipoort using time clocks and a thermostat to control the intermittent sprinkling of macadamia trees when high tempera-tures are experienced. The effect of this system of ‘evaporative cooling’ on the growth, production and quality of various horticultural crops, in comparison with those grown under normal conditions of periodic heat stress, will be studied on a long term basis. Since the system is dual purpose in that it can also be used for irrigation of the trees, the high capital outlay should be justified on high value horticultural crops.

CONCLUSION

This work has clearly shown that in a tropical plant Caricapapaya cv Money Gold, the rate of net photosynthesis is less adversely affected by high temperatures than in a subtropical species Macadamia integrifolia cv Keauhou. However it is obvious that temperatures experienced during the heat of the day in summer, and other seasons, are often too high for maximum net photosynthesis. It is hoped that evaporative cooling of the leaves of plants through intermittent overhead sprinkling with low precipitation sprinklers, will modify the plant environment sufficiently to reduce plant water stress, sod induce greater rates of net photosynthesis and hence improve yields.

CAsE sTuDY 10

COOLING OF GINGEr IN SOuTh AFrICA By T.Anderson/Plessis/Niemand, South Africa, Acta Horticulturae. 275, 1990

Ginger is cultivated in the subtropical regions of the Republic of South Africa. Being a tropical crop, it is subjected to stress factors-such as high summer temperatures associated with low humidity. With the use of an evaporative cooling system these stress factors were greatly reduced and production was increased by more than 25%. Evaporative cooling has a pronounced effect on the leaf and soil temperatures as well as the humidity between plants.

DISCUSSION

Evaporative cooling increased the cumulative yield of ginger over two seasons by more than 25%. During both seasons the number of degree hours above the threshold temperatures for the period October to March was the same, viz 457. The distribution thereof, however, was very different. The longterm average of 459 degree hours for this region is an indication that ginger in the Hazyview area will have to be cooled for optimum production. In a cooler season such as experienced in 1984/85 the same yield increase would probably not be realised since cooling would have less beneficial effect.

Evaporative cooling thus induced a modification of climate in the immediate vicinity of the plant and created a microclimate which improved the plant’s growth and yield. The threshold values at which cool ing commenced, viz 28°C in October to November, and 30°C in December to March, are arbitrary, and may not be optimal. It will only be possible to deter mine the circumstances under which stress develops and cooling becomes a necessity by physiological indicator studies.

30

COOLING GrEENhOuSESBy Menahem Dinar Removing excessive heat and humidity appears to be one of the most difficult processes in greenhouse climate control.

The issue of heat accumulation is true for growing in moderate and hot climates, but also in “cold” climates; typical areas where cropping takes place in the cold season, but also in the summer.

The strategy of heat removal from the greenhouse will be determined according to climate conditions and financial aspects.

Basically, there are several possibilities for removing excess heat: Ventilation - natural + forced ventilationshading Evaporative cooling (pad & fan system or fogging) In addition, there are other means to cool down the temperature of the crop: 1. Air circulators 2. Misting

The effect of air circulation on leaf temperature is indirect and not very significant. The removal of humidity above the leaves will enhance transpiration, followed by reduced leaf temperatures.

The effect of misting on cooling air or crop temperatures could be very helpful in many cases. Misting as a means of cooling in the greenhouse: The misting technique has two main effects as a “cooling procedure” in the greenhouse: • Effect on air temperature and humidity • Effect on leaf temperature Operation on misting by CoolNet Pro™ could fulfill both.

COOLING AIR

The cooling effect of misting on the greenhouse climate will be through evaporative cooling processes. The small drops will evaporate and will absorb the heat immediately after system’s operation, and will reduce air temperatures.

The operation of the system should be for short periods and at short intervals in order to be effective.

If the humidity in the greenhouse will be high, then the small drops will not evaporate and fall down to wet the leaves. Therefore, normally automatic control and operation will require a humidity and temperature sensor programmed to meet the required temperature and humidity.

COOLING THE LEAF

The effect of misting on reduced leaf temperatures could be a very useful tool, mainly to reduce leaf temperature on the upper part of the plant. Normally, those leaves are exposed to very high temperatures, and sometimes temporary wilting could occur, mainly when water cannot be uptaken by the roots, or cannot supply the high demand for transpiration.

The operation of misting for leaf wetting by CoolNet Pro™, is normally done for longer periods than for air cooling purposes. Operation for 20-40 seconds or even for 45 seconds with intervals of 20 minutes could serve this purpose well.

31

Cooling Greenhouses

Set points of temperature and humidity should also be determined: normally temperatures of 28° -30°C and humidity of 65% -75% could serve as good starting set points.

COOLNET PrO™ Netafim’s new very fine mist sprayer, is a efficient means -at a low cost -for improving climatic conditions in greenhouse.

During the growing period, very high heat loads are a common problem, on events that interfere with the optimal development of plants. This phenome non exists in nearly all-growing regions, and is espe cially pronounced in low greenhouses. At crops grown in high water drawing conditions, this phenomena is intensified, since the temperatures in the upper part of the greenhouse are very high, and in most cases, effect negatively the plants growing process. Reducing the heat load in a greenhouse is one of the most difficult processes, and usually requires large capital investment.

■■ The mist is made of durable materials that are resistant to chemicals and acids (marked as Anti Acid – AA). This enables cleaning of the CoolNet Pro™ by immersion in acid.

■■ The mister’s color is a very light shade of gray – thus contributing to the return radiation inside the greenhouse.

■■ The CoolNet Pro™ includes 4 nozzles assembled on a cross.

■■ Discharge capacity of each nozzle: 7.5 l/h (at 4 bar). The cross CoolNet Pro™ flow rate is 30 l/h (at 4 bar).

■■ Recommended operating pressure is 4 bar. The average drop size, at pressures of 4 bar, is 65 microns.

■■ Two types of AD valves (anti-drain)

High pressure Opening at pressure of 4.0 bar Closing at pressure of 1.8 bar Orange colored pin

Medium pressure Opening at pressure of 3.0 barClosing at pressure of 1.5 bar Green colored pin

OPERATING PRINCIPLE OF COOLING

Adding humidity to the greenhouse reduction of temperatures – when the temperatures are high and the humidity is low, the tiny water droplets evaporate, and during this process, air temperatures are reduced.

Controlled wetting of leafs exposed to very high heat loads contribute to reducing the leaf’s temperature: drops that wet the leafage, evaporate and significantly reduce the leaf’s temperature.

32

Cooling Greenhouses

SYSTEM OPERATING PRINCIPLES

■■ Short operation – the drops evaporate while still in the air – and main effect will be expressed in cooling of the greenhouse. (For example: Activating the system for 3 seconds every 10 min utes).

■■ When system activation is long – some of the drops will evaporate while still in the air, while others will wet and cool the leafage. (For example: Activating the system for 10 seconds every 15 minutes).

■■ Various combinations of duration and time inter vals between spraying times will result in a combination of the two processes

■■ Air movement during mist operation will improve the greenhouse cooling process: therefore, ventilation of the air, such as opening side windows and/or opening roof windows or ventilation using ventilators, will enhance the cooling process.

■■ You must prevent leaves from remaining wet for long periods, and make sure that they dry between the wetting cycles

■■ If activation is manual, the grower must learn and calibrate operation timing. The shorter the activation time – a majority of the drops, or sometimes all of them, will evaporate before reaching the leafage.

■■ If the system is controlled by a computer, the set points will activate the system when two conditions are met: humidity is lower than 70% and the temperature is higher than 30ºC.

PRINCIPLES OF SYSTEM PLACEMENT AND INSTALLATION

1. Try to install all CoolNet Pro™ at the maximum possible height – but, of course, prevent wetting of the greenhouse parts.

2. Optimal (at a pressure of 4 atmospheres) will be stable with placement of CoolNet Pro™ at spacing of 2.5 meters in a row, and 3 to 3.2 meters between rows.

3. Since numerous greenhouses are characterized by gable of 8 meters, the rows can be positioned at spacing of 2.5 – 3.0 – 2.5 meters across the rows. In these cases, the distance between CoolNet Pro™ in a row should be 3.0 meters.

4. The CoolNet Pro™ is usually connected to the distribu tion line using a line whose length is 30, 60 and 90 cm. Since positioning the CoolNet Pro™ as high as possible is the preferred solution – a new unit was developed, that is 15 cm. long, that consists of a short stabilizer that is 5 cm. long, whose wall is thicker, in order to improve its stability.

CAsE sTuDY 11

COOLING PrOTECTION IN GrEENhOuSES Mayim & Hashkaya, October 1998

The desirable climatic conditions in greenhouses derive from considerations concerning the growth rate, harvest, harvest quality, disease prevention, and so on. These desirable conditions are created by radiation, by temperature, and by the humidity within the greenhouse. The majority of crops benefit from high radiation, and therefore decreasing the heat by way of shading is not desirable. Maintaining the other two conditions (temperature and humidity in the greenhouse) as dependent on conditions within the surrounding environment (outside the greenhouse relative radiation, temperature and humidity) necessitates the controlling of two main parameters: the airflow through the greenhouse and the flow of water for steam. These flows are determined by calculating the balance between energy and the greenhouse’s evaporation mass (8-4) and are expressed in the following equations: Air flow (kg / sec m² - q) Presuming a stable situation, and ignoring the flow of heat to the soil and to the crop, and supposing that the correct conditions in the greenhouse (temperature and relative humidity) are known, the air flux (q) may be calculated as follows:

33

Figure 1: The airflow required to maintain the desired conditions (70%-27°C) in relation to the temperature and humidity of the surrounding environ ment

Temperature of surrounding environment in °C

Figure 2: Rate of water evaporation required to maintain the desired conditions (70%-27°C) in relation to the surrounding environment’s temperature and humidity ratio.

DESCRIBED OF THE PROPOSED SYSTEM

A proposed system includes: softener, filters, tank, pump, pressure regulator, depressurizing valve, supply piping and nozzles. The tap water, treated by softener and filters, is supplied to a tank that is controlled by a ball cock. The water is directed to the supply piping by a high pressure pump. The water pressure at the point of exit from the pump is manually regulated by a pressure regulator. The water is supplied by the pipes to the nozzles. The nozzle housings comprise a valve (that opens at a pressure of 0.5 atmosphere) that prevents leaking while the system is not in operation.

Cooling Greenhouses

34

When the system is not in operation, the electrically controlled pressure release valve opens for a short time. Opening this valve ensures fast depres surizing. Closing it at the correct time keeps the pipe full of water at a low pressure, which in turn ensures a fast pressure buildup when the system is switched back on. The speedy decrease and increase of pressure following a lower pressure than the correct range, restricts the creation of large drops (leaking) that cause foliage wetting.

Commercial systems of this type existed at the time that we started our work in this particular field. These systems were characteristically expensive. In order to reduce the cost of the proposed system, a survey on different nozzles was undertaken, which resulted in the pinpointing of nozzles of the following commercial companies: Delavan, and Spraying System. These nozzles demonstrated that they were more reliable and cheaper in comparison to the original nozzles that were installed in the commercial fog systems mentioned above. After that, a comparative test was held that showed that the performance of the nozzles was similar, from the aspects of the size of the drop, and their durability under wear and tear.

ExPERIMENTAL SYSTEM

An experimental fog system was assembled in the greenhouse at the Schittin school in central Sapir. This greenhouse was divided into two parts, with each part being made up of two sections. Each part comprised the following, computer-controlled system: desert cooler, a north curtain overlapping with the desert cooler, a south curtain, side curtains (east and west), and fans on the south wall. The fog system was assembled in both parts with one central supply system (softener, filters, and pump), and electric taps that control the whole system separately; this setup was to test the fog system in compar ison to the desert cooler, during intermittent operation of the two greenhouses (east and west). Due to the fact that the entrance of air, which is possible in this greenhouse, is done by opening the curtains (mainly on the north, west or east sides) the nozzles were distributed according to the following detail: double the density on the pipe closest to the north opening (18 nozzles to a line); all the remaining nozzles are distributed evenly throughout the whole greenhouse area (9 nozzles to a line), with two nozzles positioned at the end of each line next to the west (or east) opening.

In order to characterize the system’s operations, a measurement system was set up. This system comprised air-conditioned cells for the measurement of temperature, humidity/dryness (unit). Three of the cells were positioned the length of the internal section in each of the greenhouses, and one cell characterized the surrounding environment. The measurements were collected by a data gathering system. The measurement system calibrates at the beginning of every day by making comparisons with measurements that were made manually on the igrometer machine, of the type “Asman” from “Casella”. In addition, measurements of the speed of air through the ventilation apertures were taken.

CAsE sTuDY 12

LEAF TEmPErATurE IN GrEENhOuSES By Yiftach Ben Asher and Mordecai Shomron

In an open field, it is possible to grow leafy crops in the summer as well. In greenhouses that are sealed against insects, the temperatures reach about 35–45ºC at the hottest times of the day. These high temperatures damage the quality of the leaves by seriously scorching and discoloring them, and can even completely destroy the whole greenhouse crop.

In order to utilize greenhouses in summer, and to benefit from the favorable prices of leafy, insect-free crops, it is necessary to search for inexpensive ways to control the climate within them. Many growers spread shade nets over greenhouses where lettuce is grown in soil-less beds. It is probable that the decrease in the flow of radiation into the greenhouse caused by shading with nets, also has a negative effect on the crop, especially in summer. One of the difficulties of cooling the greenhouse by inexpensive means derives from the existing opposition to wetting the foliage due to a fear of leaf disease development.

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35

The accepted cooling air, damaging the plant’s self-cooling ability in the given temperatures. According to Jackson and Co.’s theory, in these conditions the difference in temperature between the plant foliage and the air is decreased, causing an accompanying increase in water distress methods are based on two approaches. One is to raise the humidity in the greenhouse by means of a humidity mattress and misting. The second is to use shading nets, to whitewash the greenhouse roof, and so on. The theoretical disadvantages of both these approaches are obvious.

The cooling raises the humidity in the greenhouse, thereby lessening the difference between the steam pressure (V.P.D.), the steam between the foliage, and the greenhouse air, damaging the plant’s self-cooling ability in the given temperatures. According to Jackson and Co.’s theory, in these conditions the difference in temperature between the plant foliage and the air is decreased , causing an accompanying increase in water distress(CWSI).

Shading causes a decrease in the total level of radiation that reaches the plant, and as a result there is a decrease in the temperature difference between the foliage and the air, as in the case of increasing the humidity. According to the same theory, this is also accompanied by an increase in water distress. It may be concluded, therefore, that the field experiment showed that shaded lettuce plants were of a lower quality.

As a result, we chose to test the direct wetting cooling method. The theory behind the research is as follows:

1. Direct wetting decreases the average temperature of the leaf water-drop system due to the fact that part of the latent heat in the leaf is passed to the cold water drop.

2. The evaporation procedure of the water drop from the leaf-face causes cooling (cooling by evaporation). Utilization of a larger part of the total radiation as latent heat for steaming is on account of the energy utilized for heating the leaf. In the past, this method of cooling the foliage was not favored because it created ideal temperature and humidity conditions for the development of leaf diseases, an assumption that is correct for crops with extended growing periods, such as roses and tomatoes, but not for short-term crops (30–50 days) like lettuce.

The goals of the research are as follows:

3. To test the effectiveness of the direct wetting cooling method of lettuce foliage (in accordance with the harvested crop).

4. To measure the suitable “bottom line” in cooling lettuce.

5. To measure the degree of water distress (CWSI) in lettuce that is not cooled.

CONCLUSIONS

1. The degree of water distress (CWSI) is greatly affected by cooling. Without cooling, the CWSI was measured as 0.4 as opposed to 0ºC. It must be noted that in both methods of treatment (with and without cooling) there were optimal amounts of water but the greenhouse conditions (the high humidity and the speed of the wind restricted by the insect-proof net within the greenhouse) greatly slows the transpiration rate and reduces the plant’s ability to cool itself by evaporation. In addition, wetting the foliage artificially with cold water contributes to a decrease in the average temperature of the leaf-drop system.

2. The lettuce crop is clearly affected by operating the misting system, with the plant weight being greater than the accepted non-cooled average. This also applies to a field sample harvested from commercial fields.

3. In addition, there are another two benefits brought about by using sprinklers for cooling:

4. A 30% increase in the rate of seedling survival.

Cooling Greenhouses

36

5. An improvement in the quality of the crop: without cooling, a considerable percentage of the lettuce seedlings are disqualified from marketing, because of discoloring and drying of the foliage. With cooling, this phenomenon was unknown.

The three areas of damage to lettuce grown without cooling (mentioned above)—decrease in the size and quality of the crop and the successful survival of the seedlings—meant that in the years preceding the introduction of direct cooling, there was almost no lettuce grown in greenhouses during the summer months. Financial damage resulted from the need to market two plants instead of a single plant in the product packaging (plastic bag) which in itself contributed to an approximately 50% reduction in the crop per dunam. Further, the substantial percentage of lettuce seedling failure and of scorched plants resulted in the growers deciding not to grow lettuce in summer. However, with the help of cooling, more and more growers are beginning to grow summer lettuce.

CAsE sTuDY 13

INTErmITTENT APPLICATION OF wATEr TO AN ExTErNALLy mOuNTEd GrEENhOuSE ShAdE CLOTh TO mOdIFy COOLING PErFOrmANCE By D. H. Willits, M. M. Peet, American Society of Agricultural Engineers, 2000

The cooling performance of an externally mounted, flat-woven, black-polypropylene shade cloth (manufacturers shade rating of 55% was examined under both dry and wet conditions.

Wetting was accomplished by intermittently sprinkling the cloth with water when outside solar levels were greater than 400 W m-2 .

Compared to an unshaded greenhouse, the dry shade cloth reduced the rate of energy gain by about 26%, less than one-half the amount suggested by the shade rating. At the same time, electrical energy consumption was also reduced by about 8% due to reduced operation of the cooling equipment in the shaded house.

Under the wet cloth, the reduction in rate of energy gain improved to about 41%, of which 3.5% was attributable to the increased shading provided by the water-film. Air temperature rise along the house was reduced by 18% under the dry cloth and 40% under the wet cloth. Leaf temperature rise was reduced by only about 9% under the dry cloth: however, the value is misleading because leaf temperatures were reduced nearly uniformly along the house whereas air tem peratures were reduced primarily at the exhaust end. Under wet shade, leaf temperature rise was reduced nearly 43% and electrical energy consumption by 21%.

CONCLUSIONS

The results of this study support the conclusion that dry, externally mounted, black plastic shade cloths cool significantly less (by any measure) than the amount predicted by their shade rating.

The reduction in rate of energy gain compared to an unshaded control was about 26.2%, less than half the manufacturer’s shade rating of the cloth (55%).

A small savings in electrical energy consumption (8.4% in this study) may also be expected due to a decrease in the operational time of the cooling equipment. The results also suggest that reductions in leaf temperature can be expected to be greater than reductions in air temperature, with leaf temperatures being decreased almost uniformly along the house and air temperatures being reduced primarily at the exhaust end.

Cooling Greenhouses

37

The results also support the conclusion that the application of water to external shade cloths can be expected increase cooling performance significantly.

Reductions in the rate of energy gain under wet shade (compared to an unshaded control) were found to be 41%, with only 3.3% of that attributable to increased shading from the water film. The remainder of the increase over the dry case is attributed to a reduction of cloth temperature due to evaporation of the water. Reduction of air and leaf temperature rise can be expected to be about the same as the reduc tion in the rate of energy gain. Leaf temperatures were again reduced more than air temperatures but, as with the dry case, the resulting leaf temperatures were more uniform along the house than were air temperatures.

rOOF COOLING Netafim™ Library

Roof cooling has several effects on the greenhouse climate: the indoor temperature is lowered because the evaporation of the applied water takes heat from the roof. Lowering the air temperature also indicates an increase in the relative air humidity. At the same time, the cool outside air with higher humidity enters the greenhouse and strengthens the cooling effect. Roof cooling is used not only for vegetables (tomatoes, cucumbers, and peppers) but also for flowers (roses, gerbera’s and container plants). The maximum evaporation from the roof is estimated at 1 mm/h. The installation needs some extra capacity to get this amount at the driest spot. Additionally, extra water is needed to clean the roof and prevent dirt accumulation. The amount of extra water needed depends on the weather conditions and the water quality used.

CAsE sTuDY 14

COOLING PrOTECTION OF LIvESTOCk Research and on-farm demonstrations have shown that Micro-sprinklers, spray jets and fan cooling systems can be effective in relieving heat stress in dairy cows under hot, humid conditions. Based on these results, many dairymen are considering installing sprinkler and fan cooling. Several Kentucky dairymen have already installed sprinkler cooling systems, but they could improve their performance by modifying them to take into account the principles involved and the components used in sprinkler and fan cooling.

HEAT STRESS EFFECTS

The need for such systems arises from the effects of heat stress on dairy cows. The thermoneutral temperature range, or “comfort” zone, for most dairy cows is about 4°C-24°C (40-75F). Above 24°C (75°F), increases in temperature and/or humidity begin to cause heat stress.

Heat stress can reduce feed intake, milk production, and breeding efficiency in dairy cows. Losses in the pocketbook follow when milk production and breeding efficiency drop. Declines in milk production of as much as 25% have been reported for summer conditions in the humid Southeast. Over a summer season (June l-September 30) heat-stress related losses can range from about 24 kg (55 Ib)/cow in Maine to about 454 kg (1,000 lb)/cow, or more, in Texas for a cow milking 29 kg (66 Ib)/day.

METHODS FOR HEAT STRESS RELIEF: WATER, SHADE AND VENTILATION

There are several means available for reducing heat stress in dairy cows. Providing plenty of clean and available water, enough shade, and good ventilation should be routine. These areas are the first places to concentrate if a heat stress problem is evident in the herd. Some type of cooling system can then be considered after the more routine practices are taken care of.

Cooling Greenhouses

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The most economical cooling method is evaporative cooling using spray jets or mini-sprinklers and fans. Results from research at the University of Kentucky and elsewhere have given us improved design and operation guidelines for such systems.

SPRINKLER AND FAN COOLING PRINCIPLES

In sprinkler and fan cooling, the sprinklers create droplets that wet the cow’s hair coat to the skin. Fans are then used to force air over the cow’s body, causing evaporative cooling to take place on the skin and hair coat. Heat from the cow’s body causes the moisture to evaporate. The droplet size must be large enough to wet the skin surface and must be applied intermit tently to allow time for the moisture to evaporate from the skin. Air movement is needed in fairly humid cli mates, such as that in Kentucky, to provide enough drier air above the skin to do a good job of evaporating the water.

Fog or mist systems (with very fine sprays) are not recommended for dairy cattle in Kentucky because of the humidity levels during the summer. Those systems attempt to cool the air around the cow rather than cooling her skin directly. In the arid West this works well, but in more humid areas, a “steam bath” effect can actually be created. Therefore, for the eastern and midwestern United States, sprinkler and fan cooling should be used rather than fogs or mists.

COOLING BENEFITS

Several system designs and weather conditions have been studied for sprinkler and fan cooling systems. Systems tested in Kentucky and Florida, as well as in other locations, have demonstrated the potential benefits. Feed intake, milk production and cow comfort have all been shown to increase by using sprinkler and fan cooling. Current research has reduced the amount of water used from 50-75 gal/head/day to as low as 6 gal/head/day which reduces potential damage to the livestock.

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Cooling

CAsE sTuDY 15

COOLING ITALIAN dAIry COwS By Frazzi, Calamari and Calegari of Universita, Piacenza, Italy

A summer study evaluated different cooling sys tems by observing the responses of 64 Italian Freisian cows maintained and on an experimental freestall barn located in the Po Valley in Italy. Cows were equally assigned to one of 4 treatments pens consisting: of a control (C) with no cooling, of fans plus mist ing (EM), of fans plus sprinklers (FS) and of a special cooling evaporation system (CEV).

The negative effects of heat stress on the performances of dairy cows is now well established and documented. Negative effects are not limited to reduced production (Collier et al., 1982, Thatcher et al., 1982; Johnson, 1987; Nardone et al., 1992) but also lead to a decrease in quality of milk composition (Bernabucci and Calamari, 1998), a worsening of the main cheesemaking properties of milk (Calamari and Mariani, 1998), a reduction in fertility (Berman, 199l3, and greater susceptibility of the animals to disease due to the lowering of their immune system that results from heat stress (Bertorli, 1998).

The greater the level of production of the animals involved (Johnson el al., 1988), the more severe the negative effects. A high-yielding dairy cow can adapt fairly well to cold because of the high levels of body heat generated. For the same reason, the cow has difficulty in adapting to the heat because her heat-dispersion mechanisms will often be inadequate and insufficient.

The problem of heat is acutely felt in a southern European country, such as Italy, with an environment characterized by high summer temperatures coupled with high humidity levels. The problem will become more acute as production levels continue to rise due to genetic improvements and developments in tech niques of rearing and feeding cattle.

Therefore we are faced with the dramatic necessity of finding effective methods to manage heat stress in order to better the well being of cattle and to increase production and mink quality.

Because water evaporation is an endothermal process, it is among the most effective techniques for cooling the environment and lowering body temperature.

EVAPORATIVE COOLING SYSTEM

One of the most widespread techniques is the so-called evaporative cooling system, based on the use of large coolers fitted with cooling pads through which ventilation air passes. The air, cooled and with increased humidity, is released into the cowshed to give the animals relief. This system gives good results in a closed cowshed, if adequately insulated, and if it is possible to use a system of forced and controlled ventilation. In summer 1995, in a trial conducted near Mantua, this ventilation system gave better results, than those obtained with a simple forced ventilation or with ventilation with misting (Frazzi et al., 1998a).

COMBINATION OF VENTILATORS AND MISTERS

A second technique is the combination of ventilators and misters. A series of high-pressure misters distribute water in fine droplets, part of which evaporates into the atmosphere, lowering the temperature, and part of which wets the animals. Fans operate at the same time as the misters and enhance evaporation off the animals’ skin. Cows can lose considerable quantities of heat, enough to keep body temperature constant without production losses, if evaporation is sufficient.

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Cooling

FANS WITH LOW-PRESSURE WATER SUPPLIES

A third technique is based on the combination of fans with low-pressure water supplies (spreaders). The principle is analogous to the second technique, except in this case, the aim is immediate wetting of the animals, which is achieved with greater quantities of water. Forced ventilation is necessary for water evaporation off the animals’ body.

Research projects, especially in the USA and Israel in the 80s and 90s, have evaluated these last two tech niques in reducing heat stress on dairy cattle (Igono et al., 1985; Flamenbaum et al., 1986, Beede et al., 1987, Strickland et al., 1989; Bucklin et al., 1991; Turner et al., 1992; Frazzi et al., 1997). In many cases, cooling systems that coupled wetting animals with water evaporation off the animals skin were shown to be superior to those that sought merely to lower the air temperature (Bucklin et al., 1991; Lin et al., 1998). However, this system uses greater quantities of water, giving rise to wet floors and increased quantities of liquid waste and slurry.

Systems based on water evaporation are better suited to hot, dry climates than hot, humid ones. In addition, the style of the buildings and equipment can be important in the choice of cooling techniques. Given the specific use of the dairy products in the geographic area under consideration (60% of milk produced in Po Valley is used in the production of grana cheese), the effect of these systems on microbial levels, composition and the cheesemaking properties of the milk is of great importance.

These cooling techniques are spreading now rapidly in Italy. Thus, this study was conducted to compare the systems in order to evaluate their effects on the animals, consequences on the cattle’s environment, milk composition and the cheesemaking properties of the milk, as well as problems of organizing and operating the different systems.

CONCLUSION

From our results we can conclude that the barn cooling systems that wet the animals (fans plus misting FM or fans plus sprinklers: FS), leading to evaporation of the water directly off the animals’ skin, are more effective than the special cooling evaporation system (CEV) which seems merely to lower the air temperature.

The animals in pens equipped with FM and FS cooling systems, showed lower rectal temperature and breathing rate, a lower reduction of milk yield and a better regular behavior of protein content and cheesemaking properties during hottest period when compared to group C and CEV.

The results obtained with FM and FS were similar and they were in favour of the misters which, if well placed, can achieve the same results of the sprinklers but with a whole series of advantages, including lower water consumption, avoiding the wetting of the walls and of the floor of the shed.

The use of sprinklers or misters did not increase milk somatic cells count, compared to the systems.

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Cooling

CAsE sTuDY 16

dAIry CATTLE hEAT STrESSBy Dr. Scok T. Willard, Dairy News August 2000 This summer is typical of those seen in Mississippi -hot and humid. As temperatures soar over 32°C (90°F) degrees dairy cattle are experiencing severe heat stress throughout the southern region, which can compromise cow health, milk quality and production. To combat this, many producers use various combinations of fan and sprinkler systems to cool cows in free stalls, milking parlors and cutler animal holding areas. While it is known that fans and sprinklers are of great benefit for cooling cows during summer months, how efficient these systems are in helping cows to dissi pate heat under varied climatic conditions have not been effectively quantified. Specifically, it is not known entirely how differences in relative humidity and the amount of cow surface wetting from sprinklers might interact with one another to influence the ability of a cow to cool itself effectively.

To study this more thoroughly, MSU is collaborating with Dr. Peter Hillman, a senior lecturer in environmental physiology and agricultural engineering, from Cornell University in New York. Dr. Hillman visited MSU in early July as part of a cooperative research project investigating how fan and sprinkler cooling systems interact to facilitate evaporative cooling at the level of the hair coat for coves in Mississippi. These data will be compared to similar studies performed at the University of Arizona last summer and the University of Hawaii later this year. This multi-state effort will determine how the effectiveness of fan and sprinkler systems may differ in locations with similar ambient temperature gradients, but dramatic differences in relative humidity. It is anticipated that further work in this area may provide more precise recommendations regarding the degree of cow surface wetting required to maximize the cooling effects facilitated by sprinkler and fan combinations in different climates. After all, a comfortable cow is an economical cow.

CAsE sTuDY 17

COOLING PIGS Netafim™ library

Summer heat is hard on pigs. While most animals sweat to cool themselves, pigs cannot sweat and suffer heat stress at temperatures as low as 24°C (75F). Heat stress in grower/finisher pigs reduces daily feed intake, and causes poor feed to gain ratios. During hot weather, lactating sows eat less causing decreased milk production, lower litter weights, excessive weight loss and breeding problems after weaning. In your breeding herd, heat stress can delay puberty in gilts and reduce fertility in both sows and boars.

You can eliminate summer heat stress effectively and economically by using spray cooling systems which intermittently wet the pig’s skin and evapora tion then cools the pigs.

Because evaporation does the cooling, only a small amount of water is needed.

University studies have proven that pigs over 50 pounds can gain up to 30% faster and reach market on 10% less feed when a spray cooling system is used during hot weather. Your partially slatted pens will stay cleaner too. Many producers have found that minimal use of their shower system in winter is also useful in training their pigs to develop good dunging habits.

Studies have also proven the benefits of using drip cooling during hot weather in lactating sows. Higher feed intake, heavier litters, and sows which are in better condition at weaning are all results obtained using drip cooling. Boars and sows in the breeding area also performed better when heat stress was alleviated. Fertility improvements led to increased litter size and healthier piglets.

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Cooling

CAsE sTuDY 18

COOLING POuLTry hOuSES Netafim™ Library

Poultry houses in Israel use sprinkling systems for cooling purposes.

■■ Sprinkling over the poultry house’s roof (for envi ronmental cooling).

■■ Sprinkling/Micro-sprinkling applied inside the poultry house.

■■ Evaporation of the water drops (a process con suming energy from the air surrounding the poultry during evaporation) and by cooling of the poultry’s skin surface by absorbing the heat it releases.

Two methods for cooling poultry & its surroundings are in practice in Israel: 1. Cooling by micro-sprinklers (relatively large drops) with flow rate of 40-70 l/h. 2. Cooling by mist-emitters (small drops) with a flow rate of 7-30 l/h.

In each case the method to be applied must be determined in consultation with professionals in the poultry field (regional guide).

sprinkling by 40-70 l/h micro-sprinklers -Advantages:

■■ The water quantity applied is sufficient for cooling the poultry & its surroundings.

■■ The water quantity applied complies with the require ments under extremely hot temperature conditions.

sprinkling by 40-70l/h micro-sprinklers -Disadvantages:

■■ Long-term sprinkling will wet the litter.

Cooling by mist-emitters - Advantages:

■■ Due to its low flow rate the mist-emitter does not wet the litter.

■■ The mist-emitter maintains constant temperature inside the poultry house.

Cooling by mist-emitters - Disadvantages:

■■ The system is susceptible to clogging.

■■ The system requires minimal pressures ranging between 3-4 atm.

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Cooling

POuLTry hOuSE COOLING- OPErATION-SChEduLE SPRINKLING BY MICRO-SPRINKLERS AND MIST-EMITTERS:

The sprinkler system, of which programming is poultry house’s temperature and moisture data depen dent, will be operated according to frequencies and durations indicated in the following table:

Cooling system’s temp. (c) Operation Duration (min) Frequency (min)

28-39 1 Every 15

30-33 1 Every 13

34-36 1 Every 10

37-41 1 Every 8

41 and more 1 Every 4

This table’s figures are submitted as recommendation only. However the above figures must be carefully adapted to the specific climatic conditions of each and every given territory.

Netafim™ supplies controllers that can be programmed based upon temperature and moisture data inside the poultry house.

sprinkling by mist emitters :

■■ The mist-emitters will operate in short pulses (5-8 seconds).

■■ Use must be made of controllers capable of deter mining operation frequency based upon temperature and/or relative humidity inside the poultry house.

■■ Strictly ensure that a 120 mesh filter is installed to prevent clogging.

■■ Strictly ensure that cooling is operated under the pressure range recommended by the manufacturer.

Poultry house cooling: Here are several basic rules to be followed when cooling poultry house:

■■ Temperature up to 32ºC and low humidity con dition demand moisture increase without wetting the poultry.

■■ Temperature up to 38ºC demands cooling of the poultry and its surroundings.

■■ Temperature up to 42ºC demands operation of all cooling systems inside as well as outside the poultry house.

Netafim's most recommended irrigation systems for poultry house cooling: Temperature up to 32ºC + low moisture -30l/h “CoolNet Pro™” system, (4-nozzle head), at pressure of 4 bar, 2 “CoolNet Pro™” laterals along each poultry house (based on standard 6-8m width) at 3m spacing between emitters. In case of wider houses spacing will be 3*3m.

■■ Temperature up to 38ºC will require the above mentioned “CoolNet Pro™”+ additional 70l/h SpinNet™ mini-sprinklers at 4*4m spacing between emitters.

■■ Temperature up to 42ºC will require the above mentioned systems + roof Sprinkler system including 200l/h MegaNet™ sprinklers at 10m spacing between emitters.

The Netafim™ product range includes an auto matic temperature and moisture controller for operating the cooling system based upon the atmospheric data existing inside the poultry house. Over the recent year another cooling method was developed for application in poultry houses in Israel. In this method air-cooling is achieved by laying a 50% density plastic net to be spread diagonally from the roof downwards along and around the poultry house’s walls. The laterals, in this case, are installed along the roof-side with the sprinklers mounted diagonally to achieve optimal wetting of the net, thus cooling the air around the poultry house. CoolNet Pro™ very fine mist is a recommended option for wetting the net.

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Cooling

NETAFIm™ PrOduCTS

SUPERNET™

Regulated micro-sprinkler designed to cool from above the whole area or over each tree, mainly tree crops (orchards). Recommended combinations:

MODEL PRESSURE

(BAR)

FLOW RATE

(L/HR)

PRECIPITATION

(MM/HR)

DISTANCE BETWEEN SPRINKLERS

(M)

DISTANCE BETWEEN LATERALS

(M)SR 030 2.0 30.0 10.1 Above each tree

LR 070 2.0 70.0 6.1 3.0 4.0

LR 090 2.0 90.0 5.9 4.0 4.0

GYRONET™

Micro-sprinkler designed to cool from above the whole area or above each tree, mainly for tree crops (orchards). Recommended combinations:

MODEL PRESSURE

(BAR)

FLOW RATE

(L/HR)

PRECIPITATION

(MM/HR)

DISTANCE BETWEEN SPRINKLERS

(M)

DISTANCE BETWEEN LATERALS

(M)SR 030 2.0 29.0 10.0 Above each tree

LR 070 2.0 78.0 3.0 5.0 5.0

LR 120 2.0 134.0 3.5 6.0 6.0

COOLNET PRO™

Very fine mist system, designed for evaporative cooling. Mainly for use in greenhouses and closed building. Can also be used in open areas. Recommended combinations:

MODEL PRESSURE

(BAR)

FLOW RATE

(L/HR)

PRECIPITATION

(MM/HR)

DISTANCE BETWEEN SPRINKLERS

(M)Cross body 4.0 30.0 3.0 3.0

Single body 4.0 7.5 1.0 1.5

Netafim™ products

45

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