Hydroponic Production of Vegetables and Ornamentals (Υδροπονική καλλίεργεια λαχανικών και καλλωπιστικών - έκδοση στα αγγλικά)

Hydroponic Production of Vegetables and Ornamentals

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an in-depth and up-to-date knowledge of Hydroponics?

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...the most useful book on hydroponics ever
written by some of the most internationally renowned scientists!!!

HYDROPONIC PRODUCTION OF VEGETABLES AND ORNAMENTALS
Editors: Prof. D. Savvas and Prof. H. Passam
pp. 463, 81 tables, 71 figures, hardcover, ISBN: 960-8002-12-5, Price 94 Euros
List of Contents
Chapter 1. General Introduction
Prof. Dr. D. Savvas
Chapter 2. Substrate and Substrate Analysis
Dr. M. Raviv, Prof. R. Wallach, Dr. A. Silber and Dr. A. Bar-Tal
Chapter 3. Equipment of Hydroponic Installations
Dr. E. van Os, Dr. Th. H. Gieling and Dr. M. N. A. Ruijs
Chapter 4. Hydroponic Systems
Dr. E. Maloupa
Chapter 5. Composition of Nutrient Solution
Dr. C. Sonneveld
Chapter 6. Nutritional Control in Hydroponics
Dr. P. Adams
Chapter 7. Irrigation Control in Hydroponics
Prof. F. Schroeder and Prof. J. H. Lieth
Chapter 8. Nutrient Solution Recycling
Prof. D. Savvas
Chapter 9. Nutrient Solution Disinfection
Dr. W. Wohanka
Chapter 10. Hydroponics and Product Quality
Prof. W. Schnitzler and Dr. N. Gruda
Chapter 11. Interactions between Nutrition and Climatic Conditions in Hydroponics
Dr. T. Papadopoulos and Dr. X. Hao

List of Contributors
1. Dr. Peter Adams, Former Principal Scientific Officer, Horticulture Research International, Littlehampton, UK
2. Dr. Asher Bar-Tal, Institute of Soils, Water and Environmental Science, Agricultural Research Organization, The Volcani Center, Bet Dagan, ISRAEL
3. Dr. T. Gieling, IMAG B.V. Institute of Agricultural and Environmental Engineering, Wageningen, THE NETHERLANDS
4. Dr. Nazim Gruda, Technische Universitaet Muenchen, Institute for Vegetable Sciences, Freising, GERMANY
5. Dr. Xiuming Hao, Agriculture and Agri-Food Canada, Research Centre of Harrow, Ontario, CANADA
6. Prof. Dr. J. Heinrich Lieth, Dept. of Environmental Horticulture, University of California, Davis, USA
7. Dr. Eleni Maloupa, National Agricultural Research Foundation, Thessaloniki, GREECE
8. Dr. Erik van Os, IMAG B.V. Institute of Agricultural and Environmental Engineering, Wageningen, THE NETHERLANDS
9. Dr. Tom Papadopoulos, Agriculture and Agri-Food Canada, Research Centre of Harrow, Ontario, CANADA
10. Prof. Harold Passam, Lab. of Vegetable Production, Agricultural University of Athens, GREECE
11. Dr. Michael Raviv, Head, New Ya'ar Research Center, Agricultural Research Organization, ISRAEL
12. Dr. M. N. A. Ruijs, Research Station for Floriculture and Glasshouse Vegetables, Naaldwijk, THE NETHERLANDS
13. Prof. Dr. D. Savvas, Dept. of Horticulture and Landscape Architecture, Faculty of Agricultural Technology, Technological Educational Institute of Epirus, Arta, GREECE
14. Prof. Dr. Wilfried Schnitzler, Technische Universitaet Muenchen, Institute for Vegetable Sciences, Freising, GERMANY
15. Prof. Dr. Fritz-Gerald Schroeder, Dept. of Horticulture, University of Applied Science, Dresden, GERMANY
16. Dr. Avner Silber, Institute of Soils, Water and Environmental Science, Agricultural Research Organization, The Volcani Center, Bet Dagan, ISRAEL
17. Dr. Cees Sonneveld, Former Head, Department of Plant Nutrition and Substrates at the Research Station for Floriculture and Glasshouse Vegetables, THE NETHERLANDS
18. Prof. Rony Wallach, The Seagram Center for Soil and Water Sciences, Faculty of Agricultural Food and Environmental Sciences, The Hebrew University of Jerusalem, Rehovot, ISRAEL
19. Dr. Walter Wohanka, State Research Institute, Department of Phytopathology, Geisenheim, GERMANY

Chapter 1

General Introduction

Dimitrios Savvas

Department of Floriculture and Landscape Architecture
Faculty of Agricultural Technology, Technological Educational Institute of Epirus P.O. Box 110, Arta 47100, Greece

Contents

References ...................................................................................................................... 22

The term hydroponics was firstly introduced by Gericke (1937) to describe all methods of growing plants in liquid media for commercial purposes. Gericke (1929) was also the first investigator who attempted to develop an economically feasible method of growing plants in water (nutrient solution) for commercial purposes. Up to that time, the soilless cultivation of plants served exclusively as a tool for plant nutrition studies. According to Hewitt (1966), Knop (1860) and Sachs (1860) were the first scientists who prepared standardized nutrient solutions by adding various inorganic salts to water and used them to grow plants outside the soil in an attempt to identify the essential plant nutrients. This method of studying the physiology of plant nutrition was subsequently adapted by many other scientists (Schreiner and Skinner, 1910; Tottingham, 1914; Shive, 1915, etc., cited by Hewitt, 1966) who developed various alternative techniques to achieve better growth conditions. In these studies, the plants were grown in pure nutrient solution. However, in other experiments (e.g. Hall et al., 1914, cited by Hewitt, 1966; McCall, 1916, and Robbins, 1928, cited by Cooper, 1979), an aggregate medium was introduced to provide support and aeration to the root system. To avoid any interactions between the components of the nutrient solutions and the aggregates, the latter should be chemically inactive (inert). Quartz sand and gravel (free from limestone) were the most popular aggregate materials used in studies involving soilless cultivation of plants at that time. Accordingly, water culture (or solution culture), sand culture and gravel culture were the terms used to describe these methods of growing plants.
Besides Gericke, many other investigators attempted to elaborate innovative techniques and methods of growing plants without soil on a commercial scale during the thirties (e.g. Laurie, 1931; Eaton, 1936; Withrow and Biebel, 1936; Mullard and Stoughton, 1939; Arnon and Hoagland, 1940, cited by Cooper, 1979). These studies contributed considerably to the development of commercial hydroponics. However, although the scientific and technological standards of that time were adequate for the successful soilless cultivation of crop plants in greenhouses, they were still insufficient to achieve economical success. Insufficient knowledge of the nutrient and water requirements of the plants, problems of root aeration in stationary water culture, the inefficiency and expense of irrigation equipment (which was based on galvanized pipes), as well as the limited scope for automation of the supply and recycling of the nutrient solution in aggregate culture were probably the most important factors restricting the early commercial adoption of hydroponics. However, despite the rather disappointing results obtained on a commercial scale, hydroponics attracted enormous popular interest, mainly in the U.S.A., but also in many other countries of the world (Hoagland and Arnon, 1950; Jones, 1982). The idea of growing healthy plants and producing vegetables, fruits and flowers outside the soil was fascinating to many people. Thus, besides the professional growers, many amateur gardeners attempted to grow various plant species hydroponically. The continuous demand of interested people for more information from the scientists involved in hydroponic research motivated Hoagland and Arnon (1950) to summarize in a simplified review the principles and practices involved in water culture at that time.
During, and immediately after the world war, hydroponics was used to some extend by the U.S. Army to produce vegetables for both soldiers and civilians in some non-arable islands in Pacific and regions outside the U.S.A, which were contaminated due to the war operations (Cooper, 1979; Jones, 1982). However, during the fifties and sixties, the areas covered worldwide by horticultural crops grown in water or aggregates were insignificant and the research activity in this field, especially during the fifties, was correspondingly slight. Nevertheless, a few relevant publications relating to the composition of nutrient solutions used in hydroponics originate from that time (Jacobson, 1951; Steiner, 1961 and 1966; Hewitt, 1966). The interest in applying hydroponics in commercial horticulture gradually revived by the end of the sixties. This tendency was more pronounced in the United Kingdom, the Netherlands and some of the Scandinavian countries. In the United Kingdom, the Nutrient Film Technique (NFT), which was introduced by Cooper (1975, 1979), was initially the main hydroponic system adopted by growers on a large scale. At the same time, Scandinavian and Dutch greenhouse growers, who were encountering serious problems due to the continual use of the same soil for many years, tested the possibility of using water-absorbent rockwool plates as a soil substitute (Verwer, 1976 and 1978; Ottosson, 1977; Verwer and Welleman, 1980). Chemically inactive rockwool, which is free from pathogens due to its processing at temperatures of about 1600 oC (Blaabjerg, 1983), proved to be an ideal growing medium, with optimal hydraulic properties. Thus, in the following years, there was a revolutionary expansion of rockwool grown crops in many countries. Especially in the Netherlands, the 5 ha of soilless grown crops in 1976 (Van Os, 1982) catapulted to 1,500 in 1984 (Sonneveld and Welles, 1984), 2,500 in 1989 (Sonneveld, 1989) and increased further to 4,100 by 1996 (Steiner, 1997). In most of these greenhouses, rockwool has been the preferred growing medium, due to its good growing performance and its availability at relatively low prices from local manufacturers. Besides rockwool, many alternative porous materials are used worldwide as growing media (plant substrates) for soilless culture. These include peat, perlite, pumice, polyurethane foam, zeolite, coir dust, sawdust, expanded clay, various volcanic materials such as tuff, etc. More information on the physical and chemical properties of horticultural substrates as well as on their prospects for application in soilless culture, is given by Raviv et al. in Chapter 2.
The porous materials used as substrates in soilless culture are distinguished as organic or inorganic growing media. The organic materials used in soilless culture originate from plant residuals and are therefore subjected to biological degradation. The decomposed organic materials are more or less chemically active, due to the presence of ion exchange sites, which may adsorb or release nutrients. In contrast, most inorganic materials are chemically inactive (inert). Therefore, many authors use the terms “organic” and “inorganic” growing media as synonyms to “chemically active” and “inert” substrates, respectively. However, some inorganic materials, such as zeolite and vermiculite, possess a high cation exchange capacity (Mumpton, 1984; Resh, 1997). It is therefore better to avoid the use of the above terms as synonyms. The ability or inability of a substrate to retain or release nutrients is a characteristic of major significance. Obviously, when growing on an inert medium, all nutrients must be supplied to the crop through the nutrient solution at the same concentrations as in water culture. In this case, the substrate serves merely to improve the supply of oxygen to the roots of the plants. Therefore, the use of the term hydroponics for crops grown on inert substrates seems to be reasonable and compatible with the initial sense of the word, as defined by Gericke (1937). However, when the substrates are capable of substantially modifying the composition of the supplied nutrient solution due to their ion exchange capacity, it seems more appropriate to use the term soilless culture rather than hydroponics. Nevertheless, in most crops grown on chemically active growing media, the volume of substrate per plant is as low as in crops grown on inert substrates. As a result, most of the nutrients required by the plants must be supplied via the nutrient solution. In view of this fact, many authors still use the term hydroponics as synonym to soilless culture.
The increasing interest in the commercial application of hydroponics in the last decades, has encouraged intensive research activity focusing on the development of new hydroponic systems and the improvement of the equipment used to establish soilless cultivation installations. In Chapter 3, Van Os et al. illustrate the current status and perspectives of the equipment that is required to establish and operate modern hydroponic installations. An overview of the hydroponic systems currently used in commercial practice is presented by Maloupa in Chapter 4.
The composition of nutrient solutions and the optimization of nutrition in commercial hydroponics has been a primary objective of the research work related to soilless culture during the last decades. These efforts, supported by the development of modern analytical techniques and equipment, have resulted in the formulation of new nutrient solution compositions, which are adapted to the specific requirements of most horticultural species grown under glass, as for example those suggested by Sonneveld and Straver (1994), De Kreij et al. (1997), Resh (1997), Hanan (1998), De Kreij et al. (1999), etc. An extensive review of the composition of nutrient solutions used in soilless culture is given by Sonneveld (Chapter 5), while for the management of nutrition in modern hydroponics, readers are referred to Adams (Chapter 6). From another point of view, Papadopoulos and Hao (Chapter 11) present the currently available knowledge regarding the influence of environmental conditions on crop nutrition in hydroponics. A review of the nutritional management of hydroponically grown vegetable and ornamental crops has also been given by Savvas (2001).
The supply of water is another factor that significantly influences both the growth and the quality of hydroponically grown plants. In recent years, the developments attained in irrigation technology have been impressive. In Chapter 7, Schroeder and Lieth report on the control of irrigation in modern hydroponic systems.
Many factors that influence the growth and development of plants in hydroponics are different from those of soil grown crops. Most of these factors also affect the quality of harvested vegetables and flowers. Indeed, the product quality is of even more importance than total yield for attaining competitiveness in modern horticulture. Therefore, a special chapter (Chapter 10), written by Schnitzler and Gruda, has been devoted to this topic.
The revolutionary expansion of hydroponics in many countries of the world in the last three decades may be ascribed to the ability of soilless growing systems to be independent of the soil and hence of all its related problems. The main problems arising from the soil are the presence of soil-borne pathogens at the start of the crop and the decline of soil structure and fertility due to its continual cultivation for the same or a related crop species. Hydroponics has proved to be an excellent alternative to soil sterilization, especially in view of the fact that the use of chemical soil sterilants, such as methyl bromide, is or will be soon forbidden in many countries, due to the high toxicity and the adverse effects of these compounds on the environment. Moreover, the cultivation of greenhouse crops and the achievement of high yields and good quality is possible with hydroponics even in saline or sodic soils, or non-arable soils with poor structure, which represent a major proportion of cultivable land throughout the world.
A further advantage of hydroponics is the precise control of nutrition. This is particularly true in crops grown either on inert substrates or in pure nutrient solution. However, even in soilless crops grown in chemically active growing media, the nutrition of the plants can be better controlled than in crops cultivated in the soil, due to the limited volume of substrate per plant and its standard, homogeneous constitution, which is well known to the grower. Furthermore, the preparation of the soil is avoided in hydroponics, thereby increasing the potential length of cultivation time, which, according to Peet (1985) is an effective means of increasing the total yield in greenhouses. It is also worth mentioning that usually hydroponics enhances the onset of harvesting owing to the above-ground location of the substrate or the nutrient solution, which, in heated greenhouses, results in higher temperatures in the root zone during the day.
Last, but not least, the reasons imposing a switch over to hydroponics are increasingly associated with environmental policies. In particular, the recycling of greenhouse effluents in closed hydroponic systems enables a considerable reduction of fertiliser application and a drastic restriction or even a complete elimination of nutrient leaching from greenhouses to the environment. Therefore, in many countries, legislation demands the adoption of closed hydroponic systems for the cultivation of plants in greenhouses (Avidan, 2000; De Kreij et al., 2001), particularly in environmentally protected areas, or regions with limited water resources. The environmental advantages of nutrient solution recycling are expected to contribute to a further extension of closed soilless culture systems in the near future. More information on the principles and techniques involved in the recycling of nutrients in hydroponics is given by Savvas in Chapter 8. The reuse of the nutrient solution effluents in closed soilless culture systems entails the risk of disease spread via the recycled leachate (Runia, 1995). The most efficient way to prevent this, is the installation of a solution disinfection system. This topic is discussed in detail by Wohanka in Chapter 9.
Despite the considerable advantages of hydroponics in commercial horticulture, there are still some disadvantages which restrict the further expansion of such cultivation methods. The current state of the technique normally enables the successful application of soilless culture systems in commercial practice. Hence, the efficiency of hydroponics in commercial use is no longer a disadvantage as it was, for instance, in Gericke’s era or even during the fifties and sixties. Nowadays, the only disadvantages of hydroponics are the somewhat higher costs that are normally required for the installation of soilless culture systems as well as the increased technical skills that are needed to cope with them. In countries, where the cultivation of plants in greenhouses has reached industrial dimensions, the above disadvantages are of minor importance. In such countries, the average greenhouse size per enterprise is comparatively high. Moreover, the investment costs per unit growing area for the establishment of a commercial greenhouse are high in order to maximize yield and optimize product quality by completely controlling all the growing conditions. Hence, the inclusion of equipment for hydroponics, which is a small aliquot of the total investment, constitutes the necessary supplement to enable the exclusion of the last imponderable factor that could restrict yield and impair quality: the soil. For the same reasons, most greenhouse enterprises in these countries can afford the costs of specialized personnel or external advisory services. Thus, the requirement for sufficient technical skills does not pose a problem for large greenhouse enterprises. In contrast, when the greenhouse production takes place under more simple constructions and is mainly based on favorable natural conditions, such as mild winter and increased solar irradiation, even a small increase in the installation and operation costs, that is required for the introduction of hydroponics, can often not be justified. It may be acceptable only when the problems originating from the soil become critical, water resources are limited, or the pollution of the environment by nutrient leaching is serious. This seems to be the main reason for the lower expansion of commercial hydroponics in most of the Mediterranean countries as well as in the U.S.A.

References

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