Soilless Culture: Theory and Practice

Michael Raviv, J. Heinrich Lieth, Michael Raviv, J. Heinrich Lieth

• Publisher: Elsevier Science
• Year: 2007
• ISBN:
  9780080556420
• Topic: Scienze biologiche
• Subtopic: Botanica

Plant production in hydroponics and soilless culture is rapidly expanding throughout the world, raising a great interest in the scientific community. For the first time in an authoritative reference book, authors cover both theoretical and practical aspects of hydroponics (growing plants without the use of soil). This reference book covers the state-of-the-art in this area, while offering a clear view of supplying plants with nutrients other than soil. Soilless Culture provides the reader with an understanding of the properties of the various soiless media and how these properties affect plant performance in relation to basic horticultural operations, such as irrigation and fertilization. This book is ideal for agronomists, horticulturalists, greenhouse and nursery managers, extension specialists, and people involved with the production of plants.* Comprehensive discussion of hydroponic systems, irrigation, and control measures allows readers to achieve optimal performance* State-of-the-art book on all theoretical aspects of hydroponics and soilless culture including a thorough description of the root system, its functions and limitation posed by restricted root volume* Critical and updated reviews of current analytical methods and how to translate their results to irrigation and fertilization practices * Definitive chapters on recycled, no-discharge systems including salinity and nutrition management and pathogen eradication * Up-to-date description of all important types of growing media

1

SIGNIFICANCE OF SOILLESS CULTURE IN AGRICULTURE

MICHAEL RAVIV; J. HEINRICH LIETH

Publisher Summary

This chapter explains soilless culture and describes its significance in agriculture. It begins with a historical account of facets of soilless culture in agriculture, suggesting that substrates used throughout the world differ significantly as to their make-up, while attempting to adhere to a specific set of principles. These principles are quite complex, relating to physical and chemical factors of solids, liquids, and gasses in the root zone of the plant. Today the largest industries in which soilless production dominates are greenhouse production of ornamentals and vegetables and outdoor container nursery production. In urban horticulture, virtually all containerized plants are grown without any field soil. Following this, it deals with hydroponics, which simply means, growing plants without soil. Initially scientists used hydroponics mainly as a research tool to study particular aspects of plant nutrition and root function. Progress in plastics manufacturing, automation, production of completely soluble fertilizers, and especially the development of many types of substrates complemented the scientific achievements and brought soilless cultivation to a viable commercial stage. Today various types of soilless systems exist for growing vegetables and ornamentals in greenhouses. This has resulted in a wide variety of growing systems. Finally, it presents an account of the current prevailing trends with respect to soilless media in agriculture, all over the world.

1.1 Historical Facets of Soilless Production

1.2 Hydroponics

1.3 Soilless Production Agriculture

References

1.1 HISTORICAL FACETS OF SOILLESS PRODUCTION

Although we normally think about soilless culture as a modern practice, growing plants in containers aboveground has been tried at various times throughout the ages. The Egyptians did it almost 4000 years ago. Wall paintings found in the temple of Deir el Bahari (Naville 1913) showed what appears to be the first documented case of container-grown plants (Fig. 1.1). They were used to transfer mature trees from their native countries of origin to the king's palace and then to be grown this way when local soils were not suitable for the particular plant. It is not known what type of growing medium was used to fill the containers, but since they were shown as being carried by porters over large distances, it is possible that materials used were lighter than pure soil.

FIGURE 1.1 Early recorded instance of plant production and transportation, recorded in the temple of Hatshepsut, Deir el-Bahari, near Thebes, Egypt (Naville, 1913; Matkin et al., 1957).

Starting in the seventeenth century, plants were moved around, especially from the Far and Middle East to Europe to be grown in orangeries, in order to supply aesthetic value, and rare fruits and vegetables to wealthy people. An orangery is ‘a sheltered place, especially a greenhouse, used for the cultivation of orange trees in cool climates’ (American Heritage Dictionary), so it can be regarded as the first documented case of a container-growning system, although soil was mostly used to fill these containers. Orangeries can still be found today throughout Europe. An exquisite example of an organery from Dresden, Germany, is shown in Fig 1.2.

FIGURE 1.2 The organery at Pillnitz Palace near Dresden, Germany.

The orangery at Pillnitz Palace near Dresden Germany was used to protect container-grown citrus trees during the winter. Large doors at the east side allowed trees to be moved in and out so that they could be grown outdoors during the summer and brought inside during the winter. Large floor-to-ceiling windows on the south side allowed for sunlight to enter.

As suggested by the name, the first plants to be grown in orangeries were different species of citrus. An artistic example can be seen in Fig. 1.3.

FIGURE 1.3 Orangery (from The Nederlanze Hesperides by Jan Commelin, 1676).

Two major steps were key to the advancement of the production of plants in containers. One was the understanding of plant nutritional requirements, pioneered by French and German scientists in the nineteenth century, and later perfected by mainly American and English scientists during the first half of the twentieth century. As late as 1946, British scientists still claimed that while it is possible to grow plants in silica sand using nutrient solutions, similarly treated soil-grown plants produced more yield and biomass (Woodman and Johnson, 1946 a,b). It was not until the 1970s that researchers developed complete nutrient solutions, coupled their use to appropriate rooting media and studied how to optimize the levels of nutrients, water and oxygen to demonstrate the superiority of soilless media in terms of yield (Cooper, 1975; Verwer, 1976).

The second major step was the realization that elimination of disease organisms that needed to be controlled through disinfestation was feasible in container-grown production while being virtually impossible in soil-grown plants. In the United States, a key document was the description of a production system that provided a manual for the use of substrates in conjunction with disease control for production of container-grown plants in outdoor nursery production. Entitled The U.C. System for Producing Healthy Container-grown Plants through the use of clean Soil, Clean Stock, and Sanitation (Baker, 1957), it was a breakthrough in container nursery production in the 1950s and 1960s and helped growers to such an extent that it became universally adopted since growers using the system had a dramatic economic advantage over competitors that did not use it. This manual described several growing media mixes consisting of sand and organic matter such as peat, bark or sawdust in various specific percentages (Matkin and Chandler, 1957). These became known as ‘UC mixes’. It should be noted that in this manual these mixes are called ‘soil’ or ‘soil mixes’, largely because prior to that time most container media consisted of a mix of soil and various other materials. That convention is not used in this book; here we treat the term ‘soil’ as meaning only a particular combination of sand, silt, clay and organic matter found in the ground. Thus, when we talk about soilless substrates in this book, they may include mineral components (such as sand or clay) that are also found in soil, but not soil directly. The term ‘compost’ was also used as a synonym to ‘soil mix’ for many years, especially in Europe and the United Kingdom (Robinson and Lamb, 1975), but also in the United States (Boodley and Sheldrake, 1973). This term included what is now usually termed ‘substrate’ or ‘growing medium’ and, in most cases, suggests the use of mix of various components, with at least one of them being of organic origin. In this book, we use the term ‘growing medium’ and ‘substrate’ interchangeably.

These scientific developments dispelled the notion that growing media can be assembled by haphazardly combining some soil and other materials to create ‘potting soil’. This notion was supported in the past by the fact that much of the development of ideal growing media was done by trial and error. Today we have a fairly complete picture of the important physical and chemical characteristics (described in Chaps. 3 and 6, respectively), which are achieved through the combination of specific components (e.g. UC mix) or through industrial manufacture (e.g. stone wool slabs).

Throughout the world there are many local and regional implementations of these concepts. These are generally driven by both horticultural and financial considerations. While the horticultural considerations are covered in this book, the financial considerations are not. Yet this factor is ultimately the major driving force for the formulation of a particular substrate mix that ends up in use in a soilless production setting. The financial factor manifests itself through availability of materials, processing costs, transportation costs and costs associated with production of plants/crops as well as their transportation and marketing. Disposal of used substrates is, in some cases, another important consideration of both environmental and economical implications. For example, one of the major problems in the horticultural use of mineral wool (stone- and glass-wool) is its safe disposal, as it is not a natural resource that can be returned back to nature. Various methods of stone wool recycling have been developed but they all put a certain amount of financial burden on the end-user.

In countries where peat is readily available, perhaps even harvested locally, growers find this material to be less expensive than in countries where it has to be imported from distant locations. As prices of raw materials fluctuate, growers must evaluate whether to use a ‘tried and true’ component (e.g. peat) or a replacement (e.g. coconut coir) in a recipe that may have proven to work well over the years. In some years the financial situation may force consideration of a change. Since the properties of all substrates and mixes differ from each other, replacement of one particular component (such as peat) with another component might result in other costs or lower quality crops (which may be valued less in the market place), especially if the substitution is with a material with which the grower has less experience. Thus growers throughout the world face the challenge of assembling mixes that will perform as desired at the lowest possible overall cost.

The result of this is that the substrates used throughout the world differ significantly as to their make-up, while attempting to adhere to a specific set of principles. These principles are quite complex, relating to physical and chemical factors of solids, liquids and gasses in the root zone of the plant.

Today the largest industries in which soilless production dominates are greenhouse production of ornamentals and vegetables and outdoor container nursery production. In urban horticulture, virtually all containerized plants are grown without any field soil.

1.2 HYDROPONICS

Growing plants without soil has also been achieved through water culture without the use of any solid substrates. This type of soilless production is frequently termed ‘hydroponics’. While this term was coined by Gericke (1937) to mean water culture without employing any substrate, currently the term is used to mean various things to various persons. Many use the term to refer to systems that do include some sort of substrate to anchor or stabilize the plant and to provide an inert matrix to hold water. Strictly speaking, however, hy...