Okay, most books i have are hard copy but i have one digital and hard copy - Soilless Culture - Theory and Practice - M. Raviv, J. Lieth (Elsevier, 200 BBS. I'll copy paste a page 6-10 - chapter 1.3 (i am sorry if formatting isn't right) if someone wants this i can upload it somewhere: 1.3 SOILLESS PRODUCTION AGRICULTURE World agriculture has changed dramatically over the last few decades, and this change continues, since the driving forces for these changes are still in place. These forces consist of the rapid scientific, economic and technological development of societies throughout the world. The increase in worlds’ population and the improvement in the standard of living in many countries have created a strong demand for high-value foods and ornamentals and particularly for out-of-season, high-quality produce. The demand for floricultural crops, including cut flowers, pot plants and bedding plants, has also grown dramatically. The result of these trends was the expanded use of a wide variety of protected cultivation systems, ranging from primitive screen or plastic film covers to completely controlled greenhouses. Initially this production was entirely in the ground where the soil had been modified so as to allow for good drainage. Since the production costs of protected cultivation are higher than that of open-field production, growers had to increase their production intensity to stay competitive. This was achieved by several techniques; prominent among these is the rapid increase in soilless production relative to total agricultural crop production. The major cause for shift away from the use of soil was the proliferation of soilborne pathogens in intensively cultivated greenhouses. Soil was replaced by various substrates, such as stone wool, polyurethane, perlite, scoria (tuff) and so on, since they are virtually free of pests and diseases due to their manufacturing processes. Also in reuse from crop to crop, these materials can be disinfested between uses so as to kill any microorganisms. The continuing shift to soilless cultivation is also driven by the fact that in soilless systems it is possible to have better control over several crucial factors, leading to greatly improved plant performance. Physical and hydraulic characteristics of most substrates are superior to those of soils. A soil-grown plant experiences relatively high water availability immediately after irrigation. At this time the macropores are filled with water followed by relatively slow drainage which is accompanied by entry of air into the soil macropores. Oxygen, which is consumed by plant roots and soil microflora, is replenished at a rate which may be slower than plant demand. When enough water is drained and evapotranspired, the porosity of the soil is such that atmospheric oxygen diffuses into the root zone. At the same time, some water is held by gradually increasing soil matric forces so that the plant has to invest a considerable amount of energy to take up enough water to compensate for transpiration losses due to atmospheric demand. Most substrates, on the other hand, allow a simultaneous optimization of both water and oxygen availabilities. The matric forces holding the water in substrates are much weaker than in soil. Consequently, plants grown in porous media at or near container capacity require less energy to extract water. At the same time, a significant fraction of the macropores is filled with air, and oxygen diffusion rate is high enough so that plants do not experience a risk of oxygen deficiency, such as experienced by plants grown in a soil near field capacity. This subject is quantitatively discussed in Chap. 3 and its practical translation into irrigation control is described in Chap. 4. Another factor is that nutrient availability to plant roots can be better manipulated and controlled in soilless cultivation than in most arable soils. The surface charge and chemical characteristics of substrates are the subjects of Chap. 6, while plant nutrition requirement and the methods of satisfying these needs are treated in Chap. 8. Chapter 7 isdevotedtothedescriptionoftheanalyticalmethods,usedtoselectadequatesubstrate for a specific aim, and other methods, used to control the nutritional status during the cropping period, so as to provide the growers with recommendations, aimed at optimizing plant performance. Lack of suitable soils, disease contamination after repeated use and the desire to apply optimal conditions for plant growth are leading to the worldwide trend of growing plants in soilless media. Most such plants are grown in greenhouses, generally under near-optimal production conditions. An inherent drawback of soilless vs. soilbased cultivation is the fact that in the latter the root volume is unrestricted while in containerized culture the root volume is restricted. This restricted root volume has several important effects, especially a limited supply of nutrients (Dubik et al., 1990; Bar-Tal, 1999). The limited root volume also increases root-to-root competition since there are more roots per unit volume of medium. Chapter 2 discusses the main functions of the root system while Chap. 13 quantitatively analyses the limitations imposed by a restricted root volume. Various substrates of organic origin are described in Chap. 11, while Chap. 12 describes substrates of inorganic origin and the issue of potting mixes. In both the chapters, subjects such as production, origin, physical and chemical characteristics, sterilization, re-use and waste disposal are discussed. Container production systems have advantages over in-ground production systems in terms of pollution prevention since it is possible, using these growing systems, to minimize or eliminate the discharge of nutritional ions and pesticide residues thus conserving freshwater reservoirs. Simultaneously, water- and nutrient-use efficiencies are typically significantly greater in container production, resulting in clear economic benefits.Throughoutthedevelopedcountriesmoreandmoreattentionisbeingdirected to reducing environmental pollution, and in the countries where this type of production represent a large portion of agricultural productivity, regulations are being created to force recirculation so as to minimize or eliminate run-off from the nurseries and greenhouses. The advantages and constraints of closed and semi-closed systems in an area that is currently seeing a lot of research and the state-of-the-art is described in Chap. 9. The risk of disease proliferation in recirculated production and the methods to avert this risk are described in Chap. 10. The book concludes with a chapter (Chap. 13) dealing with operational conclusions. In many cases practitioners are treating irrigation as separate from fertilization, and in turn as separate from the design and creation of the substrate in which the plants are grown. This chapter addresses the root-zone as a dynamic system and shows how such a system is put together and how it is managed so as to optimize crop production, while at the same time respecting the factors imposed by society (run-off elimination, labour savings, etc.). Another subject which is mentioned in this chapter is the emerging trend of ‘Organic hydroponics’ which seems to gain an increasing popularity in some parts of the world. One of the main future challenges for global horticulture is to produce adequate quantities of affordable food in less-developed countries. Simple, low-cost soilless production systems may be part of the solution to the problems created by the lack of fertile soils and know-how. The fact that a relatively small cultivated area can provide food for a large population can stimulate this development. This, in turn, should stimulate professionals to find alternatives to current expensive and high-tech pieces of equipment and practices, to be suitable and durable for the needs of remote areas. One of the most important advantages of soilless cultivation deserves mentioning in this context: in most of the developing countries, water is scarce and is of low quality. By superimposing the FAO’s hunger map (Fig. 1.4) on the aridity index map (Fig. 1.5), it is clear that in many regions of the world such as sub-Sahalian Africa, Namibia, FIGURE 1.4 Percentage of undernourished population around the globe (see also Plate 2; with kind permission of the FAO). FIGURE 1.5 Aridity index around the globe (see also Plate 3; with kind permission of the FAO). 10 Chapter 1 Significance of Soilless Culture in Agriculture Mongolia and so on, a large part of the population suffers hunger mainly due to water scarcity. Since water-use efficiency of soilless plant production (and especially in recirculated systems) is higher than that of soil-grown plants, more food can be produced with such systems with less water. Also, plants growing in such systems can cope better with higher salinity levels than soil-grown plants. The reason for this is the connection between ample oxygen supply to the roots and their ability to exclude toxic ions such as Na+ and to withstand high osmotic pressure (Kriedemann and Sands, 1984; Drew and Dikumwin, 1985; Drew and Lauchli, 1985). It is interesting to note, in this respect, that soilless cultivation is practised in large scale in very arid regions such as most parts of Australia, parts of South Africa, Saudi Arabia and the southern part of Israel. In none of these countries, hunger is a problem. Thescienceofplantproductioninsoillesssystemsisstillyoung,andalthoughmuch work has been done, many questions still remain unanswered. One of the purposes of this book is to focus on the main issues of the physical and chemical environment of the rhizosphere and to identify areas where future research is needed so as to take further advantage of the available substrates and to propose desirable characteristics for future substrates and growing practices to be developed by next generation of researchers.