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Preface
Since the beginning of this century the application of chemical fertilizers has increased many fold, and the production of soil-applied pesticides has become a new major industry during the past twenty five years. Fertilizers and pesticides are not the only chemicals added to the soil, because by accident or design many other compounds which enter the environment end up in the soil. The world population, increasing at a conservative estimate of 2 per cent per annum, doubles in less than thirty five years. The soil has to produce the bulk of the food and fibre to sustain this growing population.
If the soil is to continue to be both the source of our foodstuffs and the ‘sink’ for many of our wastes, it is obviously desirable that we understand its complex chemistry.
Much scientific endeavour is being directed to this end. This has resulted during the past few decades in a large volume of published literature, including several books concerned with the chemistry of the mineral and organic components of soils, or with certain chemical processes in soils. No recent book has, however, attempted to produce a coherent account of soil chemistry as a whole, suitable for students of both environmental chemistry and soil science, and for the wide range of research and other scientists who are interested in the chemistry of soils. The original intention of the editors of the present book was to attempt to fill this gap. Because of the very diverse topics involved it was felt that it would have to be written by several authors if it was to be appropriately authoritative.
The chemistry of soils falls naturally into two parts, the chemistry of the various soil compoents, and the chemistry of soil processes. At first it was intended that these, the static and dynamic aspects of soils, should form two parts of a single volume. However, to deal with the topics involved at the intended level would have produced an unwieldy volume, and so two companion volumes are being issued, The Chemistry of Soil Constituents and The Chemistry of Soil Processes.
The opening chapter of the companion volume provides a short historical outline of the development of soil science. This deals briefly with the evolution of soil chemistry and pedology, and with the development of soil mineralogy, soil physics and soil biology—disciplines which are essential for integrated studies of soils and soil processes. It also refers to some of the processes which weather rocks, transform plant and animal residues, and lead to the formation of soil constituents. Several systems exist for classifying the major soil types of the world according to their origins, and the most common of the names used to indicate the same soil types are introduced. The two chapters which follow deal with the inorganic and organic components of soils, respectively. Although the chemical structures of the major inorganic components are now reasonably well known, the same is not true of the organic (or humic) materials in soils. The relevant chapter presents an account of what has been experimentally established regarding the constitution of the peculiarly intractable complex of organic compounds found in soils.
Chemical processes in soils are largely determined by reactions at the surfaces of the soil colloids. The final three chapters of the companion volume are therefore concerned with the nature and extent of the surfaces of soil colloids, their electrical characteristics, and the ways in which ions and water are held and arranged at the surfaces.
This volume is intended to describe the chemistry of several of the important processes which take place in the soil. These are discussed in detail in the appropriate chapters which include treatments of precipitation and of ion-exchange reactions, adsorption and the formation of complexes, and of oxidation and reduction. The manuscripts do not, however, adhere exclusively to chemical processes. In contexts of soil as a medium for plant growth or as a ‘sink’ for waste products, it is not realistic to separate purely chemical from physical and biological processes. Thus the initial chapter attempts to summarize the properties of soils which are relevant to plant growth, to detoxification, and to transport processes within the soil profile, and it tries to relate the development of specific features of soils to the chemical processes operating on them.
Mass flow and diffusion, discussed fully in Chapter 2, controls the transport of molecules and of ions to plant roots, and to adsorption, exchange or deposition sites in the soil profile, or to drainage waters or the atmosphere. Such transport processes are strongly influenced by the extents of aggregation of soil components and by the nature of the aggregates; hence the important concepts of soil structure are summarized in Chapter 1. Similarly, the soil composition and structure determine the aeration and water- holding capacity of the soil, and these properties in turn influence the types, numbers, and activities of the organisms of one kind or another which inhabit it. The diversity and magnitude of the soil flora and fauna are introduced in the first chapter, and frequent mention is made of their activities throughout the volume.
Inevitably, in order to discuss the different topics in some depth it has been necessary to assume that the readership will have a significant knowledge of chemistry and an introductory knowledge of soil science. It is hoped that this book, like its companion volume, will be of use to students of soil science and environmental chemistry, as well as to those who are involved in research related to the soil.
The editors are grateful for the collaboration and patience of those who have contributed, for the encouragement of the publishers and their tolerance of delays, and for the permission which many authors and publishers have given for material to be reproduced. Special acknowledgements of the latter are made in the text.
Preface
Since the beginning of this century the application of chemical fertilizers has increased many fold, and the production of soil-applied pesticides has become a new major industry during the past twenty five years. Fertilizers and pesticides are not the only chemicals added to the soil, because by accident or design many other compounds which enter the environment end up in the soil. The world population, increasing at a conservative estimate of 2 per cent per annum, doubles in less than thirty five years. The soil has to produce the bulk of the food and fibre to sustain this growing population.
If the soil is to continue to be both the source of our foodstuffs and the ‘sink’ for many of our wastes, it is obviously desirable that we understand its complex chemistry.
Much scientific endeavour is being directed to this end. This has resulted during the past few decades in a large volume of published literature, including several books concerned with the chemistry of the mineral and organic components of soils, or with certain chemical processes in soils. No recent book has, however, attempted to produce a coherent account of soil chemistry as a whole, suitable for students of both environmental chemistry and soil science, and for the wide range of research and other scientists who are interested in the chemistry of soils. The original intention of the editors of the present book was to attempt to fill this gap. Because of the very diverse topics involved it was felt that it would have to be written by several authors if it was to be appropriately authoritative.
The chemistry of soils falls naturally into two parts, the chemistry of the various soil compoents, and the chemistry of soil processes. At first it was intended that these, the static and dynamic aspects of soils, should form two parts of a single volume. However, to deal with the topics involved at the intended level would have produced an unwieldy volume, and so two companion volumes are being issued, The Chemistry of Soil Constituents and The Chemistry of Soil Processes.
The opening chapter of the companion volume provides a short historical outline of the development of soil science. This deals briefly with the evolution of soil chemistry and pedology, and with the development of soil mineralogy, soil physics and soil biology—disciplines which are essential for integrated studies of soils and soil processes. It also refers to some of the processes which weather rocks, transform plant and animal residues, and lead to the formation of soil constituents. Several systems exist for classifying the major soil types of the world according to their origins, and the most common of the names used to indicate the same soil types are introduced. The two chapters which follow deal with the inorganic and organic components of soils, respectively. Although the chemical structures of the major inorganic components are now reasonably well known, the same is not true of the organic (or humic) materials in soils. The relevant chapter presents an account of what has been experimentally established regarding the constitution of the peculiarly intractable complex of organic compounds found in soils.
Chemical processes in soils are largely determined by reactions at the surfaces of the soil colloids. The final three chapters of the companion volume are therefore concerned with the nature and extent of the surfaces of soil colloids, their electrical characteristics, and the ways in which ions and water are held and arranged at the surfaces.
This volume is intended to describe the chemistry of several of the important processes which take place in the soil. These are discussed in detail in the appropriate chapters which include treatments of precipitation and of ion-exchange reactions, adsorption and the formation of complexes, and of oxidation and reduction. The manuscripts do not, however, adhere exclusively to chemical processes. In contexts of soil as a medium for plant growth or as a ‘sink’ for waste products, it is not realistic to separate purely chemical from physical and biological processes. Thus the initial chapter attempts to summarize the properties of soils which are relevant to plant growth, to detoxification, and to transport processes within the soil profile, and it tries to relate the development of specific features of soils to the chemical processes operating on them.
Mass flow and diffusion, discussed fully in Chapter 2, controls the transport of molecules and of ions to plant roots, and to adsorption, exchange or deposition sites in the soil profile, or to drainage waters or the atmosphere. Such transport processes are strongly influenced by the extents of aggregation of soil components and by the nature of the aggregates; hence the important concepts of soil structure are summarized in Chapter 1. Similarly, the soil composition and structure determine the aeration and water- holding capacity of the soil, and these properties in turn influence the types, numbers, and activities of the organisms of one kind or another which inhabit it. The diversity and magnitude of the soil flora and fauna are introduced in the first chapter, and frequent mention is made of their activities throughout the volume.
Inevitably, in order to discuss the different topics in some depth it has been necessary to assume that the readership will have a significant knowledge of chemistry and an introductory knowledge of soil science. It is hoped that this book, like its companion volume, will be of use to students of soil science and environmental chemistry, as well as to those who are involved in research related to the soil.
The editors are grateful for the collaboration and patience of those who have contributed, for the encouragement of the publishers and their tolerance of delays, and for the permission which many authors and publishers have given for material to be reproduced. Special acknowledgements of the latter are made in the text.