- Email: [email protected]
Soil physics with BASIC—transport models for soil plant systems
341 Soil Physics with B A S I C - - Transport models for soil-plant systems, (Developments in Soil Science 14). Gaylon S. Campbell, Elsevier, Amsterdam/Oxford/ New York/Tokyo, 1985, xvi + 150pp., Dfl. 120.00, US $41.50 (hardcover), ISBN 0-444-42557-8.
For years soil physicists have been faced with the problem of dealing with difficult differential equations which form a basis of the science. Because of most peoples' inherent fear of mathematics, many texts have tended to downplay these equations, thereby undermining the strength of soil physics in handling complex problems. Those that have dealt with the mathematics have generally resorted to analytical solutions. Such solutions can be extremely complex and often conceal the physics involved. They also usually apply only to simple, non-representative systems. In this book the author has redressed this situation, using advances in numerical methods and the microcomputer to show that the differential equations can be easily solved, even by those who lack a rigorous mathematical background. An added advantage of the methods adopted is that they demonstrate the interplay of the physical processes involved, and as such prove particularly interesting to both teachers and students of soil physics. The book itself consists of 12 chapters, an appendix, and a good index. Each chapter begins with a discussion of soil physics concepts. This is generally followed by development of simple computer programs which can be used to solve equations presented and illustrate the concepts discussed. The programs are written in Microsoft MBASIC and are available from the publisher on Apple II and IBM-PC diskettes for US $31. Notes on converting them to run on other BASIC interpreters are included in the introduction. A list of references and several problems complete each chapter. All symbols are defined when introduced in the text and with the program variables in a handy reference list. The typeface, although different from many texts, is easy to read. The overall appearance could have been improved though if the table and figure captions had been more strongly differentiated from the general text. The book begins by outlining the general philosophy adopted in solving problems of water, gas, heat, and nutrient transport in the soil-plant system. Fundamental physical properties of soil are described in chapter 2 and a relatively new representation of the soil texture diagram, which is shown to be more useful than the classic texture triangle, is presented. Chapters on gas diffusion and heat flow introduce the network analysis approach used to solve the transport equations. This approach is similar to analysis of a resistorcapacitor network in electronics, and because the resulting system of equations is tridiagonal in form, they are solved by means of the Thomas algorithm. This algorithm circumvents the need for matrix inversion routines and is particularly well suited to microcomputer applications. Chapters on water potential and hydraulic conductivity include useful background information and present methods for estimating the moisture characteristic and conductivity function from soil physical data. Other relationships, such as that for
342
estimating soil thermal conductivity from soil texture, bulk density, and water content data, are scattered throughout the book and will no doubt prove very useful in many applications of soil physics. Ways of dealing with field variability in the deterministic models presented in this book are covered in a separate chapter. A discussion of infiltration and redistribution make up the longest chapter in the book (25 pages) and introduce the complexities of non-linear differential equations. The Newton-Raphson method used to solve these equations is described in considerable detail. I think it unfortunate that the Thomas Algorithm is not discussed in similar detail. Concepts developed in earlier parts of the book are applied in chapters on evaporation, solute movement, and water transport in the soil-plant-atmosphere continuum, and illustrate the strength of the approach adopted by the author in modeling soil physics phenomena. The final chapter emphasises the need for appropriate atmospheric boundary conditions if meaningful model output is to be obtained, and presents several equations for defining these. Although the programs presented in this book are generally short and relatively simple, I, like the author, encourage the reader to " . . . experiment with each model until both the working of the model and the concepts it teaches are familiar". This will be particularly important if they are to be used as submodels in large, general purpose predictive models. Blind application may give results, but the usefulness of the results will ultimately depend on the ability of the user to separate important and subordinate aspects. This will only come from a thorough understanding of the physics involved and the way computer programs are used to describe that physics. Careful study of this excellent book will help achieve that understanding and it is highly recommended to students, teachers, and researchers involved in the soil, plant, and environmental sciences. K E I T H L. B R I S T O W
(Townsville, Australia)
World Climatic Systems. John G. Lockwood, Edward Arnold, London, 1985, x + 292pp., £17.50. The reading to write this review was restarted several times. One of the reasons was that I could not get beyond the first sentence of the actual text, saying "A system may be defined as a structural set of objects and/or attributes, where these objects and attributes consist of components or variables that exhibit discernible relationships with one another and operate together as a complex whole, according to some observed pattern". Oughfff. It could discourage someone to continue reading. And indeed, the introductional sub-chapter which should explain the title of the book is the least successful. The too-short examples used give very inaccurate descriptions of the systems used as illustrations and there is no single reference in these pages. After that the author gets into the routine on the general atmospheric circulation (GAC). Perhaps a bit
For years soil physicists have been faced with the problem of dealing with difficult differential equations which form a basis of the science. Because of most peoples' inherent fear of mathematics, many texts have tended to downplay these equations, thereby undermining the strength of soil physics in handling complex problems. Those that have dealt with the mathematics have generally resorted to analytical solutions. Such solutions can be extremely complex and often conceal the physics involved. They also usually apply only to simple, non-representative systems. In this book the author has redressed this situation, using advances in numerical methods and the microcomputer to show that the differential equations can be easily solved, even by those who lack a rigorous mathematical background. An added advantage of the methods adopted is that they demonstrate the interplay of the physical processes involved, and as such prove particularly interesting to both teachers and students of soil physics. The book itself consists of 12 chapters, an appendix, and a good index. Each chapter begins with a discussion of soil physics concepts. This is generally followed by development of simple computer programs which can be used to solve equations presented and illustrate the concepts discussed. The programs are written in Microsoft MBASIC and are available from the publisher on Apple II and IBM-PC diskettes for US $31. Notes on converting them to run on other BASIC interpreters are included in the introduction. A list of references and several problems complete each chapter. All symbols are defined when introduced in the text and with the program variables in a handy reference list. The typeface, although different from many texts, is easy to read. The overall appearance could have been improved though if the table and figure captions had been more strongly differentiated from the general text. The book begins by outlining the general philosophy adopted in solving problems of water, gas, heat, and nutrient transport in the soil-plant system. Fundamental physical properties of soil are described in chapter 2 and a relatively new representation of the soil texture diagram, which is shown to be more useful than the classic texture triangle, is presented. Chapters on gas diffusion and heat flow introduce the network analysis approach used to solve the transport equations. This approach is similar to analysis of a resistorcapacitor network in electronics, and because the resulting system of equations is tridiagonal in form, they are solved by means of the Thomas algorithm. This algorithm circumvents the need for matrix inversion routines and is particularly well suited to microcomputer applications. Chapters on water potential and hydraulic conductivity include useful background information and present methods for estimating the moisture characteristic and conductivity function from soil physical data. Other relationships, such as that for
342
estimating soil thermal conductivity from soil texture, bulk density, and water content data, are scattered throughout the book and will no doubt prove very useful in many applications of soil physics. Ways of dealing with field variability in the deterministic models presented in this book are covered in a separate chapter. A discussion of infiltration and redistribution make up the longest chapter in the book (25 pages) and introduce the complexities of non-linear differential equations. The Newton-Raphson method used to solve these equations is described in considerable detail. I think it unfortunate that the Thomas Algorithm is not discussed in similar detail. Concepts developed in earlier parts of the book are applied in chapters on evaporation, solute movement, and water transport in the soil-plant-atmosphere continuum, and illustrate the strength of the approach adopted by the author in modeling soil physics phenomena. The final chapter emphasises the need for appropriate atmospheric boundary conditions if meaningful model output is to be obtained, and presents several equations for defining these. Although the programs presented in this book are generally short and relatively simple, I, like the author, encourage the reader to " . . . experiment with each model until both the working of the model and the concepts it teaches are familiar". This will be particularly important if they are to be used as submodels in large, general purpose predictive models. Blind application may give results, but the usefulness of the results will ultimately depend on the ability of the user to separate important and subordinate aspects. This will only come from a thorough understanding of the physics involved and the way computer programs are used to describe that physics. Careful study of this excellent book will help achieve that understanding and it is highly recommended to students, teachers, and researchers involved in the soil, plant, and environmental sciences. K E I T H L. B R I S T O W
(Townsville, Australia)
World Climatic Systems. John G. Lockwood, Edward Arnold, London, 1985, x + 292pp., £17.50. The reading to write this review was restarted several times. One of the reasons was that I could not get beyond the first sentence of the actual text, saying "A system may be defined as a structural set of objects and/or attributes, where these objects and attributes consist of components or variables that exhibit discernible relationships with one another and operate together as a complex whole, according to some observed pattern". Oughfff. It could discourage someone to continue reading. And indeed, the introductional sub-chapter which should explain the title of the book is the least successful. The too-short examples used give very inaccurate descriptions of the systems used as illustrations and there is no single reference in these pages. After that the author gets into the routine on the general atmospheric circulation (GAC). Perhaps a bit