Soil Chemistry E-Book

Daniel G. Strawn

• Herausgeber: John Wiley & Sons
• Kategorie: Fachliteratur
• Sprache: Englisch

Seitenzahl: 949

Veröffentlichungsjahr: 2019

Beschreibung

Provides comprehensive coverage of the chemical interactions among organic and inorganic solids, air, water, microorganisms, and the plant roots in soil

This book focuses on the species and reaction processes of chemicals in soils, with applications to environmental and agricultural issues. Topics range from discussion of fundamental chemical processes to review of properties and reactions of chemicals in the environment. This new edition contains more examples, more illustrations, more details of calculations, and reorganized material within the chapters, including nearly 100 new equations and 51 new figures. Each section also ends with an important concepts overview as well as new questions for readers to answer. 

Starting with an introduction to the subject, Soil Chemistry, 5th Edition offers in-depth coverage of properties of elements and molecules; characteristics of chemicals in soils; soil water chemistry; redox reactions in soils; mineralogy and weathering processes in soils; and chemistry of soil clays. The book also provides chapters that examine production and chemistry of soil organic matter; surface properties of soil colloids; adsorption processes in soils; measuring and predicting sorption processes in soils; soil acidity; and salt-affected soils. 

• Provides a basic description of important research and fundamental knowledge in the field of soil chemistry
• Contains more than 200 references provided in figure and table captions and at the end of the chapters
• Extensively revised with updated figures and tables 

Soil Chemistry, 5th Edition is an excellent text for senior-level soil chemistry students.

Leseprobe

IUPAC Periodic Table of the Elements

Soil Chemistry

5th Edition

Daniel G. Strawn

Hinrich L. Bohn

George A. O’Connor

This edition first published 2020© 2020 John Wiley & Sons Ltd

Edition HistoryWiley (1e, 1979); Wiley‐Interscience (2e, 1985); Wiley (3e, 2001); Wiley‐Blackwell (4e, 2015)

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The right of Daniel G. Strawn to be identified as the author of this work has been asserted in accordance with law.

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Library of Congress Cataloging‐in‐Publication DataNames: Strawn, Daniel, author. | Bohn, Hinrich L., 1934– author. | O’Connor, George A., 1944– author.Title: Soil chemistry.Description: Fifth edition / Daniel G. Strawn (University of Idaho), Hinrich L Bohn, George A O’Connor. | Hoboken, NJ : John Wiley & Sons, [2020] | Includes index.Identifiers: LCCN 2019035987 (print) | LCCN 2019035988 (ebook) | ISBN 9781119515180 (hardback) | ISBN 9781119515159 (adobe pdf) | ISBN 9781119515258 (epub)Subjects: LCSH: Soil chemistry.Classification: LCC S592.5 .B63 2020 (print) | LCC S592.5 (ebook) | DDC 631.4/1–dc23LC record available at https://lccn.loc.gov/2019035987LC ebook record available at https://lccn.loc.gov/2019035988

Cover image: Periodic table: © ALFRED PASIEKA/SCIENCE PHOTO LIBRARY/Getty ImagesSoil image: Lithochrome_color by The John Kelly Collection / Soil Science downloaded via Flickr is licensed under CC BYCover design by Wiley

PREFACE TO FIFTH EDITION

This new edition of Soil Chemistry contains more examples, more illustrations, more details of calculations, and reorganized material within the chapters, including nearly 100 new equations and 51 new figures. Our goal remains to provide an introductory text for senior‐level soil chemistry students. This requires compromise on depth of explanation of the topics so that the main points are not lost on students, while providing sufficient information for explanation. We strive to achieve this balance throughout. Students wanting more details can review the more than 200 references provided in figure and table captions and at the end of the chapters. Additional details can also be found in textbooks in chemistry, geology, pedology, geochemistry, colloid science, soil chemistry, and soil fertility.

The textbook’s focus is on species and reaction processes of chemicals in soils, with applications to environmental and agricultural issues. Topics in the 13 chapters range from discussion of fundamental chemical processes to review of properties and reactions of chemicals in the environment.

In producing this new edition, we have corrected a few errors from the previous edition. However, with the addition of new material, introduction of new errors is inevitable. Please send notifications of errors to lead author Dan Strawn at the University of Idaho. An erratum will be made available on Dr. Strawn’s website.

PREFACE TO FOURTH EDITION

The goal of the First Edition of Soil Chemistry published in 1976 was to provide a textbook for soil science students to learn about chemical processes occurring in soils. The First Edition, and subsequent Second Edition (1985) and Third Edition (2003), focused on explaining the principles of chemical reactions in soils and the nature of soil solids. Intricacies and advanced details of theories were omitted for clarity. In the Fourth Edition, Dr. Dan Strawn, a professor at University of Idaho for 15 years, has led a revision of the classic text, working closely with original authors Dr. Hank Bohn (Professor Emeritus, University of Arizona) and Dr. George O’Connor (Professor, University of Florida). The collaboration has resulted in a new version for this classic text.

The Fourth Edition of Soil Chemistry is a major revision, including updated figures, tables, examples, and explanations; but it maintains the goal of the early editions in that it is written at a level to teach chemical properties and processes to undergraduate students. Graduate students and professionals, however, will also find the textbook useful as a resource to understand and review concepts, as well a good source to look up soil chemical properties listed in the many tables. To improve readability for undergraduates, citations have been omitted from the discussions. Many of the ideas covered, however, are emphasized in graphs and tables from the literature, for which citations are included.

The topics covered in Soil Chemistry, Fourth Edition, are presented in the same order as previous versions. We have added a chapter on surface charge properties (Chapter 9), and the adsorption chapters of the previous editions have been completely reorganized—explanation of cation, anion, and organic chemical adsorption processes are presented in Chapter 10, and quantitative modeling of adsorption processes is presented in Chapter 11. New to this version are special topics boxes that provide highlights of topics, historical information, and examples. Enhanced discussion of carbon cycling, new theories of SOM formation and structure, details of soil redox properties, and information on chemicals of emerging concern have been added. In each chapter, key words are bolded; students should use key words as study aides to ensure they understand main concepts.

We have made every effort to minimize errors. It is said that with each edit, only half the errors are found, and thus, 100% accuracy is fleeting. Please forward errors or questions to Dr. Dan Strawn at the University of Idaho. We will make an erratum available.

ACKNOWLEDGMENTS

We are like dwarves perched on the shoulders of giants, and thus we are able to see more and farther than the latter. And this is not at all because of the acuteness of our sight or the stature of our body, but because we are carried aloft and elevated by the magnitude of the giants.

John of Salisbury (1159 AD) after Bernard of Chartres, circa 1115 AD.

As this well‐known quote elegantly illustrates, the ideas presented in this book are not my own, but are compiled from the years of research and teachings of soil scientists, chemists, and physicists. I drew from many resources to write this textbook, including other textbooks, review articles, and research articles. I acknowledge the giants who have benefited my understanding.

Every effort was made to present the work of others in a careful and meaningful way to illustrate and explain the discipline of soil chemistry. In several cases, authors provided clarification, as well as encouragement to use their data and figures. I am grateful for their generosity.

Hank Bohn was unavailable to assist in the Fifth Edition. He was instrumental in the Fourth Edition overhaul, and his spirit and contributions live on in the Fifth Edition.

I appreciate George O’Connor’s collaboration in preparing the Fifth Edition. The content greatly benefited from his keen eye for relevance and attention to detail.

Writing a textbook is a labor of love. I gratefully acknowledge those who inspired my passion for soil science at University of California, Davis, where I was an undergraduate student, and Dr. Don Sparks at the University of Delaware, where I completed my PhD.

I am indebted to the students at the University of Idaho who inspired me to work hard to teach better; this text is for them. I am also grateful to my colleagues in the Department of Soil and Water Systems at the University of Idaho for providing me a home to practice my profession.

The thrill of writing a textbook is soon overshadowed by the seemingly infinite time sink. I am grateful to Kelly, Isabell, and Serena for their patience and support as I completed this project.

Dan Strawn, 2019

University of Idaho

1INTRODUCTION TO SOIL CHEMISTRY

No one regards what is at his feet; we all gaze at the stars. Quintus Ennius (239–169 BCE)

Heaven is beneath our feet as well as above our heads. Henry David Thoreau (1817–1862)

The earth was made so various that the mind of desultory man, studious of change and pleased with novelty, might be indulged. William Cowper (The Task, 1780)

The Nation that destroys its soil destroys itself. Franklin Delano Roosevelt (1937)

1.1 The soil chemistry discipline

The above quotations illustrate how differently humans see the soil that gives them life and sustenance. In recent decades, great strides in understanding the importance of soils for healthy ecosystems and food production have been made, but the need for preservation and improved utilization of soil resources remains one of society’s greatest challenges. Success requires a better understanding of soil processes.

Soil is a complex mixture of inorganic and organic solids, air, water, solutes, microorganisms, plant roots, and other types of biota that influence each other, making soil processes complex and dynamic (Figure 1.1). For example, air and water weather rocks to form soil minerals and release ions; microorganisms catalyze many soil weathering reactions; and plant roots absorb and exude inorganic and organic chemicals that change the distribution and solubility of ions. Although it is difficult to separate soil processes, soil scientists have organized themselves into subdisciplines that study physical, biological, and chemical processes, soil formation and distribution, and specialists that study applied soil science topics such as soil fertility.

The discipline of soil chemistry has traditionally focused on abiotic transformations of soil constituents, such as changes in oxidation state of elements and association of ions with surfaces. Chemical reactions in soils often lead to changes between solid, liquid, and gas states that dramatically influence the availability of chemicals for plant uptake and losses from soil that in turn are important aspects of fate and transport of nutrients and contaminants in the environment. With the ever‐increasing pressures to produce more food and extract resources such as timber, oil, and water from the environment, pressures on soil resources are increasing. Addressing these pressures and challenges requires detailed knowledge and understanding of soil processes. Modern soil chemistry strives to understand interactions occurring within soils, such as interactions between soil microbes and soil minerals.

Figure 1.1 Soils are composed of air, water, solids, ions, organic compounds, and biota. The soil in the microscopic view shows soil particles (e.g., aggregates of minerals and organic matter), air and water in pore spaces, microbes, and a plant root. Fluxes of material or energy into and out of the soil drive biogeochemical reactions, making soils dynamic. Fluxes can be to the atmosphere, eroded or leached offsite into surface water, or percolated to groundwater.

The focus of soil chemistry is chemical reactions and processes occurring in soils. A chemical reaction defines the transformation of reactants to products. For example, potassium availability for plant uptake in soils is often controlled by cation exchange reactions on clay minerals, such as:

(1.1)

where reactants are aqueous K+ and Na+ adsorbed on a clay mineral (Na‐clay), and products are aqueous Na+ and K+ adsorbed on a clay mineral (K‐clay). The adsorption reaction exchanges ions between aqueous solution in the soil pore and the soil solids (clay mineral in this case) and is thus a solid–solution interface reaction. Cation exchange reactions are a hallmark of soil chemistry.

A goal of soil chemistry is predicting whether a reaction will proceed, which can be done using thermodynamic calculations. Soils are complex, however, and predicting the fate of chemicals in the environment requires including multiple competing reaction pathways occurring simultaneously. In addition, many soil reactions are slow and fail to reach equilibrium before the system undergoes a perturbation, making prediction of chemical species a moving target. The complexity and dynamic aspect of soils make understanding chemical reactions in nature a challenging problem, but, over the past 150 years, great advances have been made. The goal of this book is to present the current state of knowledge about soil chemical processes so that students can use them to understand the environmental fate of chemicals.

1.2 Historical background

About 2500 years ago, the senate of ancient Athens debated soil productivity and voiced the same worries about sustaining and increasing soil productivity heard today: Can this productivity continue, or is soil productivity being exhausted?

In 1790, Malthus noticed that the human population was increasing exponentially, whereas food production was increasing arithmetically. He predicted that by 1850 food demands would overtake food production, and people would be starving and fighting like rats for morsels of food. Although such predictions have not come to fruition, there are real challenges to feeding the world’s increasing population, especially considering predicted changes in climate that will have significant impacts to food production systems and regional populations.

It is encouraging that food productivity has increased faster than Malthus predicted. Earth now feeds the largest human population ever, and a larger fraction of that population is better fed than ever before. Whether this can continue, and at what price to the environment, is an open question. One part of the answer lies in wisely managing soil resources so that food production can continue to increase and ecosystem functions can be maintained. Sustainable management requires careful use of soil and knowledge of soil processes. Soil chemistry is an important subdiscipline required for understanding soil processes.

Agricultural practices that increase crop growth, such as planting legumes, application of animal manure and forest litter, crop rotation, and liming were known to the Chinese 3000 years ago. These practices were also learned by the Greeks and Romans, and appeared in the writings of Varro, Cato, Columella, and Pliny, but were unexplained. Little progress on technology to increase and maintain soil productivity was made thereafter for almost 1500 years because of lack of understanding of plant–soil processes, and because of undue dependence on deductive reasoning. Deduction is applying preconceived ideas, broad generalities, and accepted truths to problems without testing if the preconceived ideas and accepted truths are valid. One truth accepted for many centuries and derived from the Greeks was that all matter was composed of earth, air, fire, and water; a weak basis, as we later learned, on which to increase knowledge.

In the early fifteenth century, Sir Francis Bacon promoted the idea that the scientific method is the best approach to gaining new knowledge: observe, hypothesize, test and measure, derive ideas from data, test these ideas again, and report findings. The scientific method brought progress in understanding our world, but the progress in understanding soil’s role in plant productivity was minimal in the ensuing three centuries.

Palissy (1563) proposed that plant ash came from the soil, and when added back to the soil could be reabsorbed by plants. Plat (1590) proposed that salts from decomposing organic matter dissolved in water and were absorbed by plants to facilitate growth. Glauber (1650) thought that saltpeter (Na, K nitrates) was the key to plant nutrition by the soil. Kuelbel (ca. 1700) believed that humus was the principle of vegetation. Boerhoeve (ca. 1700) believed that plants absorbed the “juices of the earth.” While these early theorists proposed reasonable relationships between plants and soils, accurate experimental design and proof was lacking, and their proposals were incomplete and inaccurate.

Van Helmont, a sixteenth‐century scientist, tried to test the ideas of plant–soil nutrient relationships. He planted a willow shoot in a pail of soil and covered the pail so that dust could not enter. He carefully measured the amount of water added. After five years, the tree had gained 75.4 kilograms. The weight of soil in the pot was still the same as the starting weight, less about two ounces (56 g). Van Helmont disregarded the 56 grams as what we would today call experimental error. He concluded that the soil contributed nothing to the nutrition of the plant because there was no loss of mass, and that plants needed only water for their sustenance. Although he followed the scientific method as best he could, he came to a wrong conclusion. Many experiments in nature still go afoul because of incomplete experimental design and inadequate measurement of all essential experimental variables.

John Woodruff’s (1699) experimental design was much better than Van Helmont’s. He grew plants using rainwater, river water, and sewage water for irrigation, and added garden mould to the soils. The more solutes and solids in the growth medium – the “dirtier” the water – the better the plants grew, implying that something in soil improved plant growth. The idea developed that the organic fraction of the soil supplied the plant’s needs.

In 1840 Justus von Liebig persuasively advanced the idea that inorganic chemicals were key to plant nutrition and that an input‐output chemical budget should be maintained in the soil. Liebig’s theory was most probably based on Carl Sprengel’s work in 1820–1830 that showed that mineral salts, rather than humus or soil organic matter, were the source of plant growth. Liebig’s influence was so strong that subsequent findings by Boussingault (1865) showing that more nitrogen existed in plants than was applied to the soil, implying nitrogen fixation, was disregarded for many years. Microbial nitrogen fixation did not fit into the Sprengel‐Liebig model.

Soil chemistry was first recognized as distinct from soil fertility in 1850 when J.T. Way, at Rothamsted, England, reported on the ability of soils to exchange cations (Figure 1.2). Their work suggested that soils could be studied apart from plants to discover important aspects for soil fertility. Van Bemmelen followed with studies on the nature of clay minerals in soils and popularized the theory of adsorption (published in 1863). These founding fathers of soil chemistry stimulated the beginning of much scientific inquiry into the nature and properties of soils that continues to this day.

Despite the significant advances in understanding soils and environmental processes, environmental complexity is too great for a single discipline to fully understand. Scientific training necessarily tends to specialize, learning more and more about less and less. Nature, however, is complex, and scientists of various disciplines apply their background to the whole environment with mixed results. Eighteenth‐century naturalist Alexander von Humboldt popularized the concept that natural systems are interconnected, and proposed a link between soils, flora, and fauna in many essays and books published from 1800 to 1825. von Humboldt also proposed that human activity could have devastating effects on ecosystem functions – a radical idea for his time.

Figure 1.2 Snippet of paper authored by J. Thomas Way in the 1850 Journal of the Royal Agriculture Society of England describing the discovery of the ability of soil to absorb ammonia from manure. It is now known that ammonium exchanges for other cations on the soil clay particles, which is an adsorption reaction.

Source: Way (1850).

Specialists often try to compartmentalize natural systems, and bring along biases, one of which is that their area of study is the most important. Atmospheric scientists, for example, naturally believe that the atmosphere is the most important part of the environment. The authors of this book are no different. We argue, without apology, that the soil plays the central and dominant role in the environment. However, the truth is more in line with von Humboldt’s ideas proposed over two centuries ago: soils are an intricate part of the web of nature, and a soil’s characteristics are intimately tied to the plants, microbes, atmosphere, geology, climate, and landscape surrounding it. The linkages and influences go both ways. The unique relationship between soils and plants and microbe communities associated with them is referred to as an edaphic quality.

Figure 1.3 Soils interface with Earth’s other spheres. Biogeochemical cycling within the soil influences flows of chemicals and energy into the hydrosphere, biosphere, and atmosphere. Arrows between the different spheres and the soil indicate important transformations.

1.3 The soil environment

Soils are the skin of the earth, and interface with the atmosphere, hydrosphere, lithosphere, and biosphere (Figure 1.3). The interaction of Earth’s spheres within soil results in a mixture of solid, liquid, gas, and biota, called the pedosphere. A fifth Earth component is the anthrosphere, which describes human’s interaction and influence on the environment. The critical zone is a concept that encompasses all life‐supporting parts of the earth, including soils, groundwater, and vegetation. Regardless of how the environment is compartmentalized for study, chemical processes occurring in the soil are important aspects affecting healthy and sustainable environments.

In this section, we discuss the relationships between soil chemicals, the biosphere, soil solid phases, the hydrosphere, and the soil atmosphere. A typical soil is composed of ~50% solid, and ~50% pore space; the exact amount varies as a function of the soil properties, such as aggregation, particle size distribution, and so on (Figure 1.4). Throughout this text, the term soil chemical is used as a general term that refers to all the different types of chemicals occurring in soil, including ions, liquids, gases, minerals, soil organic matter, and salts.

Figure 1.4 Typical volumetric composition of soils. Soil gases and solution fill the pore spaces at different ratios, depending on soil moisture content. The ratio of solid to pore spaces is controlled by the soil porosity.

1.3.1 Soil chemical and biological interfaces

A basic tenet of biology is that life evolves and changes to adapt to the environment, driven by reproductive success. Because soils have a significant impact on environmental conditions, there is a direct link between evolutionary processes and soils. Some even theorize that the first forms of life evolved from interactions of carbon and nitrogen with clay minerals of the type commonly observed in soils; where clays are hypothesized to have catalyzed the first organic prebiotic polymers. While such a theory is controversial, one cannot deny the role of soils in maintaining life and the environment. Even marine life is affected by chemicals and minerals that are transferred from the land to the sea by water flow or airborne dust particles. Thus, chemical processes in soils are critical for maintenance and growth of all life forms, and soils are locked in a partnership with the biosphere, hydrosphere, lithosphere, and atmosphere in providing critical ecosystem services.

The atmosphere, biosphere, and hydrosphere are weakly buffered against change in chemical composition and fluctuate when perturbed. Soils, in contrast, better resist chemical changes and are a steadying influence on the other three environmental compartments. Detrimental changes in the hydrosphere, atmosphere, and biosphere due to human activities often occur because the soil is bypassed, causing