Soil Chemistry

Daniel G. Strawn, Hinrich L. Bohn, George A. O'Connor

• Publisher: Wiley-Blackwell
• Year: 2019
• ISBN:
  9781119515258
• Edition: 5
• Topic: Technologie et ingénierie
• Subtopic: Agronomie

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.

1
INTRODUCTION 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 s...