Principles of soil physics

PRINCIPLES OF SOIL PHYSICS

BOOKS IN SOILS, PLANTS, AND THE

ENVIRONMENT

Editorial Board

Agricultural Engineering

Robert M.Peart, University of Florida, Gainesville

Animal Science

Harold Hafs, Rutgers University, New Brunswick, New Jersey

Crops

Mohammad Pessarakli, University of Arizona, Tucson

Environment

Kenneth G.Cassman, University of Nebraska, Lincoln

Irrigation and Hydrology

Donald R.Nielsen, University of California, Davis

Microbiology

Jan Dirk van Elsas, Research Institute for Plant Protection, Wageningen, The

Netherlands

Plants

L.David Kuykendall, U.S. Department of Agriculture, Beltsville, Maryland Kenneth

B.Marcum, Arizona State University, Mesa, Arizona

Soils

Jean-Marc Bollag, Pennsylvania State University, University Park, Pennsylvania

Tsuyoshi Miyazaki, University of Tokyo

Soil Biochemistry, Volume 1, edited by A.D.McLaren and G.H.Peterson

Soil Biochemistry, Volume 2, edited by A.D.McLaren and J.Skujiņš

Soil Biochemistry, Volume 3, edited by E.A.Paul and A.D.McLaren

Soil Biochemistry, Volume 4, edited by E.A.Paul and A.D.McLaren

Soil Biochemistry, Volume 5, edited by E.A.Paul and J.N.Ladd

Soil Biochemistry, Volume 6, edited by Jean-Marc Bollag and G. Stotzky

Soil Biochemistry, Volume 7, edited by G.Stotzky and Jean-Marc Bollag

Soil Biochemistry, Volume 8, edited by Jean-Marc Bollag and G.Stotzky

Soil Biochemistry, Volume 9, edited by G.Stotzky and Jean-Marc Bollag

Soil Biochemistry, Volume 10, edited by Jean-Marc Bollag and G.Stotzky

Organic Chemicals in the Soil Environment, Volumes 1 and 2, edited by C. A.I.Goring

and J.W.Hamaker

Humic Substances in the Environment, M.Schnitzer and S.U.Khan

Microbial Life in the Soil: An Introduction, T.Hattori

Principles of Soil Chemistry, Kim H.Tan

Soil Analysis: Instrumental Techniques and Related Procedures, edited by Keith A.Smith

Soil Reclamation Processes: Microbiological Analyses and Applications, edited by

Robert L.Tate III and Donald A.Klein

Symbiotic Nitrogen Fixation Technology, edited by Gerald H.Elkan

Soil–Water Interactions: Mechanisms and Applications, Shingo Iwata and Toshio

Tabuchi with Benno P.Warkentin

Soil Analysis: Modern Instrumental Techniques, Second Edition, edited by Keith A.Smith

Soil Analysis: Physical Methods, edited by Keith A.Smith and Chris E. Mullins

Growth and Mineral Nutrition of Field Crops, N.K.Fageria, V.C.Baligar, and Charles

Allan Jones

Semiarid Lands and Deserts: Soil Resource and Reclamation, edited by J. Skujiņš

Plant Roots: The Hidden Half, edited by Yoav Waisel, Amram Eshel, and Uzi Kafkafi

Plant Biochemical Regulators, edited by Harold W.Gausman

Maximizing Crop Yields, N.K.Fageria

Transgenic Plants: Fundamentals and Applications, edited by Andrew Hiatt

Soil Microbial Ecology: Applications in Agricultural and Environmental Management,

edited by F.Blaine Metting, Jr.

Principles of Soil Chemistry: Second Edition, Kim H.Tan

Water Flow in Soils, edited by Tsuyoshi Miyazaki

Handbook of Plant and Crop Stress, edited by Mohammad Pessarakli

Genetic Improvement of Field Crops, edited by Gustavo A.Slafer

Agricultural Field Experiments: Design and Analysis, Roger G.Petersen

Environmental Soil Science, Kim H.Tan

Mechanisms of Plant Growth and Improved Productivity: Modern Ap-proaches, edited

by Amarjit S.Basra

Selenium in the Environment, edited by W.T.Frankenberger, Jr., and Sally Benson

Plant–Environment Interactions, edited by Robert E.Wilkinson

Handbook of Plant and Crop Physiology, edited by Mohammad Pessarakli

Handbook of Phytoalexin Metabolism and Action, edited by M.Daniel and R.

P.Purkayastha

Soil–Water Interactions: Mechanisms and Applications, Second Edition, Re-vised and

Expanded, Shingo Iwata, Toshio Tabuchi, and Benno P. Warkentin

Stored-Grain Ecosystems, edited by Digvir S.Jayas, Noel D.G.White, and William

E.Muir

Agrochemicals from Natural Products, edited by C.R.A.Godfrey

Seed Development and Germination, edited by Jaime Kigel and Gad Galili

Nitrogen Fertilization in the Environment, edited by Peter Edward Bacon

Phytohormones in Soils: Microbial Production and Function, William T. Frankenberger,

Jr., and Muhammad Arshad

Handbook of Weed Management Systems, edited by Albert E.Smith

Soil Sampling, Preparation, and Analysis, Kim H.Tan

Soil Erosion, Conservation, and Rehabilitation, edited by Menachem Agassi

Plant Roots: The Hidden Half, Second Edition, Revised and Expanded, edited by Yoav

Waisel, Amram Eshel, and Uzi Kafkafi

Photoassimilate Distribution in Plants and Crops: Source–Sink Relation-ships, edited by

Eli Zamski and Arthur A.Schaffer

Mass Spectrometry of Soils, edited by Thomas W.Boutton and Shinichi Yamasaki

Handbook of Photosynthesis, edited by Mohammad Pessarakli

Chemical and Isotopic Groundwater Hydrology: The Applied Approach, Second Edition,

Revised and Expanded, Emanuel Mazor

Fauna in Soil Ecosystems: Recycling Processes, Nutrient Fluxes, and Agri-cultural

Production, edited by Gero Benckiser

Soil and Plant Analysis in Sustainable Agriculture and Environment, edited by Teresa

Hood and J.Benton Jones, Jr.

Seeds Handbook: Biology, Production, Processing, and Storage, B.B. Desai,

P.M.Kotecha, and D.K.Salunkhe

Modern Soil Microbiology, edited by J.D.van Elsas, J.T.Trevors, and E.M. H.Wellington

Growth and Mineral Nutrition of Field Crops: Second Edition, N.K.Fageria, V.C.Baligar,

and Charles Allan Jones

Fungal Pathogenesis in Plants and Crops: Molecular Biology and Host Defense

Mechanisms, P.Vidhyasekaran

Plant Pathogen Detection and Disease Diagnosis, P.Narayanasamy

Agricultural Systems Modeling and Simulation, edited by Robert M.Peart and R.Bruce

Curry

Agricultural Biotechnology, edited by Arie Altman

Plant–Microbe Interactions and Biological Control, edited by Greg J.Boland and

L.David Kuykendall

Handbook of Soil Conditioners: Substances That Enhance the Physical Properties of

Soil, edited by Arthur Wallace and Richard E.Terry

Environmental Chemistry of Selenium, edited by William T.Frankenberger, Jr., and

Richard A.Engberg

Principles of Soil Chemistry: Third Edition, Revised and Expanded, Kim H. Tan

Sulfur in the Environment, edited by Douglas G.Maynard

Soil–Machine Interactions: A Finite Element Perspective, edited by Jie Shen and Radhey

Lal Kushwaha

Mycotoxins in Agriculture and Food Safety, edited by Kaushal K.Sinha and Deepak

Bhatnagar

Plant Amino Acids: Biochemistry and Biotechnology, edited by Bijay K.Singh

Handbook of Functional Plant Ecology, edited by Francisco I.Pugnaire and Fernando

Valladares

Handbook of Plant and Crop Stress: Second Edition, Revised and Ex-panded, edited by

Mohammad Pessarakli

Plant Responses to Environmental Stresses: From Phytohormones to Ge-nome

Reorganization, edited by H.R.Lerner

Handbook of Pest Management, edited by John R.Ruberson

Environmental Soil Science: Second Edition, Revised and Expanded, Kim H. Tan

Microbial Endophytes, edited by Charles W.Bacon and James F.White, Jr.

Plant–Environment Interactions: Second Edition, edited by Robert E.Wil-kinson

Microbial Pest Control, Sushil K.Khetan

Soil and Environmental Analysis: Physical Methods, Second Edition, Re-vised and

Expanded, edited by Keith A.Smith and Chris E.Mullins

The Rhizosphere: Biochemistry and Organic Substances at the Soil–Plant Interface,

Roberto Pinton, Zeno Varanini, and Paolo Nannipieri

Woody Plants and Woody Plant Management: Ecology, Safety, and Envi-ronmental

Impact, Rodney W.Bovey

Metals in the Environment: Analysis by Biodiversity, M.N.V.Prasad

Plant Pathogen Detection and Disease Diagnosis: Second Edition, Revised and

Expanded, P.Narayanasamy

Handbook of Plant and Crop Physiology: Second Edition, Revised and Expanded, edited

by Mohammad Pessarakli

Environmental Chemistry of Arsenic, edited by William T.Frankenberger, Jr.

Enzymes in the Environment: Activity, Ecology, and Applications, edited by Richard

G.Burns and Richard P.Dick

Plant Roots: The Hidden Half, Third Edition, Revised and Expanded, edited by Yoav

Waisel, Amram Eshel, and Uzi Kafkafi

Handbook of Plant Growth: pH as the Master Variable, edited by Zdenko Rengel

Biological Control of Crop Diseases, edited by Samuel S.Gnanamanickam

Pesticides in Agriculture and the Environment, edited by Willis B.Wheeler

Mathematical Models of Crop Growth and Yield, Allen R.Overman and Richard

V.Scholtz III

Plant Biotechnology and Transgenic Plants, edited by Kirsi-Marja OksmanCaldentey and

Wolfgang H.Barz

Handbook of Postharvest Technology: Cereals, Fruits, Vegetables, Tea, and Spices,

edited by Amalendu Chakraverty, Arun S.Mujumdar, G.S. Vijaya Raghavan, and

Hosahalli S.Ramaswamy

Handbook of Soil Acidity, edited by Zdenko Rengel

Humic Matter in Soil and the Environment: Principles and Controversies, Kim H.Tan

Molecular Host Resistance to Pests, S.Sadasivam and B.Thayumanavan

Soil and Environmental Analysis: Modern Instrumental Techniques, Third Edition, edited

by Keith A.Smith and Malcolm S.Cresser

Chemical and Isotopic Groundwater Hydrology: Third Edition, Emanuel Mazor

Agricultural Systems Management: Optimizing Efficiency and Performance, Robert

M.Peart and W.David Shoup

Physiology and Biotechnology Integration for Plant Breeding, edited by Henry T.Nguyen

and Abraham Blum

Global Water Dynamics: Shallow and Deep Groundwater, Petroleum Hydrol-ogy,

Hydrothermal Fluids, and Landscaping, Emanuel Mazor

Principles of Soil Physics, Rattan Lal and Manoj K.Shukla

Seeds Handbook: Biology, Production, Processing, and Storage, Second Edition, Revised

and Expanded, Babasaheb B.Desai

Field Sampling: Principles and Practices in Environmental Analysis, Alfred R.Conklin,

Jr.

Sustainable Agriculture and the International Rice–Wheat System, edited by Rattan Lal,

Peter R.Hobbs, Norman Uphoff, and David O.Hansen

Plant Toxicology: Fourth Edition, Revised and Expanded, edited by Bertold Hock and

Erich F.Elstner

Additional Volumes in Preparation

PRINCIPLES OF SOIL PHYSICS

RATTAN LAL

MANOJ K.SHUKLA

The Ohio State University

Columbus, Ohio, U.S.A.

MARCEL DEKKER, INC.

NEW YORK • BASEL

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Preface

This book addresses the topic of soil’s physical properties and processes with particular

reference to agricultural, hydrological, and environmental applications. The book is

written to enable undergraduate and graduate students to understand soil’s physical,

mechanical, and hydrological properties, and develop theoretical and practical skills to

address issues related to sustainable management of soil and water resources. Sustainable

use of soil and water resources cannot be achieved unless soil’s physical conditions or

quality is maintained at a satisfactory level. Fertilizer alone or in conjunction with

improved crop varieties and measures to control pests and diseases will not preserve

productivity if soil’s physical conditions are not above the threshold level, or if

significant deterioration of physical conditions occur. Yet, assessment of physical

properties and processes of soil is not as commonly done as that of chemical or

nutritional properties, and their importance receives insufficient attention. Even when

information on soil’s physical properties is collected, it is not done in sufficient detail and

rarely beyond the routine measurement of soil texture and bulk density.

Sustainability is jeopardized when soil’s physical quality is degraded, which has a

variety of consequences. The process of decline in soil’s physical quality is set in motion

by deterioration of soil structure: an increase in bulk density, a decline in the percentage

and strength of aggregates, a decrease in macroporosity and pore continuity, or both. An

important ramification of decline in soil structural stability is formation of a surface seal

or crust with an attendant decrease in the water infiltration rate and an increase in surface

runoff and erosion. An increase in soil bulk density leads to inhibited root development,

poor gaseous exchange, and anaerobiosis. Excessive runoff lowers the availability of

water stored in the root zone, and suboptimal or supraoptimal soil temperatures and poor

aeration exacerbate the problem of reduced water uptake.

Above and beyond the effects on plant growth, soil’s physical properties and processes

also have a strong impact on the environment. Non-point source pollution is caused by

surface runoff, erosion, and drainage effluent from agricultural fields. Wind erosion has a

drastic adverse impact on air quality. An accelerated greenhouse effect is caused by

emission of trace or greenhouse gases from the soil into the atmosphere. Important

greenhouse gases emitted from soil are CO2, CH4, N2O, and NOx. The rate and amount of

their emission depend on soil’s physical properties (e.g., texture and temperature) and

processes (e.g., aeration and anaerobiosis).

The emphasis in this textbook is placed on understanding the impact of the physical

properties and processes of soil on agricultural and forestry production, sustainable use of

soil and water resources for a range of functions of interest to humans, and the

environment with special attention to water quality and the greenhouse effect. Sustainable

use of natural resources is the basic, underlying theme throughout the book.

This book is divided into 20 chapters and 5 parts. Part I is an introduction to soil

physics and contains two chapters describing the importance of soil physics, defining

basic terms and principal concepts. Part II contains six chapters dealing with soil

mechanics. Chapter 3 describes soil solids and textural properties, including particle size

distribution, surface area, and packing arrangements. Chapter 4 addresses theoretical and

practical aspects of soil structure and its measurement. There being a close relationship

between structure and porosity, Chapter 5 deals with pore size distribution, including

factors affecting it and assessment methods. Manifestations of soil structure (e.g.,

crusting and cracking) and soil strength and compaction are described in Chapters 6 and

7, respectively. Management of soil compaction is a topic of special emphasis in these

chapters. Atterberg’s limits and plasticity characteristics in terms of their impact on soil

tilth are discussed in Chapter 8.

Part III, comprising eight chapters, deals with an important topic of soil hydrology.

Global water resources, principal water bodies, and components of the hydrologic cycle

are discussed in Chapter 9. Soil’s moisture content and methods of its measurement,

including merits and demerits of different methods along with their application to specific

soil situations, are discussed in Chapter 10. The concept of soil-moisture potential and the

energy status of soil water and its measurement are discussed in Chapter 11. Principles of

soil-water movement under saturated and unsaturated conditions are described in

Chapters 12 and 13, respectively. Water infiltration, measurement, and modeling are

presented in Chapter 14. Soil evaporation, factors affecting it, and its management are

discussed in Chapter 15. Solute transport principles and processes including Fick’s laws

of diffusion, physical, and chemical nonequilibruim, its measurement, and modeling are

presented in Chapter 16.

Part IV comprises two chapters. Chapter 17 addresses the important topic of soil

temperature, including heat flow in soil, impact of soil temperature on crop growth, and

methods of managing soil temperature. Soil air and aeration, the topic of Chapter 18, is

discussed with emphasis on plant growth and emission of greenhouse gases from soil into

the atmosphere. Part V, the last part, contains two chapters dealing with miscellaneous

but important topics. Chapter 19 deals with physical properties of gravelly soils. Water

movement in frozen, saline, and water-repellent soils and scale issues in hydrology are

the themes of Chapter 20. In addition, there are several appendices dealing with units and

conversions and properties of water.

This book is of interest to students of soil physics with majors in soil science,

agricultural hydrology, agricultural engineering, civil engineering, climatology, and

topics of environmental sciences. There are several unique features of this book, which

are important in helping students understand the basic concepts. Important among these

are the following: (i) each chapter is amply illustrated by graphs, data tables, and easy to

follow equations or mathematical functions, (ii) use of mathematical functions is

illustrated by practical examples, (iii) some processes and practical techniques are

explained by illustrations, (iv) each chapter contains a problem set for students to

practice, and (v) the data examples are drawn from world ecoregions, including soils of

tropical and temperate climates. This textbook incorporates comments and suggestions of

students from around the world.

The book is intended to explain basic concepts of soil physics in a simplified manner

rather than an exhaustive treatise on the most current literature available on the topics

addressed. It draws heavily on material, data, graphs, and tables from many sources. The

authors cite data from numerous colleagues from around the world. Sources of all data

and material are duly acknowledged.

We are thankful for valuable contributions made by several colleagues, graduate

students, and staff of the soil science section of The Ohio State University. We especially

thank Ms. Brenda Swank for her assistance in typing some of the text and in preparing

the material. Help received from Pat Patterson and Jeremy Alder is also appreciated.

Thanks are also due to the staff of Marcel Dekker, Inc., Publishers for their timely effort

in publishing the book and making it available to the student community.

Rattan Lal

Manoj K.Shukla

Contents

Preface xi

Part I Introduction

1 Importance of Soil Physics 1

2 Basic Definitions and Concepts 13

Part II Soil Mechanics

3 Soil Solids 29

4 Soil Structure 86

5 Porosity 140

6 Manifestations of Soil Structure 153

7 Soil Strength and Compaction 175

8 Soil Rheology and Plasticity 214

Part III Soil Hydrology

9 Water 234

10 Soil’s Moisture Content 268

11 Soil-Moisture Potential 299

12 Water Flow in Saturated Soils 331