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Developments in Soil Science 13 ELEMENTS OF SOIL PHYSICS

Further Titles in this Series1. I. VALETON BAUXITES

2. IAHR FUNDAMENTALS OF TRANSPORT PHENOMENA IN POROUS MEDIA3. F.E. ALLISON SOIL ORGANIC MATTER AND ITS ROLE IN CROP PRODUCTION4. R. W. SIMONSON (Editor)

NON-AGRICULTURAL APPLICATIONS OF SOIL SURVEYS 5A. G.H. BOLT and M.G.M. BRUGGENWERT (Editors) SOIL CHEMISTRY. A. BASIC ELEMENTS 5B. G.H. BOLT (Editor) SOIL CHEMISTRY. B. PHYSICO-CHEMICAL MODELS6. H.E. DREGNE

SOILS OF ARID REGIONS

7 H. AUBERT and M. PINTA . TRACE ELEMENTS IN SOILS8. M. SCHNITZER and S. U.KHAN (Editors)

SOIL ORGANIC MATTER9. B.K.G. THENG

FORMATION AND PROPERTIES OF CLAY-POLYMER COMPLEXES10. D. ZACHAR SOIL EROSION

11A. L.P. WILDING, N.E. SMECK and G.F. H A L L (Editors) PEDOGENESIS AND SOIL TAXONOMY. I. CONCEPTS AND INTERACTIONS

11B. L.P. WILDING, N.E. SMECK and G.F. HALL (Editors) PEDOGENESIS AND SOIL TAXONOMY. 11. THE SOIL ORDERS12. E.B.A. BISDOM and J. DUCLOUX (Editors) SUBMICROSCOPIC STUDIES OF SOILS

Developments in Soil Science 13

ELEMENTS OF SOIL PHYSICSP. KOOREVAAR, G. MENELIK and C. DIRKSEN

Department of Soil Science and Phnt Nutrition, Agricultural University of Wageningen, Wageningen, The Netherlands

ELSEVIER Amsterdam - Lausanne - New York - Oxford - Shannon - Singapore - Tokyo

ELSEVIER SCIENCE B.V. Sara Burgerhartstraat 25 P.O. Box 21 1, 1000 AE Amsterdam, The Netherlands

First edition 1983 Second impression 1987 Third impression 1991 Fourth impression 1994 Fifth impression 1999 ISBN: 0 444 42242 0

0 1983 Elsevier Science B.V. All rights reserved, This work is protected under copyright by Elsevier Science, and the following terms and conditions apply to its use:Photocopying Single photocopies of single chapters may be made for personal use as allowed by national copyright laws. Permission of the Publisher and payment of a fee is required for all other photocopying, including multiple or systematic copying. copying for advertising or promotional purposes, resale, and all forms of document delivery. Special rates are available for educational institutions that wish to make photocopies for non-profit educational classroom use. Permissions may be sought directly from Elsevier Science Rights & Permissions Department. PO Box 800.Oxford OX5 1 DX, 1865 UK, phone: (4) 843830. fax: ( 4 4 ) 1865 853333, e-mail: permissions@elsevier.co.uk. You may also contact Rights & Permissions directly through Elseviers home page (http://www.elsevier.nl). selecting first Customer Support. then General Information. then Permissions Query Form.

In the USA, users may clear permissions and make payments through the Copyright Clearance Center. Inc., 222 Rosewood Drive, Danvers, MA 01923. USA; phone: (978) 7508400. fax: (978) 7504744,and in the UK through the Copyright Licensing Agency Rapid Clearance Service (CLARCS). 90TottenhamCourt Road, London WIP OLP. UK, phone: (+44) 171 631 5 5 5 5 ; fax: (+44) 171 631 5500. Other countries may have a local reprographic rights agency for payments.Derivative Works Tables of contents may be reproduced for internal circulation,but permission of Elsevier Scienceis required for external resale or distribution of such material. Permission of the Publisher is required for all other derivative works, including compilations and translations. Electronic Storage or Usage Permission of the Publisher is required to store or use electronicallyany material contained in this work, including any chapter or pan of a chapter. Except as outlined above, no part of this work may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic,mechanical,photocopying. recording or otherwise.without prior written permission of the Publisher. Address permissions requests to: Elsevier Science Rights & Permissions Department, at the mail, fax and e-mail addresses noted above. Notice No responsibility is assumed by the Publisher for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, inswctions or ideas contained in the material herein. Because of rapid advances in the medical sciences, in particular. independent verification of diagnoses and drug dosages should be made.

@The paper used in this publication meets the requirements of ANSYNISO 239.48-1992 (Permanence of Paper). Printed in The Netherlands

This book is not meant to be just another textbook on Soil Physics. Instead, it presents a different approach to teaching students the basic principles of Soil Physics. The main idea is that students should be forced to think through and apply immediately what they read. To achieve this goal, the text is written mostly in rather short paragraphs and is alternated with questions. Many questions are an integral part of the transfer of knowledge; these, in particular, should be answered by the student before he continues. The student can check his answers with those given at the end of each chapter. The origin of the present book goes back to lectures notes by G. H. Bolt, which eventually resulted in two lecture syllabi written in the early sixties by G. H. Bolt, A. R. P. Janse and F. F. R. Koenigs for internal use at the Department of Soil Science and Plant Nutrition of the Agricultural University, Wageningen, The Netherlands. One syllabus was on Soil Chemistry, the other on Soil Physics; both had to be studied by the students as one unit. In the course of time, several reasons developed for revising these syllabi. First, the c.g.s. system of units needed to be replaced by the new S.1.system. Secondly, in 1970 a new study program was introduced at the Agricultural University, for which some students needed to study only Soil Physics. Unfortunately, some subjects that were needed for Soil Physics were discussed only in the Soil Chemistry syllabus, e.g., the behaviour of clay particles and the diffuse electric double layer. Obviously, it is desirable to incorporate all subjects of Soil Physics in one syllabus. A third reason for revision was the need to introduce a consistent set of definitions, symbols, etc., based on a rigorous, lucid development from first principles, in agreement with the latest internationally accepted conventions. The final and most elaborate, if not most important reason for revision was the need to seek ways to improve the examination results of the students. To this end, we first handed out questions at the lectures, some of which were prepared by L. Stroosnijder. Once a week the homework was discussed in small groups of about 15 students and evaluated by the teacher. This system was used with about 150 students, and thus was very time-consuming for the teaching staff. For the students, the gain in examination results was marginal, in spite of their larger time investment. This led eventually to the idea to integrate the questions and answers with the subject matter in the syllabus and develop some kind of half-programmed text for selfstudy. During a year of experimenting with a first draft of such a text, in which about half of the subjects were given in this new form, the students liked the new approach, obtained better results at the examinations, and even needed less time to master the material than with the old method. For the teaching staff also, the new method was far more efficient. Lectures were no longer needed and were replaced by sessions in which students could ask questions about the material studied. On the average, only about ten

percent of the students made use of these sessions. From 1974 on, the new method has been used with good results. The first author played a major role in the development and implementation of the elementary study program in Soil Physics, along the lines described above. He was assisted in this by G. Muggen of the Bureau for Development and Research of Education (B.O.O.) of the Agricultural University. This effort resulted, in 1975, in a new syllabus entitled Bodemnatuurkunde. Zelfinstructieve leertekst. A. Kamphorst translated this text in English and added some material for use in a M.Sc-course on Soil Science and Water Management at the Agricultural University for students from developing countries. This English version, the experience gathered during about eight years of use with Dutch and foreign students, and many years of experience of the third author in a research environment in the USA formed the basis for the present, much expanded and revised book. G. H. Bolt wrote the epilogue. The book is meant to be a first introduction in Soil Physics, but students who already have some knowledge in this area may also benefit from working through it. It presents a rigorous, complete and consistent treatment of the definitions and relationships for the fundamental physical processes occurring in soil. In addition, it gives detailed descriptions and solutions of most elementary problems encountered in the realm of Soil Physics. The treatment normally involves many simplifications, such as homogeneous soil, isothermal conditions, isotropy, etc. Because of its elementary level, we deemed it not necessary to include references each time a new concept was introduced. Instead, at the end of each chapter we present a list of recommended literature for further study. This literature, in turn, gives references to more specific or advanced literature, which should be adequate for starting a more thorough study of a particular subject. The teacher may set a time-table for studying the various subjects and accompany the students by means of question sessions. Students could be tested only at the end of the course, but we have had good experience with giving two or three tests at regular intervals, followed by a final examination. The S.1.-system is used rigorously throughout the text.