Agronomy D VA N C E S I N VOLUME 85 Advisory Board John S. Boyer University of Delaware Paul Bertsch University of Georgia Ronald L. Phillips University of Minnesota Kate M. Scow University of California, Davis Larry P. Wilding Texas A&M University Emeritus Advisory Board Members Kenneth J. Frey Iowa State University Eugene J. Kamprath North Carolina State University Martin Alexander Cornell University Prepared in cooperation with the American Society of Agronomy Monographs Committee David D. Baltensperger, Chair Lisa K. Al-Almoodi John M. Baker Kenneth A. Barbarick David M. Burner Warren A. Dick L. Richard Drees Jeffrey E. Herrick Bingru Huang Michel D. Ransom Craig A. Roberts David L. Wright Agronomy D VA N C E S I N VOLUME 85 Edited by Donald L. Sparks Department of Plant and Soil Sciences University of Delaware Newark, Delaware Elsevier Academic Press 525 B Street, Suite 1900, San Diego, California 92101-4495, USA 84 Theobald’s Road, London WCIX 8RR, UK This book is printed on acid-free paper. Copyright ß 2005, Elsevier Inc. All Rights Reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopy, recording, or any information storage and retrieval system, without permission in writing from the Publisher. The appearance of the code at the bottom of the first page of a chapter in this book indicates the Publisher’s consent that copies of the chapter may be made for personal or internal use of specific clients. This consent is given on the condition, however, that the copier pay the stated per copy fee through the Copyright Clearance Center, Inc. (www.copyright.com), for copying beyond that permitted by Sections 107 or 108 of the U.S. Copyright Law. This consent does not extend to other kinds of copying, such as copying for general distribution, for advertising or promotional purposes, for creating new collective works, or for resale. Copy fees for pre-2005 chapters are as shown on the title pages. If no fee code appears on the title page, the copy fee is the same as for current chapters. 0065-2113/2005 $35.00 Permissions may be sought directly from Elsevier’s Science & Technology Rights Department in Oxford, UK: phone: (þ44) 1865 843830, fax: (þ44) 1865 853333, E-mail: [email protected] You may also complete your request on-line via the Elsevier homepage (http://elsevier.com), by selecting ‘‘Customer Support’’ and then ‘‘Obtaining Permissions.’’ For all information on all Elsevier Academic Press publications visit our web site at www.books.elsevier.com ISBN: 0-12-000783-5 PRINTED IN THE UNITED STATES OF AMERICA 05