ADVANCES IN AGRONOMY VOLUME 21 CONTRIBUTORS TO THIS VOLUME F. J. CARLISLE D. J. GREENLAND R. B. GROSSMAN S. B. HEATH CHARLES E. KELLOGG OLIVER E. NELSON J. M. OADES ARNOLD C . ORVEDAL W. F. RAYMOND G. D. SWINCER R. W. WILLEY ADVANCES IN AGRONOMY Prepared under the Auspices of the AMERICAN SOCIETY OF AGRONOMY VOLUME 21 Edifed by N. C. BRADY Roberts Hall, Cornell University, ithaca, New York ADVISORY BOARD R. R. DAVIS F. A. HASKINS W. D. KEMPER .I.P. MARTIN J . W. PENDLETON W. A. RANEY 1969 @ ACADEMIC PRESS 0 N e w York and London COPYRIGHT ‘C 1969, BY ACADEMIC PRESS, INC. ALL RIGHTS RESERVED. N O PART OF THIS BOOK MAY BE REPRODUCED IN ANY FORM, BY PHOTOSTAT, MICROFILM, RETRIEVAL SYSTEM, OR ANY OTHER MEANS, W I T H O U T WRITTEN PERMISSION FROM T H E PUBLISHERS. ACADEMIC PRESS, INC. 1 1 1 Fifth Avenue, New York, New York 10003 United Kingdom Edition published by ACADEMIC PRESS, INC. (LONDON) LTD. Berkeley Square House, London W 1X 6BA LIBRARY OF CONGRESS CATALOG C A R D NUMBER50-5598 PRI N TED IN T H E UNITED STATES O F AMERICA CONTRIBUTORS TO VOLUME 21 Numbers in parentheses indicate the pages on which the authors’ contributions begin. F. J . CARLISLE ( 2 3 7 ) , Soil Conservation Service, United States Department of Agriculture, Hyattsville, Maryland D. J . GREENLAND (195), Depurtment of Agricultural Biochemistry and Soil Science, Waite Agricultural Research Institute, University of Adelaide, South Australia R. B. GROSSMAN ( 2 3 7 ) , Soil Conservation Service, United States Department of Agriculture, Lincoln, Nebraska S . B. HEATH(28 11, Department of Agriculture, University of Reading, Reading Berkshire, England CHARLES E. KELLOGG( I09), Soil Survey, Soil Conservation Service, United States Department of Agriculture, Washington, D.C. OLIVER E . NELSON* (17 l ) , Purdue University, Lafayetre, Indiana J . M . OADES(195), Department of Agricultural Biochemistry and Soil Science, Waite Agricultural Research Institute, University of Adelaide, South Australia ARNOLDC. ORVEDAL ( 109), Soil Survey, Soil Conservation Service, United States Department of Agriculture, Washington, D.C. W. F . RAYMOND( I ) , The Grassland Research Institute, Hurley, England G . D. SWINCER (195), Department of Agricultural Biochemistry and Soil Science, Waite Agricultural Research Institute, University of Adelaide, South Australia R. W. WILLEY t (28 I ) , Department ofAgriculture, University of Reading, Reading Berkshire, England *Present address: University of Wisconsin, Madison, Wisconsin. t Presenr address: Makerere University College, Kampala, Uganda. V This Page Intentionally Left Blank PREFACE This volume marks a significant milestone in the history of Advances in Agronomy. The first 20 volumes were compiled under the very capable editorship of Dr. A. G. Norman, now Vice-president for Research at the University of Michigan. Mounting pressures of other responsibilities have prompted Dr. Norman to ask to be relieved as editor of this serial publication; this is the first volume that does not carry his name. It is fitting that we reflect briefly on the contributions he has made, not only to this work but to his profession as well. As editor of Advances in Agronomy, Dr. Norman has given 20 years of faithful service and leadership to agronomists and soil and crop scientists throughout the world. His extraordinarily good judgment in the selection of authors and of subject matter has been largely responsible for the success of this publication. His guidance to authors has helped both them and the quality of their papers. He has seen Advunces in Agronomy grow from a strugglin