c06-07-0460(2) Myers.indd

Soybean [Glycine max (L.) Merr.] yield in claypan soils varies systematically with soil properties and landscape position. This is likely caused by soil interactions with soybean roots. Field observations of soybean root distribution are needed to reveal its effect on yield variability. This study examined profi le distributions of soybean root length density (RLD) and average root diameter (ARD) as a function of landscape position, depth to claypan (DTC), apparent soil electrical conductivity (ECa), clay-maximum translated depth (Dt), and other soil properties. A landscape of claypan soils was sampled postharvest at two sites near Centralia, MO, in 2001. Roots were washed from soil cores in 15-cm layers (15–120 cm) and measured with image analysis. Root length density and ARD were signifi cantly related to landscape position, DTC, Dt, and ECa. Predictions of RLD and ARD were best from 15 to 60 cm, the depths with the greatest infl uence from claypan soil morphology. Soil profi le distributions of base cations, P, and pH matched root density profi les. Soybean roots were inhibited in E horizons above the claypan and stimulated 20 to 40 cm below it. Soybean roots below the claypan had about 20 to 30% smaller diameter. We conclude that DTC and rapid estimators of claypan morphology, such as ECa, can be used to predict soybean root distribution in claypan soil landscapes. D.B. Myers, Dep. of Soil Environmental and Atmospheric Sciences, Agricultural Engineering Building, Univ. of Missouri, Columbia, MO 65211; N.R. Kitchen and K.A. Sudduth, USDA-ARS Cropping Systems and Water Quality Unit, Agricultural Engineering Building, Univ. of Missouri, Columbia, MO 65211; R.E. Sharp, Division of Plant Sciences, Agriculture Building, Univ. of Missouri, Columbia, MO 65211; R.J. Miles, Dep. of Soil Environmental and Atmospheric Sciences, Anheuser-Busch Natural Resources Building, Univ. of Missouri, Columbia, MO 65211. Mention of trade names or commercial products in this article is solely for the purpose of providing specifi c information and does not imply recommendation or endorsement by the U.S. Department of Agriculture or the University of Missouri. Received 13 July 2006. *Corresponding author ([email protected]). Abbreviations: ARD, average root diameter; CEC, cation exchange capacity; EC a , apparent soil electrical conductivity; D t , clay-maximum translated depth; DTC, depth to claypan; NA, neutralizeable acidity; OM, organic matter; RLD, root length density. Published in Crop Sci. 47:1498–1509 (2007). doi: 10.2135/cropsci2006.07.0460 © Crop Science Society of America 677 S. Segoe Rd., Madison, WI 53711 USA All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Permission for printing and for reprinting the material contained herein has been obtained by the publisher. Published online July 30, 2007