A Comparison of Two Models to Evaluate Soil Physical Property Effects on Corn Root Growth

Published in Agron. J. 105:713–720 (2013) doi:10.2134/agronj2012.0104 Copyright © 2013 by the American Society of Agronomy, 5585 Guilford Road, Madison, WI 53711. 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. T goal of many soil and crop management practices is to provide a more favorable environment for crop production for the soil at a particular location. One key to the proper use of available soil management techniques is the understanding of the complex interactions among soil physical properties, root growth and development, and plant response to changing physical conditions. Soil physical and chemical conditions, as well as the genetic predisposition of the crop species, determine the root distribution for a particular crop. Skinner et al. (1998) studied the effects of banded NO3 fertilizer and furrow irrigation on corn root distribution and showed that there is a complex interaction between the stimulation of corn roots due to high NO3 concentration and the restrictive effect of dry soil on corn roots. Root response to soil conditions was even more complex due to the apparent increase in corn root density in somewhat dry soil compared with consistently moist soil. Benjamin and Nielsen (2004) showed that plant response to dry soil conditions can vary with plant species and the growth stage of a plant within a species. They found that the root system of soybean [Glycine max (L.) Merr.] was relatively unaffected by water deficit conditions, whereas field pea [Pisum sativum L. ssp. sativum var. arvense (L.) Poir.] and chickpea (Cicer arietinum L.) responded to water deficit by growing more roots deeper in the soil profile. It is obvious that an active root system with the uptake of water for transpiration greatly affects chemical leaching from the root zone compared with bare soil scenarios. Benjamin et al. (1996) predicted less NO3 leaching from under a corn crop than under bare soil due to less downward water movement in the soil profile. Jackson and Estes (2007), using three independent models, predicted a hypothetical chemical concentration at the bottom of a 1.1-m profile under corn or turfgrass to be one-half to one-tenth the concentration of the same chemical under bare soil. Models are often used to integrate these complex interactions into a form that a manager can use to make better management decisions. Complex models have been developed to investigate the effects of management practices on crop yield (Jones et al., 2003), soil erosion (Jones et al., 1991b), and water quality (Ahuja et al., 2000). These models attempt to distribute roots into the soil based on the crop and its growth stage, the amount of C available for root growth, and the soil conditions in which the crop grows. In general, these models allocate a certain amount of C for root growth and then distribute the roots in the underlying soil based on the relative suitability for root growth in the soil layers. The accuracy and usefulness of these models rely on the ability of the root growth submodel to respond to varying soil conditions. Models for simulating multidimensional root growth into variable soil have been developed (Grant, 1993a, 1993b; Benjamin et al., 1996), but the limiting criteria for altering root growth due to changes in soil physical conditions have not been well studied. The nature of root-limiting soil physical conditions is complicated by the fact that different mechanisms control root growth at different q (m3 m–3) as rb changes. In very wet soil, O2 and CO2 diffusion into and out of the soil may be limited and ABSTRACT