Particulate Organic Matter and Water-Stable Aggregation of Soil under Contrasting Management (original) (raw)

2007, Soil Science Society of America Journal

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. I nteractions among crop and soil management practices and soil condition are often clouded by variability within a system. Further, causal relationships between management and soil quality are diffi cult to extrapolate among regions because of differences in soil type, climate, and management norms. The quantity and quality of soil organic matter provides an important diagnostic link between management and sustainability of soil function. Generally, it is accepted that conversion to crop production practices has caused a decline in SOM compared with the original grassland levels throughout the Great Plains (Campbell and Souster, 1982; Monreal and Janzen, 1993; Allmaras et al., 2000). Tillage has caused SC losses from 28 to 77% depending on geographic location (climate) and soil type (Paustian et al., 1997). Summer fallow, a practice used to conserve soil water, has been associated with serious declines in SOM in a wheat (Triticum aestivum L.)-fallow crop sequence (Monreal and Janzen, 1993; Rasmussen and Parton, 1994; Biederbeck et al., 1984) compared with annual cropping systems. Conversely, changes in agricultural management from conventional tillage to NT and increased crop-rotation diversity can increase accumulation of SC (West and Post, 2002). Soil organic matter mediates many chemical and physical soil properties (Carter, 2002). Boyle et al. (1989) reviewed the infl uence of SOM on soil aggregation and water infi ltration and concluded that SOM had a disproportionate effect on soil physical properties. Soils high in SOM generally have greater available water-holding capacity than soils of similar texture with less SOM (Hudson, 1994), although Bauer and Black (1992) found that a decline in SOM did not change the available water-holding capacity of moderately coarse-textured soils. An increase in phytomass input to a loamy sand improved aggregate stability and water infi ltration (Bruce et al., 1992). In long-term tillage, residue management, and N-fertility plots, Pikul and Zuzel (1994) reported that an increase in SOM increased the porosity of surface crusts in a silt loam soil, while on a Naff silt loam, Mulla et al. (1992) were not able to establish a relation between SOM and physical properties of conventional and alternatively managed farms. The "alternative" farm studied by Mulla et al. (1992) used a cropping system that was more diverse than the "conventional" farm; however, tillage was used on both farms. Generally, soil compaction decreases with increasing SOM (Soane, 1990; Adams, 1973, Hudson, 1994). Maintenance of SOM thus is a key component in sustainability of the soil resource and crop productivity (Doran et al., 1998). Particulate organic matter is a labile intermediate in the SOM continuum from fresh organic materials to humifi ed