HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Abstract Figures Only Full Text (PDF) Free Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Pikul, J. L. Articles by Riedell, W. Search for Related Content PubMed Articles by Pikul, J. L., Jr. Articles by Riedell, W. Agricola Articles by Pikul, J. L. Articles by Riedell, W. Related Collections Structure and Properties Soil Organic Matter Other Soil Management

SOIL & WATER MANAGEMENT & CONSERVATION

Particulate Organic Matter and Water-Stable Aggregation of Soil under Contrasting Management

USDA-ARS North Central Agricultural Research Lab. 2923 Medary Ave. Brookings, SD 57006

^* Corresponding author (jpikul{at}ngirl.ars.usda.gov).

	ABSTRACT

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Soil organic matter (SOM) is important to soil function. The objectives of this work were to determine the effect of cropping rotation and soil management on SOM, components of SOM, and water-stable aggregation (WSA) of soil near the surface. Measurements were made on soil collected from the top 50 mm of seven sites representing contrasts between alternative and conventional management. Management included tillage, crop rotation, native grass pasture, and corn (Zea mays L.) stover removal as silage. At each site, approximately 10 kg of soil was collected from each replication. Soil was separated into six aggregate groups using a rotary sieve. Aggregate size ranges for Groups 1 to 6 were: <0.4, 0.4 to 0.8, 0.8 to 2, 2 to 6, 6 to 19, and >19 mm. Mean weight diameter was calculated using dry aggregate size distribution. Dry aggregate stability, WSA, soil carbon (SC), SOM, fine particulate organic matter (fPOM), and coarse POM were measured on aggregates from each aggregate group. Components of SOM were not uniformly distributed among aggregate groups. Average SC (seven sites) was significantly greater under alternative (31.0 g kg^–1) than conventional (22.3 g kg^–1) management. No tillage (NT) increased fPOM/SOM by 19 and 37% compared with tillage following 4 and 10 yr of NT, respectively. A 5-yr diverse rotation increased fPOM/SOM by 36% compared with monoculture. There was a significant, positive relationship (r² = 0.79) between WSA and fPOM/SOM. Diversity of rotation or reduction of tillage increased fPOM and WSA and this may help to curb soil loss by maintaining surface conditions resistant to erosion.

Abbreviations: ALT, alternative farming practice • CON, conventional farming practice • cPOM, coarse (2.0–0.5 mm) particulate organic matter • DAS, dry aggregate stability • DASD, dry aggregate size distribution • EF, erodible fraction • fPOM, fine (0.5–0.053 mm) particulate organic matter • LOI, loss on ignition • MWD, mean weight diameter • NT, no tillage • POM, particulate organic matter • SC, soil carbon • SOM, soil organic matter • WSA, water-stable aggregation

	INTRODUCTION

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Interactions 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 difficult 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 influence of SOM on soil aggregation and water infiltration 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 infiltration (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 humified SOM (Paul et al., 2001), and is more sensitive to changes in management than total SOM (Cambardella and Elliott, 1992 and 1993; Cambardella et al., 2001). Under no-tillage practices, aggregate formation was directly related to root-residue decomposition and POM dynamics (Gale et al., 2000a, 2000b). In undisturbed soils, POM is derived primarily from roots (Gale et al., 2000a, 2000b). New microaggregates probably form around decomposing pieces of root-derived POM inside macroaggregates (Gale et al., 2000b). An aggregate "life cycle" was proposed by Six et al. (2000) in which aggregates form and stabilize around fine POM encrusted with microbial products, and eventually destabilize due to a cessation of microbial activity. Six et al. (2004) identified five factors (soil fauna, microorganisms, roots, inorganic soil components, and physical processes) that are important in the link between soil biotic activity, SOM decomposition and stabilization, and soil aggregate dynamics.

The quantity and quality of soil organic matter affects WSA (Tisdall and Oades, 1982). Degens (1997) provided a review on the function of labile organic bonding and binding agents related to soil aggregation. Labile compounds, in the context used by Degens (1997), were considered to be components of SOM that were readily decomposable and recently deposited by roots and microorganisms. Soil organic C accounted for about 70 to 90% of the variability in soil aggregate stability of a clay loam soil (Mbagwu and Bazzoffi, 1989). Wright and Upadhyaya (1998) found a positive correlation between soil aggregate stability and glomalin (a glycoproteinaceous substance produced by arbuscular mycorrhizal fungi). Spaccini et al. (2001), however, could not account for WSA of a forested or cultivated soil in terms of SOC levels. Johnson et al. (2004) found that crude humic acid and WSA of a Langhei clay loam increased with addition of byproducts of corn stover fermentation (70% lignin).

There is a poor understanding of the effects of soil and crop management on the composition of SOM in agricultural soils. Heat and mass transport into soil is largely governed by surface properties. Small changes in soil organic matter, brought on by soil or crop management, have been shown to have significant effects on surface crusting (Pikul and Zuzel, 1994). Research has shown that the process of decomposition under different agricultural systems results in unique chemical constituents of humic materials, and presumably, resulting soil stability. Chenu et al. (2000) found that SOM associated with clay minerals gave increased hydrophobicity, and that greater WSA could be ascribed to resistance of aggregates to slaking. Eynard et al. (2004) concluded that cultivation of Ustolls (prairie soils of central South Dakota) resulted in a decline of wettability compared with historically untilled grassland. The objectives of this study were to determine the effects of cropping rotation and soil management on SOM, components of SOM, and WSA of soil near the surface.

	MATERIALS AND METHODS

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Field Sites
Studies were conducted at seven sites (Table 1). Contrasting crop or soil management practices were compared between adjacent farms or replicated field plots. The term alternative management (ALT) will be used to generally group practices of NT (Sites 1 and 7), native pasture (Sites 5 and 6), or "diversified rotation" (Sites 2 and 4). Site 3 was a comparison of a corn–soybean [Glycine max (L.) Merr.] rotation where corn was cut for silage or harvested for grain. The comparison treatment at each site will be called conventional management (CON).

Site 2
Soil was collected on replicated plot experiments located on the Eastern South Dakota Soil and Water Research Farm near Brookings, SD, in October 2002. This experiment was started in 1990. Crop rotations used for contrasting comparisons were continuous corn (CON) and an alternative management using a 4-yr (ALT) rotation of corn, soybean, spring wheat, and alfalfa (Medicago sativa L.). Primary tillage for both ALT and CON was chisel plow in the fall. The soil is a Barnes sandy clay loam (fine-loamy, mixed, superactive, frigid Calcic Hapludoll) on nearly level topography.

Field plot design was a randomized complete block with three replications (blocks) where main plot was rotation treatment and split plot was N treatment (Pikul et al., 2005). All crop phases of each rotation were present every year. In the ALT rotation, spring wheat was used as a grain crop and as a companion crop to establish alfalfa in Year 3, and alfalfa was cut for hay in Year 4. Main plots were 90 m long by 30 m wide, and subplots were 30 m long by 30 m wide (three subplots per main plot). Nitrogen treatments used for contrasting comparisons were corn fertilized for a yield goal of 8.5 Mg grain ha^–1 (CON) and corn not fertilized (ALT). Corn yield (1992–2003) and associated agronomic measurements were reported by Pikul et al. (2005).

Site 3
Soil was collected on replicated plot experiments located near Brookings, SD, in June 2003. This experiment was designed to test the effect of corn stover removal on soil condition. Plots were established in 2000 as a randomized complete block with three replications. No tillage was used on the corn–soybean rotations. The main treatment is corn residue management. Each crop phase is present each year. The soil is a Brookings clay loam on nearly level topography. Corn was fertilized with about 130 kg N ha^–1. Treatments for contrasting comparisons were all corn residue retained on plots after grain harvested (ALT) and corn cut and removed as silage (CON). Under ALT, corn stalks were chopped in the fall after harvest. Corn under CON was cut for silage at about the dent stage of development.

Site 4
Soil was collected on small plot experiments near Brookings, SD, in June 2003. This experiment was designed to test the effect of a diversified crop rotation under no tillage on soil properties. Plots were established in 1997 on a Barnes clay loam. The experimental design was a randomized complete block with four replications. Rotations used for contrasting comparisons were continuous corn (CON) and an alternative management using a 5-yr rotation (ALT) of corn–soybean–oat and pea hay (Avena sativa L. and Pisum sativum L.) mix companion seeded with alfalfa–alfalfa–alfalfa. Fertilizer N for corn was applied at the same rate for ALT and CON.

Site 5
Soil was collected on two adjacent farms about 20 km north of Brookings, SD, in July 2003. Land on one farm was native pasture (ALT) and land on the other farm has been under a corn–soybean rotation (CON) for many years. The CON farm used fall chisel plow. The soil is a Lanona–Swenoda (coarse-loamy, mixed, superactive, frigid Calcic Hapludolls and coarse-loamy, mixed, superactive, frigid Pachic Hapludolls) sandy loam. On each farm, four replications were established at similar slope positions. Sample locations between ALT and CON farms were about 90 m apart.

Site 6
Soil was collected on two adjacent farms about 20 km northwest of Brookings, SD, in June 2004. Land on one farm was native pasture (ALT) and land on the other farm has been under a corn–soybean rotation for 25 yr (CON). The CON farm used fall chisel plow. The soil is a Barnes clay loam. On each farm, four replications were established at similar slope positions. Sample locations between ALT and CON farms were about 90 m apart.

Site 7
Soil was collected on replicated plot experiments near Brookings, SD, in June 2004. Plots were established in 2000 on a Barnes clay loam on nearly level ground. Rotation was corn–soybean and the experiment was designed to test the effect of no tillage (ALT) and conventional tillage (CON) on production of corn and soybean. The experimental design was a randomized complete block with four replications. Plots under CON were chisel plowed in the fall and seedbeds prepared in spring with a field cultivator. Fertilizer application rate was the same for both ALT and CON.

Soil Collection and Aggregate Separation
For determining properties of soil aggregates, approximately 10 kg of soil was collected from the surface 50 mm of each replication at each field site (Table 1). On sites with crops, the soil was collected from in-row positions. On sites under pasture, the surface sample was broken by hand to remove soil from the sod. Typically, we took soil from six locations within each replicate (randomly collected and bulked to collect 10 kg). After collection, the samples were spread in thin layers on greenhouse benches to air dry.

Dry aggregate size distribution (DASD) was determined by separating soil into six aggregate groups using a rotary sieve (Chepil, 1962) and measuring the mass of soil within each group. Aggregate size ranges for Groups 1 to 6 were: <0.4, 0.4 to 0.8, 0.8 to 2, 2 to 6, 6 to 19, and >19 mm. Mean weight diameter (MWD) was calculated using the mass fraction of dry aggregates and particle diameter of aggregates in each of the six size groups (Kemper and Rosenau, 1986). Particle diameters used for this calculation were 0.42, 0.63, 1.42, 4.2, 12.8, and 19.2 mm for Groups 1, 2, 3, 4, 5, and 6, respectively.

Subsamples of soil from each aggregate group were further processed to meet specific sample preparation criteria appropriate to the measurement being made.

Soil Analysis
Dry Aggregate Stability
Dry aggregate stability (DAS) was estimated by running individual aggregate groups through the sieve a second time and measuring the change in mass of soil material in each aggregate group after the second run. This estimate is closely related to susceptibility of the soil to wind erosion (Chepil, 1951). A loss of mass from one group indicates aggregate breakdown into smaller size groups (the sum of increases and losses across aggregate groups is approximately zero). An increase of soil material in the finer sized groups (aggregates <0.84 mm) shows the predisposition of a particular soil to fracture into aggregate sizes that are erodible by wind (<0.84 mm). The erodible fraction (EF) is defined as the mass fraction of soil <0.84 mm in diameter, and this parameter has been related to soil wind erodibility (Merrill et al., 1999).

Water-Stable Aggregation
Water stability of dry aggregates was measured using the sieving procedure described by Kemper and Rosenau (1986). Screen size (sieve opening) on our apparatus was 0.71 mm. Tests were conducted on about 4 g of dry aggregates from Groups 2, 3, and 4. The size range of aggregates tested from Group 2 was 0.7 to 0.84 mm. Because of the large size of aggregates in Group 5 (6–19 mm), we visually selected about 7 g of aggregates that were approximately 10 mm in size (approximate mean diameter for Group 5), and these aggregates were placed on the screen without crowding. All tests were run for 5 min. Water-stable aggregation was expressed as the percentage of soil remaining on the sieve after 5 min relative to the initial mass of soil used for the test. Stability calculations were corrected for sand content by subtracting the mass of sand remaining on the sieve from the initial soil mass and the mass of soil remaining on sieve after 5 min.

Particulate Soil Organic Matter
Particulate soil organic matter consists of insoluble plant debris (mostly roots) and this material was separated from the soil by dispersion and sieving. The quantity of POM was measured by weight loss on ignition (LOI); these methods have been described by Cambardella et al. (2001) and Gajda et al. (2001). Cambardella et al. (2001) tested two temperature and time treatment combinations to overcome errors associated with the presence of hydrated clays, salts, and gypsum. They recommended an ignition temperature of 450°C for 4 h and 30- and 10-g samples for POM and SOM, respectively. We chose to follow this procedure as other investigators have (Gajda et al., 2001; Mikha et al., 2006).

Soil in Groups 4, 5, and 6 was crushed and passed through a 2-mm sieve. Visible plant residues were picked out before crushing the samples. Soil in all aggregate groups was dispersed in sodium hexametaphosphate for 24 h, stirred with a malt mixer for 5 min, and transferred to a set of nested sieves having mesh sizes of 0.5 and 0.053 mm. Organic matter remaining on the 0.5-mm sieve was termed coarse POM (cPOM) and had a size range of 0.5 to 2.0 mm. Organic matter retained on the 0.053-mm sieve was called fine POM (fPOM) and had a size range of 0.053 to 0.5 mm. Material on each sieve was transferred to aluminum weigh pans, and the mass of POM was determined by LOI.

Soil organic matter of whole soil was measured using LOI (Cambardella et al., 2001; Gajda et al., 2001). The quantity of fPOM and cPOM within each aggregate group was expressed as a percentage of the quantity of SOM within each aggregate group (fPOM/SOM and cPOM/SOM).

Soil Carbon
Total C of the soil in Groups 1 to 6 was measured by combustion using a LECO CN 2000 analyzer (Leco Corp., St Joseph, MI), and reported as SC. All samples were ground on a roller mill and passed through a 0.5-mm sieve before analysis. Aggregates from Groups 4, 5, and 6 were crushed before roller-mill processing. In all steps and for all aggregate groups, visible pieces of crop residue were removed before the roller-mill process. For noncalcareous soils, SC can be considered to be organic C (Nelson and Sommers, 1982). We did not pretreat (Nelson and Sommers, 1982) our samples to remove carbonates before dry combustion, but did test for the presence of inorganic C (Nelson and Sommers, 1982) in those samples having a pH 7.0. Generally, the pH values for calcareous soils are within a range of 7.5 to 8.5 (Loeppert and Suarez, 1996).

Statistical Analysis
Statistical comparisons for differences in DASD and DAS between treatments at each site were made using one-way analysis of variance within each aggregate group (Minitab 14, Minitab Inc., State College, PA). Values for DASD and DAS are not normally distributed across aggregate groups. The summation of values (across Groups 1–6) is approximately 100% for DASD and zero for DAS. Treatment factors (ALT or CON) were considered fixed effects. Blocks were treated as random effects. Effects were considered significant for P 0.05.

A two-way analysis of variance and Fisher's protected LSD tests were performed for management treatment (ALT vs. CON) and aggregate group (1–6) on SC, SOM, fPOM/SOM, cPOM/SOM, and WSA for each site using the GLM procedure in SAS (SAS Institute, 1999).

A two-way analysis (across all sites and sieve groups) was used to determine significant differences between treatments (ALT or CON) and aggregate size classes (1–6) for SC, SOM, fPOM/SOM, cPOM/SOM and WSA. This analysis was performed using the Mixed procedure in SAS (SAS Institute, 1999).

Linear regression (Minitab 14) was used to identify those soil properties important to the prediction of water stability.

	RESULTS AND DISCUSSION

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Soil Aggregate Properties
Dry Aggregates
The mass of aggregates within different aggregate groups differed among treatments at some sites (Table 3); however, there were two sites (Sites 4 and 7) where there were no differences between treatments in the mass of aggregates within any aggregate group. The mass of soil in the two smallest aggregate groups (Table 3, Groups 1 and 2) comprise a portion of the DASD termed EF. Merrill et al. (1999) showed that EF was more sensitive to soil management effects on wind erosion potential than were other indices describing aggregate size distribution, such as MWD. Large values of EF, shown in Table 2, indicate soil with greater wind erosion potential than a comparable soil with a smaller value. For five of the seven sites, there was a greater mass of soil in the EF under CON than ALT (Table 2).

For six of the seven sites, we found differences in dry aggregate stability between treatments (Table 4). In Table 4, a negative sign indicates a loss of soil mass within an aggregate group (typically, Groups 5 and 6). Loss of soil from Groups 5 and 6 is roughly balanced by a gain in soil mass within Groups 1 to 4. An increase in soil mass in Groups 1 or 2 (EF) on second sieving is interpreted as an undesirable soil trait. As shown by the change in mass on second sieving, aggregates from ALT treatments (Table 4, except Site 4) had less tendency, when compared with CON, to break down into sizes that would be considered as EF. We speculate that the tendency for fewer small aggregates under alternative management may be explained by the accumulation of aggregate binding (and bonding) agents such as root biomass (Mamo and Bubenzer, 2001) and root exudates (Gale et al., 2000a, 2000b). Further, under systems with tillage, new aggregation would be disrupted during annual fall tillage.

At two sites we compared SC in the top 50 mm for no tillage (ALT) and conservation tillage (CON) corn–soybean rotations (Table 5, Sites 1 and 7). There was only a 2% difference (not significant) in SC between ALT and CON following 4 yr of no tillage (Site 7). Following 10 yr of no tillage at site 1 (Table 5, Site 1), however, SC was significantly (P < 0.001) greater (7% under ALT compared with CON). West and Post (2002) analyzed C sequestration rates under 67 long-term experiments and concluded that a change from conventional to no tillage resulted in increased C sequestration and that most of the increase in C sequestration occurred in the first 10 yr following the change.

Across all sites, we found significantly (P < 0.0001) greater SOM under ALT than CON. Individual sites are shown in Table 6. Average (all sites and sieve groups) SOM in the top 50 mm was 82.1 and 66.4 g kg^–1 under ALT and CON, respectively. Across seven sites, we found significant (P = 0.0007) differences in SOM among aggregates of Groups 1 to 6. Average (sites and treatments) SOM was 69.6, 70.9, 79.1, 78.6, 74.0, and 73.4 g kg^–1 for aggregates of Groups 1, 2, 3, 4, 5, and 6, respectively. There was no significant treatment x sieve interaction, and there was a strong relationship (r² = 0.79) between SC and SOM (SC = 0.46 SOM – 6.88, scatter diagram not shown). This relationship was almost identical to the findings of Varvel et al. (2002) for a silty clay loam near Mead, NE, where SOM was found to be 45% C. Cambardella et al. (2001) found that SOM was approximately 53% C and Mikha et al. (2006) found that SOM by LOI represented 40% of SC. In our case, SOM by LOI represented 46% of SC.

Gajda et al. (2001) evaluated alternative and conventional farming practices at five locations in the northern Great Plains and also found that fPOM comprised a greater fraction of total POM than cPOM. Mikha et al. (2006) reported temporal dynamics in POM collected at eight locations in the Great Plains during 4 yr. Mikha et al. (2006) found that the temporal pattern exhibited by POM (reported as a percentage of SOM) was similar between contrasting managements at each site. They (Mikha et al., 2006) suggest that a factor, possibly weather, was affecting POM similarly in both treatments. Further, they (Mikha et al., 2006) concluded that temporal responses in POM mirrored that of SOM, suggesting that POM is the component of SOM sensitive to management. Mikha et al. (2006) also used the convention of expressing POM as a ratio to SOM rather than as a ratio to bulk soil.

The greatest differences in fPOM/SOM between ALT and CON were at Sites 5 and 6, where native pasture (ALT) was compared with corn–soybean under tillage. Fine POM/SOM and cPOM/SOM for individual sites are shown in Tables 7 and 8. The native pastures at Sites 5 and 6 also had the greatest concentration of fPOM compared with all other sites and treatments. Average fPOM/SOM was 106% greater under ALT at Site 5 and 167% greater under ALT at Site 6 compared with CON (Table 7). Gale et al. (2000a, 2000b) found clear differences in the partitioning of surface-residue- and root-derived C during decomposition and suggested that the beneficial effects of no tillage on soil organic C accrual are primarily due to the increased retention of root-derived C in the soil.

Generally, WSA increased with aggregate size for all locations (Table 9). The greatest differences in WSA between ALT and CON were at Sites 5 and 6, where native pasture (ALT) was compared with corn–soybean under tillage (CON). Linear regression was used to investigate the single best predictor of WSA among the soil parameters of fPOM/SOM, fPOM, POM, POM/SOM, SC, SOM, cPOM, and cPOM/SOM (measurements common to all sites). For the seven sites, the best single predictor of WSA was the ratio of fPOM/SOM (r² = 0.79, regression P = 0.001). Values of r² for fPOM, POM, POM/SOM, SC, SOM, cPOM, and cPOM/SOM were 0.68, 0.66, 0.59, 0.49, 0.36, 0.03, and 0, respectively.

View larger version (19K): [in this window] [in a new window]   Fig. 1. Linear regression of water-stable aggregation (WSA) on the ratio of fine particulate organic matter (fPOM) and soil organic matter (SOM) for soil aggregate groups: Group 2 was 0.7 to 0.8 mm, Group 3 was 0.8 to 2 mm, and Group 4 was 2 to 6 mm. Aggregates from Group 5 (not included in the linear regression) were approximately 10 mm in diameter and are shown as open symbols. Soil was collected from the top 50 mm of seven experimental sites under various land management treatments.

	CONCLUSIONS

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
In northern subhumid regions of the Great Plains, wind and water erosion are persistent problems. Soil conservation practices that improve soil aggregate stability also help retard soil loss by maintaining soil structure and surface conditions resistant to erosion. Under NT, significant accumulations of fPOM in the top 50 mm occurred during short periods of time. Fine POM/SOM in a corn–soybean rotation was 19% greater under NT than conventional tillage after only 4 yr. In another corn–soybean rotation following 10 yr of NT, fPOM/SOM was 37% greater under NT than conventional tillage. For comparisons of crop rotations under NT, we found that fPOM/SOM was 36% greater in a 5-yr rotation than with continuous corn. The greatest concentrations of fPOM/SOM were found in the undisturbed soils of native pastures.

Our results show significant differences in SOM components as a result of crop and soil management. Systems that used less tillage or more diverse crop rotations (alternative practices) had greater fPOM/SOM than conventional tillage and monoculture (conventional practices). Because POM has been shown to be a labile fraction of SOM, we conclude that the soil environment under ALT is either less conducive to microbial transformation of POM or highly conducive to new POM deposition (for example, through plant root systems that remain undisturbed by tillage). Importantly, we show a relationship between fPOM/SOM and WSA that was consistent across a broad spectrum of soil, soil management, and cropping practices; as fPOM/SOM increased, WSA increased.

	ACKNOWLEDGMENTS

 
ACKNOWLEDGEMENTS

We are indebted to eastern South Dakota farmers Dave Diedrich, Larry Diedrich, Larry Thielen, Duane Pankratz, and John Heylans for providing the opportunity to conduct research on their farms. We thank Darrell Granbois (USDA-NRCS) for the opportunity to conduct research on his land and for his work in locating and mapping farm sites used in this study.

We also thank Mr. David Harris for skillful laboratory work and Ms. Sharon Nichols, Ms Courtney Rambow, Ms Krystal Maras, Mr. Nathan Maas, and Mr. Brandt Baldry for technical support.

	NOTES

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
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.

Received for publication October 5, 2005.

	REFERENCES

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 

• Adams, W.A. 1973. The effect of organic matter on bulk and true densities of some uncultivated podzolic soils. J. Soil Sci. 24:10–17.[CrossRef]
• Allmaras, R.R., H.H. Schomberg, C.L. Douglas, and T.H. Dao. 2000. Soil organic carbon sequestration potential of adopting conservation tillage in U.S. croplands. J. Soil Water Conserv. 55:365–373.
• Bauer, A., and A.L. Black. 1992. Organic carbon concentration effects on available water capacity of three soil textural groups. Soil Sci. Soc. Am. J. 56:248–254.[Abstract/Free Full Text]
• Biederbeck, V.O., C.A. Campbell, and R.P. Zentner. 1984. Effect of crop rotation and fertilization on some biological properties of a loam in southwestern Saskatchewan. Can. J. Soil Sci. 64:355–367.
• Boyle, M., W.T. Frankenberger, Jr., and L.H. Stolzy. 1989. The influence of organic matter on soil aggregation and water infiltration. J. Prod. Agric. 2:290–299.
• Bruce, R.R., G.W. Langdale, L.T. West, and W.P. Miller. 1992. Soil surface modification by biomass inputs affecting rainfall infiltration. Soil Sci. Soc. Am. J. 56:1614–1620.[Abstract/Free Full Text]
• Cambardella, C.A., and E.T. Elliott. 1992. Particulate soil organic-matter changes across a grassland cultivation sequence. Soil Sci. Soc. Am. J. 56:777–783.[Abstract/Free Full Text]
• Cambardella, C.A., and E.T. Elliott. 1993. Carbon and nitrogen distribution in aggregates from cultivated and native grassland soils. Soil Sci. Soc. Am. J. 57:1071–1076.[Abstract/Free Full Text]
• Cambardella, C.A., A.M. Gajda, J.W. Doran, B.J. Wienhold, and T.A. Kettler. 2001. Estimation of particulate and total organic matter by weight loss-on-ignition. p. 349–359. In R. Lal et al. (ed.) Assessment methods for soil carbon. Lewis Publ., Boca Raton, FL.
• Campbell, C.A., and W. Souster. 1982. Loss of organic matter and potentially mineralizable nitrogen from Saskatchewan soils due to cropping. Can. J. Soil Sci. 62:651–656.
• Carter, M.R. 2002. Soil quality for sustainable land management: Organic matter and aggregation interactions that maintain soil functions. Agron. J. 94:38–47.[Abstract/Free Full Text]
• Chenu, C., Y. LeBissonnais, and D. Arrouays. 2000. Organic matter influence on clay wettability and soil aggregate stability. Soil Sci. Soc. Am. J. 64:1479–1486.[Abstract/Free Full Text]
• Chepil, W.S. 1951. Properties of soil which influence wind erosion: IV. State of dry aggregate structure. Soil Sci. 72:387–401.
• Chepil, W.S. 1962. A compact rotary sieve and the importance of dry sieving in physical soil analysis. Soil Sci. Soc. Am. Proc. 26:4–6.
• Degens, B.P. 1997. Macro-aggregation of soils by biological bonding and binding mechanisms and the factors affecting these: A review. Aust. J. Soil Res. 35:431–459.[CrossRef]
• Doran, J.W., E.T. Elliott, and K. Paustian. 1998. Soil microbial activity, nitrogen cycling, and long-term changes in organic carbon pools as related to fallow tillage management. Soil Tillage Res. 49:3–18.[CrossRef]
• Eynard, A., T.E. Schumacher, M.J. Lindstrom, D.D. Malo, and R.A. Kohl. 2004. Wettability of soil aggregates from cultivated and uncultivated Ustolls and Usterts. Aust. J. Soil Res. 42:163–170.[CrossRef]
• Gajda, J.W., J.W. Doran, T.A. Kettler, B.J. Wienhold, J.L. Pikul, Jr., and C.A. Cambardella. 2001. Soil quality evaluations of alternative and conventional management systems. p. 381–400. In R. Lal et al. (ed.) Assessment methods for soil carbon. Lewis Publ., Boca Raton, FL.
• Gale, W.J., C.A. Cambardella, and T.B. Bailey. 2000a. Surface residue- and root-derived carbon in stable and unstable aggregates. Soil Sci. Soc. Am. J. 64:196–201.[Abstract/Free Full Text]
• Gale, W.J., C.A. Cambardella, and T.B. Bailey. 2000b. Root-derived carbon and the formation and stabilization of aggregates. Soil Sci. Soc. Am. J. 64:201–207.[Abstract/Free Full Text]
• Hudson, B.D. 1994. Soil organic matter and available water capacity. J. Soil Water Conserv. 49:189–194.
• Johnson, J.M.F., D. Reicosky, B. Sharratt, M. Lindstrom, W. Voorhees, and L. Carpenter-Boggs. 2004. Characterization of soil amended with the by-product of corn stover fermentation. Soil Sci. Soc. Am. J. 68:139–147.[Abstract/Free Full Text]
• Kemper, W.D., and R.C. Rosenau. 1986. Aggregate stability and size distribution. p. 425–444. In A. Klute (ed.) Methods of soil analysis. Part 1. Physical and mineralogical methods. 2nd ed. SSSA Book Ser. 5. SSSA, Madison, WI.
• Loeppert, R.H., and D.L. Suarez. 1996. Carbonate and gypsum. p. 437–474. In D.L. Sparks (ed.) Methods of soil analysis. Part 3. Chemical methods. SSSA Book Ser. 5. SSSA, Madison, WI.
• Mamo, M., and G.D. Bubenzer. 2001. Detachment rate, soil erodibility, and soil strength as influenced by living plant roots. Part II: Field study. Trans. ASAE 44:1175–1181.
• Mbagwu, J.S.C., and P. Bazzoffi. 1989. Properties of soil aggregates as influenced by tillage practices. Soil Use Manage. 5:180–188.[CrossRef]
• Merrill, S.D., A.L. Black, D.W. Fryrear, A. Saleh, T.M. Zobeck, A.D. Halvorson, and D.L. Tanaka. 1999. Soil wind erosion hazard of spring wheat–fallow as affected by long-term climate and tillage. Soil Sci. Soc. Am. J. 63:1768–1777.[Abstract/Free Full Text]
• Mikha, M.M., M.F. Vigil, M.A. Liebig, R.A. Bowman, B. McConkey, E.J. Deibert, and J.L. Pikul, Jr. 2006. Cropping system influences on soil chemical properties and soil quality in the Great Plains. Renew. Agric. Food Syst. 21:26–35.[CrossRef]
• Monreal, C.M., and H.H. Janzen. 1993. Soil organic-carbon dynamics after 80 years of cropping a Dark Brown Chernozem. Can. J. Soil Sci. 73:133–136.
• Mulla, D.J., L.M. Huyck, and J.P. Reganold. 1992. Temporal variation in aggregate stability on conventional and alternative farms. Soil Sci. Soc. Am. J. 56:1620–1624.[Abstract/Free Full Text]
• Nelson, D.W., and L.E. Sommers. 1982. Total carbon, organic carbon, and organic matter. p. 539–579. In A.L. Page (ed.) Methods of soil analysis. Part 2. Chemical and microbiological properties. 2nd ed. Agron. Monogr. 9. ASA and SSSA, Madison, WI.
• Paul, E.A., S.J. Morris, and S. Böhm. 2001. The determination of soil C pool sizes and turnover rates: Biophysical fractionation and tracers. p. 193–206. In R. Lal et al. (ed.) Assessment methods for soil carbon. Lewis Publ., Boca Raton, FL.
• Paustian, K., H.P. Collins, and E.A. Paul. 1997. Management controls on soil carbon. p. 15–49. In E.A. Paul et al. (ed.). Soil organic matter in temperate agroecosystems: Long-term experiments in North America. CRC Press, Boca Raton, FL.
• Pikul, J.L., Jr., L. Hammack, and W.E. Riedell. 2005. Corn yield, nitrogen use and corn rootworm infestation of rotations in the northern Corn Belt. Agron. J. 97:854–863.[Abstract/Free Full Text]
• Pikul, J.L., Jr., and J.F. Zuzel. 1994. Soil crusting and water infiltration affected by long-term tillage and residue management. Soil Sci. Soc. Am. J. 58:1524–1530.[Abstract/Free Full Text]
• Rasmussen, P.E., and W.J. Parton. 1994. Long-term effects of residue management in wheat–fallow: I. Inputs, yield, and soil organic matter. Soil Sci. Soc. Am. J. 58:523–530.
• SAS Institute. 1999. The analyst applications. SAS Inst., Cary, NC.
• Six, J., H. Bossuyt, S. Degryze, and K. Denef. 2004. A history of research on the link between (micro)aggregates, soil biota, and soil organic matter dynamics. Soil Tillage Res. 79:7–31.[CrossRef]
• Six, J., E.T. Elliot, and K. Paustian. 2000. Soil macroaggregate turnover and microaggregate formation: A mechanism for C sequestration under no-tillage management. Soil Biol. Biochem. 32:2099–2103.[CrossRef]
• Soane, B.D. 1990. The role of organic matter in soil compactibility: A review of some practical aspects. Soil Tillage Res. 16:179–201.[CrossRef]
• Spaccini, R., A. Zena, C.A. Igwe, J.S.C. Mbagwu, and A. Piccolo. 2001. Carbohydrates in water-stable aggregates and particle size fractions of forested and cultivated soils in two contrasting tropical ecosystems. Biogeochemistry 53:1–22.
• Tisdall, J.M., and J.M. Oades. 1982. Organic matter and water stable aggregates. J. Soil Sci. 33:141–163.[CrossRef]
• Varvel, G.E., M.A. Liebig, and J.W. Doran. 2002. Soil organic matter assessments in a long-term cropping system study. Commun. Soil Sci. Plant Anal. 33:2119–2130.[CrossRef][Web of Science]
• West, T.O., and W.M. Post. 2002. Soil organic carbon sequestration rates by tillage and crop rotation: A global analysis. Soil Sci. Soc. Am. J. 66:1930–1946.[Abstract/Free Full Text]
• Wright, S.F., J.L. Starr, and I.C. Paltineau. 1999. Changes in aggregate stability and concentration of glomalin during tillage management transition. Soil Sci. Soc. Am. J. 63:1825–1829.[Abstract/Free Full Text]
• Wright, S.F., and A. Upadhyaya. 1996. Extraction of an abundant and unusual protein from soil and comparison with hyphal protein of arbuscular mycorrhizal fungi. Soil Sci. 161:575–586.[CrossRef]
• Wright, S.F., and A. Upadhyaya. 1998. A survey of soils for aggregate stability and glomalin, a glycoprotein produced by hyphae of arbuscular mycorrhizal fungi. Plant Soil 198:97–107.[CrossRef][Web of Science]

This article has been cited by other articles:

				K. K. Grover, H. D. Karsten, and G. W. Roth Corn Grain Yields and Yield Stability in Four Long-Term Cropping Systems Agron. J., July 7, 2009; 101(4): 940 - 946. [Abstract] [Full Text] [PDF]

				C. R. Alvarez, M. A. Taboada, F. H. Gutierrez Boem, A. Bono, P. L. Fernandez, and P. Prystupa Topsoil Properties as Affected by Tillage Systems in the Rolling Pampa Region of Argentina Soil Sci. Soc. Am. J., May 13, 2009; 73(4): 1242 - 1250. [Abstract] [Full Text] [PDF]

				G. Hernandez-Ramirez, S. M. Brouder, D. R. Smith, and G. E. Van Scoyoc Carbon and Nitrogen Dynamics in an Eastern Corn Belt Soil: Nitrogen Source and Rotation Soil Sci. Soc. Am. J., January 21, 2009; 73(1): 128 - 137. [Abstract] [Full Text] [PDF]

				J. L. Pikul Jr., G. Chilom, J. Rice, A. Eynard, T. E. Schumacher, K. Nichols, J. M. F. Johnson, S. Wright, T. Caesar, and M. Ellsbury Organic Matter and Water Stability of Field Aggregates Affected by Tillage in South Dakota Soil Sci. Soc. Am. J., January 21, 2009; 73(1): 197 - 206. [Abstract] [Full Text] [PDF]

				R. M. Lehman, S. L. Osborne, and K. A. Rosentrater No Evidence That Bacillus thuringiensis Genes and Their Products Influence the Susceptibility of Corn Residue to Decomposition Agron. J., November 7, 2008; 100(6): 1687 - 1693. [Abstract] [Full Text] [PDF]

				H. Chung, J. H. Grove, and J. Six Indications for Soil Carbon Saturation in a Temperate Agroecosystem Soil Sci. Soc. Am. J., June 18, 2008; 72(4): 1132 - 1139. [Abstract] [Full Text] [PDF]

				R. M. Lehman, S. L. Osborne, and K. A. Rosentrater No Differences in Decomposition Rates Observed between Bacillus thuringiensis and Non-Bacillus thuringiensis Corn Residue Incubated in the Field Agron. J., January 11, 2008; 100(1): 163 - 168. [Abstract] [Full Text] [PDF]

This Article Abstract Figures Only Full Text (PDF) Free Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Pikul, J. L. Articles by Riedell, W. Search for Related Content PubMed Articles by Pikul, J. L., Jr. Articles by Riedell, W. Agricola Articles by Pikul, J. L. Articles by Riedell, W. Related Collections Structure and Properties Soil Organic Matter Other Soil Management