Content uploaded by Charles Wortmann
Author content
All content in this area was uploaded by Charles Wortmann on Mar 04, 2014
Content may be subject to copyright.
RESEARCH ARTICLE
The effects of manure application on soil aggregation
C. S. Wortmann ÆC. A. Shapiro
Received: 27 April 2007 / Accepted: 8 August 2007
Springer Science+Business Media B.V. 2007
Abstract Surface application of manure may
increase the risk of phosphorus loss in runoff. Manure
application, however, often results in increased soil
aggregate stability with reduced runoff and erosion
and, therefore, reduced P transport potential. Three
field studies were conducted with silt loam or silty
clay loam soil in Nebraska to determine how water-
stable soil aggregation in the 0- to 25-mm soil depth
is affected: (1) by application of raw or composted
feedlot manure; (2) by repeated annual manure
application; and (3) by the residual effect of
composted manure applied five to seven years before
sampling. Large macro-aggregates ([2 mm) were
increased 200% or more by both manure and compost
application within 15 days after application; the
effect persisted for the seven months of study with
a greater effect due to compost application.
Aggregate stability was similar for incorporation
and no incorporation of the applied compost or
manure. Bray-P1 in large macro-aggregates was
200% more than for the whole soil sample with
manure or compost applied, but Bray-P1 in large
macro-aggregates was similar to the whole sample in
the control. Annual application of swine slurry for
several years resulted in a 20% increase in aggregates
[250 mm. After four years of no compost following
three years of compost application, aggregate size
distribution was similar for the compost- compared to
the no-compost-applied treatments. Increased macro-
aggregate formation and high Bray-P1 in these
aggregates may protect against P loss in runoff due
to reduced runoff and erosion and protection of P in
water-stable large macro-aggregates.
Keywords Aggregate stability Compost
Eutrophication Macro-aggregate
Soil porosity
Abbreviations
Ag[2mm Large soil macro-aggregates
Ag0.25–2mm Small macro-aggregates
Ag0.053–0.25mm Soil micro-aggregates
ARDC Agricultural Research and
Development Center
DAA Days after application of
manure or compost
SOM Soil organic matter
UN-L University of Nebraska-Lincoln
A contribution of the University of Nebraska Agricultural
Research Division, supported in part by funds provided through
the Hatch Act.
C. S. Wortmann (&)
Department of Agronomy and Horticulture, University
of Nebraska-Lincoln, 279 Plant Science, Lincoln,
NE 68583-0915, USA
e-mail: cwortmann2@unl.edu
C. A. Shapiro
Northeast Research and Extension Center—Haskell
Agric. Lab, University of Nebraska-Lincoln,
57905 866 Rd, Concord, NE 68728, USA
e-mail: cshapiro1@unl.edu
123
Nutr Cycl Agroecosyst
DOI 10.1007/s10705-007-9130-6
Introduction
Runoff-P concentration is typically higher with
higher soil P concentration as in fields where much
manure has been applied (Sauer et al. 2000; McDo-
well and Sharpley 2001; Andraski and Bundy 2003;
Daverede et al. 2003; Klatt et al. 2003). Dissolved
and particulate P loss in runoff can be significant,
however, even at agronomically moderate soil test P
levels because a large proportion of soil P is non-
labile (Eghball and Gilley 1999; Eghball et al. 2002;
Wortmann and Walters 2006). Runoff P loss is,
therefore, largely dependent on the rate of erosion
and runoff.
Feedlot manure is commonly applied to the soil
surface with no or shallow incorporation. Runoff P
loss was much less after one year compared with one
day after surface application of beef feedlot manure
(Eghball et al. 2002). Such reductions indicate that
soil aggregation is increased by manure application
within two weeks after application resulting in less
runoff P loss, and that the effect persists for a year or
longer.
Manure application is often credited with improv-
ing soil physical properties with benefits such as
reduced runoff and erosion, and these effects can
persist for several years following manure application
(Gilley and Risse 2000; Wortmann and Walters
2006). Celik et al. (2004) found that after five years
of application of 25 t ha
1
yr
1
of manure or com-
post incorporated by moldboard plowing, the mean
weighted diameter of water-stable aggregates was
65% greater for the 0 to 30 cm depth than where no
manure or compost were applied. Aggregation was
similar with compost and manure. They also
observed reduced bulk density, increased macro-
and micro-porosity, and increased hydraulic conduc-
tivity after application of compost or manure.
Available soil waterholding capacity was increased
by 85 and 56% compared to the control for the 0 to
30 cm depth with compost and manure applied,
respectively. Surface application of manure or com-
post may be most advantageous for improving water
infiltration but it results in very high P concentrations
at the soil surface. Much of this P may be protected
from runoff due to the increased formation of water-
stable soil aggregates associated with an increase in
organic particulates with manure application (Six
et al. 2000). While manure application does not
always result in reduced runoff and erosion (Gilley
and Eghball 1998), the effect is common enough to
be considered as partly offsetting the effect of manure
application on runoff P concentration (Angers 1998;
Six et al. 2000; Whalen and Chang 2002).
Research was conducted to test the hypotheses that
application of raw or composted manure will result in
increased macro-aggregate formation in the surface
25 mm of soil and that the effects can persist for
several years after application. The objectives of this
research were to determine how soil aggregation is
affected: (1) during the months following incorpora-
tion and surface application of raw and composted
feedlot manure; (2) by repeated applications of
feedlot solid manure and swine slurry manure; and
(3) by composted feedlot manure applied five to
seven years before sampling. The distribution of
Bray-P1 and soil organic matter (SOM) in large
macro-aggregates relative to the whole surface soil
sample at 30 days after application was determined.
These objectives were addressed using data from
three field studies.
Materials and methods
Study 1
Experiments were conducted on two soil types at
Havelock Agronomy Farm of the University of
Nebraska-Lincoln (UN-L) on the east edge of Lincoln
NE (40
o
510N, 96
o
360W). The soil types were upland
loess Crete soil (fine, smectitic, mesic Pachic Ar-
giustolls) and alluvial Nodaway soil (fine-silty,
mixed, superactive, mesic Cumulic Hapludolls). Each
site was tilled with a tandem disk before application
of the treatments.
The treatments included three manure treatments
and two tillage treatments in a complete factorial with
four replications in a randomized complete block
design. The manure treatments were: (1) 50 Mg
ha
1
, d. wt., of composted feedlot manure; (2)
50 Mg ha
1
, d. wt., of uncomposted, stockpiled
feedlot manure; and (3) the control with neither
compost nor manure applied. The amount of P
applied with the compost and manure treatments
was 610 and 452 kg ha
1
, respectively. The tillage
treatments were no tillage following application and
incorporation with a garden tiller to about 7.5 cm
Nutr Cycl Agroecosyst
123
depth. The plot size was 4.5 ·4 m. The treatments
were applied on 25 April 2005. The crop was non-
irrigated maize (Zea mays L.) planted on 10 May
2005.
Soil samples composed of six cores of 70-mm
diameter were collected for the 0- to 25-mm depth at
15, 30, 60, 90, 120, and 150 days after application
(DAA). All sampling points were determined at the
start of the research to avoid sampling of soil
disturbed by previous sampling. Wheel tracks formed
during planting were avoided during sampling. Bray-
P1 (Bray and Kurtz 1945) and soil organic matter
content by weight loss on ignition (Nelson and
Sommers 1996) were determined for the complete
soil and the individual aggregate fractions collected
30 days after application.
The percent of soil in water-stable aggregates was
assessed by a wet-sieving method (Cambardella and
Elliott 1994). Field-moist soil was gently crumbled,
air-dried, and passed through an 8-mm sieve. Material
retained on the sieve was discarded, and visible pieces
of crop residues and roots were removed. A 100 g d.
wt. sub-sample of soil was distributed on a 2-mm
sieve of 20-cm diameter and immersed in about 3 cm
of water for 5 min. After immersion, samples were
wet sieved by dipping the sieves into water 50 times
during a 2-min period, done first with the 2-mm sieve,
and then sequentially with 0.250-mm and 0.053-mm
sieves. Material retained in each sieve was washed
separately into a 150-ml beaker and allowed to settle
for about 20 min. Supernatant water was carefully
poured from the beaker and discarded, while water-
stable aggregates were transferred into a pre-weighed
aluminum tin, oven dried at 50C, and weighed.
Classes of water-stable aggregates were large macro-
aggregates ([2.0 mm, Ag[2 mm), small macro-
aggregates (0.250–2.0 mm, Ag0.25–2mm), and
micro-aggregates (0.053–0.250, Ag0.053–0.25mm)
expressed as g 100 g
1
of dry soil. The three
aggregate classes were totaled to give the percent of
soil mass in water-stable aggregates.
Analyses of variance were conducted using Sta-
tistix 8 (Analytical Software, 2003). Means were
compared with the ANOVA-protected LSD (0.05)
method. The analysis of variance was conducted with
manure and tillage treatments as main plot effects,
and with sampling time as a subplot effect in a
split-plot analysis. Differences were considered sig-
nificant at P\0.05.
Study 2
This study was conducted on two soil types at the
UN-L Northeast Research and Extension Center-
Haskell Agricultural Laboratory near Concord NE
(42
o
230N, 96
o
570W). The upland site was on a
sloping hillside with a Moody-Leisy complex silt
loam (fine-loamy, mixed mesic Udic Haplustoll and
fine-loamy, mixed mesic Udic Argiustoll; 6–11%
slope) soil and the bottomland site was on a Maskell
loam (fine-loamy, mixed mesic Cumulic Haplustoll
soil; 2–6% slope). The treatments were: beef feedlot
manure applied at a mean rate of 46 Mg ha
1
yr
1
d.
wt. with incorporation after 24 h; swine slurry
manure broadcast and incorporated after 24 h at
2.7 Mg ha
1
yr
1
dry weight; and no manure
applied. The experimental design was a randomized
complete block with three replications. The manure
was applied each year from 1999 to 2003. Composite
soil samples were collected in the fall of 2003 for the
0- to 25-mm depth. The analysis of aggregate size
distribution was as above. Analyses of variance were
conducted using Statistix 8 (Analytical Software,
2003). Differences were considered significant at
P\0.05.
Study 3
Research was conducted at the UN-L Agriculture
Research and Development Center (ARDC) near
Ithaca NE (41100N, 96280W) to determine the
residual effect of applied compost on soil aggrega-
tion. A total of 200 Mg ha
1
composted feedlot
manure was applied in three applications between
1998 and 2002 (Wortmann and Walters 2006). The
study had three treatments: compost from low P
manure; compost from high P manure; and no
compost. The experimental design was a randomized
complete block with three replications. Composite
soil samples were collected in the fall of 2003 for the
0- to 25-mm depth. The analysis of aggregate size
distribution was as above. Analyses of variance were
Nutr Cycl Agroecosyst
123
conducted using Statistix 8 (Analytical Software,
2003). Differences were considered significant at
P\0.05.
Results
Study 1
The interaction effect of soil type by DAA was
significant for all aggregate size fractions and total
aggregates, as was the DAA main effect (Table 1;
Fig. 1). However, the differences due to soil type
were inconsistent over time. Aggregation was greater
with the alluvial soil on some sampling dates but less
or not different on others compared with the loess
soil. The significant effects of the soil type ·DAA
interaction and DAA on soil aggregation may have
been due to sampling conditions rather than to
treatment effects; soil water content was observed
to be higher for the 120-day sample than at other
sampling times and soil in macro-aggregates was
more, especially for the Crete soil site, for this
sampling date than for other dates.
The DAA ·tillage ·manure and the DAA ·
tillage interactions were not significant for all aggre-
gate size fractions (Table 1). The soil type ·
tillage ·manure interaction was significant for
Ag0.25–2mm and nearly so for Ag0.053–0.25mm
(P= 0.06) but not for Ag[2 mm and total aggregates
(Fig. 2). Ag0.053–0.25mm were reduced while
Ag0.25–2mm were increased with compost and
manure application for both soil types. These effects
were less pronounced with incorporation than with
surface application, especially for the alluvial soil.
The reduction in Ag0.053–0.25mm and increase in
Ag0.25–2mm compared with the control were greater
with manure than with compost with incorporation for
the Crete loess soil and with no incorporation for the
Nodaway alluvial soil.
Total amount of soil in aggregates was not affected
by manure treatments. However, the main effect of
the manure treatments was a greater reduction in
Ag0.053–0.25mm and a greater increase in Ag0.25–
2mm with manure than with compost application as
compared with the control, while Ag[2 mm were
increased more with compost (300%) than with
manure (200%) application (Table 2).
Table 1 ANOVA results
for trials conducted on two
sites at UN-L Havelock
Agronomy Laboratory in
2005
a
NS, *, **, ***: not
significant or significant at
P\0.05, 0.01, and 0.001,
respectively
Source of variation df Soil aggregates, g 100 g
1
soil
[2 mm 0.25–2 mm 0.053–0.25 mm Total
Site (S) 1
Rep/site 6
Tillage (T) 1 NS
a
NS NS NS
Manure (M) 2 *** *** *** NS
T·M 2 NS NS NS NS
T·S 1 NS NS NS NS
M·S 2 NS NS NS NS
T·M·S 2 NS * 0.06 NS
Error a 30
DAA (D) 5 *** *** *** ***
S·D 5 ** *** *** ***
T·D 5 NS NS NS NS
M·D 10 0.07 NS NS NS
T·M·D 10 NS NS 0.06 NS
T·D·S 5 ** *** *** ***
M·D·S10NSNSNS NS
T·M·D·S10NS NS NS NS
Error b/CV 180 62.5 18.6 17.2 6.7
Nutr Cycl Agroecosyst
123
Tillage and interaction effects were not significant
for Bray-P1 at 30 DAA. However, the manure
treatment effects generally were highly significant
(Table 3). Bray-P1 was highest with compost applied
and lowest with the control. However, Bray-P1
concentration in Ag[2 mm was about three times
as high compared with the complete soil sample for
the manure and compost treatments. Although Ag[2
mm accounted for a small fraction of the soil, 13 and
8% of soil Bray-P1 was in Ag[2 mm for compost
and manure applied, respectively, while less than 1%
of Bray-P1 was in Ag[2 mm for the control.
Manure and compost application resulted in a
great increase in Ag[2 mm with high SOM con-
centration at the 0- to 25-mm soil depth. The
concentration of SOM was increased in Ag0.25–
2mm (8%) and in the whole soil (6%) with compost-
and manure-applied compared with the control. Mean
SOM was 87, 31, 28, and 32 g kg
1
for Ag[2 mm,
Ag0.25–2mm, Ag0.053–0.25mm, and the whole soil,
respectively. The relatively high SOM in Ag[2mm
for the control as well as the compost- and manure-
applied treatments indicates the importance of pres-
ence of organic material to the formation of large
macro-aggregates, probably due to consolidation of
micro-aggregates (Six et al. 2000).
Study 2
The treatment by site interaction was not significant.
Aggregate size distribution was affected by manure
application, but the total amount of soil in aggregates
[0.053 mm was not affected (Table 4). Macro-
aggregates were increased while Ag0.053–0.25mm
0
10
20
30
40
50
60
70
80
90
Cr No Cr No Cr No Cr No Cr No Cr No
Site and days since application
g001g,setagerggalioS 1-
> 2 mm
0.25 - 2 mm
0.053 - 0.25 mm
15 30 60 90 120 150
Fig. 1 Variation in soil
aggregation as affected by
the site by days after
application interaction on
upland loess Crete, Cr, and
bottomland alluvial
Nodaway, No, soil at UN-L
Havelock Agronomy
Laboratory in 2005, The
standard errors of the mean
for the site by days after
application interaction were
0.27, 1.33, 1.30, and 1.02
for the [2 mm, 0.25–
2 mm, and 0.053–0.25 mm
water-stable aggregate size
fractions, and the total of
aggregates, respectively
0
10
20
30
40
50
60
70
80
NCM NCM NCM NCM
Soil gagr getaion
,g g001
1-
> 2 mm
0.25 - 2 mm
0.053 - 0.25 mm
Tilled Not tilled Tilled Not tilled
Crete Nodaway
Fig. 2 Mean effect of the soil ·tillage ·manure application
interaction on soil aggregation on two soil types at UN-L
Havelock Agronomy Laboratory in 2005, N, C, and M
designate no compost or manure applied, composted feedlot
manure applied, and stockpiled feedlot manure applied. Crete
and Nodaway soils are upland loess soil and bottomland
alluvial soil, respectively. The standard error of the means for
the soil by tillage by manure application interaction were 0.29,
1.32, 1.27, and 0.90 for the [2 mm, 0.25–2 mm, and 0.053–
0.25 mm water-stable aggregate size fractions, and total
aggregates, respectively
Nutr Cycl Agroecosyst
123
were decreased with manure application, with the
greatest effect due to swine manure application.
Study 3
The residual effect of compost applied five to seven
years before sampling on aggregate size distribution
was not significant (Table 5). The residual effect of
compost application on total soil in aggregates
[0.053 mm was not significant.
Discussion
Generally the effect of manure application was to
increase macro-aggregates relative to Ag0.053–
0.25mm without an effect on the total amount of soil
Table 2 Mean effects of manure application treatments on soil aggregation in trials conducted on two sites at UN-L Havelock
Agronomy Laboratory in 2005
Treatments
a
Aggregate size
[2 mm 0.25–2 mm 0.053–0.25 mm \0.053 mm
g 100 g
1
Manure 2.4 a
b
37.3 a 34.9 c 25.4 a
Compost 3.2 b 34.5 b 36.8 b 25.4 a
Control 0.8 c 33.2 b 39.8 a 26.2 a
a
Tillage and interaction effects were not significant
b
Values with different letters in columns are statistically different (P\0.05)
Table 3 Mean effects of manure treatments for two soil types at 30 days after manure and compost application on Bray-P1 in the 0-
to 2.5-cm soil depth at UN-L Havelock Agronomy Laboratory in 2005
Treatments
a
Aggregate size
[2 mm 0.25–2 mm 0.053–0.25 mm \0.053 mm
Bray-P1, mg kg
1b
Manure 326.9 b
c
110.5 b 82.4 b 28.3 b
Compost 753.9 a 182.8 a 107.5 a 81.4 a
Control 32.4 c 49.9 c 51.7 c 5.3 c
a
Tillage and interaction effects were not significant
b
Bray-P1 in the complete soil sample for the 0- to 2.5-cm depth was 106.1, 208.5, and 42.7 mg kg
1
for the manure, compost and
control treatments, respectively
c
Values with different letters in columns are statistically different (P\0.05)
Table 4 The effect of types of applied manure on water-stable soil aggregate size at Haskell Agricultural Laboratory in 2004
Treatments Aggregate size
[0.25 mm 0.053 to 0.25 mm \0.053 mm
g 100 g
1
Swine manure 42.5 a
A
40.3 b 20.2 a
Beef manure 40.1 ab 45.2 ab 16.3 a
No manure 35.0 b 48.5 a 18.5 a
A
Values with different letters in columns are statistically different (P\0.05)
Nutr Cycl Agroecosyst
123
in aggregates [0.053 mm. These effects were con-
sistent across soil types with the soil by treatment
interaction accounting for little of the total variation
due to treatment effects at the Havelock and Haskell
sites. The results generally agree with the finding of
Sommerfeldt and Chang (1985), that larger aggre-
gates were increased while smaller aggregates were
decreased due to manure application, probably due to
increased consolidation of micro-aggregates into
macro-aggregates (Six et al. 2004).
The manure ·DAA interaction effect was not
significant and the effect of manure or compost
application on aggregation occurred soon after
application with a significant increase in Ag[2mm
at 15 DAA. The greatest increase was for compost
with a 240% increase in Ag[2 mm compared with
no manure or compost applied, and this increase
persisted for the 7-month duration of the Havelock
study. Bray-P1 in Ag[2 mm was much more than in
the rest of the soil sample with compost or manure
applied. Whalen and Chang (2002), however, found
that the increase in soil P with long-term manure
application was greater in the 0.5 to 2.0 mm size than
in larger or smaller dry-sieved aggregate sizes. The
increase in water-stable soil macro-aggregates with
high Bray-P1 within a short time after application of
compost or manure may be important to reducing P
loss in runoff due to increased infiltration, less soil
dispersion due to the impact of rain drops, and
protection of applied P in macro-aggregates.
Composted feedlot manure application resulted
in more Ag[2 mm but less Ag0.25–2mm macro-
aggregates than raw feedlot manure. The effect of
applied compost on soil aggregation was not
significant four years after the last application at
the ARDC site. In a related study, however, runoff
at this site continued to be less with the compost-
applied treatments compared to the no-compost
control until five years after the last application
(Wortmann and Walters 2007). This site was disk
tilled every year; the compost effect on soil
aggregation may have persisted longer with no-till
(Six et al. 1999; Wright and Hons 2005). A much
greater residual effect of applied compost was
reported by Celik et al. (2004).
Conclusion
Manure and compost application results in a signif-
icant increase in water-stable large macro-aggregates
within 15 days after application, probably due in part
to consolidation of smaller aggregates. The newly
formed large macro-aggregates were much higher in
Bray-P1 than the rest of the soil and than in the large
macro-aggregates of soil where compost and manure
were not applied. The macro-aggregation was more
with compost than with raw feedlot manure and
swine slurry manure had a similar effect as solid
feedlot manure. The effect of manure or compost
application persisted through one cropping season but
was not detectable at four years after application in a
cropping system that was tilled annually. While
manure or compost application may increase the risk
of P runoff, the risk is likely to be greatest during the
days after application as the resulting increase in
large water-stable soil macro-aggregates with a high
P concentration should reduce the risk of P runoff.
Studies involving simulated rainfall conducted
shortly after manure application may over-estimate
manure application effects on the risk of P runoff.
Manure application should be avoided at times of
Table 5 The residual effect of composted manure (4 years after application) on soil aggregate properties at the Agricultural
Research and Development Center in 2004
Treatments Aggregate size
[0.25 mm 0.053 to 0.25 mm \0.053 mm
g 100 g
1
High P compost 44.7 37.9 17.4
Low P compost 45.9 35.4 18.7
No compost 41.1 38.5 20.4
Significance NS
a
NS NS
a
NS: differences are not statistically significant at P\0.05
Nutr Cycl Agroecosyst
123
high probability of a runoff event within days of
application.
References
Angers DA (1998) Water-stable aggregation of Quebec silty
clay soils: some factors controlling its dynamics. Soil Till
Res 47:91–96
Andraski TW, Bundy LG (2003) Relationships between
phosphorus levels in soil and in runoff from corn pro-
duction systems. J Environ Qual 32:310–316
Bray RH, Kurtz LT (1945) Determination of total, organic and
available forms of phosphorus in soils. Soil Sci 59:39–45
Cambardella CA, Elliott ET (1994) Carbon and nitrogen
dynamics of soil organic matter fractions from cultivated
grassland soils. Soil Sci Soc Am J 58:123–130
Celik I, Ortas I, Kilic S (2004) Effects of compost, mycorrhiza,
manure and fertilizer on some physical properties of a
Chromoxerert soil. Soil Tillage Res 78:59–67
Daverede IC, Kravchenko AN, Hoeft RG, Nafziger ED,
Bullock DG, Warren JJ,Gonzini LC (2003) Phosphorus
runoff: effect of tillage and soil phosphorus levels. J
Environ Qual 32:1436–1444
Eghball B (2002) Soil properties as influenced by phosphorus
and nitrogen-based manure and compost applications.
Agron J 94:128–135
Eghball B, Gilley JE (1999) Phosphorus and nitrogen in runoff
following beef cattle manure or compost application.
J Environ Qual 28:1201–1210
Eghball B, Gilley JE, Baltensperger DD, Blumenthal JM
(2002) Long-term manure and fertilizer application
effects on phosphorus and nitrogen in runoff. Trans ASAE
45:687–694
Gilley JE, Eghball B (1998) Runoff and erosion following field
application of beef cattle manure and compost. Trans
ASAE 41:1289–1294
Gilley JE, Risse LM (2000) Runoff and soil loss as affected by
the application of manure. Trans ASAE 43:1583–1588
Klatt JG, Mallarino AP, Downing JA, Kopaska JA, Wittry DJ
(2003) Soil phosphorus, management practices, and their
relationship to phosphorus delivery in the Iowa Clear
Lake agricultural watershed. J Environ Qual 32:2140–
2149
McDowell RW, Sharpley AN (2001) Approximating phos-
phorus release from soils to surface runoff and subsurface
drainage. J Environ Qual 30:508–520
Nelson DW, Sommers LE (1996) Loss-on-ignition method.
p 1004–1006. In: Bigham JM (ed) Methods of soil anal-
ysis, Part 3. Chemical methods. SSSA Book Series: 5,
Madison, WI, pp 1004–1006
Sauer TJ, Daniel TC, Nichols DJ, West CP, Moore Jr. PA,
Wheeler GL (2000) Runoff water quality from poultry
litter-treated pasture and forest sites. J Environ Qual
29:515–521
Six J, Elliott ET, Paustian K (1999) Aggregate and soil organic
matter dynamics under conventional and no-tillage sys-
tems. Soil Sci Soc Am J 63:1350–1358
Six J, Elliott ET, Paustian K (2000) Soil macroaggregate
turnover and microaggregate formation: a mechanism for
C sequestration under no-tillage agriculture. Soil Biol
Biochem 32:2099–2103
Six J, Bossuyt H, Degryze S, Denef K (2004) A history of
research on the link between (micro)aggregates, soil biota,
and soil organic matter dynamics. Soil Till Res 79:7–31
Sommerfeldt TG, Chang C (1985) Changes in soil properties
under annual applications of feedlot manure and different
tillage practices. Soil Sci Soc Am J 49:983–987
Whalen JK, Chang C (2002) Macroaggregate characteristics in
cultivated soils after 25 years annual manure applications.
Soil Sci Soc Am J 66:1637–1647
Wortmann CS, Walters DT (2006) Phosphorus runoff during
four years following composted manure application.
J Environ Qual 35:651–657
Wortmann CS, Walters DT (2007) Residual effects of compost
and plowing on phosphorus and sediment in runoff.
J Environ Qual 36:1521–1527
Wright AL, Hons FM (2005) Soil carbon and nitrogen storage
in aggregates from different tillage and crop regimes. Soil
Sci Soc Am J 69:141–147
Nutr Cycl Agroecosyst
123