Vol.2, No.2, 117-124 (2011)
opyright © 2011 SciRes. Openly accessible at http://www.scirp.org/journal/AS/
Agricultural Sciences
Long-term rice-based cropping system effects on
near-surface soil compaction
Jill M. Motschenbacher, Kristofor R. Brye*, Merle M. Anders
Department of Crop, Soil, and Environmental Sciences, University of Arkansas, Fayetteville, USA;
*Corresponding Aut hor: kbrye@uark.edu
Received 7 February 2011; revised 3 March 2011; accepted 30 March 2011.
Irrigated rice (Oryza sativa L.) production is as-
sociated with frequent cycling between anaero-
bic and aerobic conditions, which can lead to a
greater rate of soil organic matter (SOM) decom-
position, thus potentially increasing soil bulk de-
nsity (BD) over time. A study was conducted in
the Mississippi River Delt a region of eastern Ark-
ansas, USA to evaluate the long-term effects of
rice-based crop rotations, tillage [conventional
tillage (CT) and no-tillage (NT)], soil fertility re-
gime (optimal and sub-optimal), and soil depth
(0-10 and 10-20 cm) after 10 years of consistent
management on near-surface soil compaction,
as measured by BD. Soil BD was greater under
NT than CT in the top 10 cm, but was similar
between NT and CT in the 10- to 20-cm depth
interval. Soil BD differed among common rice-
based cropping systems with corn, soybean,
and winter wheat, but few consistent trends
were evident. It appears that, even after 10 years
of continuous CT or NT rice production on a silt-
loam soil, substantially increased near-surface
soil BD has not occurred to the point where soil
compaction would be a likely culprit respon-
sible for a reduced early season stand estab-
lishment or crop yield differences among rice-
based copping systems.
Keywords: Bulk Density; Crop Rotation; Soil
Organic Matter; Tillage
The enhancement of soil quality is vital to sustaining
and improving long-term agricultural productivity, na me ly
crop yields [1,2]. Soil bulk density (BD), the ratio of the
dry soil mass to th e volume it occup ies, is often one of a
suite of measured soil properties that is an indicator of
soil quality [1,3,4 ]. Soil BD is related to soil compaction
in that BD is relatively greater in compacted than in
non-compacted soil. Compacted soil with a relatively
large BD can negatively affect numerous soil and plant
properties and processes. Soil BD has been shown to be
directly related to soil streng th [5-9] and soil penetration
resistance [10-14], which is another soil property that is
often used to quantify soil compaction. In contrast, soil
BD has been shown to be inversely related to soil or-
ganic matter (SOM) [6,15], water-holding capacity [6,14,
16], soil particle size [17], total porosity [18-20], infil-
tration capacity [6,21,22], hydraulic co nductivity [14,18,
20], gas exchange [23], nutrient mobility [6,24], and
invertebrate movement [12,25]. Similarly, soil BD has
been shown to be inversely related to seedling emer-
gence [19,26] and root penetration [6,12,14,16], both of
which can negatively affect yield if soil compaction is
Soil BD has also been shown to be affected by several
crop management practices, particularly tillage and crop
rotation [14,27-30]. Soil BD is generally greater under
reduced tillage, specifically no-tillage (NT), due to ma-
chinery traffic and the lack of surface soil disruption and
mixing accomplished by annual plowing [16,18,20,29,
31,32]. Since soil BD has been shown to be inversely
related to SOM [6,15], where increasing SOM generally
decreases soil BD by adding additional pore space
without adding much additional mass, crop rotations
with a large frequency of high-residue-producing crops
that are managed using cultural practices that return crop
residues to the soil could consequently at least maintain
a near-surface soil BD that is favorable for gas exchange,
water infiltration, and plant growth.
Rice (Oryza sativa L.) is one of several high-residue-
producing crops, along with corn ( Zea mays L.) and win-
ter wheat (Triticum aestivum L.), that is capable of pro-
ducing 8.1 Mg·ha–1 of above-ground biomass under op-
timal nitrogen fertilization [33,34]. Of the roughly 1.2
million ha of rice planted and 9.3 million Mg of rice
grain produced in the United States annually, over 46%
of the total rice area (566,800 ha) and over 45% of the
J. M. Motschenbacher et al. / Agricultural Sciences 2 (2011) 117-124
Copyright © 2011 SciRes. Openly accessible at http://www.scirp.org/journal/AS/
total grain production (4.2 million Mg) occur in th e Mis-
sissippi River Delta region of eastern Arkansas [35].
However, rice is unlike all other row crops in that rice is
most frequently grown under flood-irrigated conditions
after about one month post-emergence, where the upper-
most part of the soil profile is nearly to co mpletely satu-
rated [36]. To harvest rice, the flood must be released
several weeks prior to the targeted harvest window in
order to allow the soil to drain and dry out to achieve
enough structural stability to support heavy harvesting
machinery. If the soil is too wet and not sufficiently dry
to provide structur al support for a large harvest combine,
rice fields are often severely rutted, which can result in
elevated soil BD and compaction in many areas of a
field [37].
Furthermore, the decomposition of SOM is generally
slower in waterlogged soil than in well-aerated soil [2,
36]. However, flood-irrigated rice fields are unique from
other wetland soils in that they are often relatively dry
between successive rice crops in the rotation. Aerobic
soil conditions also exist during the dry periods between
flooding and heavy precipitation, which stimulates the
rapid breakdown of accumulated SOM. This decline in
SOM can, in turn, adversely affect soil productivity, soil
quality, and the overall sustainability of rice production
[38]. The frequent cycling between anaerobic and aero-
bic conditions can potentially lead to a greater rate of
SOM decomposition [39], which could essentially in-
crease the BD of the soil. Increasing soil BD over time is
a reasonable concern because compacted soil may hinder
short-term plant growth and long-term crop yield.
Since the nature of soil physical properties are gener-
ally of little concern during a rice crop-growing season
due to the flooded-soil conditions, relatively few studies
have examined the potential effects of rice rotations on
soil physical properties, particularly soil BD. Therefore,
the objective of this study was to evaluate the long-term
effects of rice-based crop rotations, tillage [conventio nal
tillage (CT) and no-tillage (NT)], soil fertility regime
(optimal and sub-optimal), and soil depth (0-10 and 10-
20 cm) after 10 years of consistent management on near-
surface soil compaction, as measured by soil BD, in the
Mississippi River Delta region of eastern Arkansas. It
was hypothesized that soil BD would be i) similar
among soil depths under CT due to the mixing action of
mechanical cultivation, but greater in the 10-20 than in
the 0-10 cm depth interval under NT, ii) different among
rice-based cropping systems and that the difference
would be related to the frequency of rice and other
high-residue-producing crops in the rotation, and iii)
generally lower under optimal than sub-optimal fertiliza-
tion due to greater SOM.
This study was conducted at the University of Arkan-
sas Rice Research and Extension Center (RREC) near
Stuttgart, AR (34o27' N, 91o24' W), which is located in
the Mississippi River Delta region of eastern Arkansas in
an area known as the Grand Prairie. This study was ini-
tiated in 1999 on a Dewitt silt loa m (fine, smectitic, ther-
mic, Typic Albaqualf) [40], which is characteristic of
Grand Prairie soils used for rice production.
Prior to 1999, the study area had been fallow for sev-
eral years due to a lack of irrigation capability. Vegeta-
tion present consisted of a mixture of grasses and weeds
that were managed by periodic mowing during the
summer. In preparation for this study, the site was
land-leveled to a 0.15% grade in fall 1998. Land-level-
ing consisted of removing and piling the top 10 cm of
soil off to the side of the area to be leveled, cutting the
field to grade, and redistributing the topsoil uniformly
over the field. Land-leveling is a common practice in the
Mississippi River Delta region, especially in areas where
rice production dominates, to facilitate uniform distribu-
tion of flood-irrigation water [41].
The climate of the region is warm and wet with a
30-yr mean annual temperature minimum of 0.22˚C in
January and maximum of 33.1˚C in July. The 30-yr
mean annual precipitation is 131.6 cm [42].
This field study consisted of two tillage treatments
[conventional tillage (CT) and no-tillage (NT)], two soil
fertility treatments (optimal and sub-optimal), and 10
rice-cropping systems arranged in a randomized com-
plete block with four replications (i.e., blocks) of treat-
ment combinations. Each block occupied an area of 120-
m long by 76-m wide (9120 m2). Soil fertility treatments
were imposed as a split of each tillage treatment, while
the rice rotations were horizontally stripped across the
tillage-fertility combinations. Each tillage-fertility-rota-
tion combination represented the experimental unit and
had dimensi on s of 19 - by 6- m.
The optimal soil fertility treatment followed a stan-
dard fertility recommendation based on the analysis of
soil samples that were collected in sp ring 1999 (Table 1).
The annual soil fertility treatment consisted of P2O5 ap-
plied as triple super phosphate and K2O applied as muri-
ate of potash, with both fertilizers broadcast pre-plant
and pre-tillage with a spreader. Nitrogen as urea was
applied with a hand-spreader pre-flood at the 5-leaf stage
of rice growth approximately one month after planting.
Phosphorous and potassium were incorporated into the
soil under CT and were left at the surface under NT.
J. M. Motschenbacher et al. / Agricultural Sciences 2 (2011) 117-124
Copyright © 2011 SciRes. Openl y accessible at http://www.scirp.org/journal/AS/
Table 1. Summary of the N, P
2O5, and K2O added to corn,
soybean, rice, and wheat to comprise the sub-optimal and op-
timal soil fertility treatments in a long-term rotation study at
the RREC near Stuttgart, AR on a silt-loam soil.
Soil Fertility (kg·ha–1)
Crop Nutrient
Sub-Optimal Optimal
N 224 337
P2O5 67 90
K2O 112 168
N 0 0
P2O5 45 67
Soybean K2O 67 135
N 112 168
P2O5 45 67
Rice K2O 67 101
N 112 168
P2O5 34 67
Wheat K2O 34 67
Following nitrogen fertilization, a 5- to 10-cm deep
permanent flood was established, which was maintained
annually on all of the rice plots until the rice reached
physiological maturity. All other summer crops present
in a given year were furrow-irrigated on an as-needed
basis approximately 3 to 4 times annually, which was
effectively based on the amount of rainfall received and
the growth of the crop. Winter wheat was rain fed only
without irrigation.
Crop varieties included in the rotation treatment of
this study consisted of the maj or agronomic crops grown
in Arkansas. Crop rotations included: continuous rice (R),
rice-soybean (RS), soybean-rice (SR), rice-corn (RC),
corn-rice (CR), rice (winter wheat) [R(W)], rice (winter
wheat)-soybean (winter wheat) [R(W)S(W)], soybean
(winter wheat)-rice (winter wheat) [S(W)R(W)], rice-
soybean-corn (RSC), and rice-corn-soybean (RCS).
‘Wells’ was the rice cultivar grown based on its local
popularity among rice producers. Rice, soybean, and
wheat were sown into 19-cm rows in tillage treatments
using an Almaco NT drill (Almaco, Nevada, IA). The
rice was drill-seeded at a rate of 100 kg seed ha–1, soy-
bean at a rate of 56 kg seed ha–1, and wheat at a rate of
67 kg seed ha–1. Corn was planted in 76-cm rows at a
plant populat i o n of 79,040 seeds ha–1 [43].
Rice management practices closely followed the Uni-
versity of Arkansas Cooperative Extension Service rec-
ommendations for stand establishment, irrigation man-
agement, and pest management [44]. In CT plots, crop
residues were burned and incorporated into the soil gen-
erally one to two months following harvest by disking
twice. Prior to planting in the spring, plots were tilled by
disking once, followed by multiple passes of a light field
cultivator (i.e., Triple-K) to achieve the desired seedbed
for rice planting. In NT plots, crop residues were left on
the surface after harvest and were not manipulated by
any means prior to planting in the spring.
Weed management for rice [44], soybean [45], corn
[46], and wheat [47] followed recommendations made by
the Arkansas Cooperative Service. Weed management for
rice consisted of a pre-emergence application of 0.34
kg·ha–1 of clomazone [2-[(2-chlorobenzyl)methyl]-4, 4-
dimethyl-3-isoxaolidinone] and a post-emergent applica-
tion of halosulfuron [3-chloro-5-[[[[(4,6-dimethoxy-2-
1H-pyrazole-4-carcoxylic acid] at 0.06 kg·ha–1 for both
tillage treatmen ts. Soybean and corn were treated of 0.06
kg·ha-1 of glyphosate [N-(phosphonomethyl)glycine] in
the spring and applications of paraquat [1,1’-dimethyl-4,
4’-bipyridinium ion] and flumioxazin [2-[7-fluro-hydro-3
rahydro-1H-isoindole-1,3(2H)-dione] in the fall follow-
ing harvest and winter-wheat planting. Corn also received
a treatment of 2.3 L·ha–1 of glufosinate-ammonium [2-
amino-4-(hydroxymethylphosphinyl)butanoic acid mono-
ammonium salt] and 0.07 L·ha–1 of halosulfuron [3-
acid]. Wheat was treated with 0.35 L·ha–1 of mesosulfu-
ron-methyl [methyl 2-[[[[(4,6-dimethoxy-2-pyrimidinyl)
mino]methyl] benzoate].
At the time of soil sampling, the R an d R(W) rotations
had produced a total of 10 rice crops, the RS, SR, RC,
CR, R(W)S(W), and S(W)R(W) rotations had produced
five rice crops with five crops in the respective rotation
with corn or soybean, and the RSC and RCS rotations
had produced four rice crops with three crops in the re-
spective rotations with corn and soybean (Table 2). Fur-
thermore, the plots that were rotated with winter wheat
produced a total of 10 wheat crops. The CT treatment
was imposed on all plots five months (late-October 2008)
prior to soil BD sampling. Soil BD samples were col-
lected in mid-March 2009 from the 0- to 10- and 10- to
20-cm depth intervals using a 4.7-cm diameter, stainless
steel core chamber that was beveled to the outside to
minimize compaction upon sampling. One BD sample
was collected from each depth (0- to 10-cm and 10- to
20-cm) per plot at a random location between previously
planted rows, for a total of 320 samples. Soil samples
were oven-dried at 70˚C for 3 days and weighed to de-
termine soil BD by dividing the oven-dry soil mass by
the sample volume. After weighing, samples were grou nd
to pass a 2-mm mesh screen to determine SOM concen-
tration by wei g ht -l oss-on-ignition at 360˚C for 2 hours.
Though soil BD was not measured at the onset of the
study in spring 1999, land-leveling activities uniformly
affected the entire study area and 10 years of consistent
J. M. Motschenbacher et al. / Agricultural Sciences 2 (2011) 117-124
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Table 2. Summary of the crop rotations and the number of rice
crops and the respective rotations grown during the 10-yr study
period at the RREC near Stuttgart, AR on a silt-loam soil.
Crops in parentheses were grown during the winter.
Number of Crops
Rotation Rice Corn SoybeanWheat
Continuous Rice 10 - - -
Rice-Soybean 5 - 5 -
Soybean-Rice 5 - 5 -
Rice-Corn 5 5 - -
Corn-Rice 5 5 - -
Rice-(Wheat) 10 - - 10
Rice-(Wheat)-Soybean-(Wheat) 5 - 5 10
Soybean-(Wheat)-Rice-(Wheat) 5 - 5 10
Rice-Soybean-Corn 4 3 3 -
Rice-Corn-Soybean 4 3 3 -
management has elapsed. Therefore, it was reasonably
assumed that any observed differences in soil BD among
treatment combinations from the 2009 sampling repre-
sented actual treatment effects rather than residual ef-
fects from inherent differences among plots from the
beginning of the study.
The effects of tillage, fertility, crop rotation, soil dep th,
replication and their interactions on soil BD and SOM
were evaluated by analysis of variance (ANOVA) using
the Mixed Model procedure in SAS (version 9.2, SAS
Institute, Inc., Cary, NC). When appropriate, means were
separated using Fisher’s protected least significant dif-
ference (LSD) at the 0.05 level. In addition, linear cor-
relation analyses were conducted to identify the rela-
tionship between soil BD and SOM for each soil depth
interval separate and combined within rotation treat-
ments (version 13.31, Minitab, Inc., State College, PA).
After 10 years of consistent rotation and fertility
management and nine years of CT or NT, soil BD was
affected by all treatments evaluated in this study. Statis-
tical analyses showed that soil BD differed among till-
age-soil depth treatment combinations (P = 0.021; Table
3) and rotation-tillage-fertility treat ment combinations (P
= 0.002; Ta ble 3). There were no statistically significant
block effects caused by treatment replications, so all
interactions observed were exclusively a result of the
imposed treatments.
In the 0- to 10-cm depth interval, soil BD was 2.38%
greater (P = 0.021) under NT (1.29 g/cm3) than CT (1.26
g/cm3; Figure 1). Since SOM concentration did not dif-
fer between tillage treatments (Ta ble 3 ), the greater BD
near the soil surface under NT can be explained by the
Table 3. Analysis of variance summary of the effects of tillage,
soil fertility, crop rotation, and soil depth on soil bulk density
(BD) and soil organic matter content (SOM) during the 10-year
rotation study at the RREC near Stuttgart, AR on a silt-loam
Treatment Effectz BD SOM
_________ P _________
Tillage 0.229 0.110
Fertility 0.452 0.029
Tillage *Fertility 0.797 0.702
Rotation < 0.0010.333
Rotation *Tillage 0.020 0.613
Rotation *Fertility 0.995 0.792
Rotation *Tillage *Fertility 0.002 0.296
Depth 0.001 < 0.001
Depth *Tillage 0.021 0.081
Depth *Fertility 0.598 0.268
Depth *Rotation 0.160 0.050
Depth *Tillage *Fertility 0.767 0.530
Depth *Tillage *Rotation 0.301 0.215
Depth *Fertility *Rotation 0.969 0.078
Depth *Tillage *Fertility *Rotation 0.585 0.765
z Block effects were not significant in both analyses.
lack of soil loosening associated with annual tillage. As
would be expected, soil BD was greater in the 10- to 20-
than in the 0- to 10-cm depth interval under NT (Figure
1). However, in contrast to that expected, soil BD was
also greater in the 10- to 20- than in the 0- to 10-cm
depth interval under CT (Figure 1). Soil BD was similar
in the 10- to 20-cm depth interval between tillage treat-
ments, averaging 1.41 g/cm3 across both tillage treat-
ments (Figure 1). Though the 10- to 20-cm soil depth
interval typically has a greater clay content than in the
top 10 cm in the alluvial soils of the Mississippi River
Delta region of eastern Arkansas, and since soil BD has
been shown to be directly related to clay content [17], it
appears that the mixing of soil due to mechanical culti-
vation in CT was not substantial enough to eliminate
dissimilarities among depth intervals as expected. The
elevated BD in 10- to 20-cm depth interval in CT, in
relation to the top 10 cm, can be partially explained by
the presence of a prominent plow pan within the sam-
pled depth. A prominent plow layer of approximately the
10 cm depth is common throughout much of the row-
crop cultivated area in the Delta region of eastern Ar-
kansas due the long h istory of annual mechanical disrup-
tion by tillage [48]. The assumption of a plow pan pre-
sent in CT plots is consistent with previous observations
made in this same study in spring 2006, which showed
that CT had significantly greater penetration resistance
than to NT beginning at the 12.7-cm depth (P < 0.001)
and continuing through the 25.4-cm depth (P = 0.031)
A subsurface compacted layer can be created when
fine soil particles dispersed during tillage settle into
spaces of the soil matrix that were previously occupied
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Table 4. Crop rotation-soil depth treatment combination effects
on soil organic matter percentage averaged across tillage and
fertility treatments after 10 years of consistent management.
Crops included rice (R), soybean (S), corn (C), and winter
wheat (W). Soil depths included 0-cm to 10-cm and 10-cm to
Soil Organic Matter (%)a
Rotation 0-10 cm 10-20 cm
R 2.085 1.428
RS 1.952 1.533
SR 1.982 1.479
RC 2.152 1.473
CR 2.237 1.499
R(W) 2.388 1.528
R(W)S(W) 2.192 1.535
S(W)R(W) 2.201 1.469
RSC 2.117 1.446
RCS 1.984 1.478
Figure 1. Tillage and soil depth effects on soil bulk density
averaged across crop rotations and soil fertility levels after 10
years of consistent management. Tillage treatments included
no-tillage (NT) and conventional tillage (CT). Bars with dif-
ferent letters are significantly different at the 0.05 level. a.The least significan t difference at t he 0.05 l evel (LSD0.05) to co mpare
among different rotations at the same depth is 0.240. All values of the
same rotation with a different depth and different rotation with a dif-
ferent depth are significantly different.
by air, thus elevating soil BD. Furthermore, this subsur-
face compacting effect of the soil can be increased by
repeated machinery traffic [20] and prolonged flooded
conditions for rice production, which causes the slaking
of soil aggregates [49].
(1.38 g·cm–3) than NT (1.33 g·cm–3) in both soil fertility
regimes (Ta ble 5), which, as mentioned previously, may
presumably be caused by the settlement of fine soil par-
ticles as a result of soil disruption from tilla ge combined
with flooded growing conditions. This outcome suggests
that greater BD associated with negative effects on plant
growth and/or yield may have a greater tendency to de-
velop in time under CT than under NT regardless of soil
fertility regime. In addition, compared to contin uous NT
(R) (1.33 g·cm–3), soil BD was 3.00% greater in the NT
R(W) rotation (1.37 g·cm–3) under both soil fertility re-
gimes and SOM was greater in the R(W) rotation in the
0- to 10-cm depth (2.388%) under both tillage treatments
and fertility regimes than (R) (2.085%; Table 4). This
result demonstrates that, despite producing a greater
amount of aboveground residue in the R(W) rotation
compared to continuous rice due to twice the number of
high-residue-producing crops per year (Table 2), the
effects of greater surface SOM decreasing soil BD are
not quickly realized. However, with twice the number of
crops grown per year, the R(W) rotation also experi-
enced twice the number of machinery passes compared
to continuous rice, so the elevated BD in the R(W) rota-
tions may possibly be associated with compaction due to
machinery traffic. Furthermore, penetration resistance
data collected in 2006 showed that the R(W) rotation
had greater resistance in the 5- to 15-cm depth (ranging
from 2.5 to 4.4 MPa) than any other rotation in the study,
whereas the CR rotation had the lowest resistance
(ranging from 1.6 to 2.8 MPa) over the same depth
Another possible contribution to greater BD in 10-to
20-cm depth in both tillage treatments was likely related
to numerically lower SOM compared to the top 10 cm.
Similar to previous research [6,15], the SOM concentra-
tion was 43.17% greater in the 0- to 10- (2.129%) than
in the 10- to 20-cm depth (1.487%) when averaged
across all other treatment combinations (P < 0.001; Ta-
ble 3; Table 4). Although SOM concentration did not
differ significantly among tillage treatments, there was a
significant interaction effect between crop rotation and
sampling depth on SOM (P < 0.050; Tab le 3). Soil OM
differed among crop rotations in the top 10 cm, but was
similar among all crop rotations in the 10- to 20-cm
depth interval. Overall, soil BD magnitudes measured in
this study were well-below the typical 1.60 g/cm3
threshold at which root penetration has been reported to
become limited when the soil is dry [17]. The results of
this study were similar to those reported from a 3-yr
rice-wheat rotation in a sandy-loam soil in Ind ia [50 ] and
from a rice-rotation study in a clay-loam soil in India
Averaged across soil depth, soil BD also differed (P =
0.002) among rotation-tillage-fertility treatment combi-
nations (Table 3). However, few consistent trends
among treatment combinations and their effect on soil
BD existed. It is interesting to note that after 10 years of
continuous rice, soil BD was 3.76% greater under CT
Openly accessible at
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Ta b le 5 . Crop rotation-tillage-fertility treatment combination effects on soil bulk density averaged across soil depths after
10 years of consistent management. Crops included rice (R), soybean (S), corn (C), and winter wheat (W). Tillage treatments
included no-tillage and conventional tillage. Soil fertility treatments included optimal and sub-optimal.
Soil Bulk Density (g/cm3) a
No-Tillage Conventional Tillage
Optimal Sub-Optimal Optimal Sub-Optimal
R 1.32 1.35 1.37 1.39
RS 1.39 1.41 1.34 1.35
SR 1.36 1.36 1.32 1.34
RC 1.38 1.35 1.35 1.36
CR 1.31 1.36 1.33 1.30
R(W) 1.35 1.39 1.37 1.34
R(W)S(W) 1.40 1.37 1.35 1.39
S(W)R(W) 1.33 1.34 1.30 1.32
RSC 1.34 1.33 1.32 1.32
RCS 1.34 1.32 1.33 1.35
aThe least si g ni ficant differen ce at t h e 0.05 lev el ( LSD0.05) to compare among same tillage, same fertility, and different rotation combinations is 0.04.
The LSD0.05 to compare among same tillage, different fertility, and same rotation combinations is 0.04. The LSD0.05 to compare among different
tillage, same or different fertility, and same rotation combinations is 0.03. The LSD0.05 to compare among same tillage, different fertility, and differ-
ent rotation combinations is 0.07. The LSD0.05 to compare among different tillage, same or different fertility, and different rotation combinations is
interval [43]. The greater resistance in the R(W) was re-
ported to be caused from a lack of a strong, deep-penetra-
ting root system as is present in the CR rotation [43].
With the exception of in the CR rotation under NT,
where soil BD was greater with the sub-optimal than
with the optimal soil fertility regime, soil fertility regime
did not affect soil BD within tillage treatments in any
rotation (Table 5). Despite differences from the hy-
pothesized outcome of BD in relation to fertility level,
SOM concentration was 4.18% greater in optimal
(1.845%) than in the sub-optimal (1.771%) fertility re-
gime (P = 0.029). Soil BD within the same fertility re-
gime differed between tillage treatments in all rotations
except in the RC, S(W)R(W) and RCS rotations (Table
5). In contrast to that hypothesized, soil BD was unre-
lated to the number of times a rice or high-residue-
producing crop (i.e., rice, corn, and wheat; Table 2) was
grown over the 10-yr study period in either soil depth
interval separately or averaged across both soil depths.
However, as might be expected, SOM concentration was
highly correlated with the number of times a high-
residue-producing crop (i.e., rice, corn, and wheat; Table
2) was grown over the 10-yr study period in the top 10
cm (r = 0.89, P = 0.001) an d when averaged across bo th
soil depths (r = 0.90, P < 0.001).
This study demonstrated that after 10 years of consis-
tent management soil BD was slightly greater under NT
than CT in the top 10 cm, but soil BD was similar be-
tween NT and CT in the 10- to 20-in depth interval.
These results indicate that, despite BD values observed
in this study being lower than the common thresho ld BD
above which it is believed that root penetration is nega-
tively affected, an infrequent deep-tillage operation may
be needed to disrupt the developing zone of relatively
compacted soil below the plow layer under CT. This
study also demonstrated that soil BD differed among
common rice-based cropping systems, but that differ-
ences in near-surface soil BD were not clearly related to
the number of high-residue-producing crops, such as rice,
corn, and wheat, that were produced in a given time pe-
riod. The frequent cycling between relatively dry and
nearly to completely saturated soil conditions over the
course of the rice growing season likely contributes to a
more complex relationship between soil BD and residue
returned to the soil and/or SOM accumulation. It appears
that, even after 10 years of continuous CT or NT rice
production on a silt-loam soil in the Mississippi River
Delta region of eastern Arkansas, sub stantially increased
near-surface soil BD has not developed to the point
where soil compaction would be a likely culprit respon-
sible for potential early season stand establishment or
crop yield differences among rice-based copping sys-
This research was partially funded by the Arkansas Rice Research
and Promotion Board. Field assistance provided by Terry Sells and
Daniel McCarty is gratefully acknowledged.
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