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Soil & Tillage Research 82 (2005) 147–160
The effects of wheel-induced soil compaction on anchorage
strength and resistance to root lodging of winter barley
(Hordeum vulgare L.)
D.I. Scotta, A.R. Tamsa, P.M. Berryb, S.J. Mooneya,*
aDivision of Agriculture and Environmental Sciences, School of Biosciences,
University of Nottingham, University Park, Nottingham NG7 2RD, UKbADAS High Mowthorpe, Duggleby, Malton, North Yorkshire YO17 8BP, UK
Received 17 November 2003; received in revised form 7 June 2004; accepted 22 June 2004
Abstract
Lodging is the permanent displacement of cereal stems from the vertical. Cereal plants growing in the edge rows next to both
wheel tracks (‘tramlines’) and the gaps between experimental plots (‘inter-plot spaces’), which are traversed by farm vehicles
during planting operations and agrochemical application, are less prone to lodge than plants growing elsewhere in fields and
plots. Previous research has attributed this phenomenon to an increase in the stem strength of edge row plants, and hence their
resistance to stem lodging, resulting from reduced competition between edge row plants for resources. However, this explanation
gives no consideration to the anchorage strength of edge row plants, and hence their resistance to root lodging. Differences in soil
and plant characteristics between the edge and centre rows of plots of winter barley (Hordeum vulgare L.) were examined on
sand, silt and clay dominated soil types. Edge rows next to tramlines were investigated on the silt and clay soil types, whereas
edge rows next to inter-plot spaces were investigated on the sand soil type. Edge row plants next to both tramlines and inter-plot
spaces had 58.8% greater anchorage strength and hence resistance to root lodging than centre row plants. This was attributed to
(1) greater soil compaction in the edge rows resulting from wheel traffic in the tramlines and inter-plot spaces, which increased
the strength of the soil matrix surrounding the roots, and (2) greater plant root growth in the edge rows resulting from reduced
competition. Bulk density, root plate spread and structural rooting depth were 19, 22, and 12% greater, respectively, in the edge
rows of all soil types. The results suggest that in order to reduce lodging risk, energies should be directed towards identifying
agricultural practices that optimise soil compaction in the seedbed without causing significant limitations to root growth.
# 2004 Elsevier B.V. All rights reserved.
Keywords: Soil compaction; Root lodging; Winter barley; Bulk density; Soil strength
* Corresponding author. Tel.: +44 115 951 3199;
fax: +44 115 951 3251.
E-mail address: sacha.mooney@nottingham.ac.uk
(S.J. Mooney).
0167-1987/$ – see front matter # 2004 Elsevier B.V. All rights reserved
doi:10.1016/j.still.2004.06.008
1. Introduction
The permanent displacement of cereal stems from
their upright position is known as lodging (Pinthus,
.
D.I. Scott et al. / Soil & Tillage Research 82 (2005) 147–160148
1973). Lodging can occur by stem failure (stem
lodging) (Neenan and Spencer-Smith, 1975) or
anchorage failure (root lodging) (Crook and Ennos,
1993). It has been hypothesised that root lodging may
have become the most common form in wheat due to
the advent of varieties with shorter and more rigid
stems (Crook and Ennos, 1994). This may also be the
case for other cereal species, such as barley and oats.
Lodging is a significant problem for farmers because it
causes large reductions in grain yield and quality
(Fischer and Stapper, 1987; Easson et al., 1993) and
extensive costs to the UK farming industry (Berry et
al., 1998). The spatial distribution of lodging in
commercial fields is rarely uniform, and usually
occurs in the field margins before spreading to the
centre of the field. The plants next to wheel tracks
(‘tramlines’) caused by farm vehicles during the
application of agro-chemicals in commercial fields
almost always remain standing, even when plants
within the rest of the field have lodged (Berry et al.,
1998). Similar observations have also been made
within experimental plots where the plants growing in
the edge rows next to the gaps between adjacent
experimental plots (‘inter-plot spaces’) are less prone
to lodge than others and often remain standing when
the middle of the plot lies flat (Watson and French,
1971). As a result, edge rows are usually considered
atypical and discarded from an experiment rather than
used as material for study.
The mechanism by which plants next to tramlines
in commercial fields or on the edges of experimental
plots next to inter-plot spaces have a greater lodging
resistance than other plants has never been experi-
mentally determined. The reason proposed by Watson
and French (1971) to account for the increased lodging
resistance of edge row plants is that they produce
wider and stronger stems as a result of reduced
competition for nutrients and light. However, this
explanation accounts only for an increase in stem
strength and hence resistance to stem lodging. It gives
no consideration to the anchorage strength and hence
resistance to root lodging of edge row plants, which is
influenced by the characteristics of the roots and soil.
Subsequent research has shown that reducing compe-
tition between plants can increase their resistance to
both stem and root lodging by influencing their shoot
and root growth respectively (Easson et al., 1993,
1995; Berry et al., 1998, 2000). In addition to reduced
competition, a further factor that may contribute to the
root lodging resistance of edge row plants is the
difference in physical soil conditions in the edge rows
compared to elsewhere in a plot. Both tramlines and
inter-plot spaces experience wheel traffic by farm
vehicles during planting and post-planting operations
(Voorhees, 1992). Consequently soil in, and close, to
wheel tracks is usually more compact than elsewhere
in a field or plot (Smith, 1987; Rowell, 1994). Based
on a soil compaction model, Smith (1987) predicted
that compaction caused by wheel traffic is accom-
modated by both vertical and horizontal compression
of soil thus resulting in an increase in bulk density both
beneath and beside a wheel track. Therefore, plants
growing in edge rows beside wheel tracks grow in
more compact soil than plants growing elsewhere in a
plot (Voorhees, 1992). This may further influence their
anchorage strength and hence resistance to root
lodging.
There are two main ways by which soil compaction
can influence the anchorage strength of plants. Firstly,
soil compaction affects soil strength, which is an
integral component of all anchorage models for
cereals. Depending on the mechanism of root lodging,
soil strength affects either the resistance of the root–
soil bond to failure by axial or shearing root
movements (Ennos, 1989, 1991b; Easson et al.,
1995), or the resistance of the soil matrix to failure
by rotation of the root–soil cone (Crook and Ennos,
1993; Ennos et al., 1993). Secondly, soil compaction
affects root growth and thus the ability of root systems
to provide anchorage to a plant. Roots are generally
unable to penetrate pores narrower than their own
diameter (Lampurlanes and Cantero-Martınez, 2003).
Consequently, the decrease in macroporosity caused
by soil compaction can cause mechanical impedance
and subsequently morphological changes to plant root
systems (Barley, 1962, 1963; Wilson et al., 1977;
Goodman and Ennos, 1999). Morphological changes
can include a reduction in length, an increase in
diameter, and alterations in the pattern of lateral root
initiation. Such changes may adversely affect the
ability of root systems to perform functions, including
anchorage (Voorhees, 1992). However, Goodman and
Ennos (1999) showed that the positive effects of
increased soil strength on the anchorage strength and
resistance to root lodging of sunflower (Helianthus
annuus L.) and maize (Zea mays L.) outweighed any
D.I. Scott et al. / Soil & Tillage Research 82 (2005) 147–160 149
negative effects resulting from morphological and
mechanical responses of the root systems.
The aim of this study was to examine the
differences in soil and plant characteristics between
edge rows and centre rows of plots in order to provide
an insight into the factors that may contribute to the
increased resistance of edge row plants to root
lodging. Edge rows next to both ‘tramlines’ and
‘inter-plot spaces’ were investigated. Examination of
these factors will help current understanding of the
lodging process and identification of the traits of soils
and plants that confer strong anchorage in field
conditions, which at present are poorly understood.
The study will focus on winter barley (Hordeum
vulgare L.), which despite its extensive growth in the
UK has received little attention in the literature to date
with respect to lodging.
2. Materials and methods
2.1. Field Sites and experimental design
Winter barley (cv. Pearl) was grown at Bunny,
South Nottingham (52.58N 1.38W) on a sand soil
(Newport Series), ADAS Rosemaund, Hereford
(52.18N 2.48W) on a silty clay loam soil (Bromyard
Series), and ADAS Boxworth, Cambridge (52.28N0.08W) on a clay soil (Hanslope Series) over the 2002/
2003 growing year. Particle size distribution deter-
mined by laser diffractometry (McCave and Syvitski,
1991) and organic matter content determined by loss
on ignition (Rowell, 1994) are shown for each soil
type in Table 1. Plants at each site were sown in six
plots (24 m � 1.5 m) separated by inter-plot spaces at
seeding densities of 100 and 400 seeds m�2. Each plot
had 12 rows of plants and the inter-row distance was
12.5 cm. Three replicate plots of each seeding rate
Table 1
Particle size distribution and organic matter content of the Ap
horizon at Bunny (sand), ADAS Rosemaund (silty clay loam)
and ADAS Boxworth (clay)
Sand Silty clay loam Clay
Sand (%) 91.9 10.0 30.4
Silt (%) 7.6 65.0 34.9
Clay (%) 0.5 25.0 34.7
Organic matter (%) 3.4 4.8 8.6
were laid out in a randomised block design. Plots at
each site were cultivated and sown in mid-October
2002. At Bunny, edge rows next to ‘inter-plot spaces’
were investigated. Inter-plot spaces were 0.5 m wide
and ran parallel with the direction of drilling. Each
inter-plot space received a total of two tractor passes
during and immediately after drilling in autumn. At
ADAS Boxworth and ADAS Rosemaund, edge rows
next to ‘tramlines’ used by farm vehicles to apply
agro-chemicals were investigated. Tramlines were
0.5 m wide and ran perpendicular to the direction of
drilling. Each tramline received a total of nine passes
by farm vehicles between October and May. The
tractor ground pressure was approximately 83 kPa at
each site. Edge row plants were growing within a
distance of 5 cm from the edges of the inter-plot
spaces and tramlines. At all sites, the centre rows of
plots running parallel with the direction of drilling
were investigated starting at a minimum distance of
1 m from the tramline.
2.2. Measurement of soil characteristics
Bulk density (BD), total porosity (TP), penetration
resistance (PR) and volumetric water content (VWC)
of the Ap horizon were determined for the edge row
and centre row of each replicate plot. Metal cylinders
of 7.3 cm diameter and 5.2 cm depth (218 cm3) were
used to obtain three replicate undisturbed soil
cores from the edge and centre row of each repli-
cate plot for BD and TP determination from dry
weight and volume measurements (assuming particle
density = 2.65 g cm�3) (Rowell, 1994). PR (kPa) was
measured at 3.5 cm depth increments to a maximum
depth of 14 cm at three positions along the edge row
and centre row of each replicate plot using a bush cone
penetrometer. The penetrometer cone had a 12.8 mm
diameter and 308 tip angle. Three replicate VWC
measurements were made for the edge row and centre
row of each replicate plot using a thetaprobe (Delta-T
Devices Ltd., Cambridge). Six VWC measurements
were also taken at random locations at each site using
both the thetaprobe and bulk soil samples for oven
drying for calibration purposes. In addition, undis-
turbed samples were also collected from each soil type
to permit the determination of a water release curve.
Samples were equilibrated using a combination of
sand baths and pressure membrane apparatus at matrix
D.I. Scott et al. / Soil & Tillage Research 82 (2005) 147–160150
potentials of 0, �5, �10, �50, �100, �500, and
�1500 kPa.
2.3. Measurement of plant characteristics
Winter barley plants were sampled between cereal
growth stage (GS) 77 and GS 87 (Tottman, 1987) at all
sites. Three plants were removed from the edge and
centre row of each replicate plot and the roots of each
plant were recovered to a depth of 10 cm. The soil
surrounding the plant roots was left intact during
transit and storage to protect the roots from damage.
Plants were stored in a cool room at 12 8C for up to 10
days prior to analysis.
2.3.1. Resistance to root lodging
Resistance to root lodging was measured in the
field for three plants at both the edge rows and centre
rows of each replicate plot using a specially designed
lodging instrument based on that described by Ennos
(1991b). The lodging instrument consisted of a
Mecmesin Smart torque cell (maximum torque
3 N m) fitted with a lodging attachment comprising
a metal rod and a handle capable of rotating both the
torque cell and lodging attachment up to 1358 from the
vertical. The lodging attachment applied a force to a
plant at a height of 105 mm from the plant base, with a
centre of rotation at 55 mm from the plant base.
Rotation of the lodging attachment by 1358 displaced
the plant to 618 from the vertical. As the plant was
rotated, the maximum torque (N m) required to
overturn the plant (‘maximum torque resistance’)
was recorded using a Mecmesin Advanced Force/
Torque Indicator (AFTI) (maximum load 250 N)
(Mecmesin Ltd., Slinfold). Each test took approxi-
mately 60 s equating to a rotational velocity of
618 min�1.
2.3.2. Shoot and root measurements
The number of fertile shoots per plant was
recorded. Plant root systems were soaked in water
so that the soil could be removed without damaging
the anchorage roots. Root plate spread (mm) and
structural rooting depth (mm) were recorded for each
plant using the rhizosheath method described by Berry
et al. (2000) for winter wheat. Individual roots
emanating from the stem base of each plant were
removed and stored in water at 12 8C for up to 10 days
prior to image analysis using WinRHIZO (Regent
Instruments Inc., Quebec). Seminal roots emanating
from the seed were not included, as these play no part
in anchorage of the mature plant (Ennos, 1991a).
Washed roots were spread out in about 10 mm depth of
water in a scanner tray. A two-D scanner was used to
acquire a digital image of the roots from which root
length was measured as a function of root diameter.
Ten root diameter classes in 0.5 mm increments were
defined ranging from <0.5 mm to >4.5 mm.
2.4. Statistical analysis
Analysis of variance (ANOVA) procedures for a
fully randomised split-split plot design were used
within Genstat 6 software (Lane and Payne, 1996) to
test for significant differences between treatments and
to calculate the standard errors of the differences
(S.E.D.s). Soil type formed the main plots, seeding
rate formed the sub-plots and row (edge or centre)
formed the sub-sub plots.
3. Results
3.1. Soil characteristics
Bulk density (BD) in the upper 5 cm of the Ap
horizon was significantly greater (P < 0.001) in the
edge rows of plots than in the centre rows (Table 2).
The difference in mean BD between rows for all soil
types was 0.23 g cm�3 indicating that the mean BD in
the edge rows of plots was 18.5% greater than in the
centre rows as a result of wheel traffic in the inter-plot
spaces. The largest difference in BD between rows
was observed in the silty clay loam (0.34 g cm�3) and
the smallest in the sand (0.14 g cm�3) indicating BD
increases in the edge rows of 26.9 and 10.8%
respectively. Similarly, there were significant differ-
ences between the edge and centre of rows for TP,
ranging between 0.13 in the silty clay loam and 0.06 in
the sandy soil. Field measured VWC was significantly
higher (P < 0.01) in the edge rows than in the centre
rows of plots in both the sand and clay, however the
opposite was observed in the silty clay loam (Table 2).
The mean difference in VWC between rows for all soil
types was small (0.01 cm3 cm�3) with the largest
difference in the clay (0.03 cm3 cm�3) and the
D.I. Scott et al. / Soil & Tillage Research 82 (2005) 147–160 151
Table 2
Bulk density (BD), total porosity (TP) and volumetric water content (VWC) of the upper 5 cm for the centre and edge rows of plots in different
soil types
Row BD (g cm�3) TP VWC (cm3 cm�3)
Centre Edge Centre Edge Centre Edge
Sand 1.31 1.45 0.51 0.45 0.12 0.13
Silty clay loam 1.27 1.61 0.52 0.39 0.20 0.19
Clay 1.12 1.31 0.58 0.51 0.38 0.41
P-values
Soil type (2 d.f.) P < 0.001 P < 0.001 P < 0.001
Row (1 d.f.) P < 0.001 P < 0.001 P < 0.01
Soil type � Row (2 d.f.) P < 0.01 P < 0.01 P < 0.001
S.E.D.s
Soil type 0.017 (4 d.f.) 0.007 (4 d.f.) 0.003 (4 d.f.)
Row 0.021 (12 d.f.) 0.008 (12 d.f.) 0.003 (12 d.f.)
Soil type � Row 0.031 (16 d.f.) 0.01 (16 d.f.) 0.005 (11 d.f.)
smallest in the sand (0.01 cm3 cm�3). During sam-
pling, the clay soil type was near saturation and the
sand was close to field capacity. In contrast, the VWC
of the silty clay loam was at less than field capacity.
Penetration resistance (PR) measurements recorded in
the Ap horizon (0–14 cm depth) were significantly
greater (P < 0.001) in the edge rows of plots than in
the centre rows (Fig. 1). This was observed in each soil
type throughout the depth profile, with the exception
of the upper 3.5 cm depth and at 14 cm depth in the
sand soil type where PR was slightly greater in the
centre rows (Fig. 1a). The difference in mean PR
between rows for the whole depth profile of all soil
types was large (10.3 kPa) with the greatest difference
in the silty clay loam (22.3 kPa) and the smallest in the
sand (0.69 kPa). PR increased significantly with depth
in each row and soil type (Fig. 1). The differences in
PR between rows were greatest at depths of 7 cm in the
silty clay loam (Fig. 1b) and clay (Fig. 1c) soil types,
and at 10 cm in the sand soil type (Fig. 1a). The
smallest differences in PR between rows occurred at
depths of 3.5 cm in the sand (Fig. 1a) and silty clay
loam (Fig. 1b) and at 14 cm in the clay (Fig. 1c). There
were no significant differences in soil characteristics
between plots sown at different seeding rates.
The gross differences in the porous environments
of the three soils can be seen from their water release
characteristics (Fig. 2). At saturation, the clay soil
clearly had the greatest water retention
(0.54 cm3 cm�3), whereas the sand and silty clay
loam behaved similarly (ca. 0.45 cm3 cm�3). These
differences were still evident at field capacity
(�5 kPa) which illustrated significantly more water
was retained in the clay soil in comparison to the silty
clay loam and sand soil. As expected, the loss of water
between field capacity and permanent wilting point
(�1500 kPa) was considerably greater in the sand soil
(water loss = 0.24 cm3 cm�3), in contrast to the clay
and silty clay loam soils, which had water losses of
0.12 and 0.13 cm3 cm�3 respectively.
3.2. Plant characteristics
The proportion of seeds drilled that established
plants was always greater at the low seed rate. The
percentage establishment for the low and high seed
rates respectively were 96 and 80% at Bunny, 78 and
65% at ADAS Rosemaund and 52 and 36% at ADAS
Boxworth. Previous seed rate experiments have also
observed lower establishment for high seed rates
(Whaley et al., 2000).
3.2.1. Resistance to root lodging
During rotation of plants from 08 to 618 from the
vertical, movement centred around the base of the
plant with the root system moving through the soil and
there was only limited bending of the stems. On
removal of the force applied by the lodging instru-
ment, plants recovered somewhat but still leaned at an
angle of ca. 20–308 from the vertical indicating that
anchorage failure had occurred. Plants growing in the
edge rows of plots had a significantly higher
D.I. Scott et al. / Soil & Tillage Research 82 (2005) 147–160152
Fig. 1. Penetration resistance (kPa) measured at 3.5 cm depth increments in the centre rows and edge rows of plots in the sand (a), silty clay loam
(b), and clay (c) soil types. Error bars indicate �1 standard error of the mean.
(P < 0.001) mean maximum torque resistance
(2.329 N m) than plants growing in the centre rows
(1.370 N m). The maximum torque resistance for
plants was not significantly different across soil types
and seeding rates. There was a significant positive
relationship between BD (and TP) and maximum
torque resistance of plants (P < 0.001), with a linear
regression accounting for 45, 72, and 74% of variation
between the parameters in the sand, silty clay loam
and clay soil types respectively (Fig. 3). Furthermore,
there was a significant positive relationship between
PR at 7 cm depth and maximum torque resistance of
plants (P < 0.001), with a linear regression account-
ing for 72 and 65% of variation between the
parameters in the silty clay loam and clay soil types
respectively (Fig. 4). However, there was no positive
relationship between these parameters in the sand soil
type.
3.2.2. Shoot and root measurements
Plants growing in the edge rows of plots had a
significantly greater number of shoots (P < 0.001)
D.I. Scott et al. / Soil & Tillage Research 82 (2005) 147–160 153
Fig. 2. Water release curve of the three soil types examined.
than those growing in the centre rows (Table 3). Also,
plants established at 100 seeds m�2 had a significantly
greater number of shoots (P < 0.01) than those
established at 400 seeds m�2 (Table 3). The difference
in shoot numbers per plant between rows was
significantly different between seeding rates
(P < 0.05), with the largest difference between the
edge and centre rows occurring at 100 seeds m�2
(Table 3). Shoot numbers per plant were also
significantly different between soil types (P < 0.05),
with the greatest number of shoots recorded for plants
growing in the silty clay loam soil type, and the
smallest number of shoots recorded for plants in the
sand soil type (Table 3). Each plant had a large number
of adventitious roots emanating from the base of the
stems and extending outwards before bending down-
wards to form an inverted cone. Each adventitious root
had a thick basal region with a dense covering of root
hairs attached to a rhizosheath of soil. The distal
portions of the adventitious roots were well branched
with large numbers of fibrous roots. Plants growing in
the edge rows of plots had a significantly greater root
plate spread (P < 0.001) and structural rooting depth
(P < 0.001) than plants growing in the centre rows
(Table 4). Both root plate spread and structural rooting
depth were also significantly greater for plants
established at 100 seeds m�2 compared to those
established at 400 seeds m�2 (P < 0.01), and for
plants growing in the clay soil type, compared to those
growing in the sand and silty clay loam soil types
(P < 0.01) (Table 4). The differences in root plate
spread and structural rooting depth between rows were
consistent across the soil types and seeding rates.
Total root length per plant increased with an
increase in shoot numbers per plant in each soil type
and seeding rate (Table 3). Plants growing in the edge
rows of plots had a significantly greater (P < 0.001)
total root length than plants growing in the centre rows
(Table 3). Total root length was also significantly
greater for plants established at 100 seeds m�2
compared to those established at 400 seeds m�2
(P < 0.001), and for plants growing in the clay soil
type, compared to those growing in the sand and silty
clay loam soil types (P < 0.05) (Table 3). The
differences in total root length per plant between
rows were consistent across seeding rates and soil
types. The diameter of plant roots ranged between
<0.5 mm to >4.5 mm, however only very short root
lengths were recorded in diameter classes >2 mm and
so these were combined to form a single diameter
class. Edge row plants had a significantly greater root
length in each diameter class (P < 0.001) than centre
row plants. An exception to this was observed for the
length of roots with a diameter >2 mm in the clay soil
type (Fig. 5c). The differences in root length in each
diameter class between rows were consistent across
seeding rates, however significantly different between
soil types (P < 0.001) (Fig. 3). The differences in root
length in each diameter class between rows were
larger in the sand (Fig. 5a) and silty clay loam (Fig. 5b)
D.I. Scott et al. / Soil & Tillage Research 82 (2005) 147–160154
Fig. 3. Relationships between bulk density (g cm�3) and maximum torque of plants (N m) in the (a) sand (y = �2.69 + 3.45x; R2 = 0.45), (b)
silty clay loam (y = �3.16 + 3.45x; R2 = 0.72), and (c) clay (y = �2.49 + 3.45x; R2 = 0.74) soil types.
soil types than in the clay soil type (Fig. 5c). The
greatest differences in root length between rows in
each soil type were observed for roots in the diameter
classes ranging 0–1.5 mm, whereas much smaller
differences were observed for roots with a diameter
>1.5 mm (Fig. 5). Plants growing in the edge rows had
a significantly smaller mean root diameter than centre
row plants (P < 0.001) (Table 3), reflecting their
greater proportion of thin roots (Fig. 3). Mean root
diameter was significantly different between soil types
(P < 0.001), with the largest values recorded in the
silty clay loam and the smallest in the sand (Table 3).
The differences in mean root diameter between rows
were also significantly larger in the silty clay loam
compared to the sand and clay soil types (P < 0.001)
(Table 3).
4. Discussion
The measurements of maximum torque resistance
indicated that plants growing in the edge rows of plots
had greater anchorage strength and hence resistance to
root lodging than plants growing in the centre rows.
D.I. Scott et al. / Soil & Tillage Research 82 (2005) 147–160 155
Fig. 4. Relationships between penetration resistance (kPa) measured at 7 cm depth and maximum torque of plants (N m) in the (a) silty clay
loam (y = 0.17 + 0.04x; R2 = 0.72), and (b) clay (y = 0.59 + 0.04x; R2 = 0.65) soil types.
Table 3
Shoot numbers per plant, total root length and mean root diameter for plants with different treatments of soil type, seed rate and row
Treatment Shoots per plant Total root length (cm) Mean root diameter
(mm)
Centre Edge Centre Edge Centre Edge
Sand 4.3 7.5 366 637 0.61 0.59
Silty clay loam 7.2 13.6 299 565 1.30 1.02
Clay 7.1 9.8 758 861 0.77 0.74
400 Seeds m�2 4.5 7.3 306 437 0.88 0.80
100 Seeds m�2 7.9 13.3 644 938 0.90 0.77
P-values
Soil type (2 d.f.) P < 0.05 P < 0.05 P < 0.001
Seed rate (1 d.f.) P < 0.01 P < 0.001 NS
Row (1 d.f.) P < 0.001 P < 0.001 P < 0.001
Soil type � row (2 d.f.) NS NS P < 0.001
Seed rate � row (1 d.f.) P < 0.05 NS NS
Soil type � seed rate � row (2 d.f.) NS NS NS
S.E.D.s
Soil type (4 d.f.) 0.77 66.4 0.048
Seed rate (6 d.f.) 1.00 149.5 0.031
Row (12 d.f.) 0.60 39.0 0.021
Soil type � row 1.06 (11 d.f.) 81.8 (9 d.f.) 0.054 (6 d.f.)
Seed rate � row 1.16 (10 d.f.) 154.5 (7 d.f.) 0.037 (11 d.f.)
Soil type � seed rate � row 1.78 (18 d.f.) 206.1 (9 d.f.) 0.071 (14 d.f.)
D.I. Scott et al. / Soil & Tillage Research 82 (2005) 147–160156
Table 4
Root plate spread and structural rooting depth for plants with
different treatments of soil type, seed rate and row
Treatment Root plate
spread (mm)
Structural rooting
depth (mm)
Sand 37.6 37.4
Silty clay loam 40.9 44.9
Clay 52.6 53.2
400 Seeds m�2 39.4 40.9
100 Seeds m�2 48.0 49.5
Centre Row 39.5 42.6
Edge Row 48.0 47.8
P-values
Soil type (2 d.f.) P < 0.01 P < 0.01
Seed rate (1 d.f.) P < 0.01 P < 0.01
Row (1 d.f.) P < 0.001 P < 0.01
Soil type � seed
rate � row (2 d.f.)
NS NS
S.E.D.s
Soil type (4 d.f.) 2.37 2.56
Seed rate (6 d.f.) 2.20 1.74
Row (12 d.f.) 1.87 1.55
Soil type � seed rate � row 4.83 (21 d.f.) 4.27 (18 d.f.)
An examination of the differences in soil and plant
characteristics between rows suggests that there were
two main differences contributing to this increased
anchorage strength. These include (1) greater BD and
PR, and reduced TP in the edge rows resulting from
compaction, and (2) greater plant root growth in the
edge rows resulting from reduced competition. The
extent to which increased BD and PR contributed to the
enhanced anchorage strength of edge row plants may
have been greater in the edge rows next to tramlines than
those next to inter-plot spaces. This is indicated by the
smaller differences in BD, TP and PR between rows at
Bunny, where edge rows next to inter-plot spaces were
investigated, than at ADAS Boxworth and ADAS
Rosemaund, where edge rows next to tramlines were
investigated, despite the difference in anchorage
strength between rows remaining the same across all
sites. Importantly, the results indicate that the greater
lodging resistance of edge row plants is caused by
greater anchorage in addition to greater stem strength as
suggested by Watson and French (1971).
The greater BD and PR in the edge rows is
attributed to compaction caused by wheel traffic in the
tramlines and inter-plot spaces during planting
operations and agro-chemical application, which
causes horizontal compression of soil either side of
the wheel track (Smith, 1987; Rowell, 1994). The
greater differences in BD and PR between rows where
edge rows next to tramlines were investigated, than
between rows where edge rows next to inter-plot
spaces were investigated, can be attributed to the seven
additional vehicle passes received by the tramlines
compared to the inter-plot spaces.
Compaction decreases the volume, size and
continuity of pores in the soil (Hillel, 1998). The
water release data (Fig. 2) supports the BD and TP
results with respect to the differences described
between the soil types. The main difference between
the three soil types was observed at high tensions
(micropores) where the sandy soil retained signifi-
cantly less water than the clay and silty clay loam
soils. This suggests that in addition to number of
tractor passes, the porous architecture of a given soil
texture has an important role in determining the nature
of the compaction mechanism since the soil types with
the greatest differences were also those with the
highest percentage of micropores (clay from ADAS
Boxworth and silty clay loam from ADAS Rose-
maund).
Importantly, changes in porosity resulting from
compaction increase the degree of contact between
plant roots and soil (Lampurlanes and Cantero-
Martınez, 2003). A reduction in pore size and
continuity increases the probability that plant roots
will encounter and penetrate soil aggregates thus
creating new root channels in which they will have
complete contact with the surrounding soil matrix
(Kooistra et al., 1992). An increase in root–soil contact
in the edge rows caused by soil compaction is likely to
increase the strength of the root–soil bond, which is
considered to be an important point of failure during
root lodging (Ennos, 1989, 1990; Easson et al., 1995).
Whilst the degree of root–soil contact was not
measured in this study, the positive relationships
between BD and maximum torque of plants in each
soil type (Fig. 3) suggest that this may be the case.
The differences in PR between edge and centre
rows indicate that wheel traffic influenced the soil
conditions in the edge rows to a depth of at least
14 cm. These differences were greatest at depths of
either 7 or 10.5 cm in each soil type (Fig. 1), which
correspond closely with the structural rooting depth of
plants growing in the edge rows (Table 4). This
D.I. Scott et al. / Soil & Tillage Research 82 (2005) 147–160 157
Fig. 5. Root length as a function of diameter for plants growing in the centre rows and edge rows of experimental field trial plots in the sand (a),
silty clay loam (b), and clay (c) soil types. Error bars indicate �1 standard error of the mean.
indicates that the soil matrix beneath the root plate of
plants growing in the edge rows had higher shear
strength than in the centre rows (Hillel, 1998). The
mechanism of root lodging in winter wheat (Crook
and Ennos, 1993) and maize (Ennos et al., 1993)
involves the rotation of a cone of rigid coronal roots at
its windward edge below the soil surface, the soil
inside the cone moving as a block and compressing the
soil beneath. If the mechanism of root lodging in
winter barley is similar to that of winter wheat and
maize, the stronger soil beneath the root plate of edge
row plants will be more resistant to plastic deforma-
tion under compression by the root–soil cone, hence
increasing anchorage strength. Evidence of this is
provided by the positive relationships between PR at
7 cm depth and maximum torque resistance of plants
in the silty clay loam and clay soil types (Fig. 4). The
absence of a positive relationship between the two
parameters in the sand soil type is probably due to the
small difference in PR between the edge and centre
rows at this site (Fig. 1). This reflects the smaller
number of vehicle passes received by the inter-plot
spaces (two vehicle passes) compared to the tramlines
(9 vehicle passes).
D.I. Scott et al. / Soil & Tillage Research 82 (2005) 147–160158
The greater number of shoots recorded for edge row
plants (Table 3) has previously been attributed to their
ability to obtain more nitrogen from the soil as a result
of reduced competition (Watson and French, 1971).
However, enhanced shoot growth in the edge rows is
unlikely to contribute directly to the increased lodging
resistance of edge row plants. This is because greater
shoot numbers per plant increase the leverage force
that the aerial parts of the plant exert on the plant base
to cause lodging (Berry et al., 2000). Instead,
increased shoot growth may indirectly increase the
lodging resistance of edge row plants by increasing the
number of roots and hence anchorage strength
(Pinthus, 1973). This is indicated by the close
relationship between shoot numbers per plant and
total root length observed in this study (Table 3).
Importantly, the greater root length in each diameter
class in the edge rows (Fig. 5) indicated that the extent
of soil compaction in the root zone was not sufficient
to limit the growth of winter barley roots. Conse-
quently, edge row plants were able to establish
extensive, adventitious root systems despite growing
in more compact soil. This is supported by research
into minimal and no tillage systems, which has shown
that plant roots can continue to extend into moderately
compacted soil that has received little or no
cultivation. Finney and Knight (1973) demonstrated
that direct drilling into uncultivated, and thus more
compact soil, had no effect on the number, elongation
and diameter of adventitious roots of winter wheat
compared to plants grown in loose ploughed soil.
Similarly, Crook (1994) showed that compaction of
the seedbed did not affect the length, number and
bending strength of the adventitious roots of winter
wheat. According to Lampurlanes and Cantero-
Martınez (2003), the unrestricted extension of plant
roots in moderately compact soil reflects their ability
to grow in the inter-aggregate spaces, provided that the
soil is reasonably well structured or has preserved
biochannels such as in non-tilled soils.
The use of the rhizosheath as an indicator of root
plate spread and structural rooting depth, as described
by Berry et al. (2000) for winter wheat, also proved
suitable for winter barley. The rhizosheath for winter
barley roots was more difficult to identify than
suggested by Berry et al. (2000) for winter wheat due
to the greater lateral branching of the adventitious
roots of winter barley with fibrous roots. However,
most roots of individual plants had a similar length of
rhizosheath, thus reducing the uncertainty in the
measurements. If the anchorage model developed by
Crook and Ennos (1993) for winter wheat is
appropriate for winter barley, the greater root plate
spread of edge row plants suggests that they have a
larger resisting moment to overturning than centre row
plants. Furthermore, the greater structural rooting
depth of edge row plants suggests that they require
more rainfall to reduce the strength of the soil
surrounding their anchorage roots than centre row
plants (Baker et al., 1998). The significantly greater
values recorded for root plate spread and structural
rooting depths in the clay soil type were probably
caused by the low proportion of plants established at
ADAS Boxworth. Edge row plants also had 98.6, 74.8
and 16.7% greater lengths of roots with a diameter of
0.5 mm or more than centre row plants in the sand,
silty clay loam, and clay soil types respectively. It has
been shown that an increase in the diameter of winter
wheat roots increases both their bending strength
(Crook and Ennos, 1993) and tensile strength (Easson
et al., 1995). Whilst these mechanical properties were
not measured in this study for winter barley roots, it is
expected that edge row plants have a higher proportion
of stronger roots than centre row plants reflecting their
greater proportion of thicker roots. This has been
shown to be an important characteristic of root
systems increasing anchorage strength for a variety of
plant species (Ennos, 1989, 1991b; Ennos et al., 1993;
Crook and Ennos, 1993).
Reduced seeding rate and subsequent reduced
competition between plants increased both shoot and
root growth of winter barley as reported by other
authors for winter wheat (Easson et al., 1993, 1995;
Berry et al., 2000). Surprisingly, reducing the seeding
rate had no significant effect on torque measurements
and hence anchorage strength. This may reflect an
increase in the variability of torque measurements
between seeding rates due to the inclusion of
measurements taken for plants growing in the edge
rows of plots.
5. Conclusion
Plants growing next to tramlines used by farm
vehicles during the application of agro-chemicals in
D.I. Scott et al. / Soil & Tillage Research 82 (2005) 147–160 159
commercial fields almost always remain upright, even
when the rest of the field has lodged. Similar patterns
have also been observed within experimental plots
where plants growing in the edge rows next to inter-
plot spaces used by farm vehicles during planting
operations are less prone to lodge than plants within
the middle of the plot. Previous research has attributed
the increased lodging resistance of edge row plants
solely to an increase in stem strength resulting from
reduced competition between edge row plants for
nutrients and light. This study provides evidence that
the increased lodging resistance of winter barley
(Hordeum vulgare L.) growing in the edge rows of
plots, 5 cm from the edges of both tramlines and inter-
plot spaces, is also likely to reflect an increase in
anchorage strength caused by two contributing factors.
These factors include (1) greater soil compaction in
the edge rows resulting from wheel traffic in the
tramlines and inter-plot spaces, and (2) greater plant
root growth in the edge rows resulting from reduced
competition. Importantly, the extent of soil compac-
tion recorded in the edge rows next to both tramlines
and inter-plot spaces was moderate and insufficient to
cause significant limitations to root growth and hence
anchorage strength. Instead, soil compaction is
thought to have increased the anchorage strength of
edge row plants by increasing the strength of the soil
matrix surrounding the anchorage roots. The extent to
which soil compaction contributed to the enhanced
anchorage strength of edge row plants may have been
greater in the edge rows next to tramlines than in the
edge rows next to inter-plot spaces. This was attributed
to the greater number of vehicle passes received by the
tramlines (nine vehicle passes) compared to the inter-
plot spaces (two vehicle passes). This study indicates
that in order to reduce lodging risk, energies should be
directed towards identifying more suitable agricultural
practices that can optimise soil compaction in the
seedbed without causing significant limitations to root
growth. Such practices may include minimum or no
tillage methods, as opposed to traditional tillage
methods that involve loosening of the seedbed to
minimise soil compaction. Also, rolling the soil after
drilling or any time up to the beginning of stem
extension has been shown to increase soil shear
strength (Berry et al., 2002). Furthermore, this study
provides experimental data to complement current
research into modelling of the lodging process (Baker
et al., 1998; Berry et al., 1998), which is being used to
identify the relative importance of different soil and
plant characteristics in affecting the risk of lodging in
field conditions.
Acknowledgments
The use of the field sites at ADAS Boxworth and
Rosemaund is gratefully acknowledged. The technical
assistance of Melanie King from the University of
Nottingham is also duly acknowledged.
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