Directory UMM :Data Elmu:jurnal:S:Soil & Tillage Research:Vol52.Issue3-4.Oct1999:
Soil & Tillage Research 52 (1999) 177±189
Soil and residue management effects on arable
cropping conditions and nitrous oxide ¯uxes
under controlled traf®c in Scotland
1. Soil and crop responses
B.C. Ball*, R.M. Ritchie
Environmental Division, SAC, West Mains Road, Edinburgh, EH9 3JG, UK
Received 16 February 1999; received in revised form 21 July 1999; accepted 5 August 1999
Abstract
Soil compaction can affect crop growth and greenhouse gas emission and information is required of how both these aspects
are affected by compaction intensity and weather. In this paper we describe treatments of compaction intensity and their
effects on soil physical conditions and crop growth in loam to sandy loam cambisol soils. Soil conditions and crop
performance were measured over three seasons in a ®eld experiment on soil compacted by wheels on freshly ploughed
seedbeds. Ploughing buried the chopped residues of the previous crop. After ploughing, traf®c was controlled such that the
experimental plots received wheel traf®c only as treatments. The overall objective was to discover how the intensity and
distribution of soil compaction just before sowing in¯uenced crop performance, soil conditions and emissions of nitrous oxide.
Compaction treatments were zero, light compaction by roller (up to 1 Mg mÿ1) and heavy compaction by loaded tractor, (up
to 4.2 Mg). The experiment was located at Boghall, near Edinburgh (860 mm average annual rainfall) for the ®rst two seasons
under spring and winter barley (Hordeum vulgare L.) and in a drier area at North Berwick (610 mm average annual rainfall)
for the third season under winter oil-seed rape (Brassica napus L.). Heavy compaction in dry soil conditions had little effect on
crop growth. However, in wet conditions heavy compaction reduced air porosity, air permeability and gas diffusivity, increased
cone resistance and limited winter barley growth and grain yield. Heavy compaction in wet conditions reduced winter barley
yields to 7.1 Mg haÿ1, in comparison to 8.8 Mg haÿ1 in the zero compaction treatment. The compaction status of the top
15 cm of soil seemed to be particularly important. Loosening of the top 10 cm of soil immediately after heavy compaction
restored soil conditions for crop growth. However, zero seed bed compaction gave patchy and uneven crop emergence in dry
conditions. Both zero and light compaction to a target depth of 10 cm gave similar crop productivity. Maintenance of a correct
compaction level near the soil surface is particularly important for establishment and overwintering of barley and oil seed
rape. # 1999 Elsevier Science B.V. All rights reserved.
Keywords: Compaction; Residues; Barley; Soil
*
Corresponding author. Tel.: 44-131-535-4392; fax.: 44-131-667-2601
E-mail address: [email protected] (B.C. Ball)
0167-1987/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved.
PII: S 0 1 6 7 - 1 9 8 7 ( 9 9 ) 0 0 0 8 0 - X
178
B.C. Ball, R.M. Ritchie / Soil & Tillage Research 52 (1999) 177±189
1. Introduction
Considerable effort has been devoted to evaluating
the effects of wheel traf®c on soil properties and crop
growth (Soane and van Ouwerkerk, 1994). Management systems which completely eliminate traf®c or
which permit a reduction in ground pressure on the
crop growing area give more favourable soil conditions and, often, better crop growth and yield than
conventional systems (Chamen et al., 1992; Dickson
and Ritchie, 1996). Extensive compaction before sowing is particularly damaging to soil structure and
subsequent crop growth (Campbell et al., 1986; Bakken et al., 1987; McAfee et al., 1989). Tractor traf®c
on wet soil can also increase denitri®cation by a factor
of 3±4 (Bakken et al., 1987). The presence of straw
residues, particularly in compacted soil, can also
contribute to waterlogging, nitrous oxide (N2O) production and reduced crop survival over winter (Ball
and Robertson, 1990). Reduced or no-tillage systems
can also increase N2O production (Aulakh et al.,
1984), particularly in the presence of straw residues
(Ball and Robertson, 1990). Nitrous oxide production
represents a loss of nutrient from the system and
contributes to global warming and the destruction
of stratospheric ozone (Crutzen, 1970). Indeed, the
signi®cance of arable agricultural soils as a source of
N2O may have been underestimated (Beauchamp,
1997).
Recent work on the in¯uence of tillage and compaction in Scotland under arable cropping and controlled traf®c conditions has involved chisel ploughing
and reduced or no-tillage (Campbell et al., 1986;
Dickson and Ritchie, 1996). These techniques are
rarely used in practice and the experiments conducted
did not include measurements of gaseous losses of
nitrogen. There is a need to consider how normal soil
management techniques involving mouldboard
ploughing can create soil conditions which suit crop
growth but which also minimise losses of nitrogen,
particularly as N2O. In the UK, crop residues are
increasingly incorporated in the soil, partly due to
legal restrictions of straw burning. Since the in¯uence
of residues on denitri®cation under different tillage
systems has been associated with compaction (Ball
and Robertson, 1990), the interactions of residue
incorporation, soil compaction and nitrous oxide
emission require assessment.
Our objective was to determine which soil properties in¯uenced crop growth in response to different
compaction intensities and depths. This then permits
identi®cation of the optimum level of seedbed compaction (including zero) after normal ploughing of
residues, which gives the best cropping conditions
whilst minimising the losses of nitrogen as N2O.
No-tillage was included as a reference treatment. This
paper reports the treatments and the soil and crop
responses. A subsequent paper reports on the nitrous
oxide emissions and the soil nitrogen status (Ball et al.,
1999).
2. Methods and materials
2.1. Location, soil and weather
The ®eld experiment was located at two sites. The
®rst, at Boghall, 10 km south of Edinburgh, contained
spring barley in 1995 and winter barley in 1995/6. The
second site, 3 km south of North Berwick, contained
winter oil-seed rape in 1996/7. The average annual
rainfall near Boghall is 880 mm and near North
Berwick is 611 mm. In addition, monthly rainfalls
at weather stations close to each site are given in
Table 1. The ®rst site was on Macmerry series (Cambisol in FAO classi®cation) and the second site was on
Kilmarnock series (Gleyic Cambisol). Macmerry series vary in texture between loam and sandy loam
whereas Kilmarnock series are mostly loams. Typical
topsoil organic matter levels are 51 g kgÿ1 for Macmerry and 38 g kgÿ1 for Kilmarnock. Both have been
described as imperfectly drained brown forest soils
(Ragg and Futty, 1967). Both soil types are in the
British land use capability class 2, where soil wetness
is a minor limitation to the choice of crops and
cultivations (Bibby et al., 1982).
2.2. Treatments, experimental design and nitrogen
fertiliser applications
The experimental design was a randomised complete block with fourfold replication, replicates being
aligned side by side. Plots were 24 m 2.4 m. The
plots were suf®ciently narrow to be straddled by wide
wheel track machinery. The residues of the previous
cereal crop had been chopped and spread over the
179
B.C. Ball, R.M. Ritchie / Soil & Tillage Research 52 (1999) 177±189
Table 1
Monthly rainfall (mm) at weather stations near the Boghall and North Berwick sites
Boghall
North Berwick
1995
1996
January
February
March
April
May
June
July
August
September
October
November
December
103
106
52
32
57
19
52
19
150
115
73
44
49
52
26
55
58
24
57
56
23
132
126
109
Total
822
767
Average
(1966±1995)
1996
1997
86
61
77
51
61
60
63
70
81
88
82
82
20
26
17
41
49
12
38
55
15
58
64
88
22
63
20
13
98
128
59
24
34
24
66
93
48
35
44
37
51
47
56
67
60
59
58
49
862
483
644
611
experimental site during harvesting. The soil was
mouldboard ploughed to 25 cm depth the day before
treatment application, thereby incorporating these
residues. Wide-wheel track machinery was used for
all management operations after ploughing, which
ensured that wheel compaction was con®ned between
each plot. All machinery operated along the long axis
of the plots ensuring that most of the variability of soil
compaction and residue incorporation would be across
the plots. Treatments were (1) zero compaction, (2)
light compaction (target depth of 10 cm) using a heavy
roller (up to 1 Mg per metre length), (3) heavy compaction (target depth of 25 cm) using a laden tractor
(up to 4.2 Mg), and (4) heavy compaction with the soil
subsequently loosened down to 10 cm depth with a
rotary cultivator. Details of the machinery used for the
compaction treatments are given in Table 2. The soil
was compacted before and after sowing except for the
®rst heavy compaction treatment at Boghall. The soil
was rotary harrowed immediately before treatment
application and before sowing in order to prepare a
uniform surface. All plots were rolled immediately
after sowing (Table 2).
Ploughing and treatment application occurred twice
in 1995 at Boghall, before sowing spring barley in
April and winter barley in September, and once in
August 1996 at North Berwick, before sowing oil-seed
rape. An additional treatment of no-tillage was
included at Boghall. Due to management constraints,
Average
(1961±1990)
this could not be included at North Berwick. At
Boghall, nitrogen fertiliser was applied to the spring
barley at sowing at 120 kg N haÿ1 on 12 April. For the
winter barley, nitrogen was applied to the growing
crop at 70 kg N haÿ1 on 7 March 1996 and at 110 kg N
haÿ1 on 17 April 1996. At North Berwick, nitrogen
fertiliser was applied to the growing crop at 78 kg haÿ1
on 3 March 1997, at 88 kg haÿ1 on 20 March 1997 and
at 43 kg haÿ1 on 25 March 1997.
2.3. Soil and crop measurements
Cone resistance to 30 cm depth (10 penetrations/
plot) was measured before and after ploughing and
treatment application with a hand-held digital penetrometer linked to an electronic data collector (O'Sullivan et al., 1983). Bulk density and porosity were
measured in October 1995 at Boghall and in March
1997 at North Berwick from 0±25 cm depth in cores of
7.3 cm diameter at increments of 5 cm. One core per
depth was taken from plots in replicates 2 and 3 only.
A pit was dug in each plot and cores taken at staggered
depth intervals. Relative gas diffusivity and air permeability were measured on the same samples at ®eld
water content, using the methods of Ball et al. (1981).
Soil gas diffusivity was also measured in situ at
Boghall in May 1995, November 1995 and June
1996 to give a direct measure of the ability of the
soils to exchange gases with minimal soil disturbance.
Table 2
Details of machinery used in the application of the compaction treatments at the Boghall and North Berwick sites
Site, crop and date of treatment
application
Boghall, spring barley, 12 April 1995
Boghall, winter barley, 27 September 1995
North Berwick, winter oil-seed rape,
27 August 1996
a
b
Light compaction by roller
Weight
(Mg mÿ1)
1
1
0.66
a
Passes
2
2
3
Weight
(Mg)
3.05
4.22
3.59
Heavy compaction by tractor
Front tyres
Rear tyres
Passes
Size
Inflation
pressure
(kPa)
Size
Inflation
pressure
(kPa)
7.5±16
7.5±16
7.5±16
220
220
220
13.6R 36
13.6R 36
13.6R 36
80
80
80
1 Ð before sowing; 2 Ð 1 before and 1 after sowing; 3 Ð 2 before and 1 after sowing.
The pass after sowing was with a tractor of weight 3.05 Mg.
1
2b
3
a
Compaction by 1 pass of roller before
sowing (all plots): Weight (Mg mÿ1)
0.33
0.33
0.54
B.C. Ball, R.M. Ritchie / Soil & Tillage Research 52 (1999) 177±189
It was measured by injecting Freon into a chamber
enclosing the soil surface and measuring its subsequent rate of escape into the soil as the decrease in
Freon concentration within the chamber (Ball et al.,
1997a). In order to calculate diffusivity, it is necessary
®rst to simulate diffusion numerically using Fick's
equation. The time axis of the simulation is expanded
or contracted until it matches the observed decrease in
concentration [see Ball et al. (1994)].
Using a gouge auger, samples for measurement of
gravimetric water content were regularly taken from
0±20 cm in 5 cm intervals at treatment application and
through the growing season. For the winter crops,
these were converted to volumetric water contents
and air-®lled porosities using the bulk densities measured in the core samples. Particle size distribution
was measured using the pipette method at Boghall in
winter 1995 from 0±30 cm depth in 10 cm intervals.
Soil temperature was recorded at 90-min intervals
using thermistor probes inserted at 2.5, 7.5 and
15 cm depth in selected plots at Boghall. Probes were
at two locations per depth and were connected to a
®eld logger which was downloaded weekly.
Grain yield and grain nitrogen content were measured at Boghall. Plot yields were assessed on a crop
area of about 50 m2 using a plot combine. The yield of
oil-seed rape could not be assessed because the wet
weather in the month prior to harvesting had caused
the crop to lodge and tangle suf®ciently for it to
require windrowing to allow harvesting. No machinery small enough to windrow individual plots was
available. However, the nitrogen content of the oilseed was determined just before harvest.
3. Results
3.1. Soil measurements
Cone resistances measured before ®rst ploughing
did not differ signi®cantly between treatments (data
not shown). However, after ploughing and treatment
application, cone resistances (Fig. 1) differed signi®cantly between some treatments on all occasions. At
Boghall in April 1995, the effect of heavy compaction
on cone resistance was small. Subsequently this treatment was made more effective by increasing the
weight of the tractor and applying the treatment both
181
before and after sowing the winter crops (Table 2). For
the winter barley, this increased cone resistance
throughout the topsoil, but particularly near the surface where the soil was wetter (270 g kgÿ1) than at the
spring treatment application (190 g kgÿ1). Cone resistance under no-tillage was similar on both occasions
indicating the persistence of soil compaction from
spring 1995. At Boghall, on both occasions of treatment application and cone resistance measurement,
water contents deeper in the topsoil were similar,
between 260 and 300 g kgÿ1. At North Berwick, the
top 30 cm of soil was considerably drier (150 g kgÿ1)
when the treatments were applied. Despite two passes
of both compaction treatments before sowing, cone
resistance (Fig. 1) in the top 8 cm soil layer was low,
though below this depth it was considerably greater
with a peak at 14±16 cm depth. However, part of this
effect may have resulted from the dryness of the
topsoil (170 g kgÿ1) increasing strength.
Dry bulk densities (Fig. 2) at most depths were
ranked in order of intensity of compaction, viz. heavy > light > zero. Density in the heavy compaction
treatment subsequently loosened to 10 cm varied more
between depths than in the heavy compaction treatment. Topsoil maximum bulk densities measured at
nearby sites (D.J. Campbell, 1999, unpublished data),
using the Proctor test were, on average, 1.59 Mg mÿ3
for Macmerry series and 1.73 Mg mÿ3 for Kilmarnock
series. The highest ®eld dry bulk densities at Boghall
(Fig. 2) were more uniformly distributed through the
topsoil and were closer to the theoretical (Proctor)
maximum than at North Berwick. At Boghall, the
highest ®eld bulk densities under heavy compaction
were 89% of the theoretical (Proctor) maximum and
under light compaction were 82% of the maximum.
Core relative diffusivities (Fig. 3) and air permeabilities (Fig. 4) covered a wider range and showed
larger treatment effects at Boghall than at North
Berwick. The in situ diffusivities measured in November 1995 at Boghall (Table 3) ranked the treatments
similarly to the cores. In situ diffusivities were also
strongly in¯uenced by changes in soil water content
throughout the season (Table 3).
Under zero compaction, at 0±10 cm depth, most air®lled porosities (Fig. 5) were about 0.1 m3 mÿ3 higher
than in the heavy compaction treatment, with the other
treatments intermediate. Such low values resulted
from the persistently wet conditions throughout the
182
B.C. Ball, R.M. Ritchie / Soil & Tillage Research 52 (1999) 177±189
Fig. 1. Cone resistance after treatment application at Boghall in April and October 1995, and North Berwick, October 1996.
winter which were established by the high rainfalls in
September and October (Table 1). In the next season,
the lower rainfalls maintained air-®lled porosities
about 0.05 m3 mÿ3 higher at North Berwick than at
Boghall. However, the rainfall at North Berwick in
June 1997 was suf®ciently high to reduce air-®lled
porosities almost to winter levels.
At Boghall, particle-size distribution (Fig. 6) varied
between experimental plots with differences in coarse
sand and clay contents of up to 60 and 70 g kgÿ1. The
soil texture became coarser from replicate 1 through to
replicate 4. This may have contributed to differences
between replicates in some measurements, notably,
soil water content, cone resistance and crop yield. The
soil in replicate 1 was wetter, on average, by 30±
60 g kgÿ1 compared with the other three replicates.
However, when coarse sand or clay content was
included as a covariate within analyses of variance
of these properties, the effect never reached signi®cance at P < 0.05.
183
B.C. Ball, R.M. Ritchie / Soil & Tillage Research 52 (1999) 177±189
Fig. 2. Dry bulk density at Boghall, October 1995 and at North Berwick, March 1997. Error bars represent the average range of the two
replicates.
Table 3
In situ Freon diffusivity and soil moisture content at 0±5 cm depth at Boghall site
Compaction treatment
Diffusivity (mm2 sÿ1)
Soil water content (g kgÿ1)
May 1995
November
1995
June 1996
May 1995
November
1995
June 1996
Zero
Light
Heavy
Heavy loosened to 100 mm
No-tillage
2.55
1.91
1.66
2.29
0.98
1.59
1.11
0.51
1.46
1.85
3.46
4.19
0.67
2.71
3.84
192
219
210
224
255
295
294
298
335
295
124
119
134
148
112
SEDa
Significance
*
0.73
ns
1.97
ns
*
55.4
ns
**
a
Standard error of the difference between two treatment means.
184
B.C. Ball, R.M. Ritchie / Soil & Tillage Research 52 (1999) 177±189
Fig. 3. Core gas diffusivity at Boghall, October 1995 and at North Berwick, March 1997. Relative diffusivity is soil gas diffusivity expressed
as a fraction of diffusivity in free air. Error bars represent the average range of the two replicates.
3.2. Crop performance and measurements
The growth of the spring barley and winter oil-seed
rape appeared not to be impaired by the compaction
treatments. Indeed, under zero compaction spring
barley emergence was slightly delayed and winter
oil-seed rape emergence was patchy. The oil-seed
rape on the compacted plots overwintered better,
resulting in a more uniform and greater crop cover
than under zero compaction. However, subsequent
growth compensated for variations in emergence
and overwintering with spring barley yields, grain
and oil seed rape nitrogen contents (Table 4) little
affected by compaction. Under spring barley, compac-
tion appeared to give a small, non-signi®cant yield
increase (Table 4). Under winter barley, the heavy
compaction and no-tillage treatments reduced and
delayed crop emergence. By November 1995, when
the soil was very wet, plants in the heavily compacted
treatment became small and upright, with yellowing of
the outer leaves and the development of ¯eshy roots.
These symptoms were attributed to transient waterlogging damage as a result of the poor soil structure
produced by the treatments. The poor, stunted growth
and appearance of the heavily compacted and notilled plots persisted until harvest when both treatments gave signi®cantly lower yields (Table 4) than
the others.
185
B.C. Ball, R.M. Ritchie / Soil & Tillage Research 52 (1999) 177±189
Fig. 4. Air permeability at Boghall, October 1995 and at North Berwick, March 1997. Error bars represent the average range of the two
replicates.
Table 4
Grain yield and grain nitrogen contents at Boghall (spring and winter barley) and oil-seed nitrogen contents at North Berwick
Compaction treatment
Grain yield (Mg haÿ1)
Nitrogen content (g kgÿ1)
Spring barley
1995
Winter barley
1996
Spring barley
1995
Winter barley
1996
Winter oil-seed
rape 1997a
Zero
Light
Heavy
Heavy loosened to 100 mm
No-tillage
7.05
7.19
7.46
7.11
6.04
8.85
8.92
7.1
8.5
6.10
17.3
17.6
16.9
16.8
17.4
16.2
16.9
15.7
15.2
20.8
19.9
20.8
21.7
21.4
±
SEDb
Significance
0.39
ns
0.4
***
LSD 0.87
0.49
ns
0.62
***
LSD 1.36
2
ns
a
b
The oil seed rape yield was not assessed because the crop could not be harvested at the plot scale.
Standard error of the difference between two treatment means.
186
B.C. Ball, R.M. Ritchie / Soil & Tillage Research 52 (1999) 177±189
Fig. 5. Air-filled porosity at 0±10 cm depth during the growing season for winter barley at Boghall and winter oil-seed rape at North Berwick.
4. Discussion
4.1. Soil responses
Cone resistance was used as the main indicator of
the effectiveness of the compaction treatments, mainly
because it can indicate layers of differential compaction (Campbell and O'Sullivan, 1991). Although core
dry bulk densities revealed that the compaction treatments were more effective at Boghall than at North
Berwick, the pro®les of cone resistance proved to be
more sensitive indicators of the soil physical changes
among the compaction treatments. Blunden et al.
(1994) came to a similar conclusion when comparing
traf®cked and untraf®cked soil.
At Boghall, heavy compaction gave particularly
low gas diffusivities at 10±15 cm depth and low air
permeabilities between 0 and 15 cm depth. Air permeability is very sensitive to the size of the largest air®lled pores (Ball, 1981). This indicates that heavy
compaction (under wet conditions) was particularly
effective in reducing the size and continuity of the
pores. The greater effectiveness of the treatments
under the winter crop was also shown by the greater
B.C. Ball, R.M. Ritchie / Soil & Tillage Research 52 (1999) 177±189
187
Fig. 6. Particle size distribution within individual plots at Boghall. Plots were adjacent and were not separated by discard areas except for
plots 10 and 11 which were separated by 10 m.
differences in gas diffusivities between treatments
under winter barley (November 1995 and June
1996) than under spring barley. Compaction of moist
soils is important when air-®lled porosity is reduced to
below the commonly quoted critical level for satisfactory aeration of 0.1 m3 mÿ3. This occurred after heavy
compaction under winter barley. Etana and HaÊkansson
(1996), who also found this effect, attributed it to the
high mass of the compacting vehicle. However, Bakken et al. (1987) found little effect of the weight of the
tractor (1800 kg vs 4800 kg) on soil properties in a
similar experiment on compaction of seedbeds.
4.2. Crop responses
Our heavy compaction treatment only caused problems with crop growth when applied to wet soil that
remained wet during early growth. This resulted in air®lled porosities of generally less than 0.1 m3 mÿ3, and
cone resistances and bulk densities of nearly 2 MPa
and 1.4 Mg mÿ3 throughout the topsoil. The latter are
close to the critical values for barley growth of
2.5 MPa and 1.41 Mg mÿ3 on the same soil type (Ball
and O'Sullivan, 1982). A critical value of bulk density
of 1.48 Mg mÿ3 was quoted by Styk and Sochaj
(1992) using a similar experimental approach to ours
but on a Polish loess soil. Compaction of the top 15 cm
soil layer appeared to be the most important in terms
of restricting crop growth. Campbell et al. (1986)
attributed the restriction in crop growth and yield after
heavy compaction to a combination of seed bed waterlogging and high soil strength below sowing depth.
They found soil strength, measured as cone resistance
at 15 cm depth, correlated well with winter barley
yield. Similarly, Dickson and Ritchie (1996) attributed
much of the variability of barley yield associated with
compaction to cone resistance between 0 and 27 cm
depth.
The satisfactory winter barley growth and yield of
the treatment of heavy compaction loosened to 10 cm
(Table 4) revealed the importance of shallow tillage
for ameliorating compaction. The top 10 cm of soil is
particularly important in controlling gas and water
movement and drainage (Ball et al., 1997b). Air
permeability showed a marked minimum at this depth
with values of
Soil and residue management effects on arable
cropping conditions and nitrous oxide ¯uxes
under controlled traf®c in Scotland
1. Soil and crop responses
B.C. Ball*, R.M. Ritchie
Environmental Division, SAC, West Mains Road, Edinburgh, EH9 3JG, UK
Received 16 February 1999; received in revised form 21 July 1999; accepted 5 August 1999
Abstract
Soil compaction can affect crop growth and greenhouse gas emission and information is required of how both these aspects
are affected by compaction intensity and weather. In this paper we describe treatments of compaction intensity and their
effects on soil physical conditions and crop growth in loam to sandy loam cambisol soils. Soil conditions and crop
performance were measured over three seasons in a ®eld experiment on soil compacted by wheels on freshly ploughed
seedbeds. Ploughing buried the chopped residues of the previous crop. After ploughing, traf®c was controlled such that the
experimental plots received wheel traf®c only as treatments. The overall objective was to discover how the intensity and
distribution of soil compaction just before sowing in¯uenced crop performance, soil conditions and emissions of nitrous oxide.
Compaction treatments were zero, light compaction by roller (up to 1 Mg mÿ1) and heavy compaction by loaded tractor, (up
to 4.2 Mg). The experiment was located at Boghall, near Edinburgh (860 mm average annual rainfall) for the ®rst two seasons
under spring and winter barley (Hordeum vulgare L.) and in a drier area at North Berwick (610 mm average annual rainfall)
for the third season under winter oil-seed rape (Brassica napus L.). Heavy compaction in dry soil conditions had little effect on
crop growth. However, in wet conditions heavy compaction reduced air porosity, air permeability and gas diffusivity, increased
cone resistance and limited winter barley growth and grain yield. Heavy compaction in wet conditions reduced winter barley
yields to 7.1 Mg haÿ1, in comparison to 8.8 Mg haÿ1 in the zero compaction treatment. The compaction status of the top
15 cm of soil seemed to be particularly important. Loosening of the top 10 cm of soil immediately after heavy compaction
restored soil conditions for crop growth. However, zero seed bed compaction gave patchy and uneven crop emergence in dry
conditions. Both zero and light compaction to a target depth of 10 cm gave similar crop productivity. Maintenance of a correct
compaction level near the soil surface is particularly important for establishment and overwintering of barley and oil seed
rape. # 1999 Elsevier Science B.V. All rights reserved.
Keywords: Compaction; Residues; Barley; Soil
*
Corresponding author. Tel.: 44-131-535-4392; fax.: 44-131-667-2601
E-mail address: [email protected] (B.C. Ball)
0167-1987/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved.
PII: S 0 1 6 7 - 1 9 8 7 ( 9 9 ) 0 0 0 8 0 - X
178
B.C. Ball, R.M. Ritchie / Soil & Tillage Research 52 (1999) 177±189
1. Introduction
Considerable effort has been devoted to evaluating
the effects of wheel traf®c on soil properties and crop
growth (Soane and van Ouwerkerk, 1994). Management systems which completely eliminate traf®c or
which permit a reduction in ground pressure on the
crop growing area give more favourable soil conditions and, often, better crop growth and yield than
conventional systems (Chamen et al., 1992; Dickson
and Ritchie, 1996). Extensive compaction before sowing is particularly damaging to soil structure and
subsequent crop growth (Campbell et al., 1986; Bakken et al., 1987; McAfee et al., 1989). Tractor traf®c
on wet soil can also increase denitri®cation by a factor
of 3±4 (Bakken et al., 1987). The presence of straw
residues, particularly in compacted soil, can also
contribute to waterlogging, nitrous oxide (N2O) production and reduced crop survival over winter (Ball
and Robertson, 1990). Reduced or no-tillage systems
can also increase N2O production (Aulakh et al.,
1984), particularly in the presence of straw residues
(Ball and Robertson, 1990). Nitrous oxide production
represents a loss of nutrient from the system and
contributes to global warming and the destruction
of stratospheric ozone (Crutzen, 1970). Indeed, the
signi®cance of arable agricultural soils as a source of
N2O may have been underestimated (Beauchamp,
1997).
Recent work on the in¯uence of tillage and compaction in Scotland under arable cropping and controlled traf®c conditions has involved chisel ploughing
and reduced or no-tillage (Campbell et al., 1986;
Dickson and Ritchie, 1996). These techniques are
rarely used in practice and the experiments conducted
did not include measurements of gaseous losses of
nitrogen. There is a need to consider how normal soil
management techniques involving mouldboard
ploughing can create soil conditions which suit crop
growth but which also minimise losses of nitrogen,
particularly as N2O. In the UK, crop residues are
increasingly incorporated in the soil, partly due to
legal restrictions of straw burning. Since the in¯uence
of residues on denitri®cation under different tillage
systems has been associated with compaction (Ball
and Robertson, 1990), the interactions of residue
incorporation, soil compaction and nitrous oxide
emission require assessment.
Our objective was to determine which soil properties in¯uenced crop growth in response to different
compaction intensities and depths. This then permits
identi®cation of the optimum level of seedbed compaction (including zero) after normal ploughing of
residues, which gives the best cropping conditions
whilst minimising the losses of nitrogen as N2O.
No-tillage was included as a reference treatment. This
paper reports the treatments and the soil and crop
responses. A subsequent paper reports on the nitrous
oxide emissions and the soil nitrogen status (Ball et al.,
1999).
2. Methods and materials
2.1. Location, soil and weather
The ®eld experiment was located at two sites. The
®rst, at Boghall, 10 km south of Edinburgh, contained
spring barley in 1995 and winter barley in 1995/6. The
second site, 3 km south of North Berwick, contained
winter oil-seed rape in 1996/7. The average annual
rainfall near Boghall is 880 mm and near North
Berwick is 611 mm. In addition, monthly rainfalls
at weather stations close to each site are given in
Table 1. The ®rst site was on Macmerry series (Cambisol in FAO classi®cation) and the second site was on
Kilmarnock series (Gleyic Cambisol). Macmerry series vary in texture between loam and sandy loam
whereas Kilmarnock series are mostly loams. Typical
topsoil organic matter levels are 51 g kgÿ1 for Macmerry and 38 g kgÿ1 for Kilmarnock. Both have been
described as imperfectly drained brown forest soils
(Ragg and Futty, 1967). Both soil types are in the
British land use capability class 2, where soil wetness
is a minor limitation to the choice of crops and
cultivations (Bibby et al., 1982).
2.2. Treatments, experimental design and nitrogen
fertiliser applications
The experimental design was a randomised complete block with fourfold replication, replicates being
aligned side by side. Plots were 24 m 2.4 m. The
plots were suf®ciently narrow to be straddled by wide
wheel track machinery. The residues of the previous
cereal crop had been chopped and spread over the
179
B.C. Ball, R.M. Ritchie / Soil & Tillage Research 52 (1999) 177±189
Table 1
Monthly rainfall (mm) at weather stations near the Boghall and North Berwick sites
Boghall
North Berwick
1995
1996
January
February
March
April
May
June
July
August
September
October
November
December
103
106
52
32
57
19
52
19
150
115
73
44
49
52
26
55
58
24
57
56
23
132
126
109
Total
822
767
Average
(1966±1995)
1996
1997
86
61
77
51
61
60
63
70
81
88
82
82
20
26
17
41
49
12
38
55
15
58
64
88
22
63
20
13
98
128
59
24
34
24
66
93
48
35
44
37
51
47
56
67
60
59
58
49
862
483
644
611
experimental site during harvesting. The soil was
mouldboard ploughed to 25 cm depth the day before
treatment application, thereby incorporating these
residues. Wide-wheel track machinery was used for
all management operations after ploughing, which
ensured that wheel compaction was con®ned between
each plot. All machinery operated along the long axis
of the plots ensuring that most of the variability of soil
compaction and residue incorporation would be across
the plots. Treatments were (1) zero compaction, (2)
light compaction (target depth of 10 cm) using a heavy
roller (up to 1 Mg per metre length), (3) heavy compaction (target depth of 25 cm) using a laden tractor
(up to 4.2 Mg), and (4) heavy compaction with the soil
subsequently loosened down to 10 cm depth with a
rotary cultivator. Details of the machinery used for the
compaction treatments are given in Table 2. The soil
was compacted before and after sowing except for the
®rst heavy compaction treatment at Boghall. The soil
was rotary harrowed immediately before treatment
application and before sowing in order to prepare a
uniform surface. All plots were rolled immediately
after sowing (Table 2).
Ploughing and treatment application occurred twice
in 1995 at Boghall, before sowing spring barley in
April and winter barley in September, and once in
August 1996 at North Berwick, before sowing oil-seed
rape. An additional treatment of no-tillage was
included at Boghall. Due to management constraints,
Average
(1961±1990)
this could not be included at North Berwick. At
Boghall, nitrogen fertiliser was applied to the spring
barley at sowing at 120 kg N haÿ1 on 12 April. For the
winter barley, nitrogen was applied to the growing
crop at 70 kg N haÿ1 on 7 March 1996 and at 110 kg N
haÿ1 on 17 April 1996. At North Berwick, nitrogen
fertiliser was applied to the growing crop at 78 kg haÿ1
on 3 March 1997, at 88 kg haÿ1 on 20 March 1997 and
at 43 kg haÿ1 on 25 March 1997.
2.3. Soil and crop measurements
Cone resistance to 30 cm depth (10 penetrations/
plot) was measured before and after ploughing and
treatment application with a hand-held digital penetrometer linked to an electronic data collector (O'Sullivan et al., 1983). Bulk density and porosity were
measured in October 1995 at Boghall and in March
1997 at North Berwick from 0±25 cm depth in cores of
7.3 cm diameter at increments of 5 cm. One core per
depth was taken from plots in replicates 2 and 3 only.
A pit was dug in each plot and cores taken at staggered
depth intervals. Relative gas diffusivity and air permeability were measured on the same samples at ®eld
water content, using the methods of Ball et al. (1981).
Soil gas diffusivity was also measured in situ at
Boghall in May 1995, November 1995 and June
1996 to give a direct measure of the ability of the
soils to exchange gases with minimal soil disturbance.
Table 2
Details of machinery used in the application of the compaction treatments at the Boghall and North Berwick sites
Site, crop and date of treatment
application
Boghall, spring barley, 12 April 1995
Boghall, winter barley, 27 September 1995
North Berwick, winter oil-seed rape,
27 August 1996
a
b
Light compaction by roller
Weight
(Mg mÿ1)
1
1
0.66
a
Passes
2
2
3
Weight
(Mg)
3.05
4.22
3.59
Heavy compaction by tractor
Front tyres
Rear tyres
Passes
Size
Inflation
pressure
(kPa)
Size
Inflation
pressure
(kPa)
7.5±16
7.5±16
7.5±16
220
220
220
13.6R 36
13.6R 36
13.6R 36
80
80
80
1 Ð before sowing; 2 Ð 1 before and 1 after sowing; 3 Ð 2 before and 1 after sowing.
The pass after sowing was with a tractor of weight 3.05 Mg.
1
2b
3
a
Compaction by 1 pass of roller before
sowing (all plots): Weight (Mg mÿ1)
0.33
0.33
0.54
B.C. Ball, R.M. Ritchie / Soil & Tillage Research 52 (1999) 177±189
It was measured by injecting Freon into a chamber
enclosing the soil surface and measuring its subsequent rate of escape into the soil as the decrease in
Freon concentration within the chamber (Ball et al.,
1997a). In order to calculate diffusivity, it is necessary
®rst to simulate diffusion numerically using Fick's
equation. The time axis of the simulation is expanded
or contracted until it matches the observed decrease in
concentration [see Ball et al. (1994)].
Using a gouge auger, samples for measurement of
gravimetric water content were regularly taken from
0±20 cm in 5 cm intervals at treatment application and
through the growing season. For the winter crops,
these were converted to volumetric water contents
and air-®lled porosities using the bulk densities measured in the core samples. Particle size distribution
was measured using the pipette method at Boghall in
winter 1995 from 0±30 cm depth in 10 cm intervals.
Soil temperature was recorded at 90-min intervals
using thermistor probes inserted at 2.5, 7.5 and
15 cm depth in selected plots at Boghall. Probes were
at two locations per depth and were connected to a
®eld logger which was downloaded weekly.
Grain yield and grain nitrogen content were measured at Boghall. Plot yields were assessed on a crop
area of about 50 m2 using a plot combine. The yield of
oil-seed rape could not be assessed because the wet
weather in the month prior to harvesting had caused
the crop to lodge and tangle suf®ciently for it to
require windrowing to allow harvesting. No machinery small enough to windrow individual plots was
available. However, the nitrogen content of the oilseed was determined just before harvest.
3. Results
3.1. Soil measurements
Cone resistances measured before ®rst ploughing
did not differ signi®cantly between treatments (data
not shown). However, after ploughing and treatment
application, cone resistances (Fig. 1) differed signi®cantly between some treatments on all occasions. At
Boghall in April 1995, the effect of heavy compaction
on cone resistance was small. Subsequently this treatment was made more effective by increasing the
weight of the tractor and applying the treatment both
181
before and after sowing the winter crops (Table 2). For
the winter barley, this increased cone resistance
throughout the topsoil, but particularly near the surface where the soil was wetter (270 g kgÿ1) than at the
spring treatment application (190 g kgÿ1). Cone resistance under no-tillage was similar on both occasions
indicating the persistence of soil compaction from
spring 1995. At Boghall, on both occasions of treatment application and cone resistance measurement,
water contents deeper in the topsoil were similar,
between 260 and 300 g kgÿ1. At North Berwick, the
top 30 cm of soil was considerably drier (150 g kgÿ1)
when the treatments were applied. Despite two passes
of both compaction treatments before sowing, cone
resistance (Fig. 1) in the top 8 cm soil layer was low,
though below this depth it was considerably greater
with a peak at 14±16 cm depth. However, part of this
effect may have resulted from the dryness of the
topsoil (170 g kgÿ1) increasing strength.
Dry bulk densities (Fig. 2) at most depths were
ranked in order of intensity of compaction, viz. heavy > light > zero. Density in the heavy compaction
treatment subsequently loosened to 10 cm varied more
between depths than in the heavy compaction treatment. Topsoil maximum bulk densities measured at
nearby sites (D.J. Campbell, 1999, unpublished data),
using the Proctor test were, on average, 1.59 Mg mÿ3
for Macmerry series and 1.73 Mg mÿ3 for Kilmarnock
series. The highest ®eld dry bulk densities at Boghall
(Fig. 2) were more uniformly distributed through the
topsoil and were closer to the theoretical (Proctor)
maximum than at North Berwick. At Boghall, the
highest ®eld bulk densities under heavy compaction
were 89% of the theoretical (Proctor) maximum and
under light compaction were 82% of the maximum.
Core relative diffusivities (Fig. 3) and air permeabilities (Fig. 4) covered a wider range and showed
larger treatment effects at Boghall than at North
Berwick. The in situ diffusivities measured in November 1995 at Boghall (Table 3) ranked the treatments
similarly to the cores. In situ diffusivities were also
strongly in¯uenced by changes in soil water content
throughout the season (Table 3).
Under zero compaction, at 0±10 cm depth, most air®lled porosities (Fig. 5) were about 0.1 m3 mÿ3 higher
than in the heavy compaction treatment, with the other
treatments intermediate. Such low values resulted
from the persistently wet conditions throughout the
182
B.C. Ball, R.M. Ritchie / Soil & Tillage Research 52 (1999) 177±189
Fig. 1. Cone resistance after treatment application at Boghall in April and October 1995, and North Berwick, October 1996.
winter which were established by the high rainfalls in
September and October (Table 1). In the next season,
the lower rainfalls maintained air-®lled porosities
about 0.05 m3 mÿ3 higher at North Berwick than at
Boghall. However, the rainfall at North Berwick in
June 1997 was suf®ciently high to reduce air-®lled
porosities almost to winter levels.
At Boghall, particle-size distribution (Fig. 6) varied
between experimental plots with differences in coarse
sand and clay contents of up to 60 and 70 g kgÿ1. The
soil texture became coarser from replicate 1 through to
replicate 4. This may have contributed to differences
between replicates in some measurements, notably,
soil water content, cone resistance and crop yield. The
soil in replicate 1 was wetter, on average, by 30±
60 g kgÿ1 compared with the other three replicates.
However, when coarse sand or clay content was
included as a covariate within analyses of variance
of these properties, the effect never reached signi®cance at P < 0.05.
183
B.C. Ball, R.M. Ritchie / Soil & Tillage Research 52 (1999) 177±189
Fig. 2. Dry bulk density at Boghall, October 1995 and at North Berwick, March 1997. Error bars represent the average range of the two
replicates.
Table 3
In situ Freon diffusivity and soil moisture content at 0±5 cm depth at Boghall site
Compaction treatment
Diffusivity (mm2 sÿ1)
Soil water content (g kgÿ1)
May 1995
November
1995
June 1996
May 1995
November
1995
June 1996
Zero
Light
Heavy
Heavy loosened to 100 mm
No-tillage
2.55
1.91
1.66
2.29
0.98
1.59
1.11
0.51
1.46
1.85
3.46
4.19
0.67
2.71
3.84
192
219
210
224
255
295
294
298
335
295
124
119
134
148
112
SEDa
Significance
*
0.73
ns
1.97
ns
*
55.4
ns
**
a
Standard error of the difference between two treatment means.
184
B.C. Ball, R.M. Ritchie / Soil & Tillage Research 52 (1999) 177±189
Fig. 3. Core gas diffusivity at Boghall, October 1995 and at North Berwick, March 1997. Relative diffusivity is soil gas diffusivity expressed
as a fraction of diffusivity in free air. Error bars represent the average range of the two replicates.
3.2. Crop performance and measurements
The growth of the spring barley and winter oil-seed
rape appeared not to be impaired by the compaction
treatments. Indeed, under zero compaction spring
barley emergence was slightly delayed and winter
oil-seed rape emergence was patchy. The oil-seed
rape on the compacted plots overwintered better,
resulting in a more uniform and greater crop cover
than under zero compaction. However, subsequent
growth compensated for variations in emergence
and overwintering with spring barley yields, grain
and oil seed rape nitrogen contents (Table 4) little
affected by compaction. Under spring barley, compac-
tion appeared to give a small, non-signi®cant yield
increase (Table 4). Under winter barley, the heavy
compaction and no-tillage treatments reduced and
delayed crop emergence. By November 1995, when
the soil was very wet, plants in the heavily compacted
treatment became small and upright, with yellowing of
the outer leaves and the development of ¯eshy roots.
These symptoms were attributed to transient waterlogging damage as a result of the poor soil structure
produced by the treatments. The poor, stunted growth
and appearance of the heavily compacted and notilled plots persisted until harvest when both treatments gave signi®cantly lower yields (Table 4) than
the others.
185
B.C. Ball, R.M. Ritchie / Soil & Tillage Research 52 (1999) 177±189
Fig. 4. Air permeability at Boghall, October 1995 and at North Berwick, March 1997. Error bars represent the average range of the two
replicates.
Table 4
Grain yield and grain nitrogen contents at Boghall (spring and winter barley) and oil-seed nitrogen contents at North Berwick
Compaction treatment
Grain yield (Mg haÿ1)
Nitrogen content (g kgÿ1)
Spring barley
1995
Winter barley
1996
Spring barley
1995
Winter barley
1996
Winter oil-seed
rape 1997a
Zero
Light
Heavy
Heavy loosened to 100 mm
No-tillage
7.05
7.19
7.46
7.11
6.04
8.85
8.92
7.1
8.5
6.10
17.3
17.6
16.9
16.8
17.4
16.2
16.9
15.7
15.2
20.8
19.9
20.8
21.7
21.4
±
SEDb
Significance
0.39
ns
0.4
***
LSD 0.87
0.49
ns
0.62
***
LSD 1.36
2
ns
a
b
The oil seed rape yield was not assessed because the crop could not be harvested at the plot scale.
Standard error of the difference between two treatment means.
186
B.C. Ball, R.M. Ritchie / Soil & Tillage Research 52 (1999) 177±189
Fig. 5. Air-filled porosity at 0±10 cm depth during the growing season for winter barley at Boghall and winter oil-seed rape at North Berwick.
4. Discussion
4.1. Soil responses
Cone resistance was used as the main indicator of
the effectiveness of the compaction treatments, mainly
because it can indicate layers of differential compaction (Campbell and O'Sullivan, 1991). Although core
dry bulk densities revealed that the compaction treatments were more effective at Boghall than at North
Berwick, the pro®les of cone resistance proved to be
more sensitive indicators of the soil physical changes
among the compaction treatments. Blunden et al.
(1994) came to a similar conclusion when comparing
traf®cked and untraf®cked soil.
At Boghall, heavy compaction gave particularly
low gas diffusivities at 10±15 cm depth and low air
permeabilities between 0 and 15 cm depth. Air permeability is very sensitive to the size of the largest air®lled pores (Ball, 1981). This indicates that heavy
compaction (under wet conditions) was particularly
effective in reducing the size and continuity of the
pores. The greater effectiveness of the treatments
under the winter crop was also shown by the greater
B.C. Ball, R.M. Ritchie / Soil & Tillage Research 52 (1999) 177±189
187
Fig. 6. Particle size distribution within individual plots at Boghall. Plots were adjacent and were not separated by discard areas except for
plots 10 and 11 which were separated by 10 m.
differences in gas diffusivities between treatments
under winter barley (November 1995 and June
1996) than under spring barley. Compaction of moist
soils is important when air-®lled porosity is reduced to
below the commonly quoted critical level for satisfactory aeration of 0.1 m3 mÿ3. This occurred after heavy
compaction under winter barley. Etana and HaÊkansson
(1996), who also found this effect, attributed it to the
high mass of the compacting vehicle. However, Bakken et al. (1987) found little effect of the weight of the
tractor (1800 kg vs 4800 kg) on soil properties in a
similar experiment on compaction of seedbeds.
4.2. Crop responses
Our heavy compaction treatment only caused problems with crop growth when applied to wet soil that
remained wet during early growth. This resulted in air®lled porosities of generally less than 0.1 m3 mÿ3, and
cone resistances and bulk densities of nearly 2 MPa
and 1.4 Mg mÿ3 throughout the topsoil. The latter are
close to the critical values for barley growth of
2.5 MPa and 1.41 Mg mÿ3 on the same soil type (Ball
and O'Sullivan, 1982). A critical value of bulk density
of 1.48 Mg mÿ3 was quoted by Styk and Sochaj
(1992) using a similar experimental approach to ours
but on a Polish loess soil. Compaction of the top 15 cm
soil layer appeared to be the most important in terms
of restricting crop growth. Campbell et al. (1986)
attributed the restriction in crop growth and yield after
heavy compaction to a combination of seed bed waterlogging and high soil strength below sowing depth.
They found soil strength, measured as cone resistance
at 15 cm depth, correlated well with winter barley
yield. Similarly, Dickson and Ritchie (1996) attributed
much of the variability of barley yield associated with
compaction to cone resistance between 0 and 27 cm
depth.
The satisfactory winter barley growth and yield of
the treatment of heavy compaction loosened to 10 cm
(Table 4) revealed the importance of shallow tillage
for ameliorating compaction. The top 10 cm of soil is
particularly important in controlling gas and water
movement and drainage (Ball et al., 1997b). Air
permeability showed a marked minimum at this depth
with values of