Directory UMM :Data Elmu:jurnal:S:Soil & Tillage Research:Vol57.Issue1-2.Sept2000:
Soil & Tillage Research 57 (2000) 83±91
Soil compactibility in relation to physical and organic
properties at 156 sites in UK
B.C. Balla,*, D.J. Campbella,1, E.A. Hunterb
a
b
Environment Division, Scottish Agricultural College, West Mains Road, Edinburgh EH9 3JG, UK
Biomathematics and Statistics, Scotland, James Clerk Maxwell Building, The King's Buildings, Edinburgh EH9 3JZ, UK
Received 9 February 2000; received in revised form 19 June 2000; accepted 28 June 2000
Abstract
The variation of soil compactibility and its relationship to plasticity, texture, organic matter and particle density is
considered for 156 sites and for one intensively sampled site. These sites were concentrated in east Scotland and were the
locations of Scottish Agricultural College (SAC) ®eld experiments and surveys related to tillage and compaction.
Compactibility was determined by a rammer method on sieved soil. The coef®cient of variability of compactibility (as
maximum dry bulk density) was relatively low between sites (9.5%) and within site (4%). The soils covered a wide range of
textures; sand contents ranged from 1.7 to 93.5 g 100 gÿ1 and clay contents ranged from 2.5 to 49.1 g 100 gÿ1. However,
liquid limit was more important than particle size fractions in the prediction of compactibility. Loss-on-pretreatment prior to
measurement of particle soil distribution was taken as a measure of readily oxidisable soil organic matter. This fraction was
more variable and more relevant than total organic matter in determining mechanical behaviour. Compactibility was predicted
adequately by a combination of loss-on-pretreatment and liquid limit. Maximum dry bulk density and liquid limit were
identi®ed as important characteristics of the dataset and would be suitable parameters for measurement of soil physical/
behavioural quality. Although particle density was not particularly important in predicting compactibility, it ranged from 2.36
to 2.87 Mg mÿ3. Awareness of this variability is important for properties estimated by a calculation involving particle density.
# 2000 Elsevier Science B.V. All rights reserved.
Keywords: Compaction; Organic matter; Plasticity; Survey
1. Introduction
Soil physical and mechanical properties were measured in order to characterise soils used in laboratory
and ®eld experiments on soil tillage and compaction
in south-east Scotland. Soane et al. (1972) tested 58
*
Corresponding author. Tel.: 44-131-535-4392;
fax: 44-131-667-2601.
E-mail address: [email protected] (B.C. Ball).
1
Present address: 11 Broomhill Road, Penicuik, Midlothian,
EH26 9EE, UK.
of these agricultural soils and found that compactibility and plasticity were better related to intrinsic
soil properties such as particle size distribution and
clay mineralogy than to classi®cations of soil type,
such as soil series, based on parent material and
drainage.
Many researchers have attempted to predict properties that are dif®cult or expensive to measure from
simpler, cheaper or more readily obtained measurements such as particle size distribution or organic
matter. Compactibility is time-consuming and expensive to measure because it requires measurement of
0167-1987/00/$ ± see front matter # 2000 Elsevier Science B.V. All rights reserved.
PII: S 0 1 6 7 - 1 9 8 7 ( 0 0 ) 0 0 1 4 5 - 8
84
B.C. Ball et al. / Soil & Tillage Research 57 (2000) 83±91
the response of soils to stress repeated at a range of
water contents (Horn and Lebert, 1994). Compactibility is usually speci®ed as a maximum bulk density
which can be used as a reference in describing the
relative compaction state of ®eld soils (Carter, 1990).
Compactibility is in¯uenced not only by the content of
organic matter but also the type of organic material
(Soane, 1990). Partly decomposed material, highly
humi®ed material and material of fungal origin are
particularly important in increasing resistance to compaction. In our tests, a simple method of destroying
organic material with hydrogen peroxide was used
prior to measurement of particle size distribution and
was used as an estimate of oxidisable organic matter
(Day, 1965).
Compactibility has also been related to clay content
(Gupta and Allmaras, 1987). Particle density also
varies with clay content and soil mineralogy, particularly with the content of iron-containing minerals
(Culley, 1993) and may in¯uence compactibility.
This paper considers a database of soil compactibility and other physical, mechanical and organic
matter properties created from analysis of soils collected from 156 sites over a period of 30 years at the
Scottish Agricultural College (SAC). Our objective is
to identify readily measured soil properties which
relate to compactibility. These include organic matter
determined as loss-on-pretreatment, plasticity indices
and particle density. We also show how compactibility
indices relate to other soil variables and vary between
sites, and within a single site.
2. Materials and methods
2.1. Soils
Soil samples were obtained from 156 sites, mainly
of experiments or areas monitored for advisory purposes. The regional distribution of sites is given in
Table 1. Most of the sites are in eastern Scotland near
the location of SAC in Edinburgh. All samples came
from within the cultivated layer and usually from a
depth of about 100 mm; six to eight sub-samples from
an area of about 0.3 ha typically being combined to
form the sample tested. In addition, a detailed analysis
of variation within one site was made in 1975±1976 by
taking 48 samples from an experimental ®eld site at
Table 1
Location of 156 sites
Symbol used
in Fig. 2
Location
No. of
samples
A
B
C
D
E
F
North-east Scotland
Angus, Fife and central Scotland
Lothians and Borders
South-west Scotland
North England and south-west Wales
South-east England
12
37
93
3
5
6
South Road, Bush estate, near Edinburgh. Pidgeon
(1980) described this experiment in detail. The samples were taken from the top 36 cm of soil (sampled at
6 cm depth intervals) from eight replicate plots of four
tillage treatments located on two soil types. Plots were
48 m 12 m. Samples were combined over replicates
prior to measurement.
2.2. Soil measurements
Soil properties were determined essentially by the
methods described in British Standards Institution
(1990) but with some minor modi®cations as
described below. The dry bulk density/water content
relationship was determined using the 2.5 kg `Proctor' rammer method (British Standards Institution,
1990). This provided both the maximum dry bulk
density and the optimum water content for compaction (the water content at maximum density). We also
include the total porosity at maximum density. Particle size distribution was determined by pretreatment
with 20 volume hydrogen peroxide followed by dry
sieving and then sedimentation using the pipette
method. The estimate of ``readily oxidisable organic
matter'' is the loss-on-pretreatment expressed as a
gravimetric fraction of the original mass of soil.
Particle density was measured on the treated residue.
The small pyknometer method was used with kerosene as the displacement ¯uid (British Standards
Institution, 1990). The cone penetrometer method
was used for the liquid limit. Plastic limit was determined by the standard method. For a limited number
of soils, total organic matter was obtained by the acid±
dichromate oxidation method described by Tinsley
(1950), a factor of 1.724 being used to convert from
organic carbon.
85
B.C. Ball et al. / Soil & Tillage Research 57 (2000) 83±91
2.3. Statistical analysis
Summary statistics (Table 2) were derived for the
``156 sites'' data set and histograms of each variable
were produced. The histograms for compactibility and
some of the more important and interesting related
variables are given in Fig. 1. Experimental data from
the ``South Road'' site were used to determine the
within-site variability as measured by the coef®cient
of variation from an analysis of variance (Table 2).
The method of Orchard and Woodbury (1972) as
implemented by the GenstatTM procedure MULTMISS was used to ®ll gaps in the data matrix (mainly
for plastic limit and plasticity index, but also for liquid
limit) prior to the computation of the correlation
matrix, given in Table 3. This technique allows units
with only partial data to be used.
The correlation matrix (Table 3) led naturally to a
principal components analysis (PCA) Ð see, e.g.
Krzanowski (1993). This technique is used to summarise the data whilst still preserving the major
features. Instead of trying to interpret 10 variables
which are correlated (Table 3), the data were reduced
to a smaller number (two) of summary variables
(scores) which were not correlated with each other.
The formulae for transforming the original variables
to the summary variables are called the loadings.
Using this technique the data were summarised by
the two principal scores which separated the sites best
and are used to plot them in Fig. 2. The scores are
de®ned by the equations (loadings) given in Table 4.
The correlations in columns 4 and 5 of Table 4 are
between the scores and the original variables. The
higher the correlation the more important the variable
is for forming the score. Correlations of contrasting
sign indicate contrasting effects of variables on the
scores. Multiple correlation (column 6 of Table 4)
integrates the correlations of the two scores.
Partial least squares (PLS), which was originally
developed as a calibration method for chemical data
(Hoskuldsson, 1988), was used to determine predictive equations for compactibility properties from
other properties (Table 5). Principal components
regression (PCR) summarises the independent variates by deriving principal component scores for a
smaller number of signi®cant components. Multiple
linear regression (MLR) is then used to estimate a
prediction equation. These equations are then converted into equations in the original independent
variables using the matrix of PCA loadings. A
Table 2
Variation of soil properties for the 156 sites and for the South Road ®eld experiment (48 samples)
Variable
Maximum dry bulk density (Mg mÿ3)
Water content at maximum density (g 100 gÿ1)
Total porosity at maximum density (cm3 cmÿ3)
Liquid limit (g 100 gÿ1)
Plastic limit (g 100 gÿ1)
Plasticity index
Treated particle density (Mg mÿ3)
Loss-on-pretreatment (g 100 gÿ1)
Total organic matter (g 100 gÿ1)
Total sand (2±0.06 mm) (g 100 gÿ1)
Coarse sand (2±0.6 mm) (g 100 gÿ1)
Medium sand (0.6±0.2 mm) (g 100 gÿ1)
Fine sand (0.2±0.06 mm) (g 100 gÿ1)
Total silt (0.06±0.002 mm) (g 100 gÿ1)
Coarse silt (0.06±0.02 mm) (g 100 gÿ1)
Medium silt (0.02±0.006 mm) (g 100 gÿ1)
Fine silt (0.006±0.002 mm) (g 100 gÿ1)
Clay (
Soil compactibility in relation to physical and organic
properties at 156 sites in UK
B.C. Balla,*, D.J. Campbella,1, E.A. Hunterb
a
b
Environment Division, Scottish Agricultural College, West Mains Road, Edinburgh EH9 3JG, UK
Biomathematics and Statistics, Scotland, James Clerk Maxwell Building, The King's Buildings, Edinburgh EH9 3JZ, UK
Received 9 February 2000; received in revised form 19 June 2000; accepted 28 June 2000
Abstract
The variation of soil compactibility and its relationship to plasticity, texture, organic matter and particle density is
considered for 156 sites and for one intensively sampled site. These sites were concentrated in east Scotland and were the
locations of Scottish Agricultural College (SAC) ®eld experiments and surveys related to tillage and compaction.
Compactibility was determined by a rammer method on sieved soil. The coef®cient of variability of compactibility (as
maximum dry bulk density) was relatively low between sites (9.5%) and within site (4%). The soils covered a wide range of
textures; sand contents ranged from 1.7 to 93.5 g 100 gÿ1 and clay contents ranged from 2.5 to 49.1 g 100 gÿ1. However,
liquid limit was more important than particle size fractions in the prediction of compactibility. Loss-on-pretreatment prior to
measurement of particle soil distribution was taken as a measure of readily oxidisable soil organic matter. This fraction was
more variable and more relevant than total organic matter in determining mechanical behaviour. Compactibility was predicted
adequately by a combination of loss-on-pretreatment and liquid limit. Maximum dry bulk density and liquid limit were
identi®ed as important characteristics of the dataset and would be suitable parameters for measurement of soil physical/
behavioural quality. Although particle density was not particularly important in predicting compactibility, it ranged from 2.36
to 2.87 Mg mÿ3. Awareness of this variability is important for properties estimated by a calculation involving particle density.
# 2000 Elsevier Science B.V. All rights reserved.
Keywords: Compaction; Organic matter; Plasticity; Survey
1. Introduction
Soil physical and mechanical properties were measured in order to characterise soils used in laboratory
and ®eld experiments on soil tillage and compaction
in south-east Scotland. Soane et al. (1972) tested 58
*
Corresponding author. Tel.: 44-131-535-4392;
fax: 44-131-667-2601.
E-mail address: [email protected] (B.C. Ball).
1
Present address: 11 Broomhill Road, Penicuik, Midlothian,
EH26 9EE, UK.
of these agricultural soils and found that compactibility and plasticity were better related to intrinsic
soil properties such as particle size distribution and
clay mineralogy than to classi®cations of soil type,
such as soil series, based on parent material and
drainage.
Many researchers have attempted to predict properties that are dif®cult or expensive to measure from
simpler, cheaper or more readily obtained measurements such as particle size distribution or organic
matter. Compactibility is time-consuming and expensive to measure because it requires measurement of
0167-1987/00/$ ± see front matter # 2000 Elsevier Science B.V. All rights reserved.
PII: S 0 1 6 7 - 1 9 8 7 ( 0 0 ) 0 0 1 4 5 - 8
84
B.C. Ball et al. / Soil & Tillage Research 57 (2000) 83±91
the response of soils to stress repeated at a range of
water contents (Horn and Lebert, 1994). Compactibility is usually speci®ed as a maximum bulk density
which can be used as a reference in describing the
relative compaction state of ®eld soils (Carter, 1990).
Compactibility is in¯uenced not only by the content of
organic matter but also the type of organic material
(Soane, 1990). Partly decomposed material, highly
humi®ed material and material of fungal origin are
particularly important in increasing resistance to compaction. In our tests, a simple method of destroying
organic material with hydrogen peroxide was used
prior to measurement of particle size distribution and
was used as an estimate of oxidisable organic matter
(Day, 1965).
Compactibility has also been related to clay content
(Gupta and Allmaras, 1987). Particle density also
varies with clay content and soil mineralogy, particularly with the content of iron-containing minerals
(Culley, 1993) and may in¯uence compactibility.
This paper considers a database of soil compactibility and other physical, mechanical and organic
matter properties created from analysis of soils collected from 156 sites over a period of 30 years at the
Scottish Agricultural College (SAC). Our objective is
to identify readily measured soil properties which
relate to compactibility. These include organic matter
determined as loss-on-pretreatment, plasticity indices
and particle density. We also show how compactibility
indices relate to other soil variables and vary between
sites, and within a single site.
2. Materials and methods
2.1. Soils
Soil samples were obtained from 156 sites, mainly
of experiments or areas monitored for advisory purposes. The regional distribution of sites is given in
Table 1. Most of the sites are in eastern Scotland near
the location of SAC in Edinburgh. All samples came
from within the cultivated layer and usually from a
depth of about 100 mm; six to eight sub-samples from
an area of about 0.3 ha typically being combined to
form the sample tested. In addition, a detailed analysis
of variation within one site was made in 1975±1976 by
taking 48 samples from an experimental ®eld site at
Table 1
Location of 156 sites
Symbol used
in Fig. 2
Location
No. of
samples
A
B
C
D
E
F
North-east Scotland
Angus, Fife and central Scotland
Lothians and Borders
South-west Scotland
North England and south-west Wales
South-east England
12
37
93
3
5
6
South Road, Bush estate, near Edinburgh. Pidgeon
(1980) described this experiment in detail. The samples were taken from the top 36 cm of soil (sampled at
6 cm depth intervals) from eight replicate plots of four
tillage treatments located on two soil types. Plots were
48 m 12 m. Samples were combined over replicates
prior to measurement.
2.2. Soil measurements
Soil properties were determined essentially by the
methods described in British Standards Institution
(1990) but with some minor modi®cations as
described below. The dry bulk density/water content
relationship was determined using the 2.5 kg `Proctor' rammer method (British Standards Institution,
1990). This provided both the maximum dry bulk
density and the optimum water content for compaction (the water content at maximum density). We also
include the total porosity at maximum density. Particle size distribution was determined by pretreatment
with 20 volume hydrogen peroxide followed by dry
sieving and then sedimentation using the pipette
method. The estimate of ``readily oxidisable organic
matter'' is the loss-on-pretreatment expressed as a
gravimetric fraction of the original mass of soil.
Particle density was measured on the treated residue.
The small pyknometer method was used with kerosene as the displacement ¯uid (British Standards
Institution, 1990). The cone penetrometer method
was used for the liquid limit. Plastic limit was determined by the standard method. For a limited number
of soils, total organic matter was obtained by the acid±
dichromate oxidation method described by Tinsley
(1950), a factor of 1.724 being used to convert from
organic carbon.
85
B.C. Ball et al. / Soil & Tillage Research 57 (2000) 83±91
2.3. Statistical analysis
Summary statistics (Table 2) were derived for the
``156 sites'' data set and histograms of each variable
were produced. The histograms for compactibility and
some of the more important and interesting related
variables are given in Fig. 1. Experimental data from
the ``South Road'' site were used to determine the
within-site variability as measured by the coef®cient
of variation from an analysis of variance (Table 2).
The method of Orchard and Woodbury (1972) as
implemented by the GenstatTM procedure MULTMISS was used to ®ll gaps in the data matrix (mainly
for plastic limit and plasticity index, but also for liquid
limit) prior to the computation of the correlation
matrix, given in Table 3. This technique allows units
with only partial data to be used.
The correlation matrix (Table 3) led naturally to a
principal components analysis (PCA) Ð see, e.g.
Krzanowski (1993). This technique is used to summarise the data whilst still preserving the major
features. Instead of trying to interpret 10 variables
which are correlated (Table 3), the data were reduced
to a smaller number (two) of summary variables
(scores) which were not correlated with each other.
The formulae for transforming the original variables
to the summary variables are called the loadings.
Using this technique the data were summarised by
the two principal scores which separated the sites best
and are used to plot them in Fig. 2. The scores are
de®ned by the equations (loadings) given in Table 4.
The correlations in columns 4 and 5 of Table 4 are
between the scores and the original variables. The
higher the correlation the more important the variable
is for forming the score. Correlations of contrasting
sign indicate contrasting effects of variables on the
scores. Multiple correlation (column 6 of Table 4)
integrates the correlations of the two scores.
Partial least squares (PLS), which was originally
developed as a calibration method for chemical data
(Hoskuldsson, 1988), was used to determine predictive equations for compactibility properties from
other properties (Table 5). Principal components
regression (PCR) summarises the independent variates by deriving principal component scores for a
smaller number of signi®cant components. Multiple
linear regression (MLR) is then used to estimate a
prediction equation. These equations are then converted into equations in the original independent
variables using the matrix of PCA loadings. A
Table 2
Variation of soil properties for the 156 sites and for the South Road ®eld experiment (48 samples)
Variable
Maximum dry bulk density (Mg mÿ3)
Water content at maximum density (g 100 gÿ1)
Total porosity at maximum density (cm3 cmÿ3)
Liquid limit (g 100 gÿ1)
Plastic limit (g 100 gÿ1)
Plasticity index
Treated particle density (Mg mÿ3)
Loss-on-pretreatment (g 100 gÿ1)
Total organic matter (g 100 gÿ1)
Total sand (2±0.06 mm) (g 100 gÿ1)
Coarse sand (2±0.6 mm) (g 100 gÿ1)
Medium sand (0.6±0.2 mm) (g 100 gÿ1)
Fine sand (0.2±0.06 mm) (g 100 gÿ1)
Total silt (0.06±0.002 mm) (g 100 gÿ1)
Coarse silt (0.06±0.02 mm) (g 100 gÿ1)
Medium silt (0.02±0.006 mm) (g 100 gÿ1)
Fine silt (0.006±0.002 mm) (g 100 gÿ1)
Clay (