Directory UMM :Data Elmu:jurnal:S:Soil & Tillage Research:Vol56.Issue3-4.Aug2000:
Soil & Tillage Research 56 (2000) 185±196
Compressibility of soils in a long term ®eld experiment
with intensive deep ripping in Romania
A. Canarachea,*, R. Hornb, I. Colibasc
a
b
Research Institute for Soil Science and Agrochemistry, Bd. Marasti 61, Bucharesti 71331, Romania
Institute for Plant Nutrition and Soil Science, Christian-Albrechts UniversitaÈt, Olshausenstrasse 40-60, 24118 Kiel, Germany
c
Agricultural Research Station Oradea, Sos. Aradului 4, Oradea, Romania
Received 23 March 1999; received in revised form 7 March 2000; accepted 28 June 2000
Abstract
Laboratory compressibility tests were done on soil samples taken from a ®eld experiment 21 years old, located on a Stagnic
Luvisol, with deep ripping performed with various frequencies: no ripping, ripping every 8, 4 and 2 years, and ripping yearly.
Precompression stress was found to increase with depth of the soil pro®le down to some 60 cm, and somewhat decreasing at
the depth of 70±75 cm, which corresponds to the Bt horizon. Due to ripping, the values of the precompression stress
decreased; for soils from experimental treatments with different periodicity of ripping operations, the differences were small,
and not in a very de®nite direction. The estimation procedures suggested by Lebert to predict precompression stress for
``normal'' arable soils could not be applied to ameliorated soil samples investigated in this paper because repeated ripping
prevents a continuous aggregate formation and results mainly in structural texture dependent relations. The compression index
showed an increase down to 60 cm and a decrease in the Bt horizon (70±75 cm). In the different experimental treatments, it
showed a less clear variation, although some trend of increasing with increased number of rippings may be considered. As
inferred from these parameters, soil strength and compressibility do not affect directly crop yields. # 2000 Elsevier Science
B.V. All rights reserved.
Keywords: Precompression stress; Compression index; Stagnic Luvisol; Deep ripping
1. Introduction
1.1. General review
Deep ripping of soils with a heavy textured, compact and impervious subsoil (Schulte-Karing, 1970;
Wildman, not dated; Zaidelman, 1985) is expanding
nowadays in many countries, including Romania
(Canarache, 1978). In this country, due to speci®c
*
Corresponding author. Tel.: 40-1-2271331;
fax: 40-1-2225979.
E-mail address: [email protected] (A. Canarache).
soil and climatic conditions, the positive effect of deep
ripping is rapidly decreasing, leading to the need of
repeating this practice every 4±6 years (Stanga et al.,
1975; Colibas et al., 1989).
Mechanical soil properties are less studied in this
context. The differentiation of soil strength by
mechanical and physical measurements always
includes a ``normal'' strength increase by aggregate
formation, as well as the soil reaction to external
forces creating an anthropopgenic strength increase.
Thus, the determination of the precompression stress
is a measure to quantify this ``summed'' effect. The
effect of subsoiling however coincides with a loosen-
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 3 - 4
186
A. Canarache et al. / Soil & Tillage Research 56 (2000) 185±196
ing or deterioration of the aggregate strength, which
especially in hardsetting and in overcompacted soils
results in a weaker, less stable soil, which is even more
susceptible for a subsequent intense overcompaction.
There are several papers, mentioned above, which
report the bene®ts of such loosening on crop yields,
however it is unclear how far you can quantify the
``reloosening'' and ``reaggregation'' processes by
means of the precompression test.
Shear strength and stress distribution were determined in a slit-plough ®eld experiment on a silty sandy
Luvisol (Horn et al., 1998). Laboratory compressibility tests are frequently used as related to studies on soil
compaction (Horn, 1981). Curves describing the relationship between applied load (logarithmic) and bulk
density (or void ratio) are well known to consist of two
parts: a linear one, the virgin compression line of
which slope is called the compression index (Terzaghi
and Peck, 1967), and a non-linear one resulting from
re-compression of the previously loosened soil. The
intercept of the two components of the curve is the
precompression stress (Casagrande, 1936), also called
reference normal stress (McNabb and Boersma,
1996), widely accepted as a good index to describe
soil compressibility. Estimation of the precompression
stress from current soil properties has been suggested
by Lebert and Horn (1991) for agricultural soils without often repeated aggregate deterioration by deep
loosening techniques.
1.2. Earlier research in the ®eld experiment used in
this paper
The current technique practiced in Romania, with
repeated deep ripping every 4±6 years as mentioned
above, was considered as possibly having some long
range effects, perhaps negative ones. To get some
knowledge in this sense, a ®eld experiment simulating
such changes was established at Sanmartin (northwestern Romania) in the fall of 1977 and conducted
until 1998. Results on crop yields, some current
physical and chemical properties, moisture regime,
etc. from this experiment have been published 6 and
14 years after starting the experiment (Colibas et al.,
1985, 1994). It was concluded that at those stages no
negative effects occur, while earlier conclusions showing signi®cant increases in crop yield and net economic output due to deep ripping, as well as the need
to repeat this practice every 4±6 years, were con®rmed.
1.3. Objectives
This paper refers to new data resulting from the long
term ®eld experiment with repeated deep ripping
mentioned earlier:
results of compressibility tests, not undertaken
previously, performed on soil samples from the
Sanmartin intensive deep ripping experiment;
results on some physical soil properties from the
same field experiment, not included in earlier
publications, and relationships of these data with
the results of the compressibility tests;
final data on crop yields for the 21 years, thus
completing earlier data which referred to only the
first and the second stage of the experiment, and
relationships of crop yields with the soil physical
properties and with the results of the compressibility tests in the various treatments.
2. Materials and methods
The Sanmartin intensive deep ripping ®eld experiment was located on a pseudogleyed Albic Luvisol
(Romanian classi®cation; approximate WRB equivalent: Stagnic Luvisol). The soil (Table 1) is a silt loam
in the upper horizons, and a silty clay in the lower
ones. Bulk density is high all-over the soil pro®le.
Saturated hydraulic conductivity is very low, especially in the lower horizons. Yearly average climatic
data (Fig. 1) are characterized by a temperature of
10.58C, rainfall of 635 mm, potential evapotranspiration of 689 mm, and length of the frost-free season of
180 days.
The ®eld experiment was established in 1977 and
continued until 1998, with some non-signi®cant interruptions in actual performing of deep ripping during
the last 8 years. Deep ripping was always done late
autumn, usually under dry soil conditions (16±18%
(w/w), pF 3±3.5), at a depth of 70±75 cm, with a
spacing of 100 cm between rippers, following every
time the same traces; the volume of soil effectively
loosened was 41±46% of the whole soil volume on a
depth of 80 cm. An alternation of winter wheat and
187
A. Canarache et al. / Soil & Tillage Research 56 (2000) 185±196
Table 1
Soil properties of the Stagnic Luvisol at Sanmartin
Horizon
Ap
El
E/B
Bt
Depth
(cm)
0±21
21±42
42±58
58±122
Soil texture (%, w/w)
Humus
Saturated
(%)
hydraulic
conductivity
(mm hÿ1)
pH in
water
Compressibility of soils in a long term ®eld experiment
with intensive deep ripping in Romania
A. Canarachea,*, R. Hornb, I. Colibasc
a
b
Research Institute for Soil Science and Agrochemistry, Bd. Marasti 61, Bucharesti 71331, Romania
Institute for Plant Nutrition and Soil Science, Christian-Albrechts UniversitaÈt, Olshausenstrasse 40-60, 24118 Kiel, Germany
c
Agricultural Research Station Oradea, Sos. Aradului 4, Oradea, Romania
Received 23 March 1999; received in revised form 7 March 2000; accepted 28 June 2000
Abstract
Laboratory compressibility tests were done on soil samples taken from a ®eld experiment 21 years old, located on a Stagnic
Luvisol, with deep ripping performed with various frequencies: no ripping, ripping every 8, 4 and 2 years, and ripping yearly.
Precompression stress was found to increase with depth of the soil pro®le down to some 60 cm, and somewhat decreasing at
the depth of 70±75 cm, which corresponds to the Bt horizon. Due to ripping, the values of the precompression stress
decreased; for soils from experimental treatments with different periodicity of ripping operations, the differences were small,
and not in a very de®nite direction. The estimation procedures suggested by Lebert to predict precompression stress for
``normal'' arable soils could not be applied to ameliorated soil samples investigated in this paper because repeated ripping
prevents a continuous aggregate formation and results mainly in structural texture dependent relations. The compression index
showed an increase down to 60 cm and a decrease in the Bt horizon (70±75 cm). In the different experimental treatments, it
showed a less clear variation, although some trend of increasing with increased number of rippings may be considered. As
inferred from these parameters, soil strength and compressibility do not affect directly crop yields. # 2000 Elsevier Science
B.V. All rights reserved.
Keywords: Precompression stress; Compression index; Stagnic Luvisol; Deep ripping
1. Introduction
1.1. General review
Deep ripping of soils with a heavy textured, compact and impervious subsoil (Schulte-Karing, 1970;
Wildman, not dated; Zaidelman, 1985) is expanding
nowadays in many countries, including Romania
(Canarache, 1978). In this country, due to speci®c
*
Corresponding author. Tel.: 40-1-2271331;
fax: 40-1-2225979.
E-mail address: [email protected] (A. Canarache).
soil and climatic conditions, the positive effect of deep
ripping is rapidly decreasing, leading to the need of
repeating this practice every 4±6 years (Stanga et al.,
1975; Colibas et al., 1989).
Mechanical soil properties are less studied in this
context. The differentiation of soil strength by
mechanical and physical measurements always
includes a ``normal'' strength increase by aggregate
formation, as well as the soil reaction to external
forces creating an anthropopgenic strength increase.
Thus, the determination of the precompression stress
is a measure to quantify this ``summed'' effect. The
effect of subsoiling however coincides with a loosen-
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 3 - 4
186
A. Canarache et al. / Soil & Tillage Research 56 (2000) 185±196
ing or deterioration of the aggregate strength, which
especially in hardsetting and in overcompacted soils
results in a weaker, less stable soil, which is even more
susceptible for a subsequent intense overcompaction.
There are several papers, mentioned above, which
report the bene®ts of such loosening on crop yields,
however it is unclear how far you can quantify the
``reloosening'' and ``reaggregation'' processes by
means of the precompression test.
Shear strength and stress distribution were determined in a slit-plough ®eld experiment on a silty sandy
Luvisol (Horn et al., 1998). Laboratory compressibility tests are frequently used as related to studies on soil
compaction (Horn, 1981). Curves describing the relationship between applied load (logarithmic) and bulk
density (or void ratio) are well known to consist of two
parts: a linear one, the virgin compression line of
which slope is called the compression index (Terzaghi
and Peck, 1967), and a non-linear one resulting from
re-compression of the previously loosened soil. The
intercept of the two components of the curve is the
precompression stress (Casagrande, 1936), also called
reference normal stress (McNabb and Boersma,
1996), widely accepted as a good index to describe
soil compressibility. Estimation of the precompression
stress from current soil properties has been suggested
by Lebert and Horn (1991) for agricultural soils without often repeated aggregate deterioration by deep
loosening techniques.
1.2. Earlier research in the ®eld experiment used in
this paper
The current technique practiced in Romania, with
repeated deep ripping every 4±6 years as mentioned
above, was considered as possibly having some long
range effects, perhaps negative ones. To get some
knowledge in this sense, a ®eld experiment simulating
such changes was established at Sanmartin (northwestern Romania) in the fall of 1977 and conducted
until 1998. Results on crop yields, some current
physical and chemical properties, moisture regime,
etc. from this experiment have been published 6 and
14 years after starting the experiment (Colibas et al.,
1985, 1994). It was concluded that at those stages no
negative effects occur, while earlier conclusions showing signi®cant increases in crop yield and net economic output due to deep ripping, as well as the need
to repeat this practice every 4±6 years, were con®rmed.
1.3. Objectives
This paper refers to new data resulting from the long
term ®eld experiment with repeated deep ripping
mentioned earlier:
results of compressibility tests, not undertaken
previously, performed on soil samples from the
Sanmartin intensive deep ripping experiment;
results on some physical soil properties from the
same field experiment, not included in earlier
publications, and relationships of these data with
the results of the compressibility tests;
final data on crop yields for the 21 years, thus
completing earlier data which referred to only the
first and the second stage of the experiment, and
relationships of crop yields with the soil physical
properties and with the results of the compressibility tests in the various treatments.
2. Materials and methods
The Sanmartin intensive deep ripping ®eld experiment was located on a pseudogleyed Albic Luvisol
(Romanian classi®cation; approximate WRB equivalent: Stagnic Luvisol). The soil (Table 1) is a silt loam
in the upper horizons, and a silty clay in the lower
ones. Bulk density is high all-over the soil pro®le.
Saturated hydraulic conductivity is very low, especially in the lower horizons. Yearly average climatic
data (Fig. 1) are characterized by a temperature of
10.58C, rainfall of 635 mm, potential evapotranspiration of 689 mm, and length of the frost-free season of
180 days.
The ®eld experiment was established in 1977 and
continued until 1998, with some non-signi®cant interruptions in actual performing of deep ripping during
the last 8 years. Deep ripping was always done late
autumn, usually under dry soil conditions (16±18%
(w/w), pF 3±3.5), at a depth of 70±75 cm, with a
spacing of 100 cm between rippers, following every
time the same traces; the volume of soil effectively
loosened was 41±46% of the whole soil volume on a
depth of 80 cm. An alternation of winter wheat and
187
A. Canarache et al. / Soil & Tillage Research 56 (2000) 185±196
Table 1
Soil properties of the Stagnic Luvisol at Sanmartin
Horizon
Ap
El
E/B
Bt
Depth
(cm)
0±21
21±42
42±58
58±122
Soil texture (%, w/w)
Humus
Saturated
(%)
hydraulic
conductivity
(mm hÿ1)
pH in
water