Directory UMM :Data Elmu:jurnal:S:Soil & Tillage Research:Vol53.Issue3-4.Feb2000:
Soil & Tillage Research 53 (2000) 231±243
Effects of mechanical energy inputs on soil respiration
at the aggregate and ®eld scales
C.W. Wattsa,*, S. Eichb, A.R. Dexterc
a
Silsoe Research Institute, Wrest Park, Silsoe, Bedford MK45 4HS, UK
Norwegian Agricultural University, PO Box 5028, 1432 Aas, Norway
c
Institute of Soil Science and Plant Cultivation, ul. Czartoryskich 8, 24-100 Pulawy, Poland
b
Accepted 21 October 1999
Abstract
Cultivation machinery applies large amounts of mechanical energy to the soil and often brings about a decrease in soil
organic carbon (SOC). New experiments on the effects of mechanical energy inputs on soil respiration are reported and the
results discussed. In the laboratory, a speci®c energy, K, of 150 J kgÿ1, similar to that experienced during typical cultivation
operations, was applied to soil aggregates using a falling weight. Respiration (carbon dioxide, CO2 emission) of the samples
was then measured by an electrical conductimetric method. Basal respiration (when K0) measured on Chromic Luvisol
aggregates, was found to increase with increasing SOC, from 1.88 mg CO2 gÿ1 hÿ1 for a permanent fallow soil
(SOC11 g kgÿ1) to 8.25 mg CO2 gÿ1 hÿ1 for a permanent grassland soil (SOC32 g kgÿ1). Basal respiration of a Calcic
Cambisol, more than doubled (2.0±5.2 mg CO2 gÿ1 hÿ1) with increasing gravimetric soil water contents. Mechanical energy
inputs caused an initial burst of increased respiration, which lasted up to 4 h. Over the following 4±24 h period, arable soils
with lower SOC contents, (11±21 g kgÿ1), respiration rates dropped back to a level, approximately 1.14 times higher than the
basal value. However, grassland soils with higher SOC contents (28±32 g kgÿ1), increases in this longer-term respiration rate
following 150 J kgÿ1 of energy, were negligible. A ®eld experiment, in which CO2 was measured by infra-red absorption, also
showed that tillage stimulated increased levels of soil respiration for periods ranging from 12 h to more than one week. The
highest respiration rates, 80 mg CO2 mÿ2 hÿ1 were associated with high energy, powered tillage on clay soils. On the same
soil, low energy draught tillage resulted in a respiration rate of approximately half this value. The results of these experiments
are discussed in relation to equilibrium levels of soil organic matter. The application of known quantities of mechanical energy
to soil aggregates under laboratory conditions, in order to simulate the effect of different cultivation practices, when combined
with the subsequent measurement of soil respiration, can provide useful indication of the likely consequences of soil
management on SOC. # 2000 Elsevier Science B.V. All rights reserved.
Keywords: Mechanical energy; Organic matter; Physical protection; Respiration; Respirometer
1. Introduction
*
Corresponding author. Tel.: 44-1525-860000; fax: 44-1525860156.
E-mail address: chris.watts@bbsrc.ac.uk (C.W. Watts).
For many years, increased intensity of arable cultivation, particularly under wet conditions, has been
0167-1987/00/$ ± see front matter # 2000 Elsevier Science B.V. All rights reserved.
PII: S 0 1 6 7 - 1 9 8 7 ( 9 9 ) 0 0 1 0 8 - 7
232
C.W. Watts et al. / Soil & Tillage Research 53 (2000) 231±243
linked to a decline in soil physical conditions (Greenland et al., 1975). The increasing dif®culty in managing these soils is thought to be partly associated with
a reduction in soil organic carbon (SOC). In turn, this
has resulted in more intensive cultivations. The depletion of the carbon pool by cultivations thus has signi®cant implications for soil quality and greenhouse
gas emission (Kern and Johnson, 1993).
Soil organic carbon has been shown to be very
important for many aspects of soil physical quality.
For example, greater contents of SOC have been
associated with greater stability in water (Oades,
1984), greater porosity and lower bulk density leading
to lower dry strength, increased friability (Watts and
Dexter, 1998) and a greater resistance to mechanical
damage (Watts and Dexter, 1997). Other desirable
properties of agricultural soils such as good water
holding capacity and good aeration status are also
found to be positively correlated with SOC.
For soils in a steady state, the annual loss of carbon
(C) is equal to the annual input. The inputs of organic
C are usually through photosynthesis by plants and the
incorporation of the carbon is thus `®xed' into soil
organic matter pools. The greatest route for output
from agricultural or forest soils is by respiration of
carbon dioxide (CO2) by organisms which are decomposing the compounds containing the SOC. When a
system is disturbed, such as by a change in land use,
cropping or other management practices including
cultivation, it is likely no longer to be in a steady
state. Numerous studies have been conducted in the
®eld to evaluate the change in microbial activity as a
result of different cultivation systems (Carter, 1992;
Chan et al., 1992; Beare et al., 1994; Franzluebbers
et al., 1994). These studies also suggest that tillage
opens up pores thus exposing previously physically
protected SOC to attack by organisms. Other changes
likely to in¯uence microbial activity following cultivation include changes to soil climate, water status and
aeration.
The mechanical disturbance of soil, by cultivation
for example, has been shown to increase the rate of
loss of organic C by increasing microbial activity as
measured by soil respiration (Rovira and Greacen,
1957; Reicosky et al., 1995; Watts et al., 1999). In
general, it has been found that the increasing levels of
mechanical energy applied to soil, have produced
increased rates of respiration. Such measurements
can give a sensitive indication of the short term of
changes which take many years to reach new equilibria values.
The energy inputs to soil following different cultivation operations have been measured in long-term
experiments by Patterson et al. (1980). Some typical
energy values are given in Table 1 for different
cultivation systems. In commercial agriculture, total
inputs of mechanical energy to soil during primary and
secondary cultivation and seeding operations can
often approach 300 J kgÿ1.
In order to obtain a better understanding of the
relationship between the application of different
amounts of mechanical energy and soil respiration
there is a need for controlled laboratory experiments to
complement ®eld experiments. In a recent study of the
effects of mechanical energy on aggregate stability,
Watts et al. (1996a,b) used a simple falling weight to
simulate similar energy levels to those used during
cultivation operations. In this study, we use the same
apparatus to investigate the effects of different
mechanical energy inputs on the respiration of collections of aggregates. The aggregates were obtained
from soils with long histories of different management
Table 1
Examples of speci®c mechanical energy inputs to two soils by different tillage systemsa
Cultivation system
Plough, cultivator drill
Chisel plough (2 passes), cultivator drill
Shallow plough, combined cultivator drill
Spring tine, cultivator (2 passes)
a
Data adapted from Patterson et al. (1980).
Redbourne,
90 g kgÿ1 clay
(J kgÿ1)
68
124
82
72
Silsoe,
510 g kgÿ1 clay
(J kgÿ1)
132
177
161
90
233
C.W. Watts et al. / Soil & Tillage Research 53 (2000) 231±243
practices and consequently different SOC contents.
Measurements were then made under controlled
laboratory conditions at different water contents,
but at a constant temperature.
The object of this work was to develop a technique
for assessing, under laboratory conditions, the effect
of applying to soil aggregates, mechanical energies
similar in magnitude to those experienced during
cultivation operations, and from this assess the effects
on soil respiration. In addition, we measured respiration in the ®eld following cultivation operations of
differing intensities.
2. Materials and methods
2.1. Soil
Laboratory experiments were carried out on soils
from High®eld and Boot Field sites while ®eld experiments were conducted on Boot Field and Pavillion
Fields.
High®eld is one of the ley-arable experiments on
Rothamsted Experimental Station. The soil is of the
Batcombe Series, (approximate FAO equivalent is the
Chromic Luvisol; Avery, 1980), and is de®ned as ®ne
silty over clayey drift with siliceous stones (Clayden
and Hollis, 1984). The original experiments were
conducted to compare contrasting crop rotational
systems and to determine their effects on the yields
of three arable test crops. These experiments were
started in 1949, before which High®eld had been very
old permanent grassland. Cultivation, drilling, harvesting and other management practices are described
in Johnston (1972). Soil samples were taken from the
0±100 mm horizon of ®ve plots with contrasting
management regimes, which have caused different
reductions in SOC over 50 years. Some important
properties of these samples are given in Table 2.
Boot Field, Silsoe (the site of the ®rst ®eld experiment) had previously grown cereals but had been in
set-aside for approximately 18 months prior to this
experiment. The soil is a typical calcarious pelosol
(Gleyic and Calcic Cambisols, Calcaric Gleysols in
the FAO System; Avery, 1980) of the Evesham Series,
i.e., swelling-clayey material passing to clay or soft
mudstone (Clayden and Hollis, 1984). The texture is
classi®ed as clay.
Pavilion Field, Silsoe (the site of the second ®eld
experiment) had also been set-aside for 18 months.
The soil differs considerably from that in Boot Field. It
is a typical brown earth (Dystric and Eutric Cambisols
in the FAO System; Avery, 1980) of the Bearsted
Series, comprising coarse loamy material passing to
sand or soft sandstone (Clayden and Hollis, 1984). The
texture is classi®ed as a sandy loam. Compositions of
these soils are given in Table 2.
2.2. Sample collection and preparation
For the laboratory experiments, the soil samples
were collected from the 0±100 mm horizon, air-dried,
Table 2
Composition of the experimental soils
Site
Rothamsted
Highfield
Silsoe
Boot Field
Pavilion Field
a
Treatment
Sand (g kgÿ1)a
Silt (g kgÿ1)b
Clay (g kgÿ1)c
SOC (g kgÿ1)
Permanent grass
Reseeded grass
Ley-arable rotation
Continuous arable
Permanent fallow
110
110
110
120
90
670
620
630
640
660
230
270
250
240
250
32
28
21
15
11
Arable
Arable
90
700
180
170
730
130
35
16
Sand2.0±0.063 mm.
Silt63ÿ2 mm.
c
Clay
Effects of mechanical energy inputs on soil respiration
at the aggregate and ®eld scales
C.W. Wattsa,*, S. Eichb, A.R. Dexterc
a
Silsoe Research Institute, Wrest Park, Silsoe, Bedford MK45 4HS, UK
Norwegian Agricultural University, PO Box 5028, 1432 Aas, Norway
c
Institute of Soil Science and Plant Cultivation, ul. Czartoryskich 8, 24-100 Pulawy, Poland
b
Accepted 21 October 1999
Abstract
Cultivation machinery applies large amounts of mechanical energy to the soil and often brings about a decrease in soil
organic carbon (SOC). New experiments on the effects of mechanical energy inputs on soil respiration are reported and the
results discussed. In the laboratory, a speci®c energy, K, of 150 J kgÿ1, similar to that experienced during typical cultivation
operations, was applied to soil aggregates using a falling weight. Respiration (carbon dioxide, CO2 emission) of the samples
was then measured by an electrical conductimetric method. Basal respiration (when K0) measured on Chromic Luvisol
aggregates, was found to increase with increasing SOC, from 1.88 mg CO2 gÿ1 hÿ1 for a permanent fallow soil
(SOC11 g kgÿ1) to 8.25 mg CO2 gÿ1 hÿ1 for a permanent grassland soil (SOC32 g kgÿ1). Basal respiration of a Calcic
Cambisol, more than doubled (2.0±5.2 mg CO2 gÿ1 hÿ1) with increasing gravimetric soil water contents. Mechanical energy
inputs caused an initial burst of increased respiration, which lasted up to 4 h. Over the following 4±24 h period, arable soils
with lower SOC contents, (11±21 g kgÿ1), respiration rates dropped back to a level, approximately 1.14 times higher than the
basal value. However, grassland soils with higher SOC contents (28±32 g kgÿ1), increases in this longer-term respiration rate
following 150 J kgÿ1 of energy, were negligible. A ®eld experiment, in which CO2 was measured by infra-red absorption, also
showed that tillage stimulated increased levels of soil respiration for periods ranging from 12 h to more than one week. The
highest respiration rates, 80 mg CO2 mÿ2 hÿ1 were associated with high energy, powered tillage on clay soils. On the same
soil, low energy draught tillage resulted in a respiration rate of approximately half this value. The results of these experiments
are discussed in relation to equilibrium levels of soil organic matter. The application of known quantities of mechanical energy
to soil aggregates under laboratory conditions, in order to simulate the effect of different cultivation practices, when combined
with the subsequent measurement of soil respiration, can provide useful indication of the likely consequences of soil
management on SOC. # 2000 Elsevier Science B.V. All rights reserved.
Keywords: Mechanical energy; Organic matter; Physical protection; Respiration; Respirometer
1. Introduction
*
Corresponding author. Tel.: 44-1525-860000; fax: 44-1525860156.
E-mail address: chris.watts@bbsrc.ac.uk (C.W. Watts).
For many years, increased intensity of arable cultivation, particularly under wet conditions, has been
0167-1987/00/$ ± see front matter # 2000 Elsevier Science B.V. All rights reserved.
PII: S 0 1 6 7 - 1 9 8 7 ( 9 9 ) 0 0 1 0 8 - 7
232
C.W. Watts et al. / Soil & Tillage Research 53 (2000) 231±243
linked to a decline in soil physical conditions (Greenland et al., 1975). The increasing dif®culty in managing these soils is thought to be partly associated with
a reduction in soil organic carbon (SOC). In turn, this
has resulted in more intensive cultivations. The depletion of the carbon pool by cultivations thus has signi®cant implications for soil quality and greenhouse
gas emission (Kern and Johnson, 1993).
Soil organic carbon has been shown to be very
important for many aspects of soil physical quality.
For example, greater contents of SOC have been
associated with greater stability in water (Oades,
1984), greater porosity and lower bulk density leading
to lower dry strength, increased friability (Watts and
Dexter, 1998) and a greater resistance to mechanical
damage (Watts and Dexter, 1997). Other desirable
properties of agricultural soils such as good water
holding capacity and good aeration status are also
found to be positively correlated with SOC.
For soils in a steady state, the annual loss of carbon
(C) is equal to the annual input. The inputs of organic
C are usually through photosynthesis by plants and the
incorporation of the carbon is thus `®xed' into soil
organic matter pools. The greatest route for output
from agricultural or forest soils is by respiration of
carbon dioxide (CO2) by organisms which are decomposing the compounds containing the SOC. When a
system is disturbed, such as by a change in land use,
cropping or other management practices including
cultivation, it is likely no longer to be in a steady
state. Numerous studies have been conducted in the
®eld to evaluate the change in microbial activity as a
result of different cultivation systems (Carter, 1992;
Chan et al., 1992; Beare et al., 1994; Franzluebbers
et al., 1994). These studies also suggest that tillage
opens up pores thus exposing previously physically
protected SOC to attack by organisms. Other changes
likely to in¯uence microbial activity following cultivation include changes to soil climate, water status and
aeration.
The mechanical disturbance of soil, by cultivation
for example, has been shown to increase the rate of
loss of organic C by increasing microbial activity as
measured by soil respiration (Rovira and Greacen,
1957; Reicosky et al., 1995; Watts et al., 1999). In
general, it has been found that the increasing levels of
mechanical energy applied to soil, have produced
increased rates of respiration. Such measurements
can give a sensitive indication of the short term of
changes which take many years to reach new equilibria values.
The energy inputs to soil following different cultivation operations have been measured in long-term
experiments by Patterson et al. (1980). Some typical
energy values are given in Table 1 for different
cultivation systems. In commercial agriculture, total
inputs of mechanical energy to soil during primary and
secondary cultivation and seeding operations can
often approach 300 J kgÿ1.
In order to obtain a better understanding of the
relationship between the application of different
amounts of mechanical energy and soil respiration
there is a need for controlled laboratory experiments to
complement ®eld experiments. In a recent study of the
effects of mechanical energy on aggregate stability,
Watts et al. (1996a,b) used a simple falling weight to
simulate similar energy levels to those used during
cultivation operations. In this study, we use the same
apparatus to investigate the effects of different
mechanical energy inputs on the respiration of collections of aggregates. The aggregates were obtained
from soils with long histories of different management
Table 1
Examples of speci®c mechanical energy inputs to two soils by different tillage systemsa
Cultivation system
Plough, cultivator drill
Chisel plough (2 passes), cultivator drill
Shallow plough, combined cultivator drill
Spring tine, cultivator (2 passes)
a
Data adapted from Patterson et al. (1980).
Redbourne,
90 g kgÿ1 clay
(J kgÿ1)
68
124
82
72
Silsoe,
510 g kgÿ1 clay
(J kgÿ1)
132
177
161
90
233
C.W. Watts et al. / Soil & Tillage Research 53 (2000) 231±243
practices and consequently different SOC contents.
Measurements were then made under controlled
laboratory conditions at different water contents,
but at a constant temperature.
The object of this work was to develop a technique
for assessing, under laboratory conditions, the effect
of applying to soil aggregates, mechanical energies
similar in magnitude to those experienced during
cultivation operations, and from this assess the effects
on soil respiration. In addition, we measured respiration in the ®eld following cultivation operations of
differing intensities.
2. Materials and methods
2.1. Soil
Laboratory experiments were carried out on soils
from High®eld and Boot Field sites while ®eld experiments were conducted on Boot Field and Pavillion
Fields.
High®eld is one of the ley-arable experiments on
Rothamsted Experimental Station. The soil is of the
Batcombe Series, (approximate FAO equivalent is the
Chromic Luvisol; Avery, 1980), and is de®ned as ®ne
silty over clayey drift with siliceous stones (Clayden
and Hollis, 1984). The original experiments were
conducted to compare contrasting crop rotational
systems and to determine their effects on the yields
of three arable test crops. These experiments were
started in 1949, before which High®eld had been very
old permanent grassland. Cultivation, drilling, harvesting and other management practices are described
in Johnston (1972). Soil samples were taken from the
0±100 mm horizon of ®ve plots with contrasting
management regimes, which have caused different
reductions in SOC over 50 years. Some important
properties of these samples are given in Table 2.
Boot Field, Silsoe (the site of the ®rst ®eld experiment) had previously grown cereals but had been in
set-aside for approximately 18 months prior to this
experiment. The soil is a typical calcarious pelosol
(Gleyic and Calcic Cambisols, Calcaric Gleysols in
the FAO System; Avery, 1980) of the Evesham Series,
i.e., swelling-clayey material passing to clay or soft
mudstone (Clayden and Hollis, 1984). The texture is
classi®ed as clay.
Pavilion Field, Silsoe (the site of the second ®eld
experiment) had also been set-aside for 18 months.
The soil differs considerably from that in Boot Field. It
is a typical brown earth (Dystric and Eutric Cambisols
in the FAO System; Avery, 1980) of the Bearsted
Series, comprising coarse loamy material passing to
sand or soft sandstone (Clayden and Hollis, 1984). The
texture is classi®ed as a sandy loam. Compositions of
these soils are given in Table 2.
2.2. Sample collection and preparation
For the laboratory experiments, the soil samples
were collected from the 0±100 mm horizon, air-dried,
Table 2
Composition of the experimental soils
Site
Rothamsted
Highfield
Silsoe
Boot Field
Pavilion Field
a
Treatment
Sand (g kgÿ1)a
Silt (g kgÿ1)b
Clay (g kgÿ1)c
SOC (g kgÿ1)
Permanent grass
Reseeded grass
Ley-arable rotation
Continuous arable
Permanent fallow
110
110
110
120
90
670
620
630
640
660
230
270
250
240
250
32
28
21
15
11
Arable
Arable
90
700
180
170
730
130
35
16
Sand2.0±0.063 mm.
Silt63ÿ2 mm.
c
Clay