Directory UMM :Data Elmu:jurnal:S:Soil & Tillage Research:Vol52.Issue3-4.Oct1999:

Soil & Tillage Research 52 (1999) 223±232

Soil physical quality of a Brazilian Oxisol under two tillage
systems using the least limiting water range approach
Cassio Antonio Tormenaa,*, Alvaro Pires da Silvab, Paulo Leonel Libardic
a

Departamento de Agronomia, Universidade Estadual de MaringaÂ, Av. Colombo, 5790, MaringaÂ-PR, 87090-000, Brazil
b
Escola Superior de Agricultura Luiz de Queiroz, Departamento de CieÃncia do Solo, Universidade de SaÄo Paulo,
Bolsista do CNPq, Piracicaba-SP, 13418-900, Brazil
c
Escola Superior de Agricultura Luiz de Queiroz, Departamento de FõÂsica, Universidade de SaÄo Paulo,
Bolsista do CNPq, Piracicaba-SP, 13418-900, Brazil
Received 30 November 1998; received in revised form 2 June 1999; accepted 13 September 1999

Abstract
Plant growth is directly affected by soil water, soil aeration, and soil resistance to root penetration. The least limiting water
range (LLWR) is de®ned as the range in soil water content within which limitations to plant growth associated with water
potential, aeration and soil resistance to root penetration are minimal. The LLWR has not been evaluated in tropical soils.
Thus, the objective of the present study was to evaluate the LLWR in a Brazilian clay Oxisol (Typic Hapludox) cropped with

maize (Zea mays L. cv. Cargil 701) under no-tillage and conventional tillage. Ninety-six undisturbed soil samples were
obtained from maize rows and between rows and used to determine the water retention curve, the soil resistance curve and
bulk density. The results demonstrated that LLWR was higher in conventional tillage than in no-tillage and was negatively
correlated with bulk density for values above 1.02 g cmÿ3. The range of LLWR variation was 0±0.1184 cm3 cmÿ3 in both
systems, with mean values of 0.0785 cm3 cmÿ3 for no-tillage and 0.0964 cm3 cmÿ3 for conventional tillage. Soil resistance to
root penetration determined the lower limit of LLWR in 89% of the samples in no-tillage and in 46% of the samples in
conventional tillage. Additional evaluations of LLWR are needed under different texture and management conditions in
tropical soils. # 1999 Elsevier Science B.V. All rights reserved.
Keywords: Least limiting water range; Bulk density; No-tillage; Available water; Soil resistance to root penetration

1. Introduction
In tropical soils, the loss of organic matter and the
degradation of soil structure are responsible for the
decline in productive potential (Cassel and Lal, 1992;
*

Corresponding author.
E-mail addresses: catormen@cca.uem.br (C.A. Tormena), apisilva@carpa.ciagri.usp.br (A.P. da Silva)

Matson et al., 1997). This process starts with mechanized land clearing of the areas (Alegre et al., 1986;

Ghuman and Lal, 1992) and is intensi®ed with the large
scale implantation of mechanized agricultural systems
(Kayombo et al., 1991). Many reports are available
about the structure and physical properties of tropical
soils (Sanchez, 1976; Lal, 1979; Theng, 1980; Cassel
and Lal, 1992; Kayombo and Lal, 1993). The responses
of various crops to these modi®cations have led to

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 6 - 0

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C.A. Tormena et al. / Soil & Tillage Research 52 (1999) 223±232

changes in crop productivity in tropical regions
(Kayombo and Lal, 1994), with the magnitude of such
changes depending on the soils, crops and management.
The structure and physical behavior of tropical soils
have been evaluated on the basis of properties and

physical processes indirectly related to plant growth,
such as bulk density, porosity, in®ltration, hydraulic
conductivity, and aggregate stability (Kemper and
Derpsch, 1981; Roth et al., 1988).
Plant growth is directly affected by soil water, soil
aeration, and by soil resistance to root penetration. The
least limiting water range (LLWR) is de®ned as the
range in soil water content within which limitations to
plant growth associated with water potential, aeration
and mechanical impedance to root penetration are
minimal. Once limiting values of matric potential,
aeration and mechanical impedance are de®ned, the
water contents are determined experimentally for each
of these limiting conditions and the LLWR is computed. The LLWR has been proposed as an index of soil
structural quality for plant growth (Da Silva et al., 1994;
Topp et al., 1994). Evaluation of soils in temperate
regions have demonstrated that the LLWR is affected
by the soil organic matter content (Kay et al., 1997),
soil structure (Da Silva et al., 1994; Da Silva and Kay,
1997; Stirzaker, 1997), and soil texture (Da Silva et al.,

1994; Da Silva and Kay, 1997). Maize growth was
found to be positively correlated with LLWR and
negatively correlated with the frequency of occurrence
of soil water content outside the LLWR limits (Da Silva
and Kay, 1996). The LLWR concept has been incorporate in a soil science text book (Brady et al., 1999).
No information is available in the literature about
the management±structure relations in tropical soils
evaluated by joint changes in water availability, soil
resistance to root penetration and soil aeration, i.e., by
the LLWR. Thus, the objective of the present study was
to characterize and evaluate the LLWR in a tropical
clay Oxisol (Typic Hapludox) cropped with maize
using no-tillage (NT) and conventional tillage (CT).

2. Material and methods
2.1. Experimental site and tillage
Undisturbed soil samples were collected in August
1996 from a commercial farm located in the north-

eastern region of the State of SaÄo Paulo, Brazil

(208190 1300 latitude South and 488180 0300 longitude
West). The climate of the region is of the tropical
type, with mean annual temperatures and precipitation
of 22.78C and 1420 mm, respectively. The soil is
classi®ed as Rhodic Ferralsol (Typic Hapludox) with
particle-size distribution consisting of 800 g kgÿ1
clay, 150 g kgÿ1 silt and 50 g kgÿ1 sand. The clay
fraction is dominated by kaolinite and various sesquioxides of iron and aluminum (Costa, 1996).
The study was performed using two contiguous
plots cultivated by the NT and CT systems. In the
NT area, the system had been set up 4 years before, and
in the CT area the system had been used for 10 years.
Conventional tillage was carried out with a disk
plough followed by cultivation in April 1996. Both
areas were irrigated with a central sprinkler. By the
time of sampling, water had been applied in the area
20 times with 16 mm water head each time. The
irrigation control was based on a class-A evaporation
pan. In both areas, crop rotation consisted of soybean
(Glycine max, L. Merril), maize and beans (Phaseolus

vulgaris, L.). At the time of sampling (silking stage),
both areas were cropped with maize at row spacing of
0.90 m. Basic fertilization was 330 kg haÿ1 04±20±
20 ‡ Zn and additional fertilizations were performed
20 days after plant emergence (APE) with 145 kg haÿ1
20±00±20 and at 35 and 50 APE with 40 kg haÿ1 urea.
2.2. Soil sampling and analysis
Sampling was performed in August 1996. Undisturbed cores (5 cm diameter, 5 cm length) were taken
from the center of the layer at 0±0.10 m depth. The
sampling points were located in a transect of 43.2 m
transverse to the culture rows for both tillage systems.
Samples were taken at 0.45 m intervals, resulting in 96
samples per tillage system sequentially located along
the row and between rows.
The soil water retention curve was determined by
the procedure of Da Silva et al. (1994). The samples
were divided into 12 groups of 16, with four samples
per position and potential for each tillage system. The
following potentials were applied using a tension table
adapted from Topp and Zebtchuck (1979): ÿ0.001,

ÿ0.003, ÿ0.005, ÿ0.006, and ÿ0.008 MPa. Pressure
plates (Klute, 1986) were used to equilibrate samples
at potentials: ÿ0.01, ÿ0.03, ÿ0.05, ÿ0.07, ÿ0.1,

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C.A. Tormena et al. / Soil & Tillage Research 52 (1999) 223±232

ÿ0.5 and ÿ1.5 MPa. After equilibrium, the samples
were utilized to determine soil resistance to penetration (SR) and then dried in an oven at 105±1108C for
the determination of soil water content and bulk
density (Ds).
The SR was measured using an electronic penetrometer with a cone of 4 mm diameter and semi-angle
of 308. The rate of penetration was set up to
1.0 cm minÿ1. The measurements obtained from 1
to 4 cm of depth were averaged for each core.
The soil water retention curve was ®tted to the
equation proposed by Van Genuchten (1980).
h
i

(1)
 ˆ r ‡ …s ÿr †=‰…1 ‡  †n Š1ÿ1=n ;
3

ÿ3

where  is the volumetric water content (cm cm ),
the matric potential (cm), r is the residual water
content (cm3 cmÿ3), and  (cmÿ1) and n are constants.
The Ds, position and tillage effects on the model
parameters were evaluated following the procedure
described by Da Silva and Kay (1997) using SAS
Institute (1991).
The SR data were regressed against Ds (g cmÿ3) and
soil water content () using the model proposed by
Busscher (1990).
SR ˆ ab Dcs ;

(2)

where a, b and c are constants and SR is the soil
resistance (MPa). The influence of tillage and sampling position were assessed according to Da Silva et
al. (1994).
The LLWR was determined for each core by the
method of Da Silva et al. (1994). The soil water
content () at the critical limits of the matric potential,
soil resistance and air-®lled porosity were obtained
considering ®eld capacity (fc) to be the soil water
content at ˆ ÿ0.01 MPa (Haise et al., 1955). For
the permanent wilting point (wp) we considered soil
water content at ˆ ÿ1.5 MPa (Savage et al., 1996),
for SR (sr) we used the 2.0 MPa value (Taylor et al.,
1966), and for air-®lled porosity (afp) we used the
value of 10% (Grable and Siemer, 1968). Both fc
and wp were obtained using Eq. (1). The sr was
obtained by Eq. (2), while afp was obtained as
[(1ÿDs/Dp)ÿ0.1], where Ds is the measured bulk
density and Dp is the particle density (assumed to be
2.65 g cmÿ3). At each Ds, the LLWR is the difference
between the upper limit and the lower limit.

The upper limit is the drier  of either fc or afp
whereas the lower limit is the wetter  of either wp
or sr.

3. Results and discussion
The soil physical properties determined in the
samples are presented in Table 1. Estimates of fc
and wp were made using Eq. (1). Only Ds was
incorporated in the model via n, i.e.,
h
i
 ˆ 0:1342 ‡ …s ÿ0:1342†=‰…1 ‡ 1:3355 †n Š1ÿ1=n ;
(3)
n ˆ 2:5181ÿ2:064Ds ‡

0:7373D2s ;

R2 ‰1ÿ…SSerrors =SSmodel †Š ˆ 0:89:
The soil resistance curve was in¯uenced by the

tillage system but not by sample position. The coef®cients of the models demonstrated that SR was positively correlated with Ds and negatively with . The
increase in SR with decreasing  is a well-known
process and is due to an increase in effective stress
(Snyder and Miller, 1985), which is magni®ed by the
increased Ds.
The model used to estimate SR in both tillage
systems were
NT :
CT :

SR ˆ 0:0223ÿ2:6908 Ds8:2080 ;
ÿ2:6908

SR ˆ 0:0194

(4)

Ds8:2080 ;

(5)

R2 ˆ 0:88:

Table 1
Soil physical parameters measured in NT and CT in an Oxisol
(Typic Hapludox) cropped with maize, at a depth of 0±0.10 ma
Variable

Mean

Standard deviation

Minimum

Maximum

NT
SR
Ds


1.426
1.153
0.356

0.936
0.065
0.059

0.306
0.950
0.239

5.082
1.320
0.459

CT
SR
Ds


1.116
1.129
0.346

0.745
0.075
0.058

0.312
0.930
0.213

3.603
1.330
0.457

a
SR: soil penetrometer resistance (MPa), Ds: bulk density
(g cmÿ3), and : soil water content (cm3 cmÿ3).

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C.A. Tormena et al. / Soil & Tillage Research 52 (1999) 223±232

Fig. 1. Soil water content variation with bulk density at critical levels of field capacity (fc), at wilting point (wp), at air-filled porosity (afp)
and at soil resistance (sr) in NT (a) and CT (b). Shaded area represents LLWR.

Several studies have demonstrated a higher SR in
NT compared to CT (Cornish and Lymbery, 1987;
Hill, 1990; McCoy and Cardina, 1997; Opoku et al.,
1997) and the differences were as explained by the

variation in Ds and . The results obtained demonstrated that, under the same soil moisture and Ds, SR
was higher in NT, in agreement with data reported by
Cornish (1993). In CT, mobilization of the soil results

C.A. Tormena et al. / Soil & Tillage Research 52 (1999) 223±232

in the break of bonds between particles and/or aggregates, reducing SR (Dexter et al., 1988). The greater
SR in NT may be related to the occurrence of the
process of ``age hardening'' of the aggregates by
which the aggregates reacquire and maintain resistance a long time after the initial mobilization of the
soil (Utomo and Dexter, 1981; Kemper and Rosenau,
1984). According to Grant et al. (1985) and Semmel et
al. (1990), the persistence of the effects of drying and
wetting cycles as well as traf®c results in larger and
denser aggregates, leading to higher SR in the NT
system (Cornish, 1993).
The LLWR limits, i.e., fc, wp, sr and afp are
presented in Fig. 1a and b for both tillage systems. Ds
increased fc up to Ds of 1.27 g cmÿ3 in NT and
1.26 g cmÿ3 in CT. According to Hill (1990), the
increase in water retention with Ds under elevated
potentials occurs due to the reduction in macroporosity. In contrast, wp was positively affected throughout
the Ds range in both systems. The magnitude of the
effects of Ds on water retention was lower under
higher than under low , resembling the behavior
of sandy soils described by Hill and Sumner (1967).
This is related to the fact that clayey Oxisols have
stable and well developed microstructure. According
to Van den Berg et al. (1997), in tropical soils with
strongly microaggregated structures, the greater water
retention at lower potentials with increasing Ds is due
to a larger amount of particles available for water
absorption allied to an increase in soil microporosity.
Other investigators have demonstrated a negative
effect of Ds on water retention under elevated potentials and a positive effect at low potentials (Smedemma, 1993; Gupta and Larson, 1979). These
investigators argue that, in the presence of elevated
, soil water retention is in¯uenced by total porosity,
whereas at low , soil water retention is controlled by
the volume of micropores, which in turn depend on Ds
(Carter, 1988). The available water content
(AWC ˆ FCÿWP) varied positively up to a Ds of
1.02 g cmÿ3 in both systems and, starting from this
value, AWC was reduced by the positive effect of Ds
on wp and its negative effect on fc. The greater
reduction in AWC under NT conditions is due to
higher Ds compared to CT.
An increase in sr and a decrease in afp occurred
with increasing Ds in both tillage systems (Fig. 1a and
b). afp was progressively reduced with increasing Ds,

227

as also reported by Archer and Smith (1972) and Da
Silva et al. (1994). The observations afp > fc suggests
that, even in the presence of greater Ds, the stable
microstructure preserves the porous space necessary
for gas exchange in soil. These results contrast with
those obtained for clay soils by Topp et al. (1994), who
reported that air-®lled porosity frequently reached
values considered to be limiting for an appropriate
aeration of the plant root system. For the Ds values
determined, afp did not replace fc at the upper limit of
water availability. For higher Ds's, afp may represent a
limitation, especially under conditions of high oxygen
demand in soil (Hadas, 1997). Hamblin (1985) suggested that a limitation caused by aeration may frequently occur in clay soils since with increasing Ds the
roots occupy pores of smaller size with decreasing
drainage. Furthermore, soil compression during root
growth contributed to a reduction of the proportion of
root surface exposed to free oxygen ¯ow in soil. The
low bulk densities values associated with high porosities may be associated with the microstructure present
in the tropical Oxisol (Sanchez, 1976; Igwe et al.,
1995). The Ds had a strong effect on sr in both tillage
systems. This was more pronounced in NT where sr
was the lower limit in 89% of the samples and replaced
wp at Ds values 1.06 g cmÿ3. In contrast, in CT, sr
was the lower limit in 46% of the Ds value and
replaced wp for Ds  1.13 g cmÿ3. Similar results
were obtained by Topp et al. (1994) and Da Silva et
al. (1994) in Canadian soils.
The LLWR was positively correlated where
Ds < 1.02 g cmÿ3, and negatively correlated with
Ds > 1.02 g cmÿ3 in both tillage systems (Fig. 2). This
behavior was similar to that reported by Topp et al.
(1994), Da Silva et al. (1994) and Stirzaker (1997). For
same Ds, LLWR NT < LLWR CT. The LLWR ranged
from 0 to 0.1184 cm3 cmÿ3 in both tillage systems,
with mean values of 0.0785 cm3 cmÿ3 for NT and
0.0964 cm3 cmÿ3 for CT, which were statistically
different (p < 0.05). At the row position, LLWR
CT ˆ 0.1078 cm3 cmÿ3 and LLWR NT ˆ 0.0869
cm3 cmÿ3 whereas in the interrow position, LLWR
CT ˆ 0.0857 cm3 cmÿ3 and LLWR NT ˆ 0.0701
cm3 cmÿ3. These values were statistically different
(p < 0.05). At the average Ds values there were minimal physical limitations to plant growth in both CT
and NT. However, the temporal variability of Ds
during the crop season may increase Ds to values

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C.A. Tormena et al. / Soil & Tillage Research 52 (1999) 223±232

Fig. 2. Variation in LLWR with bulk density in NT and CT systems.

associated with severe physical limitation to crop
growth (Carter, 1990; Carter et al., 1999).
Both sr and afp were more strongly affected by Ds
than fc or wp. The effect of Ds was more marked on
sr, suggesting that in this soil LLWR is more sensitive
to the effects of structure on SR than on available
water. Da Silva et al. (1994) reported that the sensitivity of LLWR to Ds is dependent on the limits of SR.
In the soil studied, SR was the most limiting factor.
The limit values of SR selected to analyze the sensitivity of LLWR were 1.0, 2.0, 3.0 and 4.0 MPa. The
sensitivity of LLWR variation differed between the
tillage systems (Fig. 3a and b), being higher in NT.
The effect of high SR on root growth may be
minimized by the presence of macropores formed
by the mesofauna and by the crop roots. Macropores
favor root growth, although the ef®ciency of these
roots in absorbing water and nutrients has been questioned by Passioura (1991) and Smucker and Aiken
(1992). However, several studies have demonstrated
that NT increases the frequency and number of macropores compared to CT and that these macropores are
preserved due to lower soil mobilization. The utilization of these biopores as alternative routes permits root
growth under conditions of higher SR, as observed by
Ehlers et al. (1983), Cornish (1993) and Martino and

Shaykewich (1994) under ®eld conditions, and by
Stirzaker et al. (1996) in a study on potted plants.
Ehlers et al. (1983) observed that the limit SR values
for oat (Avena sativa L.) root growth were 3.6 and
4.9 MPa, respectively, for CT and NT, and these
results were attributed to the presence of biopores
that are not detected by penetrometers.
Considering the occurrence of these conditions in
the present study and assuming the critical SR established by Ehlers et al. (1983), the LLWR was recalculated. LLWR was similar (p > 0.05) for both tillage
systems (Fig. 4). However, at higher Ds, LLWR
NT > LLWR CT.
Excessive tillage and the absence of a soil cover
may expose these soils to high drying rates and an
abrupt increase in SR, as suggested by Weaich et al.
(1992) and Townend et al. (1996). In NT system the
presence of residues contributes to a greater water
content in soil, thus maintaining the physical properties within an optimum range for crop productivity
(Kladivko, 1994).
Evaluations of the physical quality of tropical soils
in the presence of a wide variation of mineralogy,
texture and management conditions should be performed by employing the LLWR. The use of pedotransfer functions may be an alternative to facilitate

C.A. Tormena et al. / Soil & Tillage Research 52 (1999) 223±232

Fig. 3. Sensitivity of LLWR with different levels criticals of the soil penetration resistance in NT (a) and CT (b).

229

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C.A. Tormena et al. / Soil & Tillage Research 52 (1999) 223±232

Fig. 4. The LLWR in critical soil penetration resistance of 4.9 MPa in NT and 3.6 MPa in CT.

the LLWR estimation from routinely measured soil
properties (Da Silva and Kay, 1997; Kay et al., 1997).

4. Conclusions
The use of the LLWR concept allowed the identi®cation of physical factors that control the physical
quality of the soil studied in terms of plant growth. The
SR was the physical parameter that limited the LLWR
in both tillage systems. Air-®lled porosity did not
represent a limitation of the LLWR for either tillage
system studied. Detailed studies are needed to establish the limits of SR of plant growth, with priority in
tropical soils, in order to establish the lower LLWR
limits for the determination of the physical quality of
these soils.

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