Soil physical quality of a Brazilian Oxisol under two tillage systems using the least limiting water...

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

aDepartamento de Agronomia, Universidade Estadual de MaringaÂ, Av. Colombo, 5790, MaringaÂ-PR, 87090-000, BrazilbEscola Superior de Agricultura Luiz de Queiroz, Departamento de CieÃncia do Solo, Universidade de SaÄo Paulo,

Bolsista do CNPq, Piracicaba-SP, 13418-900, BrazilcEscola 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;

Matson et al., 1997). This process starts with mechan-

ized 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

Soil & Tillage Research 52 (1999) 223±232

* Corresponding author.

E-mail addresses: [email protected] (C.A. Tormena), apisil-

[email protected] (A.P. da Silva)

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

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 com-

puted. 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 incor-

porate 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

(2081901300 latitude South and 4881800300 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 sesqui-

oxides of iron and aluminum (Costa, 1996).

The study was performed using two contiguous

plots cultivated by the NT and CT systems. In the

NTarea, 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. Undis-

turbed 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,

224 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 penetra-

tion (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 penet-

rometer 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).

� � �r � ��sÿ�r�=��1� � �n�1ÿ1=nh i

; (1)

where � is the volumetric water content (cm3 cmÿ3), 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 � a�bDcs ; (2)

where a, b and c are constants and SR is the soil

resistance (MPa). The influence of tillage and sam-

pling 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 � ÿ0.01 MPa (Haise et al., 1955). For

the permanent wilting point (�wp) we considered soil

water content at � 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.,

� � 0:1342� ��sÿ0:1342�=��1� 1:3355 �n�1ÿ1=nh i

;

(3)

n � 2:5181ÿ2:064Ds � 0:7373D2s ;

R2�1ÿ�SSerrors=SSmodel�� 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 posi-

tively 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 : SR � 0:0223�ÿ2:6908D8:2080s ; (4)

CT : SR � 0:0194�ÿ2:6908D8:2080s ; (5)

R2 � 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 1.426 0.936 0.306 5.082

Ds 1.153 0.065 0.950 1.320

� 0.356 0.059 0.239 0.459

CT

SR 1.116 0.745 0.312 3.603

Ds 1.129 0.075 0.930 1.330

� 0.346 0.058 0.213 0.457

aSR: soil penetrometer resistance (MPa), Ds: bulk density

(g cmÿ3), and �: soil water content (cm3 cmÿ3).

C.A. Tormena et al. / Soil & Tillage Research 52 (1999) 223±232 225

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 demon-

strated 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

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.


in the break of bonds between particles and/or aggre-

gates, 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 resis-

tance 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 macroporos-

ity. 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 poten-

tials and a positive effect at low potentials (Sme-

demma, 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 � 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,

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) sug-

gested that a limitation caused by aeration may fre-

quently 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 poros-

ities 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 � 0.1078 cm3 cmÿ3 and LLWR NT � 0.0869

cm3 cmÿ3 whereas in the interrow position, LLWR

CT � 0.0857 cm3 cmÿ3 and LLWR NT � 0.0701

cm3 cmÿ3. These values were statistically different

(p < 0.05). At the average Ds values there were mini-

mal 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


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 sensi-

tivity 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 sensi-

tivity 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 ques-

tioned by Passioura (1991) and Smucker and Aiken

(1992). However, several studies have demonstrated

that NT increases the frequency and number of macro-

pores compared to CT and that these macropores are

preserved due to lower soil mobilization. The utiliza-

tion 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 estab-

lished by Ehlers et al. (1983), the LLWR was recal-

culated. 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 proper-

ties 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 per-

formed by employing the LLWR. The use of pedo-

transfer functions may be an alternative to facilitate

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


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


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 estab-

lish 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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Soil physical quality of a Brazilian Oxisol under two tillage systems using the least limiting water...

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