Directory UMM :Data Elmu:jurnal:S:Soil & Tillage Research:Vol54.Issue3-4.Apr2000:

Soil & Tillage Research 54 (2000) 129±138

Wheel traf®c impact on soil conditions as in¯uenced
by tillage system in Central Anatolia
H. GuÈcluÈ Yavuzcan*
Faculty of Agriculture, Department of Agricultural Machinery, Ankara University, 06130 Aydinlikevler, Ankara, Turkey
Received 12 April 1999; accepted 14 October 1999

Abstract
The increased limiting effects of soil compaction on Central Anatolian soils in the recent years demonstrate the need for a
detailed analysis of tillage system impacts. This study was undertaken to ascertain the effects of seven different tillage systems
and subsequent wheel traf®c on the physical and mechanical properties of typical Central Anatolian medium textured clay
loam soil (Cambisol), south of Ankara, Turkey. Both tillage and ®eld traf®c in¯uenced soil bulk density, porosity, air voids and
strength signi®cantly except the insigni®cant effect of traf®c on moisture content. Traf®c affected the soil properties mostly
down to 20 cm. However, no excessive compaction was detected in 0±20 cm soil depth. The increases of bulk density
following wheel traf®c varied between 10±20% at 0±5 cm and 6±12% at 10±15 cm depth. In additions, traf®c increased the
penetration resistance by 30±74% at 0±10 cm and 7±33% at 10±20 cm. Less wheel traf®c-induced effects were found on chisel
tilled plots, compared to ploughed plots. Soil stress during wheel passage was highly correlated with soil strength. Also, both
tillage and traf®c-induced differences were observed in mean soil aggregate sizes, especially for mouldboard ploughed plots.
The obtained data imply that chisel‡cultivator-tooth harrow combination provides more desirable soil conditions for resisting
further soil compaction. # 2000 Elsevier Science B.V. All rights reserved.

Keywords: Soil compaction; Tillage; Traf®c; Bulk density; Soil strength

1. Introduction
Soil compaction has been identi®ed as one of the
leading causes of soil degradation threatening future
productivity of Central Anatolian farm lands in the
*
Present address: Institut fuÈr Landtechnik, Technische UniversitaÈt MuÈnchen, Am Staudengarten 2, 85350 Freising-Weihenstephan,
Germany. Tel.: ‡49-8161-713447/‡49-8161-498838; fax: ‡498161-713895.
E-mail addresses: yavuzcan@tec.agrar.tu-muenchen.de,
yavuzcan@agri.ankara.edu.tr (H.G. Yavuzcan)

recent years (Anonymous, 1991, 1994, 1997). This
problem became evident in relatively level areas,
particularly after the wide introduction of tractors
and agricultural machinery. Many Central Anatolian
soils are low in organic matter and are subjected to low
annual rainfall amounts (Akalan, 1983; Anonymous,
1997). Most importantly, the greatest portion of the
annual rainfall occurs in the early or mid spring, when

most ®eld operations are performed, providing a soil
condition that is very conductive to compaction.
The cropland in the region accounts for around 6
million ha, most (80%) of which is devoted to grain

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 0 9 3 - 3

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H.G. Yavuzcan / Soil & Tillage Research 54 (2000) 129±138

production (Anonymous, 1994, 1997). The production
system of annual crops includes seedbed preparation
for each crop cycle. Conventional local tillage system
involves soil loosening by mouldboard ploughing and
then crumbling the soil for the seedbed through disc
harrowing.
Many farmers in the Central Anatolia perform
tillage operations without knowledge or regard

for effects on soil properties and crop responses.
The irregularity through freezing and thawing as
well as wetting and drying create dif®culties in
quantifying the traf®c-induced consequences of soil
compaction. It is a fairly common practice for
farmers to periodically subsoil cropland to alleviate
perceived compaction caused by vehicular wheel
traf®c. Waste of energy and soil degradation by
erosion and compaction are recognised problems
caused by inadequate tillage management. Although
natural processes such as freezing and thawing,
wetting and drying, shrinking and swelling and
fracturing and aggregation caused by plant root
growth and organic matter tend to alleviate soil
compaction (Bicki and Siemens, 1991), these may
be effective only to shallow soil depths.
Studies evaluating the effects of wheel traf®c on soil
properties in Central Anatolia have been limited.
Research has generally focused on conventional
tillage systems and rotary tilling. Comparisons of

conventional and reduced (rotary tilling) till indicated
that relative increase of penetration resistance after
wheel traf®c was greater in conventionally tilled
È zguÈven and Aydinbelge, 1990;
plots at 0±15 cm (O
Carman, 1996). Other research conducted in the
region reported that a classical conventional tillage
(plough‡disc‡tooth harrow) provides better conditions for resisting further compaction (Taser and
Metinoglu, 1997). However, the interactive roles that
tillage system Ð especially conservation tillage systems and traf®c on soil compaction have not been
clari®ed.
An important step towards understanding and controlling compaction is the ability to predict compaction. However, the soil conditions that in¯uence
compaction and that are changed by compaction are
dif®cult to de®ne and to quantify. After analysing the
impacts of four different tillage systems (chisel,
mouldboard plough, no-till and ridge-till) and subsequent ®eld traf®c, Bauder et al. (1985) found that

tillage system had no effect on porosity and gravimetric water content while both tillage and traf®c had
signi®cant effects on bulk density and penetration
resistance down to a depth of 22 cm on a Nicollet±

Webster soil in south-central Minnesota. Gruber and
TebruÈgge (1990) reported that the highest ground
pressure and rut depth were obtained in conventional
tillage systems and susceptibility of subsoil compaction is much lower for reduced tillage systems due to
the even distribution of wheel loads.
A soil that has developed suf®cient load-carrying
capacity can resist further changes in bulk density or
total porosity (Anonymous, 1992). In such a soil,
wheel traf®c may change the pore distribution slightly
by elastic deformation. Ngunjiri and Siemens (1995)
investigated the effects of different wheel traf®c patterns during ploughing and reported that wheel traf®c
was found to increase soil bulk density and cone index
to a depth of 30 cm with the most important impacts in
the 0±15 cm depth on a silt loam soil of Illinois. A
study to determine soil cone index variability under
no-till, conventional and reduced tillage systems in
Watkinsville, GA (Manor et al., 1991) indicated that
much of the variability in cone index under ®eld
conditions is caused by tillage and traf®c. Another
study reported that ploughing loosens soil more than

chiseling, however, natural processes and tillage for
seedbed preparation caused the soil after planting to be
re-compacted to about the same density as before
(Erbach et al., 1992).
Recommendations on how to minimise or remove
excessive compaction are hindered by dif®culty in
de®ning, measuring, predicting and evaluating soil
compaction. The main objectives of this study were
(1) to evaluate and compare the effects of conventional
(plough), conservation (chisel) and reduced (rotary
tiller) tillage systems on important physical and
mechanical properties of a typical Central Anatolian
soil; (2) to compare the effects of compaction following tillage on soil properties; and (3) to determine
the most appropriate tillage system that ®ts with
the effective controlling of subsequent compaction
and provide data base for a better understanding
of alterations due to traf®c. The hypothesis to be
tested was that conservation (chisel) or reduced tillage systems may be more bene®cial in this respect
than conventional tillage that is commonly used in
the region.

H.G. Yavuzcan / Soil & Tillage Research 54 (2000) 129±138

2. Materials and methods
2.1. Site, soil and experimental design
Experiments were carried out at the research
farm of Ankara University, 40 km south of Ankara,
Turkey where the average rainfall was 410 mm in
1996 and 426 mm in 1997. The site altitude is 1050 m
and the soil is an imperfectly drained, medium textured clay loam soil of the Central Anatolian series
(Cambisol) with 210, 580 and 210 g kg±1of clay, silt
and sand, respectively. Soil pH averaged 7.8 and
organic matter 11.3 g kg±1. The experiment was
arranged in three blocks each consisting of seven
tillage treatments. The plots were 25 m wide and
75 m long. Tillage practices were performed on wheat
(Triticum aestivum L.) stubble. Climatological data
were obtained from the farm station. Monthly rainfall
and precipitation were compared to the long term
averages.

2.2. Field equipment and procedures
A 65 kW, two wheel drive tractor weighed to
32.4 kN was used for both tillage and traf®c treatments. The rear axle was ®tted with 13.6/12±36 biasply single tires, in¯ated to 160 kPa while the front axle
was ®tted with 7.50±16 bias-ply single tires, in¯ated to
240 kPa. This type of tractor and wheels are most
commonly used in Central Anatolia.
A total of seven tillage systems were performed in
this study as mentioned below:
1. No-till (control) (S0);
2. Chisel‡disc harrow (chiselling to a depth of
28 cm followed by two passes of a disc harrow
to a depth of 13 cm) (S1);
3. Chisel‡cultivator-tooth harrow combination (chiselling to a depth of 28 cm followed by two passes
of a cultivator-tooth harrow combination to a
depth of 12 cm) (S2);
4. Mouldboard plough‡cultivator-tooth harrow combination (ploughing to a depth of 22 cm followed
by two passes of a cultivator-tooth harrow
combination to a depth of 12 cm) (S3);
5. Mouldboard plough‡disc harrow (ploughing to a
depth of 22 cm followed by two passes of a disc

harrow to a depth of 10 cm) (S4);

131

6. Rotary tiller Ð horizontal axis-rotary harrow
combination to a depth of 13 cm (S5);
7. Rotary tiller Ð vertical axis-rotary harrow combination to a depth of 13 cm (S6).
At the beginning of the study, in the early spring of
1996, the entire experimental area was subsoiled down
to a depth of 40 cm with a three leg subsoiler (legs
spaced at 0.5 m). The randomly selected plots were
then subjected to the above-mentioned tillage systems,
and received the same subsequent ®eld operations
(drilling, fertilising, spraying) for production of Gerek
79 wheat variety. In the late September 1996, the
wheat was harvested and plots were fallowed until
the early spring 1997 when spring tillage was seeded.
As soon as the tillage treatments had been completed traf®c treatment was performed twice, with
1.5 m/s forward speed and 22 kN rear axle load before
planting. It was accomplished by making repeated

passes with the tractor so that alternate plant rows
would be located in a wheel track (Bicki and Siemens,
1991). Nine passes were made at approximately equal
distances along each plot. Thus, approximately 25%
of the plots were traf®cked. The second passes were
made exactly over the established traf®c lanes. At the
time of traf®c, moisture content of the plots were
checked and no signi®cant difference was found
compared to the values obtained after tillage.
2.3. Soil measurements
Measurements were taken in the spring of 1997.
Soil bulk density, moisture content, penetration resistance and shear strength were measured both after
tillage and after wheel traf®c treatments. All measurements related with soil physical properties and
strength were performed with regard to row position
rather than randomly within each plot in order to
reduce sampling error. Accordingly, equally distanced
six transects perpendicular to the rows in each plot
were determined and measurement points were
selected within these transects (Manor et al., 1991).
Orientation and position of transects were always the

same. After traf®c, the measurements were taken from
the centre of tracks.
Bulk density was measured on 100 cm3 undisturbed
soil cores down to 30 cm depth, sectioned into 5 cm
increments. Sample depth intervals were 0±5, 10±15

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H.G. Yavuzcan / Soil & Tillage Research 54 (2000) 129±138

and 20±25 cm. Three set of samples were collected on
each plot transect following tillage and traf®c. Soil
moisture content was determined gravimetrically from
bulk density samples. Total porosity was also calculated from bulk density assuming a particle speci®c
gravity of 2.65. Percentage air voids was calculated
from the ratio of volume of air to the total volume of
soil. All of these parameters were calculated after oven
drying of cores at 1058C.
The changes in soil strength resulting from tillage
and traf®c treatments were evaluated by the measurements of both shear vane and cone penetrometer. A
vane borer with a 16 mm32 mm bladed vane and
measurement range of 0±260 kPa was used for shear
strength measurements. Vane shear strength was measured to a depth of 30 cm at 5 cm increments using
three replications on each plot transect. Penetration
resistance was measured with a hand operated recording type cone penetrometer which had a 308 steel cone
of 1 cm2 base area. Penetration values were recorded
at each 1 cm depth interval down to 30 cm at three
positions within each plot transect. The data were
reduced by averaging in 0.10 m increments.
Vertical stress in soil under wheel load (after wheel
passage) was measured with a developed pressure
gage (Gruber and TebruÈgge, 1990). Vertical stress
measurements were performed at 10 and 20 cm depths
and at least six replications per plot. In each plot, rut
depth of the rear tire was measured after traf®c treatments with a pro®le meter. The pro®le meter consists
of vertical metal rods sliding through a 100 cm long
iron bar at a regular spacing of 2.5 cm. The bar was

placed across the wheel tracks to measure the shape of
the depression (Carman, 1996).
Five kg soil samples were taken from randomly
selected three transects of each plot at 0±15 cm both
after tillage and traf®c. After air drying, samples were
sieved with a rotary sieve to determine size distribution of aggregates (Voorhees et al., 1985). The mean
weight diameter was calculated as the sum of the
product of aggregate diameters in each size and the
fractional weight of aggregate in that size (Adam and
Erbach, 1992).
The effects of various tillage system and wheel
traf®c on the above soil properties were evaluated
by analysis of variance with tillage as the main effect,
wheel traf®c as the ®rst split plot and depth as the
second split plot. Comparisons of mean values were
accomplished using least signi®cant differences
(LSD) at a0.05.

3. Results and discussion
Summary of ANOVA representing the effects of
tillage, wheel traf®c and depth on some physical and
mechanical properties are shown in Table 1. Tillage
and traf®c had signi®cant effects (p0.05). Tillage had also
considerable effects on soil stress and rut depth during
subsequent ®eld traf®c (p