an approach for draft prediction of combination tillage implements in sandy clay loam soil

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Soil & Tillage Research 90 (2006) 145–155

An approach for draft prediction of combination

tillage implements in sandy clay loam soil

Rohit K. Sahu, Hifjur Raheman *

Agricultural and Food Engineering Department, Indian Institute of Technology, Kharagpur, West Bengal 721302, India

Received 6 August 2004; received in revised form 12 July 2005; accepted 26 August 2005

Abstract

A methodology to predict the draft requirements of combination tillage implements in any soil and operating conditions was

developed. This methodology required the draft requirements of individual tillage implements in undisturbed soil condition and

draft utilization ratio of the rear passive set of combination tillage implement, which is defined as the ratio of the drafts of the rear

passive set operating in combination and individually. Laboratory experiments were conducted to measure the draft requirements of

a reference tillage tool (single disk), three scale-model individual (moldboard plow, cultivator and disk gang) and two combination

(moldboard plow with disk gang and cultivator with disk gang) tillage implements at different depths (5, 7.5 and 10 cm), speeds

(1.2, 2.2, 3.2 and 4.2 km/h), wet bulk densities (in the range of 1.27–1.85 g/cm3) and cone index penetration resistance values (in the

range of 445–1450 kPa) in soil bin filled with sandy clay loam soil. The average draft utilization ratio of the reference tillage tool

obtained were analyzed by both orthogonal and multiple regression techniques to develop the regression equation considering soil

properties, operating and tool parameters. The developed draft equation based on the above mentioned methodology was verified

with the data obtained for the draft of scale-model and prototype combination tillage implements in the laboratory and field

conditions, respectively. It was found that the developed equation predicted the draft of both combination tillage implements within

an average absolute variation of 18.0 and 13.5%, respectively.

# 2005 Elsevier B.V. All rights reserved.

Keywords: Draft; Combination tillage implement; Reference tillage tool; Regression analysis

1. Introduction

Many changes in tillage practices have been found

during the last 15 years. Conservation tillage practices

are replacing moldboard plowing and other major

seedbed preparation practices on a large portion of the

total area under cropping in the developed countries

(Harrigan and Rotz, 1995). The use of combination

tillage implements for land preparation is one such

practice that combines multiple tillage operations in a

* Corresponding author. Fax: +91 03222 282244/255303.

E-mail address: [email protected] (H. Raheman).

0167-1987/$ – see front matter # 2005 Elsevier B.V. All rights reserved.

doi:10.1016/j.still.2005.08.015

single pass, and thus reduces the number of field trips

as compared to conventional tillage practices resulting

in a reduction of labor and fuel cost and saving in time.

Most of the studies on draft, energy and tillage

performance of different combination tillage imple-

ments have been carried out in America and European

countries. Several combination tillage implements

comprising of rotary and passive elements were

developed and found to be more energy efficient than

a similar single passive tillage implement when tested

in actual field conditions (Chamen et al., 1979; Wilkes

and Addai, 1988; Shinners et al., 1990, 1993; Sigitov,

1992; Weise, 1993; Upadhyaya et al., 2001). The

active elements of combination implements can

R.K. Sahu, H. Raheman / Soil & Tillage Research 90 (2006) 145–155146

produce negative draft, which requires further energy

inputs to control tractor steering and the three-point

hitch and is also harmful to the drive train of tractor

(Wismer et al., 1968). A few researchers have also

conducted studies on the performance of semi-

mounted and trailed type passive–passive combination

tillage implements (Bukhari et al., 1981; Yusuf and

Asota, 1998; Tuhtakuziev and Utepbergenov, 2002). It

was observed that the use of combination tillage

implements in land preparation outperformed the

conventional land preparing practices in fuel con-

sumption, time requirement and cost of operation and

did not produce negative draft. Spoor and Godwin

(1978) performed field tests with tandem tool

configurations (two chisel plows followed by a deeper

winged subsoiler) on a clay soil. The results showed

that the draft of the tandem tool configurations at

different spacing and depths of chisel plows was less

than the draft of the winged subsoiler alone due to

loosening of the top layer of soil by the chisel plows. A

few studies on development and performance evalua-

tion of 2WD tractor drawn active–passive combination

tillage implements have also been conducted in India

(Kumar and Manian, 1986; Manian et al., 1999;

Kailappan et al., 2001a, b) and confirmed the same

results as obtained in western countries.

Information on the draft requirements of combina-

tion tillage implements is limited. The lack of

information about the implement compels the farmers

to rely mostly on past experience for selection of

implements and tractors. The farmers’ experience may

be of little value in selecting the efficient tillage system

as the size and speed of operation of new agricultural

implements are increasing. Therefore, prediction of

draft requirements of a combination tillage implement

is necessary for the design and selection of machinery

and the matching of tractors with implements for its

efficient operation. Many researchers have developed

various regression equations for draft prediction of

individual tillage implements in different soils and

operating conditions (Collins et al., 1978; Kepner et al.,

1982; Kydd et al., 1984; Nicholson et al., 1984;

Upadhyaya et al., 1984; Glancey and Upadhyaya, 1995;

Glancey et al., 1996; Grisso et al., 1996; Desbiolles

et al., 1997; ASAE, 2000a; Sahu and Raheman, 2004).

All these models are site, soil and implement specific.

However, from the literature reviewed it was found that

no mathematical equation is available to predict the

draft requirement of combination tillage implements.

Considering the above facts, an attempt was made to

develop a draft prediction equation for passive–passive

combination tillage implements.

2. Materials and methods

2.1. Approach for draft prediction of combination

tillage implement

Although many research projects have been con-

ducted on combination tillage implements, except for

Bernacki et al. (1972) there is no theory available to

determine the draft of these implements from the

knowledge of individual implement sets used, soil and

operating conditions. Based on the theoretical approach

for active–passive combination tillage implements as

proposed by Bernacki et al. (1972), the present study on

draft prediction of passive–passive combination tillage

implements was carried out.

The specific draft of the combination tillage

implement ‘Rc’ consists of the specific draft of both

passive sets used.

Rc ¼ Rfc þ Rrc (1)

where Rfc is the specific draft of the front passive set in

the combination tillage implement, and Rrc is the spe-

cific draft of the rear passive set in the combination

tillage implement. The specific draft of the combination

tillage implement can also be expressed as:

Rc ¼ Rf þ lRr (2)

where Rf is the specific draft of the front passive set as

operating individually (Rf = Rfc, because in both the

cases the front set will be operating in same soil

condition); Rr is the specific draft of the rear passive

set as operating individually, and l is the fraction of the

draft of the rear passive set operating as an individual

implement and is named as draft utilization ratio for the

rear passive implement. For various combination tillage

implements, the maximum value of l could be 1 and it

may depend on type and width of rear passive imple-

ment (Wr), soil type, wet bulk density (rw) and cone

index (CI) of soil, speed (V) and depth (d) of operation

(Bernacki et al., 1972).

Comparing the Eqs. (1) and (2), the draft utilization

ratio for the rear passive implement can be expressed as:

l ¼ Rrc

Rr

(3)

¼�

Drc

Dr

��Ar

Arc

�(3a)

¼�

Dc � Dfc

Dr

��dr

drc

��Wr

Wrc

�(3b)

R.K. Sahu, H. Raheman / Soil & Tillage Research 90 (2006) 145–155 147

Assuming Dfc = Df, (dr/drc) = 1 and (Wr/Wrc) = 1,

Eqs. (3a) and (3b) can be written as:

l ¼�

Drc

Dr

�(3c)

¼�

Dc � Df

Dr

�(3d)

where Drc is the resistance of the rear passive set in

combination tillage implement, Dr is the resistance of

the rear passive set as an individual, Arc is the cross-

sectional area of furrow made by the rear passive set in

combination tillage implement, Ar is the cross-sectional

area of furrow made by the rear passive set as an

individual, Df is the resistance of the front passive set

as an individual (Df = Dfc, because in both the cases the

front set will be operating in same soil condition), drc is

the depth of the rear passive set in combination tillage

implement, Wrc is the width of the rear passive set in

combination tillage implement, dr is the depth of the

rear passive set as an individual implement, and Wr is

the width of the rear passive set as an individual

implement.

On rearranging Eq. (3d), the draft for combination

tillage implement can be expressed as:

Dc ¼ Df þ lDr (4)

Based on the above equation, the draft of a

combination tillage implement in any soil and operating

conditions can be found out by knowing the draft of the

front and rear passive sets as individual implements in

the same soil and operating conditions, and l. The draft

of an individual passive tillage implement can be

predicted using the equation developed by Sahu and

Raheman (2004) and is given as below:

Dp

Dst

¼�

rw

rws

�a�CI

CIs

�b�Wp

Wt

�c

(5)

where Dp is the draft of any prototype/scale-model

implement in any soil condition, N, Dst is the draft of

the reference tillage tool in the reference soil condition,

N, rw is the wet bulk density of soil, g/cm3, rws is the

wet bulk density of the reference soil condition, 1.28 g/

cm3, CI is the cone index of soil, kPa, CIs is the cone

index of the reference soil condition, 472 kPa, Wp is the

prototype/scale-model implement width, cm for mold-

board plow and disk harrow, number of tine for culti-

vator, Wt is the reference tillage tool width, 10 and 9 cm

for moldboard plow and disk harrow, 1 for cultivator,

and a, b and c are regression coefficients for soil and

individual tillage implement.

The draft of the reference tillage tools in the

reference soil condition (Dst ) at different speeds and

depths can be given as (Sahu and Raheman, 2004):

Dst ¼ ðc0 þ c1VÞd (6)

where V is the speed of operation, km/h, d is the depth of

operation, cm and c0, and c1 are soil and tool specific

regression coefficients.

Therefore, for predicting the draft requirements of a

combination tillage implement based on the Eq. (4),

only l need to be predicted by the various factors

affecting it. For a given combination tillage implement,

l can be expressed by the following function:

l ¼ f1ðrw;CI;Wr;V ; dÞ (7)

Following the approach for predicting the draft of

individual tillage implement (Sahu and Raheman,

2004), the expression for l similar to Eq. (5) can be

formulated as:

lp

lsr

¼�

rw

rws

�g�CI

CIs

�h�Wrp

Wrr

�i

(8)

where lp is the draft utilization ratio of the rear passive

set of prototype/scale-model combination tillage imple-

ment in any soil condition, lsr is the draft utilization ratio

of the reference rear passive set in reference soil con-

dition, Wrp is the width of the rear passive set of

prototype/scale-model combination tillage implement,

Wrr is the width of the reference rear passive set, and g, h

and i are soil and combination tillage implement spe-

cific regression coefficients. Similar to the draft of

individual tillage tool, the draft utilization ratio (lsr)

of a reference rear passive set in a reference soil at

different speeds and depths can be expressed by the

following function (Glancey and Upadhyaya, 1995;

Sahu and Raheman, 2004):

lsr ¼ f2ðd;VÞ (9)

The above function can be expressed by multiple

regression equation. The various coefficients of the

equation can be found out using the data obtained from

the controlled laboratory experiments.

2.2. Experimental procedure

Laboratory experiments were conducted to find the

various regression coefficients in Eq. (8) and function

( f2) in the soil bin of the Agricultural and Food

Engineering Department, Indian Institute of Technol-

ogy, Kharagpur, India. The study was limited to one soil

type (sandy clay loam) and one soil moisture content in


Fig. 1. Detail of experimental set up.

order to keep the experiments within manageable limits.

The moisture content was chosen to coincide with the

normal moisture level for tillage operations for this soil

type.

2.2.1. Soil bin

The soil bin comprised a stationary bin, a common

carriage that supports the implement and soil processing

trolleys, power transmission system, control unit and

the required instrumentation as shown in Fig. 1. The bin

was 15.0 m long, 1.8 m wide and 0.6 m deep. The two

rails, one on top of each side, of the bin wall were used

for supporting the soil processing as well as the

implement trolleys. The soil processing trolley com-

prised a frame, rotary tiller, leveling blade and roller for

tilling, leveling and compacting the soil, respectively, to

obtain the desired soil strength and a water sprayer for

spraying water on the soil to maintain the desired

average moisture content. The different speeds of

operation were obtained by choosing suitable gears of a

gear reduction unit coupled to the input shaft of the

revolving drum, which was attached to soil processing

trolley with stainless steel rope. A control unit, placed

outside the soil bin, controlled the direction of

movement of the soil processing trolley. The testing

tool/implement was mounted on the frame of the

implement trolley, where screw jack arrangements were

provided to vary the depth of operation.

Table 1

Particle size distribution, bulk density and moisture content of the farm so

Soil depth (cm) Particle size distribution (%) B

Sand Silt Clay

0–15 57.7 19.7 22.6 1

15–30 55.2 19.4 25.4 1

30–45 52.5 20.2 27.3 1

45–60 52.2 19.2 28.6 1

The instrumentation for measuring the draft require-

ments of reference tillage tool, scale-model individual

and combination tillage implements in laboratory

consisted of an extended octagonal ring transducer

and a four-channel thermal write-out chart recorder

with universal amplifier. The transducer was designed

and fabricated for a maximum force of 3 kN based on

Godwin et al. (1993) and O’Dogherty (1996). The draft

values were continuously recorded in the recorder after

amplifying the signal coming from the extended

octagonal ring transducer.

2.2.2. Soil description and soil bed preparation

The soil at the research farm of the department is an

acid lateritic sandy clay loam and taxonomically

grouped under Oxyaquic haplustalf (order Alfisol).

The climate is sub-humid and sub-tropical with an

average rainfall of 1200 mm concentrated over the

months of June–September. The soil is partly eroded

due to high intensity rainfall in the area during the

monsoon season. In order to quantify the soil conditions

of field, bulk density, moisture content and cone index

data were obtained with core sampler and hand-

operated soil cone penetrometer. The cone base used

was of size 323 mm2 and diameter 20.27 mm. The

particle size distribution, bulk density, moisture content

and cone index of the farm soil are given in Table 1.

To get a simulated model of a field situation, the real

soil (sandy clay loam) was collected from the research

farm and filled in the bin up to a depth of 0.5 m with

crumb in layers of 10 cm. Each layer of soil in the bin was

compacted with roller to achieve the bulk density

measured in the field. After filling the soil in the bin, the

bulk densities of the soil were again measured with core

sampler at soil depth of 15 cm interval at four locations. It

was found that the differences between the bulk densities

of the soil in the field and in the bin were comparable. The

water was sprayed in the bin to get moisture content close

to field capacity. Some physical properties of the top

15 cm soil in the bin are given in Table 2.

Before starting the experiments, the soil bed was

prepared to achieve the desired cone index and bulk

il at different soil depths

ulk density (g/cm3) Moisture content g/(100 g of dry soil)

.61 11.3

.56 12.1

.59 13.2

.63 13.8


Table 2

Some physical properties of the experimental soil

Soil type Oxyaquic haplustalf

Soil texture Sandy clay loam

Sand 57.1%

Silt 19.9%

Clay 23%

Particle density 2.65 g/cm3

Moisture content 10.3 g/(100 g of dry soil)

Cohesion 11.76 kPa

Adhesion 7.66 kPa

Frictional angle 228

Fig. 2. Combination tillage implements used for laboratory experi-

ments.

density. In order to get this, first the tiller was used to

pulverize the soil after spraying water as desired. Then,

the soil was leveled with the leveling blade and

compacted by the roller to the desired cone index and

bulk density in layers. At the end of each soil

preparation, a hand-operated soil cone penetrometer

was used for measuring the cone index to a depth of

15 cm at intervals of 2.5 cm at six locations in the soil

bin following the procedures outlined in the ASAE

Standards (ASAE, 2000b). The locations were 2 m

apart along the center of the bin and were selected to

check the soil condition near the starting of the soil bed,

at the middle and towards the far end. At each of these

locations, two samples were taken across the bin (50 cm

apart). The locations were chosen so as not to interfere

with actual tillage tests. To get soil uniformity, the soil

bed preparation was repeated if the cone indices and

bulk densities were significantly different from each

other.

2.2.3. Tillage implements used

The two models of combination tillage implement

used in the experiments are shown in Fig. 2. The model

moldboard plow/cultivator was selected as front passive

sets while a model disk gang was selected as rear passive

set for the combination tillage implements due to their

better cutting and pulverization action, respectively. The

width of cut for each model moldboard plow and

cultivator tine was 150 and 75 mm, respectively. The

diameter and concavity of the disk in the model disk gang

were 300 and 30 mm, respectively. The spacing between

tines and disks were kept at 230 and 130 mm,

respectively. The two moldboard plows were so arranged

that there was no overlapping between plows during

operation. The actual working width of the cultivator with

disk gang (CTI-1) and the moldboard plow with disk gang

(CTI-2) combination tillage implement was 350 and

520 mm, respectively. Each passive set of the model

combination tillage implements such as the 2-tine

cultivator, the 2-bottom moldboard plow and the 3-disk

disk gang was also tested separately. To get the values of

various coefficients in Eqs. (8) and (9), two disk gangs

(33.7 and 36.7 cm width) along with single disk as

reference tillage tool for rear passive set were tested at

different depths, speeds and soil conditions. A frame

of 600 mm � 500 mm was fabricated with 50 mm�50 mm � 5 mm mild steel angle for mounting the tillage

implements during the experiment. In addition to these

tool and scale-model implements, two developed proto-

type combination tillage implements were tested in field

conditions to verify the developed regression equation.

2.2.4. Experiment layout

2.2.4.1. Laboratory experiments. Laboratory tests to

measure the draft requirements of five scale-model

implements (two combination and three individual

tillage implements) and a reference tillage tool (single

disk) were conducted at different depths, speeds, bulk

densities and cone indices. To determine the regression

coefficients of Dsrt (Eq. (6)) and ls

r (Eq. (9)), the

reference tillage tool was operated at different depths

and speeds before and after passage of front passive set

in the reference soil condition for both combination

tillage implements. The detail experimental plan is


Table 3a

Effect of different parameters on draft utilization ratio (l)

Experiment 1—Effect of speed and depth on l of reference tillage tool

Reference tillage tool Disk (width of cut = 9 cm)

Soil condition Soft (CI = 469 � 28 kPa, rw = 1.28 � 0.02 g/cm3)—reference soil

Speed 1.2, 2.2, 3.2 and 4.2 km/h

Depth 5, 7.5 and 10 cm

Experiment 2—Effect of scale factors of soil condition and implement geometry on l

Model implements Two disk gang (width of cut = 33.7 and 36.7 cm, disk diameter = 30 and 40 cm, number of disk in each gang = 3)

Soil condition Average CI = 468, 743, 947, 1244 and 1433 kPa and the corresponding rw = 1.28, 1.48, 1.61, 1.76 and 1.85 g/cm3

Speed 3.2 km/h

Depth 7.5 cm

given in Table 3a. A soft soil condition that is easy to

prepare was selected as the reference soil condition. To

find the regression constants of the scale factors related

to soil properties and implement geometry on l value,

the various levels used are also shown in Table 3a. The

performance of the developed draft equation in

predicting the experimental results of combination

tillage implements and its validation with separate set of

experiment data were carried out later (Table 3b).

The soil data were collected using core sampler and

hand-operated soil cone penetrometer before each

tillage experiment. After fixing the desired depth and

selecting a gear for particular speed, the implement

trolley along with tool/implement was pulled in the soil

by keeping the pulling arm horizontal to the soil bed and

the draft data from the calibrated extended octagonal

ring transducer were continuously acquired in a four-

channel thermal write-out chart recorder after ampli-

fication. The depths of operation for both front and rear

passive sets were kept to be same during a test.

Simultaneously, the time taken to cover a fixed distance

of 10 m was noted with the help of a mechanical

stopwatch to calculate the speed of operation.

2.2.4.2. Field experiments. To validate the developed

draft equation, field experiments were carried out with

37 kW 2WD tractor to measure the draft requirements

Table 3b

Effect of speed, depth and soil condition on draft of different scale-model

Model implements 2-Tine cultiva

2-Bottom mol

3-Disk disk ga

Two combinat

Soil condition Average CI =

Speed 1.2, 2.2, 3.2 a

Depth 5, 7.5, and 10

of two developed prototype combination tillage

implements (2 � 30 cm moldboard plow with 0.84 m

single disk gang ‘MBP-DG’ and 9-tine cultivator

with 1.68 m single acting disk harrow ‘C-DH’) in

hard (CI = 1433 kPa and rw = 1.68 g/cm3) and soft

(CI = 658 kPa and rw = 1.33 g/cm3) soil conditions at

different speeds (in the range of 1.7–5.2 km/h) and at

two depths of operation (14.5 and 18.8 cm for the MBP-

DG and 6.5 and 10 cm for the C-DH combination

tillage implements). The depths of operation of the rear

passive set in the MBP-DG combination tillage

implement were 9 and 13.5 cm corresponding to

14.5 and 18.8 cm depth of operation of the front

passive set. However, in case of C-DH combination

tillage implement, the depths of operation of the rear

passive set were same as the front passive set. All field

tests were conducted in sandy clay loam soil. A barren

land, approximately 0.25 ha after rainy season was

selected as hard soil condition. On another plot of

0.25 ha, the soft soil condition was achieved by

plowing followed by twice disking and twice cultivat-

ing. Before starting the experiments, the data on bulk

density, moisture content and cone index were

collected and are summarized in Table 4.

The draft measurements were carried out for both

combination tillage implements using a developed force

measuring system employing the electrical strain

implements

tor (tine width = 7.5 cm, spacing between tines 23 cm)

dboard plow (width of each bottom = 15 cm)

ng (width of cut = 33.7 cm, disk diameter = 30 cm)

ion tillage implements (width of cut 35 and 52 cm)

826 and 1219 kPa and the corresponding rw = 1. 54 and 1.75 g/cm3)

nd 4.2 km/h

cm


Table 4

Mean and deviation of soil bulk density, moisture content and cone index data in the field before experiments

Soil condition Bulk density (g/cm3) Moisture content g/(100 g of dry soil) Cone index (kPa)

Hard 1.49 � 0.05 12.5 � 1.1 1433 � 61

Soft 1.19 � 0.02 11.6 � 0.9 658 � 37

gauges on the three-point linkage system of the tractor.

The strain gauges were mounted on each of the two

lower links and proving ring attached to the top link.

The strain gauges were then connected in the

Wheatstone bridge to measure the draft. The depth of

operation of the implement, horizontal and vertical

angles of the lower and top links were measured using

potentiometer circuits. The experimental data from the

force measuring system and potentiometers were

logged with HP data logger. Simultaneously, the time

taken to cover a fixed distance of 50 m was noted from a

mechanical stopwatch to calculate the operating speed

of the tractor and implement combination.

3. Results and discussion

3.1. Experimental results

The average moisture content during the tests was

9.9 g/(100 g dry matter) with a maximum variation of

�1.3 g/(100 g dry matter). The effect of depth, speed

and soil condition on draft utilization ratio and draft of

reference tillage tool and combination tillage imple-

ments were presented as below.

3.1.1. Effect of depth and speed on draft utilization

ratio of reference tillage tool

Both orthogonal and multiple regression analyses

were performed using a computer-based software (SPSS)

package on the average l values of the reference tillage

tool (single disk) to determine the speed-depth response

curve in the reference soil conditions and the results are

Table 5

Regression coefficients of draft utilization ratio (l) for single disk in the r

Regression coefficients Orthogonal regression

CTI-1 CTI-2

C0 0.371 0.344

C1 �0.019 �0.021

C2 0.0 0.0

C3 �0.009 �0.011

C4 0.0 0.0

C5 0.0 0.0

R2 0.947 0.982

summarized in Table 5. The orthogonal regression was

carried out to determine the significant terms and to avoid

multicollinearity problems (Glancey and Upadhyaya,

1995). To predict the lvalues beyond the depth and speed

ranges of the reference tillage tool, multiple regression

analysis was carried out with the real depth and speed

variables considering the significant terms obtained from

the orthogonal regression analysis and the regression

results are also presented in Table 5. Except depth and

speed terms, no other terms were found to be significant

and hence are set to zeroes. Considering the result of

multiple regression analysis, the draft utilization ratio

(lsr) of the reference tillage tool in the reference soil

condition could be expressed as:

lrs ¼ c0 þ c1d þ c3V (10)

The high values of R2 in Table 5 indicate that the

variables depth and speed in the regression equation can

explain most of the variability in the experimental data.

3.1.2. Effect of scale factors on lThe l value of prototype/scale-model implements at

any speed, depth and soil conditions could be predicted

using Eq. (8). Taking log on both sides of Eq. (8), we get:

log

�lp

lsr

�¼g log

�rw

rws

�þ h log

�CI

CIs

�þ i log

�Wrp

Wrr

�

(11)

where g, h and i are regression coefficients and are

specific to soil and combination tillage implements and

their values were determined applying multiple regres-

eference soil condition

Regression coefficients Multiple regression

CTI-1 CTI-2

c0 0.478 0.468

c1 �0.007 �0.008

c2 0.0 0.0

c3 �0.019 �0.022

c4 0.0 0.0

c5 0.0 0.0

R2 0.947 0.982


Fig. 3. Comparison of observed and predicted l values for both model

combination tillage implements in soil bin.

Table 6

Multiple regression constants of draft utilization ratio (l) for single

disk-disk gang combination based on the reference soil condition

Combination tillage implement g h i R2

CTI-1 0 �0.19 0.0 0.897

CTI-2 0 �0.38 0.0 0.966

sion technique. The results for each combination tillage

implement are presented in Table 6. The high values of

R2 indicate a good prediction of ratio of draft utilization

ratios ðlp=lsrÞ for both combination tillage implements.

Fig. 4. Effect of speed on draft of both combination tillag

Comparing the various regression coefficients of the

Eq. (11), it could be concluded that soil condition had

more effect on ratio of draft utilization ratios than the

implement geometry.

3.1.3. Validation of the developed l equation

The developed regression equation for l was verified

against the data collected from separate set of

laboratory experiments (Table 3b) conducted with

two combination and three individual scale-model

tillage implements at different depths, speeds, bulk

densities and cone indices. The observed and predicted

l values for both scale-model combination tillage

e implements at different depths and soil conditions.


Fig. 5. Effect of speed on l values of both combination tillage implements at different depths and soil conditions.

implements were plotted in Fig. 3. From this figure, it

can be seen that the slopes of the best-fitted lines were

close to unity and hence the equation developed was

verified. The developed equation predicted the l values

of the CTI-1 and CTI-2 with average absolute variation

of 2.2 and 4.3%, respectively, from the observed values.

In view of the experimental errors in the measurement

of draft of different tillage implement, these values were

considered acceptable.

3.1.4. Effect of depth and speed on draft of

combination tillage implements

The draft data collected from the laboratory

experiments (Table 3b) were presented in Fig. 4 for

both combination tillage implements. It was found from

ANOVA that the draft of the combination tillage

implements was significantly affected by depth and

speed of operation at a 5% significance level. It can be

seen from Fig. 4 that with increase in depth and speed of

operation, the draft of the combination tillage imple-

ments increased. This was because of the higher soil

resistance and more volume of soil handled with

increase in depth and higher force required to

accomplish the soil acceleration with increase in speed

of operation. It can also be seen from Fig. 4 that the CTI-

2 implement experienced higher draft requirement

compared to the CTI-1 implement under similar soil and

operating conditions. This was because of more

working width for the CTI-2 implement as compared

to the CTI-1 implement.

From these experimental results, it was found that

the draft contribution of the front passive set to the total

draft of a combination tillage implement was 75–85%

and 65–80% for the CTI-1 and CTI-2 combination

tillage implement, respectively, and it increased with

increase in either bulk density, cone index, depth or

speed of operation. Hence, the reverse trend for l was

noticed (Fig. 5) with increases in bulk density, cone

index, depth and speed of operation. It was found from

the experimental data that the computed l values for

both scale-model combination tillage implements in the

in the test range were varied from 0.27 to 0.40 and 0.21

to 0.33 for the CTI-1 and CTI-2 combination tillage

implements, respectively.

3.2. Developed draft equation for a combination

tillage implement

Based on the Eq. (4), the draft requirements of

combination tillage implements could be predicted


Fig. 6. Comparison of the observed and predicted draft for both

combination tillage implements.

with the help of Eqs. (5), (6), (8) and (9). Sahu and

Raheman (2004) reported the values of the various

regression coefficients of Eqs. (5) and (6) from the draft

analysis for individual tillage implements. In the

present study, the regression coefficients of Eqs. (8) and

(9) are summarized in Tables 5 and 6 to predict the l

value of the rear passive set of combination tillage

implements.

3.2.1. Validation of the developed draft equation

3.2.1.1. In laboratory. The developed draft equation

was verified for both combination tillage implements

against the data collected from laboratory experiments

(Table 3b) conducted in the same soil. The observed and

predicted values of draft for all the tillage implements

were plotted in Fig. 6a. From this figure, it can be seen

that the slopes of the best-fitted lines were close to unity

and hence the equation developed was verified. The

developed regression equation predicted the draft of the

CTI-1 and CTI-2 combination tillage implement with

an average absolute variation of 14.5 and 13.4%,

respectively.

3.2.1.2. In field. The draft values measured during the

field tests were used to validate the developed draft

equation for both combination tillage implements. The

observed and predicted values of draft for all the tillage

implements were plotted in Fig. 6b. A good general

agreement between observed and predicted values of

draft was found with slope close to unity. The developed

regression equation predicted the draft of the C-DH and

MBP-DG combination tillage implement with an average

absolute variation of 18.0 and 12.8%, respectively.

4. Conclusions

1. A new methodology was successfully developed to

estimate the draft requirements of cultivator with

disk harrow and moldboard plow with disk gang

combination tillage implements in sandy clay loam

soil from the knowledge of the draft requirements of

individual tillage implements in the same soil and the

draft utilization ratio (l) of the rear passive sets of

these combination tillage implements.

2. F
rom the experimental results and regression
analyses, it was found that the total draft require-

ments of combination tillage implements and the

draft utilization ratio of the rear passive set were

significantly affected by depth, speed of operation

and soil condition. It was also found that the draft of

all the tillage implements increased with increase in

soil compaction, depth and speed of operation.

However, the reverse trend was obtained for l with

the same parameters.

3. T
he developed draft equation estimated the draft
requirements of both combination tillage implements

within an average absolute variation of 18.0 and

13.5%, respectively, in both laboratory and field

conditions. Hence, the concept of reference tillage

tool and reference soil condition could be used

successfully to predict the drafts of various combina-

tion tillage implements and draft utilization ratio for

rear passive set of the combination tillage implement

in field conditions with scale factors related to soil

properties and implement geometry. This concept

could save time, energy and cost by reducing the

number of field experiments.

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an approach for draft prediction of combination tillage implements in sandy clay loam soil

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