laboratory investigation of cutting forces and soil disturbance resulting from different manure...

Laboratory investigation of cutting forces and soil disturbanceresulting from different manure incorporation

tools in a loamy sand soil

S. Rahman, Y. Chen*

Department of Biosystems Engineering, University of Manitoba, Winnipeg, Man, Canada R3T 5V6

Received 24 November 1999; received in revised form 6 June 2000; accepted 2 October 2000

Abstract

Injection of manure is becoming more popular than surface spreading due to its agronomical and environmental bene®ts. In

this study, four different existing tools (two sweep types and two disc types) for liquid manure incorporation were tested in an

indoor soil bin located in the Department of Biosystems Engineering at the University of Manitoba with loamy sand, to

investigate the effects of working depth (50, 100 and 150 mm) and speed (0.57 and 1.4 m/s) on soil cutting forces and soil

disturbance. Draft forces and soil disturbance for all tools signi®cantly increased with working depth, but not with working

speed. Owing to its wider soil cutting width, sweep B required 80% more draft force than sweep A. For the same reason,

sweep B disturbed a 44% wider soil surface along the tool passage, compared to sweep A. On the average, sweep type tools

created 27% new soil pores, which would be available for containing injected manure. For the discs, vertical forces decreased

with increased working depth. As compared with disc A, wider surface disturbances along the tool passage were observed for

disc B due to its two concave disc design. Comparing soil disturbance for different depths, disc B may not be suitable for

manure incorporation at shallow depths (50 and 100 mm). At greater depths (150 mm) both disc-type tools will favor manure

coverage. # 2001 Elsevier Science B.V. All rights reserved.

Keywords: Incorporation tools; Working depth and speed; Soil cutting force; Soil surface disturbance; Bulk density; Loamy sand; Manure

1. Introduction

Land application of liquid manure with broadcast

spreaders causes nutrient losses (by volatilization of

ammonia) and odour emissions. This has led to the

adoption of liquid manure incorporation techniques,

including manure injection (Warner et al., 1991)

which can reduce odour and ammonia emission up

to 95% (Phillips et al., 1988). However, existing

manure incorporation equipment, especially injectors,

requires great draft force or tractor power and may not

cover all the manure with soil (Hultgreen and Stock,

1999). These have become limiting factors for a wide

use of incorporation techniques.

An injection tool must create suf®cient new soil

pores to contain manure (McKyes et al., 1977; Par-

kinson et al., 1994). Failure to meet this requirement

will result in exposure of manure on the soil surface

and increase odour and ammonia emissions (McKyes

et al., 1977). To meet agronomic requirements, man-

ure should be placed in an aerobic soil environment

Soil & Tillage Research 58 (2001) 19±29

* Corresponding author. Tel.: �1-204-474-6292;

fax: �1-204-474-7512.

E-mail address: [email protected] (Y. Chen).

0167-1987/01/$ ± see front matter # 2001 Elsevier Science B.V. All rights reserved.

PII: S 0 1 6 7 - 1 9 8 7 ( 0 0 ) 0 0 1 8 1 - 1

and mixed with the soil to favor biological stabiliza-

tion of manure (Godwin et al., 1976; McKyes et al.,

1977). Bulk density is an important parameter indi-

cative of soil porosity. Disturbing a larger volume of

soil usually creates more pores (Chen et al., 1998).

Moseley et al. (1998) concluded that the soil distur-

bance pro®le is an indicator of manure±soil mixing

state. For example, they found that a narrow channel

within the disturbed soil volume indicates poor soil±

manure mixing while its absence suggests better

mixing.

Disturbance of the soil surface is an important

performance indicator for manure incorporation tools

in all cases, particularly under grassland situations. In

western Canada, hogs were often raised within close

proximity to pastureland. Thus, applications of the

manure to pastureland would be an inexpensive prac-

tice in terms of manure transportation from barn to

application site. On the other hand, pastureland often

does not reach its full production potential because it

is usually not fertilized due to the high costs of

chemical fertilizer. A concern on grassland, whether

pasture or hay, is palatability or even pathogen con-

tamination of cattle grazing. In this case, injecting

manure below the soil surface should be used. Injec-

tion tools should create minimum surface disturbance

to prevent excessive grass damage (Hann et al., 1987).

Great surface disturbance by an injection tool causes

extensive root damage for perennial crops (Warner

et al., 1991).

The draft force requirement and soil disturbance, in

terms of soil volume disturbed and bulk density

changes, vary with different injection tools. McKyes

et al. (1977) found that, to cut a speci®ed volume of

soil, a wide tine working at a shallow depth requires

less draft force than a narrow tine working at a deeper

depth. Similarly, a winged injector can incorporate a

much larger volume of manure with adequate soil

cover at a shallower depth than a simple non-winged

tine (Warner and Godwin, 1988). It was also found

that a winged injector required 35% more draft force

than a simple non-winged tine for the same injection

depth, but could incorporate twice the volume of

manure.

Discs have also been used for manure incorpora-

tion. Discs lift and invert the soil and at the same time

bury the injected manure (Reaves et al., 1981). The

draft and vertical force on rolling disc generally

increase with soil penetration depth (Morrison et al.,

1996). The rolling motion of a disc helps to cut

through the soil surface residue (Tice and Hendrick,

1992). The draft force increases with penetration since

rolling disc must always be forced into the soil

(Kepner et al., 1987).

Most existing manure incorporation tools were

derived from tillage tools. Their cutting forces and

soil disturbance patterns, which are critical for manure

incorporations, have not been well documented. The

objectives of this study were: (1) to investigate effects

of the tool working depths and speeds on cutting

forces and soil surface disturbance, and (2) to evaluate

performances of different commercially available

tools for liquid manure incorporation.

2. Materials and methods

2.1. Equipment and testing facilities

Four different types of incorporation tools were

tested in an indoor soil bin. Two of them were

sweep-type: `̀ sweep A'' and `̀ sweep B'' and the

remaining were disc-type: `̀ disc A'' and `̀ disc B''.

A coulter can be optionally used in front of sweep B;

however, the coulter was removed to compare perfor-

mance with sweep A. Disc A features a single vertical

disc, while disc B consists of two concave discs

mounted on a ¯exible spring shank. The con®gura-

tions of these tools are shown in Fig. 1 and their

geometric parameters are listed in Table 1. Except for

disc B, all the other tools were designed for liquid

manure injection where manure would be placed into

the soil and covered by a layer of soil. Disc B is a

surface incorporation tool, where manure is placed on

the soil surface in the middle of the two concave discs

and mixed with the loose soil by the two discs during

incorporation. Therefore, the term manure incorpora-

tion refers to both manure injection and surface

incorporation in this paper.

The indoor soil bin, located in the Department of

Biosystems Engineering at the University of Mani-

toba, is 1.5 m wide, 15 m long and 0.6 m deep and

contains a loamy sand soil (860 g kgÿ1 sand and

100 g kgÿ1 clay, by weight). A variable speed motor

was connected to the soil bin carriage to control tool

working speeds. Tool working depths were controlled

20 S. Rahman, Y. Chen / Soil & Tillage Research 58 (2001) 19±29

by adjusting the vertical position of the tool bar on the

bin carriage. To maintain uniform soil conditions of

moisture content and bulk density throughout the tests,

an equal amount of water was sprayed over the soil

and left to in®ltrate for 24 h. Then the soil was roto-

tilled at a greater depth than the maximum experi-

mental working depth designed. The last step for soil

preparation was to level and compact with a 162 kg

smooth ¯at roller. The ®nal soil moisture and dry bulk

density were measured before the test runs. The

internal friction angle (f) and cohesion of soil (c)

(Table 2) were measured with a square shear box of

60 mm length for the same soil moisture content and

bulk density as listed in Table 2. Tests were conducted

with three different vertical loads (210, 480 and

745 N).

Fig. 1. Manure incorporation tools used in this study: (a) Sweep A, (b) Sweep B, (c) Disc A, and (d) Disc B.

Table 1

Geometrical parameters of the manure incorporation tools tested

Parameters Incorporation tools

Sweep A Sweep B Disc A Disc B

Sweep width (mm) 330 570

Sweep length (mm) 240 490

Sweep angle (8) 67 63

Rake angle (8) 21.5 18.5

Disc diameter (mm) 635 560

Disc angle (8) 0 6

Tilt angle (8) 0 18

S. Rahman, Y. Chen / Soil & Tillage Research 58 (2001) 19±29 21

2.2. Experimental design and measurements

A �3� 2� completely factorial experiment with

three working depths (50, 100 and 150 mm) and

two working speeds (0.57 and 1.4 m/s) was conducted

for each incorporation tool. The selected working

depths and speeds were commonly used by producers

for manure incorporations. Each treatment was repli-

cated three times. Thus, a total of 72 test runs were

performed in this study.

Before test runs, three random soil cores (52 mm

diameter) were taken for measuring initial soil mois-

ture content and dry bulk density. The force measuring

set-up included a tillage tool dynamometer (compris-

ing six force transducers to measure orthogonal

forces) and a data acquisition unit. The transducers

were arranged so as to determine the draft (Fx),

vertical (Fz) and side (Fy) forces as well as moments

about the respective axes. Data were recorded for each

second for each treatment. After each test run, the soil

surface disturbance pro®le and the cross-sectional area

disturbed by the tool were measured at ®ve random

locations. Three soil cores were also collected at

random locations along the tool's passage to examine

the changes of bulk density. The density and cross-

sectional dimension measurements were performed

only for three injection tools. The measurement meth-

ods used were described in Rahman and Chen (1999).

Due to the limitation of the indoor test facility used,

manure was not applied during the testing. However,

investigations made on tool draft forces and soil

disturbance were independent of manure application.

Moseley et al. (1998) successfully used an indoor soil

bin to evaluate the performance of an injection tool on

draft forces and soil disturbance characteristics.

2.3. Data analyzes

Analyzes of variance were performed on the data to

test the effects of working depths and travel speeds on

the cutting forces, soil surface disturbances and soil

bulk density. Statistical inferences were made at the

0.1 level of probability.

3. Results and discussion

3.1. Soil cutting forces

No particular trends were observed for Fy, Mx

and Mz for all the tools. Therefore, the following

discussion is focused mainly on draft force (Fx),

vertical force (Fz) and moment (My), which were

the most critical cutting forces associated with tool

performance.

3.1.1. Sweep A and sweep B

3.1.1.1. Measured forces. For both sweep type

injection tools, the draft force (Fx) significantly

increased with working depths (Fig. 2) but not with

working speed. The draft, Fx, for sweep B was 80%

higher than that for sweep A, since sweep B has a

wider cutting width. For sweep B, Fx increased

Table 2

Soil conditions (moisture content and bulk density) and inputs for the universal soil cutting equation to predict forces for sweep tools

Symbol Description Values for soil bin soil

y Soil moisture content (g kgÿ1) 160

rb Dry bulk density (Mg mÿ3) 1.35

f Soil internal friction angle (8) 29

c Soil cohesion (kPa) 9.23

ca Soil adhesion (kPa) 0

d Soil±tool friction angle (8) 22

a Tool cutting angle (8) Sweep A, 21.5; sweep B, 18.5

g Specific weight (kN mÿ3) 15.35

w Tool cutting width (m) Sweep A, 0.33; sweep B, 0.57

d Cutting depth (m) 0.05, 0.10 and 0.15

q Soil surface surcharge pressure (kPa) 0

v Tool travel speed (m sÿ1) 0.6 and 1.4


linearly from 50 to 150 mm depth. Therefore,

minimizing the injection depth will be an effective

way to minimize the draft force required for liquid

manure injection. For sweep A, there was a higher in-

crease rate in the draft force requirement as the depth

increased from 100 to 150 mm. Therefore, injection

depths under 100 mm may be suggested for using

sweep A to inject manure under the specified soil

condition. The effects of working depths and speeds

on My had a similar trend (data not shown) as those

of Fx.

The vertical force signi®cantly increased with

depths and speeds, and the effects of depths were

more prominent over speeds (data not shown). Sweep

B required 78% more vertical force than sweep A (577

versus 325 N, in average). In ®eld conditions, this

vertical force will directly contribute to the vertical

load on the tractor rear wheel (Kepner et al., 1987).

However, this amount of load would not cause sig-

ni®cant load transfer from the front wheels to the rear

wheels.

3.1.1.2. Comparison between predicted and mea-

sured draft force. To compare the measured value

with the theoretical prediction, the three-dimen-

sional cutting model of McKyes and Ali (1977) was

used. The values of adhesion (ca) and soil±tool friction

angle (d) were taken from the study by Godwin et al.

(1984) on a similar soil condition. The input

parameters for the universal equation are presented

in Table 2. The degree of agreement between predicted

and measured values is shown in Fig. 3. The predicted

draft forces agreed well with the measured values for

sweep A with a coefficient of determination (R2) of

0.95, while they were slightly lower than the measured

values for sweep B with a coefficient of determination

(R2) of 0.92. Similarly, the predicted vertical force

requirement agreed with the measured values with a

coefficient of determination of about 0.58 and 0.97 for

sweep A and B, respectively (data not shown).

3.1.2. Disc A and disc B

Except for disc B, precise experimental depths

could be obtained with the same tool bar position.

The actual penetration depths for disc B were always

shallower due to its ¯exible spring shank and the

upward soil force. Therefore, in ®eld conditions,

additional force might be needed to keep an appro-

priate downward pressure to ensure penetration to the

target depth.

Fig. 4 shows the variation of draft force with the

actual tool working depths, which in case of disc B

were different than the depth designed for the experi-

ment. Its actual three working depths were measured

as 40, 80 and 110 mm. For both discs, Fx signi®cantly

increased with depth but not with speed. The trend

shows that disc B requires more draft force than disc A

at similar working depths. This is because disc B has

Fig. 2. Comparison of drafts force (Fx) averaged over two working speeds versus working depths for the sweep-type injection tools. N,

Newton.


two discs penetrating into the soil, and a larger disc

angle and tilt angle (Table 1).

Unlike the sweep type tools, Fz for disc-type tools

decreased with increasing depths. On the average, for

disc A, Fz decreased from 545 to 222 N, and for disc B

from 620 to 20 N. According to Kepner et al. (1987),

increased speed would help to improve the soil pene-

tration by discs. However, this was not the case in this

study. Increasing speed from 0.57 to 1.4 m/s did not

signi®cantly change values of Fz.

3.2. Soil disturbance

3.2.1. Sweep A and sweep B

Soil cross-sections disturbed by both the sweeps

were of a trapezoidal shape (Fig. 5). The bottom of a

trapezoid was close to the sweep width and the height

to the working depth. Sweep B disturbed a larger

cross-section area; consequently, it should favor a

higher manure application rate (Chen et al., 1999),

compared to sweep A. Sweep A created a shallow

Fig. 3. Comparison between predicted and measured draft force for sweep type injection tools. N, Newton.

Fig. 4. Comparison of drafts force (Fx) averaged over two working speeds versus working depths for the disc-type injection tools. N, Newton.


narrow channel in the center of tool path and

mounds soil to the side (Fig. 5a), while sweep B

spread soil more evenly over the cutting width of

the surface (Fig. 5b). The disturbance for sweep A

indicates that soil moved toward the sides during the

cutting, which may not favor manure coverage but

consume extra power. Surface disturbance was char-

acterized as width (W) of the loose soil mound and

height (H) shown in Fig. 5. Effects of working speed

on soil disturbance were not detected. Increased

working depths signi®cantly increased W (Fig. 6),

H and the cross-section disturbed (data not shown).

A 44% higher W with sweep B was found since it has a

72% larger cutting width than sweep A. Higher sur-

face disturbance of soil might require additional til-

lage operations for seedbed preparation. A larger W

may also imply greater crop damage for grassland

application of manure.

3.2.2. Disc A and disc B

Disc A created a clear cut furrow in the soil cross-

section and moved the soil to one side forming a

mound (Fig. 7). The furrow was of a triangular shape

with a width of W1 on the soil surface and a depth

equal to the working depth (d). Manure would be

placed into the furrow in the case of manure injection.

An increased W1 may indicate that more manure can

be placed as larger cross-sectional area of the furrow

will favor higher manure application rates (Chen et al.,

1999). No particular trends were observed for W1

which ranged from 20 to 96 mm. The overall width

of the surface disturbance, W2 increased signi®cantly

with increased working depth and speed (Fig. 8) but

not by their interaction. Deep injection depth

(150 mm) and higher speed will favor soil±manure

Fig. 5. Soil disturbance pro®les for (a) sweep A and (b) sweep B.

H�mound height; W�surface disturbance width.

Fig. 6. Comparison of soil surface disturbance width (W ) averaged over two working speeds versus working depths for the sweep-type

injection tools.

Fig. 7. Soil disturbance pro®le for disc A. W1�furrow width;

W2�surface disturbance width; H1�mound height; d�working

depth.


mixing since the furrow was re®lled with disturbed

soil, and consequently, nutrient losses and odour

emissions could be reduced. There were no particular

trends observed for the mound height H1 which

ranged from 23 to 54 mm.

Disc B inverted soil to the surface, forming two

mounds at 40 mm depth and one mound at 110 mm

depth (Fig. 9). At a depth of 40 mm, an area between

the two discs, represented by a width W3 (Fig. 9a), was

not covered by loose soil at both working speeds.

Manure would not be incorporated adequately at this

depth, increasing risks for nutrient losses and odour

emissions. As the working depth increased, the mag-

nitude of W3 was reduced signi®cantly with depth and

speed (Fig. 10) but not by their interaction. At greatest

working depth (110 mm), the entire area between two

discs was covered with loose soil up to a depth of (H2)

(Fig. 9b). At this depth, values of W3 reduced to zero

for two working speeds (Fig. 10), where complete

manure incorporation could be expected. No consis-

tent trend was observed for H2 which varied from 39

to 64 mm. Values of W4 were similar to the distance

between the two discs, regardless of working speed

and depth.

3.3. Changes of soil bulk density

Differences in bulk density between the two sweep

type tools were insigni®cant. For both tools, an aver-

age bulk density decreased from initial density of 1.35

to about 0.84 Mg mÿ3 as the depths increased from 50

to 150 mm (Fig. 11). For all depths, higher speeds

further reduced the bulk density for sweep A. On

average, about 27% new soil pores were created by

the tool. According to Negi et al. (1978), these new

pores would be available to absorb injected liquid

manure. This information can be used for selecting

injection depth (Chen et al., 1999).

3.4. Speci®c resistance

Field ef®ciency of a manure injection tool needs to

be evaluated for both the draft force requirement and

the amount of manure that can be injected (Ren and

Chen, 1999). Magnitudes of cross-sectional areas of

disturbed soil plus the change in density re¯ect the

Fig. 8. Soil surface disturbance width (W2) versus working depths for disc A at different speeds (m/s).

Fig. 9. Soil disturbance pro®les for the disc B at (a) 40 mm depth

and (b) 110 mm depth. W3�uncovered width; W4�surface

disturbance width; H2�mound height.


Fig. 11. Changes of soil bulk density averaged over two working speeds for sweep injection tools.

Fig. 10. Soil surface disturbance width (W3) versus working depths for Disc B at different speeds (m/s).

Fig. 12. Comparison of speci®c resistance averaged over two working speeds, versus working depths for the sweep-type injection tools. N, Newton.

maximum amount of manure which the soil can

potentially absorb (Godwin et al., 1976). Therefore,

speci®c resistance (draft force per unit cross-sectional

area of soil disturbed) can be used to evaluate the

loosening performance of the sweep-type manure

injection tools theoretically.

Although sweep B disturbed a larger soil cross-

sectional area, sweep A resulted in an average of 23%

lower speci®c resistance than sweep B (Fig. 12), since

sweep B required a much higher draft force (Fig. 2).

As depth increased, the speci®c resistance for sweep B

was about the same level. However, the speci®c

resistance for sweep A was lower at 100 mm depth.

As speci®c resistance should be minimized (Godwin

et al., 1984), an injection depth of 100 mm is sug-

gested for sweep A.

4. Conclusions

For all tools and operation speeds tested, the work-

ing depth is more critical than the working speed, in

terms of effects on draft force and soil disturbance.

Greater working depth caused more soil to be dis-

turbed. Draft forces increased more or less linearly

with the working depth. For sweep A, a depth less than

100 mm is recommended. Owing to its wider soil

cutting width, sweep B injector disturbed more soil,

which may favor higher manure application rates.

However, 80% more draft force is required than for

sweep A. Larger surface widths were disturbed by

sweep B due to its larger size. Compared to sweep B,

sweep A showed a lower speci®c resistance, indicating

potentially higher ®eld ef®ciency. With the same

initial soil conditions, both sweeps can create 27%

new soil pores potentially for containing injected

manure. Increased working depth and speed create

more pore space, which is favorable for manure

absorption.

For disc B, used at working depths shallower than

80 mm, a section between two discs was uncovered,

which may not be desirable for manure coverage. At a

depth of 110 mm the surface area between the two

discs was completely covered. Therefore, disc B

should be used for manure incorporation at a depth

greater than 80 mm. In ®eld conditions, additional

weight might be needed for soil penetration purposes.

Disc A creates a clear furrow at the shallow depth

used, which would not favor manure±soil mixing. It

should work at a depth greater than 100 mm where the

furrow was re®lled with the loose soil.

As compared to the sweep type tools, the disc type

tools required lower draft force when working at the

same depths. For example, draft forces for sweep B

were about three times higher than those for disc A.

Comparing the soil disturbance pattern, disc type tools

have lower capacity in terms of manure application

rates.

Acknowledgements

The authors wish to acknowledge the ®nancial

assistance received from the Department of Manitoba

Agriculture and the Triple S Hog Manure Manage-

ment Initiative and Dr. Sylvio Tessier, Manitoba

Agriculture, for reviewing this paper.

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