Soil & Tillage Research 124 (2012) 203–210

Design and evaluation of ground-driven rotary subsoilers

Ahmet Celik a,*, Randy L. Raper b

a Ataturk University, Faculty of Agriculture, Department of Agricultural Machinery, 25240 Erzurum, Turkeyb Oklahoma State University, Field & Research Service Unit, Stillwater, OK 74078, USA

A R T I C L E I N F O

Article history:

Received 27 March 2012

Received in revised form 5 June 2012

Accepted 7 June 2012

Keywords:

Soil compaction

Subsoiler

Tillage

Draft

Conservation tillage system

A B S T R A C T

Compacted soil hardpans restrict crop growth by limiting root access to moisture and nutrients in the

subsoil. Mechanically disrupting this hardpan profile is necessary in many soils to promote proper root

elongation and crop growth. Subsoiling is the primary deep soil tillage practice which needs to be done

once every two to three years depending on soil type and conditions. To maintain an adequate amount of

residue for conservation systems, subsoiling should be performed without excessively disturbing the soil

surface. However, most subsoilers disrupt the soil surface excessively and cover valuable crop residues.

The objective of this study was, therefore, to design an alternative subsoiler for conservation tillage

systems that minimized soil disturbance and energy requirements while adequately disrupting

compacted soil profiles. Ground-driven rotary subsoilers were designed and manufactured by dividing a

1.2 m diameter coulter into multiple blades. Minimizing the sliding soil resistance on the side of the

coulter was one of the main considerations in forming the shape and number of blades. An experiment

was conducted in the soil bins of the USDA-ARS National Soil Dynamics Laboratory in Auburn, AL, USA to

determine the effects of ground-driven rotary subsoilers on soil disturbance and energy requirements

compared with a large coulter and a typical subsoiler. Treatments were four different types of subsoilers

(coulter-no-blade, coulter-5-blade normal direction, coulter-5-blade reverse direction, and shank-type)

and two tillage depths (25 and 38 cm). Soil disturbance, cone index, bulk density and draft were

measured and statistical analyses conducted to determine the differences between subsoilers. The

coulter-5-blade normal direction and coulter-5-blade reverse direction subsoilers required considerably

less draft power (from 10 to 68%) for both operation depths than coulter-no-blade and shank type

subsoilers. Coulter subsoilers minimized soil disturbance and required higher draft energy (from 22.5 to

33.5%) per volume of disturbed soil than the shank-type subsoiler. The soil disruption paths of coulter-5-

blade subsoilers have an advantage for row crops due to limited above-ground disturbance if seeds can

be placed in the middle of the disrupted zone.

� 2012 Elsevier B.V. All rights reserved.

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Soil & Tillage Research

jou r nal h o mep age: w ww.els evier . co m/lo c ate /s t i l l

1. Introduction

Soil compaction is the movement of soil particles closertogether due to naturally occurring or machinery-induced forces(Pikul and Aase, 1999; Raper, 2003; Petersen et al., 2004). The soilbecomes denser, pores become smaller and strength increases. Soiltype has an important effect on compaction. Poorly graded soils,which are coarse grained and contain fines between 5 and 15%,tend to be more resistant to compaction. Well-graded soils have amixture of large and small particles, and therefore, little void space,so they have little pore space for plant root expansion. Coastal Plainsoils tend to be particularly susceptible to this problem due to theirsandy topsoil and clay subsoil. At depths where the two soil layerscontact one another, hardpans tend to form (Raper et al., 2005).

* Corresponding author. Tel.: +90 442 231 2552; fax: +90 442 236 09 58.

E-mail addresses: ahcelik@atauni.edu.tr, ahcelik@yahoo.com (A. Celik).

0167-1987/$ – see front matter � 2012 Elsevier B.V. All rights reserved.

http://dx.doi.org/10.1016/j.still.2012.06.010

This compacted layer restricts root growth, restricts water and airmovement in the soil, and ultimately reduces yield (Petersen et al.,2004; Wells et al., 2005). Machine-induced compaction is directlyaffected by field machine weight, tire size, tire inflation pressure,and field traffic. While lighter axle loads may cause only surfacecompaction, heavier loads cause deep compaction. Compaction isinfluenced by various factors, including the number of wheelpasses, soil type, soil moisture, tire size, and tire inflation pressure.Deep soil compaction is difficult to alleviate by tillage (Hamlettet al., 1990; Raper et al., 1994; Petersen et al., 2004; Wells et al.,2005).

Subsoiling alleviates problems of excessive soil strength withinsoils, and results in improved conditions for crop growth. Thus,mechanical disturbance of subsoiling increases water holdingcapacity and reduces impedance to root penetration (Wells et al.,2005). Conventional subsoiling is the creation of 25–60 cm deepand 60–150 cm spaced channels, without inversion, using knife-like shanks that are pulled through the soil to create continuous

A. Celik, R.L. Raper / Soil & Tillage Research 124 (2012) 203–210204

grooves. The main aims of this operation are to improve waterinfiltration through the tillage pan, and to enhance soil conserva-tion, soil moisture storage, and crop yield (Williams et al., 2006).Subsoiling in severely compacted soils reduces the soil resistanceand provides an increased rooting depth that helps the plantswithstand short-term drought conditions (Raper et al., 1998).Subsoiling also significantly increases yields, reduces soil bulkdensity, and improves root growth (Abu-Hamdeh, 2003).

The subsoiler shape, the tillage depth, and the soil moisturehave important effects on the required draft and soil disruption.Raper (2005) reported that an angled shank positioned at a 528angle from horizontal plane in the direction of travel had a lowerdraft requirement compared to a curved shank. The soil disruptionwas equal for the two shanks. Smith and Williford (1988) reportedthat a parabolic subsoiler required less draft than a conventionalsubsoiler. Upadhyaya et al. (1984) found a straight shank mountedat a positive rake angle gave reduced draft compared to a curvedsubsoiler in sandy loam soils.

An important consideration concerning subsoiling is theamount of soil disruption for different soil conditions to increasethe long-term benefits of subsoiling (Raper and Sharma, 2004).Abu-Hamdeh (2003) stated that subsoiling removed the compac-tion effect and improved soil properties, crop growth and yield.Reeder et al. (1993) compared five subsoiler types on a compactedfield, in terms of soil physical properties and crop yield. For alltypes of subsoilers, they observed improvements in air porosityand cone index measurements two years after tillage, inuntrafficked areas. However, to maintain long-term benefits fromsubsoiling, controlled traffic is considered essential.

Rotary subsoiling is a new concept, not widespread in commonhardpan loosening practices and has rarely been studied or used incommercial agriculture. Using rotary subsoilers instead of pullingshanks through the soil can be partially justified by the higherefficiency of power being transferred to the soil rather thanthrough the tractor wheels (Miszczak, 2005). In his study, Miszczak(2005) stated that the coulter tines of rotary subsoilers exertedpressure on soil, causing soil disturbance and loosening, similar topassive narrow tines. Williams et al. (2006) used a rotary subsoilerto improve infiltration in frozen soil for newly planted winterwheat. They found that water storage in winter was significantlyincreased, and runoff and erosion were decreased by rotarysubsoiling, as compared with the control. Sakai et al. (1993)reported that a vibrating four-shank subsoiler reduced draft by 60%and increased power by 2% compared to a four-shank non-vibrating subsoiler.

The subsoiling operation is often conducted at unnecessarilydeep depths which require an excessive amount of energy (ASAEStandards, 2003; Raper et al., 2007). In this respect, a reduction intillage depth can save a significant amount of energy (Fulton et al.,1996; Raper, 1999). As well as subsoiling depth, soil moisturecontent also has an important effect on energy requirements.Swarnkar and Sharma (2009) stated that energy requirements intillage decreased as soil moisture content increased from 5.5 to15.5% d.b. Their results showed that at higher soil moisture contents,subsoilers with straight shanks were more energy efficient thanother tillage equipment. Raper and Bergtold (2007) estimated that ifproducers used the proper subsoiler, at the correct tillage depth,with controlled traffic and with the correct tillage timing, the cost ofsubsoiling can be substantially reduced.

Many different types of subsoilers have been designed andtested, using a number of subsoiling techniques for alleviatingcompacted layers of various types and conditions of soils. Rotarysubsoiling has the potential to reduce power requirementsassociated with pulling shanks through the soil and causesminimum damage to soil which is important for conservationtillage systems. Effects of rotary subsoiling on soil properties and

power requirements are not well defined. Thus, there is a need forresearch on the efficacy of ground-driven rotary subsoilers.

The objectives of this study were to:

- Design a ground-driven rotary subsoiler for conservation tillagesystems that minimizes soil surface disturbance.

- Determine the energy requirements and soil disruption ofground-driven rotary subsoilers at various tillage depths.

2. Materials and methods

The experiment was conducted in an indoor soil bin at theUSDA-ARS National Soil Dynamics Laboratory in Auburn, AL, USA.Norfolk sandy loam soil (72% sand, 17% silt, 11% clay) was selectedbecause it is found in many locations where subsoiling iscommonly used to disrupt compacted soil layers in conservationtillage systems. This soil is a Coastal Plain soil commonly found inthe southeastern USA.

A hardpan was formed in the soil bin to simulate a conditionthat is commonly found in the southeastern USA. This naturallyoccurring and sometimes traffic-induced hardpan can be foundapproximately 0.1–0.5 m below the soil surface (Raper, 2005). Thehardpan in the soil bin was created by using a moldboard plow tolaterally move the soil, followed by a rigid wheel to pack the soilleft exposed in the furrow. This procedure was then repeated untilthe entire width of the bin had been traversed. The soil surface wasthen leveled with a scraper blade.

Four subsoilers; coulter without blade (CNOB), normal shanktype (KMCS), coulter 5 blade normal direction (C5BN) and coulter 5blade reverse direction (C5BR) were used in the experiments(Fig. 1). The coulter-type subsoilers (coulter without blade andcoulter with 5 blades) were designed for use as ground-drivenrotary subsoilers and were manufactured from a 1.2 m diameterand 12.7 mm thick steel. A coulter with 5 blades, which had 40% ofthe surface area of a 1.2 m diameter circle, was used for bothforward (C5BN) and reverse (C5BR) directions to determinebenefits of direction of rotation on the parameters investigated.

The purpose of ground-driven rotary subsoiling was to create anarrow furrow that would cause minimum disruption of the soilsurface and would disrupt the hardpan, while reducing the powerrequirement compared to a conventional subsoiler. Minimizing thesliding soil resistance on the side of the coulter was one of the mainconsiderations in forming the shape of the blades and the number ofblades. The cutting edge of the coulter without blades and thecoulter with five blades were shaped and sharpened to easilypenetrate into soil, to provide the desired depth, and reduce soilresistance during coulter rotation and forward travel. The edges ofboth sides of each coulter type subsoiler were beveled withsharpening angles of 158. To promote penetration of the rotarysubsoilers and to maintain a constant set depth, an additional weight(270 kg) was placed on each side of the frame to which each rotarysubsoiler was mounted (Fig. 1). The frame equipped with bearingswas designed to maintain a straight path in the soil during tillage.The shank-type subsoiler manufactured by KMC Corp. (Tifton, GA,USA) was made of 3.2 cm thick steel. The subsoiler was equippedwith wear plate and tips (Fig. 1).

One at a time, the subsoilers were mounted on a three-dimensional dynamometer, which has an overall draft loadcapacity of 44 kN. Draft, vertical force, side force, speed, anddepth of operation were recorded continuously for each test. Thespeed of tillage for all tests was held constant at 0.45 m s�1. Twodepths of operation were conducted for each subsoiler: approxi-mately 25 and 38 cm.

The soil bin was partitioned into four blocks along the length ofthe bin. Eight plots of dimensions 1.5 m wide by 5 m long werecreated within each block to investigate subsoilers at two different

KMCS

CNOB C5BN

C5BR30°52°

40

0

250

Ø 1200

Ø450

Ø450

Ø 1200

130

130

Ø 1200

Fig. 1. Subsoilers used in the experiment (the arrow denotes direction of travel).

A. Celik, R.L. Raper / Soil & Tillage Research 124 (2012) 203–210 205

depths. A total of 32 plots were arranged in a randomized completeblock design with four subsoiler types, two tillage depths and fourreplications. Spacing across the bin was sufficient to ensure thatdisturbed soil resulting from a nearby subsoiler run would notaffect another subsoiler run. The mean draft, vertical force, and sideforce was calculated for each run.

Before a subsoiler test was conducted in a given plot, cone indexmeasurements were acquired (ASAE Standards, 2004) with amultiple-probe recording penetrometer down to 50 cm in 5 cmincrements. A penetrometer with five probes (cones), which wereequally spaced at a 20 cm interval across the soil, with the middlemeasurement being directly in the path of the subsoilers, was used.After the experiment, cone index measurements were taken inclose proximity to the previous measurements. Soil samples werealso taken from each plot down to 50 cm in 5 cm increments todetermine initial soil moisture content and bulk density. Thecollected samples were weighed and dried at 105 8C for 24 h toobtain average gravimetric water content and dry bulk density.

After the tillage experiment was conducted, a laser profilometer(Raper et al., 2004) was used to determine the cutting paths of theC5BN and C5BR subsoilers. Disturbed soil was manually excavatedfrom the subsoiled zone for approximately 1 m along the travelpath to allow measurements of the subsoiled zone. Care was takento ensure that only soil loosened by tillage was removed.

An appropriate ANOVA model was selected for analysis ofvariance using the SAS statistical software package (SAS InstituteInc., Cary, NC, USA). Means were compared using Duncan’smultiple range tests. Statistical significance was evaluated at theP < 0.05 level.

3. Results and discussion

Initial soil moisture content, bulk density and cone index forthe 0–50 cm depth range are given in Fig. 2. The gravimetricmoisture content of the soil was approximately 8.5% d.b. near thesurface and 9.5% d.b. in the hardpan. Bulk density values showedthat the top of the hardpan that was formed in the soil bin was20 cm beneath the soil surface (Fig. 2). The soil within the hardpan,at a depth of 20–30 cm, had the highest average bulk density(1.93 Mg m�3). The upper layer (10–15 cm) bulk density was1.58 Mg m�3 and the soil below the hardpan (30–35 cm) had a bulkdensity of 1.80 Mg m�3. The cone index values increased graduallyfrom the depth of 10 cm to beneath the hardpan layer. The coneindex values indicated that the top of the hardpan was at anapproximate depth of 40 cm and was below the 25–30 cm depth ofthe hardpan identified by the bulk density values (Fig. 2). Thedifferences are probably caused by the slightly elevated moisturecontent of the soil at a 20–30 cm depth and could have causedslightly decreased cone index values, thus causing the hardpandepth to be sensed slightly below the depth identified by the bulkdensity data.

The results of the statistical analysis on draft power, specificpower, vertical force and side force values of subsoilers are given inTable 1. Subsoiler type and tillage depth both significantly affecteddraft power (P < 0.001). The CNOB subsoiler required greater draftpower compared to the KMCS, C5BN and C5BR subsoilers. TheKMCS followed the CNOB subsoiler and required the secondgreatest draft power (Table 1). Draft values of the C5BN and C5BRsubsoilers at both tillage depths showed a cyclical path (Fig. 3).

Fig. 2. Initial soil moisture content (MC), bulk density (BD) and cone index (CI) for the soil bin experiment.

A. Celik, R.L. Raper / Soil & Tillage Research 124 (2012) 203–210206

This may indicate that maximum draft was measured when bladesentered the soil. The horizontal interval of tip points wasdetermined by subsoiler diameter and blade intervals. The draftdifference between the minimum and maximum points of eachcycle was about 2 kN for the C5BN at both depths. For the C5BRsubsoiler it was 1 kN at the 25 cm depth and 1.5 kN for the 38 cmdepth (Fig. 3).

The draft power of the subsoiling was calculated by multiplyingthe draft by the constant forward speed (0.45 m s�1) of operation(ASAE Standards, 2003; Raper et al., 2005). For each of the two tillagedepths, the draft power for the CNOB subsoiler was significantlygreater than for the KMCS, C5BN and C5BR subsoilers (Fig. 4a). Thedraft power of the KMCS subsoiler was significantly greater than forthe C5BN and C5BR subsoilers for the 38 cm depth. However, at the25 cm depth, the draft power was similar for the three subsoilers.Specific energy, the energy per volume of disrupted soil wascalculated (Celik et al., 2007) and is shown in Fig. 4b. The rotarysubsoilers disrupted minimum amounts of soil with their narrowerbody than KMCS. Therefore, the rotary subsoilers’ draft power perdisrupted volume of soil was much higher than for the KMCSsubsoiler, which disrupted a much larger volume of soil. The C5BRsubsoiler had significantly higher specific energy values than theCNOB and C5BN subsoilers for both tillage depths. The CNOB andC5BN subsoilers required the same energy per volume of disruptedsoil in both operational depths (Fig. 4b). The specific energyrequirement increased with tillage depth for all subsoilers.

Vertical force, which is a positive downward force on asubsoiler, is defined as suction force and is generally necessary

Table 1Comparison of means for draft power, specific power, vertical force and side force of s

Treatments Draft power (kW) Speci

Subsoilers CNOB 3.54 a* 0.96

C5BN 2.33 c 0.96

C5BR 2.29 c 1.28

KMCS 2.97 b 0.04

P 0.000 0.000

Tillage depth

25 cm 1.65 b 0.68

38 cm 3.91 a 0.94

P 0.000 0.000

SEMa 0.231 0.089 0.815

a Standard error of means.* Within each column; within the subsoilers and tillage depth groups means followe

for keeping the shank or blade inserted into the soil. Small values ofvertical force are acceptable, but for conventional subsoilers, largevalues of vertical force cause excessive penetration and increaseddraft. All rotary subsoilers had negative vertical force (upwardforce) while the KMCS shank had positive values of vertical force(downward force). Negative vertical force indicated that thesubsoilers were being pushed into the soil by the experimental carand required additional weights. The CNOB subsoiler required themaximum vertical force and the KMCS subsoiler required theminimum force for both tillage depths (Fig. 5a). Vertical forces ofall subsoilers increased approximately 40% as tillage depthincreased from 25to 38 cm. The CNOB subsoiler had the largestsoil contact area (Fig. 1). This may increase friction and cause ahigher vertical force (upward) than the other subsoilers. Thesecond largest vertical force (upward) was found for both the C5BNand C5BR subsoilers which had the second largest soil contact area(Fig. 1).

For the CNOB and KMCS subsoilers, the trends of magnitudes ofside forces were similar to the trends for vertical forces (Fig. 5).However, for the C5BN and C5BR subsoilers the trends for thevertical forces were different from the trends of the side forces.The largest side force was found for the CNOB (0.976 kN) and thenext largest for the C5BN subsoiler (0.664 kN) at the 38 cm depthwhile the minimum value occurred for the KMCS shank (0.037 kN)at the 25 cm depth. Increasing tillage depth from 25 to 38 cmcaused significantly higher side forces for all subsoilers. The C5BNsubsoiler had higher side forces for both tillage depths comparedto the C5BR while their vertical forces were statistically similar

ubsoilers.

fic power (J cm�3) Vertical force (kN) Side force (kN)

b �8.86 c 0.76 a

b �5.26 b 0.43 b

a �5.26 b 0.28 bc

c 2.84 a 0.06 c

0.000 0.002

b �3.31 a 0.22 b

a �4.96 b 0.55 a

0.000 0.008

0.075

d by the same letter are not significantly different (a = 0.05).

Fig. 3. Average draft values of subsoilers operating at 25 and 38 cm tillage depths.

A. Celik, R.L. Raper / Soil & Tillage Research 124 (2012) 203–210 207

(Fig. 5b). Side forces, which were perpendicular to the direction oftravel, were measured for all subsoilers, but their magnitudes aresmall compared to the draft and vertical forces. The side forceswere greatest for the CNOB and for that coulter, the ratio of themaximum side force to the maximum draft force was 0.16 forthe 25 cm depth and 0.13 for the 38 cm depth. These side forceswere probably caused by variations in the uniformity of the soilfirmness and subsoilers’ geometry. When the soil condition wasprepared, a weighted 30 cm width cylindrical steel wheel wasused for compacting the soil before a wide roller to compact andsmooth the soil surface as the last step in soil preparation. Thiswheel ran along the length of the soil bin, parallel to the traveldirection for the subsoilers, whose runs were made after the soilcondition was prepared. Probably there was some difference inthe firmness of soil beneath one pass of the steel wheel, comparedto the firmness of soil beneath an adjacent pass, and this variation

Fig. 4. Average draft power (a) and specific energy requirement (b) of subsoilers. B

in soil firmness across the width of the soil bin likely caused sideforces on the subsoilers.

The average cone index values obtained with five conepenetrometer probes across each tilled path following its subsoilerpass were examined for differences in the soil penetrationresistance as a result of subsoiling (Fig. 6). The probe spacingacross the tilled path was 20 cm. Probe 3, which was located at thecenterline of the subsoilers path, had the minimum cone indexvalues for all subsoilers compared to the other probes. Averagecone index values of the KMCS for probes 2, 3 and 4 were smallerthan those for the rotary-type subsoilers, for both tillage depths.This was because the wider disruption path occurred for the KMCSsubsoiler than for the rotary-type subsoilers. Disruption widths ofthe rotary-type subsoilers were equal to the coulter thickness of12.7 mm. The KMCS shank had a wedge effect on the soil, so itdisrupted the upper layers of soil wider than the shank body.

ars denoted by the same letter are not statistically different at the 0.05 level.

Fig. 5. Vertical force (a) and side force (b) of subsoilers at two tillage depths. Bars denoted by the same letter are not statistically different at the 0.05 level.

A. Celik, R.L. Raper / Soil & Tillage Research 124 (2012) 203–210208

Two locations were considered on the center path of the C5BNand C5BR subsoilers for cone index measurements. One was fromthe spoil area (L1) which was the area laterally outboard of the slitarea of each blade and the other was from slit area of each blade(L2). Spoils occurred on the tilled soil surface with the soil takenaway from the slits by the blades of the subsoilers. The coulter-typesubsoiler with blades produced an intermittent pattern: distinctareas of slits (L2) and spoils (L1), separated by areas of undisturbedsoil (Fig. 7). As expected, cone index values measured from L2locations were lower than those measured from L1. This isprobably because the L2 locations had soil disturbed below the soilsurface while the L1 locations may not have.

The cone index values measured in the paths of the subsoilersare shown in Fig. 8. The cone index increased slightly as depthincreased from 0 to 40 cm and began to decline after this depth.This trend was similar to that of the initial soil cone index values(Fig. 2). The C5BN and C5BR subsoilers’ curves were similar to oneanother for both tillage depths; the greatest cone index values

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

54321

Co

ne in

dex

(M

Pa

)

Probes

CNOB C5BNL1

C5BNL2 C5BRL1

C5BRL2 KMCS

(a) (

Fig. 6. Average cone index values measured with the five cone penetrometer probes acro

was 20 cm.

were measured in the spoils while the KMCS had the lowest coneindex. Cone index values in the slits (channels) were lower thanthose measured at the spoil locations. Naturally, the spoil locationsproduced cone index values similar to those of the initial soilconditions. Cone index values of all subsoilers slightly increased atdepths greater than the tillage depth and decreased at depthsgreater than the hardpan depth. Cone index values for the KMCSand CNOB were similar to those measured in the slits of the C5BNand C5BR subsoilers, and were significantly lower than those of thespoils of the C5BN and C5BR subsoilers.

Examination of the spoils, slits and the channels created bysubsoilers (Fig. 7) reveals a great amount of difference between thesubsoilers’ above- and below-ground disruption. The coulter-typesubsoilers created 12.7 mm width slits (channels) without or witha limited amount of spoils. The CNOB left the soil surface clean withno spoil while the C5BN and C5BR subsoilers caused only minimalspoils on the soil surface. The KMCS disrupted large channels withwider, higher and continuous spoils on the tillage path. The soil

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

54321

Co

ne in

dex

(M

Pa

)

Probes

CNOB C5BNL1

C5BNL2 C5BRL1

C5BRL2 KMCS

b)

ss the paths for tillage depths of 25 cm (a) and 38 cm (b). Spacing of the five probes

Fig. 7. Spoils, slits and channels formed by subsoilers.

(b)(a)

-50

-45

-40

-35

-30

-25

-20

-15

-10

-5

0

876543210

Dep

th (

cm)

Cone index (MPa)

CNOB

C5BNL1

C5BNL2

C5BRL1

C5BRL2

KMCS

St.Dev

CNOB : 2.29

C5BNL1: 2.22C5BNL2: 2.18C5BRL1 : 2.15

: 2.02C5BRL2KMCS : 1.87 -50

-45

-40

-35

-30

-25

-20

-15

-10

-5

0

876543210

Dep

th (

cm)

Cone index (MPa)

CNOB

C5BNL1

C5BNL2

C5BRL1

C5BRL2

KMCS

St. Dev

CNOB : 2.06

C5BNL1 : 2.07C5BNL2 : 2.30C5BRL1 : 1.92

C5BRL2 : 2.16KMCS : 2.43

Fig. 8. Cone index measurements from the path of subsoilers for tillage depths of 25 cm (a) and 38 cm (b). St. Dev. values are standard deviations of the cone index

values (MPa).

A. Celik, R.L. Raper / Soil & Tillage Research 124 (2012) 203–210 209

disruption paths of the coulter-5-blade subsoilers have anadvantage for row crops due to limited aboveground disturbanceif seeds can be placed in the middle of disrupted zone. However,the lack of continuously disrupted slits (channels) may not channelas much water into the soil for storage so the presence of a covercrop could be important to ensure adequate infiltration and waterstorage.

As determined using profilometer measurements, the cuttingpaths of C5BN and C5BR subsoilers, which were formed byrotating blades and relative forward movement, were substan-tially different (Fig. 9). Also, the blade tip and blade edge form had

Fig. 9. Cutting path of C5BN (a) and C5BR (b) subsoilers for b

an effect on this difference. As the blade rotated the sharpenedblade edge of the C5BN subsoiler cut soil the deepest near thebeginning (forward portion) of path (Fig. 9a) and less deep nearthe ending point (rear portion). In contrast, the C5BR subsoilercut soil shallower at the beginning (forward portion) of the pathand deeper at the ending point (rear portion) (Fig. 9b). Both theC5BN and C5BR subsoilers had similar spoil length, whereas theC5BR produced wider and higher spoils than the C5BN. Spoillength for both the C5BN and C5BR subsoilers decreased withtillage depth. The C5BN subsoiler produced longer slits than theC5BR subsoiler.

oth directions of use (arrow denotes direction of travel).

A. Celik, R.L. Raper / Soil & Tillage Research 124 (2012) 203–210210

4. Conclusions

The conclusions that were drawn from this experiment were:

� The coulter type subsoiler without blades (CNOB) had thehighest draft power requirements followed by shank-typesubsoiler (KMCS).� Draft of the coulter-5-blade for both directions of use (C5BN and

C5BR) was cyclical and was synchronized with the disruptionpath in the soil.� The coulter type subsoiler without blade (CNOB) required the

greatest vertical force to keep the subsoiler in the soil, while theshank-type subsoiler (KMCS) required the minimum verticalforce.� The shank-type subsoiler (KMCS) required minimum energy per

volume of disrupted soil.� The rotary-type subsoilers (CNOB, C5BN, and C5BR) produced

less soil disruption compared with the shank-type subsoiler(KMCS).� The coulter-5-blade subsoiler, for both directions of use (C5BN

and C5BR) disrupted soil in a cyclical manner varying with traveldistance. The longitudinal distance between cycles can bearranged by coulter diameter and the number of blades.� The soil disruption paths of coulter-5-blade subsoilers have an

advantage for row crops in a conservation tillage system. Theaboveground disturbance is limited and seeds can then be placedin the middle of the disrupted zones.

Acknowledgements

This research was completed by contribution of USDA-ARSNational Soil Dynamics Laboratory and TUBITAK, The Scientific &Technological Research Council of Turkey.

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