J . agric . Engng Res . (1996) 65 , 151 – 158

Improvement of Planosol Solum : Part 6 , Field Experiments with a Three-Stage Subsoil Mixing Plough

K . Araya ; * M . Kudoh ; * D . Zhao ; † F . Liu ; † H . Jia †

* Environmental Science Laboratory , Senshu University , Bibai , Hokkaido 079-01 , Japan

† Hejiang Agricultural Research Institute , Jiamusi , Heilongjiang , P . R . of China

( Recei y ed 2 January 1 9 9 6 ; accepted in re y ised form 1 5 May 1 9 9 6 )

This paper deals with the design of a three-stage subsoil mixing plough and field experiments in a planosol solum field in China to obtain mixing of the second (Aw) and third (B) horizons to improve the planosol solum , leaving the first (Ap) horizon undisturbed .

The field test results showed that the three-stage subsoil mixing plough was considerably improved over the two-stage subsoil mixing plough used in earlier tests , in terms of soil mixing , clod size produced and draught requirement . The optimum specification for the elements of the three-stage subsoil mixing plough was as follows .

First plough body : working depth should be 250 mm and working width 460 mm .

Second plough body : working depth should be 200 mm from the bottom of the first plough body and working width 300 mm .

Third plough body : working depth should be 138 mm from the bottom of the second plough body and working width 300 mm .

With this combination , there was a good draught balance with each plough body requiring about 10 kN , and giving a total of about 30 kN overall .

÷ 1996 Silsoe Research Institute

1 . Introduction

In the field tests made by Zhao et al . 1 and the soil investigations of Araya , 2 it was found possible to improve planosol solum by mixing the Aw and B horizons in a one to one ratio below the soil surface leaving the Ap horizon undisturbed .

Notation A clod size , mm 2

F x horizonal force , draught , N M x mixing rate [(no mixing) 0 < M x < 1

(perfect mixing)] T Aw 5 B transfer rate of Aw horizon into B

horizon [(no transfer) 0 < T Aw 5 B < 1 (perfect transfer)]

T Aw ,B 5 Ap transfer rate of Aw and B horizons into Ap horizon [(no transfer) 0 < T Aw ,B 5 Ap < 1 (perfect transfer)]

T Ap 5 Aw ,B transfer rate of Ap horizon into Aw and B horizon [(no transfer) 0 < T Ap 5 Aw ,B < 1 (perfect transfer)]

b operational cutting width , mm c soil – interface cohesion , Pa

c 9 soil – metal adhesion , Pa h operational depth , mm w soil moisture , %d . b . w angle of soil – interface friction , deg

d 9 angle of soil – metal friction , deg

In the previous Part 4 paper , 3 a two-stage subsoil mixing plough (the first experimental drop-down plough) shown in Fig . 1 a was ef fective for the one-to -one mixing of the second (Aw) and third (B) horizons to improve the planosol solum in China , leaving the first (Ap) horizon undisturbed . However , this machine had the following disadvantages : (1) it produced large soil clods , (2) it had a large draught requirement , (3) it required a furrow following system , (4) it had poor frame strength , and (5) it was necessary to remove the first plough body to open the first furrow . Basic soil bin tests were conducted in Japan to develop a new three-stage subsoil mixing

151 0021-8634 / 96 / 100151 1 08 $25 . 00 / 0 ÷ 1996 Silsoe Research Institute

K . A R A Y A E T A L . 152

Fig . 1 . Prototype ploughs for impro y ing the planosol solum ( a ) first experimental drop - down type plough ( two - stage subsoil mixing plough ) ; ( b ) second experimental drop - down

type plough ( three - stage subsoil mixing plough )

(a)

(b)

plough to solve these problems using half-size model ploughs as reported in Part 5 . 4

Based on the results of the soil bin tests in Part 5 , 4

the prototype three-stage subsoil mixing plough (the second experimental drop – down plough) was de- signed as shown in Fig . 1 . In the full size prototype plough , to solve problem (1) of large clods , disk harrows were set at the end of the plough frame which would pulverize the large clods if they were produced when the Aw and B horizons were tilled .

To solve problem (3) , the centre of the tractor on which the plough was mounted and the centre of the plough bodies were of fset and the set positions of the top and lower links were adjusted to set the plough bodies behind the right rear tyre of the tractor . Hence , the tractor did not run in the furrow but on the land ,

so a moment would act on the tractor when in operation .

In order to solve the problem of poor frame strength (4) , where the first experimental plough body frame was assembled using steel plates with bolts , the second experimental plough frame was constructed using square sections that were 100 3 100 mm in size with a thickness of 6 mm welded together to form a stronger frame . In Fig . 1 b , three plough bodies were all mounted on a square section of the plough frame and all draughts would be carried by this square section . The strength of the square section was tested by the application of a load corresponding to the loads that would be applied in the field and a yield deformation occurred at 160 kN . As the draught of the first experimental plough 3 in planosol solum was 65 kN , the frame was considered to be suf ficiently durable . In the first experimental plough , the Aw and B horizons were tilled by the one drop-down plough body (the first plough body in Figs 1 a and 2 a ) , with a

(a)

2nd 1st50°

460

460

2nd

1st

200

200

200

30°

400

240

Ap

Aw

B

b

(b)

3rd 2nd 1st

460

240

3rd 2nd1st

30°

30°

200

200

200

Ap

Aw

B

90

650

Fig . 2 . Schematic diagram of ploughs ( a ) two - stage subsoil mixing plough ; ( b ) three - stage subsoil mixing plough

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draught 4 of 55 kN on this plough body . In the second experimental plough , the Aw and B horizons were tilled by two plough bodies (the second and third plough bodies in Figs 1 b and 2 b ) and a draught reduction would be expected from the results of the model tests reported in Part 5 . 4

In order to solve problem (5) , the mouldboard plough body for the Ap horizon , which was at the rear (second plough body) in the first experimental plough in Figs 1 a and 2 a , was set as the first plough body in the second experimental plough , as shown in Figs 1 b and 2 b . In the first experimental plough , the plough body to till the Ap horizon (the second plough body) and the first plough body to till the Aw and B horizons were in dif ferent furrows but in the second experimental plough , these were set in the same furrow and the three plough bodies were in line , as shown in Fig . 2 b . Consequently , with the second experimental plough , removal of the second and third plough bodies was not required when the first furrow was opened in order to prepare the furrow for the first plough body , as was required with the first ex- perimental plough .

The second experimental three-stage subsoil mixing plough in Figs 1 b and 2 b was designed in Japan and sent to China , and actual field tests were conducted in a planosol solum field . This paper deals with the soil mixing rate and the draught of the plough in the planosol solum .

2 . Experimental details

The principle of mixing of the Aw and B horizons has been shown in Part 5 . 4 The optimum shape of the second and third plough bodies in Fig . 2 b were determined by the soil bin tests reported in Part 3 . 5

The 90 mm height of the second plough body was determined as the optimum shape to cause breakage of the Aw horizon and to transfer the soil backwards , with the lowest draught . 5 The 240 mm height of the third plough body was also determined as the op- timum shape to till the B horizon , and to drop the soil down from the end of the mouldboard , while obtain- ing good mixing with the lowest draught . 5 The 30 8 inclined angle of the third plough body was deter- mined where soil was compressed on the sloping mouldboard , causing slip between the B and Aw horizons , so that a good random mixing was obtained when dropping down . 5

Three working widths , b , of the second and third plough bodies were prepared , namely , 460 mm which was same as that of the first plough body , 300 mm , and 230 mm in order to decrease the draught .

The plough in Fig . 1 b was mounted on a Russian tracked vehicle (D75 , 55kW) which was used to support the plough but did not provide power . This was drawn by another D75 tractor through a traction dynamometer (capacity 100 kN) as shown in Fig . 3 . Hence , only the horizontal force (draught) of the plough was measured once a reduction for the running resistance of the D75 tractor was made .

To determine the draught of each of the three plough bodies separately and all of them together , the first plough body was operated alone , following re- moval of the second and third plough bodies . The second body was then set and the draught of the first and second plough bodies was then determined to- gether . The third plough body was then set and the draught of all three plough bodies was then deter- mined together .

The mechanical properties of the planosol solum are shown in Table 1 . The mechanical properties for two dif ferent soil moistures measured in 1994 and 1995 are shown . The soil moisture of the Aw horizon was smaller than that of the Ap and B horizons because of the non-permeable layer . Cohesion ( c ) of the Aw horizon was larger than that of the other horizons .

The mean soil hardness before ploughing measured at three dif ferent places is shown in Fig . 4 . At depths from 200 to 400 mm , there was an Aw horizon where the soil hardness was more than 5 ? 0 MPa (a cone penetrometer having a 30 8 cone angle and 20 mm base diameter) . At depths below 400 mm , there was a B horizon where the soil hardness was about 4 ? 0 MPa which was less than the Aw horizon .

The soil section in the test field was first investi- gated and the thickness of the Ap horizon was 260 mm

Fig . 3 . Traction test using Russian tracked y ehicles

K . A R A Y A E T A L . 154

Table 1 Mechanical properties of planosol solum in the field

Soil and horizon Year

Moisture content w % d .b

Cohesion c kPa

Angle of internal friction f deg .

Adhesion c 9 kPa

Angle of soil – metal

friction d 9 deg .

Plastic limit PL

% d .b

Liquid limit LL

% d .b

Planosol Ap

Planosol Aw

Planosol B

1994 1995 1994 1995 1994 1995

38 ? 5 26 ? 2 25 ? 0 20 ? 6 31 ? 0 25 ? 0

2 ? 0 4 ? 8 4 ? 5 5 ? 5 3 ? 0 4 ? 0

34 ? 0 45 ? 0 46 ? 0 36 ? 0 31 ? 0 39 ? 0

4 ? 5 3 ? 9 5 ? 7 4 ? 2 6 ? 6 6 ? 0

7 ? 7 8 ? 0

16 ? 4 17 ? 5 17 ? 2 18 ? 3

27 ? 2 27 ? 2 18 ? 3 18 ? 3 26 ? 1 26 ? 1

39 ? 3 39 ? 3 32 ? 0 32 ? 0 60 ? 2 60 ? 2

and that of the Aw horizon was 170 mm as shown in Fig . 5 . Hence , the working depth of the first plough body in Fig . 2 b was set at 250 mm from the soil surface and that of the second plough body at 200 mm from the bottom of the first plough body (450 mm from the soil surface) . The working depth of the third plough body was varied in four stages as shown in Fig . 5 ; 14 mm from the bottom of the second plough body (464 mm from the soil surface) , 76 mm (526 mm from

0

100

200

300

400

500

600

Dep

th, m

m

1 2 3 4 5

Soil hardness, MPa

Beforeploughing

After ploughing

Untilled part

Fig . 4 . Soil hardness before and after ploughing ( cone penetrometer , 3 0 8 cone angle and 2 0 mm base diameter )

the soil surface) , 138 mm (588 mm from the soil surface) and 200 mm (650 mm from the soil surface) . From the soil section and the above depths , the ratio of the Aw and B horizons were 1 – 0 ? 2 , 1 – 0 ? 565 , 1 – 0 ? 929 and 1 – 1 ? 294 , respectively .

Two to five experiments were carried out for each condition .

3 . Results and discussion

3 . 1 . Soil mixing and transfer rates

The soil hardness after ploughing by the three-stage subsoil mixing plough in Fig . 1 b is shown in Fig . 4 . For the case shown , the working width of the first plough body was 460 mm and those of the second and third plough bodies were 300 mm . The total working

Ap

Aw

B

260

170

h25

020

0

Fig . 5 . Thicknesses of the Ap and Aw horizons in the test field and the working depths of three plough bodies ; when h 5 1 4 mm ; Aw : B 5 1 7 0 : 3 4 5 1 : 0 ? 2 ; h 5 7 6 mm ; Aw : B 5 1 7 0 : 1 5 8 5 1 : 0 ? 9 2 9 ; h 5 2 0 0 mm ; Aw : B 5 1 7 0 : 2 2 0 5

1 : 1 ? 2 9 4

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Fig . 6 . Soil section after ploughing . Working widths of the second and third plough bodies were 3 0 0 mm and the total

working depth was 5 8 8 mm

depth was 588 mm . The soil hardness after ploughing was much lower than that before ploughing .

A typical soil section is shown in Fig . 6 . The mixing rates , as a function of working depth of the third plough body , which were determined by photographic analysis of Fig . 6 by methods described in Part 4 , 3 are shown in Fig . 7 . The mixing and transfer rates have also been defined in Part 4 . 3 With increasing working depth of the third plough body , as the ratio of the Aw and B horizons approached one to one , better soil mixing was obtained and the soil mixing rate in- creased . However , above the ratio of about one to one , the mixing rate did not increase due to the larger proportion of the B horizon . The soil mixing was constant regardless of the working widths of the second and third plough bodies . In the pseudogley soil in Japan , when the working width was small such as 230 mm , the second plough body operated as a

Soi

l mix

ing

rate

, Mx

Working depth of third plough body from bottom ofsecond plough body h, mm

1·0

0·5

00 50 100 150 200

1:0·

2

1:0·

565

1:0·

929

Aw

:B=

1:1·

294

Fig . 7 . Soil mixing rate as a function of working depth of third plough body . Working widths ( b ) of second and third

plough bodies ; s 2 3 0 mm ; d 3 0 0 mm ; and n 4 6 0 mm

subsoiler , soil was not raised on the mouldboard and hence no soil mixing was obtained . 6 Here , in the planosol solum , such a phenomenon was not ob- served . This was because the soil moisture of the planosol solum in 1995 was low and the soil was brittle .

Zhao 1 reported that the proportion of the Aw and B horizons should be between the range of 1 – 1 to 1 – 0 ? 5 for plant growth and that the mixing rate should be high , hence , the working depth of the third plough body should be 138 – 200 mm from Fig . 7 . However , as shown later in this paper , the draught when working at 200 mm depth is higher than that of the 138 mm depth and hence , the best working depth of the third plough body would be 138 mm from the bottom of the second plough body .

In Fig . 8 the soil mixing and the transfer rates are shown with a 250 mm working depth for the first plough body , 200 mm for the second plough body and 138 mm for the third plough body (a total working depth of 588 mm) . The mixing rate , M x , was scattered and varied in the investigated soil section because soil dropped randomly from the plough body . The mean value of mixing rate was about 0 ? 7 as shown in Fig . 8 e . The mean T Aw 5 B was about 0 ? 3 as shown in Fig . 8 d . Ideally this should be 0 ? 5 . The transfer rates of the Aw and B horizons to the Ap horizon , T Aw ,B 5 Ap was sometimes close to zero in Fig . 8 c but when the Ap horizon was thin as shown in Fig . 6 , the first plough body tilled the Ap horizon with the top of the Aw horizon and inverted them and hence , a thin layer of Aw horizon was occasionally placed on the soil surface giving T Aw ,B 5 Ap of 0 ? 1 – 0 ? 3 . However , such a case was rare and the volume of the Aw horizon mixed into the Ap horizon was small and hence the mixing of the Aw horizon would not af fect soil improvement .

The transfer rate of the Ap horizon to the Aw or B horizon , T Ap 5 Aw ,B , was about 0 ? 2 in Fig . 8 b . With such a low dropping down rate of the Ap horizon , there was no reduction in the tilled Ap horizon and even if the Ap horizon is mixed into the Aw and B horizons , subsoil improvement can still be obtained . Consequently , dropping down of 10 – 20% of the Ap horizon would be within tolerance .

The soil clods produced were all small as shown in Fig . 8 a . This is because the Aw and B horizons were tilled by the second and third plough bodies , respec- tively , and even if large soil clods were produced , they were pulverized by the disk harrows mounted on the end of the plough frame . As the soil moisture in this year (1995) was less than that for the previous year (1994) , large soil clods were hardly produced .

In Fig . 8 , the results of the two-stage subsoil mixing

K . A R A Y A E T A L . 156

(a) (b)

(c) (d)

(e)

10

5

0

Clo

d si

ze, A

, mm2

104

+

1·0

0·5

0

Tra

nsfe

r ra

te o

f Ap

to A

w &

B, T

Ap

–A

w,

B

1·0

0·5

0T

rans

fer

rate

of

Aw

B, T

Aw

–B

1·0

0·5

0

Tra

nsfe

r ra

te o

f Aw

& B

to A

p, T

Aw

,B–

Ap

1·0

0·5

0

Mix

ing

rate

, Mx

Ap

Aw

B

260

170

250

200

138

Three-stage plough

Two-stage plough

Three-stage plough

Two-stage plough

Fig . 8 . Soil mixing rate , transfer rates and clod size produced by the two and three - stage subsoil mixing ploughs

plough (the first experimental plough 3 ) developed in 1994 are also shown . The mixing rate , M x , and the transfer rate of the Aw horizon to the B horizon , T Aw 5 B , were almost the same as those of the three- stage subsoil mixing plough . However , T Aw ,B 5 Ap was about 0 ? 2 as shown in Fig . 8 c . This was caused as large soil clods of the Aw and B horizons were produced and moved into the Ap horizon . With the large soil clods , the Ap horizon crumbled between the large soil clods and reached lower layers . Consequently , T Ap 5 Aw ,B sometimes became 0 ? 5 in the investigated soil sections as shown in Fig . 8 b . Many dif ferent sizes of soil clods were produced by the two stage plough ; the largest one was about 1000 cm 2 as shown in Fig . 8 a .

From Fig . 8 , it is concluded that the three-stage subsoil mixing plough gave considerably improved results over the two-stage subsoil mixing plough in both soil transfer rates and clod sizes produced .

3 . 2 . Draught

The results of the draught tests are shown in Fig . 9 . The running resistance of the tracked vehicle (D75) on which the plough was mounted , was about 10 kN ( ñ 1 ) , and the draught of the first plough body which tilled the Ap horizon was also about 10 kN ( ñ 2 ) with a working depth of 250 mm . The draught of the second plough body , which tilled the Aw horizon , was also about 10 kN ( ñ 3 ) regardless of the dif ferent working widths (working depth was 200 mm from the bottom of the first plough body and 450 mm from the soil surface) . This was because after ploughing , all section areas were about 1 ? 2 3 10 5 mm 2 because the working depths were 200 mm and comparatively shallow . Hence , there would have been no draught dif ference with the three working widths . The same phenomenon was observed in the soil bin tests using half-scale model ploughs . 4

I M P R O V E M E N T O F P L A N O S O L S O L U M : 6 157D

raug

ht F

x, k

N

100

80

60

40

20

0

Run

ning

res

ista

nce

1st p

loug

h bo

dy

2nd

plou

gh b

ody

1 2 3 4 5 6 70 50 100 150 200

(1994)Two-stage plough

3rd

plou

gh

body

Working depth of third plough body h, mm

Ap

Aw

B

260

170

250

200

h

RussianD75

1st + 2ndplough bodies

Firstplough body

1st + 2nd + 3rdplough bodies

Fig . 9 . Draught of the two and three - stage subsoil mixing ploughs ( planosol solum ) s working width of second and third plough bodies , b was 2 3 0 mm ; d 3 0 0 mm ; and n 4 6 0 mm . The running resistance of the tractor has not been substracted from

the y alues of the draught forces of the plough bodies

With a four-stage variation in the working depth of the third plough body , which tilled the B horizon , the draught of the third plough body was determined . The draught of the third plough body increased almost linearly from 14 – 136 mm depth ( ñ 4 – ñ 6 ) and then more steeply between 136 mm and 200 mm depth ( ñ 7 ) .

There was no draught dif ference between the work- ing widths of 200 mm and 300 mm , but with a 460 mm working width , the draught increased . The working widths of the second and third plough bodies were smaller than that of the first plough body , and hence , theoretically untilled soil remained . When the working

widths of the second and third plough bodies were 300 mm and that of the first plough body was 460 mm , there theoretically remains untilled soil of a 160 mm width . In Fig . 6 , there were untilled soils with 130 and 140 mm width . The height of the untilled soils was 130 – 220 mm because of soil crumbling . The soil hard- ness for this part is also shown in Fig . 4 . The soil hardness here was almost the same as that of the tilled soil and was perfectly broken down . In the untilled part of the soil , there is no soil mixing but it should not af fect soil improvement due to the small area .

From Figs 7 , 8 and 9 the optimum plough body

K . A R A Y A E T A L . 158

specification for the three-stage subsoil mixing plough for both soil mixing and draught would appear to be as follows .

The first plough body : working depth should be 250 mm and working width 460 mm .

The second plough body : working depth should be 200 mm from the bottom of the first plough body and working width 300 mm .

The third plough body : working depth should be 138 mm from the bottom of the second plough body and working width 300 mm .

For this combination , the draught of the third plough body was about 10 kN ( ñ 6 ) from Fig . 9 and a good draught balance was achieved since each plough body required about 10 kN draught , giving a total draught of about 30 kN .

In Fig . 9 , the draught of the two-stage subsoil mixing plough developed in 1994 is also shown ( ñ 6 ) . The draught was about 65 kN . In Table 1 , the soil strength in 1994 was less than that in 1995 due to higher soil moisture and hence , the draught of the two-stage subsoil plough would be expected to be lower than that of the three-stage subsoil mixing plough . However , it was about twice as large as that of the three-stage subsoil mixing plough . One of the reasons could be because when the planosol solum , especially the Aw soil layer becomes drier , the shear- ing strength becomes stronger as shown in Table 1 but becomes more brittle and hence , the soil would be more easily broken . It would be desirable to deter- mine the relation between soil brittleness and machine draught . Another reason would be because of the plough shape . In three-stage subsoil mixing plough , based on the soil bin tests , 4 the slatted mouldboards were used for the second and third plough bodies to decrease soil – metal friction and the three plough bodies were used to prevent the formation of large clods and to obtain a smooth flow of soil over the plough bodies .

4 . Conclusions

1 . With the three-stage subsoil mixing plough , the mean soil mixing rate , M x , was 0 ? 7 and the mean transfer rate of the Aw to the B horizon , T Aw 5 B was about 0 ? 3 . Ideally this should be 0 ? 5 and the Aw horizon should transfer more into the B horizon . The transfer rate of the Aw and B horizons to the Ap horizon , T Aw ,B 5 Ap was almost zero . The transfer rate

of the Ap horizon to the Aw or B horizon , T Ap 5 Aw ,B , was about 0 ? 2 and it is considered that this level can be tolerated . There was no reduction in the tilled Ap horizon and even if the Ap horizon is mixed into the Aw and B horizons , subsoil improvement can still be obtained .

2 . The soil clods produced by the three-stage sub- soil mixing plough were all small .

3 . The total draught of the three-stage subsoil mixing plough was about 30 kN .

4 . The three-stage subsoil mixing plough was a considerable improvement over the two-stage subsoil mixing plough in terms of soil mixing , clod size produced and the draught requirement .

5 . The optimum plough body specification was determined to be as follows .

The first plough body : working depth should be 250 mm and working width 460 mm .

The second plough body : working depth should be 200 mm from the bottom of the first plough body and working width 300 mm .

The third plough body : working depth should be 138 mm from the bottom of the second plough body and working width 300 mm .

References

1 Zhao D ; Liu F ; Jia H Transforming constitution of planosol solum . Journal of Chinese Scientia Agricultural Sinica 1989 , 22 (5) : 47 – 55

2 Araya K Influence of particle size distribution in soil compaction of planosol solum . Journal of Environmen- tal Science Laboratory , Senshu University – Hokkaido 1991 , 2 : 181 – 192

3 Araya K ; Kudoh M ; Zhao D ; Liu F ; Jia H Improvement of planosol solum : Part 4 , Field experiments with prototype roll-in and drop-down ploughs . Journal of Agricultural Engineering Research 1996 , 63 : 275 – 282

4 Araya K ; Kudoh M ; Zhao D ; Liu F ; Jia H Improvement of planosol solum : Part 5 , Three-stage subsoil mixing plough in soil bin experiments . Journal of Agricultural Engineering Research 1996 , 65 : 143 – 149 .

5 Araya K ; Kudoh M ; Zhao D ; Liu F ; Jia H Improvement of planosol solum : Part 3 , Optimisation of design of drop-down ploughs in soil bin experiments . Journal of Agricultural Engineering Research 1996 , 63 : 269 – 274

6 Araya K ; Kudoh M ; Zhao D ; Liu F ; Jia H Ploughs for improvement of planosol solum : Part 7 , Pseudogley soil field experiments with a three-stage subsoil mixing plough . Journal of Environmental Science Laboratory , Senshu University-Hokkaido , submitted