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Effects of PTO-powered disk tilling on some physical properties of Bangkok clay soil
Soll & Image ~,~&
E LS EV I E R
Soil & Tillage Research 32 (1994) 93-104
.
Kesearcn
Effects of PTO-powered disk tilling on some physical properties of Bangkok clay soil M.S. Islam", V.M. Salokhe a'*, C.P. Gupta a, M. Hoki b "Agricultural and FoodEngineering Program, Asian Institute of Technology, GPO Box 2 754, Bangkok 10501, Thailand bDepartment of Bioproduction and Machinery, Mie University, Tsu, 514 Japan Accepted 7 July 1994
Abstract Experiments were conducted to investigate the effects of tilling with a PTO-powered disk tiller on some physical properties of Bangkok clay soil. Tests were conducted at I, 2, 3, 4 and 5 km h-~ forward speeds and 28 ° and 33 ° gang angles. Average moisture content of the soil was 26 g 100g-L The effects of disk tilling were assessed in terms of changes in bulk density, total porosity, cone index, clod size distribution and soil inversion during the first and second passes. Tests were also conducted in the unpowered mode at a 28: disk gang angle setting during a single pass. The study revealed that the bulk density and cone index were reduced, and the total porosity, content of clods of < 15 mm diameter and soil inversion were increased with an increase in the number of passes and forward speed. At any given pass and forward speed, the reduction in bulk density and cone index, and increase in total porosity and content of clods of < 15 m m diameter, were greater at a 28 disk gang angle setting compared with a 33 ° setting. More soil inversion was recorded at a 33 ° than at 28 ° gang angle setting. A comparison of performance between powered and unpowered modes revealed that, in the unpowered mode, the tilling effects on soil physical properties were less than that obtained in the powered mode. Keywords: Powered disk tiller; Gang angle; Soil properties; Number of passes and speed
1. Introduction T h e P T O - d r i v e n p o w e r e d disk tiller is a n e w l y d e v e l o p e d tillage i m p l e m e n t w h i c h was i n t r o d u c e d in practical usage in J a p a n ( K a w a m u r a , 198 5 ). Its a d v a n * Corresponding author. 0167-1987/94/$07.00 © 1994 Elsevier Science B.V. All rights reserved SSDI0167-1987(94)00422-6
94
M.S. Islam et al. ~Soil & Tillage Research 32 (1994) 93-104
tage is that, due to its positive cutting and throwing action, proper soil inversion, pulverization and plant residue incorporation take place, and the soil becomes suitable for planting after about two passes. During the conventional method, land is plowed and then harrowed, thus it takes more trips and a longer time to prepare the soil for planting. Stihne ( 1963 ), in a comparative study of the quality of work between the conventional disk plow and the powered disk plow, observed that with a powered disk more soil pulverization results, whereas with the free rolling disk larger clods resulted. Young (1976 ) conducted a field evaluation of a powered disk harrow called the "Dynatil" and concluded that although in some conditions the Dynatil consumed more power than an unpowered disk, the benefits of increased soil pulverization, improved mulch incorporation and greater efficiency through reduction in tractor slippage appeared to outweigh the potential overall increase in power requirement. Hoki et al. (1988) in a study of a PTO-driven powered disk tiller concluded that the implement had better ability to cut through crop residue and weeds and produce more soil pulverization compared with an unpowered disk implement. Tingxi and Zengrui (1989) studied the turning process and trash covering performance of a powered disk. They observed that the weeds and rice stubble were buried perfectly in the adjoining crevice left by the two adjacent rows of powered disking. During the above mentioned studies, only visual observations on the general aspects of tillage were made. The effects of powered disk tilling on the physical properties of a particular soil were not quantified. Therefore, in this particular study, a comprehensive evaluation of the effects of powered disk tilling on some of the physical properties of Bangkok clay soil was undertaken.
2. Criteria for the performance of tillage implements The performance of a tillage implement has frequently been evaluated in terms of change in soil bulk density (Ong, 1977; Yassen et al., 1992), total porosity (AUamaras, 1966; Ong, 1977), cone index (Burov et al., 1973; Soane and Pidgeon, 1975; Ong, 1977), clod size distribution (Ong, 1977; Montemayor, 1992; Yassen et al., 1992) and soil inversion (RNAM, 1983; Bukhari et al., 1988, 1989). Ong ( 1977 ) investigated the tillage effects on some physical properties of Bangkok clay soil by different combinations of moldboard plow, disk plow and disk harrow. He found that the change in bulk density, total porosity, cone index and the clod size distribution were significantly different for different combinations. Hoki et al. ( 1988 ), during field testing of a powered disk tiller, observed excellent soil pulverization with clod size considerably smaller than with an unpowered disk tillage. Many researchers have reported the required range of change in soil physical properties for crop establishment. Rosenberg (1964) stated that there is no common plant whose roots can penetrate a soil which has a bulk density above 1.9 g cm -3. For clays, a bulk density of 1.6-1.7 g cm -3 has sometimes been found to be the critical limit for root penetration. Larson (1964) gave the figure of bulk
M.S. Islam et al. / Soil & Tillage Research 32 (1994) 93-104
95
density for satisfactory growth in several corn belt soils of the United States as 1.0-1.4 g cm -a. Zrazhevskiy and Nazarenko (1969) also reported that the optimum bulk density for grain crops ranges from 1.1-1.4 g c m -3, while for most root crops it usually should not exceed 1.15-1.2 g c m - 3. Baver et al. ( 1972 ) stated that the optimum air porosity ranges for several crops were as follows: Sudan grass, 6-10 m a 100m-3; wheat and oats, 10-15 m a 1 0 0 m - a ; barley and sugar beet, 15-20 m a 1 0 0 m -3. He noted that yields were reduced when the air space became too high or too low. Raney and Zingg (1957) mentioned that the best size of aggregates or clods theoretically ranges from 1-5 mm diameter, but the soil composed of smaller clods is less well-drained. Taylor et al. ( 1966 ) observed that while other plant growth conditions remain adequate, increase in soil strength would reduce the rate of seedling emergence or rate of root elongation.
3. Materials and methods
The experiments were conducted in Bangkok clay soil with 61.5 g 100g-~ clay, 32 g 100g- ~silt and 6.5 g 100g- 1 sand (Islam, 1993 ). The average cone index for the top 15 cm soil was 1.87 MPa and soil moisture content was 26 g 100g -1. The liquid and plastic limits were 51 g 100g- ~ and 26.2 g 100g- 1, respectively. A 51kW four-wheel tractor was used for mounting the powered disk tiller. The powered disk tiller had two gangs of disks, each containing four disks (Fig. 1 ). In between the two disk gangs a small rotavator was provided. The disks were driven by the tractor PTO shaft, running at an average speed of 540 rpm, which gave a disk peripheral speed of 2.65 m s -I. Fig. 1 also shows the work produced by the disk tiller during the operation in the field. Tests were conducted at five different forward speeds of the tractor ( l, 2, 3, 4 and 5 km h - t ). These speeds were achieved
Fig. 1. Powered disk tiller in operation.
M.S. Islam et aL ~.Soil& TillageResearch32 (1994,)93-104
96
by adjusting the engine throttle and gear position. The effect of gang angle was investigated by changing the gang angle from 28 ° to 33 ° . The gang angle was defined as the angle made by the disk gangs with a line perpendicular to the direction of travel. The effect of the number of passes on soil physical properties was assessed by comparing the effect of one and two disk tiller passes. Each experiment was replicated three times. The tilling effects on the soil were measured through changes in bulk density, total porosity, cone index, clod size distribution and soil inversion. Bulk density was determined on a dry basis. Samples were collected before tilling, and after one and two passes. A cylindrical core sampler of 100 mm inside diameter, 100 mm height and 2 mm wall thickness was used for sample collection. The core samples were dried at 105°C for 24 h (RNAM, 1983). Bulk density was calculated from the weight of oven-dried samples and the volume of the respective wet samples. Particle density of the test soil was determined by the pycnometer method. Total porosity was calculated from bulk and panicle densities. Soil cone index was measured at several locations by using an automatic recording type cone penetrometer. The cone base diameter was 12.83 mm and the cone angle was 30 °. An almost constant cone penetration speed of 3 cm s- 1 was maintained. The average cone index value up to the depth of tillage (150-130 mm at different forward speeds) was taken as the cone index of the tilled soil. To measure the clod size distribution, soil samples up to the tillage depth were collected randomly in a tray, air dried and sieve analysis was done manually. A sieve series with 100, 80, 55, 40, 30, 20 and 15 mm openings was used for clod size analysis. Soil inversion was measured in terms of the amount of stubble and weeds covered by a single pass of the tiller. For this purpose a 1 × 1 m 2 wooden frame was used for the collection of weed samples (RNAM, 1983). Samples were collected from the soil surface at randomly selected places before and after tilling operations. Soil inversion was calculated using the following equation:
I = ( Wb#DWa ) I O0
(1)
w h e r e / = i n d i c a t o r of soil inversion (g 100g-~), Wb=weight of weed and crop residue per unit area before tilling (g), Wa=weight of weed and crop residue per unit area after tilling (g). For testing the implement in the unpowered mode, the PTO shaft was disengaged. The disk tiller was set at a 28 ° gang angle and operated at 2, 3 and 4 km h - t forward speed during the first pass only. The other test conditions were the same as the tests with the PTO power supply. 4. Results and discussion
4.1. Bulk density The average initial bulk density of the test soil was 1.4 g c m - 3 . Bulk density was affected by the number of passes and the relative effects were different at
M.S. Islam et al. / Soil & Tillage Research 32 (1994) 93-104
97
different forward speeds and gang angle settings. Fig. 2 shows the effect of the number of passes on the bulk density at different forward speeds and gang angles. At the 28 ° gang angle setting, the maximum reduction in bulk density (about 32%) was obtained after pass 2 at 5 km h - t forward speed. The minimum reduction in bulk density at this gang angle was about 20% after the first pass at 1 km h-~ forward speed. At the 33 ° gang angle setting, the maximum and minimum reductions in bulk density were 28% and 18%, respectively, at the same forward speeds and number of passes as at the 28 ° gang angle setting. Thus, both the number of passes and the forward speed showed a positive effect on the reduction in bulk density. As the number of passes increased, further breaking of soil clods occurred, which in turn reduced bulk density. At a higher forward speed during 1.6
Forward
speed kmli I
1.4
~4
km]~IF7
5
Gang
kraft'
angle
28"
]
1.2 b
J J J J J J J J J J
O. 4 ,\x, O. 2
b
©
©d
cd
,,'x\x~
~.~
J
J J
0.0
1
2
1.6
Gang
1,4
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angle
1.2 ~b
b
b
¢
2"
cd
'~l.O
.~" O. 8
~
0.6
0.4
0.2
0.0
2
1
Pass
number
Fig. 2. Effect of number of passes on the bulk density at different forward speeds and gang angles. Bars with different letters at the top differ significantly ( P < 0.05 ).
98
M.S. Islam et al. ~Soil & Tillage Research 32 (1994) 93-104
any pass, more soil pulverization occurred due to greater kinetic energy imparted to soil clods which further reduced bulk density. At the same forward speed and number of passes, the reduction in bulk density at the 28 ° gang angle setting was higher than at the 33 ° gang angle setting. A statistical analysis by the " F " test revealed that the number of passes affected bulk density significantly at the 95%level of significance while the gang angle settings and forward speed did not have a statistically significant effect on bulk density. 4.2. Total porosity
The average particle density of the test soil was 2.4 g c m - 3 . The average initial total porosity of the untilled soil was 41 m 3 100m-3. Fig. 3 shows the effect of the number of passes on the increase in total porosity at different forward speeds and gang angles. At the 28 ° gang angle setting the maximum and minimum values of the increase in total porosity compared with the initial total porosity were about 19.42 and 12.33 m 3 100m -3 after pass 2 at 5 km h -1 speed and after pass 1 at 1 km h - i speed, respectively. At the 33 ° gang angle setting the maximum increase was about 17.33 m 3 100m -3 after pass 2 at 5 km h -1 speed and the minimum increase was about 11 m 3 100m- 3 after pass 1 at 1 km h - 1 speed. The increase in total porosity was higher at the 28 ° gang angle setting than at the 33 ° gang angle setting at any given forward speed and pass. The number of passes and gang angle affected total porosity significantly at the 95%-level of significance but the forward speed did not have a statistically significant effect on total porosity. 4.3. Cone index
Fig. 4 shows that the reduction in cone index increased as the number of passes increased at all speeds and gang angle settings. At the 28 ° gang angle setting, the reduction in cone index compared with the cone index before tilling was about 60%, 66%, 67%, 68% and 75% after the second pass at 1, 2, 3, 4 and 5 km h -1 forward speeds, respectively. At the 33 ° gang angle setting, the reduction in cone index after pass 2 increased from 57% to 65% when forward speed increased from 1 to 5 km h - 1. A higher reduction in cone index means the tilled soil layer is softer and more favorable for seedling emergence and root growth. The reduction in cone index increased with an increase in the number of passes. Increase in forward speed at the same pass and gang angle setting also increased the reduction in cone index. A higher reduction was obtained at the 28 ° gang angle setting than at the 33 ° gang angle setting for the same number of passes and forward speed. Both the number of passes and gang angle settings had a significant effect on the reduction in cone index when analyzed by the " F " test at the 95%-level of significance, while the forward speed did not show statistically significant effects. 4.4. Clod size
Fig. 5 shows the effect of the number of passes on the content of clods < 15 mm in diameter at different forward speeds and gang angles. An increase in the num-
M.S. Islam et al. ~Soil& Tillage Research 32 (1994) 93-104 BO
70
L~'~I
]Forward k m li t l'--J 2
speed kl~t I:. t E'73
~4
kmSl~5
kss~li I
I Gang angle 60
ab
A-" oo
b
k~li
99
i
28" i
b
cd
c
d
d
no
o
~o
10
1
2
80 Gang
70
angle
33"
]
60 et
e ~
~
f
f
It
Ih
~xxx
0
,x.\'~
~..40
/J
- ~
\\\,
~
JJ
!!
o
~.'~o
....
2O
10
. . . . . . . . .
xx\~
1
_
, 2
Pass
number
Fig. 3. Effect of number of passes on the total porosity at different forward speeds and gang angles. Bars with different letters at the top differ significantly (P< 0.05 ).
ber of passes increased the content of clods < 15 mm in diameter. An increase in forward speed at any given pass and gang angle setting also increased the content of clods < 15 mm. The maximum content of clods < 15 mm in size at 28 ° and 33 ° gang angles were about 49 and 32 g 100g-1, respectively, after pass 2 at 5 km h - l forward speed. The minimum content of clods < 15 mm in size at the above gang angle settings were about 17 and 16 g 100g -~, respectively, after the first pass at 1 km h - ~ forward speed. A higher content of clods < 15 mm in diameter mean better pulverization of the tilled soil. At higher forward speeds and number of passes, more pulverization occurred, which caused an increase in the content of smaller clods. The number of pass and gang angle setting had significant effects
100
M.S. Islam et al. / Soil & Tillage Research 32 (1994) 93-104 1.2
1.0
Forward
k-~-~l
kmli
'F-~ 2
~84
k m l / ~ f-q 5 ] Gang
b
0.8
~
speed
kmli'l'~
3
kmli'
kmli'
28"
angle
}
d
0.6
0.4
r
~i
J
I i!I i !!
0.2
0.0
2
1
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angle
33*
]
1.0
i 0.8
~
,~ / / ~
0.6
,x\~ /
.......
~0.4 ~ / ~ u ~ :
ii¸ii~i!¸¸¸¸¸!
......
z- mil il
0.2
iili ii!iiil
0.0
2
1 pass
number
Fig. 4. Effect of number of passes on the cone index at different forward speeds and gang angles. Bars with different letters at the top differ significantly (P< 0.05 ). on the content of clods < 15 mm in diameter at the 95%-level of significance, but the forward speed did not show statistically significant effects.
4.5. Soil inversion Fig. 6 shows the effect of forward speed on soil inversion by a single pass of the powered disk tiller at different gang angle settings. As forward speed increased, soil inversion increased at both gang angle settings. At any forward speed, the 33 ° gang angle setting inverted a little more soil than the 28 ° gang angle setting. At the 33 ° gang angle setting the maximum and minimum soil inversion were about 85 and 77 g 100g -1 at 5 and 1 km h -1 forward speeds, respectively. At the 28 °
M.S. Islam et al. / Soil & Tillage Research 32 (1994) 93-104 6O
Forward
[
50
speed
FFI1
kmliJ~2
kmlil~713
k-~4
kml/Ir-]5
kml~ t
kmli
1 d
Gang
101
d
angle
m m ~3o v
~2o
I0
0
1
2
60
Gang
5O
angle
33 °
]
__.3o v ~20
sh
•
m
10
1
2
Pass
number
Fig. 5. Effect of number of passes on content of clods < 15 mm at different forward speeds and gang angles. Bars with different letters at the top differ significantly ( P < 0.05).
gang angle setting these values were about 80 and 64 g 100g-l at 5 and 1 km h-1 forward speeds, respectively. The soil inversion obtained at any forward speed and gang angle setting of the powered disk tiller was much higher than the soil inversion values obtained earlier by Bukhari et al. ( 1988, 1989) for the unpowered disk plow. The following equations could be fitted to the soil inversion data recorded at different forward speeds: I=3.47S+63.08
(at 28 ° gang angle);
r2=0.87
(2)
I=2.73S+73.01
(at 33 ° gang angle);
r2=0.90
(3)
where I = soil inversion (g 100g- l ), S = forward speed (km h - ~), r = coefficient of correlation.
102
M.S. Islam et al. / Soil & Tillage Research 32 (1994) 93-104
e.o
.~
60
40
o
0
11
Gang
angle
I 2
I 3
28*
I
I 4
I 5
100
80
60
.~
,tO
~
20
Oo
11
I 2
Forward
ang
angle
I 3 speed
33*
]
I 4 ( k m h -1
5
6
)
Fig. 6. Effect of forwardspeed on soil inversionat different gangangle settings duringthe first pass. These equations are valid only for the test conditions used in this study. A statistical analysis by the "F" test showed that gang angle settings had a significant effect but forward speed had no significant effect on soil inversion at the 95% -level of significance. After two passes of the disk tiller at the 28 ° gang angle setting, the soil was almost ready for planting.
4.6. Comparison of performance between powered and unpowered modes To compare the tillage effects on soil physical properties by the powered disk tiller in the powered and unpowered modes, tests were conducted at the 28 ° gang angle setting and at 2, 3 and 4 km h-1 forward speeds during pass 1. Table 1 shows the relative increase or decrease in the change in soil physical properties as well as the total energy requirement per unit volume of tilled soil as a result of tilling the soil in the unpowered mode compared with the powered mode when
M.S. Islam et al. /Soil & Tillage Research 32 (1994) 93-104
103
Table 1 Performance of the disk tiller in the unpowered mode, relative to the powered mode, at the 28 ° gang angle setting during the first pass Forward speed (kmh -l)
Increase in bulk density (gcm -3)
Reduction in total porosity (m 3100m -3)
Increase in cone index (MPa)
Increase in MWD a of clods (mm)
Reduction in soil inversion (gl00g -I)
Increase in total energ~ ( k J m -3)
2 3 4
0.15 0.15 0.11
6.6 6.1 4.5
0.32 0.36 0.39
34.2 32.1 30.8
23.5 22.0 27.1
-42.84 - 12.64 18.36
a MWD, mean weight diameter.
other conditions were the same. For both tests the initial setting for depth of tillage was 15 cm. At the same forward speed and gang angle setting, in the unpowered mode, the tillage depth was up to 48% less than that in the powered mode. The bulk density of the tilled soil was 0.11-0.15 g cm -3 higher, total porosity was 4.5-6.6 m 3 100m -3 less, the cone index of the tilled soil was higher by 0.32-0.39 MPa, the mean weight diameter of the clods was increased by 30.8-34.2 mm, and the soil inversion was reduced by 23.5-27.1 g 100g-1 compared with the powered mode at the same forward speed for one pass. The total energy requirement per unit volume of tilled soil was less in the unpowered mode at 2 and 3 km h-1 forward speed but it was higher at 4 km h - 1 forward speed (Table 1 ). This reveals that, an increase in forward speed affects the total energy requirement more in the unpowered mode than in the powered mode. This was because in the powered mode, a major part of the total energy requirement was supplied through the tractor PTO which was less affected by the forward speed. It was also visually observed that the disk gangs revolved more slowly in the unpowered mode than in the powered mode. The performance of the disk tiller in the powered mode was superior to the performance in the unpowered mode in all respects.
5. Conclusions
Tilling with a powered disk tiller caused significant changes in the physical properties of the soil. Tilling with this implement reduced bulk density and cone penetration resistance and increased total porosity and the content of clods < 15 mm in diameter. The number of passes, forward speed and gang angle setting were found to affect the soil physical properties considerably. Better tillage performance was observed at a 28 ° gang angle setting although the soil inversion was slightly better at the 33 ° gang angle setting. Field testing of the disk tiller in the unpowered mode resulted in less reduction in bulk density and cone index, less increase in total porosity and in the content of clods < 15 m m in diameter and less soil inversion compared with the performance of the disk tiller in the pow-
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M.S. Islam et al. / Soil & Tillage Research 32 (I 994) 93-104
ered mode. In the powered mode, the soil was almost ready for planting after 2 passes of the disk tiller at the 28 ° gang angle setting.
References Allamaras, R.R., 1966. Total porosity and random roughness of the interrow zone as influenced by tillage. USDA, Washington, DC, USA, Conservation Research Report No.7. Baver, L.D., Gardner, W.H. and Gardner, W.R., 1972. Soil Physics. John Wiley, New York, USA. Bukhari, S., Bhutto, M.A., Baloch, J.M., Bhutto, A.B. and Mirani, A.N., 1988. Performance of selected tillage implements. Agric. Mech. Asia Africa Latin America, 19: 9-14. Bukhari, S., Baloch, J.M. and Mirani, A.N., 1989. Soil manipulation with tillage implements. Agric. Mech. Asia Africa Latin America, 20:17-19. Burov, D.I., Dudintsev, Y.V. and Kazakov, G.I., 1973. Modification of the agro-physical properties of ordinary chernozen by tillage. Soviet Soil Sci., 5: 100-109. Hoki, M., Thomas, H.B., Wilkinson, R.H. and Tanoue, T., 1988. Study of PTO driven powered disk tiller. Trans. ASAE, 31: 1355-1360. Islam, M.S., 1993. Field testing ofa PTO powered disk tiller in Bangkok clay soil. M. Eng. Thesis No. AE93-8, Asian Inst. Technol., Bangkok, Thailand, (unpublished). Kawamura, N., 1985. Soil dynamics and its application to tillage machineries. Res. Rep. Agric. Machinery, Kyoto Univ., Japan. 15: 1-22. Larson, W.E., 1964. Soil parameters for evaluating tillage needs and operations. Proc. Soil Sci. Soc. Am., 28:118-122. Montemayor, M.B., 1992. Cotton and wheat seedling emergence as affected by seedbed preparation. Agric. Mech. Asia Africa Latin America, 23:39-41. Ong, K.H., 1977. Effect of plowing and harrowing on some physical properties of a typical Bangkok clay soil. M. Eng. Thesis No. 1236, Asian Inst. Technol., Bangkok, Thailand, (unpublished). Raney, W.A. and Zingg, A.W., 1957. Principles of tillage. Yearbook Agric., USDA, Washington, DC, USA. RNAM, 1983. Test codes and procedures for farm machinery. Publication of Regional Network for Agric. Machinery, Philippines, Technical Series No. 12, pp. 10, 56. Rosenberg, N.J., 1964. Response of plants to physical effects of soil compaction. Adv. Agron., 16: 181-195. Soane, B.D. and Pidgeon, J.D., 1975. Tillage requirements in relation to soil physical properties. Soil Sci., 119: 376-384. S6hne, W.H., 1963. Tillage aspects. Canadian J. Agric. Eng., 5: 2-3, 8. Taylor, H.M., Parker, J.J. and Roberson, G.M., 1966. Soil strength and seedling emergence relations. II. A generalized relations for Gramineae. Agron. J., 58: 393-395. Tingxi, M. and Zengrui, X., 1989. An experimental study of power disk tool driven by tractor P.T.O. Proc. Int. Symp. on Agric. Eng., Beijing, PR China, 12-15 September 1989, International Academic Publishers, pp. 250-256. Yassen, H.A., Hassan, H.M. and Hammadi, I.A., 1992. Effect of plowing depths using different plow types on some physical properties of soil. Agric. Mech. Asia Africa Latin America, 23:21-24. Young, P., 1976. A machine to increase productivity of a tillage operation. Trans. ASAE, 19:10551061. Zrazhevskiy, A.I. and Nazarenko, G.V., 1969. The effect of the physical state of the plow layer of the soil on the growth of crop plants. Soviet Soil Sci., 6: 691-701.
E LS EV I E R
Soil & Tillage Research 32 (1994) 93-104
.
Kesearcn
Effects of PTO-powered disk tilling on some physical properties of Bangkok clay soil M.S. Islam", V.M. Salokhe a'*, C.P. Gupta a, M. Hoki b "Agricultural and FoodEngineering Program, Asian Institute of Technology, GPO Box 2 754, Bangkok 10501, Thailand bDepartment of Bioproduction and Machinery, Mie University, Tsu, 514 Japan Accepted 7 July 1994
Abstract Experiments were conducted to investigate the effects of tilling with a PTO-powered disk tiller on some physical properties of Bangkok clay soil. Tests were conducted at I, 2, 3, 4 and 5 km h-~ forward speeds and 28 ° and 33 ° gang angles. Average moisture content of the soil was 26 g 100g-L The effects of disk tilling were assessed in terms of changes in bulk density, total porosity, cone index, clod size distribution and soil inversion during the first and second passes. Tests were also conducted in the unpowered mode at a 28: disk gang angle setting during a single pass. The study revealed that the bulk density and cone index were reduced, and the total porosity, content of clods of < 15 mm diameter and soil inversion were increased with an increase in the number of passes and forward speed. At any given pass and forward speed, the reduction in bulk density and cone index, and increase in total porosity and content of clods of < 15 m m diameter, were greater at a 28 disk gang angle setting compared with a 33 ° setting. More soil inversion was recorded at a 33 ° than at 28 ° gang angle setting. A comparison of performance between powered and unpowered modes revealed that, in the unpowered mode, the tilling effects on soil physical properties were less than that obtained in the powered mode. Keywords: Powered disk tiller; Gang angle; Soil properties; Number of passes and speed
1. Introduction T h e P T O - d r i v e n p o w e r e d disk tiller is a n e w l y d e v e l o p e d tillage i m p l e m e n t w h i c h was i n t r o d u c e d in practical usage in J a p a n ( K a w a m u r a , 198 5 ). Its a d v a n * Corresponding author. 0167-1987/94/$07.00 © 1994 Elsevier Science B.V. All rights reserved SSDI0167-1987(94)00422-6
94
M.S. Islam et al. ~Soil & Tillage Research 32 (1994) 93-104
tage is that, due to its positive cutting and throwing action, proper soil inversion, pulverization and plant residue incorporation take place, and the soil becomes suitable for planting after about two passes. During the conventional method, land is plowed and then harrowed, thus it takes more trips and a longer time to prepare the soil for planting. Stihne ( 1963 ), in a comparative study of the quality of work between the conventional disk plow and the powered disk plow, observed that with a powered disk more soil pulverization results, whereas with the free rolling disk larger clods resulted. Young (1976 ) conducted a field evaluation of a powered disk harrow called the "Dynatil" and concluded that although in some conditions the Dynatil consumed more power than an unpowered disk, the benefits of increased soil pulverization, improved mulch incorporation and greater efficiency through reduction in tractor slippage appeared to outweigh the potential overall increase in power requirement. Hoki et al. (1988) in a study of a PTO-driven powered disk tiller concluded that the implement had better ability to cut through crop residue and weeds and produce more soil pulverization compared with an unpowered disk implement. Tingxi and Zengrui (1989) studied the turning process and trash covering performance of a powered disk. They observed that the weeds and rice stubble were buried perfectly in the adjoining crevice left by the two adjacent rows of powered disking. During the above mentioned studies, only visual observations on the general aspects of tillage were made. The effects of powered disk tilling on the physical properties of a particular soil were not quantified. Therefore, in this particular study, a comprehensive evaluation of the effects of powered disk tilling on some of the physical properties of Bangkok clay soil was undertaken.
2. Criteria for the performance of tillage implements The performance of a tillage implement has frequently been evaluated in terms of change in soil bulk density (Ong, 1977; Yassen et al., 1992), total porosity (AUamaras, 1966; Ong, 1977), cone index (Burov et al., 1973; Soane and Pidgeon, 1975; Ong, 1977), clod size distribution (Ong, 1977; Montemayor, 1992; Yassen et al., 1992) and soil inversion (RNAM, 1983; Bukhari et al., 1988, 1989). Ong ( 1977 ) investigated the tillage effects on some physical properties of Bangkok clay soil by different combinations of moldboard plow, disk plow and disk harrow. He found that the change in bulk density, total porosity, cone index and the clod size distribution were significantly different for different combinations. Hoki et al. ( 1988 ), during field testing of a powered disk tiller, observed excellent soil pulverization with clod size considerably smaller than with an unpowered disk tillage. Many researchers have reported the required range of change in soil physical properties for crop establishment. Rosenberg (1964) stated that there is no common plant whose roots can penetrate a soil which has a bulk density above 1.9 g cm -3. For clays, a bulk density of 1.6-1.7 g cm -3 has sometimes been found to be the critical limit for root penetration. Larson (1964) gave the figure of bulk
M.S. Islam et al. / Soil & Tillage Research 32 (1994) 93-104
95
density for satisfactory growth in several corn belt soils of the United States as 1.0-1.4 g cm -a. Zrazhevskiy and Nazarenko (1969) also reported that the optimum bulk density for grain crops ranges from 1.1-1.4 g c m -3, while for most root crops it usually should not exceed 1.15-1.2 g c m - 3. Baver et al. ( 1972 ) stated that the optimum air porosity ranges for several crops were as follows: Sudan grass, 6-10 m a 100m-3; wheat and oats, 10-15 m a 1 0 0 m - a ; barley and sugar beet, 15-20 m a 1 0 0 m -3. He noted that yields were reduced when the air space became too high or too low. Raney and Zingg (1957) mentioned that the best size of aggregates or clods theoretically ranges from 1-5 mm diameter, but the soil composed of smaller clods is less well-drained. Taylor et al. ( 1966 ) observed that while other plant growth conditions remain adequate, increase in soil strength would reduce the rate of seedling emergence or rate of root elongation.
3. Materials and methods
The experiments were conducted in Bangkok clay soil with 61.5 g 100g-~ clay, 32 g 100g- ~silt and 6.5 g 100g- 1 sand (Islam, 1993 ). The average cone index for the top 15 cm soil was 1.87 MPa and soil moisture content was 26 g 100g -1. The liquid and plastic limits were 51 g 100g- ~ and 26.2 g 100g- 1, respectively. A 51kW four-wheel tractor was used for mounting the powered disk tiller. The powered disk tiller had two gangs of disks, each containing four disks (Fig. 1 ). In between the two disk gangs a small rotavator was provided. The disks were driven by the tractor PTO shaft, running at an average speed of 540 rpm, which gave a disk peripheral speed of 2.65 m s -I. Fig. 1 also shows the work produced by the disk tiller during the operation in the field. Tests were conducted at five different forward speeds of the tractor ( l, 2, 3, 4 and 5 km h - t ). These speeds were achieved
Fig. 1. Powered disk tiller in operation.
M.S. Islam et aL ~.Soil& TillageResearch32 (1994,)93-104
96
by adjusting the engine throttle and gear position. The effect of gang angle was investigated by changing the gang angle from 28 ° to 33 ° . The gang angle was defined as the angle made by the disk gangs with a line perpendicular to the direction of travel. The effect of the number of passes on soil physical properties was assessed by comparing the effect of one and two disk tiller passes. Each experiment was replicated three times. The tilling effects on the soil were measured through changes in bulk density, total porosity, cone index, clod size distribution and soil inversion. Bulk density was determined on a dry basis. Samples were collected before tilling, and after one and two passes. A cylindrical core sampler of 100 mm inside diameter, 100 mm height and 2 mm wall thickness was used for sample collection. The core samples were dried at 105°C for 24 h (RNAM, 1983). Bulk density was calculated from the weight of oven-dried samples and the volume of the respective wet samples. Particle density of the test soil was determined by the pycnometer method. Total porosity was calculated from bulk and panicle densities. Soil cone index was measured at several locations by using an automatic recording type cone penetrometer. The cone base diameter was 12.83 mm and the cone angle was 30 °. An almost constant cone penetration speed of 3 cm s- 1 was maintained. The average cone index value up to the depth of tillage (150-130 mm at different forward speeds) was taken as the cone index of the tilled soil. To measure the clod size distribution, soil samples up to the tillage depth were collected randomly in a tray, air dried and sieve analysis was done manually. A sieve series with 100, 80, 55, 40, 30, 20 and 15 mm openings was used for clod size analysis. Soil inversion was measured in terms of the amount of stubble and weeds covered by a single pass of the tiller. For this purpose a 1 × 1 m 2 wooden frame was used for the collection of weed samples (RNAM, 1983). Samples were collected from the soil surface at randomly selected places before and after tilling operations. Soil inversion was calculated using the following equation:
I = ( Wb#DWa ) I O0
(1)
w h e r e / = i n d i c a t o r of soil inversion (g 100g-~), Wb=weight of weed and crop residue per unit area before tilling (g), Wa=weight of weed and crop residue per unit area after tilling (g). For testing the implement in the unpowered mode, the PTO shaft was disengaged. The disk tiller was set at a 28 ° gang angle and operated at 2, 3 and 4 km h - t forward speed during the first pass only. The other test conditions were the same as the tests with the PTO power supply. 4. Results and discussion
4.1. Bulk density The average initial bulk density of the test soil was 1.4 g c m - 3 . Bulk density was affected by the number of passes and the relative effects were different at
M.S. Islam et al. / Soil & Tillage Research 32 (1994) 93-104
97
different forward speeds and gang angle settings. Fig. 2 shows the effect of the number of passes on the bulk density at different forward speeds and gang angles. At the 28 ° gang angle setting, the maximum reduction in bulk density (about 32%) was obtained after pass 2 at 5 km h - t forward speed. The minimum reduction in bulk density at this gang angle was about 20% after the first pass at 1 km h-~ forward speed. At the 33 ° gang angle setting, the maximum and minimum reductions in bulk density were 28% and 18%, respectively, at the same forward speeds and number of passes as at the 28 ° gang angle setting. Thus, both the number of passes and the forward speed showed a positive effect on the reduction in bulk density. As the number of passes increased, further breaking of soil clods occurred, which in turn reduced bulk density. At a higher forward speed during 1.6
Forward
speed kmli I
1.4
~4
km]~IF7
5
Gang
kraft'
angle
28"
]
1.2 b
J J J J J J J J J J
O. 4 ,\x, O. 2
b
©
©d
cd
,,'x\x~
~.~
J
J J
0.0
1
2
1.6
Gang
1,4
33- ]
angle
1.2 ~b
b
b
¢
2"
cd
'~l.O
.~" O. 8
~
0.6
0.4
0.2
0.0
2
1
Pass
number
Fig. 2. Effect of number of passes on the bulk density at different forward speeds and gang angles. Bars with different letters at the top differ significantly ( P < 0.05 ).
98
M.S. Islam et al. ~Soil & Tillage Research 32 (1994) 93-104
any pass, more soil pulverization occurred due to greater kinetic energy imparted to soil clods which further reduced bulk density. At the same forward speed and number of passes, the reduction in bulk density at the 28 ° gang angle setting was higher than at the 33 ° gang angle setting. A statistical analysis by the " F " test revealed that the number of passes affected bulk density significantly at the 95%level of significance while the gang angle settings and forward speed did not have a statistically significant effect on bulk density. 4.2. Total porosity
The average particle density of the test soil was 2.4 g c m - 3 . The average initial total porosity of the untilled soil was 41 m 3 100m-3. Fig. 3 shows the effect of the number of passes on the increase in total porosity at different forward speeds and gang angles. At the 28 ° gang angle setting the maximum and minimum values of the increase in total porosity compared with the initial total porosity were about 19.42 and 12.33 m 3 100m -3 after pass 2 at 5 km h -1 speed and after pass 1 at 1 km h - i speed, respectively. At the 33 ° gang angle setting the maximum increase was about 17.33 m 3 100m -3 after pass 2 at 5 km h -1 speed and the minimum increase was about 11 m 3 100m- 3 after pass 1 at 1 km h - 1 speed. The increase in total porosity was higher at the 28 ° gang angle setting than at the 33 ° gang angle setting at any given forward speed and pass. The number of passes and gang angle affected total porosity significantly at the 95%-level of significance but the forward speed did not have a statistically significant effect on total porosity. 4.3. Cone index
Fig. 4 shows that the reduction in cone index increased as the number of passes increased at all speeds and gang angle settings. At the 28 ° gang angle setting, the reduction in cone index compared with the cone index before tilling was about 60%, 66%, 67%, 68% and 75% after the second pass at 1, 2, 3, 4 and 5 km h -1 forward speeds, respectively. At the 33 ° gang angle setting, the reduction in cone index after pass 2 increased from 57% to 65% when forward speed increased from 1 to 5 km h - 1. A higher reduction in cone index means the tilled soil layer is softer and more favorable for seedling emergence and root growth. The reduction in cone index increased with an increase in the number of passes. Increase in forward speed at the same pass and gang angle setting also increased the reduction in cone index. A higher reduction was obtained at the 28 ° gang angle setting than at the 33 ° gang angle setting for the same number of passes and forward speed. Both the number of passes and gang angle settings had a significant effect on the reduction in cone index when analyzed by the " F " test at the 95%-level of significance, while the forward speed did not show statistically significant effects. 4.4. Clod size
Fig. 5 shows the effect of the number of passes on the content of clods < 15 mm in diameter at different forward speeds and gang angles. An increase in the num-
M.S. Islam et al. ~Soil& Tillage Research 32 (1994) 93-104 BO
70
L~'~I
]Forward k m li t l'--J 2
speed kl~t I:. t E'73
~4
kmSl~5
kss~li I
I Gang angle 60
ab
A-" oo
b
k~li
99
i
28" i
b
cd
c
d
d
no
o
~o
10
1
2
80 Gang
70
angle
33"
]
60 et
e ~
~
f
f
It
Ih
~xxx
0
,x.\'~
~..40
/J
- ~
\\\,
~
JJ
!!
o
~.'~o
....
2O
10
. . . . . . . . .
xx\~
1
_
, 2
Pass
number
Fig. 3. Effect of number of passes on the total porosity at different forward speeds and gang angles. Bars with different letters at the top differ significantly (P< 0.05 ).
ber of passes increased the content of clods < 15 mm in diameter. An increase in forward speed at any given pass and gang angle setting also increased the content of clods < 15 mm. The maximum content of clods < 15 mm in size at 28 ° and 33 ° gang angles were about 49 and 32 g 100g-1, respectively, after pass 2 at 5 km h - l forward speed. The minimum content of clods < 15 mm in size at the above gang angle settings were about 17 and 16 g 100g -~, respectively, after the first pass at 1 km h - ~ forward speed. A higher content of clods < 15 mm in diameter mean better pulverization of the tilled soil. At higher forward speeds and number of passes, more pulverization occurred, which caused an increase in the content of smaller clods. The number of pass and gang angle setting had significant effects
100
M.S. Islam et al. / Soil & Tillage Research 32 (1994) 93-104 1.2
1.0
Forward
k-~-~l
kmli
'F-~ 2
~84
k m l / ~ f-q 5 ] Gang
b
0.8
~
speed
kmli'l'~
3
kmli'
kmli'
28"
angle
}
d
0.6
0.4
r
~i
J
I i!I i !!
0.2
0.0
2
1
1.2 Gang
angle
33*
]
1.0
i 0.8
~
,~ / / ~
0.6
,x\~ /
.......
~0.4 ~ / ~ u ~ :
ii¸ii~i!¸¸¸¸¸!
......
z- mil il
0.2
iili ii!iiil
0.0
2
1 pass
number
Fig. 4. Effect of number of passes on the cone index at different forward speeds and gang angles. Bars with different letters at the top differ significantly (P< 0.05 ). on the content of clods < 15 mm in diameter at the 95%-level of significance, but the forward speed did not show statistically significant effects.
4.5. Soil inversion Fig. 6 shows the effect of forward speed on soil inversion by a single pass of the powered disk tiller at different gang angle settings. As forward speed increased, soil inversion increased at both gang angle settings. At any forward speed, the 33 ° gang angle setting inverted a little more soil than the 28 ° gang angle setting. At the 33 ° gang angle setting the maximum and minimum soil inversion were about 85 and 77 g 100g -1 at 5 and 1 km h -1 forward speeds, respectively. At the 28 °
M.S. Islam et al. / Soil & Tillage Research 32 (1994) 93-104 6O
Forward
[
50
speed
FFI1
kmliJ~2
kmlil~713
k-~4
kml/Ir-]5
kml~ t
kmli
1 d
Gang
101
d
angle
m m ~3o v
~2o
I0
0
1
2
60
Gang
5O
angle
33 °
]
__.3o v ~20
sh
•
m
10
1
2
Pass
number
Fig. 5. Effect of number of passes on content of clods < 15 mm at different forward speeds and gang angles. Bars with different letters at the top differ significantly ( P < 0.05).
gang angle setting these values were about 80 and 64 g 100g-l at 5 and 1 km h-1 forward speeds, respectively. The soil inversion obtained at any forward speed and gang angle setting of the powered disk tiller was much higher than the soil inversion values obtained earlier by Bukhari et al. ( 1988, 1989) for the unpowered disk plow. The following equations could be fitted to the soil inversion data recorded at different forward speeds: I=3.47S+63.08
(at 28 ° gang angle);
r2=0.87
(2)
I=2.73S+73.01
(at 33 ° gang angle);
r2=0.90
(3)
where I = soil inversion (g 100g- l ), S = forward speed (km h - ~), r = coefficient of correlation.
102
M.S. Islam et al. / Soil & Tillage Research 32 (1994) 93-104
e.o
.~
60
40
o
0
11
Gang
angle
I 2
I 3
28*
I
I 4
I 5
100
80
60
.~
,tO
~
20
Oo
11
I 2
Forward
ang
angle
I 3 speed
33*
]
I 4 ( k m h -1
5
6
)
Fig. 6. Effect of forwardspeed on soil inversionat different gangangle settings duringthe first pass. These equations are valid only for the test conditions used in this study. A statistical analysis by the "F" test showed that gang angle settings had a significant effect but forward speed had no significant effect on soil inversion at the 95% -level of significance. After two passes of the disk tiller at the 28 ° gang angle setting, the soil was almost ready for planting.
4.6. Comparison of performance between powered and unpowered modes To compare the tillage effects on soil physical properties by the powered disk tiller in the powered and unpowered modes, tests were conducted at the 28 ° gang angle setting and at 2, 3 and 4 km h-1 forward speeds during pass 1. Table 1 shows the relative increase or decrease in the change in soil physical properties as well as the total energy requirement per unit volume of tilled soil as a result of tilling the soil in the unpowered mode compared with the powered mode when
M.S. Islam et al. /Soil & Tillage Research 32 (1994) 93-104
103
Table 1 Performance of the disk tiller in the unpowered mode, relative to the powered mode, at the 28 ° gang angle setting during the first pass Forward speed (kmh -l)
Increase in bulk density (gcm -3)
Reduction in total porosity (m 3100m -3)
Increase in cone index (MPa)
Increase in MWD a of clods (mm)
Reduction in soil inversion (gl00g -I)
Increase in total energ~ ( k J m -3)
2 3 4
0.15 0.15 0.11
6.6 6.1 4.5
0.32 0.36 0.39
34.2 32.1 30.8
23.5 22.0 27.1
-42.84 - 12.64 18.36
a MWD, mean weight diameter.
other conditions were the same. For both tests the initial setting for depth of tillage was 15 cm. At the same forward speed and gang angle setting, in the unpowered mode, the tillage depth was up to 48% less than that in the powered mode. The bulk density of the tilled soil was 0.11-0.15 g cm -3 higher, total porosity was 4.5-6.6 m 3 100m -3 less, the cone index of the tilled soil was higher by 0.32-0.39 MPa, the mean weight diameter of the clods was increased by 30.8-34.2 mm, and the soil inversion was reduced by 23.5-27.1 g 100g-1 compared with the powered mode at the same forward speed for one pass. The total energy requirement per unit volume of tilled soil was less in the unpowered mode at 2 and 3 km h-1 forward speed but it was higher at 4 km h - 1 forward speed (Table 1 ). This reveals that, an increase in forward speed affects the total energy requirement more in the unpowered mode than in the powered mode. This was because in the powered mode, a major part of the total energy requirement was supplied through the tractor PTO which was less affected by the forward speed. It was also visually observed that the disk gangs revolved more slowly in the unpowered mode than in the powered mode. The performance of the disk tiller in the powered mode was superior to the performance in the unpowered mode in all respects.
5. Conclusions
Tilling with a powered disk tiller caused significant changes in the physical properties of the soil. Tilling with this implement reduced bulk density and cone penetration resistance and increased total porosity and the content of clods < 15 mm in diameter. The number of passes, forward speed and gang angle setting were found to affect the soil physical properties considerably. Better tillage performance was observed at a 28 ° gang angle setting although the soil inversion was slightly better at the 33 ° gang angle setting. Field testing of the disk tiller in the unpowered mode resulted in less reduction in bulk density and cone index, less increase in total porosity and in the content of clods < 15 m m in diameter and less soil inversion compared with the performance of the disk tiller in the pow-
104
M.S. Islam et al. / Soil & Tillage Research 32 (I 994) 93-104
ered mode. In the powered mode, the soil was almost ready for planting after 2 passes of the disk tiller at the 28 ° gang angle setting.
References Allamaras, R.R., 1966. Total porosity and random roughness of the interrow zone as influenced by tillage. USDA, Washington, DC, USA, Conservation Research Report No.7. Baver, L.D., Gardner, W.H. and Gardner, W.R., 1972. Soil Physics. John Wiley, New York, USA. Bukhari, S., Bhutto, M.A., Baloch, J.M., Bhutto, A.B. and Mirani, A.N., 1988. Performance of selected tillage implements. Agric. Mech. Asia Africa Latin America, 19: 9-14. Bukhari, S., Baloch, J.M. and Mirani, A.N., 1989. Soil manipulation with tillage implements. Agric. Mech. Asia Africa Latin America, 20:17-19. Burov, D.I., Dudintsev, Y.V. and Kazakov, G.I., 1973. Modification of the agro-physical properties of ordinary chernozen by tillage. Soviet Soil Sci., 5: 100-109. Hoki, M., Thomas, H.B., Wilkinson, R.H. and Tanoue, T., 1988. Study of PTO driven powered disk tiller. Trans. ASAE, 31: 1355-1360. Islam, M.S., 1993. Field testing ofa PTO powered disk tiller in Bangkok clay soil. M. Eng. Thesis No. AE93-8, Asian Inst. Technol., Bangkok, Thailand, (unpublished). Kawamura, N., 1985. Soil dynamics and its application to tillage machineries. Res. Rep. Agric. Machinery, Kyoto Univ., Japan. 15: 1-22. Larson, W.E., 1964. Soil parameters for evaluating tillage needs and operations. Proc. Soil Sci. Soc. Am., 28:118-122. Montemayor, M.B., 1992. Cotton and wheat seedling emergence as affected by seedbed preparation. Agric. Mech. Asia Africa Latin America, 23:39-41. Ong, K.H., 1977. Effect of plowing and harrowing on some physical properties of a typical Bangkok clay soil. M. Eng. Thesis No. 1236, Asian Inst. Technol., Bangkok, Thailand, (unpublished). Raney, W.A. and Zingg, A.W., 1957. Principles of tillage. Yearbook Agric., USDA, Washington, DC, USA. RNAM, 1983. Test codes and procedures for farm machinery. Publication of Regional Network for Agric. Machinery, Philippines, Technical Series No. 12, pp. 10, 56. Rosenberg, N.J., 1964. Response of plants to physical effects of soil compaction. Adv. Agron., 16: 181-195. Soane, B.D. and Pidgeon, J.D., 1975. Tillage requirements in relation to soil physical properties. Soil Sci., 119: 376-384. S6hne, W.H., 1963. Tillage aspects. Canadian J. Agric. Eng., 5: 2-3, 8. Taylor, H.M., Parker, J.J. and Roberson, G.M., 1966. Soil strength and seedling emergence relations. II. A generalized relations for Gramineae. Agron. J., 58: 393-395. Tingxi, M. and Zengrui, X., 1989. An experimental study of power disk tool driven by tractor P.T.O. Proc. Int. Symp. on Agric. Eng., Beijing, PR China, 12-15 September 1989, International Academic Publishers, pp. 250-256. Yassen, H.A., Hassan, H.M. and Hammadi, I.A., 1992. Effect of plowing depths using different plow types on some physical properties of soil. Agric. Mech. Asia Africa Latin America, 23:21-24. Young, P., 1976. A machine to increase productivity of a tillage operation. Trans. ASAE, 19:10551061. Zrazhevskiy, A.I. and Nazarenko, G.V., 1969. The effect of the physical state of the plow layer of the soil on the growth of crop plants. Soviet Soil Sci., 6: 691-701.