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Effects of direction of rotation of a rotary tiller on properties of Bangkok clay soil
Soil & Tillage Research 63 (2001) 65±74
Effects of direction of rotation of a rotary tiller on properties of Bangkok clay soil V.M. Salokhe*, N. Ramalingam School of Environment, Resources and Development, AASE Program, Asian Institute of Technology, P.O. Box 4, Klang Luang, Pathumthani 12120, Thailand Received 19 April 2000; received in revised form 20 July 2001; accepted 1 August 2001
Abstract Experiments were conducted in a Bangkok clay soil to investigate the effects of reverse rotation of a rotary tiller on soil properties. Tests were conducted in wet land as well as in dry land. The performance was compared with that of the conventional C-type rotary tiller under similar conditions. New types of blades were designed for mounting on the reverserotary tiller. Tests were conducted at tractor forward speeds of 1.0, 1.5 and 2.0 km/h. The results indicated that the reverse-rotary tiller performed better than the C-type rotary tiller in terms of chopping and burial of weeds. The C-type rotary tiller performed slightly better than the reverse-rotary tiller in terms of puddling index (maximum 33% compared to 26.3% by rotary tiller), viscosity, falling cone penetration (minimum cone index of 116.7 kPa compared to 180.1 kPa for rotary tiller) and bulk density reduction. Shear strength and cone index values (% reduction in cone index ranged from 25.8 to 27.5%) were not signi®cantly different for the reverse-rotary and C-type rotary tiller. In the dry land tests, the reverse-rotary tiller performed better than the C-type rotary tiller in terms of reduction of shear strength and cone index. # 2001 Elsevier Science B.V. All rights reserved. Keywords: Rotary tiller; Clay soil; Reverse rotation; Soil properties
1. Introduction Almost 80% of the paddy in Asia is grown in wet lands. Puddling destroys the weeds and facilitates the transplanting of paddy seedlings. Rautary et al. (1997) stated that puddling up to a 10±15 cm depth is adequate to disperse organic matter at the bottom of the puddle and that there is no justi®cation to puddle any deeper. For measuring the degree of puddling, the viscosity of puddled soil has been used as an index. Some other indices used are aggregate size distribution, decrease in percolation rate and speci®c weight of puddled soil. It *
Corresponding author. Tel.: 66-2-524-5479; fax: 66-2-524-6200. E-mail address: [email protected] (V.M. Salokhe).
must be noted that no single index can be used to describe the quality of a puddled bed because of various limiting soil characteristics. Rotary tillers prepare the seed bed fundamentally different than the conventional method of plowing. The soil is pulverized by the cutting and chopping action of a number of blades that receive energy from the engine of the prime mover. It was reported that the performance of the transplanter lowered when the soil was not suf®ciently soft and leveled after puddling. As far as the quality of the seedbed is concerned, one pass of the rotary tiller is equivalent to several conventional tillage operations (Mandang et al., 1993). Shibusawa (1993) found that the reverse-rotary tiller cuts and throws the soil backwards in the form of large sliced soil clods. Because of this, there is reduction in re-tillage of tilled
0167-1987/01/$ ± see front matter # 2001 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 7 - 1 9 8 7 ( 0 1 ) 0 0 2 3 5 - 5
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soil, and the power requirement is reduced. The rotary axle rotates against the direction of the tractor tires. Deep rotary tillage provides a better mixing of the soil. Sakai (1978) observed that soil slices of medium soil of paddy ®elds cannot be thrown by one cutting pass of the blade. The action of a rotary machine on the soil and plant roots is mostly by impact, during which there is a sudden concentration of stresses in the soil being tilled due to its inertia. That is why the knives of a rotary cultivator can pulverize hard clods on the ®eld surface and till peat soils with high organic content and mineral soils without getting clogged (Bernacki et al., 1972). Boccafogli et al. (1992) veri®ed the cyclic behavior of the soil cutting effect. Their tests clearly showed the existence of cyclic phenomena in¯uencing the behavior of the force in the time domain. The conventional rotary tiller with forward motion can add to forward thrust. Kosutic et al. (1997) found that the best combination with respect to minimum energy requirement and highest rate of work for a rotary tiller was 4.87 km/h working speed, 12 cm depth of tillage and 5.91 m/s peripheral tine velocity. Shibusawa (1993) stated that a noticeable reduction of tiller power requirements was achieved by using a reverse-rotary tillage. The soil movement depended upon the direction of rotation and the ratio of tilling depth to blade radius. Kataoka et al. (1995) stated that reverse-rotary tillers equipped with special blades called ``Sukui-zume'' could successfully do deep rotary tillage with reduced power requirements due to their superior backward throwing of the tilled soil. No work has been done on the reverse rotation of rotary tillers in Bangkok clay soil. This study was intended to investigate the effects of reverse rotation on the rotary tiller in an actual paddy ®eld under puddled conditions as well as in dry land conditions. Salokhe and Ramlingam (2001) have reported the results of the effect of rotation on power and draft requirements of the rotavator in another paper. 2. Materials and method Experiments were conducted in Bangkok clay soil at the institute's experiment farm located at 148040 N latitude and 1008370 E longitude (Ramlingam, 1998). The soil contained 61% clay, 34% silt and 5% sand.
Fig. 1. (a) Scoop type blades used on reverse-rotary tiller; (b) Ctype blades used on conventional rotavator.
The liquid and plastic limits were 47 and 27%, respectively. The sticky limit was 34%. The last crop planted in the ®eld was rice, and the ®eld was left fallow for 4 months. The whole ®eld was sub-divided into six equally sized rectangular plots of 48 m 48 m. A four-wheel tractor was used to pull and power the rotavator. New types of blades with straight tines and a scoop surface at the end were designed and fabricated in a workshop (Fig. 1). Two rotary tillers of the same width of 1.38 m were used for performance evaluation. One was a conventional rotavator with 32 C-type tines, and the other was a rotary tiller with reverse rotation having scoop-type blades with 32 tines on the rotor. Each rotavator was tested in the wet land, which was irrigated 1 week before the test runs. At least 3±5 cm of water level was maintained during the tests. Three passes were made on each plot. Tests were also conducted in a dry ®eld with moisture
V.M. Salokhe, N. Ramalingam / Soil & Tillage Research 63 (2001) 65±74
content near the ®eld capacity. The same procedure as used in the wet land testing was used in these tests too. Tests were conducted at forward speeds of 1.0, 1.5 and 2.0 km/h. During the experiment, width of cut (1380 mm), depth of standing water (3±5 cm) and average depth of cut (15 cm) were kept constant. The soil properties were also measured for 0 pass (before test runs). The soil properties were measured both in the wet and dry land. The following soil properties were assessed and analyzed after every test run. Moisture content of the soil samples were determined by the oven method. For a falling cone penetrometer test, the cone penetrometer of 3.6 cm diameter, 4.4 cm height, and 115 g weight was used (Kanai, 1980). It was dropped from a height of 1 m in clay loam textured soil. A cone of the same speci®cation was used to determine the strength of the puddled soil. For each replication, at least ®ve tests were conducted at randomly selected places. The penetration readings were taken after 0.5± 1 h of puddling. The standard cone of 3.14 cm2 base area was used to measure the cone penetration resistance. Viscosity was determined using the Brook®eld viscometer after the removal of trash from the samples. Quality of puddling was assessed by using the method suggested by Badhe et al. (1984). The slurry used for measuring the viscosity was also used for measuring the puddling index. The slurry was allowed to settle for 24 h after which puddling index was directly measured from the settled soil and volume of the total sample. Puddling index can be determined using the following formula (Badhe et al., 1984): IP %
Vs 100 Vt
where IP is the index of puddling (%), Vs the volume of settled soil (cm3), Vt the total volume of sample (cm3). Shear strength of the soil was measured using the vane tester. The results were multiplied by the vane factor to achieve values in kilogram per square centimeter. Soil pulverization was quanti®ed in the case of dry land tests. The pulverized soil was observed visually and soil samples were taken and analyzed by performing a sieve analysis. The method followed by Ram et al. (1980) was used for this analysis. The tests consisted of determination of the amount of clods retained in each ASTM (American Standard for Testing Materials) standard sieve.
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The ®eld was irrigated several days before starting the experiments, so that the soil was saturated before puddling. The required soil properties (moisture content, bulk density, cone index, hydraulic conductivity and shear strength) were measured. The instruments, like transducers, ampli®er and data recorder, were checked for proper functioning and kept ready for use. Each test was replicated thrice. 3. Results and discussion 3.1. Soil properties before puddling The results were statistically analyzed using a T-test at 95% level of signi®cance for comparing the initial ®eld conditions before puddling. The results showed that the initial conditions of the different ®eld plots were almost the same. The soil properties after puddling were compared with those soil properties before puddling. They were compared in terms of % bulk density reduction, % increase in dropping cone penetration, % reduction in cone index, % variation of puddling index and viscosity ratio. The particle size distribution of the soil at the test site was measured. 3.2. Effects of C-type blades on wet clay soil properties The number of passes as well as tractor forward speed affected both the moisture content and bulk density. Moisture content is inversely proportional to the bulk density. Moisture content increased as the number of passes increased, whereas the bulk density decreased as the number of passes increased. This may be because the soil became more pulverized as the number of passes increased, and porosity reduced as the air space was ®lled with water. At 1.0 km/h forward speed, moisture content increased from 56.8% at pass 1 to 57.3% at pass 2, and to 63.5% at pass 3. At 1.5 km/h forward speed, it increased from 51.9% at pass 1 to 58.9% at pass 2, and to 60.8% at pass 3 (Table 1). At 2.0 km/h forward speed, it increased from 56.0% at pass 1 to 61.0% at pass 2, and to 66.9% at pass 3. The statistical tests showed that the forward speed affected the moisture content signi®cantly at a 95% level. The number of passes also affected the moisture content signi®cantly at a
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Table 1 Effect of number of pass and tractor forward speed on different wet soil propertiesa Rotor type
Forward speed (km/h)
Pass
MC (d.b.) (%)
BD (10
Rotary tiller with scoop-type blades
1.0
1 2 3 1 2 3 1 2 3
51.8 63.8 75.5 56.9 69.2 83.8 64.8 70.3 79.4
j f c i d a f d b
1 2 3 1 2 3 1 2 3
56.8 57.3 63.5 51.9 58.9 60.8 56.0 61.0 66.9
i i f j h g i g e
1.5 2.0
Rotary tiller with C-type blades
1.0 1.5 2.0
LSD 5%
1.71
FCP (cm)
CI (kPa)
Viscosity (P)
PI (%)
1137.9 a 975.3 j 959.5 n 1072.8 e 937.7 o 859.3 p 991.0 i 968.8 k 962.0 m
8.9 hij 11.9 cde 13.3 abc 8.7 hij 10.1 fgh 11.9 cde 7.9 j 11.0 efg 11.5 def
212.8 180.1 158.0 305.4 239.2 226.0 258.7 225.1 192.5
f i k a c e b e h
0.039 0.044 0.047 0.034 0.041 0.045 0.033 0.035 0.039
g cd ab hij efg bc ij hi g
17.4 21.2 26.3 14.1 19.2 23.2 13.1 16.8 19.9
h fg d i g e i h fg
1104.8 d 1058.0 f 990.5 i 1111.2 c 1073.8 e 1050.8 g 1122.6 b 1040.4 h 966.98 l
9.7 ghi 12.7 abcd 14.1 a 8.6 hij 11.4 def 13.8 ab 8.2 ij 10.8 efg 12.3 bcde
154.7 125.5 116.7 198.6 180.1 143.9 227.8 211.9 169.5
l n o g j m d f j
0.040 0.043 0.048 0.036 0.042 0.044 0.032 0.036 0.040
fg cde a h def cd j h fg
22.9 27.1 33.0 19.2 26.2 30.1 18.3 25.6 28.4
ef cd a g d b gh d bc
1.71
1.64
1.71
4
kN/m3)
0.002
1.71
a MC: moisture content; d.b.: dry basis; BD: bulk density; FCP: falling cone penetration; CI: cone index; PI: puddling index. Columns compared, not rows. Data with the same following letter indicates no signi®cant difference in values at 5% level.
95% level of signi®cance, whereas the values of bulk density were signi®cantly different at a 95% level of signi®cance. 3.2.1. Falling cone penetration The strength of the soil reduced after every pass of rotavator. Hence the falling cone penetration level increased after each pass at all forward speeds. Tractor forward speed also affected the falling cone penetration level. When the forward speed increased, the soil clods formed were of larger size and pulverization was less. This contributed to a decrease in the levels of falling cone penetration at increasing forward speeds. Statistical test results proved that the forward speed affected the falling cone penetration signi®cantly at a 95% level, whereas the number of passes affected it signi®cantly at a 99% level. 3.2.2. Cone index The percentage reduction in cone penetration resistance measured by cone penetrometer indicated the puddling quality. The higher the reduction, the better the puddling quality. Cone index was reduced by
24.56% between the ®rst and third passes at 1.0 km/ h forward speed. At 1.5 km/h forward speed, the cone index reduced by 27.5% between the ®rst and third passes. At 2.0 km/h forward speed, it reduced by 25.5% between the ®rst and third passes. This shows that the number of passes had a considerable effect on the percentage reduction in the cone index values. 3.2.3. Puddling index Puddling index indicates the quality of puddling. If the puddling is proper, there is better churning of soil. Hence the soil particles take more time for settling. After the ®rst pass, the soil clods are larger in size and settle down more quickly than the soil clods after the third pass that were dispersed and kept in suspension for a longer time. The maximum value of puddling index was 33.0% after pass 1 at 1.0 km/h forward speed. The minimum value of puddling index was 18.3% after pass 1 at 2.0 km/h forward speed. As the forward speed increased, the bite length became longer and the soil clods were larger in size. Statistical analysis showed that the forward speed affected the puddling index values signi®cantly at a 95% level. The
V.M. Salokhe, N. Ramalingam / Soil & Tillage Research 63 (2001) 65±74
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strength at 5 cm depth between the ®rst and third passes at 1.0 km/h forward speed was 72.1%. It was 69.8% at 10 cm depth and 72.9% at 15 cm depth. Since the depth of operation was restricted to 15 cm, the percentage reduction at 20 cm was not very high. Still there was some reduction in the shear strength values after three passes. As the soil became weak with the increase in the number of passes, the depth of operation might have exceeded 15 cm. The same trend followed for other forward speeds also. Statistical results proved that the number of passes did not affect the shear strength signi®cantly. Forward speed also did not affect the shear strength values signi®cantly. This might be due to the dif®culty of measuring the minute differences in the shear strength values of the puddled soil.
number of passes also affected the puddling index signi®cantly at a 95% level. 3.2.4. Viscosity As the number of passes increased, the viscosity of the puddled slurry also increased at all forward speeds. The increase in forward speed reduced the viscosity of the slurry for the corresponding passes. The maximum viscosity of the slurry of 0.049 P was obtained at 1.0 km/h forward speed after the third pass. The minimum viscosity was 0.033 P at 2.0 km/h forward speed after the ®rst pass. The forward speed affected the viscosity signi®cantly at a 99% level. The number of passes affected the viscosity signi®cantly at a 99% level. 3.2.5. Shear strength Puddling quality is indicated by the shear strength of the puddled soil. As the number of passes increased, the shear strength reduced sharply. As the moisture content of the soil increased, there was a reduction in the shear strength of the soil. This was explained by Salokhe and Gee-Clough (1988) who reported that the shear strength of the clay soil falls when the moisture content increases. The percentage reduction in shear
3.3. Effects of reverse rotation on wet clay soil properties 3.3.1. Moisture content and bulk density Moisture content of the soil increased from 51.8% after pass 1 to 75.5% after pass 3 at 1.0 km/h forward speed (Table 2). It increased from 56.9% after pass 1 to
Table 2 Percentage reduction in cone index valuesa Type of tine
Forward speed (km/h)
Pass number
Rotary tiller with C-type blades
1.0
1 2 3 1 2 3 1 2 3
1.5 2.0
Rotary tiller with scoop-type blades
1.0 1.5 2.0
LSD 5% a
1 2 3 1 2 3 1 2 3
% reduction in cone index value
Total % reduction
18.8 bc 7.0 h
25.8
9.3 g 17.4 c
26.7
6.9 h 20.0 ab
26.9
15.3 d 12.2 f
27.5
21.6 a 5.7 h
27.3
12.9 ef 14.1 de
27.0
1.77
Columns compared not rows. Data with the same following letter indicates no signi®cant difference in values at 5% level.
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V.M. Salokhe, N. Ramalingam / Soil & Tillage Research 63 (2001) 65±74
83.8% after pass 2 at 1.5 km/h, and 64.8% after pass 1 to 79.4% after pass 3 at 2.0 km/h forward speed. Moisture content increased after every pass as the soil became very loose and held more moisture. The same trend of the rotary tiller with C-type blades was followed for the rotary tiller with reverse rotation having scoop-type blades also. Statistical results showed that the forward speed affected the moisture content signi®cantly at a 99% level of signi®cance. The number of passes also affected the moisture content signi®cantly at a 99% level of signi®cance for all forward speeds. Bulk density reduced after every pass at all forward speeds. The same reason for the reduction in the bulk density, which was stated for the forward rotation, can be attributed to the reverse rotation also. Statistical test results indicated that all the forward speeds affected the bulk density signi®cantly at a 90% level. The number of passes affected the bulk density at 1.0 and 1.5 km/h forward speeds signi®cantly at a 95% level, but there was no signi®cant difference between the passes at a 2.0 km/h forward speed. 3.3.2. Falling cone penetration The falling cone penetration level reduced as the forward speed increased, whereas it increased as the number of passes increased. The soil became very loose after each pass and the strength of the soil became less because of this. The details of falling cone penetration level for each pass at different forward speeds are given in Table 1. The maximum value of 13.3 cm was recorded after the third pass at 1.0 km/ h forward speed. The minimum falling cone penetration value was 7.9 cm after the ®rst pass at 2.0 km/h forward speed. The statistical test results indicated that increase in the number of passes decreased the falling cone penetration level signi®cantly at a 95% level at all forward speeds, whereas there was no signi®cant difference in the falling cone penetration level for different forward speeds. 3.3.3. Cone index There was a signi®cant reduction in the cone index values after every pass at all forward speeds. The cone index values dropped from 212.8 kPa after the ®rst pass to 158.0 kPa after the third pass (25.75% reduction) at 1.0 km/h forward speed. It reduced from 305.4 kPa after the ®rst pass to 226.0 kPa after the
third pass (25.9% reduction) at 1.5 km/h forward speed, and from 258.7 kPa after the ®rst pass to 192.5 kPa after the third pass (25.5% reduction) at 2.0 km/h forward speed (Table 1). Statistical test results indicated that the forward speed and the number of passes did not affect the cone index values signi®cantly. 3.3.4. Puddling index Puddling index increased with every pass at all forward speeds. It increased from 17.4% after the ®rst pass to 26.32% after the third pass at 1.0 km/h forward speed. The degree of increase was lower with an increase in the forward speed. It increased from 14.1% after the ®rst pass to 23.2% after the third pass at 1.5 km/h forward, and from 13.1% after the ®rst pass to 19.8% after the third pass at 2.0 km/h forward speed (Table 1). Statistical test results showed that both the forward speed and the number of passes affected the puddling index signi®cantly at a 95% level of signi®cance. 3.3.5. Viscosity The viscosity of the puddled slurry increased as the number of passes increased. The percentage increase of viscosity lowered as the forward speed increased. The soil clods were larger in size as the forward speed increased. The maximum viscosity of 0.047 P was obtained after the third pass at 1.0 km/h forward speed. The minimum viscosity of 0.033 P was obtained after the ®rst pass at 2.0 km/h forward speed. Statistical test results showed that both the forward speed and the number of passes affected the viscosity at a 99% level. 3.3.6. Shear strength As the number of passes increased, the shear strength values lowered considerably. The same trend was followed for all forward speeds. The percentage reduction in shear strength at 5 cm depth between the ®rst and third passes at 1.0 km/h forward speed was 60.52%. It was 65.62% at 10 cm depth and 67.3% at 15 cm depth. The same trend was seen for other forward speeds also. Statistical test results showed that the shear strength did not differ signi®cantly for both the number of passes and forward speeds. The same reason attributed for the cone index could be attributed for shear strength also.
V.M. Salokhe, N. Ramalingam / Soil & Tillage Research 63 (2001) 65±74
3.4. Comparison of effect on soil properties by conventional and reverse-rotary tillers 3.4.1. Moisture content and bulk density The increase in the number of passes increased the moisture content at all forward speeds for both types of rotary tillers. The moisture content values for the different forward speeds were nearly the same for both rotary tillers (Table 2). Statistical tests by one-way ANOVA indicated that the number of passes affected the moisture content signi®cantly at a 95% level. The forward speed also affected the moisture content signi®cantly at a 95% level for 1.0 and 1.5 km/h and at a 99% level for 2 km/h forward speed. 3.4.2. Bulk density The bulk density reduction was higher for the rotary tiller with reverse rotation having scoop-type blades than that for the C-type for all passes and forward speeds (Table 1). The percentage reduction of bulk density was higher between the ®rst and second passes than that of the second and third passes for all the forward speeds for both the types of rotary tillers. Statistical tests showed that the pass numbers and forward speeds affected the bulk density signi®cantly at a 90% level for both rotary tillers. At 1.5 km/h forward speed, the number of passes affected the bulk density at a 99% level of signi®cance. During the second pass at 1 km/h forward speed, the bulk density was signi®cantly different at 99% level. This happened during the second pass at 2 km/h forward speed also. During the third pass at 2 km/h forward speed, there was no signi®cant difference in the bulk density. 3.4.3. Falling cone penetration The falling cone penetration was higher for the rotary tiller with C-type blades than for the rotary tiller with reverse rotation having scoop-type blades for nearly all passes and at all forward speeds. The rotary tiller with reverse rotation having scoop-type blades made bigger soil clods than the C-type blade due to its scoop-shaped edge. There was a better churning action in the case of the C-type blade due to its curvature, whereas the reverse-rotary blade is straight in shape. Thus the falling cone penetration is higher for the C-type blades. Statistical tests showed that the falling cone penetration values were signi®cantly different at a 99% level of signi®cance for the
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third pass at 1.5 km/h forward speed, and at a 90% level of signi®cance for the second pass at 1.5 and 1.0 km/h forward speeds. For other passes and other speeds, the values were not signi®cantly different. Hence, both blades gave almost equal performance from the cone penetration point of view. 3.4.4. Cone index The percentage reduction of cone index values was greater for the rotary tiller with C-type blades than for the rotary tiller with reverse rotation having scooptype blades. The % reductions in cone index values up to 21 cm depth for each plot are given in Table 2 for both rotary tillers. The number of passes did have a considerable effect on the percentage reduction in the cone index values, whereas the forward speed did not have any effect in the % cone index reduction. The statistical test showed that the number of passes and forward speed did not affect the cone index values signi®cantly for both types of rotary tillers. Hence, the puddling quality in terms of percentage reduction of cone index values was the same for both rotary tillers. 3.4.5. Puddling index Maximum value of puddling index (33.0%) was obtained after the third pass of the rotary tiller with Ctype blades at 1.0 km/h forward speed. As the number of passes increased, the puddling index also increased. The soil was churned completely after the third pass for both blades. Minimum value of puddling index (13.1%) was obtained after the ®rst pass of the reverserotary tiller at 2.0 km/h forward speed. This shows that, when the forward speed increased, the puddling index reduced for the corresponding passes. Puddling index increased with the number of passes at all forward speeds. Under all conditions, the puddling index was higher for the rotary tiller with C-type blades. Statistically the puddling index was signi®cantly different at a 95% level for all forward speeds and passes. 3.4.6. Viscosity Viscosity increased as the number of passes increased for both blades. It reduced as the forward speed increased. Viscosity followed the same trend as that of the puddling index. Statistical tests indicated that the viscosity of the slurry was signi®cantly different at a 95% level for the ®rst pass at 1.5 km/h, after
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V.M. Salokhe, N. Ramalingam / Soil & Tillage Research 63 (2001) 65±74
the third pass at 2.0 km/h, and all the passes at 1.0 km/ h forward speed. Under these conditions, the viscosity of the slurry was higher for the rotary tiller with C-type blades than that for the rotary tiller with reverse rotation having scoop-type blades. At all other conditions, the viscosity of the slurry was the same for both rotary tillers. 3.4.7. Shear strength Shear strength lowered after every pass for all forward speeds for both rotary tillers. As the number of passes increased, not only was the soil churned more but the moisture content also increased. As the moisture content increased, the shear strength was lowered. This happened at all forward speeds for both blades. Statistically, the shear strength values were not signi®cantly different under any condition. Hence shear strength cannot be used as a criterion for determining the puddling quality of the blades. 3.5. Performance tests in dry land The performance of rotavators with both kinds of blades was evaluated in the dry ®eld. The quality of tilling was compared by visual observation and was substantiated by photographic evidence. The soil properties measured are tabulated in Table 3. The number of passes did not have any effect on the moisture content of the ®elds, which was about 20% when the experiments were conducted. The number of passes had a signi®cant effect on the bulk density reduction. The bulk density was reduced by 14.52%
between the zero and third passes for the rotary tiller with reverse rotation having scoop-type blades. For the rotary tiller with C-type blades, the reduction was 16.21%. Hence, both the rotary tillers performed equally well in terms of bulk density reduction. As the number of passes increased, the bulk density reduced (Table 3). Statistical test results indicated that the number of passes affected the bulk density signi®cantly at a 95% level of signi®cance. In terms of % reduction in cone index values, the rotary tiller with reverse rotation having scoop-type blades performed better than the rotary tiller with Ctype blades in dry soil. The % reduction in cone index values between the ®rst pass and third pass was 50.19% for the rotary tiller with reverse rotation having scoop-type blades. The corresponding value for the rotary tiller with C-type blades was 18.8%. In the case of the rotary tiller with reverse rotation having scoop-type blades, the cone index value reduced from 471.2 kPa (Table 3) after the ®rst pass to 269.2 kPa after the second pass (42.9% reduction). It was further reduced to 234.8 kPa after the third pass (13% reduction between the second and third passes). This shows that the soil was pulverized to a greater extent in one pass itself, whereas this phenomenon did not happen in the case of the rotary tiller with C-type blades, and the cone index reduced gradually at every pass. Shear strength of the soil decreased when the number of passes increased for both rotary tillers. The shear strength did not change at 20 cm depth as the depth of operation was restricted to 15 cm. It reduced from 0.05 kPa at zero pass to 0.006 kPa after
Table 3 Effect of pass and tractor forward speed on different dry soil propertiesa Rotor type
Forward speed (km/h)
Pass
Moisture content (d.b.) (%)
Bulk density (k/m3)
Cone index (kPa)
Rotary tiller with reverse rotation
1.5
0 1 2 3
19.4 20.6 19.1 19.2
a a a a
1146.6 c 1062.2 d 1002.3 e 979.5 g
686.7 471.2 269.2 234.8
b f g h
Rotary tiller with C-type blades
1.5
0 1 2 3
19.1 17.0 19.8 17.4
a a a a
1177.5 a 1158.4 b 1144.6 c 986.6 f
728.5 600.1 556.2 487.5
a c d e
5.13
5.13
LSD 5% a
5.13
Columns compared not rows. Data with the same following letter indicates no signi®cant difference in values at 5% level.
V.M. Salokhe, N. Ramalingam / Soil & Tillage Research 63 (2001) 65±74
the third pass for the rotary tiller with C-type blades at 5 cm depth (87.1% reduction). The corresponding values for the rotary tiller with reverse rotation having scoop-type blades were 0.048±0.005 kPa (90.0% reduction). The % reduction in the shear strength values between the zero pass and the ®rst pass was greater for the rotary tiller with reverse rotation having scoop-type blades at all depths. The required soil tilt and pulverization were achieved in fewer number of passes for the rotary tiller with reverse rotation having scoop-type blades, whereas at least three passes were required for the rotary tiller with C-type blades to achieve similar soil conditions. Statistical tests indicated no signi®cant difference, hence both tillers gave
73
almost equal performance in terms of shear strength reduction. 3.5.1. Clod size aggregate It was found that the rotary tiller with C-type blades produced clods of larger size than the rotary tiller with reverse rotation having scoop-type blades. This happened at all passes. The soil inversion of the rotary tiller with reverse rotation having scoop-type blades was good because of the scoop-shaped edge. This provided complete burial of the weeds even after the ®rst pass itself. The subsequent passes reduced the clods formed after the ®rst pass. Bigger soil clods were produced by both rotary tillers at the end of the
Fig. 2. Clod size distribution after tilling with C-type blade at 1.5 km/h forward speed.
Fig. 3. Clod size distribution after tilling with reverse-rotary blade at 1.5 km/h forward speed.
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®rst pass, and after the subsequent passes, the clod size reduced considerably. At the end of the ®rst pass, there was more uneven clod distribution for both rotary tillers, whereas at the end of the third pass, the clod size distribution was almost the same. The number of passes had a signi®cant effect on the clod size reduction. In the case of the rotary tiller with reverse rotation having scoop-type blades, pulverization was excessive. Figs. 2 and 3 show the effect of rotor passes on the soil aggregate sizes. Statistical analysis showed that aggregate sizes produced by C-type blades were different at 95% level of signi®cance (LSD0:5 0:92). The interaction effects of number of passes and aggregate size were also statistically signi®cant at 95% level (LSD0:5 1:59). A similar statistical result was also obtained for reverse-rotary tiller. 4. Conclusions The bulk density reduction was greater in wet land for the rotary tiller with reverse rotation having scooptype blades rather than C-type blades. In the dry land, the bulk density reduction was slightly more for the rotary tiller with C-type blades. The falling cone penetration and cone index values increased with every pass at all forward speeds for both rotary tillers. Cone index values reduced after every pass at all forward speeds for both rotary tillers. Cone index decreased when the number of passes increased at the same forward speed, but it decreased when the forward speed decreased at the same pass. The viscosity and puddling index of puddled soil were greater for the rotary tiller with C-type blades at all passes for all forward speeds. Both the number of passes and the forward speed had a signi®cant effect on viscosity of the puddled soil. It increased when the number of passes increased for all forward speeds, but reduced when the forward speed increased for all passes. Shear strength lowered after every pass for all forward speeds for both the rotary tiller with reverse rotation having scoop-type blades and the rotary tiller with C-type blades in the wet land and dry land. The rotary tiller with C-type blades produced clods of larger size than the rotary tiller with reverse rotation having scoop-type blades at all passes at 1.5 km/h forward speed.
In general, it can be concluded that the performance of the rotary tiller with reverse rotation having scooptype blades was better than that of the rotary tiller with C-type blades both in the wet land and dry land conditions at any pass and forward speed. References Badhe, V.T., Gupta, C.P., Bhole, N.G., 1984. Performance index for puddler. Paper Presented at XXI ISAE Conference, New Delhi, India. Bernacki, H., Haman, J., Kanfojki, C.Z., 1972. Agricultural Machines: Theory and Construction, Vol. 1. The Scienti®c Publications Foreign Cooperative. Center of Central Institute for Scienti®c Technical and Information, Warsaw, Poland, pp. 382±387. Boccafogli, A., Busatti, G., Gherardi, F., Malaguti, F., Paoluzzi, R., 1992. Experimental evaluation of cutting dynamic models in soil bin facility. J. Terramech. 29, 95±105. Kanai, K., 1980. Performance of rice transplanter as evaluation by National Test Center in Japan. Jpn. Agric. Res. Quart. 14, 84± 87. Kataoka, T., Onodera, K., Shibusawa, S., Ota, Y., 1995. A model for backward throwing of sliced soil clods by a reverserotational rotary tiller using rigid body kinematics. In: Proceedings of the Fourth Asia±Paci®c Conference of the ISTVS, Okinawa, Japan, November 20±22, 1995, pp. 339± 346. Kosutic, S., Filipovic, D., Gospodaric, Z., 1997. Agro-technical and energetic characteristics of a rotary cultivator with spike tines in seedbed preparation. Agric. Eng. J. 6, 137±144. Mandang, T., Al, F., Hayashi, N., Watanabe, S., Tojo, S., 1993. Studies on the overturning properties of soil by rotary blade using CT image analyzer. ASAE Paper No. 93-3035. American Society of Agricultural Engineers, St. Joseph, MI. Ram, R.B., Singh, S., Verma, S.R., 1980. Comparative performance of some new and conventional tillage equipment. J. Agric. Eng. ISAE 17, 7±13. Ramlingam, N., 1998. Effects of direction of rotation on the performance of a rotary tiller in Bangkok clay soil. M.E. Thesis No. AE-98-1. Asian Institute of Technology, unpublished. Rautary, S.K., Watts, C.W., Dexter, A.R., 1997. Puddling effects on soil physical parameters. Agric. Mech. Asia, Africa and Latin America 28, 37±40. Sakai, J., 1978. Designing process and theories of rotary blades for better rotary tillage (Part I). Jpn. Agric. Res. Quart. 12, 86±93. Salokhe, V.M., Gee-Clough, D., 1988. Working with Bangkok clay soil Ð some experiences. Agric. Mech. Asia, Africa and Latin America 19, 33±41. Salokhe, V.M., Ramlingam, N., 2001. Effect of reverse-rotation on power and draft requirement of a rotavator. J. Terramech., in press. Shibusawa, S., 1993. Reverse rotational rotary tiller for reduced power requirement in deep tillage. J. Terramech. 30, 205±217.
Effects of direction of rotation of a rotary tiller on properties of Bangkok clay soil V.M. Salokhe*, N. Ramalingam School of Environment, Resources and Development, AASE Program, Asian Institute of Technology, P.O. Box 4, Klang Luang, Pathumthani 12120, Thailand Received 19 April 2000; received in revised form 20 July 2001; accepted 1 August 2001
Abstract Experiments were conducted in a Bangkok clay soil to investigate the effects of reverse rotation of a rotary tiller on soil properties. Tests were conducted in wet land as well as in dry land. The performance was compared with that of the conventional C-type rotary tiller under similar conditions. New types of blades were designed for mounting on the reverserotary tiller. Tests were conducted at tractor forward speeds of 1.0, 1.5 and 2.0 km/h. The results indicated that the reverse-rotary tiller performed better than the C-type rotary tiller in terms of chopping and burial of weeds. The C-type rotary tiller performed slightly better than the reverse-rotary tiller in terms of puddling index (maximum 33% compared to 26.3% by rotary tiller), viscosity, falling cone penetration (minimum cone index of 116.7 kPa compared to 180.1 kPa for rotary tiller) and bulk density reduction. Shear strength and cone index values (% reduction in cone index ranged from 25.8 to 27.5%) were not signi®cantly different for the reverse-rotary and C-type rotary tiller. In the dry land tests, the reverse-rotary tiller performed better than the C-type rotary tiller in terms of reduction of shear strength and cone index. # 2001 Elsevier Science B.V. All rights reserved. Keywords: Rotary tiller; Clay soil; Reverse rotation; Soil properties
1. Introduction Almost 80% of the paddy in Asia is grown in wet lands. Puddling destroys the weeds and facilitates the transplanting of paddy seedlings. Rautary et al. (1997) stated that puddling up to a 10±15 cm depth is adequate to disperse organic matter at the bottom of the puddle and that there is no justi®cation to puddle any deeper. For measuring the degree of puddling, the viscosity of puddled soil has been used as an index. Some other indices used are aggregate size distribution, decrease in percolation rate and speci®c weight of puddled soil. It *
Corresponding author. Tel.: 66-2-524-5479; fax: 66-2-524-6200. E-mail address: [email protected] (V.M. Salokhe).
must be noted that no single index can be used to describe the quality of a puddled bed because of various limiting soil characteristics. Rotary tillers prepare the seed bed fundamentally different than the conventional method of plowing. The soil is pulverized by the cutting and chopping action of a number of blades that receive energy from the engine of the prime mover. It was reported that the performance of the transplanter lowered when the soil was not suf®ciently soft and leveled after puddling. As far as the quality of the seedbed is concerned, one pass of the rotary tiller is equivalent to several conventional tillage operations (Mandang et al., 1993). Shibusawa (1993) found that the reverse-rotary tiller cuts and throws the soil backwards in the form of large sliced soil clods. Because of this, there is reduction in re-tillage of tilled
0167-1987/01/$ ± see front matter # 2001 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 7 - 1 9 8 7 ( 0 1 ) 0 0 2 3 5 - 5
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soil, and the power requirement is reduced. The rotary axle rotates against the direction of the tractor tires. Deep rotary tillage provides a better mixing of the soil. Sakai (1978) observed that soil slices of medium soil of paddy ®elds cannot be thrown by one cutting pass of the blade. The action of a rotary machine on the soil and plant roots is mostly by impact, during which there is a sudden concentration of stresses in the soil being tilled due to its inertia. That is why the knives of a rotary cultivator can pulverize hard clods on the ®eld surface and till peat soils with high organic content and mineral soils without getting clogged (Bernacki et al., 1972). Boccafogli et al. (1992) veri®ed the cyclic behavior of the soil cutting effect. Their tests clearly showed the existence of cyclic phenomena in¯uencing the behavior of the force in the time domain. The conventional rotary tiller with forward motion can add to forward thrust. Kosutic et al. (1997) found that the best combination with respect to minimum energy requirement and highest rate of work for a rotary tiller was 4.87 km/h working speed, 12 cm depth of tillage and 5.91 m/s peripheral tine velocity. Shibusawa (1993) stated that a noticeable reduction of tiller power requirements was achieved by using a reverse-rotary tillage. The soil movement depended upon the direction of rotation and the ratio of tilling depth to blade radius. Kataoka et al. (1995) stated that reverse-rotary tillers equipped with special blades called ``Sukui-zume'' could successfully do deep rotary tillage with reduced power requirements due to their superior backward throwing of the tilled soil. No work has been done on the reverse rotation of rotary tillers in Bangkok clay soil. This study was intended to investigate the effects of reverse rotation on the rotary tiller in an actual paddy ®eld under puddled conditions as well as in dry land conditions. Salokhe and Ramlingam (2001) have reported the results of the effect of rotation on power and draft requirements of the rotavator in another paper. 2. Materials and method Experiments were conducted in Bangkok clay soil at the institute's experiment farm located at 148040 N latitude and 1008370 E longitude (Ramlingam, 1998). The soil contained 61% clay, 34% silt and 5% sand.
Fig. 1. (a) Scoop type blades used on reverse-rotary tiller; (b) Ctype blades used on conventional rotavator.
The liquid and plastic limits were 47 and 27%, respectively. The sticky limit was 34%. The last crop planted in the ®eld was rice, and the ®eld was left fallow for 4 months. The whole ®eld was sub-divided into six equally sized rectangular plots of 48 m 48 m. A four-wheel tractor was used to pull and power the rotavator. New types of blades with straight tines and a scoop surface at the end were designed and fabricated in a workshop (Fig. 1). Two rotary tillers of the same width of 1.38 m were used for performance evaluation. One was a conventional rotavator with 32 C-type tines, and the other was a rotary tiller with reverse rotation having scoop-type blades with 32 tines on the rotor. Each rotavator was tested in the wet land, which was irrigated 1 week before the test runs. At least 3±5 cm of water level was maintained during the tests. Three passes were made on each plot. Tests were also conducted in a dry ®eld with moisture
V.M. Salokhe, N. Ramalingam / Soil & Tillage Research 63 (2001) 65±74
content near the ®eld capacity. The same procedure as used in the wet land testing was used in these tests too. Tests were conducted at forward speeds of 1.0, 1.5 and 2.0 km/h. During the experiment, width of cut (1380 mm), depth of standing water (3±5 cm) and average depth of cut (15 cm) were kept constant. The soil properties were also measured for 0 pass (before test runs). The soil properties were measured both in the wet and dry land. The following soil properties were assessed and analyzed after every test run. Moisture content of the soil samples were determined by the oven method. For a falling cone penetrometer test, the cone penetrometer of 3.6 cm diameter, 4.4 cm height, and 115 g weight was used (Kanai, 1980). It was dropped from a height of 1 m in clay loam textured soil. A cone of the same speci®cation was used to determine the strength of the puddled soil. For each replication, at least ®ve tests were conducted at randomly selected places. The penetration readings were taken after 0.5± 1 h of puddling. The standard cone of 3.14 cm2 base area was used to measure the cone penetration resistance. Viscosity was determined using the Brook®eld viscometer after the removal of trash from the samples. Quality of puddling was assessed by using the method suggested by Badhe et al. (1984). The slurry used for measuring the viscosity was also used for measuring the puddling index. The slurry was allowed to settle for 24 h after which puddling index was directly measured from the settled soil and volume of the total sample. Puddling index can be determined using the following formula (Badhe et al., 1984): IP %
Vs 100 Vt
where IP is the index of puddling (%), Vs the volume of settled soil (cm3), Vt the total volume of sample (cm3). Shear strength of the soil was measured using the vane tester. The results were multiplied by the vane factor to achieve values in kilogram per square centimeter. Soil pulverization was quanti®ed in the case of dry land tests. The pulverized soil was observed visually and soil samples were taken and analyzed by performing a sieve analysis. The method followed by Ram et al. (1980) was used for this analysis. The tests consisted of determination of the amount of clods retained in each ASTM (American Standard for Testing Materials) standard sieve.
67
The ®eld was irrigated several days before starting the experiments, so that the soil was saturated before puddling. The required soil properties (moisture content, bulk density, cone index, hydraulic conductivity and shear strength) were measured. The instruments, like transducers, ampli®er and data recorder, were checked for proper functioning and kept ready for use. Each test was replicated thrice. 3. Results and discussion 3.1. Soil properties before puddling The results were statistically analyzed using a T-test at 95% level of signi®cance for comparing the initial ®eld conditions before puddling. The results showed that the initial conditions of the different ®eld plots were almost the same. The soil properties after puddling were compared with those soil properties before puddling. They were compared in terms of % bulk density reduction, % increase in dropping cone penetration, % reduction in cone index, % variation of puddling index and viscosity ratio. The particle size distribution of the soil at the test site was measured. 3.2. Effects of C-type blades on wet clay soil properties The number of passes as well as tractor forward speed affected both the moisture content and bulk density. Moisture content is inversely proportional to the bulk density. Moisture content increased as the number of passes increased, whereas the bulk density decreased as the number of passes increased. This may be because the soil became more pulverized as the number of passes increased, and porosity reduced as the air space was ®lled with water. At 1.0 km/h forward speed, moisture content increased from 56.8% at pass 1 to 57.3% at pass 2, and to 63.5% at pass 3. At 1.5 km/h forward speed, it increased from 51.9% at pass 1 to 58.9% at pass 2, and to 60.8% at pass 3 (Table 1). At 2.0 km/h forward speed, it increased from 56.0% at pass 1 to 61.0% at pass 2, and to 66.9% at pass 3. The statistical tests showed that the forward speed affected the moisture content signi®cantly at a 95% level. The number of passes also affected the moisture content signi®cantly at a
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Table 1 Effect of number of pass and tractor forward speed on different wet soil propertiesa Rotor type
Forward speed (km/h)
Pass
MC (d.b.) (%)
BD (10
Rotary tiller with scoop-type blades
1.0
1 2 3 1 2 3 1 2 3
51.8 63.8 75.5 56.9 69.2 83.8 64.8 70.3 79.4
j f c i d a f d b
1 2 3 1 2 3 1 2 3
56.8 57.3 63.5 51.9 58.9 60.8 56.0 61.0 66.9
i i f j h g i g e
1.5 2.0
Rotary tiller with C-type blades
1.0 1.5 2.0
LSD 5%
1.71
FCP (cm)
CI (kPa)
Viscosity (P)
PI (%)
1137.9 a 975.3 j 959.5 n 1072.8 e 937.7 o 859.3 p 991.0 i 968.8 k 962.0 m
8.9 hij 11.9 cde 13.3 abc 8.7 hij 10.1 fgh 11.9 cde 7.9 j 11.0 efg 11.5 def
212.8 180.1 158.0 305.4 239.2 226.0 258.7 225.1 192.5
f i k a c e b e h
0.039 0.044 0.047 0.034 0.041 0.045 0.033 0.035 0.039
g cd ab hij efg bc ij hi g
17.4 21.2 26.3 14.1 19.2 23.2 13.1 16.8 19.9
h fg d i g e i h fg
1104.8 d 1058.0 f 990.5 i 1111.2 c 1073.8 e 1050.8 g 1122.6 b 1040.4 h 966.98 l
9.7 ghi 12.7 abcd 14.1 a 8.6 hij 11.4 def 13.8 ab 8.2 ij 10.8 efg 12.3 bcde
154.7 125.5 116.7 198.6 180.1 143.9 227.8 211.9 169.5
l n o g j m d f j
0.040 0.043 0.048 0.036 0.042 0.044 0.032 0.036 0.040
fg cde a h def cd j h fg
22.9 27.1 33.0 19.2 26.2 30.1 18.3 25.6 28.4
ef cd a g d b gh d bc
1.71
1.64
1.71
4
kN/m3)
0.002
1.71
a MC: moisture content; d.b.: dry basis; BD: bulk density; FCP: falling cone penetration; CI: cone index; PI: puddling index. Columns compared, not rows. Data with the same following letter indicates no signi®cant difference in values at 5% level.
95% level of signi®cance, whereas the values of bulk density were signi®cantly different at a 95% level of signi®cance. 3.2.1. Falling cone penetration The strength of the soil reduced after every pass of rotavator. Hence the falling cone penetration level increased after each pass at all forward speeds. Tractor forward speed also affected the falling cone penetration level. When the forward speed increased, the soil clods formed were of larger size and pulverization was less. This contributed to a decrease in the levels of falling cone penetration at increasing forward speeds. Statistical test results proved that the forward speed affected the falling cone penetration signi®cantly at a 95% level, whereas the number of passes affected it signi®cantly at a 99% level. 3.2.2. Cone index The percentage reduction in cone penetration resistance measured by cone penetrometer indicated the puddling quality. The higher the reduction, the better the puddling quality. Cone index was reduced by
24.56% between the ®rst and third passes at 1.0 km/ h forward speed. At 1.5 km/h forward speed, the cone index reduced by 27.5% between the ®rst and third passes. At 2.0 km/h forward speed, it reduced by 25.5% between the ®rst and third passes. This shows that the number of passes had a considerable effect on the percentage reduction in the cone index values. 3.2.3. Puddling index Puddling index indicates the quality of puddling. If the puddling is proper, there is better churning of soil. Hence the soil particles take more time for settling. After the ®rst pass, the soil clods are larger in size and settle down more quickly than the soil clods after the third pass that were dispersed and kept in suspension for a longer time. The maximum value of puddling index was 33.0% after pass 1 at 1.0 km/h forward speed. The minimum value of puddling index was 18.3% after pass 1 at 2.0 km/h forward speed. As the forward speed increased, the bite length became longer and the soil clods were larger in size. Statistical analysis showed that the forward speed affected the puddling index values signi®cantly at a 95% level. The
V.M. Salokhe, N. Ramalingam / Soil & Tillage Research 63 (2001) 65±74
69
strength at 5 cm depth between the ®rst and third passes at 1.0 km/h forward speed was 72.1%. It was 69.8% at 10 cm depth and 72.9% at 15 cm depth. Since the depth of operation was restricted to 15 cm, the percentage reduction at 20 cm was not very high. Still there was some reduction in the shear strength values after three passes. As the soil became weak with the increase in the number of passes, the depth of operation might have exceeded 15 cm. The same trend followed for other forward speeds also. Statistical results proved that the number of passes did not affect the shear strength signi®cantly. Forward speed also did not affect the shear strength values signi®cantly. This might be due to the dif®culty of measuring the minute differences in the shear strength values of the puddled soil.
number of passes also affected the puddling index signi®cantly at a 95% level. 3.2.4. Viscosity As the number of passes increased, the viscosity of the puddled slurry also increased at all forward speeds. The increase in forward speed reduced the viscosity of the slurry for the corresponding passes. The maximum viscosity of the slurry of 0.049 P was obtained at 1.0 km/h forward speed after the third pass. The minimum viscosity was 0.033 P at 2.0 km/h forward speed after the ®rst pass. The forward speed affected the viscosity signi®cantly at a 99% level. The number of passes affected the viscosity signi®cantly at a 99% level. 3.2.5. Shear strength Puddling quality is indicated by the shear strength of the puddled soil. As the number of passes increased, the shear strength reduced sharply. As the moisture content of the soil increased, there was a reduction in the shear strength of the soil. This was explained by Salokhe and Gee-Clough (1988) who reported that the shear strength of the clay soil falls when the moisture content increases. The percentage reduction in shear
3.3. Effects of reverse rotation on wet clay soil properties 3.3.1. Moisture content and bulk density Moisture content of the soil increased from 51.8% after pass 1 to 75.5% after pass 3 at 1.0 km/h forward speed (Table 2). It increased from 56.9% after pass 1 to
Table 2 Percentage reduction in cone index valuesa Type of tine
Forward speed (km/h)
Pass number
Rotary tiller with C-type blades
1.0
1 2 3 1 2 3 1 2 3
1.5 2.0
Rotary tiller with scoop-type blades
1.0 1.5 2.0
LSD 5% a
1 2 3 1 2 3 1 2 3
% reduction in cone index value
Total % reduction
18.8 bc 7.0 h
25.8
9.3 g 17.4 c
26.7
6.9 h 20.0 ab
26.9
15.3 d 12.2 f
27.5
21.6 a 5.7 h
27.3
12.9 ef 14.1 de
27.0
1.77
Columns compared not rows. Data with the same following letter indicates no signi®cant difference in values at 5% level.
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V.M. Salokhe, N. Ramalingam / Soil & Tillage Research 63 (2001) 65±74
83.8% after pass 2 at 1.5 km/h, and 64.8% after pass 1 to 79.4% after pass 3 at 2.0 km/h forward speed. Moisture content increased after every pass as the soil became very loose and held more moisture. The same trend of the rotary tiller with C-type blades was followed for the rotary tiller with reverse rotation having scoop-type blades also. Statistical results showed that the forward speed affected the moisture content signi®cantly at a 99% level of signi®cance. The number of passes also affected the moisture content signi®cantly at a 99% level of signi®cance for all forward speeds. Bulk density reduced after every pass at all forward speeds. The same reason for the reduction in the bulk density, which was stated for the forward rotation, can be attributed to the reverse rotation also. Statistical test results indicated that all the forward speeds affected the bulk density signi®cantly at a 90% level. The number of passes affected the bulk density at 1.0 and 1.5 km/h forward speeds signi®cantly at a 95% level, but there was no signi®cant difference between the passes at a 2.0 km/h forward speed. 3.3.2. Falling cone penetration The falling cone penetration level reduced as the forward speed increased, whereas it increased as the number of passes increased. The soil became very loose after each pass and the strength of the soil became less because of this. The details of falling cone penetration level for each pass at different forward speeds are given in Table 1. The maximum value of 13.3 cm was recorded after the third pass at 1.0 km/ h forward speed. The minimum falling cone penetration value was 7.9 cm after the ®rst pass at 2.0 km/h forward speed. The statistical test results indicated that increase in the number of passes decreased the falling cone penetration level signi®cantly at a 95% level at all forward speeds, whereas there was no signi®cant difference in the falling cone penetration level for different forward speeds. 3.3.3. Cone index There was a signi®cant reduction in the cone index values after every pass at all forward speeds. The cone index values dropped from 212.8 kPa after the ®rst pass to 158.0 kPa after the third pass (25.75% reduction) at 1.0 km/h forward speed. It reduced from 305.4 kPa after the ®rst pass to 226.0 kPa after the
third pass (25.9% reduction) at 1.5 km/h forward speed, and from 258.7 kPa after the ®rst pass to 192.5 kPa after the third pass (25.5% reduction) at 2.0 km/h forward speed (Table 1). Statistical test results indicated that the forward speed and the number of passes did not affect the cone index values signi®cantly. 3.3.4. Puddling index Puddling index increased with every pass at all forward speeds. It increased from 17.4% after the ®rst pass to 26.32% after the third pass at 1.0 km/h forward speed. The degree of increase was lower with an increase in the forward speed. It increased from 14.1% after the ®rst pass to 23.2% after the third pass at 1.5 km/h forward, and from 13.1% after the ®rst pass to 19.8% after the third pass at 2.0 km/h forward speed (Table 1). Statistical test results showed that both the forward speed and the number of passes affected the puddling index signi®cantly at a 95% level of signi®cance. 3.3.5. Viscosity The viscosity of the puddled slurry increased as the number of passes increased. The percentage increase of viscosity lowered as the forward speed increased. The soil clods were larger in size as the forward speed increased. The maximum viscosity of 0.047 P was obtained after the third pass at 1.0 km/h forward speed. The minimum viscosity of 0.033 P was obtained after the ®rst pass at 2.0 km/h forward speed. Statistical test results showed that both the forward speed and the number of passes affected the viscosity at a 99% level. 3.3.6. Shear strength As the number of passes increased, the shear strength values lowered considerably. The same trend was followed for all forward speeds. The percentage reduction in shear strength at 5 cm depth between the ®rst and third passes at 1.0 km/h forward speed was 60.52%. It was 65.62% at 10 cm depth and 67.3% at 15 cm depth. The same trend was seen for other forward speeds also. Statistical test results showed that the shear strength did not differ signi®cantly for both the number of passes and forward speeds. The same reason attributed for the cone index could be attributed for shear strength also.
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3.4. Comparison of effect on soil properties by conventional and reverse-rotary tillers 3.4.1. Moisture content and bulk density The increase in the number of passes increased the moisture content at all forward speeds for both types of rotary tillers. The moisture content values for the different forward speeds were nearly the same for both rotary tillers (Table 2). Statistical tests by one-way ANOVA indicated that the number of passes affected the moisture content signi®cantly at a 95% level. The forward speed also affected the moisture content signi®cantly at a 95% level for 1.0 and 1.5 km/h and at a 99% level for 2 km/h forward speed. 3.4.2. Bulk density The bulk density reduction was higher for the rotary tiller with reverse rotation having scoop-type blades than that for the C-type for all passes and forward speeds (Table 1). The percentage reduction of bulk density was higher between the ®rst and second passes than that of the second and third passes for all the forward speeds for both the types of rotary tillers. Statistical tests showed that the pass numbers and forward speeds affected the bulk density signi®cantly at a 90% level for both rotary tillers. At 1.5 km/h forward speed, the number of passes affected the bulk density at a 99% level of signi®cance. During the second pass at 1 km/h forward speed, the bulk density was signi®cantly different at 99% level. This happened during the second pass at 2 km/h forward speed also. During the third pass at 2 km/h forward speed, there was no signi®cant difference in the bulk density. 3.4.3. Falling cone penetration The falling cone penetration was higher for the rotary tiller with C-type blades than for the rotary tiller with reverse rotation having scoop-type blades for nearly all passes and at all forward speeds. The rotary tiller with reverse rotation having scoop-type blades made bigger soil clods than the C-type blade due to its scoop-shaped edge. There was a better churning action in the case of the C-type blade due to its curvature, whereas the reverse-rotary blade is straight in shape. Thus the falling cone penetration is higher for the C-type blades. Statistical tests showed that the falling cone penetration values were signi®cantly different at a 99% level of signi®cance for the
71
third pass at 1.5 km/h forward speed, and at a 90% level of signi®cance for the second pass at 1.5 and 1.0 km/h forward speeds. For other passes and other speeds, the values were not signi®cantly different. Hence, both blades gave almost equal performance from the cone penetration point of view. 3.4.4. Cone index The percentage reduction of cone index values was greater for the rotary tiller with C-type blades than for the rotary tiller with reverse rotation having scooptype blades. The % reductions in cone index values up to 21 cm depth for each plot are given in Table 2 for both rotary tillers. The number of passes did have a considerable effect on the percentage reduction in the cone index values, whereas the forward speed did not have any effect in the % cone index reduction. The statistical test showed that the number of passes and forward speed did not affect the cone index values signi®cantly for both types of rotary tillers. Hence, the puddling quality in terms of percentage reduction of cone index values was the same for both rotary tillers. 3.4.5. Puddling index Maximum value of puddling index (33.0%) was obtained after the third pass of the rotary tiller with Ctype blades at 1.0 km/h forward speed. As the number of passes increased, the puddling index also increased. The soil was churned completely after the third pass for both blades. Minimum value of puddling index (13.1%) was obtained after the ®rst pass of the reverserotary tiller at 2.0 km/h forward speed. This shows that, when the forward speed increased, the puddling index reduced for the corresponding passes. Puddling index increased with the number of passes at all forward speeds. Under all conditions, the puddling index was higher for the rotary tiller with C-type blades. Statistically the puddling index was signi®cantly different at a 95% level for all forward speeds and passes. 3.4.6. Viscosity Viscosity increased as the number of passes increased for both blades. It reduced as the forward speed increased. Viscosity followed the same trend as that of the puddling index. Statistical tests indicated that the viscosity of the slurry was signi®cantly different at a 95% level for the ®rst pass at 1.5 km/h, after
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V.M. Salokhe, N. Ramalingam / Soil & Tillage Research 63 (2001) 65±74
the third pass at 2.0 km/h, and all the passes at 1.0 km/ h forward speed. Under these conditions, the viscosity of the slurry was higher for the rotary tiller with C-type blades than that for the rotary tiller with reverse rotation having scoop-type blades. At all other conditions, the viscosity of the slurry was the same for both rotary tillers. 3.4.7. Shear strength Shear strength lowered after every pass for all forward speeds for both rotary tillers. As the number of passes increased, not only was the soil churned more but the moisture content also increased. As the moisture content increased, the shear strength was lowered. This happened at all forward speeds for both blades. Statistically, the shear strength values were not signi®cantly different under any condition. Hence shear strength cannot be used as a criterion for determining the puddling quality of the blades. 3.5. Performance tests in dry land The performance of rotavators with both kinds of blades was evaluated in the dry ®eld. The quality of tilling was compared by visual observation and was substantiated by photographic evidence. The soil properties measured are tabulated in Table 3. The number of passes did not have any effect on the moisture content of the ®elds, which was about 20% when the experiments were conducted. The number of passes had a signi®cant effect on the bulk density reduction. The bulk density was reduced by 14.52%
between the zero and third passes for the rotary tiller with reverse rotation having scoop-type blades. For the rotary tiller with C-type blades, the reduction was 16.21%. Hence, both the rotary tillers performed equally well in terms of bulk density reduction. As the number of passes increased, the bulk density reduced (Table 3). Statistical test results indicated that the number of passes affected the bulk density signi®cantly at a 95% level of signi®cance. In terms of % reduction in cone index values, the rotary tiller with reverse rotation having scoop-type blades performed better than the rotary tiller with Ctype blades in dry soil. The % reduction in cone index values between the ®rst pass and third pass was 50.19% for the rotary tiller with reverse rotation having scoop-type blades. The corresponding value for the rotary tiller with C-type blades was 18.8%. In the case of the rotary tiller with reverse rotation having scoop-type blades, the cone index value reduced from 471.2 kPa (Table 3) after the ®rst pass to 269.2 kPa after the second pass (42.9% reduction). It was further reduced to 234.8 kPa after the third pass (13% reduction between the second and third passes). This shows that the soil was pulverized to a greater extent in one pass itself, whereas this phenomenon did not happen in the case of the rotary tiller with C-type blades, and the cone index reduced gradually at every pass. Shear strength of the soil decreased when the number of passes increased for both rotary tillers. The shear strength did not change at 20 cm depth as the depth of operation was restricted to 15 cm. It reduced from 0.05 kPa at zero pass to 0.006 kPa after
Table 3 Effect of pass and tractor forward speed on different dry soil propertiesa Rotor type
Forward speed (km/h)
Pass
Moisture content (d.b.) (%)
Bulk density (k/m3)
Cone index (kPa)
Rotary tiller with reverse rotation
1.5
0 1 2 3
19.4 20.6 19.1 19.2
a a a a
1146.6 c 1062.2 d 1002.3 e 979.5 g
686.7 471.2 269.2 234.8
b f g h
Rotary tiller with C-type blades
1.5
0 1 2 3
19.1 17.0 19.8 17.4
a a a a
1177.5 a 1158.4 b 1144.6 c 986.6 f
728.5 600.1 556.2 487.5
a c d e
5.13
5.13
LSD 5% a
5.13
Columns compared not rows. Data with the same following letter indicates no signi®cant difference in values at 5% level.
V.M. Salokhe, N. Ramalingam / Soil & Tillage Research 63 (2001) 65±74
the third pass for the rotary tiller with C-type blades at 5 cm depth (87.1% reduction). The corresponding values for the rotary tiller with reverse rotation having scoop-type blades were 0.048±0.005 kPa (90.0% reduction). The % reduction in the shear strength values between the zero pass and the ®rst pass was greater for the rotary tiller with reverse rotation having scoop-type blades at all depths. The required soil tilt and pulverization were achieved in fewer number of passes for the rotary tiller with reverse rotation having scoop-type blades, whereas at least three passes were required for the rotary tiller with C-type blades to achieve similar soil conditions. Statistical tests indicated no signi®cant difference, hence both tillers gave
73
almost equal performance in terms of shear strength reduction. 3.5.1. Clod size aggregate It was found that the rotary tiller with C-type blades produced clods of larger size than the rotary tiller with reverse rotation having scoop-type blades. This happened at all passes. The soil inversion of the rotary tiller with reverse rotation having scoop-type blades was good because of the scoop-shaped edge. This provided complete burial of the weeds even after the ®rst pass itself. The subsequent passes reduced the clods formed after the ®rst pass. Bigger soil clods were produced by both rotary tillers at the end of the
Fig. 2. Clod size distribution after tilling with C-type blade at 1.5 km/h forward speed.
Fig. 3. Clod size distribution after tilling with reverse-rotary blade at 1.5 km/h forward speed.
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V.M. Salokhe, N. Ramalingam / Soil & Tillage Research 63 (2001) 65±74
®rst pass, and after the subsequent passes, the clod size reduced considerably. At the end of the ®rst pass, there was more uneven clod distribution for both rotary tillers, whereas at the end of the third pass, the clod size distribution was almost the same. The number of passes had a signi®cant effect on the clod size reduction. In the case of the rotary tiller with reverse rotation having scoop-type blades, pulverization was excessive. Figs. 2 and 3 show the effect of rotor passes on the soil aggregate sizes. Statistical analysis showed that aggregate sizes produced by C-type blades were different at 95% level of signi®cance (LSD0:5 0:92). The interaction effects of number of passes and aggregate size were also statistically signi®cant at 95% level (LSD0:5 1:59). A similar statistical result was also obtained for reverse-rotary tiller. 4. Conclusions The bulk density reduction was greater in wet land for the rotary tiller with reverse rotation having scooptype blades rather than C-type blades. In the dry land, the bulk density reduction was slightly more for the rotary tiller with C-type blades. The falling cone penetration and cone index values increased with every pass at all forward speeds for both rotary tillers. Cone index values reduced after every pass at all forward speeds for both rotary tillers. Cone index decreased when the number of passes increased at the same forward speed, but it decreased when the forward speed decreased at the same pass. The viscosity and puddling index of puddled soil were greater for the rotary tiller with C-type blades at all passes for all forward speeds. Both the number of passes and the forward speed had a signi®cant effect on viscosity of the puddled soil. It increased when the number of passes increased for all forward speeds, but reduced when the forward speed increased for all passes. Shear strength lowered after every pass for all forward speeds for both the rotary tiller with reverse rotation having scoop-type blades and the rotary tiller with C-type blades in the wet land and dry land. The rotary tiller with C-type blades produced clods of larger size than the rotary tiller with reverse rotation having scoop-type blades at all passes at 1.5 km/h forward speed.
In general, it can be concluded that the performance of the rotary tiller with reverse rotation having scooptype blades was better than that of the rotary tiller with C-type blades both in the wet land and dry land conditions at any pass and forward speed. References Badhe, V.T., Gupta, C.P., Bhole, N.G., 1984. Performance index for puddler. Paper Presented at XXI ISAE Conference, New Delhi, India. Bernacki, H., Haman, J., Kanfojki, C.Z., 1972. Agricultural Machines: Theory and Construction, Vol. 1. The Scienti®c Publications Foreign Cooperative. Center of Central Institute for Scienti®c Technical and Information, Warsaw, Poland, pp. 382±387. Boccafogli, A., Busatti, G., Gherardi, F., Malaguti, F., Paoluzzi, R., 1992. Experimental evaluation of cutting dynamic models in soil bin facility. J. Terramech. 29, 95±105. Kanai, K., 1980. Performance of rice transplanter as evaluation by National Test Center in Japan. Jpn. Agric. Res. Quart. 14, 84± 87. Kataoka, T., Onodera, K., Shibusawa, S., Ota, Y., 1995. A model for backward throwing of sliced soil clods by a reverserotational rotary tiller using rigid body kinematics. In: Proceedings of the Fourth Asia±Paci®c Conference of the ISTVS, Okinawa, Japan, November 20±22, 1995, pp. 339± 346. Kosutic, S., Filipovic, D., Gospodaric, Z., 1997. Agro-technical and energetic characteristics of a rotary cultivator with spike tines in seedbed preparation. Agric. Eng. J. 6, 137±144. Mandang, T., Al, F., Hayashi, N., Watanabe, S., Tojo, S., 1993. Studies on the overturning properties of soil by rotary blade using CT image analyzer. ASAE Paper No. 93-3035. American Society of Agricultural Engineers, St. Joseph, MI. Ram, R.B., Singh, S., Verma, S.R., 1980. Comparative performance of some new and conventional tillage equipment. J. Agric. Eng. ISAE 17, 7±13. Ramlingam, N., 1998. Effects of direction of rotation on the performance of a rotary tiller in Bangkok clay soil. M.E. Thesis No. AE-98-1. Asian Institute of Technology, unpublished. Rautary, S.K., Watts, C.W., Dexter, A.R., 1997. Puddling effects on soil physical parameters. Agric. Mech. Asia, Africa and Latin America 28, 37±40. Sakai, J., 1978. Designing process and theories of rotary blades for better rotary tillage (Part I). Jpn. Agric. Res. Quart. 12, 86±93. Salokhe, V.M., Gee-Clough, D., 1988. Working with Bangkok clay soil Ð some experiences. Agric. Mech. Asia, Africa and Latin America 19, 33±41. Salokhe, V.M., Ramlingam, N., 2001. Effect of reverse-rotation on power and draft requirement of a rotavator. J. Terramech., in press. Shibusawa, S., 1993. Reverse rotational rotary tiller for reduced power requirement in deep tillage. J. Terramech. 30, 205±217.