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Water leakage control by using vibratory roller on a dry-seeded rice field in southwestern Japan
G Model STILL 3746 No. of Pages 9
Soil & Tillage Research xxx (2016) xxx–xxx
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Water leakage control by using vibratory roller on a dry-seeded rice field in southwestern Japan Koichiro Fukamia,* , Toshifumi Mukunokib , Keiko Nakanoa , Naoki Matsuoa , Takashi Okayasuc a b c
National Agriculture and Food Research Organization, Kyushu Okinawa Agricultural Research Center, 496 Izumi, Chikugo, Fukuoka 833-0041, Japan X-Earth Center, Graduate School of Science and Technology, Kumamoto-University, 1-39-2 Kurokami, Kumamoto 860-8555, Japan Department of Agro-Environmental Sciences, Faculty of Agriculture, Kyushu-University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka 812-8581, Japan
A R T I C L E I N F O
Article history: Received 11 March 2016 Received in revised form 17 September 2016 Accepted 18 September 2016 Available online xxx Keywords: Dry-seeded rice Vibratory roller Leakage prevention Vibration acceleration Soil structure Micro-electro mechanical system
A B S T R A C T
Dry-seeded rice cultivation is an effective low-cost cultivation method in Japan, but preventing water leakage from cultivated rice fields remains a challenge. Here we assessed the efficiency of using a vibratory roller in a dry-seeded rice field for preventing water leakage. The tests were conducted at two different soil-water contents (WC: 32 and 39%) before roller compaction. We measured the acceleration response of the vibrating roller by using a micro-electro mechanical system (MEMS) accelerometer, and we determined the volume of water leakage from the field by using a rapid leakage capacity tester. We analyzed the changes in the soil structure by using a micro-focused X-ray CT scanner. We analyzed all of the resulting data to identify any correlation. We observed that water leakage from the field was sufficiently prevented when prior to roller compaction, soil moisture content was 39%. The shape of the soil pores that could efficiently prevent water leakage was flatter than that of the inefficiently compacted soil. In addition, the total porosity decreased, but the small-sized pore fraction increased. The vibration acceleration of the roller significantly increased with the decrease in the volume of water leakage. Thus, in addition to assessing the efficiency of vibratory rollers in reducing water leakage, our data suggest that it is to some extent possible to estimate the water leakage prevention effect from the acceleration response of a vibrating roller. ã 2016 Elsevier B.V. All rights reserved.
1. Introduction Rice (Oryza sativa L.) is the most important cultivated food crop in Japan, and it is thus of primary importance to ensure low rice production costs and labor-saving. Generally, expansion of the management scale leads to a reduction in production costs because the efficiency of the machinery used for the large-scale production increases. However, in the transplanting system that accounts for 90% of Japan’s rice production, the raising of seedlings becomes a disincentive for scale expansion. In recent years the use of direct seeding systems in Japan has thus increased. Direct seeding in Japan can be roughly classified as the direct seeding of rice on well-drained paddy fields (dry seeding) versus the direct seeding of rice on submerged soil (wet seeding) (Chosa
Abbreviations: MEMS, micro-electro mechanical system; CT, computed tomography; PTO, power take-off. * Corresponding author. E-mail address: [email protected] (K. Fukami).
et al., 2014). For example, a seed-shooting seeder of rice (Togashi et al., 2001a,b) combined with a tractor-mounted paddy harrow is widely used in submerged soil (Fig. 1, wet seeding). In western Japan, the requirements for the use of this method include the puddling of the field and seed coating by iron powder (Yamauchi, 2012) or calcium dioxide (CaO2) before seeding, and controlling apple snails (Wada, 2004). In contrast, dry seeding (Fig. 1) is lowcost and enables the saving of labor compared to wet seeding, because dry seeding does not have the requirements mentioned above (Farooq et al., 2011; Tasaka et al., 2013). However, with the upcoming upland cropping systems in southwestern Japan, in which rice is rotated with wheat, soybean and barley within a twoyear period, a plow pan rich in macropores has developed. Thus, the prevention of water leakage from the cultivated field is a principal challenge during dry-seeding cultivation. Compaction by using a tractor-mounted roller is effective to prevent water leakage from a dry-seeded rice field (Kanmuri et al., 2012; Fukami et al., 2014). However, the upsizing of the roller and the tractor are required to obtain sufficient effects of the static compaction produced by the weight of the roller. The use of a
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Please cite this article in press as: K. Fukami, et al., Water leakage control by using vibratory roller on a dry-seeded rice field in southwestern Japan, Soil Tillage Res. (2016), http://dx.doi.org/10.1016/j.still.2016.09.011
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Fig. 1. The method used for the direct seeding of rice.
assessed the volume of water leakage from the field by using a rapid leakage capacity tester. We evaluated the changes in the soil structure by using a micro-focused X-ray CT scanner. We analyzed the resulting data to identify any correlation. 2. Materials and methods 2.1. The vibratory roller
Fig. 2. Photograph of the vibratory roller.
vibratory roller as an alternative could be expected to have a higher compaction effect by dynamic compression even when the roller load is small. A cost reduction could also be expected due to the general-purpose use of the vibratory roller machine, because the work can be done by a general-sized tractor (power 14.7–29.4 kW, 20–40 PS). The acceleration response of a vibratory roller is also useful for the evaluation of the stiffness of compacted soil (Fujiyama and Tateyama, 2000; Fujiyama et al., 2002; Mooney and Rinehart, 2007). The water permeability and water retention of a field depend on the soil’s structure, and changes in soil structure have a close relation to the growth of crop roots. Thus, analyses of soil structure based on X-ray computed tomography (CT) images (Munkholm et al., 2003; Peth et al., 2010; Garbout et al., 2013; Ferro et al., 2014; Tracy et al., 2015) have increased in recent years. However, few studies have analyzed the structure of roller-compacted soil for the purpose of prevention of water leakage from a dry-seeded rice field. To reduce water-supply rates to 2 cm/day, it is desirable to compact the subsoil during tractor operations, preferably when water content is high. Studies by Kanmuri et al. (2012) have shown that, particularly medium to fine textured soils are most susceptible to compaction when wet. In this study, we assessed how well a vibratory roller could prevent water leakage in a dry-seeded rice field. To assess the effect of antecedent water content, the tests were conducted at two different soil-water contents (WC: 32 and 39%). We measured the acceleration response of the vibrating roller by using a microelectro mechanical system (MEMS) accelerometer, and we Table 1 Specifications of the vibratory roller. Manufacturer: KAWABE Noken Sangyo Co., Ltd. Model: SV3-T Roller weight/width: 350 kg/150 cm Compaction weight: 750–3125 kg (PTO:800–1100 rpm) Appropriate power of tractor: 22–37 kw (30–50 PS)
Fig. 2 and Table 1 provide a photograph and the specifications of the vibratory roller (model SV3-T, Kawabe Noken Sangyo Co., Tokyo). This machine is mainly composed of a vibration generator and a roller part. The roller’s total weight (without vibrating) is 350 kg, and the roller’s width and diameter are 150 and 40 cm, respectively. The roller compaction weight (vibrating) is 750– 3125 kg (power takeoff [PTO]: 800–1100 rpm). The appropriate power of the tractor is 22–37 kW (30–50 PS). This machine can also be used as a vibrating wide subsoiler by changing the roller part to the curved shank (Tanaka et al., 2000). 2.2. Test conditions We conducted field experiments in 2013 at the Kyushu Okinawa Agricultural Research Center (KARC), Chikugo, Fukuoka, Japan (33120 N, 130 300 E, 10 m elevation). The basic soil characteristics of the 0–200 mm layer are given in Table 2. The soil texture was Light clay (classification: International system). The plastic and liquid limits were 38% and 56% (gravimetric water content), respectively. Before the roller compaction test, the experimental field was tilled to 13 cm deep using a rotary tiller. The conditions during the compaction test with the roller are given in Table 3. The test tractor power was 25 kW (34 PS). We set the rotational speed of the PTO at 1100 rpm, the operating speed of the roller at 1 and 2 km/h, and the pass number of the roller as two. The test days were April 11 and 18, and there was rain (10 and 28 mm) on April 14 and 17 (Japan Meteorological Agency data), respectively. Thus, the moisture conditions varied according to the experiment day. We measured the soil gravimetric water content (% dry basis) by core sampling (core size: dia. 50 mm, height 51 mm; depth: 20–70, 70–120, and 120–170 mm). The water
Table 2 Soil characteristics of the test field. Soil texture
Light clay
Clay (<2 mm), % Silt (2–20 mm), % Fine sand (20–200 mm), % Coarse sand (200–2000 mm), %
36.5 37.8 15.7 9.9
Plastic limit (% d. b.)a Liquid limit (% d. b.)a
38 56
a
Gravimetric water content.
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Table 3 The conditions during the compaction test with the roller. Tractor Vibratory roller
25 kW (34 PS) SV3-T
PTO (rpm) Operating speed (km/h) Pass number Water content (% d.b.)a
1100 1, 2 2 32, 39
Test dates: 32%, April 11; 39%, April 18. PTO: power take-off; d.b.: dry basis. a Mean value of three depths (20–70, 70–120, and 120–170 mm).
Fig. 4. Measurement set-up of the rapid leakage capacity tester.
Table 5 Specifications of the rapid leakage capacity tester. Manufacturer: Daiki Rika Kogyo Co., Ltd. Model: DIK-4350 Infiltrating drum inside dimensions: DIA144.5 H80 mm Infiltrating drum material: Stainless steel Float type scale tube inside diameter: 3.8 mm Measurement time: 1–5 min
Fig. 3. Measurement set-up of the MEMS accelerometer.
contents (WCs) before compaction were 32% (April 11) and 39% (April 18). A test section was 1.5 20 m plot with two replicates. After the 2nd pass compaction test, we measured the penetration resistance and distribution of the three soil phases, i.e., vapor, liquid and solid phase fraction. We measured the penetration resistance using a digital cone penetrometer (CP40II, Rimik, Queensland, Australia; cone top angle 30 ; cross-sectional area of the cone, 2 cm2; data acquisition intervals, 1.5 cm, three places per plot). We used a digital actual volumenometer (DIK1150, Daiki Rika Kogyo Co., Saitama, Japan) to measure the threephase distribution after the core sampling. All statistical analyses (ANOVA) were performed using SAS Add-in for Microsoft Office 6.1 software (SAS Institute Inc., Cary, North Carolina). 2.3. Acceleration response of vibratory roller
2.4. Volume of water leakage from the test field The volume of water leakage from the test field was measured with a rapid leakage capacity tester (DIK-4350, Daiki Rika Kogyo). Fig. 4 and Table 5 show the measurement set-up and the specifications of the tester, which measures the quantity of falling permeation by inserting a bottomless infiltrating drum into the test field. Since this does not measure the permeation as the water level, due to the enlarged variation of the receded water, the tester can measure the quantity of daily falling permeation within 1–5 min. After all of the compaction tests were finished, we filled the field with water to a depth of approx. 10 cm and measured the water leakage volume (Fig. 4). The measurement time was set at 1 min. Based on a study by Kanmuri et al. (2012), the water leakage at 2 cm/day is considered as acceptable (meaning that water leakage is prevented). After we measured the quantity of water
We measured the acceleration response of the vibratory roller with a MEMS accelerometer (LP-WS0902 (5G/300 dps), Logical Product Co., Fukuoka, Japan). Fig. 3 and Table 4 provide the measurement set-up and the specifications of the accelerometer. The accelerometer had a sensor that we attached to the vibration generator. The sampling frequency was set to 200 Hz. With this sensor, we measured not only the acceleration but also the angular velocity of the roller. The measurement data were taken with a notebook personal computer (PC) in real time (Fig. 3). We used the response wave form of the vibration acceleration to calculate the spectrum distribution by the discrete Fourier transform (DFT) method. The DFT analysis program was part of Microsoft Visual Basic 2010 Express software. Table 4 Specifications of the MEMS accelerometer. Manufacturer: LOGICAL PRODUCT Co., Ltd. Model: LP-WS0902 (5 G/300 dps) Sampling frequency: 1–1000 Hz (9 levels) Modulation scheme: DS-SS External dimensions: W40 H20 D55 mm Sensor weight: 35 g (Contains one AAA battery) Fig. 5. Sampling method for the soil structure analysis.
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Table 6 Specifications of soil sampling device. Sampler: FUJIWARA SCIENTIFIC Co., Ltd. Model: HS-30S Sample size: DIA50 L300 mm Material of sample case: Polyvinyl chloride (PVC) Electric drill: TOSHIBA CORPORATION (DR-20S1)
Table 7 Three-phase distribution, porosity, saturation percentage and PR in the rollercompacted field (after 2nd Pass). WC (%)
Conditiona Depth Vapor Liquid Solid Porosity Saturation PR (cm) (%) (%) (%) (%)b (%)c (MPa)d
32
BC
1.0 km/h
leakage, we drained away the water of the field to perform soil sampling.
2.0 km/h
2.5. Structure analysis of compacted soil Fig. 5 and Table 6 show the sampling method and the specifications of soil sampling device used for the soil structure analysis. Each sample for analysis was collected with an electric sampler and placed in a transparent cylinder made of polyvinyl chloride (PVC; 50 mm dia. 300 mm long). We photographed a perpendicular section of the entire sample with an industrial X-ray CT scanner (TOSCANER-20000RE, Toshiba, Tokyo; voxel size 0.195 mm, slice thickness 1 mm) to determine the rough soil structure. We also used a micro X-ray CT scanner (TOSCANNER32300FPD, Toshiba; voxel size 0.079 mm, slice thickness 0.159 mm) for more detailed photography and to obtain a three-dimensional section. We calculated the spatial distribution of the pore diameters and the pore shapes of the soil with an analysis program (Mukunoki et al., 2009, 2010, 2011, 2016) based on the micro X-ray CT images of the pores. Our analysis was based on an image processing technique that uses mathematical morphology (Soille, 2003) to evaluate the 3D distribution of the pore scale in the compacted soils. Fig. 6 shows the results of the 3D soil structure analysis using the morphological openings (Soille, 2003). With this method, various sizes of structuring elements are fitted to a binary image of soil pore. First,
39
BC
1.0 km/h
2.0 km/h
2–7 7–12 12–17 2–7 7–12 12–17 2–7 7–12 12–17
40 37 34 27 29 23 28 30 29
27 29 30 33 32 37 33 33 29
33 34 36 39 39 40 39 37 42
67 66 64 61 61 60 61 63 58
40 44 47 54 52 62 54 52 50
0.01 0.03 0.12 0.64 0.61 0.75 0.61 0.59 0.69
2–7 7–12 12–17 2–7 7–12 12–17 2–7 7–12 12–17
30 16 7 11 2 2 13 3 1
34 42 47 41 48 48 41 48 50
36 42 46 47 49 50 46 49 49
64 58 54 53 51 50 54 51 51
53 72 87 77 94 96 76 94 98
0.04 0.05 0.20 0.70 0.49 0.43 0.56 0.43 0.40
Average value of two replicates. a BC: Before compaction. 1.0 km/h, 2.0 km/h: operating speed. b Porosity is 100 – Solid. c Saturation is (Liquid/Porosity) * 100. d Measurement depth are 4.5, 9.0, 15.0 cm.
we fit structure element 1 (dia. 0.079 mm) to the binary image, and then we extracted its total porosity. By the same procedure, we determined the pore structure by creating the extracted image of each element (For example: element 2, 3, 4, 5; dia. 0.237, 0.395, 0.553, 0.711 mm). Finally, we obtained a 3D pore diameter distribution by adding together all the separate images (Mukunoki et al., 2016).
Fig. 6. Results of the 3D soil structure analysis using the morphological openings.
Fig. 7. Penetration resistance of the roller-compacted field (after 2nd pass). WC: water content; BC: before compaction; 1.0 km/h, 2.0 km/h: operating speed. Bars indicate standard error.
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3. Results and discussion 3.1. Penetration resistance of the roller-compacted field Fig. 7 shows the results of the comparison of the penetration resistance (PR) of the roller-compacted field at the WC values of 32% and 39%. The PR at a range of 0–15 cm depth was increased by the roller compaction in both moisture conditions, and the PR at this range slightly decreased with the increase in operating speed in both moisture conditions. In addition, at the highest WC of 39%, a PR decrease at approx. 12 cm depth was observed. However, no clear relationship was observed at 20–60 cm depth. 3.2. Comparison of the PR and the three-phase distribution in the roller-compacted field Table 7 shows the values of the three-phase distribution, porosity, saturation percentage and PR in the roller-compacted field (after 2nd pass). In all conditions, the vapor-phase fraction was decreased by roller compaction, and the liquid-phase and solid-phase fractions increased. As for the vapor-phase fraction, the decrease produced by the roller compaction became remarkable in a high water condition (WC 39%). In addition, the decrease
5
in the PR at approx. 12 cm depth with overall WC 39% (Fig. 7) seems to have occurred because the saturation percentage of this part was considerable higher than WC 32%. The ANOVA results of the effect of WC and operating speed on three-phase distribution, porosity, saturation percentage and PR in the roller-compacted field per depth (2–7, 7–12, 12–17 cm) are shown in Table 8 (based on the data in Table 7). The vapor-phase fraction at WC 39% was significantly smaller than that at WC 32% at all depths. The liquid-phase fraction and saturation percentage at WC 39% were significantly larger than that at WC 32% at all depths. The solidphase fraction (porosity) at WC 39% was significantly larger (smaller) than that at WC 32% in 2–12 cm depth. The PR at WC 39% was significantly smaller than that at WC 32% in 7–17 cm depth. In addition, the PR at operating speed 2 km/h was significantly smaller than that at operating speed 1 km/h in 2–7 cm depth. A significant WC operating speed interaction was found on the PR in 2–7 cm depth (Table 8). 3.3. Frequency analysis of the vibration accelerations Fig. 8 shows an example (1st pass, WC 32% and 39%, operating speed 2.0 km/h, PTO 1100 rpm and analysis time 20 s) of the spectrum distributions of the vibration accelerations. The
Table 8 The ANOVA results of the effect of WC and operating speed on three-phase distribution, porosity, saturation percentage and PR in the roller-compacted field per depth. Depth (cm)
Fixed source of variation
Vapor (%) P>F
Liquid (%)
Solid (%)
Porosity (%)
Saturation (%)
PR (MPa)
2–7
WCa Speedb WC Speed
0.003 nsc ns
0.010 ns ns
<0.001 ns ns
<0.001 ns ns
0.005 ns ns
ns 0.001 0.008
7–12
WC Speed WC Speed
<0.001 ns ns
<0.001 ns ns
<0.001 ns ns
<0.001 ns ns
<0.001 ns ns
0.021 ns ns
12–17
WC Speed WC Speed
<0.001 ns ns
0.004 ns ns
ns ns ns
ns ns ns
<0.001 ns ns
0.014 ns ns
a b c
WC: water content of before compaction. Speed: operating speed of the roller. ns: not significant at P < 0.05.
Fig. 8. Spectrum distributions of a vibration acceleration (during 1st pass, operating speed 2.0 km/h, PTO 1100 rpm and analysis time 20 s). WC: water content of before compaction.
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Table 9 The frequency and amplitude of the MFC in the vertical direction of the roller. WCb (%)
Operating speed (km/h)
32
1.0 2.0 1.0
39
2.0
a b
1st pass
2nd pass
PTO (rps)
Frequency (Hz)
Amplitude (G)
PTO (rps)
Frequency (Hz)
Amplitude (G)
19 18 19 18 19 19 19 19
19 –a 18 18 19 – 19 19
2.2 – 2.7 1.9 3.9 – 3.5 3.2
18 19 18 19 19 19 19 19
19 19 19 19 19 – 19 19
2.3 2.5 2.3 2.5 3.3 – 2.6 4.1
Loss of the vibration acceleration data. WC: water content of before compaction.
Table 10 Water leakage of the roller-compacted field (after 2nd pass) and the ANOVA results of the effects of WC and operating speed. Water leakage (cm/day) WC (%)
1 km/h
2 km/h
32
15.4 12.3 1.8 1.4
48.3 41.0 2.3 1.7
39
Fixed source of variation
P>F
a
<0.001 0.001 0.002
WC Speedb WC Speed a b
WC: water content of before compaction. Speed: operating speed of the roller.
frequencies of the main frequency component (MFC) in the longitudinal and vertical directions of the vibration acceleration were both 19 Hz, and the frequency in the horizontal direction was unclear. In addition, the frequency of the MFC in pitching (i.e., the angular velocity of the roller) was 19 Hz, and yawing and rolling were indistinct in both moisture conditions (data not shown). We thus observed that the frequency of the MFC in the pitching of the roller and the longitudinal and vertical directions of the vibration acceleration paralleled the PTO rotation frequency, because the PTO turns approx. 19 times per sec (1100 rpm). Table 9 shows the frequency and amplitude of the MFC in the vertical direction of the roller. Generally, the roller response is affected by the type and water content of soil (Fujiyama et al., 2002). A tendency to increase was seen in the amplitude with the increase in the WC in all operating speeds.
3.4. The water leakage of the compacted field Table 10 shows the water leakage of the roller-compacted field (after 2nd pass) and the ANOVA results of the effects of WC and operating speed. The effect of vibrating compaction on water leakage was increased significantly by slowing the operating speed. This is because the number of vibrations per unit time per unit area depends on the operating speed. The hydraulic conductivity, decreases with the increase of moisture content (Lambe, 1958). The water leakage of WC 39% was significantly smaller than that of WC 32%. In addition, a significant WC operating speed interaction was found on the water leakage. Water leakage from the field was sufficiently prevented (to 2 cm/day or less) when the water content was WC 39%. Fig. 9 shows the relationship between the water leakage and the amplitude of the MFC in the vertical direction. The amplitude of the MFC increased significantly with a decrease in the volume of water leakage. However, we found that a more detailed analysis was necessary to improve the predictive precision, because the coefficient of determination was small.
Amplitude of MFC (G)
4.5
4.0
y = 3.47 x-0.11 R = 0.77* *: significant at P < 0.05
3.5 3.0 2.5 2.0 0
10
20 30 40 Water leakage (cm/day)
50
Fig. 9. Relationship between the water leakage and the amplitude of the MFC (during 2nd pass) in the vertical direction.
Fig. 10. X-ray CT images of the inefficiently (water leakage: 41.0 cm/day) and efficiently (1.7 cm/day) compacted soils. WC: water content of before compaction. Use of the industrial X-ray CT scanner (TOSCANER-20000RE, Toshiba, Tokyo; voxel size 0.195 mm, slice thickness 1 mm).
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Fig. 11. Micro X-ray CT images of the inefficiently (water leakage: 41.0 cm/day) and efficiently (water leakage: 1.7 cm/day) compacted soils. WC: water content of before compaction. Use of the micro X-ray CT scanner (TOSCANNER-32300FPD, Toshiba; voxel size 0.079 mm, slice thickness 0.159 mm).
3.5. The X-ray CT analysis of the compacted soil We analyzed the soil structure to understand the difference between the water leakage values of 41.0 cm/day (WC 32%, operating speed 2.0 km/h) and 1.7 cm/day (WC 39%, operating speed 2.0 km/h) in Table 10. Fig. 10 provides the industrial X-ray CT images (voxel size 0.195 mm, slice thickness 1 mm) of the inefficiently compacted (WC 32%, water leakage 41.0 cm/day) and efficiently compacted (WC 39%, water leakage 1.7 cm/day) soils. The vertical section views of the sampling soils (50 mm dia. 300 mm long) confirmed that there was structural difference at the top soil layer compared to the underlying soil layer (Fig. 10). Fig. 11 provides the micro X-ray CT images (voxel size 0.079 mm, slice thickness 0.159 mm) of the inefficiently compacted and efficiently compacted soils. From the vertical section view (depth
20–90 mm) and the horizontal section views (depth 35, 55 and 77 mm), we confirmed that the pores (black-colored) showed a flatter shape in the efficiently compacted soil (WC 39%) than the inefficiently compacted soil (WC 32%). Fig. 12 shows the 3D pore diameter distributions of the inefficiently and efficiently compacted soils based on micro X-ray CT images. The range of the analysis depth was 20–90 mm, and the sample size was 31.6 31.6 71.1 mm. From this figure, we found that the area of small pore diameters (blue-colored in the figure) in the efficiently compacted soil was darker than that of the inefficiently compacted soil. Fig. 13 shows the occupation ratio to the total porosity based on the data in Fig. 12. It should be noted that total porosities in Fig. 13 were about half those in Table 7 and thus this method misses a large part of the pores. However, from Fig. 13, we found that the total porosity of the efficiently compacted
Fig. 12. The 3D pore diameter distributions.(For interpretation of the references to color in the text, the reader is referred to the web version of this article.)
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Fig. 13. Occupation rate to the total porosity.
soil was lower than that of the inefficiently compacted soil, but the small-sized pore fraction of the efficiently compacted soil was greater than that of the inefficiently compacted soil. 4. Conclusions The tests were conducted at two different soil-water contents (WC: 32 and 39%) before roller compaction. The results of the present study demonstrated that water leakage from the field was sufficiently prevented when the soil moisture content was WC 39%. The shape of the soil pores that could efficiently prevent water leakage was flatter than that of the inefficiently compacted soil (WC 32%). In addition, the total porosity decreased, but the smallsized pore fraction increased. On the other hand, the amplitude of the MFC in the vertical direction of the vibration acceleration of the roller was significantly increased with the decrease in the volume of water leakage. Thus, in addition to establishing the efficiency of vibratory rollers in reducing water leakage, our findings suggest that it is to some extent possible to estimate the water leakage prevention effect from the acceleration response of a vibrating roller. In the future, we plan to (1) reexamine the sampling range and the method of analyzing the soil, (2) conduct further analyses of the soil structure, the compaction conditions, and the relationship between them, and (3) perform a soil structure analysis that includes the root system of the rice. Acknowledgements This study was supported by the Grants-in-Aid for Scientific Research (No. 25850175) from the Ministry of Education, Culture, Sports, Science and Technology. We are grateful to Dr. Tatsuo Hiroma of the ex-Saga-University professor for DFT analysis, Mr. Takahiro Sato of the X-Earth Center for X-ray CT analysis, Mr. Yukinari Kawahara, Mr. Teruyuki Miike, Mr. Akitoshi Honbu, Mr. Hiroyuki Itoh, Mr. Sadahiro Higashi, Ms. Tamiko Shimogawa and Ms. Kaori Sonoda of the KARC for their field management and data collection in this experiment.
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Tracy, R.S., Black, R.C., Roberts, A.J., Dodd, C.I., Mooney, J.S., 2015. Using X-ray computed tomography to explore the role of abscisicacid in moderating the impact of soil compaction on root systemarchitecture. Environ. Exp. Bot. 110, 11–18. Wada, T., 2004. Strategies for controlling the apple snail pomacea canaliculata (Lamarck) (Gastropoda: Ampullariidae) in Japanese direct-sown paddy fields. Jpn. Agric. Res. Q. 38 (2), 75–80. Yamauchi, M., 2012. Direct seeding of rice crop in flooded paddy fields using ironcoated seeds. Jpn. J. Crop Sci. 81 (2), 148–159.
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Water leakage control by using vibratory roller on a dry-seeded rice field in southwestern Japan Koichiro Fukamia,* , Toshifumi Mukunokib , Keiko Nakanoa , Naoki Matsuoa , Takashi Okayasuc a b c
National Agriculture and Food Research Organization, Kyushu Okinawa Agricultural Research Center, 496 Izumi, Chikugo, Fukuoka 833-0041, Japan X-Earth Center, Graduate School of Science and Technology, Kumamoto-University, 1-39-2 Kurokami, Kumamoto 860-8555, Japan Department of Agro-Environmental Sciences, Faculty of Agriculture, Kyushu-University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka 812-8581, Japan
A R T I C L E I N F O
Article history: Received 11 March 2016 Received in revised form 17 September 2016 Accepted 18 September 2016 Available online xxx Keywords: Dry-seeded rice Vibratory roller Leakage prevention Vibration acceleration Soil structure Micro-electro mechanical system
A B S T R A C T
Dry-seeded rice cultivation is an effective low-cost cultivation method in Japan, but preventing water leakage from cultivated rice fields remains a challenge. Here we assessed the efficiency of using a vibratory roller in a dry-seeded rice field for preventing water leakage. The tests were conducted at two different soil-water contents (WC: 32 and 39%) before roller compaction. We measured the acceleration response of the vibrating roller by using a micro-electro mechanical system (MEMS) accelerometer, and we determined the volume of water leakage from the field by using a rapid leakage capacity tester. We analyzed the changes in the soil structure by using a micro-focused X-ray CT scanner. We analyzed all of the resulting data to identify any correlation. We observed that water leakage from the field was sufficiently prevented when prior to roller compaction, soil moisture content was 39%. The shape of the soil pores that could efficiently prevent water leakage was flatter than that of the inefficiently compacted soil. In addition, the total porosity decreased, but the small-sized pore fraction increased. The vibration acceleration of the roller significantly increased with the decrease in the volume of water leakage. Thus, in addition to assessing the efficiency of vibratory rollers in reducing water leakage, our data suggest that it is to some extent possible to estimate the water leakage prevention effect from the acceleration response of a vibrating roller. ã 2016 Elsevier B.V. All rights reserved.
1. Introduction Rice (Oryza sativa L.) is the most important cultivated food crop in Japan, and it is thus of primary importance to ensure low rice production costs and labor-saving. Generally, expansion of the management scale leads to a reduction in production costs because the efficiency of the machinery used for the large-scale production increases. However, in the transplanting system that accounts for 90% of Japan’s rice production, the raising of seedlings becomes a disincentive for scale expansion. In recent years the use of direct seeding systems in Japan has thus increased. Direct seeding in Japan can be roughly classified as the direct seeding of rice on well-drained paddy fields (dry seeding) versus the direct seeding of rice on submerged soil (wet seeding) (Chosa
Abbreviations: MEMS, micro-electro mechanical system; CT, computed tomography; PTO, power take-off. * Corresponding author. E-mail address: [email protected] (K. Fukami).
et al., 2014). For example, a seed-shooting seeder of rice (Togashi et al., 2001a,b) combined with a tractor-mounted paddy harrow is widely used in submerged soil (Fig. 1, wet seeding). In western Japan, the requirements for the use of this method include the puddling of the field and seed coating by iron powder (Yamauchi, 2012) or calcium dioxide (CaO2) before seeding, and controlling apple snails (Wada, 2004). In contrast, dry seeding (Fig. 1) is lowcost and enables the saving of labor compared to wet seeding, because dry seeding does not have the requirements mentioned above (Farooq et al., 2011; Tasaka et al., 2013). However, with the upcoming upland cropping systems in southwestern Japan, in which rice is rotated with wheat, soybean and barley within a twoyear period, a plow pan rich in macropores has developed. Thus, the prevention of water leakage from the cultivated field is a principal challenge during dry-seeding cultivation. Compaction by using a tractor-mounted roller is effective to prevent water leakage from a dry-seeded rice field (Kanmuri et al., 2012; Fukami et al., 2014). However, the upsizing of the roller and the tractor are required to obtain sufficient effects of the static compaction produced by the weight of the roller. The use of a
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Fig. 1. The method used for the direct seeding of rice.
assessed the volume of water leakage from the field by using a rapid leakage capacity tester. We evaluated the changes in the soil structure by using a micro-focused X-ray CT scanner. We analyzed the resulting data to identify any correlation. 2. Materials and methods 2.1. The vibratory roller
Fig. 2. Photograph of the vibratory roller.
vibratory roller as an alternative could be expected to have a higher compaction effect by dynamic compression even when the roller load is small. A cost reduction could also be expected due to the general-purpose use of the vibratory roller machine, because the work can be done by a general-sized tractor (power 14.7–29.4 kW, 20–40 PS). The acceleration response of a vibratory roller is also useful for the evaluation of the stiffness of compacted soil (Fujiyama and Tateyama, 2000; Fujiyama et al., 2002; Mooney and Rinehart, 2007). The water permeability and water retention of a field depend on the soil’s structure, and changes in soil structure have a close relation to the growth of crop roots. Thus, analyses of soil structure based on X-ray computed tomography (CT) images (Munkholm et al., 2003; Peth et al., 2010; Garbout et al., 2013; Ferro et al., 2014; Tracy et al., 2015) have increased in recent years. However, few studies have analyzed the structure of roller-compacted soil for the purpose of prevention of water leakage from a dry-seeded rice field. To reduce water-supply rates to 2 cm/day, it is desirable to compact the subsoil during tractor operations, preferably when water content is high. Studies by Kanmuri et al. (2012) have shown that, particularly medium to fine textured soils are most susceptible to compaction when wet. In this study, we assessed how well a vibratory roller could prevent water leakage in a dry-seeded rice field. To assess the effect of antecedent water content, the tests were conducted at two different soil-water contents (WC: 32 and 39%). We measured the acceleration response of the vibrating roller by using a microelectro mechanical system (MEMS) accelerometer, and we Table 1 Specifications of the vibratory roller. Manufacturer: KAWABE Noken Sangyo Co., Ltd. Model: SV3-T Roller weight/width: 350 kg/150 cm Compaction weight: 750–3125 kg (PTO:800–1100 rpm) Appropriate power of tractor: 22–37 kw (30–50 PS)
Fig. 2 and Table 1 provide a photograph and the specifications of the vibratory roller (model SV3-T, Kawabe Noken Sangyo Co., Tokyo). This machine is mainly composed of a vibration generator and a roller part. The roller’s total weight (without vibrating) is 350 kg, and the roller’s width and diameter are 150 and 40 cm, respectively. The roller compaction weight (vibrating) is 750– 3125 kg (power takeoff [PTO]: 800–1100 rpm). The appropriate power of the tractor is 22–37 kW (30–50 PS). This machine can also be used as a vibrating wide subsoiler by changing the roller part to the curved shank (Tanaka et al., 2000). 2.2. Test conditions We conducted field experiments in 2013 at the Kyushu Okinawa Agricultural Research Center (KARC), Chikugo, Fukuoka, Japan (33120 N, 130 300 E, 10 m elevation). The basic soil characteristics of the 0–200 mm layer are given in Table 2. The soil texture was Light clay (classification: International system). The plastic and liquid limits were 38% and 56% (gravimetric water content), respectively. Before the roller compaction test, the experimental field was tilled to 13 cm deep using a rotary tiller. The conditions during the compaction test with the roller are given in Table 3. The test tractor power was 25 kW (34 PS). We set the rotational speed of the PTO at 1100 rpm, the operating speed of the roller at 1 and 2 km/h, and the pass number of the roller as two. The test days were April 11 and 18, and there was rain (10 and 28 mm) on April 14 and 17 (Japan Meteorological Agency data), respectively. Thus, the moisture conditions varied according to the experiment day. We measured the soil gravimetric water content (% dry basis) by core sampling (core size: dia. 50 mm, height 51 mm; depth: 20–70, 70–120, and 120–170 mm). The water
Table 2 Soil characteristics of the test field. Soil texture
Light clay
Clay (<2 mm), % Silt (2–20 mm), % Fine sand (20–200 mm), % Coarse sand (200–2000 mm), %
36.5 37.8 15.7 9.9
Plastic limit (% d. b.)a Liquid limit (% d. b.)a
38 56
a
Gravimetric water content.
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Table 3 The conditions during the compaction test with the roller. Tractor Vibratory roller
25 kW (34 PS) SV3-T
PTO (rpm) Operating speed (km/h) Pass number Water content (% d.b.)a
1100 1, 2 2 32, 39
Test dates: 32%, April 11; 39%, April 18. PTO: power take-off; d.b.: dry basis. a Mean value of three depths (20–70, 70–120, and 120–170 mm).
Fig. 4. Measurement set-up of the rapid leakage capacity tester.
Table 5 Specifications of the rapid leakage capacity tester. Manufacturer: Daiki Rika Kogyo Co., Ltd. Model: DIK-4350 Infiltrating drum inside dimensions: DIA144.5 H80 mm Infiltrating drum material: Stainless steel Float type scale tube inside diameter: 3.8 mm Measurement time: 1–5 min
Fig. 3. Measurement set-up of the MEMS accelerometer.
contents (WCs) before compaction were 32% (April 11) and 39% (April 18). A test section was 1.5 20 m plot with two replicates. After the 2nd pass compaction test, we measured the penetration resistance and distribution of the three soil phases, i.e., vapor, liquid and solid phase fraction. We measured the penetration resistance using a digital cone penetrometer (CP40II, Rimik, Queensland, Australia; cone top angle 30 ; cross-sectional area of the cone, 2 cm2; data acquisition intervals, 1.5 cm, three places per plot). We used a digital actual volumenometer (DIK1150, Daiki Rika Kogyo Co., Saitama, Japan) to measure the threephase distribution after the core sampling. All statistical analyses (ANOVA) were performed using SAS Add-in for Microsoft Office 6.1 software (SAS Institute Inc., Cary, North Carolina). 2.3. Acceleration response of vibratory roller
2.4. Volume of water leakage from the test field The volume of water leakage from the test field was measured with a rapid leakage capacity tester (DIK-4350, Daiki Rika Kogyo). Fig. 4 and Table 5 show the measurement set-up and the specifications of the tester, which measures the quantity of falling permeation by inserting a bottomless infiltrating drum into the test field. Since this does not measure the permeation as the water level, due to the enlarged variation of the receded water, the tester can measure the quantity of daily falling permeation within 1–5 min. After all of the compaction tests were finished, we filled the field with water to a depth of approx. 10 cm and measured the water leakage volume (Fig. 4). The measurement time was set at 1 min. Based on a study by Kanmuri et al. (2012), the water leakage at 2 cm/day is considered as acceptable (meaning that water leakage is prevented). After we measured the quantity of water
We measured the acceleration response of the vibratory roller with a MEMS accelerometer (LP-WS0902 (5G/300 dps), Logical Product Co., Fukuoka, Japan). Fig. 3 and Table 4 provide the measurement set-up and the specifications of the accelerometer. The accelerometer had a sensor that we attached to the vibration generator. The sampling frequency was set to 200 Hz. With this sensor, we measured not only the acceleration but also the angular velocity of the roller. The measurement data were taken with a notebook personal computer (PC) in real time (Fig. 3). We used the response wave form of the vibration acceleration to calculate the spectrum distribution by the discrete Fourier transform (DFT) method. The DFT analysis program was part of Microsoft Visual Basic 2010 Express software. Table 4 Specifications of the MEMS accelerometer. Manufacturer: LOGICAL PRODUCT Co., Ltd. Model: LP-WS0902 (5 G/300 dps) Sampling frequency: 1–1000 Hz (9 levels) Modulation scheme: DS-SS External dimensions: W40 H20 D55 mm Sensor weight: 35 g (Contains one AAA battery) Fig. 5. Sampling method for the soil structure analysis.
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Table 6 Specifications of soil sampling device. Sampler: FUJIWARA SCIENTIFIC Co., Ltd. Model: HS-30S Sample size: DIA50 L300 mm Material of sample case: Polyvinyl chloride (PVC) Electric drill: TOSHIBA CORPORATION (DR-20S1)
Table 7 Three-phase distribution, porosity, saturation percentage and PR in the rollercompacted field (after 2nd Pass). WC (%)
Conditiona Depth Vapor Liquid Solid Porosity Saturation PR (cm) (%) (%) (%) (%)b (%)c (MPa)d
32
BC
1.0 km/h
leakage, we drained away the water of the field to perform soil sampling.
2.0 km/h
2.5. Structure analysis of compacted soil Fig. 5 and Table 6 show the sampling method and the specifications of soil sampling device used for the soil structure analysis. Each sample for analysis was collected with an electric sampler and placed in a transparent cylinder made of polyvinyl chloride (PVC; 50 mm dia. 300 mm long). We photographed a perpendicular section of the entire sample with an industrial X-ray CT scanner (TOSCANER-20000RE, Toshiba, Tokyo; voxel size 0.195 mm, slice thickness 1 mm) to determine the rough soil structure. We also used a micro X-ray CT scanner (TOSCANNER32300FPD, Toshiba; voxel size 0.079 mm, slice thickness 0.159 mm) for more detailed photography and to obtain a three-dimensional section. We calculated the spatial distribution of the pore diameters and the pore shapes of the soil with an analysis program (Mukunoki et al., 2009, 2010, 2011, 2016) based on the micro X-ray CT images of the pores. Our analysis was based on an image processing technique that uses mathematical morphology (Soille, 2003) to evaluate the 3D distribution of the pore scale in the compacted soils. Fig. 6 shows the results of the 3D soil structure analysis using the morphological openings (Soille, 2003). With this method, various sizes of structuring elements are fitted to a binary image of soil pore. First,
39
BC
1.0 km/h
2.0 km/h
2–7 7–12 12–17 2–7 7–12 12–17 2–7 7–12 12–17
40 37 34 27 29 23 28 30 29
27 29 30 33 32 37 33 33 29
33 34 36 39 39 40 39 37 42
67 66 64 61 61 60 61 63 58
40 44 47 54 52 62 54 52 50
0.01 0.03 0.12 0.64 0.61 0.75 0.61 0.59 0.69
2–7 7–12 12–17 2–7 7–12 12–17 2–7 7–12 12–17
30 16 7 11 2 2 13 3 1
34 42 47 41 48 48 41 48 50
36 42 46 47 49 50 46 49 49
64 58 54 53 51 50 54 51 51
53 72 87 77 94 96 76 94 98
0.04 0.05 0.20 0.70 0.49 0.43 0.56 0.43 0.40
Average value of two replicates. a BC: Before compaction. 1.0 km/h, 2.0 km/h: operating speed. b Porosity is 100 – Solid. c Saturation is (Liquid/Porosity) * 100. d Measurement depth are 4.5, 9.0, 15.0 cm.
we fit structure element 1 (dia. 0.079 mm) to the binary image, and then we extracted its total porosity. By the same procedure, we determined the pore structure by creating the extracted image of each element (For example: element 2, 3, 4, 5; dia. 0.237, 0.395, 0.553, 0.711 mm). Finally, we obtained a 3D pore diameter distribution by adding together all the separate images (Mukunoki et al., 2016).
Fig. 6. Results of the 3D soil structure analysis using the morphological openings.
Fig. 7. Penetration resistance of the roller-compacted field (after 2nd pass). WC: water content; BC: before compaction; 1.0 km/h, 2.0 km/h: operating speed. Bars indicate standard error.
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3. Results and discussion 3.1. Penetration resistance of the roller-compacted field Fig. 7 shows the results of the comparison of the penetration resistance (PR) of the roller-compacted field at the WC values of 32% and 39%. The PR at a range of 0–15 cm depth was increased by the roller compaction in both moisture conditions, and the PR at this range slightly decreased with the increase in operating speed in both moisture conditions. In addition, at the highest WC of 39%, a PR decrease at approx. 12 cm depth was observed. However, no clear relationship was observed at 20–60 cm depth. 3.2. Comparison of the PR and the three-phase distribution in the roller-compacted field Table 7 shows the values of the three-phase distribution, porosity, saturation percentage and PR in the roller-compacted field (after 2nd pass). In all conditions, the vapor-phase fraction was decreased by roller compaction, and the liquid-phase and solid-phase fractions increased. As for the vapor-phase fraction, the decrease produced by the roller compaction became remarkable in a high water condition (WC 39%). In addition, the decrease
5
in the PR at approx. 12 cm depth with overall WC 39% (Fig. 7) seems to have occurred because the saturation percentage of this part was considerable higher than WC 32%. The ANOVA results of the effect of WC and operating speed on three-phase distribution, porosity, saturation percentage and PR in the roller-compacted field per depth (2–7, 7–12, 12–17 cm) are shown in Table 8 (based on the data in Table 7). The vapor-phase fraction at WC 39% was significantly smaller than that at WC 32% at all depths. The liquid-phase fraction and saturation percentage at WC 39% were significantly larger than that at WC 32% at all depths. The solidphase fraction (porosity) at WC 39% was significantly larger (smaller) than that at WC 32% in 2–12 cm depth. The PR at WC 39% was significantly smaller than that at WC 32% in 7–17 cm depth. In addition, the PR at operating speed 2 km/h was significantly smaller than that at operating speed 1 km/h in 2–7 cm depth. A significant WC operating speed interaction was found on the PR in 2–7 cm depth (Table 8). 3.3. Frequency analysis of the vibration accelerations Fig. 8 shows an example (1st pass, WC 32% and 39%, operating speed 2.0 km/h, PTO 1100 rpm and analysis time 20 s) of the spectrum distributions of the vibration accelerations. The
Table 8 The ANOVA results of the effect of WC and operating speed on three-phase distribution, porosity, saturation percentage and PR in the roller-compacted field per depth. Depth (cm)
Fixed source of variation
Vapor (%) P>F
Liquid (%)
Solid (%)
Porosity (%)
Saturation (%)
PR (MPa)
2–7
WCa Speedb WC Speed
0.003 nsc ns
0.010 ns ns
<0.001 ns ns
<0.001 ns ns
0.005 ns ns
ns 0.001 0.008
7–12
WC Speed WC Speed
<0.001 ns ns
<0.001 ns ns
<0.001 ns ns
<0.001 ns ns
<0.001 ns ns
0.021 ns ns
12–17
WC Speed WC Speed
<0.001 ns ns
0.004 ns ns
ns ns ns
ns ns ns
<0.001 ns ns
0.014 ns ns
a b c
WC: water content of before compaction. Speed: operating speed of the roller. ns: not significant at P < 0.05.
Fig. 8. Spectrum distributions of a vibration acceleration (during 1st pass, operating speed 2.0 km/h, PTO 1100 rpm and analysis time 20 s). WC: water content of before compaction.
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Table 9 The frequency and amplitude of the MFC in the vertical direction of the roller. WCb (%)
Operating speed (km/h)
32
1.0 2.0 1.0
39
2.0
a b
1st pass
2nd pass
PTO (rps)
Frequency (Hz)
Amplitude (G)
PTO (rps)
Frequency (Hz)
Amplitude (G)
19 18 19 18 19 19 19 19
19 –a 18 18 19 – 19 19
2.2 – 2.7 1.9 3.9 – 3.5 3.2
18 19 18 19 19 19 19 19
19 19 19 19 19 – 19 19
2.3 2.5 2.3 2.5 3.3 – 2.6 4.1
Loss of the vibration acceleration data. WC: water content of before compaction.
Table 10 Water leakage of the roller-compacted field (after 2nd pass) and the ANOVA results of the effects of WC and operating speed. Water leakage (cm/day) WC (%)
1 km/h
2 km/h
32
15.4 12.3 1.8 1.4
48.3 41.0 2.3 1.7
39
Fixed source of variation
P>F
a
<0.001 0.001 0.002
WC Speedb WC Speed a b
WC: water content of before compaction. Speed: operating speed of the roller.
frequencies of the main frequency component (MFC) in the longitudinal and vertical directions of the vibration acceleration were both 19 Hz, and the frequency in the horizontal direction was unclear. In addition, the frequency of the MFC in pitching (i.e., the angular velocity of the roller) was 19 Hz, and yawing and rolling were indistinct in both moisture conditions (data not shown). We thus observed that the frequency of the MFC in the pitching of the roller and the longitudinal and vertical directions of the vibration acceleration paralleled the PTO rotation frequency, because the PTO turns approx. 19 times per sec (1100 rpm). Table 9 shows the frequency and amplitude of the MFC in the vertical direction of the roller. Generally, the roller response is affected by the type and water content of soil (Fujiyama et al., 2002). A tendency to increase was seen in the amplitude with the increase in the WC in all operating speeds.
3.4. The water leakage of the compacted field Table 10 shows the water leakage of the roller-compacted field (after 2nd pass) and the ANOVA results of the effects of WC and operating speed. The effect of vibrating compaction on water leakage was increased significantly by slowing the operating speed. This is because the number of vibrations per unit time per unit area depends on the operating speed. The hydraulic conductivity, decreases with the increase of moisture content (Lambe, 1958). The water leakage of WC 39% was significantly smaller than that of WC 32%. In addition, a significant WC operating speed interaction was found on the water leakage. Water leakage from the field was sufficiently prevented (to 2 cm/day or less) when the water content was WC 39%. Fig. 9 shows the relationship between the water leakage and the amplitude of the MFC in the vertical direction. The amplitude of the MFC increased significantly with a decrease in the volume of water leakage. However, we found that a more detailed analysis was necessary to improve the predictive precision, because the coefficient of determination was small.
Amplitude of MFC (G)
4.5
4.0
y = 3.47 x-0.11 R = 0.77* *: significant at P < 0.05
3.5 3.0 2.5 2.0 0
10
20 30 40 Water leakage (cm/day)
50
Fig. 9. Relationship between the water leakage and the amplitude of the MFC (during 2nd pass) in the vertical direction.
Fig. 10. X-ray CT images of the inefficiently (water leakage: 41.0 cm/day) and efficiently (1.7 cm/day) compacted soils. WC: water content of before compaction. Use of the industrial X-ray CT scanner (TOSCANER-20000RE, Toshiba, Tokyo; voxel size 0.195 mm, slice thickness 1 mm).
Please cite this article in press as: K. Fukami, et al., Water leakage control by using vibratory roller on a dry-seeded rice field in southwestern Japan, Soil Tillage Res. (2016), http://dx.doi.org/10.1016/j.still.2016.09.011
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Fig. 11. Micro X-ray CT images of the inefficiently (water leakage: 41.0 cm/day) and efficiently (water leakage: 1.7 cm/day) compacted soils. WC: water content of before compaction. Use of the micro X-ray CT scanner (TOSCANNER-32300FPD, Toshiba; voxel size 0.079 mm, slice thickness 0.159 mm).
3.5. The X-ray CT analysis of the compacted soil We analyzed the soil structure to understand the difference between the water leakage values of 41.0 cm/day (WC 32%, operating speed 2.0 km/h) and 1.7 cm/day (WC 39%, operating speed 2.0 km/h) in Table 10. Fig. 10 provides the industrial X-ray CT images (voxel size 0.195 mm, slice thickness 1 mm) of the inefficiently compacted (WC 32%, water leakage 41.0 cm/day) and efficiently compacted (WC 39%, water leakage 1.7 cm/day) soils. The vertical section views of the sampling soils (50 mm dia. 300 mm long) confirmed that there was structural difference at the top soil layer compared to the underlying soil layer (Fig. 10). Fig. 11 provides the micro X-ray CT images (voxel size 0.079 mm, slice thickness 0.159 mm) of the inefficiently compacted and efficiently compacted soils. From the vertical section view (depth
20–90 mm) and the horizontal section views (depth 35, 55 and 77 mm), we confirmed that the pores (black-colored) showed a flatter shape in the efficiently compacted soil (WC 39%) than the inefficiently compacted soil (WC 32%). Fig. 12 shows the 3D pore diameter distributions of the inefficiently and efficiently compacted soils based on micro X-ray CT images. The range of the analysis depth was 20–90 mm, and the sample size was 31.6 31.6 71.1 mm. From this figure, we found that the area of small pore diameters (blue-colored in the figure) in the efficiently compacted soil was darker than that of the inefficiently compacted soil. Fig. 13 shows the occupation ratio to the total porosity based on the data in Fig. 12. It should be noted that total porosities in Fig. 13 were about half those in Table 7 and thus this method misses a large part of the pores. However, from Fig. 13, we found that the total porosity of the efficiently compacted
Fig. 12. The 3D pore diameter distributions.(For interpretation of the references to color in the text, the reader is referred to the web version of this article.)
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Fig. 13. Occupation rate to the total porosity.
soil was lower than that of the inefficiently compacted soil, but the small-sized pore fraction of the efficiently compacted soil was greater than that of the inefficiently compacted soil. 4. Conclusions The tests were conducted at two different soil-water contents (WC: 32 and 39%) before roller compaction. The results of the present study demonstrated that water leakage from the field was sufficiently prevented when the soil moisture content was WC 39%. The shape of the soil pores that could efficiently prevent water leakage was flatter than that of the inefficiently compacted soil (WC 32%). In addition, the total porosity decreased, but the smallsized pore fraction increased. On the other hand, the amplitude of the MFC in the vertical direction of the vibration acceleration of the roller was significantly increased with the decrease in the volume of water leakage. Thus, in addition to establishing the efficiency of vibratory rollers in reducing water leakage, our findings suggest that it is to some extent possible to estimate the water leakage prevention effect from the acceleration response of a vibrating roller. In the future, we plan to (1) reexamine the sampling range and the method of analyzing the soil, (2) conduct further analyses of the soil structure, the compaction conditions, and the relationship between them, and (3) perform a soil structure analysis that includes the root system of the rice. Acknowledgements This study was supported by the Grants-in-Aid for Scientific Research (No. 25850175) from the Ministry of Education, Culture, Sports, Science and Technology. We are grateful to Dr. Tatsuo Hiroma of the ex-Saga-University professor for DFT analysis, Mr. Takahiro Sato of the X-Earth Center for X-ray CT analysis, Mr. Yukinari Kawahara, Mr. Teruyuki Miike, Mr. Akitoshi Honbu, Mr. Hiroyuki Itoh, Mr. Sadahiro Higashi, Ms. Tamiko Shimogawa and Ms. Kaori Sonoda of the KARC for their field management and data collection in this experiment.
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Please cite this article in press as: K. Fukami, et al., Water leakage control by using vibratory roller on a dry-seeded rice field in southwestern Japan, Soil Tillage Res. (2016), http://dx.doi.org/10.1016/j.still.2016.09.011