Comparative Performance of Various Disc-Type Furrow Openers in No-Till Paddy Field Conditions

Different furrow openers are required to be evaluated for their suitability to manage rice straw for direct planting of wheat in paddy fields. This study was carried out to assess the straw-cutting ability and draft requirements of four different disc-type furrow openers (notched, toothed, smooth-edge single disc, and double disc) in no-till paddy fields. The openers were attached to an in-field traction rig equipped with S-type load cells, and tested using three operating depths of 30, 60, and 90 mm, and three traveling speeds of 0.1, 0.2, and 0.3 m s−1. Vertical and horizontal forces acting on the openers were observed using LabVIEW software based data acquisition system. The results of this study indicated that the furrow opener type, operating depth, and speed significantly influenced the horizontal and vertical forces, as well as straw-cutting ability of the furrow openers. The highest draft and vertical force were noted for double disc-type furrow openers. The mean straw-cutting efficiency of notched, toothed, and smooth-edge single disc and double disc furrow openers were 12.4, 46.2, 11.4, and 78.5%, respectively. The double disc furrow opener (DD) produced the lowest level of hair-pinned straw and had the highest straw-cutting efficiency with a value of 88.6% at 90 mm operating depth, and therefore had the best performance in comparison with other furrow openers.


Introduction
Tillage operations are aimed at improving the physical properties of soil for achieving enhanced crop production.Continuous application of conventional tillage and burning of crop residue decline soil fertility [1], that ultimately reduces soil productivity [2].Soil organic carbon (SOC), water holding capacity, nutrient flow, and biological life are negatively affected by conventional tillage due to the degradation of soil structure [3,4].Maintenance of soil health and energy-efficient technologies are essential for sustainable crop production [5].Conservation tillage is recognized as a low-cost and energy-efficient tillage system for crop production [6,7].
Conservation tillage activities are preferred because of their advantages in improvement of soil structure and water and soil conservation by incorporation of crop residues near the soil surface [8].Further, this has positive impacts on the soil micro-flora and micro-fauna [9].Conservation tillage is abroad term that often includes no-tillage and shallow surface tillage (minimum tillage) [10,11].Crop reaction to tillage systems is dissimilar because of the composite connections between weather, in a paddy field after the rice crop harvesting at Jangpu Agricultural Farm, Nanjing Agricultural University, in December 2013.The rice-wheat cropping pattern was followed at the experiment field for a long time.

Measurements of Soil Properties
Soil physical properties (moisture content, bulk density) were determined by collecting 24 undisturbed soil samples (3 cm long and 5 cm diameter) at random from the experimental field prior to the commencement of the experiment.The soil was weighed before and after oven-drying at 105 • C for 24 h to quantify the bulk density and dry basis soil moisture content [35,41].Cohesion, internal friction angle, and shear strength were determined using direct shear box apparatus [42].Soil surface penetration resistance (cone index) was measured up to a depth of 10 cm with a digital penetrometer (TJSD-750, Zhejiang Top Instrument Co. Ltd, China) from ten random spots in the experimental area.The soil physical and mechanical properties are presented in Table 1.
Table 1.Soil physical and mechanical properties.

Specifications ofTest Rigand Disc Furrow Openers
Four various types of furrow openers (smooth, toothed, and notched single disc, and smooth-edge double disc-hereafter referred to as double disc-with an external diameter of 450 mm) were selected for the tests (Figure 1).Single discs were installed vertically as to have no inclined angle, whereas for double disc openers, each disc had a 7 • inclined angle.The details of the main parameters of the furrow openers are presented in Table 2. Furrow openers were tested in the paddy field by using a test rig designed and developed in the Key Laboratory of Intelligent Agricultural Equipment of Jiangsu province, Nanjing (Figure 2).The main aim of designing the test rig (used in the field conditions for the experiment) was to control the operating conditions of the tools and to avoid tractor tire compaction in the field.The test rig consisted of a tool moving frame/trolley, a tool hitching frame, a power source, two load transducers named as LSR-2A (2KN, Shanghai, Zhendan Sensor and Instrument Factory, China) for measuring draft and vertical forces, and a data acquisition system.One load cell was attached between the trolley rings and a wire was used to pull the opener for horizontal force, and the other one was fixed between the hitching frame and a depth-controlling rod for the vertical force measurements.These transducers were calibrated before running the tests.To run the data acquisition system (computer and sensors) a battery was used, whereas, in order to operate the furrow openers, power was supplied by power take-off (PTO) of a two-wheel tractor.
Instrument Factory, China) for measuring draft and vertical forces, and a data acquisition system.One load cell was attached between the trolley rings and a wire was used to pull the opener for horizontal force, and the other one was fixed between the hitching frame and a depth-controlling rod for the vertical force measurements.These transducers were calibrated before running the tests.To run the data acquisition system (computer and sensors) a battery was used, whereas, in order to operate the furrow openers, power was supplied by power take-off (PTO) of a two-wheel tractor.

2.4.Test Procedure
A randomized complete block design with three-way factorial arrangements (4 × 3 × 3) was followed to carry out the study.Four different types of furrow openers (toothed, notched, smoothedge single disc, and smooth-edge double disc) were tested at three operating depths (30, 60, and 90 mm) and three traveling speeds (0.1, 0.2, and 0.3 m s −1 ).The selected travelling speeds were a little low as there was no option for higher speed with field test rig.The working depth was measured from the edges of notches and teeth for notched and tooth-type furrow openers, respectively.Each test was replicated three times.A deep furrow perpendicular to the tool was dug to secure and measure the operating depth of the tool.The tool was first adjusted in the furrow according the

Test Procedure
A randomized complete block design with three-way factorial arrangements (4 × 3 × 3) was followed to carry out the study.Four different types of furrow openers (toothed, notched, smooth-edge single disc, and smooth-edge double disc) were tested at three operating depths (30, 60, and 90 mm) and three traveling speeds (0.1, 0.2, and 0.3 m s −1 ).The selected travelling speeds were a little low as there was no option for higher speed with field test rig.The working depth was measured from the edges of notches and teeth for notched and tooth-type furrow openers, respectively.Each test was replicated three times.A deep furrow perpendicular to the tool was dug to secure and measure the operating depth of the tool.The tool was first adjusted in the furrow according the required depth.As the depth of the furrow was more than the required depth, before operation of the tool it was in the air and did not touch the ground surface.The straw-cutting efficiency of the furrow openers was determined following Kushwaha et al. [34], Magalhães et al. [38], and Bianchini and Magalhães [6].Firstly, the stubbles were cut to clean the soil surface, leaving the roots in the soil.Then 200 g m −2 of freshly harvested straw was uniformly spread in front of the furrow opener under no-till conditions following similar methodology as adopted in previous studies.The average length of the straw was 43 cm.A hitching frame with a depth-adjustable screw rod was attached to the furrow openers and then fixed to the trolley; the trolley had the ability to move freely on the main frame of the rig (Figure 3).furrow openers and then fixed to the trolley; the trolley had the ability to move freely on the main frame of the rig (Figure 3).

2.5.Data Recording
The data acquisition system consisted of software and hardware components.The software program used in this study was the LabVIEW (National Instruments, Austin, TX, USA) programming test system, and hardware was composed of a data acquisition card, signal amplifier, computer, battery, and inverter.To assist the data collection, a USB-4711A Advantech bus multifunction data acquisition card was attached with the system.The data acquisition card, with 12 bits per channel, had a maximum sampling frequency of 150 kHz, and 16 single-ended or eight differential combination analog inputs.
The LabVIEW two-channel data acquisition system was applied to record the draft and vertical force signal data (Figure 4a,b).The millisecond voltage data was recorded in EXCEL spreadsheet format.A digital camera (Canon, Canon Inc., Beijing, China) was used to record straw and soil cutting patterns.The snapshots were recovered from recorded videos and analyzed.Furthermore, the laid straw was carefully collected and separated into cut and uncut straw for weighing, to determine the straw-cutting capacity of the furrow openers.Equation ( 1) was used to calculate the straw cutting efficiency:

Data Recording
The data acquisition system consisted of software and hardware components.The software program used in this study was the LabVIEW (National Instruments, Austin, TX, USA) programming test system, and hardware was composed of a data acquisition card, signal amplifier, computer, battery, and inverter.To assist the data collection, a USB-4711A Advantech bus multifunction data acquisition card was attached with the system.The data acquisition card, with 12 bits per channel, had a maximum sampling frequency of 150 kHz, and 16 single-ended or eight differential combination analog inputs.
The LabVIEW two-channel data acquisition system was applied to record the draft and vertical force signal data (Figure 4A,B).The millisecond voltage data was recorded in EXCEL spreadsheet format.
A digital camera (Canon, Canon Inc., Beijing, China) was used to record straw and soil cutting patterns.The snapshots were recovered from recorded videos and analyzed.Furthermore, the laid straw was carefully collected and separated into cut and uncut straw for weighing, to determine the straw-cutting capacity of the furrow openers.Equation ( 1

2.6.Data Analysis
To analyze the data, analysis of variance (ANOVA) was executed using the Statistix Statistical Software Package (version 8.1, Analytical Software, Tallahessee, FL, USA).When the F-test indicated statistical significance at the p = 0.05 probability level, treatment means were separated by the least significant difference (LSD0.05)test [43].

Results and Discussion
Statistical mean values of draft, vertical force, and straw-cutting efficiency for all treatments are presented in Table 3. Further, at the plastic phase of the paddy field (moisture content of 33.3%), a typical variation of forces (draft and vertical) on the double disc furrow opener has been presented in Figure 5.The vertical force line shows that as the furrow opener's disc touched the soil surface, resistance appeared.Means for each factor in the same column followed by the same superscript are not significantly different at p < 0.05 as tested by LSD.

Data Analysis
To analyze the data, analysis of variance (ANOVA) was executed using the Statistix Statistical Software Package (version 8.1, Analytical Software, Tallahessee, FL, USA).When the F-test indicated statistical significance at the p = 0.05 probability level, treatment means were separated by the least significant difference (LSD 0.05 ) test [43].

Results and Discussion
Statistical mean values of draft, vertical force, and straw-cutting efficiency for all treatments are presented in Table 3. Further, at the plastic phase of the paddy field (moisture content of 33.3%), a typical variation of forces (draft and vertical) on the double disc furrow opener has been presented in Figure 5.The vertical force line shows that as the furrow opener's disc touched the soil surface, resistance appeared.Means for each factor in the same column followed by the same superscript are not significantly different at p < 0.05 as tested by LSD.

3.1.Draft Force (Fh) Requirement of Furrow Openers
The results indicated that the influences of operating depth traveling speed and furrow opener type on the draft force in no-till paddy fields were significant.The interaction effects of depth × furrow opener type, furrow opener type × speed, depth × speed, and depth ×furrow opener × speed on the draft force were also significant.The test results indicated that the double disc furrow opener showed significantly higher draft force than the other type of disc openers for all operating depths and speeds.The comparison among discs indicated that the drafts of toothed and notched single disc openers did not differ significantly from each other, whereas, drafts of smooth and notched single disc openers were significantly different at 30, 60, and 90 mm depths (Table 4).At a 90 mm operating depth, toothed single disc furrow openers expressed the lowest draft force requirement, whereas double disc furrow openers exhibited the highest draft force requirement.The higher draft force of the double disc opener concurs with existing soil failure and cutting theories [44], which elaborate that tillage tools with greater cutting wideness require higher draft force.Likewise, Darmora and Pandey [45] also concluded, on the basis of results of evaluation of seven different furrow openers, that opener width affected the draft force.Hasimu and Chen [35] reported that the winged hoe-type openers showed higher draft force and specific draft requirements than other hoe-type openers.In soil bin conditions, Kushwaha et al. [34] also observed the raise in draft force with depth for disc-type (smooth, notched, and serrated) furrow openers.Chaudhuri [24] analyzed different seed openers and found that with increasing operating depth, draft force on tillage tools also increases.The draft force results are in agreement with Bianchini and Magalhães [6] who reported that horizontal draft forces ranged from 0.94 to 1.36 kN for smooth-type, 0.32 to 0.5 kN for toothed-type, and 0.6 to 0.78 kN for notched-type single disc furrow openers, when cutting sugarcane residue at 80 mm and 100 mm operating depths, respectively.
The mean values of the effect of speed and the furrow opener type on draft force are presented in Table 5.The lowest draft force was observed at the speed of 0.1 m s −1 for toothed-type furrow openers, while the highest draft force was achieved for double disc furrow openers operating at 0.3 m s −1 speed (Table 5).Kushwaha et al. [34] observed the increase in draft force with the increase in rotation speed of coulters.The speed of the tool may help the tool to penetrate soil, thus increasing the draft force, while high penetration may also be responsible for higher soil vertical resistance acting on the opener.

Draft Force (Fh) Requirement of Furrow Openers
The results indicated that the influences of operating depth traveling speed and furrow opener type on the draft force in no-till paddy fields were significant.The interaction effects of depth × furrow opener type, furrow opener type × speed, depth × speed, and depth ×furrow opener × speed on the draft force were also significant.The test results indicated that the double disc furrow opener showed significantly higher draft force than the other type of disc openers for all operating depths and speeds.The comparison among discs indicated that the drafts of toothed and notched single disc openers did not differ significantly from each other, whereas, drafts of smooth and notched single disc openers were significantly different at 30, 60, and 90 mm depths (Table 4).At a 90 mm operating depth, toothed single disc furrow openers expressed the lowest draft force requirement, whereas double disc furrow openers exhibited the highest draft force requirement.The higher draft force of the double disc opener concurs with existing soil failure and cutting theories [44], which elaborate that tillage tools with greater cutting wideness require higher draft force.Likewise, Darmora and Pandey [45] also concluded, on the basis of results of evaluation of seven different furrow openers, that opener width affected the draft force.Hasimu and Chen [35] reported that the winged hoe-type openers showed higher draft force and specific draft requirements than other hoe-type openers.In soil bin conditions, Kushwaha et al. [34] also observed the raise in draft force with depth for disc-type (smooth, notched, and serrated) furrow openers.Chaudhuri [24] analyzed different seed openers and found that with increasing operating depth, draft force on tillage tools also increases.The draft force results are in agreement with Bianchini and Magalhães [6] who reported that horizontal draft forces ranged from 0.94 to 1.36 kN for smooth-type, 0.32 to 0.5 kN for toothed-type, and 0.6 to 0.78 kN for notched-type single disc furrow openers, when cutting sugarcane residue at 80 mm and 100 mm operating depths, respectively.
The mean values of the effect of speed and the furrow opener type on draft force are presented in Table 5.The lowest draft force was observed at the speed of 0.1 m s −1 for toothed-type furrow openers, while the highest draft force was achieved for double disc furrow openers operating at 0.3 m s −1 speed (Table 5).Kushwaha et al. [34] observed the increase in draft force with the increase in rotation speed of coulters.The speed of the tool may help the tool to penetrate soil, thus increasing the draft force, while high penetration may also be responsible for higher soil vertical resistance acting on the opener.Means for each parameter followed by the same superscript are not significantly different at p ≤ 0.05, as tested by LSD.

Vertical Force Performance (Fv) of Furrow Openers
Upward vertical force was significantly influenced by furrow opener type, operating depth, and speed according to the analysis of the variance.The highest vertical draft force was noted for double disc furrow openers, followed by notched-type, toothed-type, and smooth-type single disc furrow openers, respectively.Previously, a similar working behavior was noted for smooth-type, toothed-type, and notched-type single disc furrow openers in sugarcane residue conditions [6].Kushwaha et al. [34], Magalhães et al. [38], and Choi and Erbach [40] also found variations of vertical force with changes in opener type and diameter.
The interaction effect between operating depth and the furrow opener type was significant (Table 4).The results indicated that increasing the operating depth increased the soil vertical resistance acting on the furrow opener.The penetration resistance increases in lower layers of soils because of hardpan in paddy fields, developed as a result of puddling [7,20,46].Bianchini and Magalhães [6] recorded the range of vertical forces as 3.54 to 3.72 kN for smooth-type, 2.12 to 2.26 kN for notched-type, and 1.24 to 1.65 kN for toothed-type single disc furrow openers at the operating depths of 80 and 100 mm, respectively, for sugarcane residue.At 30 mm depth, toothed-type single disc showed the lowest vertical force, whereas, double disc furrow openers expressed the highest vertical force at 90 mm operating depth.
The influence of the interaction between furrow opener type and working speed on vertical force is presented in Table 5.Double disc furrow openers showed the highest vertical force of 1776.7 N at the speed of 0.3 m s −1 , whereas toothed-type single disc demonstrated the lowest vertical force of 811.2 N at the speed of 0.1 m s −1 .Kushwaha et al. [34] concluded similar results and found that vertical force increased with the speed of the disc-type furrow openers.The work of Magalhães et al. [38] incicatedthat the vertical load requirement for toothed disc tool penetration at 70 mm operating depth varied between 1.5 to 2.1 kN in soil covered by sugarcane residue.The emergence rate is also affected by penetration depth.Karayel and Šarauskis [28] concluded that at downward forces of 1150 and 1400 N of the furrow opener, the emergence percentage of maize was highest because of having the best sowing uniformity.The high sowing uniformity ultimately leads to the highest crop emergence and yield.

Straw Cutting Efficiency of Various Disc-Type Furrow Openers
The straw used for the test had a moisture content of 41.4%.The statistical results showed that the effects of furrow opener type, operating depth, and traveling speed on the straw-cutting efficiency in no-till paddy fields were significant.The interaction effects of depth × furrow opener, furrow opener × speed, depth × speed, and depth × furrow opener × speed on straw-cutting efficiency were significant.Toothed-type furrow openers showed the second best straw-cutting performance among all four furrow opener types under test conditions with mean values of 33.0, 46.9, and 58.7% at operating depths of 30, 60, and 90 mm, respectively.However, we observed the issue of straw-rolling due to the backward-pushing action of the teeth.The notched-type single disc opener showed a straw-cutting capacity with mean values of 9.9, 10.4.0, and 13.7% at operating depths of 30, 60, and 90 mm (Figure 6), respectively.Notched-type furrow openers nearly had efficiency similar to the smooth-type single disc furrow openers.Notched-type and smooth-type single disc furrow openers pushed the straw into the paddy field (straw hair-pinning), which might reduce crop emergence due to decreased soil-seed contact.

3.3.Straw Cutting Efficiency of Various Disc-Type Furrow Openers
The straw used for the test had a moisture content of 41.4%.The statistical results showed that the effects of furrow opener type, operating depth, and traveling speed on the straw-cutting efficiency in no-till paddy fields were significant.The interaction effects of depth ×furrow opener, furrow opener × speed, depth × speed, and depth × furrow opener × speed on straw-cutting efficiency were significant.Toothed-type furrow openers showed the second best straw-cutting performance among all four furrow opener types under test conditions with mean values of 33.0, 46.9, and 58.7% at operating depths of 30, 60, and 90 mm, respectively.However, we observed the issue of straw-rolling due to the backward-pushing action of the teeth.The notched-type single disc opener showed a straw-cutting capacity with mean values of 9.9, 10.4.0, and 13.7% at operating depths of 30, 60, and 90 mm (Figure 6), respectively.Notched-type furrow openers nearly had efficiency similar to the smooth-type single disc furrow openers.Notched-type and smooth-type single disc furrow openers pushed the straw into the paddy field (straw hair-pinning), which might reduce crop emergence due to decreased soil-seed contact.As observed in the case of double disc openers, the straw was cut due to the application of tensile force on the straw and soil (Figure 7).Paddy soils are mostly sticky soils [18].Therefore, hairpinning phenomena was observed less in double disc furrow openers, and they showed the highest strawcutting efficiency.Straw-cutting performance is also affected by straw mechanical properties such as tensile, shear, and bending strengths [34].The moisture content of straw also affects the mechanical properties of the straw [47].The dependence of straw-cutting on moisture content has been reported by researchers [39] previously.As observed in the case of double disc openers, the straw was cut due to the application of tensile force on the straw and soil (Figure 7).Paddy soils are mostly sticky soils [18].Therefore, hairpinning phenomena was observed less in double disc furrow openers, and they showed the highest straw-cutting efficiency.Straw-cutting performance is also affected by straw mechanical properties such as tensile, shear, and bending strengths [34].The moisture content of straw also affects the mechanical properties of the straw [47].The dependence of straw-cutting on moisture content has been reported by researchers [39] previously.From the results, it can be concluded that straw-cutting efficiency in paddy fields can be increased by increasing tensile action through increased disc incline angles, along with the bending and shearing actions of cutting tillage tools.The design and development of further tillage and strawcutting tools should focus on the magnitude of tensile force exerted by the tool on soil and straw in no-till paddy fields, because bending forces appear to cause hair-pinning rather than cutting of straw in paddy soils which have high moisture content.Previous studies [6,34] concluded that straw in front of smooth-type single disc furrow openers was cut by a simple shearing and rolling-action, whereas, the soil acts like a cutting board for a knife.This means that if the soil does not offer adequate support to hold the straw in position during the cutting process, the straw ultimately bends, and soil permits the uncut straw to get pushed into the soil due to the compressive load from the furrow opener.Straw-cutting efficiency is further affected by straw moisture content.When straw has high moisture content, it is easy to push the straw into the soil without it being cut.In the present study, hair-pinning was facilitated due to these reasons: (1) the paddy field was in the plastic phase, and (2) the straw had high moisture content (41.4%).Thus, it was easy for smooth-type, toothed-type, and notchedtype single disc furrow openers to fold the straw and push it into the furrow.The observed results related to smooth-type, notched-type, and toothed-type single disc furrow openers are also in agreement with the findings of Bianchini and Magalhães [6], who concluded that toothed-type furrow openers provided higher sugarcane residue cutting efficiency than notched-type and smoothtype single disc openers.Smooth-type single disc openers produced nearly114% more hairpinned sugarcane residue than that obtained from notched-type openers.Magalhaes et al. [38] compared the performance of different sizes of toothed-type openers and observed that toothed-type openers with a diameter of 711 mm left 26 g m −1 of uncut sugarcane residue, which was significantly higher than the amount of uncut residue presented by 508 and 610 mm diameter toothed-type furrow openers.
The straw-cutting efficiency of smooth-type, toothed-type, and notched-type single disc, and double disc furrow openers at different traveling speeds is shown in Figure 8. Straw-cutting efficiency increased with an increase in operating speed.Straw-cutting efficiencies ranged from 11.2 to 13.8% for the smooth-type, from 11.1 to 11.5% for the notched-type, from 42.5 to 49.9% for the toothed-type single disc, and from 72.4 to 87.4% for double disc furrow openers, as the speed changed from 0.1 to 0.3 m s −1 , respectively.From the results, it can be concluded that straw-cutting efficiency in paddy fields can be increased by increasing tensile action through increased disc incline angles, along with the bending and shearing actions of cutting tillage tools.The design and development of further tillage and straw-cutting tools should focus on the magnitude of tensile force exerted by the tool on soil and straw in no-till paddy fields, because bending forces appear to cause hair-pinning rather than cutting of straw in paddy soils which have high moisture content.Previous studies [6,34] concluded that straw in front of smooth-type single disc furrow openers was cut by a simple shearing and rolling-action, whereas, the soil acts like a cutting board for a knife.This means that if the soil does not offer adequate support to hold the straw in position during the cutting process, the straw ultimately bends, and soil permits the uncut straw to get pushed into the soil due to the compressive load from the furrow opener.Straw-cutting efficiency is further affected by straw moisture content.When straw has high moisture content, it is easy to push the straw into the soil without it being cut.In the present study, hair-pinning was facilitated due to these reasons: (1) the paddy field was in the plastic phase; and (2) the straw had high moisture content (41.4%).Thus, it was easy for smooth-type, toothed-type, and notched-type single disc furrow openers to fold the straw and push it into the furrow.The observed results related to smooth-type, notched-type, and toothed-type single disc furrow openers are also in agreement with the findings of Bianchini and Magalhães [6], who concluded that toothed-type furrow openers provided higher sugarcane residue cutting efficiency than notched-type and smooth-type single disc openers.Smooth-type single disc openers produced nearly114% more hairpinned sugarcane residue than that obtained from notched-type openers.Magalhaes et al. [38] compared the performance of different sizes of toothed-type openers and observed that toothed-type openers with a diameter of 711 mm left 26 g m −1 of uncut sugarcane residue, which was significantly higher than the amount of uncut residue presented by 508 and 610 mm diameter toothed-type furrow openers.
The straw-cutting efficiency of smooth-type, toothed-type, and notched-type single disc, and double disc furrow openers at different traveling speeds is shown in Figure 8. Straw-cutting efficiency increased with an increase in operating speed.Straw-cutting efficiencies ranged from 11.2 to 13.8% for the smooth-type, from 11.1 to 11.5% for the notched-type, from 42.5 to 49.9% for the toothed-type single disc, and from 72.4 to 87.4% for double disc furrow openers, as the speed changed from 0.1 to 0.3 m s −1 , respectively.The influence of operating depth on furrow opener crop residue-cutting efficiency at different speeds has been presented in Figure 9. Notched-type openers had better straw-cutting performance than that of smooth-type single disc furrow openers.Figure 10 shows straw-cutting performance by the notched-type, toothed-type, smooth-type single disc, and double disc furrow openers.It can be observed from this figure that the straw was cut where the double disc furrow opener passed over the straw (Figure 10d) because the straws were completely segmented, whereas the smooth-type and notched-type single disc openers pushed the straw into the soil and caused hair-pinning (Figure 10a,c).The influence of operating depth on furrow opener crop residue-cutting efficiency at different speeds has been presented in Figure 9. Notched-type openers had better straw-cutting performance than that of smooth-type single disc furrow openers.Figure 10 shows straw-cutting performance by the notched-type, toothed-type, smooth-type single disc, and double disc furrow openers.It can be observed from this figure that the straw was cut where the double disc furrow opener passed over the straw (Figure 10d) because the straws were completely segmented, whereas the smooth-type and notched-type single disc openers pushed the straw into the soil and caused hair-pinning (Figure 10a,c).The influence of operating depth on furrow opener crop residue-cutting efficiency at different speeds has been presented in Figure 9. Notched-type openers had better straw-cutting performance than that of smooth-type single disc furrow openers.Figure 10 shows straw-cutting performance by the notched-type, toothed-type, smooth-type single disc, and double disc furrow openers.It can be observed from this figure that the straw was cut where the double disc furrow opener passed over the straw (Figure 10d) because the straws were completely segmented, whereas the smooth-type and notched-type single disc openers pushed the straw into the soil and caused hair-pinning (Figure 10a,c).The toothed-type single disc opener rolled the straw over itself and demonstrated lower straw cutting performance comparable with the double disc furrow opener (Figure 10b).Sarauskis et al. [39] reported that higher capacity of straw cut was observed at maximum speeds (speed ratio λ > 1.27 and λ = 1.5) of an active disc coulter than by an inactive disc coulter (λ = 1.0).It was reported that inactive disc coulters (λ = 1.0) cut approximately 30% of winter wheat straw with natural moisture content (mc = 10.1%) and only 12% of humid straw (mc = 22.3%).The results from the present study showed the double disc furrow opener as an efficient straw-cutting device in no-till paddy fields.

Conclusions
Appropriate furrow openers are required for direct-drill sowing of wheat in no-till paddy fields covered by rice straw and stubble.In this research, force requirements and straw-cutting efficiency of four furrow openers (notched, toothed, smooth single disc, and double disc) were measured at different operating depths and speeds.Force requirements and straw-cutting efficiency were considerably influenced by the operating depth, opener-type, and speed.Double disc and smooth-type single disc furrow openers had the highest and lowest straw-cutting efficiencies, respectively.The draft and vertical forces for double disc and toothed-type single disc furrow openers were the highest and lowest, respectively, whereas the straw-cutting efficiency of toothed-type single disc furrow openers was only 58% of that of double disc furrow openers.In no-till paddy soils, it can be concluded that the double disc furrow opener had optimum efficiency in view of straw-cutting efficiency and less hair-pinning, in comparison with the single disc (smooth, notched, and toothed)-type furrow openers.It is recommended that, in paddy field conditions, the best tool for no-till direct seeding is the double disc furrow opener.Therefore, the present study was helpful in the appropriate selection of a furrow opener as a direct-drill machine and its implications in paddy fields.Moreover, non-disc-type furrow openers should be compared with disc-type furrow openers, and sowing uniformity should be determined at field level using computer simulations.

Figure 3 .
Figure 3. (a) ProE 3D view of test rig; (b) ProE 3D view of a furrow opener attached to a hitching frame and movable trolley.

Figure 3 .
Figure 3. (a) ProE 3D view of test rig; (b) ProE 3D view of a furrow opener attached to a hitching frame and movable trolley.
) was used to calculate the straw cutting efficiency: Straw Cutting Efficiency (%) = Weight of Cut Straw Total weight of Straw Applied ×

Figure 5 .
Figure 5.Typical variation, with distance, of the draft and vertical forces acting on a double disc opener.

Figure 5 .
Figure 5.Typical variation, with distance, of the draft and vertical forces acting on a double disc opener.

Figure 6 .
Figure 6.Changes in straw-cutting efficiency with operating depth for different furrow openers.

Figure 6 .
Figure 6.Changes in straw-cutting efficiency with operating depth for different furrow openers.

Figure 7 .
Figure 7. Soil failure and a furrow opened by a double disc opener.

Figure 7 .
Figure 7. Soil failure and a furrow opened by a double disc opener.

Figure 8 .
Figure 8. Changes in straw-cutting efficiency with traveling speed for different furrow openers.

Figure 9 .Figure 8 .
Figure 9.Effect of operating depth and traveling speed on straw-cutting.

Figure 9 .Figure 9 .
Figure 9.Effect of operating depth and traveling speed on straw-cutting.

Table 2 .
Detailed descriptions of furrow openers.

Table 2 .
Detailed descriptions of furrow openers.

Single Disc Notched-Type Toothed-Type Double Disc
Figure 2. Test rigalong with data aqusition system.

Table 3 .
Mean values of draft, vertical force, and straw-cutting efficiency.

Table 3 .
Mean values of draft, vertical force, and straw-cutting efficiency.

Table 4 .
Effect of furrow opener × depth interaction on draft and vertical forces for furrow openers working at various depths in no-till paddy fields.

Table 5 .
Effect of furrow opener × speed interaction on draft and vertical forces for furrow openers working at various speeds in no-till paddy fields.