IntroductionTop
The penetration and movement of a tool into the soil is an action that can be described by a composite behavior, since the soil is usually disturbed by some combination of cutting, shearing, compaction and flow, as the device is forced into the soil (Portella, 1983).
The phenomena arising from the performance of soil tools can be divided into two actions: vertical soil displacement and soil disturbance area. To determine these actions, three profiles should be studied: natural soil surface, soil surface elevation, and internal profile of disturbed soil. The soil disturbance area is the area between the natural profile and the bottom of the furrow, while the elevation area is the one between the original profile and the soil surface after its disturbance. The evaluation of the area between the profiles can be determined by means of graphical representations; the different representations of their areas can be surveyed by means of planimetric techniques and/or computer software programs, as recommended by Conte et al. (2009), Santos et al. (2010), Hasimu & Chen (2014) and Francetto et al. (2015).
Another important feature that results from the elevation area is swelling, which represents the increase in soil volume after the use of tools (Brandelero et al., 2014), due to the increase in the voids between solid particles.
Soil disturbance depends on working depth, length and width of the tool, as stated by Spoor & Godwin (1978) and Chen et al. (2013), besides soil moisture and density. According to Collares et al. (2006) and Mazurana et al. (2011), this action results in reduced soil density and mechanical resistance, and increased macroporosity (Marcolan et al., 2007; Rosa et al., 2008; Nunes et al., 2015), which provides reduction of critical soil density according to Logsdon & Karlen (2004), basic conditions for the proper development and productivity of agricultural crops, as evidenced by Debiasi et al. (2010). Veiga et al. (2007) explain that soil disturbance at the sowing row decreases soil resistance to penetration up to twelve centimeters when using a hoe furrow opener, and there is no formation of compacted layers with higher resistance to root penetration in the soil.
According to Jin et al. (2012) and Brandelero et al. (2014), different furrow opener devices have a direct effect on seeding quality, since they behave differently and provide different conditions. Furrow-opening tools for line seeders differ in coulters, used for vegetation cover management, and furrow openers, which can be fixed, as in the case of the hoe, or rotary, namely, double-discs. To characterize the performance of seeders’ furrow-opening tools, Mion & Benez (2008) and Levien et al. (2011), while evaluating soil disturbance caused by different tools, showed that the hoe opener disturbs the soil to a larger extent, in comparison to double-discs. Modolo et al. (2012) also confirmed that the hoe causes more soil disturbance than the double-discs, and found values of 0.0045 m² for the former and 0.0037 m² for the latter. Moreover, Casão Júnior et al. (2000) found that the hoe reduces plant residue on the furrows, although this effect may also be associated with speed, which is also reflected in other types of furrow openers, as explained by Celik & Altikat (2012).
Coulters also produce different effects, and according to Silva et al. (2012), the offset fluted and smooth coulters generally increase disturbance of the seedbed soil, the effect of the former being more significant. Mion et al. (2009) corroborated this statement, since they found significant differences in soil disturbance by these mechanisms, with 0.0015 m² values for smooth coulters and 0.0041 m² for the offset fluted. However, Santos et al. (2010), while also analyzing different coulters, found higher disturbance area values for the smooth (0.0087 m²) in comparison with offset fluted coulters (0.0074 m²). These two studies focused on coulters alone, and did not associate them with other mechanisms.
Casão Júnior et al. (2000) and Silveira et al. (2011) evaluated the influence of operating speed on maize sowing with a row crop planter fitted with the hoe opener, and concluded that furrow depth was reduced by operating speed and that the soil disturbance area was increased with higher speed. Cepik et al. (2005), when evaluating the volume of soil disturbance by a row crop planter with five lines, fitted with hoe openers, according to the speed, found a mean value of 121.80 and 135.90 m³/ha, showing a 12% increase when sowing speed went from 1.25 m/s to 1.81 m/s. However, Bellé et al. (2014) and Gassen et al. (2014), when evaluating hoe openers for soil scarification, and Francetto et al. (2015), when analyzing furrowers of planters, found no influence of increased speed on soil mobilization.
The objective of this study was to evaluate the performance, in relation to the disturbance of the soil, of different associations of coulters and fertilizer furrow openers of a row crop planter for the no-tillage system, under different forward speeds, in a red Ultisol soil.
Material and methodsTop
The experiment was conducted on a farm in the municipality of Santa Maria (Rio Grande do Sul). The geographical coordinates of the site are 29º54’08’’ south latitude and 53º49’39’’ west longitude, with an average altitude of 97 m asl. Soil cover was characterized by ryegrass (Lolium multiflorum), weeds and soybean (Glycine max) crop residues, with 287.20 g/m2 dry matter, measured by oven-drying. Historically, there is alternation between soybean crops and grass for grazing activity in the area in the winter, under the no-tillage system.
The physical characterization of the soil was carried out by field sampling at the depth of 0 to 0.20 m, following the methodology proposed by EMBRAPA Solos (1997) for the determination of soil density and moisture content. There was an average value of 1.64 g/cm3 in the first sampling, and 13.15% in the second. Soil texture was characterized with the use of the Vettori method: 17.59% clay, 28.44% silt and 53.97% sand; thus, the soil was considered to be a sandy loam. It was classified as red Ultisol by EMBRAPA Solos (2013). Soil penetration resistance was determined by using a Falker PLG 1020 electronic penetrometer; a mean value of 1,220 kPa was found. The evaluation was conducted at depth from 0 to 0.40 m, with data being collected every 0.01 m deep.
The overall assessment set allowed the installation of associations between coulters and furrow openers, which characterized the treatments applied, consisting of a New Holland, TL75E Exitus 4×2-wheel drive farm tractor with front wheel assist (FWA), with shipping weight of 3,390 kg, used to pull a mobile tool holder structure characterized by a chassis structure, coupling, wheels and tool suspension systems for maneuvers (Fig. 1e). During the experiment, the differential lock was not activated and the FWA was turned off. Internal pressure of front tires (12.4-24) was 190.0 kPa and that of rear tires (18.4-30) was 180.0 kPa.
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The furrow opener elements used were a hoe furrow opener (HFO) (Fig. 1a) and the mismatched double-disc (Fig. 1b) (MFO). Both furrow openers were manufactured in Brazil. The hoe had a 55º angle of attack, 20 mm tip thickness and 10 mm shank thickness. The double-discs have a diameter of 390 mm, 12º angle between the rotary planes of the discs, and 70 mm height for the point of contact. By adjusting the tool holder, the working depth was 0.12 m for the hoe opener and 0.07 m for the double-discs.
The cutting discs used were a smooth coulter (SC), shown in Fig. 1c, and a offset fluted with 20 waves (OC), shown in Fig. 1d, as well as a no-coulter condition (NC). The coulters both measured 460 mm in diameter and worked to a 50 mm cutting depth. The associations between furrow openers and cutting discs are shown in Fig. 2.
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The treatments consisted of the interaction between the following factors: furrow opener mechanism (with 2 levels: HFO and MFO), type of coulter (with 3 levels: NC, SC and OC) and seeding speeds (with four levels: 1.11, 1.67, 2.22 and 2.78 m/s). The experiment used a randomized complete block design, consisting of 24 treatments with three replications each, in a 2×3×4 factorial arrangement, in a total area of 4,320 m². The plots measured 180 m², 3 m wide and 60 m long.
The effects of the coulters and furrow openers were determined in three stages, evaluating the natural soil profile (1), the elevation profile (2) and the soil disturbance profile (3). The first was performed before the passage of the equipment, the second and the third after its passage, at the same location, thus obtaining the geometric shape of the furrow. A micro-profilometer has been used; it was successively placed at the same point in each stage, marked by stakes, along the passage line of tools, demarcating in A2 millimeter paper. When evaluating the natural soil profile (1), the evaluation point was marked in order to reposition the equipment after the passage of the tools. After the verification of the elevation profile (2), the soil was removed manually until the depth where the tool was used, carefully avoiding changes to the profile of subsurface disturbed soil, then the disturbance profile (3) was obtained.
Subsequently, the graphs of the profiles were photographed, with the camera kept in stationary position (position x, y and z). After this, the images were loaded into the Auto Cad software to draw the contour lines of the profiles and, through the use of tools for the scanning of the area, to determine the area in square meters. The difference between the first and third measurements yielded the disturbance area (Da), whereas the discount of this value in the area of the second measurement indicated the elevated area (Ea). Furthermore, maximum depth (Mfd) and width (Mfw) were determined, as shown in Figure 3.
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Soil disturbance volume (Dv) was determined by the equation:
Dv = (Da × 10,000)/IS
where Da refers to the disturbance area; the value 10,000 corresponds to the area of one hectare. Interrow spacing (IS) used for the calculations was 0.45 m; it is the spacing value usually used in soybean sowing.
The ratio between soil elevated area and disturbance area is the soil swelling (Ss); it was determined by the equation:
Ss = (Ea/Da) × 100
After their collection, the data underwent analysis of variance by using Tukey’s analysis test at 5% error probability. Normality of errors was tested with the Kolmogorov-Smirnov test, and homogeneity of variances with Cochran’s test. Analyses were performed using the software Assistat 7.7 beta 2016.
Results and discussionTop
Analysis of variance (ANOVA) of the variables, with their respective means, levels and results of the F-tests are shown in Table 1. Normality of data and homogeneity of variances were observed.
Table 1. Summary of statistical analysis of variance with means for factors, their levels and the results of the F-test
Maximum furrow depth
Maximum depth responded to the effects of the type of furrow opener; there was an average of 0.12 m for the hoe and 0.07 m for the mismatched double-disc (Fig. 4a). The double-disc showed a shallower working depth, as reported by Palma et al. (2010) considering that they are bigger, and it is more difficult for them to penetrate the soil, as stressed by Seidi (2012). Similar results were also found by Koakoski et al. (2007) and Mion et al. (2009); according to the authors, such results are related to the fact that the hoe furrow opener reaches a greater depth due to the action of the tip, which causes a downward vector that tends to suck down the tip of the hoe.
There was no significant effect of the interaction between type of furrow opener and coulter; this suggests that the use or lack of use of coulters with both furrow openers has no influence on depth; a mean value of 0.09 m was found for all treatments.
The effects of speed were significant only when considered alone, or in interaction with the type of furrow opener, which indicates that coulter selection does not change maximum depth, even under the effect of increased speed. The average maximum depth of the two furrow openers was reduced with increasing speed, reaching 0.10 m in 1.11 m/s and 0.09 m at a speed of 2.78 m/s, when they were analyzed in combination. The interaction between furrow opener and speed had a significant effect on maximum depth only for the hoe opener, with values between 0.12 and 0.01 m for the first three levels (1.11, 1.67 and 2.22 m/s), with significant reduction under the effect of higher speed, when depth was 0.10 m. The mismatched double-disc yielded an average depth of 0.07 m for the tested speeds. Silveira et al. (2011), while evaluating furrow depth by a hoe during maize seeding, also identified reduction of this variable when increasing seeding speed. The authors stressed that this behavior is due to the fact that the hoe furrow opener tends to move closer to the surface at higher speeds, and the possible causes for this variation are penetration resistance, soil moisture and roughness.
Maximum furrow width
As expected, the furrow opener that worked at a greater depth created wider furrows, corroborating the results of Hasimu & Chen (2014). In addition to the significant effects of the furrow opener, the coulters also influenced maximum width (Fig. 4b). The hoe furrow opener showed the highest maximum furrow width (0.26 m), while the mismatched double-disc made a narrower furrow (0.24 m); the values were significantly different. The absence of coulter resulted in a width of 0.23 m, while the smooth and offset fluted coulters increased width to 0.26 m and 0.25 m for the first and second coulters, respectively, and there was no difference between them. By contrast, speed did not affect width, as it maintained an average of 0.25 m, and there was no statistical difference between the different speeds.
Soil disturbance area
It was observed an effect of the type of furrow opener on the soil disturbance area (Fig. 4c), where the hoe had the largest movement (0.0126 m²). In comparison, the mismatched double-disc moved 31.25% less than the hoe, with 0.0096 m². This was due to i) the greater working depth used for the hoe, as noted by Hasimu & Chen (2014), ii) the different action of the furrow opening mechanisms, and iii) the differences between the size of the elements, which affects cutting, shear and compaction that they cause to the soil. This result corroborates the findings of Herzog et al. (2004), Mion & Benez (2008) and Modolo et al. (2012), who also concluded that the hoe openers disturb the soil more than mismatched double-discs. However, the values were higher than those in the literature, mainly due to lower gravimetric moisture, which reduces the lubricating effect of water and therefore provides greater disturbance. Furthermore, the differences between the technical specifications of the furrow openers used in this experiment, and the contrasts between soil density, penetration resistance and other physical characteristics of the studied soils, may have caused different effects in the processes of cutting, shear, compaction and flow in soil behavior, as described by Portella (1983).
The cutting discs presented a statistically significant effect on soil disturbance, particularly the fluted coulters, which affect the sides of the furrows, as confirmed by larger width (0.25 m); it is thus evident that the coulters caused greater soil disturbance under the studied conditions. The use of smooth coulters reduced soil disturbance by 12.26% when compared with the offset fluted; there was no difference from the treatment without coulters. Mion et al. (2009) and Silva et al. (2012), while working with different coulters, also found statistical differences between soil disturbance caused by different types of coulters, and the offset fluted coulters also caused more disturbance than the smooth discs.
The use of different seeding speeds for the whole set did not affect the soil disturbance area, which averaged 0.01 m². This is indicative that this factor is not limiting for adequate disturbance in the furrow for no-tillage systems, thus suggesting the possibility of using speeds up to 2.78 m/s without reducing soil disturbance. These results are similar to those found by Bellé et al. (2014) and Gassen et al. (2014), while working with chisel plows in tillage systems, and by Francetto et al. (2015), while analyzing the performance of associations between cutting discs and furrow openers. This effect may be associated with the friable soil consistency at the time of the experiment, confirming the results found by Casão Junior et al. (2000), who observed no increase of the soil disturbance area only in this moisture condition.
Soil elevation area
The most disturbed area was by the hoe opener, around 12%, it was higher in the elevated area, which was 89.28% higher compared with the mismatched double-disc furrow opener. The hoe opener resulted in an increase of 0.0028 m², while the double-discs accounted for 0.0053 m² (Fig. 4d). This possibly occurred because the double-discs were arranged at a shallower depth and made narrower furrows, resulting in a smaller elevated soil area. Another reason may be the fact that culters have a cutting action rather than shearing when opening furrows.
There was no statistical difference between the elevated soil area by either the smooth coulter or the offset fluted coulter. However, there was a contrast when the offset fluted coulter was compared to the absence of coulter; the wavy coulter elevated the soil at least 48.48% less. This may be due to the higher fractionation of soil caused by this type of mechanism, as explained by Francetto et al. (2015), compared with the no-coulter condition, because of the larger contact area of this element with the ground, confirmed by greater furrow width.
The furrow opener and speed factors showed significant interaction, demonstrating that the elevated area by the hoe was notably higher at all speed levels, with values ranging between 0.0025 m² and 0.0032 m² for the double-discs, and from 0.0051 m² to 0.0055 m² for the hoe furrow opener. In addition to this double interaction, there was a significant interaction between hoe furrow openers, coulters and speed on elevated area, as shown in Table 2.
Table 2. Interaction between furrow opener, coulter, and speed in the elevated soil area
The use of coulters only showed statistical difference in soil elevation when the association between offset fluted and mismatched double-disc furrow opener was compared with the combination of hoe opener and no-coulter at seeding speeds of 2.22 and 2.78 m/s. Furthermore, there was a difference between double-disc and smooth coulter with the hoe opener without coulters at the speed of 1.11 m/s. In both situations, the use of the hoe furrow opener showed the highest soil elevation. In the other situations, no differences were evidenced between the mechanisms, especially at the speed of 1.67 m/s, where there was no difference in soil elevation for any combination of elements. The use of coulters associated with the hoe opener did not influence the elevated area, obtaining an average value of 0.0053 m². However, using the offset fluted with the double-disc opener reduced this variable by roughly 50%, when compared to the remaining treatments with this furrow opener, and by 67% for the furrows made by the hoe opener.
Disturbed soil volume
The effects of the hoe openers on the evaluated areas were reflected in the highest disturbed soil volume values; there was a soil volume of 68.31 m³/ha higher than that of the mismatched double-disc furrow opener, representing an increase of 32.10% (Fig. 4e). This is due to the greater working depth of this mechanism, as evidenced by Herzog et al. (2004) and Conte et al. (2009), who evaluated the soil disturbance volume at two depths by a hoe opener. Regarding the effect of coulters, when the offset fluted coulter was used for both furrow openers, this accounted for the largest disturbance: 11.66% and 10.05% higher than the smooth coulter and the no-coulter condition, respectively. By contrast, the different seeding speeds caused no changes in disturbed soil volume.
Soil swelling
The hoe opener, in comparison to the double-disc, caused the most swelling: 42.33% compared with 30.26%, respectively (Fig. 4f). This difference represents an increase by 39.89% in soil volume. This result occurred because the hoe causes greater voids between soil particles than double-discs, because they perform a shearing rather than a cutting action on the soil.
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There was no statistical difference between the use of the smooth coulter and combinations without this kind of mechanism, when the coulter factor was analyzed alone. On the other hand, they both showed contrast when compared with the use of the offset fluted coulter. Swelling was reduced by 42.90% and 72.71% for the smooth coulter and associations without cutting elements, respectively. It was due to higher disturbance area, where the aforementioned treatment had the highest value compared to the others, and to the lower elevated area provided by this type of structure; however, it is explained by the resulting higher maximum width. Consequently, this type of mechanism causes a more horizontal soil disruption than the smooth coulter and the association that used no-coulter. This situation is similar to the one observed by Brandelero et al. (2014) when evaluating hoe furrow openers, coulters, row cleaners and covering mechanisms in a no-till seeder. Furthermore, the use of coulters associated to furrow openers reduces swelling because they promote a cut in a section of the soil prior to the passage of the furrower, especially in association with the hoe, where it was observed an average decrease of 20%.
Soil swelling is due to the ratio between elevated and disturbed soil area, and neither of them is subject to changes resulting from the increase in seeding speed; this way, there were no statistical differences when the speed factor was evaluated; and it was verified a mean value of 36.29%.
As final conclusions, the soil disturbance area was not affected by speed; being greater when the hoe furrow opener was used. Among the combinations with coulters, the offset fluted favored the greatest disturbance and the lowest elevation and soil swelling. Furthermore, the use of coulters associated with furrow openers reduced swelling in approximately 8% for the smooth and 20% for the offset fluted coulter. The double-disc furrow opener had the least working depth, and there was no change to this variable when coulters were used in association with different furrow openers. Moreover, speed was inversely proportional to maximum depth for the furrows made by the hoe opener, with a 15% reduction. The hoe furrow opener showed the highest maximum furrow width. Additionally, the use of different coulters increases furrow width in approximately 10%, regardless of whether the edge of the coulter is smooth or fluted. By contrast, speed did not affect this variable.