The developed tractor-mounted vegetable transplanter was made up of two seedling holding trays, an operator seat, a speed reduction gearbox, cranks and connecting rods, two feeding mechanisms, a chain sprocket transmission system, a single lugged drive wheel with a diameter of 521 mm, body frame plates, and compaction wheels. The transplanter was constructed with the plug seedling spacing of 450 mm between plants and 600 mm between rows in mind. The seedling was manually placed into the mechanical feeding mechanisms when the machine moved ahead. The transplanting unit rose upward, releasing the seedling from the feeding unit. The operators began placing seedlings into the hollow pipes, the empty pit, and the planter within the casings of the horizontal magazine-style feeding mechanism and the revolving multi-chamber disc. After taking the seedling from the feeding unit, the transplanting unit moves downward, punches or digs a hole in the ground to the appropriate depth, and then opens the mouth of the digging unit of the transplanting unit by pushing the opening lever through the position of the vertical plates. The transplanter handled every seedling transplant in the same manner every time. The soil around the transplanted seedling was compressed by the press wheel on the rear of the machine. The drive for the whole system, including the feeding and transplanting mechanism, came from the chain and sprocket system, powered by the drive wheel, which rotates with the tractor’s forward motion. The transplanter’s stationary view is shown in Fig. 1.

The feeding mechanism is the key component of every transplanter, and its job is to distribute seedlings evenly at the right time and place. Successful performance of the transplanter depends on the proper selection and design of the feeding mechanism. In the current study, two feeding mechanisms were designed and constructed. These mechanisms, a multi-chamber disc and dragging magazine with revolving and horizontal motion regarding the machine’s forward motion, performed the function of feeding vegetable seedlings to the transplanting unit to carry out the seedling transplanting operation.

This section discusses the methodologies, materials and methods used to design and develop the revolving multi-chamber disc feeding mechanism (FM _RMD ) and horizontal dragging magazine feeding mechanism (FM _HDM ). Computer-aided design (CAD) software (Solid Works) was used to conceptualise FM _RMD and FM _HDM based on the attributes of plug seedlings of tomato and eggplant crops. Following the 3D modelling process, an FM _RMD and FM _HDM mounted on a mechanical vegetable transplanter was designed and built using two-dimensional drafting and a bill of materials. The procedure adopted, and the material used to conduct this study has been presented under the following sub-heads;

In the present study, the FM _RMD (with the numerical arrangement in clock-like chambers on its periphery) was selected due to its easy manoeuvrability and simplicity in construction. Two circular 14-gauge mild steel (M.S.) plates of 762 mm (diameter) were used to fabricate a FM _RMD The plates were joined to each other by welding an M.S. sheet, keeping a 76 mm distance between them, making it a multi-chamber disc. The 12 chambers of diameter 70 mm and length 76 mm were made on the multi-chamber disc to resemble the 12 numerical numbers printed on the wall clock. The 12 M.S. circular plates of 100 diameters were attached to one side every 12 chambers made on the multi-chamber disc via a nut and bolt system. A spring was attached between each circular plate and the opposite side of the pit to open and close the plates. The conceptual and fabricated view of the FM _RMD is shown in Fig. 2.

The primary function of the circular holes/chamber/grooves on the feeding unit is to hold the seedling upright during transplanting. The number of holes/grooves/chambers in the feeding unit was calculated using the following formula (Ningthoujam et al., 2016; Soyoye, 2020).

where, N _g : No. of grooves/chambers on the revolving disc;

D : Diameter of the drive wheel, m;

I : speed ratio = ratio of the drive wheel shaft to metering shaft = (No. of teeth on metering shaft (T _m )/No. of teeth on drive wheel shaft (T _d ) = T _m /T _d

Z : plant to plant spacing = 0.45 m

On substituting D: 0.521 m, I: 4, and Z: 0.45 m in the above equation, the number of grooves/chambers (N _g ) obtained was 14.54, but for the requirement of maintaining uniformity in row spacing and to match the planting device timing, the number of grooves/chambers on rotating disc was taken as 12.

The diameter of the FM _RMD chamber was selected based on the spread diameter of the vegetable seedlings. The canopy size of the plug seedling determines the necessary pipe through which a healthy plug seedling apposite for transplanting can travel vertically without being trapped. To evade seedling feed tube blockage, the diameter of the seedling feed chambers of the revolving multi-chamber disc should be higher than the essential canopy diameter of the seedling. The height of the FM _RMD feeding mechanism was selected based on the length of the seedlings of the selected vegetable crops. The selected diameter and length of the chamber in the present study were 70 and 76 mm, respectively. It was also found during the study that a commercially available hand-held vegetable transplanter, which has a tube-like structure, has a diameter and length of 50 and 900 mm, and the seedlings of tomato and eggplant quickly passed through this tube without getting stuck. Therefore, a chamber of size 70 mm was found appropriate for the present study.

The frequency of the rotation (rpm) of the revolving multi-chamber disc of the machine at a known speed of the machine and selected plant-to-plant distance between seedlings is given (Narang et al., 2011) by the following relation:

where, n: rotation of the multi-chamber disc (rpm); V _m : machine speed (m·s^-1)

Z: number of chambers on the disc; A _g : seedlings plant-to-plant distance (m)

On substituting the V _m : 0.28 m s^-1, Z : 14.54, A _g : 0.45 m in the above equation, give n = 2.56 rpm. The expression mentioned above shows that the frequency of the rotation of the revolving multi-chamber disc increases with increasing the speed of the machine. Two metal sheets of 760 mm diameter were taken and welded together, keeping a 76 mm distance between them. Based on the seedling spread, twelve holes/pits of 70 mm diameter were made on the circular periphery of the disc with a depth of 76 mm at an angle of 30^o (π/6) between each pair of chambers. The developed revolving multi-chamber disc was attached to the reduction gearbox output shaft from the center of the disc. The reduction gearbox was installed on the metal sheet and fixed on the machine frame. The drive to the reduction gearbox was provided from the ground/driver wheel through the chain sprocket system. The drive given to the reduction gearbox makes the multi-chamber disc (attached to the gearbox’s output shaft) rotate.

In the present study, the FM _HDM was selected due to its simplicity in construction and easy availability of materials required. A quick return motion mechanism, essentially an offset slider-crank mechanism in which the slider has different average velocities in forward and return strokes, was employed to produce the quick horizontal dragging of the magazine. One of the strokes (forward/reverse) takes less time than the other because of the offset. As a result, even though the crank turns evenly, the slider completes one stroke faster than the other. It converts circular motion into reciprocating motion and reciprocating motion into circular motion. An offset slider-crank mechanism was employed (Fig. 3) to achieve the goals of the FM _HDM mentioned above because the stroke line of the slider does not cross through the axis of the rotation of the crank.

The multi-chamber disc body was used as a base for the FM_HDM. A solid temper rod of length 864 mm and 10 mm diameter was joined to the circular plate attached to the drive shaft with the help of a link and arm. On the temper rod, six hollow pipes (three for each row) were attached with the help of clamps which can be easily loosened and tightened with the help of the revolving screw. The M.S. hollow pipes of size 60 mm and 50 mm diameter and length of 102 mm were used. The dimensional and fabricated view of the FM _HDM is shown in Fig. 4.

For the displacement analysis of an OSC mechanism, the quick return ratio and the stroke length must be determined. The quick return ratio (Q _RR ) is the ratio of time taken for a forward stroke to time taken for a return stroke. This is the same as the angle swept by the crank in the respective strokes. The kinematic diagram of the OSC mechanism having ‘r’, ‘l’ and ‘e’ as crank length (O₂A), connecting rod (AB) and offset, respectively, is shown in Fig. 5a.

The condition l > r+e must be satisfied for the crank to revolve entirely, where ‘r’ is the crank length, ‘l’ is the length of the link connecting the crank and the slider, and ‘e’ is the offset of the slider. The kinematic model view of the OSC mechanism is shown in Fig. 5b. Assuming the crank (O₂A) is rotating in a circular motion with uniform angular velocity (ω) in a counter clockwise direction. Considering the fixed point O₂, the distance of O₂ from the B_R (extreme right position) becomes l+r (also the radius of arc C) with a crank position at A_R, whereas the distance of O₂ from (extreme left position) becomes l-r (also the radius of arc D) with crank position A_L. When the crank rotates from A_R to A_L, the slider moves from point B_R to point B_L, which is the forward stroke, and the corresponding angle travel by the crank is θ _f. On the other hand, in a return stroke, the slider moves from B_L to B_R with the corresponding movement of the crank from A_L to A_R with an angle travel of θ _r . The equation used to determine the Q _RR is as follows:

Q _RR = time taken by forward stroke/time taken by return stroke

The equation for finding Q _RR can be written as below:

Q _RR = (θ _f /ω)/(θ _r /ω) = θ _f /θ _r

By considering <O₂B_LB_R as <θ, from the geometry of kinematic diagram, it is estimated that, θ _f = 180 + θ, θ _r = 180 – θ.

Therefore, equation for determination of Q _RR can be written as

Q _RR = (180 + θ)/ (180 – θ)

By considering <O₂B_RB_R1 as <α and <O₂B_LB_L1 as <β from the geometry of kinematic diagram, it is estimated that, θ = β – α

Again, from the geometry of kinematic diagram, α and β can be determined as below:

sinα = (e/(l+r)), α = sin^-1((e/(l+r)), and sinβ = (e/(l-r)), β = sin^-1((e/(l-r))

Therefore, θ = sin^-1((e/(l-r)) – sin^-1((e/(l+r))

Finally, the equation for determination of becomes as follow:

Q _RR = (180 + sin^-1((e/(l-r)) – sin^-1((e/(l+r)))/(180 – sin^-1((e/(l-r)) – sin^-1((e/(l+r)))

Now, from the kinematic diagram stroke can be written as below:

stroke = B_LB_R = O₂B_R’ - O₂B_L’ = (l+r)cosα – (l-r)cosβ

where, O₂B_R’ = (l+r)cosα, O₂B_L’ = (l-r)cosβ

Therefore, stroke (S) = (l+r)cosα – (l-r)cosβ

Substituting the values of l: 152 mm, r: 64 mm, e: 50 mm

α = 13.38, β = 34.62, θ = 21.24, Q _RR = 1.27, S = 137.72 mm

As a result, for each row, three hollow pipes were positioned to drag the seedling to the guided hole in the stroke length of the slider (temper rod). With the help of rotating clamps, two 60 mm hollow pipes were fixed on the right side of the temper rod at a distance of 15 mm (keeping the outermost pipe centre coinciding with the right side guided hole) and a third 50 mm hollow pipe was fixed at a distance of 5 mm from the next fixed hollow pipe, considering the machine’s forwarding direction. On the other hand, two 60 mm pipes were set at a distance of 15 mm on the left side of the temper rod, with the innermost pipe centre aligned with the left side guided hole, and a 50 mm hollow pipe was fixed on the rod’s outermost side at a distance of 5 mm from the next fixed hollow pipe.

In the FM _HDM , with the help of a chain sprocket and reduction gearbox system, the rotary motion of the drive wheel is converted to the horizontal motion of the temper rod on which three hollow pipes (for each row) are attached, making it a horizontally moving magazine type feeding system. The rod on which hollow pipes are attached performed the reciprocating motion, which dragged the seedling to the opening point from where the seedlings were dropped to the transplanting unit. In this mechanism, the seedlings are manually placed in the hollow pipes, which move horizontally relative to the forward motion of the transplanter. The hollow pipes dragged the seedling to the drop point. The functional view of the FM _HDM is shown in Fig. 6. At rest, hollow pipes 1, 2, 4 and 5 were filled manually with the seedling. As the horizontal motion starts (to the left), hollow pipes 2 and 5 drag the seedling over guided/drop whole, and pipes 3 and 6 are filled manually with the seedling. On further horizontal motion to the left, hollow pipes 1 and 4 drag the seedling to the guided/drop whole, and pipes 2 and 5 are filled manually with the seedlings. In the same way the seedling drops to the planter, the mechanism occurs when horizontal motion starts to the right.

The power from the driving wheel to the main shaft was transferred employing a chain and sprocket with 39 (T₁) and 13 (T₂) teeth on each sprocket. Another sprocket with 29 (T₃) teeth was attached to another end of the main shaft, which drove the intermediate shaft with the same 29 (T₄) number of teeth sprocket on one end. Then, the power was transmitted from the intermediate shaft to the input shaft of the reduction gearbox with the help of the identical 16 (T₅, T₆) number of teeth sprocket on both shafts in the case of FM _RMD and the case of FM _HDM , the power is transmitted by 39 (T₅) teeth sprocket of the intermediate shaft to 13 (T₆) teeth sprocket on the input shaft of the gearbox. The power was then transmitted to the feeding system after a reduction in the ratio of 12:1 with the help of a gear reduction box. The speed ratios of 4:1 and 1.33:1 were maintained to deliver seedlings appropriately with the proper spacing for the revolving disc and magazine feeding mechanism. The complete power path of the drive train system from the ground wheel is shown in Fig. 7. The drive train calculation is given under:

Speed ratio in FM _RMD :

Speed ratio in FM _HDM :

where, N₁ and N₄: rpm of drive wheel and driven gear

The dragging magazine was fitted on the tempered rod in the FM_HDM. The gearbox drives the seedling dragging magazine of the feeding device horizontally towards the left and right guided holes (also called the seedling injection port), which were spaced at row spacing. If the feeding device rotates too fast, the plug seedlings do not entirely fall at the injection port. This will cause the plug seedlings to be clamped or lay down. The equations 1, 2 and 3 were used similarly as in the case of FM _RMD for the calculation of D₂, q and q _m . Substituting the values related to the FM _HDM from Table 1 into equations 1, 2 and 3, we obtained D₂: 0.0079 m, q (single row planting frequency) : 30 plant∙min^-1, q _m : 34.87 plant·min^-1.

The developed transplanter were mounted on the transplanter and tested in the field to investigate the effects of plug shape types, seedling ages and feeding mechanisms on Missing Index (MI) percentages for tomato (Solanum lycopersicum L.) and eggplant (Solanum melongena L.). The MI indicates the number of times a seedling misses the desired spacing. It was considered a miss if the distance between two plants was more significant than 1.5 times the theoretical spacing (Bakhtiari & Loghavi, 2009). The distance between two successive plants planted in the field along the six-meter length of the machine-transplanted field was measured for each trial. The machine was set for the row-to-row spacing of 600 mm and plant-to-plant spacing of 450 mm (± 50 mm) for the selected crop to be transplanted. The size and shape of the seedling tray cell influence plug-type seedlings’ development. The seedlings’ development is regulated by their control over the allocation of nutrients and water (Singh et al., 2005; Vijayreddy & Kumar, 2023). Increased cell size will accommodate a greater volume of medium, providing a higher quantity of nutrients for the growth and maturation of the seedlings. Although some Indian academics have examined the influence of tray cell size and shape on the creation of vegetable transplanters (Narang et al., 2011; Bhambota et al., 2018), more investigation is required to understand this subject thoroughly. Transferring the seedlings after 32 days is recommended for the chosen crops. In order to investigate the effects of varying seedling age, two additional seedling ages were chosen: one week before the allowed seedling age and one week beyond it. These ages were picked in addition to the conventional seedling transplanting age.

For testing purposes, two plug-shape types (P₁: square, P₂: round), three seedling ages (S₁: 25 days, S₂: 32 days, S₃: 40 days) and three seedling feeding methods (M₁: FM _RMD , M₂: FM _HDM , M₃: FM _DMF ) were selected. The chambers and the hollow pipes of the FM _RMD and FM _HDM feeding system were filled with the seedling before transplanting, and the remaining seedling trays were placed on each of the seedling trays. On the other hand, in direct manual feeding (FM _DMF ), the transplanter was operated without a feeding mechanism, and the seedling was directly placed in the transplanter unit by uprooting the seedlings from the nursery trays and placing them in the well-prepared field. The tractor’s throttle lever was set to the correct position, and the first low gear was engaged to obtain the needed forward speed for the study to ensure proper planting operation and regular plant-to-plant spacing. Statistical analysis of the MI data for tomato and eggplant was done using a factorial randomized block design. The factorial analysis of variance was used to pair up each level and component, which made it simpler to comprehend how the levels and factors interact. The statistical program statistics package for the social sciences (SPSS 26) was used for variance analysis and mean comparisons at a 5% significance level.

The working ability of the developed feeding mechanisms was initially tested in the laboratory. The drive wheel was rotated manually, and synchronization of the movement of the FM _RMD and FM _HDM was observed. A canister filled with soil was kept below the planting device, and seedling was placed in the feeding mechanism. The feeding mechanism was revolved/dragged by rotating the driving wheel, dropping the seedling at the drop point, which was captured by the planting device at its top position (closed) and then transplanted into a canister filled with soil when it reached its bottom position (open). Both the feeding mechanisms were tested in the same way, and the performance of the transplanter was found satisfactory.

The effect of the feeding methods (M₁, M₂, M₃), plug types (P₁, P₂), and seedling ages (S₁, S₂, S₃) on the MI percentage for tomato and eggplant are presented in Table 2 & 3 and are graphically illustrated in Fig. 8 and Fig. 9. The effect of the individual parameters on the MI is discussed below:

The percentages of the MI for the feeding methods M₁, M₂, and M₃ for all the treatment combinations under research varied from 2.78 to 6.95, 5.56 to 8.79, and 4.17 to 8.33, respectively. The maximum MI percentage of 6.95 for M₁ was attained at a treatment combination of P₁S₂, whereas the minimum MI percentage of 2.78 for M₁ was attained at a treatment combination of P₂S₂. The maximum and minimum MI percentages of 8.79 and 5.56 for feeding mechanism M₂ were attained at a treatment combination of P₂S₁ and P₁S₂, respectively. Similarly, the maximum and minimum MI percentages of 8.33 and 4.17 for feeding mechanism M₃ were attained at a treatment combination of P₁S₃ and P₂S₃, respectively.

In the case of eggplant, the MI percentages for feeding mechanism type M₁, M₂ and M₃ for all the treatment combinations ranged from 2.78 to 6.94, 6.48 to 9.72 and 4.17 to 8.79, respectively. The maximum MI percentage of 6.94 for M₁was attained at a treatment combination of P₁S₂, whereas the minimum MI percentage of 2.78 for M₁ was attained at a treatment combination of P₂S₂. The maximum MI percentage of 9.72 for M₂ was attained at a treatment combination of P₂S₁, whereas the minimum MI percentage of 6.48 for feeding mechanism M₂ was attained at a treatment combination of P₂S₂. Similarly, the maximum MI percentage of 8.79 for M₃ was attained at a treatment combination of P₁S₃ and P₂S₁, whereas the minimum MI percentage of 4.17 for feeding mechanism M₃ was attained at a treatment combination of P₂S₃.

The MI percentages for plug type P₁ and P₂ for all treatment combinations ranged from 4.17 to 8.33 and 2.78 to 8.79, respectively. The maximum MI percentage of 8.33 for P₁ was attained at a treatment combination of M₃S_3, whereas the minimum MI percentage of 4.17 for P₁ was attained at a treatment combination of M₁S₃. On the other hand, the maximum MI percentage of 8.79 for P₂ was attained at a treatment combination of M₂S_1, whereas the minimum MI percentage of 2.78 for P₂ was attained at a treatment combination of M₁S₂.

In the case of eggplant, the MI percentages for plug type P₁ and P₂ for all the treatment combinations under study ranged from 4.17 to 8.79 and 2.78 to 9.72, respectively. The maximum MI percentage of 8.79 for P₁was attained at a treatment combination of M₃S₃, whereas the minimum MI percentage of 4.17 for P₁ was attained at a treatment combination of M₁S₃. On the other hand, the maximum MI percentage of 9.72 for P₂ was attained at a treatment combination of M₂S₁, whereas the minimum MI percentage of 2.78 for P₂ was attained at a treatment combination of M₁S_2.

The MI percentages for seedling age S₁, S₂ and S₃ for all the treatment combinations ranged from 4.63 to 8.79, 2.78 to 8.33 and 3.71 to 8.33, respectively. The maximum MI percentage of 8.79 for S₁ was attained at the combination of P₂M₂, whereas the minimum MI percentage of 4.63 for S₁ was attained at the treatment combination of P₂M₁. The maximum MI percentage of 8.33 was attained at P₂M₂, whereas the minimum MI percentage of 2.78 for S₂ was attained at a treatment combination of P₂M₁. Similarly, the maximum MI percentage of 8.33 was attained at a treatment combination of P₁M₃, whereas the minimum MI percentage of 3.71 for S₃ was attained at a treatment combination of P₂M₁.

In the case of eggplant, the MI percentages for seedling age S₁, S₂ and S₃ for all treatment combinations under study ranged from 5.56 to 9.72, 2.78 to 8.33 and 3.24 to 8.79, respectively. The maximum MI percentage of 9.72 for S₁ was attained at the treatment combination of P₂M₂, whereas the minimum MI percentage of 5.56 for S₁ was attained at the treatment combination of P₁M₃. The maximum MI percentage of 8.33 was attained at P₁M₂, whereas the minimum MI percentage of 2.78 for S₂ was attained at a treatment combination of P₂M₁. Similarly, the maximum MI percentage of 8.79 was attained at a treatment combination of P₁M₃ and P₂M₂, whereas the minimum MI percentage of 3.24 for S₃ was attained at a treatment combination of P₂M₁.

The factors’ mean and analysis of variance of the MI for tomatoes are depicted in Table 2. The mean percentages value of the MI for tomato crops varied from 4.55 to 7.33 among all the treatments, and the differences were statistically non-significant at a 5% significance level. The MI percentages was statistically at par for plug type and seedling age and varied between 5.81 to 6.17 and 5.86 to 6.25. The first-order interaction of plug type and feeding mechanism (P×M) and the main effect of the feeding mechanism was statistically significant (Fig. 10 & 11) on the MI at a 5% significance level. For feeding techniques, the MI percentages ranged from 4.55 to 7.33 and was highest for M₂ and lowest for M₁. The interaction among plug type, feeding methods, and seedling age was statistically non-significant on the MI at a 5% significance level.

The factors mean and analysis of variance of the MI for the eggplant are depicted in Table 3. The mean percentages value of the MI for the eggplant varied from 4.86 to 7.87 among all the treatment combinations, and the differences were statistically non-significant at a 5% significance level. The MI percentages was statistically at par for the plug type and seedling age and varied between 6.17 to 6.79 and 6.09 to 7.17. The first-order interaction of plug type and seedling age (P×S) was significant (Fig. 12) at a 5% significance level. The MI was the least with the P₂ plug type and S₂ seedling age. This could be because the P₂ plug type and S₂ seedling age have more base and adequate root growth, allowing the seedling to remain vertical when placed in the feeding mechanism. The main effect of the feeding method was statistically significant (Fig. 12) on the MI. In the feeding method, the MI percentages varied from 4.86 to 7.87 and was maximum for the M₂ and minimum for the M₁. The interaction among the plug type, feeding method, and seedling age was statistically non-significant on the MI at a 5% significance level.

According to numerous studies by other scientists, the percentage of missed plantings ranges from 3 to 15.7. In their study, Chaudhuri et al. (2001) documented a plant loss rate ranging from 3.70% to 6.67% during mechanical transplantation using a two-row vegetable transplanter for tomato and cauliflower crops. In investigating a tractor-operated single-row vegetable transplanter, Dixit & Garg (2002) discovered that 15.7 percent of brinjal plants were absent. Han et al. (2021) reported that when transplanting 60-day-old pepper seedlings with a high-speed seedling auto-transplanter, a 3% of missed planting occurred. A missing percentage of 5.33 was documented by Dhupal & Sahu (2020) during the process of transplanting tomatoes using a manually operated two-row tomato transplanter.