Use of conventional seeding devices has higher seed rate application which leads to wastage of costly seeds, adds the cost of thinning and results in increased production cost. Dixit et al. (2011) compared theperformance of inclined plate planter and pneumatic planter and found that pneumatic planter performed much better for cotton. Using pneumatic planter, seed germination efficiency has increased many folds at reduced seed rate compare to conventional planters. Inter row and intra row spacing for sorghum is an important factor in order to achieve optimum crop yield. The parameters for the evaluation of performance of the planter include spacing between seeds or plants (Hollewell, 1992; Parish et al., 1991), percent multiples and misses (Brooks and Church, 1987; Singh et al., 2005; Singh et al., 2007; Sun et al., 2012; yasir et al., 2012) and precision in spacing (Hofman, 1988; Jasa and Dickey, 1982). Important factor of the pneumatic seed-metering device is its uniformity of seed spacing. Besides the design of the metering devices, field and operational parameters affect the precision distribution of seeds.

 

Karayel and Ozmerzi (2001) stated that variability in the seed spacing with a precision vacuum seeder increased with increasing forward speed. Use of conventional planting machines does not maintain precise plant spacing and seed rate (Khambalkar et al., 2014). Therefore, an attempt was made to evaluate the pneumatic planter developed at CIAE (Central Institute of Agricultural Engineering), Bhopal both in laboratory and field conditions to justify its use  in  planting   of   sorghum seeds in dry land cultivation of sorghum. 

The pneumatic planter consists of main frame, aspirator blower, disc with cell type metering plate, individual hopper, furrow openers, PTO driven shaft, ground drive wheel etc. Pictorial view of the pneumatic planter is shown in Figure 1. Specifications of the pneumatic planter are given in Table 1.

 

Power transmission system of the pneumatic planter

 

Power transmission system with different gear arrangement of the pneumatic planter is shown in the Figure 2. Various gear ratios were used to get desired seed rate. Two gears were mounted on the axle of the ground wheel having 14 and 20 teeth. The power from the ground wheel was then transferred through chain to the primary driving shaft having gears with 20 and 14 teeth at each ends. The primary driving shaft had five gears 26, 22, 20, 16 and 14 in first, second, third, fourth and fifth, respectively. The power from primary driving shaft is transferred to the secondary driving shaft with the help of chain and idler gears. Seven idle gears were of 14 teeth in the secondary driving shaft. One gear on the secondary driving shaft is connected to one of the five gears on the primary driving shaft through chain. The power from the secondary driving shaft is transferred to the seed metering plate. The other gears on the secondary driving shaft were attached to the gear on the axle of seed metering device with the help of chain. The gears on the seed metering mechanism had 20 teeth, as shown in Figure 1. 

 

 

 

Working principle of pneumatic planter

 

The metering  device  was  powered  by  a  pair  of  ground   wheels through chain and sprocket. Power to the aspirator blower was given by PTO shaft of the tractor with the help of cordon shaft. The disc was mounted to a vacuum retaining plate made of Bakelite material having outer diameter 295 mm and thickness 40 mm. Suction pressures inside the metering unit was created by connecting it to a vacuum pump. The  vacuum  retaining  plate  wasequipped with a baffle to release the vacuum pressure of the seed disc. The rotating seed disc carried the seeds attached to the seed holes under negative pressure and dropped only when the holes passed through the baffle that released the suction pressure. The dropped seed fall in the furrow opened by furrow opener and cover with the soil. To view the movement of the seeds inside the metering disc, the seed disc was provided with a protective cover made of mild steel and transparent acrylic plastic.

 

Laboratory evaluations

 

The pneumatic planter was calibrated with sorghum seeds in the laboratory. PTO was connected to the aspirator air blower of the pneumatic planter. The gear combination at left and right hand side of ground wheel was set and the main driving shaft of gear was laid on the first gear. Then the PTO was operated at 550 rpm resulting in the rotation of the blower at 2720 rpm to create proper vacuum in the seed metering unit for proper metering of the seed. Then the ground wheel of the pneumatic planter was rotated 20 times with constant speed manually. Seeds were collected in the poly-ethylene bag underlying the furrow opener. Simultaneously the rpm of PTO shaft was taken by the tachometer to about 550 rpm. The seed quantity was measured in grams. Similar procedure was adopted for the different gears of main driving shaft at same setting of side gears of ground wheel. The side gear combination of ground wheel was changed and again the observations were taken at different gears of main driving shaft as stated earlier. Three replications were taken for each setting and average values are given Table 2.

 

Performance parameters measured during field evaluation

 

Speed of operation

 

The time taken (s) to distance travelled (m) during operation was determined using stopwatch. The forward speed of tractor (km/h) was calculated by following equation.

 

 

Where AFC = actual field capacity (ha/h), TFC = theoretical field capacity (ha/h), Ac = actual area covered (ha), Tt = time taken (hr), FC = field efficiency (%), W = width of machine (m), and S = forward speed (km/h). 

 

 

Miss index

 

The miss index (I_ms) is the ratio of number of spacing (Nms) greater than 1.5 times of set spacing and total number of measured spacings (N):

 

 

Multiple index

 

The multiple index (I_mt) is the ratio of number of spacing (Nmt) ≤ 0.5 times of set spacing and total number of measured spacings (N):

 

 

Pneumatic planter was set based on the results obtained in laboratory. The procedure outlined in RNAM Test code and procedure (1983) for seedling equipment was followed. Parameters and their values of field, seed and operational parameters is shown in Table 2.

                                                           

The pneumatic planter was powered by 29.84 kW tractor (TAFE 585 DI). The tractor was operated at an average forward speed of 3.6 km/h. Pre-experimental trials had been undertaken to adjust the working parts such as speed of PTO shaft, furrow openers, depth adjustment. A mark was made on the lever of the three point linkage to set the depth of operation of the furrow opener at 30 mm. Pneumatic planter during field operation is shown in Figure 3. 

 

 

The  pneumatic  planter was  tested  in  the  laboratory  as  well  as  in field conditions of Department of Farm Machinery and Power Engineering and Crop Research Center of GBPUA and T Pantnagar, respectively. The tests were carried out for sorghum seeds at different gear combinations to obtain the recommended seed rate. The seed rate obtained for different combination and for different gears of primary driving shaft is shown in the Figure 4.

 

Gear having 14 teeth mounted on the axle of ground wheel is attached to the gear having 20 teeth mounted  at the ends of the primary driving shaft, and second gear, that is, having 14 teeth mounted on the middle of the primary driving shaft gives the required seed rate of 7.98 kg/ha and was within the recommended seed rate of 7.5 to 8 kg/ha. Based on the results obtained in laboratory, performance of the pneumatic planter was carried out in field. Data on performance parameters of the planter such as the plant to plant spacing, miss index and multiple index, actual field capacity and field efficiency was collected and analyzed. The average values of the field trials conducted were found as 101 mm, 2.07%, 3.8%, 0.773 ha/h, 79.7%, respectively. The average values of all the performance  parameters  are  given  in Table 3. Standard deviation and standard error was 5.8, 3.4, 9.2 and 1.7, 0.7, 1.5 for miss index, multiple index and field capacity respectively. 

 

The pneumatic planter was found suitable for sorghum with the best suited gear combination, that is, gear having 14 teeth mounted on the axle of ground wheel and 20 gear teeth mounted at the ends of the primary driving shaft with 14 gear teeth mounted at the middle of the primary driving shaft of pneumatic planter with tractor PTO shaft speed of 550 rpm. Performance of the pneu-matic planter was evaluated in the field and the average values of plant to plant spacings, mean miss index and multiple index, actual field capacity and field efficiency were found to be 101 mm, 2.07%, 3.8%, 0.77 ha/h, 79.7%, respectively. All the observed values were within the recommended levels. Hence, this planter was found suitable for planting of sorghum seeds in dry land. 

The authors have not declared any conflict of interest.