ARTICLE IN PRESS. Optimisation of Design and Operational Parameters of a Pneumatic Seed Metering Device for Planting Cottonseeds

Transcription

1 Biosystems Engineering (005) 9 (), 9 8 doi:0.06/j.biosystemseng PM Power and Machinery ARTICLE IN PRESS Optimisation of Design and Operational Parameters of a Pneumatic Seed Metering Device for Planting Cottonseeds R.C. Singh ; G. Singh ; D.C. Saraswat Department of Farm Machinery and Power Engineering, Allahabad Agricultural Institute (Deemed University), Allahabad 007, Uttar Pradesh, India Mahatma Gandhi Chitrakoot Gramodaya University, Chitrakoot, District Satna, Madhya Pradesh 85, India; of corresponding author: drgsingh@rediffmail.com (Received 9 March 00; accepted in revised form July 005; published online 0 October 005) The performance of the seed-metering device of a pneumatic planter was investigated under laboratory and field conditions to optimise the design and operating parameters for cottonseed planting. The effect of operational speed of the disc, vacuum pressure and shape of the entry of seed hole were evaluated by examining the mean seed spacing, precision in spacing (coefficient of variation), miss index, multiple index, and highest quality of feed index. For picking single seeds, the planter disc had a seed hole of 5mm in diameter. The entry cone angle of the hole was varied from 90 to 50, the speed varied from 09 to 069 m/s, and the vacuum pressure from to 5 kpa. The metering system of the planter was set to place the seeds at 50 mm spacing. It was observed that the planter disc with a 0 entry cone angle gave superior performance at all speeds and operating pressures. However, there was no conclusive statistical evidence to identify a single value of disc speed or vacuum pressure. Lower miss indices were observed at higher pressures and lower speeds, and lower multiple indices at lower pressure and higher speeds. The metering system with a speed of 0 m/s, and a vacuum pressure of kpa produced superior results with a feed index of 97% and a coefficient of variation in spacing of 86%, recording a mean seed spacing of 5 mm. Optimisation of the regression equations incorporating speed of the disc and operating vacuum pressure through iteration further revealed that a disc, operating at speeds from 0 to 0 m/s and a vacuum pressure of kpa, yielded similar performance. Based on the optimised operational parameters, performance indices of the pneumatic planter were determined under field condition by measuring the distribution of cotton plants spacing. A mean plant spacing of 98 mm was found in the field with a 9% precision (coefficient of variation). Within the range of 0 00 mm, 9% cotton plants were distributed compared to 88% seeds spacing distribution observed on the laboratory test rig. Displacement of seeds in the field (due to rolling and bouncing) can affect the plant spacing distribution in the field. r 005 Published by Elsevier Science Ltd on behalf of Silsoe Research Institute. Introduction Precision planting is defined as the placement of single seeds in the soil at the desired plants spacing. Usually, plant scientists use hand dibblers to achieve this accuracy. The sowing devices equipped with single seed metering devices are called precision planters. Horizontal plate planters with cells on the periphery were the first precision planters developed (Datta, 97). Although, horizontal seed metering was popular and widely used, problems occurred with higher seed damage, and missing and multiple drops. To reduce these losses, inclined and vertical plate planters were developed and used. Further research led to the development of the pneumatic seed-metering device (Shafii & Holmes, 990; Guarella et al., 996). This mechanism has the advantage of metering irregular shaped seeds, besides spherical seeds. The most 57-50/$ r 005 Published by Elsevier Science Ltd on behalf of Silsoe Research Institute

2 0 R.C. SINGH ET AL. commonly adopted pneumatic planters are equipped to release single seeds in furrows as per the desired plant spacing by using a modular rotating seed disc under negative pressure. The spacing of the seeds are affected where the mechanism fails to select or drop a seed resulting in large spacing between seeds; or because the mechanism selects and drops multiple seeds causing small spacing between seeds. To achieve accurate seed spacing, different parameters that affect the placement need to be optimised for a specific size of seed such as: (i) the shape of the seed hole on the disc for singulation of seed; (ii) the speed of the disc, to regulate seed spacing; and (iii) the vacuum pressure required to hold, transport and drop the seed. metering system, field and operational parameters affect the precision distribution of seeds. Karayel and Ozmerzi (00) stated that variability in the seed spacing with a precision vacuum seeder increased with increasing forward speed. They revealed that forward speed of m/s consistently produced a better seed pattern than 5 and m/s for precision sowing of melon and cucumber seeds. In the present analysis, mean seed spacing, miss index, multiple drop index, quality of feed index, and precision in spacing (coefficient of variation) have been included to evaluate the performance of the pneumatic planter under laboratory and field conditions, as adopted by Kachman and Smith, 995 (Appendix A).. Literature review The performance of a planter depends upon uniformity of seed distribution in furrows, which is difficult to measure in the field due soil coverage after planting operation. A conveyor belt smeared with grease has generally been used in the laboratory, and these results have been compared with seed distribution in the field. Kocher et al. (998) and Lan et al. (999) developed an opto-electronic seed spacing measurement system that measured time intervals between the seeds, and detected front and back seed drop location events to determine the seed spacing uniformity of a planter in the laboratory. They used a seed detection sensor consisting of a rectangular photo-gate with photo transistors receiving light beams from light-emitting diodes. The space measurement obtained based on time intervals between seeds drop events were strongly correlated with the space measurements obtained on a greased belt test stand. The accuracy, however, depended upon the size of the seeds and photo-gate. The opto-electronic sensor system was also used by Panning et al. (000) for the measurement of seed spacing uniformity in the field and laboratory test stand. These were within75 mm of the theoretical spacing. They reported that laboratory testing with opto-electronic sensor system did not account for seed bounce and roll in the furrow, and while being covered by soil, it did not adequately predict seed spacing uniformity of planters in the field. The parameters for the evaluation of performance of the planter include mean and standard deviation of spacing between seeds or plants (Hollewell, 99; Parish et al., 99), percent multiples and misses (Brooks & Church, 987) and precision in spacing index (Hofman, 988; Jasa & Dickey, 98). The uniformity of seed spacing is an important factor in designing the pneumatic seed-metering device. Besides the design of the. Equipment and procedures.. Seed singulation metering system of the pneumatic planter A modular pneumatic seed-metering system having a disc of 5 mm outside diameter and 7 mm thickness with equidistant holes at a distance of mm pitch circle diameter was used. Seed spacing was regulated by changing the rotational speed or by changing the number of holes/cells on the metering disc. The disc was mounted to a vacuum retaining plate made of Bakelite material having 75 mm outside diameter and 0 mm thickness (Fig. ). A drive wheel was connected to the pneumatic seed-metering system through chain and sprockets to provide rotation to the seed disc. Suction pressure inside the metering unit was created by connecting it to a vacuum pump. The vacuum retaining plate was equipped with a baffle to release the vacuum pressure of the seed disc. A plastic pipe having inside diameter of 5 mm was provided in the baffle at 0 kpa Fig.. A modular unit of the pneumatic seed metering device.

3 OPTIMISATION OF DESIGN AND OPERATIONAL PARAMETERS positive pressure to facilitate release of lightweight seeds. 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. 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. The seed hole of the metering disc was determined based on the p50% size of the geometric mean diameter of the cotton seeds. To prevent the seed entering the seed hole, it was made conical to completely close it with the seed to avoid multiple seeds pick up by the metering disc. Three included angles as 90, 0, and 50 were selected for optimisation. The geometric mean diameter of the seed was calculated as d s ¼ ðlwtþ = () where: d s, is geometric mean diameter in mm; l, w and t are the mean length, width and thickness in mm, respectively. The geometric mean diameter and sphericity (defined as ratio of diameter of the largest inscribed circle over diameter of the largest circumscribed diameter of the seed) were measured from 00 samples of randomly selected cottonseeds, and are given in Table along with other physical characteristics of the cotton seeds. A metered seed is held stationary against the conical hole in a pneumatic planter under negative pressure if the gravitational force is balanced by the static pressure acting on the projected area of the seed (Fig. ). The pressure difference P in Pa between one point above and one point below the seed being held in position in this static case denoted by P 0 is given as P 0 ¼ mg=a s () where: m is the mass of a single seed in kg; g is the acceleration due to gravity in m/s ; and A s is the projected area of the seed in m. The contact force per unit length of contact for a seed under static equilibrium is also expressed by Fallack and Persson, (98) as F c ðtan a þ mþ ¼ P P 0 =cos a ðds =Þ () where: F c is the contact force per unit length of the contact in N/mm; P is the pressure difference across the nozzle in Pa; a is the entrance section cone angle in degrees; m is the coefficient of friction of seed on nozzle; d s is the geometrical mean diameter of seed in mm. The lowest pressure differential value designated as P hm that will hold the seed against the nozzle occurs when contact force F c is zero, and substituting this in Eqn (): P hm ¼ P 0 =cos a () The seed may remain in contact with the edge of nozzle orifice D 0, when its geometrical mean diameter d s is greater than the diameter of nozzle orifice, d s D 0 Xd s cos a. Substituting, Eqn () reduces to P hm ¼ P 0 ðd s =D 0 Þ (5) In the dynamic case, the air velocity must be equal to or higher than the terminal velocity of seed V t in m/s, and the pressure difference P t in Pa holding the seed in D 0 P 0 A s mg d s Fig.. Forces acting on a seed held in a conical nozzle of a pneumatic planter; A s is the projected area of the seed; d s, geometric mean diameter of seed; D 0, diameter of nozzle orifice; F c, contact force; g, gravitational acceleration; m, mass of a single seed; P 0, pressure difference, a, entrance section cone angle α F c Table Physical characteristics of cotton seed Physical properties Minimum Maximum Mean Standard error of mean 95% confidence limit Length l, mm Width w, mm Thickness t, mm Sphericity Frontal area A s,mm seed mass, g Sphericity, defined as ratio of diameter of the largest inscribed circle over diameter of the largest circumscribed diameter of the seed.

4 R.C. SINGH ET AL. the orifice of the nozzle as given by Fallack and Persson (98): and P t ¼ 05 r a V t (6) mg ¼ 05r a C d A s V t (7) Therefore, from Eqns (), (6) and (7) P 0 ¼ C d P t (8) where: C d is the drag coefficient; P t is pressure difference in Pa at terminal velocity; and r a is the density of air kg/m. The sphericity and drag coefficient C d of cottonseeds were calculated as 068 and 06, respectively (Table ). Hence, the required minimum pressure difference P hm, holding the seed of 5 mm geometric mean diameter and 0 g mass would be 09 kpa. The seeds during angular motion in pneumatic planter are subjected to inertial and vibratory forces. If the seed holding pressure P hm is just sufficient, it loses contact with the seed hole, and falls back into the seed box. Therefore, the seedholding pressure must always be appreciably greater than the value of P hm in order to retain the seed throughout the seed metering and transport process. For the estimation of the optimum vacuum pressure of a precision vacuum seeder a mathematical model was developed by Karayel et al. (00) by using physical properties of seeds viz. thousand seed kernel mass, projected area, sphericity and kernel density. The model satisfactorily described the required vacuum pressure of the precision vacuum seeder with the mean square of the deviation of 5 0, root mean square error of 7 0, and modelling efficiency of 099. The predicted vacuum pressure values by the models were: maize, kpa; cotton, soya bean, and watermelon, kpa; melon and cucumber, 5 kpa; sugar beet, kpa; and onion seeds, 5 kpa. In the present study the seed holding pressures were determined empirically for different types of seeds, and values ranged from to 5 kpa... Metering system for the testing of pneumatic planter under laboratory To optimise the design and operational parameters, the metering system of the pneumatic planter was tested under laboratory condition (Fig. ). A rubber conveyor belt moved between 0 and 5 km/h over two rollers (00 mm diameter each) mounted on a stand at a distance of 0 m apart. A 5 kw advanced variable speed motor was used to drive the two rollers. The belt was Fig.. Laboratory test for testing of metering device of the pneumatic planter smeared with grease to secure the seeds to the belt surface, preventing rolling or bouncing. An ultrasonic sensor measured the linear speed of conveyor belt, which was then recorded on a X micro-logger. The seedmetering device was positioned over the belt by placing its drive wheel on the surface of the moving belt that provided rotational speed to the seed-metering disc. The speed was measured with an electronic digital tachometer. A vacuum pump with a pressure-regulating valve provided the desired negative pressure inside the seed disc. The seeds released by the metering disc were dropped onto the greased belt, and the distribution of seed spacing was measured with a metre scale... Performance parameters for the planter For optimisation of the factors affecting the performance of the pneumatic planter, experiments were conducted with: four speeds of metering disc [() 09 m/s, () 0 m/s, () 058 m/s, and () 069 m/s]; four levels of vacuum pressure [() 0 kpa, () 5 kpa, () 0 kpa, and () 5 kpa]; and three entry shapes of seed-hole of the disc [() 90, () 0, and () 50], keeping a three-factor factorial split-split experimental design. The tests were replicated three times for each entry shape of seed-hole. Seed spacing of 0 seeds with misses and multiples were measured on the greased belt. The data were statistically analysed to determine the effect of entry shapes of the seed-hole, vacuum pressure and linear speed of disc on performance indices, namely, mean seed spacing, miss index, multiples index, quality of feed index, and precision in spacing. These indices are defined in Appendix A.

5 OPTIMISATION OF DESIGN AND OPERATIONAL PARAMETERS The pneumatic disc with a 5 mm hole and 0 cone angle entry shape yielded the lowest miss index, multiple index, and consequently the highest quality of feed index, and minimum coefficient of variation in distribution of spacing at all the speed and pressure combinations (Figs (a) (e)). The disc with a 0 cone angle, therefore, was adopted for further analysis to optimise the operational parameters, namely speed of operation and vacuum pressure... Field performance evaluation of the pneumatic planter Field evaluation of the pneumatic planter equipped with the optimised metering system was conducted in black soil with cottonseeds having a viability of 85%. The moisture content of the soil at the time of planting was about %. Three modular seed-metering units were mounted on the main frame of the pneumatic planter at 900 mm row spacing (Fig. 5). The seedmetering units were connected to the ground drive wheel through a sprocket and chain linkage to get the desired speed of the metering disc. The tractor was operated at an average speed of 78 km/h, to get the desired plant spacing of 50 mm. The rotational speed of aspirator blower, driven by the power take off (PTO) of the tractor, was adjusted to obtain an optimum vacuum pressure of kpa at the seed disc. After completion of the planting operation, spacing between plants was recorded randomly within a length of 5 m at three locations by counting seed germination up to 7 days after planting, as spacing between seeds was difficult to measure in the furrows (Ozmerzi et al., 00). These observations were statistically analysed and compared with the laboratory test results. The frequency distribution of plant spacing was also drawn. Statistical software packages (Windostat and SPSS ) were used to find the least significant difference (LSD) of different performance parameters.. Results and discussion.. Evaluation of metering system of pneumatic planter under laboratory conditions... Effect of disc speed and vacuum pressure on performance of pneumatic metering system The mean seed spacing obtained at a disc speed of 09 m/s with a vacuum pressure of kpa is close to the set spacing of the system [Fig. (a)], but the values obtained at 09 and 0 m/s are statistically the same. However, the precision in spacing measured through the coefficient of variation for the distribution of seed spacing is lowest at a vacuum pressure of kpa and a disc speed of 09 m/s [Fig. (b)]. The mean seed spacing and precision in spacing are affected by miss index and multiple index. Figure (c) reveals that the miss index is lowest at 5 kpa vacuum pressure. However, the effect of disc speed on miss index is not distinguishable as the values obtained at 09 and 0 m/s speeds are statistically the same at 95% level of confidence. The multiple index value is observed to be minimum at operating pressure of kpa [Fig. (d)]; the influence of operating speeds is not statistically significant, although it reduces at higher speeds. The quality of feed index [Fig. (e)], which is influenced by both the miss index and multiple index, is highest with disc speeds of 0 m/s, and at vacuum pressures of kpa, which is statistically the same as observed at the sped of 09 m/s and 5 kpa pressure.... Effect of disc speed and vacuum pressure on miss index, multiple index and feed index Miss index values reduce as the pressure is increased but increase with increased speed (Fig. 6); with lower vacuum pressure and at higher speeds, the metering disc does not get enough time to pick up seeds, resulting in higher miss indices. The multiple indices on the other hand are low at higher speed but increase as the pressure is increased. Panning et al. (000), and Zulin et al. (99) also reported similar findings. The multiple regression equations for the miss index I miss and multiple index I mult for the disc with a cone angle of 0, incorporating the operating disc speed v in m/s, and vacuum pressure p in kpa, are given as I miss ¼ 877 9v þ 85v 5 p þ 0p 79vp I mult ¼ 78 v þ 7v 85p þ 0p þ vp (0) with values for the coefficient of determination R of 098 and 09, respectively. It may be noted from Eqns (9) and (0) that the speed of the disc has a more pronounced effect than the pressure on both the miss index and multiple index. For the minimum miss index and multiple index, the above expressions have been optimised through iteration. At disc speeds from 05 to 0 m/s and an operating vacuum pressure of kpa, the miss index values obtained from Eqn (9) are less than %. At these speeds, however, multiple index values range from % to %. On the other hand, multiple indices are computed to be less than % at speeds greater than 055 m/s. The lowest effect of velocities on the values of ð9þ

6 R.C. SINGH ET AL. Mean seed spacing, mm (a) Speed Vacuum pressure Seed hole shape Precision in spacing % (b) Speed Vacuum pressure Seed hole shape 0 Miss index, % 8 6 (c) Speed Vacuum pressure Seed hole shape Multiple index, % (d) Speed Vacuum pressure Seed hole shape (e) Quality of feed index, % Speed Vacuum pressure Seed hole shape Fig.. Comparison of different performance indices (level of significance, 5%): (a) mean seed spacing; (b) precision in spacing; (c) miss index; (d) multiple index; (e) quality of feed index. The values indicate levels of values in ascending order (speed: 09, 0, 056 and 069 m/s; pressure:, 5, 0 and 5 kpa; cone angle, 90, 0 and 50; the horizontal bars at the bottom indicate the values are not significantly different

7 OPTIMISATION OF DESIGN AND OPERATIONAL PARAMETERS 5 quality of feed indices (an interaction of miss indices and multiple indices) is shown in Fig. 7 at kpa vacuum pressure. The multiple regression equation for the quality of feed index I fq at different speeds and vacuum pressures of the 0 cone angle of the disc is given as Ifq ¼ 887 v 6v þ 76p p þ 58vp () with a value for R of 09. At the vacuum pressure of kpa and operating disc speeds of 0 0 m/s, Eqn () yields feed index values of E9%. At these speeds, miss indices range from 0% to 6%, and multiple indices from 96% to 8%.... Effect of speed of disc and vacuum pressure on mean seed spacing and precision in spacing The mean seed spacing and precision in spacing define the pattern of seed distribution of a planter. The effect of speed of the disc and operating vacuum pressure on these values are shown in Figs 8 and 9. It is observed that mean seed spacing and precision in spacing both are affected by the speed and operating pressure of the metering disc. At pressures lower than kpa, seeds are not able to adhere to the hole and, thus, result in a higher miss index. However, at pressure higher than kpa, more number of seeds are attached to the disc hole, giving a greater number of seeds in a unit length, and thus a higher multiple index. Quality of feed index, % Vacuum pressure, kpa Linear speed of disc, m/s Fig. 5. A three row tractor operated pneumatic cotton planter under field evaluation Fig. 7. Effect of linear disc speed and vacuum pressure on quality of feed index for a 5 mm seed hole with 0 cone angle 5 Miss and multiple index, % Miss Multiple Miss Multiple Miss Multiple Miss Multiple Linear speed of disc, m/s Fig. 6. Effect of linear disc speed on miss and multiple index for a 5 mm seed hole with 0 cone angle at four vacuum pressures:, kpa;,5 kpa, kpa;,5 kpa

8 6 R.C. SINGH ET AL. Mean seed spacing, mm Vacuum pressure, kpa The effect of speed and vacuum pressure of the metering disc on the precision in spacing index I p, could be expressed through the multiple regressions, Eqn (): Ip ¼ 080 0:57v þ 78v p þ 078p 66vp () with a value for R of 096. Equation () reveals that the effect of the speed of the disc is much more pronounced than vacuum pressure in influencing in precision in spacing. Iteration of Eqn () yields a better precision in spacing (coefficient of variation, 87 89%) for disc speeds from 0 to 0 m/s at a vacuum pressure of kpa. For these operating parameters, a feed index of 9% is achieved... Field evaluation of the pneumatic planter Linear speed of disc, m/s Fig. 8. Effect of linear disc speed and vacuum pressure on mean seed spacing for 5 mm seed hole with 0 cone angle Precision in spacing, % Vacuum pressure, kpa Linear speed of disc, m/s Fig. 9. Effect of linear disc speed and vacuum pressure on precision in spacing for 5 mm seed hole with 0 cone angle... Miss index, multiple index and feed index The tractor-operated pneumatic planter was evaluated by planting cottonseeds having 85% seed viability in black soil using a metering disc with a entry cone angle of 0. The speed of the tractor was so adjusted that it enabled the planter to operate at a disc speed of 0 m/s under a vacuum pressure of kpa. Seed germination and associated plant spacing distribution in the field were recorded up to 7 days after sowing. Comparative statements of the statistical analysis of the results with least significant differences for each factor at the 5% level of significance under laboratory and field conditions are given in Table. This reveals that the lowest miss index of %, and multiple index of % are found at the disc speed of 0 m/s and vacuum pressure of kpa, yielding the highest quality of feed index of 967% under laboratory conditions. At these settings, the miss index, multiple index, quality feed index, mean seed/plant spacing, and precision in spacing observed in the laboratory and field conditions are significantly different at the 5% level of significance, and these are not correlated. From laboratory condition to the field condition, mean miss index increased from % to 888%, and multiple index from % to 69%. Consequently, the quality of feed index is reduced to 7% compared to 966% observed in the laboratory. The calculated statistical mean difference under laboratory and field conditions are: mean plant spacing, 7 mm; precision in spacing, 06%; miss index, 76%; multiple index, %; and quality of feed index, 99%.... Mean plant spacing and precision in spacing The lower feed index of the planter under field conditions has affected the mean seed spacing and precision in spacing. The seed spacing observed under laboratory conditions varied from 0 to 0 mm with a mean of 5 mm, while in the field, these varied from 00 to 760 mm with a mean of 98 mm, against the planter set to plant seeds at 50 mm spacing. Further, analysis of distribution of seed spacing shown in Figs 0 and, reveals that under the laboratory conditions, 88% of the seeds are distributed in the range of 0 00 mm, 8% between 00 and 00 mm and % between 0 and 00 mm, with a precision in spacing of 855%. Under field conditions however, 9% of the plants are distributed with a seed spacing in the range of 0 00 mm, % in the range of mm, % in the range of 0 00 mm and the remaining 6% plants with more than 00 mm seed spacing, yielding a mean precision in spacing of 9%. Plant spacing distribution in the field, as seen in Fig. 0 is skewed with a higher percentage of plants distributed with more than 50 mm spacing, revealing greater misses than multiples.

9 OPTIMISATION OF DESIGN AND OPERATIONAL PARAMETERS 7 Table Performance indices of pneumatic seed planter under laboratory and field conditions Laboratory/field Mean Standard deviation S.E. Confidence interval, 95% Mean difference d.f. t Co-rrelation () Seed spacing, mm Laboratory Field () Precision in spacing, I p Laboratory Field () Miss index, I miss Laboratory Field () Multiple index, I mult Laboratory Field (5) Quality feed index, I fq Laboratory Field Significant at 5% level of significance; S.E., standard error: d.f., degree of freedom; t, statistical t test values. Frequency of occurrence,% Spacing between seeds, mm Fig. 0. Frequency distribution of seed spacing in the laboratory Frequency of occurrence, % Spacing between plants, mm Fig.. Frequency distribution of plant spacing in the field 5. Conclusion Statistical analysis revealed that over a range of operational variables tested, a seed metering disc with a 5 mm seed hole and 0 entry cone angle, operating at a disc speed of 0 m/s and a vacuum pressure of kpa yielded a mean seed spacing of 5 mm with a precision in spacing of 855% against the set spacing of 50 mm. The mean miss index and multiple index at these settings were recorded as % and %, respectively. Consequently, a quality feed index of 97% was achieved. Evaluation of the pneumatic planter based on the optimised design and operational parameters revealed that the performance indices observed under laboratory and field conditions were significantly different at 5% level of significance. The mean plant spacing observed in the field was 98 mm with a precision in spacing of 9% compared to 5 mm mean seed spacing recorded on sticky belt with a precision in spacing of 86%. Under laboratory condition, 88% seeds were distributed in the range of 0 00 mm seed spacing, but in the field under the same settings, 9% plants were found in this range after 7 days of planting. The large differences observed in the performance indices of the laboratory and field tests are attributed to a higher miss index and multiple index. Therefore, the metering of seeds is as important a factor as the method of placement for achieving a better plant spacing distribution.

10 8 R.C. SINGH ET AL. References Brooks D; Church B (987). Drill performance assessment: a changed approach. British Sugar Beet Review, 55(), 50 5 Datta R K (97). Development of some seeders with particular reference to pneumatic seed drills. The Harvester, Indian Institute of Technology, Kharagpur, India, 6, 6 9 Fallack S S; Persson S P E (98). Vacuum nozzle design for seed metering. Transactions of the ASAE, 7(), Guarella P; Pellerano A; Pascuzzi S (996). Experimental and theoretical performance of a vacuum seed nozzle for vegetable seeds. Journal of Agricultural Engineering Research, 6(), 9 6 Hofman V (988). Maximum yields need accurate planting. The Sunflower, (), 0 Hollewell W (99). Drill performance assessments. British Sugar Beet Review, 50(), 5 Jasa P J; Dickey E C (98). Tillage factors affecting corn seed spacing. Transactions of the ASAE, 5(6), Kachman S D; Smith J A (995). Alternate measures of accuracy in plant spacing for planters using single seed metering. Transactions of the ASAE, 8(), Karayel D; Ozmerzi A (00). Effect of forward speed and seed spacing uniformity on a precision vacuum metering unit for melon and cucumber seeds. Journal of Faculty of Agriculture, (), 6 67 Karayel D; Barut Z B; Ozmerzi A (00). Mathematical modeling of vacuum pressure on a precision seeder. Biosystem Engineering, 87(), 7 Kocher M F; Lan Y; Chen C; Smith J A (998). Opto-electronic sensor system for rapid evaluation of planter seed spacing uniformity. Transactions of the ASAE, (), 7 5 Lan Y; Kocher M F; Smith J A (999). Opto-electronic sensor system for laboratory measurement of planter seed spacing with small seeds. Journal of Agricultural Engineering Research, 7(), 9 7 Ozmerzi A; Karayel D; Topakei M (00). Effect of sowing depth on precision seeder uniformity. Biosystems Engineering, 8(), 7 0 Panning J W; Kocher M F; Smith J A; Kachman S D (000). Laboratory and field testing of seed spacing uniformity for sugar beet planters. Applied Engineering in Agriculture, 6(), 7 Parish R L; Bergeron P E; Bracy R P (99). Comparison of vacuum and belt seeders for vegetable planting. Applied Engineering in Agriculture, 7(5), Shafii S; Holmes R G (990). Air jet seed metering a theoretical and experimental study. Transactions of the ASAE, (5), 8 Zulin Z; Upadhyay S K; Safii S; Garret R E (99). A hydropneumatic seeder for primed seeds. Transactions of the ASAE, (), 6 Appendix A: Performance parameters of the pneumatic planter A.. Miss index The miss index I miss is the percentage of spacing greater than 5 times the set planting distance S in mm. I miss ¼ n (A) N where: n is number of spacing 5S; and N is total number of measured spacings. A.. Multiple index The multiple index I mult is the percentage of spacing that are less than or equal to half of the set plant distance S in mm. I mult ¼ n (A) N where n is number of spacing p05s. A.. Quality of feed index The quality of feed index I q is the percentage of spacings that are more than half but not more than 5 times the set planting distance S in mm. The quality of feed index is an alternate way of presenting the performance of misses and multiples. A.. Precision in spacing I fq ¼ 00 ði miss þ I mult Þ (A) Precision in spacing I p is a measure of the variability (coefficient of variation) in spacing S, between seeds or plants after accounting variability due to both multiples and misses. I p ¼ S d (A) S where S d is standard deviation of the spacing more than half but not more than 5 times the set spacing S in mm.