Design, development and testing of a transplanting mechanism for conventional paddy seedling

Abstract

For over half of the world’s population, rice provides the main dietary source of energy and hence is one of the most important food materials. In the Far – East, where 90 per cent of world’s rice is grown, transplanting is widely practised due to numerous advantages offered by this method. Manual transplanting being a rather tedious operation, paddy transplanters had been developed and introduced in several countries notably Japan. Transplanters using conventional seedlings, however, are still receiving world wide attention as the commercial transplanters such as in use in Japan were costlier and employed special type of nursery raised with much care and skill. It was, therefore, decided to develop and test a new type of paddy transplanting mechanisms, with the following specific objectives: 1. To design and develop a mechanisms for transplanting conventional paddy seedlings 2. To test the transplanting mechanisms under laboratory conditions 3. To identify the important parameters of the mechanism and establish their range for optimal operation of the unit designed under objective (1). Accordingly, a paddy transplanting mechanisms was designed and developed. Attempts were made to overcome, as far as possible, the drawbacks of similar mechanisms already developed and reported. It was a single - row unit with provision to add more such units, as as to make a multi - row machine with a row - spacing of 20 cm. It was designed to transplant washed - root seedlings of 20 to 30 cm length at a hill to hill distances of 15 cm, with 2 to 3 seedlings/hill, to a depth of 3 to 4 cm, with not more than 5 per cent missing hills and 1 per cent seedling damage. Made mainly of M. S. and supported on a wooden float, the mechanism weighted 9.5 kg without seedlings. The important components of the mechanism were a seedling box to hold the seedlings, a seedling rake and seedling ejector for positive conveyance of the seedlings into the picker – jaws, a pair of picker sets mounted on the main shaft and actuated by a stationary cam to pick and release the seedlings, and a planting finger to plant the seedlings, laid horizontally on the ground after release, by the pickers. The main shaft was rotated by a ground wheel, as the mechanism was drawn forward by manual, animal or tractor power. In order to study the effect of reduced tip velocity of the pickers, another mechanism with four picker-sets, based on the same concept as the first one, but with proportionately larger dimensions of pickers and stationary cam, was also fabricated. The components like seedling box, rake, ejector and main shaft were retained with the same specifications as for the mechanism with two picker - sets. This mechanism weighed 11.75 kg against 9.5 kg for the first mechanism. The mechanism with two picker sets was designated as mechanism – A and that with four picker sets as mechanism – B for convenience. The two mechanisms were tested in the laboratory to compare their performance in respect of the plant hill missing, seedling damage, seedling distribution, average number of seedlings per hill and the power consumption. The tests were conducted with 4 rates of picking, i.e. 60, 90, 120 and 150 hills/min and 3 seedling heights i.e. 30, 25 and 20 cm for both mechanism A and B. The laboratory tests revealed that as the rate of picking increased from 60 to 150 hills/min, the missing hills increased from 4.09 to 16.8 per cent and 6.95 to 16.44 per cent; seedling damage from 0.8 to 1.43 per cent and 0.53 to 0.89 per cent; and power consumption from 13.6 to 33.6 and 17.1 to 42.1 watts for mechanisms A and B respectively. The average number of seedlings for both the mechanisms studied, decreased from 2.4 to 2.0 for 30 cm long seedlings as the rate of picking increased from 60 to 150 hills/min. However, upto a picking rate of 120 hills/min, the missing hills were 5.69 and 10.69 per cent for mechanisms A and B respectively, as against the desired 5 per cent missing hills. Seedling damage was less than 1 per cent and average number of seedlings/hill was above 2.00 in both the mechanisms with a variation of 0 to 8 seedlings/hill with a maximum standard deviation of 1.32. As the seedling height was reduced from 30 to 20 cm, the average number of seedlings/hill was found to increase from 2.36 to 2.55 at the rate of picking of 60 hills/min, 2.11 to 2.39 at 90 hills/min, 2.07 to 2.39 at 120 hills/min and 1.99 to 2.09 at 150 hills/min. At all seedling heights, upto 120 hills/min, the average number of seedling/hill was above 2.00, which was within the required limit. On comparing the performance of the two mechanisms, it was found that there was no difference between the two regarding their ability to pick the number of seedlings/hill. However, missing hills were more in mechanism B as compared to mechanism A. For a rate of picking, upto 120 hills/min mechanism A had acceptable missing hill of 5.69 per cent as against the recommended 5 per cent, while mechanism B, had 10.67 per cent which was considerably higher than the acceptable limit. The seedling damage, upto 120 hills/min rate of picking was under 1 per cent for both the mechanisms. Limited field trials revealed that the planting finger provided in the mechanism did not function satisfactorily and as such the plants were not properly planted. Deposition of mud on the stationary cam and seedling ejector was a problem noticed in the field. Consequently, the free rotation of the main shaft was hampered which in turn led to the skidding of the ground wheel. This called for further improvements in the design of the planting finger and groundwheel drive. It was concluded that mechanism A could pick the seedlings from the seedling box and release them satisfactorily on the ground upto a picking rate of 120 hills/min. The missing hills and seedling damage were within acceptable limits. Trouble – free working of the transplanter fitted with such mechanism would have a capacity of about 0.0216 ha/hr per row. The forward speed for the rate of picking viz. 120 hills/min comes to about 1.08 kmph. The mechanism could not plant the seedlings erect and improvement on planting finger was needed. About 125 man – hrs/ha were required to wash and load the seedlings and if a 4-row bullock drawn version could be used, it would require about 140 man-hrs/ha as against 200 to 250 man-hrs/ha in hand transplanting. This would justify further developmental efforts and refinement of the mechanism.