Increasing the Speed of a Semi-Automatic Onion Transplanter with the Use of Simultaneous Planting of Multiple Seedlings

A semi-automatic 9-row transplanter for bare root seedlings has recently been developed at the Isfahan Center for Agricultural Research that plants 80 seedlings/m2 using 9 operators at a capacity of 0.3 ha/d (8 h). Separating a single seedling from a bunch and dropping it into a distributer cell by hand takes 1 s on average. At a density of 700-800 thousand/ha, the travel speed should not exceed 6-8 cm/s, which is a limitation to improving machine field capacity. Increasing the speed to >8 cm/s to improve machine efficiency can only be achieved if more than one seedling is allocated to each cell. A randomized complete block design was used to drop 1, 2 and 3 seedlings per cell at speeds of 8, 12 and 16 cm/s, respectively, with manual transplanting as the control treatment. The treatments were compared for stand establishment, crop yield components, machine field capacity and economic benefit. The results showed that dropping two seedlings per cell and increasing speed 50% and produced a about a 24% increase in stand establishment and bulb yield compared to the single seedling/cell treatment. Three seedlings per cell produced a 53% increase in stand establishment but only about 17% improvement in bulb yield. This can be attributed to the smaller sizes and weights of the individual bulbs. The number of established seedlings in the 1 seedling per cell pattern produced results that were similar to the manual single transplanting treatment. Economic appraisal of treatments revealed that replacing 1 seedling per cell with 2 and 3 seedlings per cell produced a net increase in profits of 33% and 12%, respectively. The 2 and 3 seedlings per cell methods increased machine field capacity 50% and 100%, respectively. It can be concluded that, from the economic standpoint, 2 seedlings per cell is preferred over the 3 seedling per cell treatment; however when planting must be completed rapidly, the 3 seedling per cell treatment is also economically justified.