Zaki Dizaji - Faculty of Agriculture, Tarbiat Modarres University, Tehran, Islamic Republic of Iran
Minaei - Faculty of Agriculture, Tarbiat Modarres University, Tehran, Islamic Republic of Iran

One of the important applications of pneumatic systems is in seed planting machines. A seed knockout device is one of the main components of precision-pneumatic planters for sowing small seeds. Examination of different commonplace plate-type vacuum planters shows that the main reason for low success of plate-type vacuum planters in planting small seeds is the current deficiency in their seed metering mechanism. On the other hand, studies about seed ejection by seed knockout devices are very limited. Therefore, the main objective of the present research is studying seed ejection by the seed knockout mechanism in order to improve the available plate-type vacuum planters. Hence, first, the effective parameters in seed ejection were determined theoretically. Then an air-jet seed knockout device was developed and the influence of effective parameters in seed ejection and that of the knockout device on planter’s performance was tested. Effective parameters in seed ejection are numerous, but three parameters are more important than the others, namely, rotational velocity of the seed plate, air velocity of the air-jet seed knockout device, and the distance of nozzle tip from the seed plate holes. The new air-jet seed knockout system was mounted for testing on the seed metering device of the vacuum-precision planter made by Behkesht (Agrifarm) company. Test independent variables were: rotational velocity of the seed plate at three levels (40, 68 and 99 rpm) and air velocity of the air-jet seed knockout device at three levels (0, 7-8 and 15-16 m/s). Dependent variables included: three different types of seed damage, cell filling percentage, and seed viability. Results of the analysis of variance indicated that all types of mechanical damage decreased, as air velocity increased. Test results indicated that not only did the air-jet seed knockout device decreased seed damage, but also due to clearing the seed metering plate cells clogged by broken seeds and plant debris, it increased cell filling percentage and improved overall performance of the seed metering system.

vacuum-precision planter, design, small seeds, air-jet seed knockout