Abstract
Seven vacuum nozzles were evaluated in a stationary device similar to horticultural seedflat seeders to learn correct seed orientation, air pressure for pickup, holding and transport, brush-off method, and seen ejection. Theoretical derivations and experiments showed that the pressure difference needed for pickup of a seed increased with the fourth power of the pickup height for heights of more than one seed radius. An exponential relationship was found to apply closer to the nozzle. Recommendations for a suitable pneumatic metering device for nearly spherical seeds were made with regard to nozzle type, seed lift height, seed orientation, brush-off device, and seed ejection.