Improving seed spacing uniformity of precision vegetable planters

Equidistant, uniform seed placement of seed is important in lettuce production as seeds are typically sown only 2 inches apart. When seeds are sown too close together, it is time consuming to thin seedlings to the desired plant spacing of 8-12 inches by hand and very difficult to do mechanically. The goals of this project were to 1) develop practical modifications for vacuum planters to improve lettuce seed placement accuracy and reduce the percentage of seeds spaced closely together and 2) compare vacuum and belt type planter configurations to determine which style of planter provides better planting performance. Vacuum planter modifications included adding furrow openers and altering metering box configurations to reduce seed drop height. Five planter configurations were tested in the field at four travel speeds ranging from 1.0 to 2.5 mph. The mid-level drop height planter had significantly better seed placement precision and fewer closely spaced seed spacings as compared to the unmodified vacuum planter. No differences in planter performance were found between the two belt planter configurations tested. Vacuum and belt planters both provided acceptable levels of performance at speeds below 1.5 mph, but at higher speeds, seed placement accuracy declined rapidly. Belt planter performance was significantly better than that of the vacuum planter. These findings are important in that they illustrate the significance travel speed has on planter performance and contradict the common perception that vacuum planters deliver seed more precisely and with fewer close spaced seeds as compared to belt planters.