Improving Seed Spacing Uniformity of Precision Vegetable Planters

Abstract

Equidistant, uniform seed placement is important in lettuce production as seeds are densely planted within the row, typically only about 5 cm apart. When seeds are sown too close together, it is time consuming to thin seedlings to the desired plant spacing of 20 to 30 cm by hand and very difficult to do mechanically. The overall goal of the project was to improve lettuce seed placement accuracy and reduce the percentage of seeds spaced closely together. Specific objectives were: 1) to compare vacuum and belt-type planters to determine which style of planter provides better planting performance, 2) to evaluate belt planter seeding performance with different types of furrow openers, and 3) to develop practical modifications for vacuum planters to improve lettuce seed placement accuracy. Three vacuum planter configurations, an unmodified and two reduced seed drop height designs and a belt planter equipped with two types of furrow openers were tested in situ with pelleted lettuce seed at four travel speeds ranging from 1.6 to 4.0 kph. Belt planter performance was significantly better than that of the vacuum planter. Vacuum and belt planters both provided acceptable levels of performance at speeds below 2.4 kph, but at higher speeds, seed placement accuracy declined rapidly. No differences in planter performance were found between the two belt planter configurations tested. The mid-level drop height vacuum planter configuration had significantly better seed placement precision and fewer closely spaced seed spacings as compared to the unmodified vacuum planter. These findings illustrate the significant effect planter type, travel speed, and drop height have on planter performance. They also contradict the common perception that vacuum planters deliver seed more precisely and with fewer closely-spaced seeds as compared to belt planters. Further study is needed to determine the extent to which planter performance affects hand thinning labor costs, automated machine performance, final plant stand uniformity, and crop yield.