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Automated thinning increases uniformity of in-row spacing and plant size in romaine lettuce

Chu, Qingquan, Liu, Jiangang, Bali, Khaled, Thorp, Kelly R., Smith, Richard, Wang, Guangyao Sam
HortTechnology 2016 v.26 no.1 pp. 12-19
Lactuca sativa, crop yield, farm labor, farms, growers, romaine lettuce, row spacing, technology, thinning (plants), California
Low availability and high cost of farm hand labor make automated thinners a faster and cheaper alternative to hand thinning in lettuce (Lactuca sativa L.). However, the effects of this new technology on uniformity of plant spacing and size as well as crop yield are not proven. Three experiments were conducted in commercial romaine heart lettuce fields in 2013 and 2014 in Imperial Valley, California to compare the effects of automated thinning and hand thinning on uniformity of in-row spacing, plant size, and crop yield. Analysis of overhead images indicate that thinning 8 to 11 days earlier by automated thinners did not affect plant size compared to the hand thinning treatment at one week after hand thinning. However, lettuce plants in the automated thinning treatment were larger than plants in the hand thinning treatment at 2 to 3 weeks after hand thinning. Automated thinners increased uniformity of in-row spacing, increased the percentage of plants with desired in-row spacing of 24 to 32 cm, and almost completely removed plants with undesirable in-row spacing of 4 to 20 cm. As a result, individual lettuce plant weight and heart weight in the automated thinning treatment were larger and more uniform than the hand thinning treatment. Despite increases in lettuce plant size and uniformity in all three experiments, yield benefits of automated thinning were only significant in one of the three experiments due to larger plant population in the hand thinning treatment. This study suggests that automated thinning increases lettuce plant size and uniformity and makes it possible for growers to increase plant population and crop yield by optimizing in-row spacing.