|CHU, Q. - China Agricultural University|
|LIU, J. - China Agricultural University|
|BALI, K. - University Of California|
|SMITH, R. - University Of California|
|WANG, G. - Bridgestone Americas Tire Operations|
Submitted to: HortTechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/15/2016
Publication Date: 2/1/2016
Publication URL: https://handle.nal.usda.gov/10113/62265
Citation: Chu, Q., Liu, J., Bali, K., Thorp, K.R., Smith, R., Wang, G. 2016. Automated thinning increases uniformity of in-row spacing and plant size in romaine lettuce. HortTechnology. 26(1):12-19.
Interpretive Summary: Romaine heart lettuce plants must be thinned after planting to ensure that the final lettuce products are of high quality and uniform size. Traditionally, lettuce thinning has been performed using manual labor crews. However, machine-based automated thinners now provide a faster and cheaper alternative to hand thinning. This study compared effects of automated versus hand thinning on uniformity of plant spacing, plant size, and romaine lettuce yield. Overhead digital images of the lettuce plants were used to quantify plant growth and plant spacing in treatments plots managed with the two thinning methods. Automated thinning increased the uniformity of plant spacing and increased the fraction of plants with desired spacing. Lettuce plants thinned by machine were larger and had more uniform size than plants thinned by hand. Lettuce yield was generally similar among the thinning methods, because hand thinning resulted in higher plant population. The results are useful for lettuce growers in the southwestern United States.
Technical Abstract: 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.