INCREASING CELL-SIZE AND REDUCING MEDIUM COMPRESSION ENHANCE LETTUCE TRANSPLANT QUALITY AND FIELD PRODUCTION

'South Bay' lettuce (Lactuca sativa L,) seedlings were grown in a gree nhouse during winter, spring, and fall to investigate the effect of ce ll size and medium compression on transplant quality and yield, Four S peedling planter flats (1.9-, 10.9-, 19.3-, 39.7-cm(3) cells) and two medium compression levels [noncompressed and compressed (1.5 times in weight)] were tested. The two larger cell sizes and compression of the medium led to increased plant shoot growth. Conversely, root weight r atio [RWR = (final root dry weight divided by final total dry weight initial root dry weight divided by initial total dry weight) divided by 2] was highest with the smaller cells without medium compression, L ettuce transplants were field-grown on sand and muck soils, The larger cells delayed harvest by >2 weeks for plants grown on muck soil, but yield was unaffected, When grown on sandy soil, earliness was enhanced from plants grown in 19- and 40-cm(3) cells, but head weights were no t affected in the spring planting, In fall, heads were heavier for pla nts grown in 11-, 19-, or 40-cm(3) cells compared with those from 2-cm (3) cells, On sandy soil, harvest was delayed 13 days in spring and 16 days in fall for plants grown in the smallest cell size, Using the tw o smaller cell sizes saved medium and space in the greenhouse and incr eased the root growth ratio, but it led to reduced plant growth compar ed to using the bigger cells. Yield and earliness were more related to season and soil type than to transplant quality, On sandy soil, plant s grown in 2- and 11-cm(3) cells matured later, and yield was signific antly decreased (8.6%) in fall by using plants from the 2-cm(3) cells compared to the other sizes, From our results, compressing the medium in the cells was not justified because it is more costly and did not b enefit yield in the field.