Of the seven intercropping treatments evaluated, the additive
treatments (L100 + A100 and L100 + A30) may be the most efficient
intercropping approach for producing romaine lettuce hearts
where smaller lettuce plants are desired. This additive approach
was most efficient because lettuce density was not reduced and
alyssum transplants in the additive treatments were able to produce
78% as many open alyssum inflorescences per transplant as
the replacement treatments. However, the competition between
alyssum and lettuce grown exclusively for hearts may be slightly
greater than occurred in this study because lettuce densities for romaine
heart are generally greater than those used in the present
study. Romaine lettuce heart production typically occurs on
203.2 cm wide beds that have five or six rows on the 152 cm wide
bed top. For transplanted lettuce, the additive approach would require
that alyssum transplants be planted by hand by the crew of
workers that typically follow the transplanter implement to fill
in lettuce skips and uncover plants that were planted too deep.
At a cost of U.S. $19.50 per 1000 alyssum transplants and $ 21.50
per 1000 romaine transplants (which includes the labor cost for
transplanting), L100 + A100 would have the highest transplanting
cost ($1509) and A100 the lowest ($1394). More research is needed
to determine if the higher transplanting cost of this additive treatment
would be offset by the higher potential lettuce yields.