Shoot dry matter (DM) was determined for lettuce and alyssum
at 42 d after transplanting, on 15 and 16 June in 2009 and 2008,
respectively; these harvest dates were 7 and 4 d prior to when
the lettuce in the remainder of the field was harvested by a commercial
crew in 2008 and 2009, respectively. Lettuce shoots are hereafter
referred to as ‘heads’. For L100 and A100, the DM harvests included
one transplant from one randomly chosen row in each bed in 2008,
and one transplant from both rows in each bed in 2009. A similar
procedure was used to determine lettuce and alyssum DM in the
treatments with both plant types by harvesting one adjacent alyssum–
lettuce transplant pair from one randomly chosen row in each
bed in 2008, and one adjacent alyssum–lettuce transplant pair from
both rows in each bed in 2009 (Fig. 1). Harvests occurred at least 1 m
from the end of each bed. Harvested plant tissue was oven-dried at
65 C for at least 48 h until the weights had stabilized. Prior to
oven-drying the alyssum shoots in 2008, the number of open inflorescences
per transplant were counted to determine the relationship
between alyssum transplant DM and the number of open inflorescences
using regression analysis; open inflorescences were inflorescences
with at least 1 open flower. The regression analysis of open
inflorescences in 2008 was based on 1 randomly chosen alyssum
plant from all four blocks harvested on 16 June and an additional
randomly chosen plant from three blocks on 17 June. The equation
derived from the regression analysis was used to estimate the number
of open inflorescences per ha and the number of open inflorescences
per head of lettuce assuming the strip intercropping
patterns for a 1 ha field described in 2.3 and table 1. To estimate
the number of open alyssum inflorescences per unit area and open
inflorescences per lettuce head in the asymmetrical treatment,
L25A75, the DM of the alyssum transplants in A100 was used for
alyssum transplants adjacent only to alyssum within the row. This
procedure was used for the of the asymmetrical treatments because
a separate experiment had determined that there was no significant
difference betweenDMof alyssum transplants in A100 and alyssum
transplants adjacent only to alyssum within a row in L25A75 (Brennan,
unpublished data).