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1:0, 1:1, 1:2, 1:3 and 1:4 of C. argentea to A. spinosus. A distance
of 6 cm was maintained between and among stands of combining
species. In the field trial, the same treatment combinations
were established but in a randomized complete block design
with three replicates. Each block was 2 x 1 m 2 . The plots were
bed-raised with hoes. The plots were 0.5m apart. Seeds of C.
argentea were drilled at 15cm spacing between rows and later
thinned to 15cm within rows to have a plant density of 444,444
plants per hectare.. Seeds of A. spinosus were ring-broadcast
at 6cm intervals and later thinned to the required density ratios
at 2 WAP. The performance of both C. argentea and A. spinosus
was monitored in terms of plant height, stem diameter, number
of leaves/plant, leaf area and plant biomass at harvest.
S. OGUNYEMI et al.
Experiment II. Corchorus olitorius versus Amaranthus
spinosus: The design of the experiment followed the two
component model as described by Hall et al. (1992). The 1 st
component is the maximum length of time weeds emerging
with the crop can remain before they reduce yield (weedy and
subsequently weedfree, wd-wf) and the 2 nd component is the
length of time that a crop must be kept weed-free after planting
so that weeds emerging later do not reduce yield (weedfree
and subsequently weedy, wf-wd). A. spinosus was allowed to
associate with C. olitorius for varying periods of time (as
indicated in Table 1). The same treatments were established in
pots and in the field. In the pots, two seeds of C. olitorius and
4 of A. spinosus were sown in each pot to give a ratio of 1:2 crop
to weed. Weed-crop distance was 8cm in all pots. The pot trial
was a completely randomized design while the field was a
randomized complete block design with 3 replicates. Each block
was (12 x 2) m 2 and each plot was 2 x 1 m 2 . C. olitorious was
planted in rows with 30cm inter-row spacing and later thinned
to the required population densities. Seeds of A. spinosus were
planted in rows 8cm from C. olitorious and a crop to weed ratio
of 1:2 was also maintained. Data recorded for C. olitorius at 12
weeks after planting (WAP) were plant height, stem diameter,
number of leaves per plant and plant dry weight at harvest. All
dry weights were obtained by oven drying harvested materials
for 48 hours at 70 0 C before weighing. All data collected were
subjected to ANOVA and mean differences were compared
using DMRT at 5% level of probability (Gomez and Gomez,
1983).
Results
Density and Duration of Interaction between A. spinosus and
C. argentea. In the presentation of results the four control
treatments were pooled into one treatment (D0). Different
densities of A. spinosus growing in association with Celosia
argentea exerted significant pressure on the performance of
the potherb. In the pot trial, regardless of duration of weed
association, density presssure caused significant reduction in
the stem height and the number of leaves per plant of Celosia
argentea (Table 2). However, the treatments were not
significantly different with regards to stem diameter. In the field
trial, A. spinosus induced significant reduction in stem height,
stem diameter and number of leaves per plant of Celosia
argentea (Table 2). Dry matter production was also
significantly reduced by increasing weed density regardless
of duration of competition especially in the field trial, although
fresh weight of Celosia a rgentea was not significantly affected
by interference from A. spinosus (Table 3). It was informative
that dry weight suffered as high as 50% reduction when four A.
spinosus competed with one Celosia argentea for eight weeks.
Critical period of interference of A. spinosus with Corchorus
olitorius. In the two trials at 12 WAP the C. olitorius exposed
to weedy treatment (Treatment 7) had significantly reduced
height (Table 4). They were similar to plants that were weedy
for at least four weeks (Treatments 3, 4, 5 & 6). The weedfree
plants (Treatment 1) and those that were weedy in the first
two weeks and subsequently weedfree (Treatment 2) had
good height growth and were similar to those plants that
were weedfree for at least two weeks (Treatments 8, 9, 10, 11
& 12). The treatments followed the same trend in terms of all
growth parameters considered. With regards to dry matter
accumulation in the field trial, plants that were weedy for at
least the first 2 weeks (Treatments 1 & 2) and those that
were weedfree for at least the first four weeks (Treatments 9,
10, 11 & 12) were similar and had significantly (P