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Competitive impact of Amaranthus spinosus and Corchorus olitorius in Nigeria. 57
Amaranthus spinosus and Celosia argentea are members
of the same family. They probably have similar growth
requirements, hence the keen competition between the two
species for nutrients and probably moisture. The duration
of competition probably contributed to the competitive
effects as weed density and duration of association induced
significant reduction in the stem diameter. In the field, stem
diameter was significantly reduced beyond three weeds/
plant and four weeks of competitive interaction. Ogunyemi
et al.(2001) showed similar reduction in crop performance
when Solanum nigrum grew in association with Amaranthus
cruentus. Ogunyemi et al (2000) also obtained similar results
in the study of the competitive interaction between
Amaranthus spinosus and Glycine max.
The performance of Corchorus olitorius was adversely
affected by competition from Amaranthus spinosus.
It is clear from the study that the critical period of interference
of A. spinosus with C. olitorius lies between the first 2-4
weeks of growth. This agrees with Biswas (1986) who
reported 2WAP as the critical period of weed competition
for Corchorus olitorius. Smith (1974) reported similar results
for rice in competition with Echinochloa crus-galli. Abamu
(1995) also reported that reduction in rice grain dry weight
resulted from increase in the time of crop-weed association.
In both potherbs, the parameters plant height, stem diameter
and number of leaves are of great value in the
marketability of the vegetables. Any weed interaction that
causes significant reductions in these parameters deserves
serious attention. Vegetable growers do not normally sell
by dry weight or even fresh weight in Nigeria, but by size as
indicated by height and leafiness. The subsequent presence
of weed after weedfree period (wf-wd) from four weeks
onward probably enhanced the yield of C. olitorius by
ameliorating crop environment, especially if moisture is not
limiting. Awodoyin (2000) reported that at 1600 hours in 5
cm soil depth the presence of weed on soil surface compared
to weedfree plot had 8.8% reduction on soil temperature.
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