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Competitive impact of Amaranthus spinosus and Corchorus olitorius in Nigeria. 57<br />
Amaranthus spinosus and Celosia argentea are members<br />
of the same family. They probably have similar growth<br />
requirements, hence the keen competition between the two<br />
species for nutrients and probably moisture. The duration<br />
of competition probably contributed to the competitive<br />
effects as weed density and duration of association induced<br />
significant reduction in the stem diameter. In the field, stem<br />
diameter was significantly reduced beyond three weeds/<br />
plant and four weeks of competitive interaction. Ogunyemi<br />
et al.(2001) showed similar reduction in crop performance<br />
when Solanum nigrum grew in association with Amaranthus<br />
cruentus. Ogunyemi et al (2000) also obtained similar results<br />
in the study of the competitive interaction between<br />
Amaranthus spinosus and Glycine max.<br />
The performance of Corchorus olitorius was adversely<br />
affected by competition from Amaranthus spinosus.<br />
It is clear from the study that the critical period of interference<br />
of A. spinosus with C. olitorius lies between the first 2-4<br />
weeks of growth. This agrees with Biswas (1986) who<br />
reported 2WAP as the critical period of weed competition<br />
for Corchorus olitorius. Smith (1974) reported similar results<br />
for rice in competition with Echinochloa crus-galli. Abamu<br />
(1995) also reported that reduction in rice grain dry weight<br />
resulted from increase in the time of crop-weed association.<br />
In both potherbs, the parameters plant height, stem diameter<br />
and number of leaves are of great value in the<br />
marketability of the vegetables. Any weed interaction that<br />
causes significant reductions in these parameters deserves<br />
serious attention. Vegetable growers do not normally sell<br />
by dry weight or even fresh weight in Nigeria, but by size as<br />
indicated by height and leafiness. The subsequent presence<br />
of weed after weedfree period (wf-wd) from four weeks<br />
onward probably enhanced the yield of C. olitorius by<br />
ameliorating crop environment, especially if moisture is not<br />
limiting. Awodoyin (2000) reported that at 1600 hours in 5<br />
cm soil depth the presence of weed on soil surface compared<br />
to weedfree plot had 8.8% reduction on soil temperature.<br />
References<br />
Abamu, J.A. 1995. Evaluating a crop-weed simulation model as<br />
a tool for weed management in irrigated transplanted rice<br />
(Oryza sativa). Ph.D thesis submitted to the faculty of the<br />
graduate school, University of the Philippines, Los Banos.<br />
174pp.<br />
Awodoyin, R. O. 2000. Biology of sicklepod [Senna obtusifolia<br />
(L.) Irwin and Barneby] and its potential in weed control.<br />
Ph.D Thesis, University of Ibadan, Nigeria. 247pp.<br />
Biswas, D.K. 1996. Integrated weed control in Jute. In<br />
Abstract of papers, India Soc. of Weed Science. p68.<br />
Burkhill, J.M. 1985. Flora of West Tropical Africa (1 st edition,<br />
London) Crown Agent, Vol. 2:346-352.<br />
Gomez, K. A., & Gomez, A.A. 1984. Statistical procedure for<br />
agricultural Research. John Wiley and Sons. 2nd Edition<br />
680pp.<br />
Hall, M.R., Swanton, J.C. & Anderson, G.W. 1992. The critical<br />
period of wed control in grain corn ( Zea may). Weed Science<br />
40, 441-447.<br />
Holm, L.G., Plucknett, D.l., Panchap, J.O. & Herbeger, J.P.<br />
(1997). The world’s worst weeds: distribution and biology.<br />
University press, Hawaii, Honolulu, 602p. Horticulture<br />
Agencyof International development, Washington.<br />
Ogunyemi, Sola, Awodoyin, R. O. & Otu, N. A. 2000.<br />
Chemical Control of Ageratum conyzoides, Amaranthus<br />
spinosus and Cyperus rotundus in soyabeans [ Glycine max<br />
(L.) Merril.]. Journal of Tropical Forest Resources 16(1):143-<br />
151.<br />
Ogunyemi, Sola, Ngwanyi, C.V. & Awodoyin, R.O. 2002.<br />
Interference of Solanum nigrum L. with the performance of<br />
Amaranthus cruentus L. Nigerian Journal of Plant Protection<br />
19, 56-64<br />
Shrefter, J.W., Stall, W.M. & Dusky, J.A.1996. Spiny<br />
Amaranth ( Amaranthus spinosus L.), a serious competitor<br />
to crisped head lettuce (Lactuca sativa L.) Hortscience<br />
31, 347-348.<br />
Smith(Jr.), R.J. 1974. Competition of Barnyard grass with<br />
Rice cultivars. Weed Science 22, 423-426.