56 S. OGUNYEMI et al.
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. References Abamu, J.A. 1995. Evaluating a crop-weed simulation model as a tool for weed management in irrigated transplanted rice (Oryza sativa). Ph.D thesis submitted to the faculty of the graduate school, University of the Philippines, Los Banos. 174pp. Awodoyin, R. O. 2000. Biology of sicklepod [Senna obtusifolia (L.) Irwin and Barneby] and its potential in weed control. Ph.D Thesis, University of Ibadan, Nigeria. 247pp. Biswas, D.K. 1996. Integrated weed control in Jute. In Abstract of papers, India Soc. of Weed Science. p68. Burkhill, J.M. 1985. Flora of West Tropical Africa (1 st edition, London) Crown Agent, Vol. 2:346-352. Gomez, K. A., & Gomez, A.A. 1984. Statistical procedure for agricultural Research. John Wiley and Sons. 2nd Edition 680pp. Hall, M.R., Swanton, J.C. & Anderson, G.W. 1992. The critical period of wed control in grain corn ( Zea may). Weed Science 40, 441-447. Holm, L.G., Plucknett, D.l., Panchap, J.O. & Herbeger, J.P. (1997). The world’s worst weeds: distribution and biology. University press, Hawaii, Honolulu, 602p. Horticulture Agencyof International development, Washington. Ogunyemi, Sola, Awodoyin, R. O. & Otu, N. A. 2000. Chemical Control of Ageratum conyzoides, Amaranthus spinosus and Cyperus rotundus in soyabeans [ Glycine max (L.) Merril.]. Journal of Tropical Forest Resources 16(1):143- 151. Ogunyemi, Sola, Ngwanyi, C.V. & Awodoyin, R.O. 2002. Interference of Solanum nigrum L. with the performance of Amaranthus cruentus L. Nigerian Journal of Plant Protection 19, 56-64 Shrefter, J.W., Stall, W.M. & Dusky, J.A.1996. Spiny Amaranth ( Amaranthus spinosus L.), a serious competitor to crisped head lettuce (Lactuca sativa L.) Hortscience 31, 347-348. Smith(Jr.), R.J. 1974. Competition of Barnyard grass with Rice cultivars. Weed Science 22, 423-426.