Maize Response to Competition from Speargrass (Imperata cylindrica (L.) Raeuschel) Regrowth II: Competitive Relationship-Relative Yield Total

Field study was conducted to evaluate the competitive effect of speargrass regrowth on subsequent maize crop. The competitive relationship study was laid out in a Randomized Complete Block Design with three replications. The study was conducted at the International Institute of Tropical Agriculture Ibadan, Nigeria, between September 2005 and September 2006. In this study maize and speargrass were monitored in eight monoculture densities (10,000, 20,000, 30,000, 40,000, 50,000, 80,000, 120,000 and 160,000 plants per hectare and eight total densities in a mixture of 1:1 ratio of maize and speargrass (5,000:5,000-80,000:80,000) per hectare. Relative yields total (RYT) indicated that maize and speargrass were competing for the same resources especially at 8:8 plants of both species in mixture, and there was mutual antagonism from severe competition for light, especially at high densities of both species (10:10-32:32 plants) in mixture. RYT of speargrass regrowth competition with maize was neither significantly higher nor lower than 2.0 for shoot competition (P=0.522); and was not significantly different (P=0.475) for rhizome competition among the various speargrass densities and proportions in competition with maize. Speargrass regrowth and maize interaction captured three resource competition scenarios of their association as follows: avoidance of competition, whereby individual species exploited the limiting resources separately (where, RYT>2.0); both species competed fully or partial, possibly at all densities in mixture since RYT values were not significantly higher or lower than 2.0; and both species may also have antagonized each other during their growth association (where, RYT<2.0).