Maize Response to Competition from Speargrass (Imperata cylindrica (L.) Raeuschel) Regrowth I: Species Growth Relationship, Yield and Yield Components

Field study was conducted to evaluate the effect of speargrass shoot regrowth from previously planted rhizomes on the growth and yield of subsequent maize crop.
This study was evaluated 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 (4, 8, 12, 16, 20, 32, 48 and 64 plants per plot and eight total densities in a mixture of 1:1 ratio of maize and speargrass (2:2-32:32) per plot.
Results suggest that both, maize and speargrass competed for the same resources. However, maize was more competitive than speargrass in 1:1 mixture. Intraspecific competition between maize plants was responsible for maize grain yield loss of about 28.4%, while the overall interspecific competition effect from speargrass regrowth densities was responsible for a yield of about 18%. There was high and significant negative correlation between speargrass parameters and maize grain yield (r≥-0.56≤-0.78) and maize biomass per plant (r≥-0.49≤-0.67). For speargrass, interspecific competition was greater than intraspecific competition causing a speargrass biomass loss of about 35% from maize competition; while intraspecific competition accounted for about 17.9% biomass reduction. Speargrass densities of 8-16 plants m-2, in mixture with maize had enormous rhizome biomass, and hence caused a grain yield reduction of 43% due to vigorous regrowth. Farmers should try to use optimum maize population that will give between 5 and 6 plants m-2; this will reduce the effect of speargrass regrowth from the rhizome, especially where land preparation is by slashing.