1Weed Science Section, Institute for Agricultural Research, Ahmadu Bello University, Samaru - Zaria, Nigena
2Agronomy, University of lbadan, Ibadan, Nigeria
Trials were conducted to study the effect of nitrogen, maize population, weeding and speargrass density on speargrass-maize competition at lbadan (7°22’N, 3°54’E), Nigeria. Speargrass competition with maize was influenced by nitrogen level and maize plant population. Weeding of speargrass at three and seven weeks after sowing significantly increased maize grain yield under a population of 80,000 plant/ha, especially with the application of 112 kg N/ha To alleviate grain losses due to speargrass competition with the crop at this maize population 224 kg N was required. At population of 160,000 plants per hectare, application of 112 kg N/ha reduced grain losses due to infestation while 224 kg N/ha enhanced speargrass competition with the crop. Speargrass removal at three and seven weeks after crop sowing significantly increased grain yield and enhanced maize response to nitrogen application. Speargrass density and dry matter production were however, decreased by maize population of 160,000 plants/ha as compared to other maize populations. Maize dry matter was unaffected by speargrass stand count of 20 per square metre, and below. The threshold level of infestation was between 20 and 30 stands. Maize dry matter correlated most with speargrass fresh weight although it also correlated with the stand and tiller count. Intraspecific competition occurred betwesn speargrass stands and resulted in decreasing fresh weight and tiller count per stand with increase in stand count.
