THE PERFORMANCE OF SOYBEAN (GLYCINE MAX (L.) MERRILL) UNDER VARYING WEEDING REGIMES IN SOUTH WESTERN NIGERIA

Two field  trials were conducted at the Teaching and Research Farm, the University of Ibadan, Ibadan, in 1999 and 2001, to study the performance of two soybean cultivars subjected to varying  weeding regimes, viz: no weeding, weeding at 2 and 4 weeks after sowing (WAS), 2 and 6 WAS and 2 and 8 WAS. The experiments were a factorial combination of variety and weeding regimes in randomized complete block design with four replications. Data were taken at maturity on some vegetative, dry matter and yield parameters. The competing weeds were also identified, sampled, dried and weighed. Data were analyzed using ANOVA and means separated by LSD (P=0.05). Results showed that weeds did not adversely affect the performance of the two soybean varieties at 2 WAS. In addition, two weedings were adequate for the two soybean varieties but the interval of weeding was absolutely important in yield determination. The growth stage when these weeds prove to be harmful competition on soybeans,  as evidenced from the results of this study, was between 4 and 6 WAS. The results also showed that plots left unwedded inevitably had the highest yield reduction in both varieties. On the other hand, plots weeded at 2 and 6 WAS showed the best performance in all aspects for both varieties of soybean, than other weeding regimes. It is clear from this study, therefore, that weeding at 2 and 6 WAS ensured that most parts of vegetative and reproductive stages were weed-free, so that in conclusion, weeding soybean crop twice is appropriate using the 2 and 6 WAS sequence, for optimum performance in south west Nigeria.