Growth and yield response of selected improved soybean (Glycine max [L.] Merrill) varieties to varying weeding regimes under a tropical condition

The field trial was conducted at the Teaching and Research Farm, Abia State University, Umuahia Campus, Umudike to study the performance of three highly improved soybean varieties (`TGX 1835-10E', 'TGX 1987-62F' and 'TGX 1448-2E') to different weeding regimes (weed free, inweeded, weeded once, weeded twice and weeded three times) and to estimate character association and contribution toward seed yield per hectare. The experiment was a factorial combination of variety and weeding regimes in randomized complete block design with three replications. Vegetative data which included plant height, number of branches and number of leaves were taken at 10 weeks after planting (WAP) while at harvest, the following yield data: pod length, pod width, number of pods per plant, number of seeds per plant, pod weight per plant, 100 seed weight and seed yield per hectare were taken. The only phenological trait taken was number of days to 50% flowering. The competing weeds were also identified, sampled, counted, dried, weighed and recorded at 9 WAP and at harvest. Data were analyzed using the procedure outlined for ANOVA and means separated by LSD (P=0.05). Correlation and Path coefficients analyses were also carried out. The results showed a highly significant difference (P<0.01) among the varieties in all the traits studied. 'TGX 1835-10E' variety gave the highest seed yield/ha while weed regimes like weed free, weeded twice and three times showed non-significantly the best performance in all aspect. The results also showed that plots left inweeded and weeded once inevitably had the highest yield reduction in all the varieties. Plant height, number of branches, number of leaves at 10 WAP, number of seeds and pod weight per plant, 100 seed weight as well as soybean dry weight at 9 WAP showed high positive magnitude and significant (P<0.01) correlations with seed yield per hectare. The highest positive direct effect on yield was recorded in plant height at 10 WAP.