Influence of two contrasting cassava (manihot esculenta crantz) canopies on weed control and cassava yield
The study assessed the effect of cassava canopy on weed biomass reduction and determined its effect on weed floral composition. It also evaluated the relative effect of weed incidence on the yield of two varieties of cassava with a view to evaluating the influence of two contrasting cassava canopies on weed control and cassava yield. Two cassava cultivars with contrasting canopy architectures (TMS 30572 and TME 1) were selected for this study in two locations of different soil characteristics at the Teaching and Research Farm, Obafemi Awolowo University, Ile-Ife, Nigeria using a randomized complete block with a split plot arrangement laid in three replications. The weed control treatments (hand-weeded, herbicidal treatment, unweeded check) constituted the main plot while cassava cultivars (TMS 30572, TME 1) were the sub-plots. The weed control treatments were separated from one another by 1 m spacing while an alley of 2 m separated the replicates. The cassava cultivars were planted 1 m × 1 m to have 12 rows per sub-plot with 288 plant density. This amounted to 5,184 per hectare. Each sub-plot was separated by 1 m. Crop data collected were establishment count, crop height, canopy diameter, stem diameter, number of sprouts per stand, number of leaves, and leaf area. Data taken on weeds were fallow weed species composition, weed density, frequency of occurrence, fresh weight and dry weight. These data were collected at monthly interval until nine months after planting. Data taken at harvest were total number of tubers, total number of rotten tubers, fresh root weight, shoot fresh weight, root dry matter, Similarity Index and Shannon Wiener index (H′). Data collected were subjected to analysis of variance (ANOVA) to analyze main plot effect, sub-plot effect and interaction between the main plot and sub-plot effects. The significant effect mean values were compared using the Least Significant Difference (LSD) and the Duncan Multiple Range Test (DMRT) at 5 % level of probability, where appropriate. The results of the study revealed that in Location 1, the canopy diameter of TMS 30572 was broader than that of TME 1 by 45.4%. TMS 30572 significantly (P<0.05) lowered weed flora (species) composition by 55.5% but not the frequency of weed occurrence in the unweeded plots. TMS 30572 suppressed weed growth by 20% in unweeded plots when compared to TME 1. The weed interference in unweeded TMS 30572 reduced cassava fresh root yield by 63% when compared to the yield in the hand-weeded plots. In the same location, TME 1 reduced weed flora (species) composition by 44% but not the frequency of weed occurrence. The root fresh yield of TME 1 was reduced by 70.8% in the unweeded plots when compared to the yield in the hand-weeded plots. In Location 2, the canopy diameter of TMS 30572 was broader than that of TME 1 by 42.4%. TMS 30572 significantly (P<0.05) reduced weed flora (species) composition by 53.3% but not the frequency of weed occurrence in unweeded plots. TMS 30572 in the unweeded plots suppressed weed growth by 30% when compared to TME 1. The fresh root yield of TMS 30572 was reduced by 68.5% due to season-long weed interference when compared to the yield in the hand-weeded plots. However, in the same location, TME 1 lowered weed flora (species) composition by 33.3% but not the frequency of weed occurrence which was generally high. The root fresh yield of TME 1 was reduced by 77.5% in the unweeded plots when compared to the yield in the hand-weeded plots. The study concluded that TMS 30572 has a better weed-suppressing ability than TME 1. The broader canopy architecture of TMS 30572 enabled the cultivar to intercept maximum solar radiation for greater assimilate supply to the storage roots and higher fresh root yield than TME 1, even when weeds were left to grow with the crop throughout the season.