Suppressive Effects of Sunflower(Hellianthus Annuus L.) on Local Rain-Fed Weeds in Zambia

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Kambikambi, ,Tamala Tonga
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The University of Zambia
One of the constraints to crop productivity is weed infestation. Options in weed management are varied and can be associated with high costs unaffordable by small-scale farmers. Biological weed management through allelopathy presents an attractive option. Sunflower has been reported to possess allelopathic effects. This study was hence initiated with the aim of establishing the weed suppressive potential of sunflower linked to its allelopathic activity with the following strategic objectives: to evaluate weed infestation under different sunflower varieties with maize used as the control; to determine effects of season, location and time of sampling on allelopathic activity measured as weed infestation; and to determine the effects of weeds on yield of the two crops. The study was conducted over two growing seasons at two locations using a Randomized Complete Block Design (RCBD) arrangement with four replications. Six local sunflower varieties (Chongwe, Milika, Saona, Record, PAN7352 and PAN7371) were grown with two local maize varieties (MRI455 and MRI514) included as control, using standard cultural practices. Data were collected on weed diversity and density, weed biomass and crop yield. These data were subjected to Analysis of Variance (ANOVA) with mean separation done using the Least Significant Difference (LSD) method. Multivariate analysis through Principal Component Analysis (PCA) and Cluster Analysis were conducted for the three-way interactions. ANOVA results revealed significant differences for weed density within a season varied across location and time of sampling under both sunflower and maize. The amount of weed biomass that grew under different varieties varied by season, location and time under sunflower and to a greater extent under maize. Weed biomass within location significantly varied across seasons and time of sampling under sunflower and to a lesser degree under maize. Sunflower yields varied significantly between seasons and between locations while maize yields did not. Maize yields however were significantly influenced by the significant interaction between season x location. Both crops had significant variety x season x location interaction. Results for PCA showed the differences in the two crops and within each crop through loading separately for the different principal components. Cluster Analysis revealed the level of similarities between the two crops and within each crop separately through the centroid linkages and the Euclidean distances separating them. These results showed that sunflower varieties interacted with weeds differently from the maize varieties and that both weed density and weed biomass under sunflower were lower than those observed under maize. Further, crop yields for sunflower were marginally lower than the optimum for sunflower as compared to those of maize which were appreciably lower due to the weeds. In conclusion, the study established that indeed there was weed suppression by some of the local sunflower varieties and deduced that this was probably due to the involvement of allelopathy in the interference competition the crop was engaged in with weeds. Weed intensity was higher in maize that in sunflower and this intensity was affected by location, season and time of sampling. On average, sunflower yielded better in the presence of weeds than maize. No varietal differences for weed suppression and yield were observed under maize but these were observed in sunflower and from this the cost incurred by the sunflowers in allelochemical production was deduced. The study recommended that sunflower can be encouraged as an alternative crop for small holder farming since it will grow with reduced weed pressure and lessen the weeding requirement. Breeders should consider the potential cost of allelochemical production on plant metabolic processes so that they can come up with sunflower varieties that have high allelopathic activities without compromising the overall crop yield. Further research in this field is also recommended.
Weeds--Biological control , Weeds--Control , Sunflowers , Weeds