Field experiment was conducted at Lower Niger River Basin Development Authority, Ejiba in 2016 and 2017 cropping seasons to investigate the effect of Siam weed (Chromolaena odorata L.) residues, phosphorus fertilizer and manure application time on soil properties, growth and root yield of sweet potato in acidic soil. Treatments constituted of 4 x 4 factorial arrangements in a Completely Randomized Block Design. Four levels of amendments which were 5t/ha Chromoleana odorata residues, 60 kg/ha phosphorus, 2.5t/ha Chromoleana odorata residues plus 30 kg/ha phosphorus, No Chromoleana odorata residue and no single superphosphate fertilizer (control) and four levels of time of application of the residues which were three (3) weeks before planting (3WBP), manure application at planting (ATP), manure application at three (3) weeks after planting (3WAP) and manure application at six (6) weeks after planting (6WAP). Data on soil pH, growth and yield parameters were collected and subjected to analysis of variance. Significantly different means were separated using Duncan Multiple Range Test at 5% level of probability. The results indicated that soil acidity increased in plots with mineral fertilizer alone in both years. Plot with combined application of Chromolaena odorata residues and phosphorus at reduce rate were better in all the growth and yield characters compared with plots with either Chromolaena odorata residues or phosphorus fertilizer alone. The least values of vine length shoot weight, number of primary branches, and number of tubers per plant, weight of tubers per plant and tuber weight per land area occurred in the control plots. When Chromolaena odorata residues were applied 3 weeks before planting, maximum growth and yield characters were observed. Manure Applied at three (3) weeks before planting gave best growth and yield of sweet potato in this experiment. Application of Chromolaena odorata residues at 2.5 t/ha combined with phosphorus at 30 kg/ha is therefore recommended to the sweet potato farmers for maximum production of sweet potato. Also, Chromolaena odorata residues should be applied into the soil three (3) weeks before planting as it gives maximum values performance parameters.
Keywords: Chromolaena odorata, Phosphorus, Siam weed, manure, potato
