ABSTRACT

Field trials were conducted in 2015, 2016 and 2017 cropping seasons at the National Cereal Research Institutes’ farm, (NCRI), Amakama (07˚29′N latitude and 05˚28΄E longitude), South Eastern Nigeria to investigate complementary weed control potential of time of planting and population of sweet potato on cassava (TME 419). The study was laid out in a split plot arrangement in a Randomized Complete Block Design (RCBD) with three replicates. Intercropping patterns which included two populations of sweet potato (10,000 and 20,000 plants ha^-1) between rows of cassava, planted at 0, 4 and 8 weeks after planting (WAP) cassava, sole cassava and sole sweet potato constituted the main-plots, while four weed control treatments viz pre-emergence application of S-metolachlor+atrazine at 1.16+1.48 kg a.i ha^-1 alone (P), S-metolachlor+atrazine at 1.16+1.48 kg a.i ha^-1 followed by supplementary hoe weeding at 8WAP (PHW1), three hoe weedings at 4, 8 and 12 WAP (3HW) and a weedy check (0W) were assigned to the sub-plots. Broadleaves, grasses and sedges dominated the field in the ratio of 53.3, 26.2 and 17.5%, respectively averaged over the three years. The major weed species in the study area were Oldenlandia corymbosa > Panicum maximum > Spermacoce verticillata > Lindernia antipoda > Cyperus esculentus > Killinga bulbosa > Charmaecrista rotundifolia > Digitaria horizontalis. Apart from weed seedling emergence, the results indicated significant differences between cropping patterns. Intercropping significantly suppressed weed infestation than sole cassava. Cassava intercropped at the same time with sweet potato at 20,000 plant ha^-1 (CS200) significantly (P≤0.05) reduced weed density, dry matter as well as the growth and yield of cassava when compared with the sole cassava treatment which gave the lowest weed control. Weed density and dry matter were higher with intercropped sweet potato introduced at 8 WAP at both populations (CS108 and CS208) comparable to sole cassava due to reduced rainfall during the period of sweet potato growth resulting in lower ground cover.  Similarly, the highest cassava plant height, leaf area as well as root yields were obtained with sole cassava which did not differ from CS108 and CS208, whereas CS200 had the highest sweet potato ground cover as well as tuber yield. There were statistically significant differences in weed seedling emergence, growth and yield of cassava and sweet potato between the different weed control methods. P and PHW1 significantly suppressed weed seedling emergence up to 6 WAP in the three years of study when compared to weedy check. Three hoe weeding resulted in the best growth and yield of cassava whereas PHW1 gave the best sweet potato growth and yield. The weedy check (0W) and P recorded the poorest weed control and performance of these crops. In general, CS200 combined with PHW1 gave the highest total intercrop yield, benefit-cost, land equivalent ratios and return on investment better than other combinations. Total land saved under this treatment was 24% which could be used for other agricultural purposes. Therefore, under the soil and weather conditions of the experiment, the cropping pattern and weed control method identified for TME 419 cassava production was cassava intercropped with sweet potato at 20,000 plants ha^-1 (CS200) combined with S-metolachor+atrazine at 1.16+1.48 kg ai ha^-1 followed by one hoe weeding at 8 WAP (PHW1) and is therefore recommended in cassava-sweet potato based intercrop for effective weed control, optimum yield and a good return on investment.