Sweet potato is a major root storage crop in Swaziland, whereas maize ( Zea mays L.) is the staple food crop in Swaziland. In this experiment, sweet potato cv. Kenya was grown in the field and intercropped with maize cv. SC 603 with the objective of determining the effects of crop association on soil temperature, weed infestation and crop yields. Five plant population treatments (T) were investigated: T 1, Maize alone at 40,000 plants/ha; T 2, sweetpotato alone at 33,333 plants/ha; T 3, maize at 40,000 plants/ha, intercropped with sweetpotato at 33,333 plants/ha; T 4, maize at 40,000 plants/ha, intercropped with sweet potato at 16,666 plants/ha and T 5, sweet potato alone at 16,666 plants/ha. Soil surface temperatures were generally higher than temperatures at 10 cm depth; nonetheless there were no significant differences in soil temperatures among the cropping systems. The three most dominant weed species in all plots were Bidens pilosa L. (37.5-59.3% relative abundance), followed by Cynodon dactylon L. (15.7-43.6%) and Oxalis latifolia (7.1-18.7%). Sida rhombifolia (0-0.4%); Schkuhria pinnata (0-0.4%) and Leucas martinicensis (0-0.4%) were the three least abundant weed species. Land equivalent ratio (LER) values indicated that Sweet potato-maize mixture at the recommended sole sweet potato population (33,333 plants per hectare) was a better cropping system (LER, 0.77) than intercropping at 50% of the recommended Sweet potato (LER, 0.74). Correlation data showed that maize cob yield was not significantly correlated to the 100-grain mass (r=0.508; R 2=0.2581; N, 12); the resultant correlation of determination showed that 25.8% in the variation in cob yield could be ascribed to 100-grain mass. In sweet potato, correlation data showed that the number of tubers per plant was positively correlated to tuber yield ha -1 (r=0.676; R 2=0.4570; N, 16); from the co-efficient of determination, 45.7% of tuber yield could be associated with the number of tubers per plant. In conclusion, sweet potato monocropping was the best system; nonetheless, if it has to be intercropped with maize, there should be 33,333 and 40,000 plants ha -1 of sweet potato and maize, respectively.
