Sweet Potato

Two field experiments were conducted at the Isabela and Juana Díaz Research Centers in 1982-83 to determine the effect of pigweed (Amaran thus dubius Mart.) density on yield of sweetpotato [ Ipomoea batatas (I.) Lam], Pigweed densities of 0, 4, 7, 13 and 27 plants/m 3 were adjusted by hand at Isabela and those of 0, 11, 23, 45 and 91 plants/m 2 were main tained at Juana Díaz. Pigweed population averaged 27 plants/m 2 at Isabela and 91 plants/m* at Juana Díaz under natural infestation. Sweet potato yield was reduced significantly from 4 plants/m 2 at Isabela and from 11 plants/m 3 at Juana Díaz. The highest sweetpotato yield was ob tained on weed-free plots with 11,823 kg/ha at Isabela and 27,724 kg/ha ai Juana Díaz. The greatest yield reduction (91%) resulting from pigweed competition (at Juana Díaz) was at a density of 91 plants/m'. At Isabela, a density of 13 plants/m 2 caused the greatest yield reduction (78%). The effect of pigweed on number of root-tubers followed a similar trend as the effect on yield. Dry weight of pigweed per plant was significantly greater at population densities of 4 and 7 plants/m 3 at Isabela. At Juana Díaz, dry weight of pigweed was significantly higher at a population density of 11 plants/m 2 . The regression between sweetpotato yield and the different population densities of pigweed showed an inverse linear relationship at both localities. will overeóme competition from weeds. Weed-crop competition research has been focused on the study of critical periods of competition but indi vidual weed species involved are not indicated (6, 11). The Amaranthaceae family includes the most important weeds in the United States and the Tropics (1, 5). The adverse effects of pigweed density on yield has been studied in different crops (4, 8, 11). For exam ple, at a population of 1 plant per 2.43 m of crop row, pigweed reduced soybean yield by 30% (4). At the same time 32 plants per 2.43 m of crop