AbstractTwo field experiments were conducted at the Isabela and Juana Díaz Research Centers in 1982-83 to determine the effect of pigweed (Amaranthus dubius Mart.) density on yield of sweetpotato [Ipomoea batatas (L.) Lam]. Pigweed densities of 0, 4, 7, 13 and 27 plants/m2 were adjusted by hand at Isabela and those of 0, 11, 23, 45 and 91 plants/m2 were maintained at Juana Díaz. Pigweed population averaged 27 plants/m2 at Isabela and 91 plants/m2 at Juana Díaz under natural infestation. Sweetpotato yield was reduced significantly from 4 plants/m2 at Isabela and from 11 plants/m2 at Juana Díaz. The highest sweetpotato yield was obtained on weed-free plots with 11,823 kg/ha at Isabela and 27,724 kg/ha at Juana Díaz. The greatest yield reduction (91%) resulting from pigweed competition (at Juana Díaz) was at a density of 91 plants/m2. At Isabela, a density of 13 plants/m2 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/m2 at Isabela. At Juana Díaz, dry weight of pigweed was significantly higher at a population density of 11 plants/m2. The regression between sweetpotato yield and the different population densities of pigweed showed an inverse linear relationship at both localities.
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