Título en español.

The effect of five different row spacings (90, 60, 45, 38 and 30 cm) and two fertilizer levels (111 and 222 kg/ha) each of N, P2O5 and K2O, on yield, dry bulb weight, and diameter of onion cultivar Texas Grano 502, were evaluated in a San Antón loam (Cumulic Haplustolls), fine-loamy, mixed, isohyperthermic on the sourthern irrigated coastal plain of Puerto Rico, and in a Fraternidad soil (Udic Chromusterts), very fine, montmorillonitic, isohyperthermic in the southwestern part of the island. The fertilizer was side-dressed in one application immediately after planting. Main results were as follows: At Fortuna yields from the 30 cm spacing were statistically superior to those from all other treatments, except those of the 60 cm spacing; the lower fertilizer level produced significantly higher yields than the higher level. At Lajas there were no significant differences among the yields of the various treatments; 90 cm between rows seems to be the most practical planting distance. Some mechanical weeding could be possible at this spacing. There were no significant differences between the two fertilizer levels; thus the lower level could reduce fertilizer costs. There were no differences in either bulb weight or size due to plant density.