Effect of planting date, nitrogen rate and in-row plant spacing on the maturity, disease infection severity, pungency, bolting and double incidence, and yield of select short-day onions

Vita.An experiment to evaluate the effect of planting date, in-row plant spacing and N rate on quality and yield factors of short-day onion cultivars was conducted in Rio Grande City, TX during the 1993-1994 onion season. Nitrogen rates of 175, 197 and 219 kgha-1 kgha-1 combined with 5, 1 0 and 15 cm between plants and 3 planting dates (September 22, 1993, October 12, 1993 and October 25, 1995) were the treatments used in this experiment. Early season plantings of 'TG1015Y', 'TEW' and 'Y33' onions in late-September required more days to reach their physiological maturity. While the two October plantings of 'TG1015Y' and 'Y33" onions required less days to reach maturity, as the temperatures increased and daylengths were longer late in the winter, 'TEW' onions of the October 12 planting required 2 days more than the September 22 planting and 4 days more than the October 25 planting to mature. Foliage disease was found to be influenced markedly by cultivar. Within each cultivar a delay in planting date resulted in more purple blotch. Planting date and cultivar characteristics were the only factors that affected the pyruvic acid content of the onions used in this research. Early season plantings of the 3 short day onions resulted in more pungent onions. According to the data obtained from this research, the planting of October 12 seemed to be the most adequate for any of the 3 short-day onion cultivars tested. This planting grew 'TG1015Y' tops with an average length of 68 cm and these tops were strong enoughtotolerateapurpleblotch disease severitylevelof4. 'TG1015Y' onions in this planting produced less than 20% doubles and 5% bolters, developed 60% mediums and 28% jumbos and had a marketable yield of 25.50 tha-1 when a 10 cm in-row plant spacing was used. 'TEW' grew 70 cm long tops, tolerated a purple blotch disease severity level of 3 or lower, had 4% doubles, 1% bolters, 64% mediums, 3 0% jumbos, and produced a marketable yield of 27.35 tha- 1 if planted using a 10 cm spacing between plants. 'Y33' onions in the mid-October planting grew with 75 cm long tops and tolerated a purple blotch disease severity of 3.8, produced less than 30% doubles and 2% bolters if planted at 5 cm between plants. A plant spacing of 10 cm resulted in almost 20% more doubles and 2% more bolters. 'Y33' onions grown in this planting date with 5 cm between plants produced 70% mediums and 18% jumbos, and a marketable yield of 21.85 tha-1