Plant Density and Nitrogen Fertilizer Rate on Yield and Nutrient Content of Onion Developed from Greenhouse-grown Transplants

Onions (Allium cepa L.) can be established from seed or transplants. The latter planting material can be dormant or actively growing when transplanted to the field. Onion transplants can be produced in a greenhouse, but additional information is needed regarding the cultural requirements after transplanting. Greenhouse-grown transplants of 'Candy', intermediate-day variety, and 'Texas Grano 1015 Y', short-day variety, were established at densities of ≈34,000, 68,000, or 102,000 plants/ha and 100 (recommended) and 400 kg-ha ' of nitrogen in mid-March of 2006 and 2007. Nitrogen fertilizer rate did not affect yield. Yield of 'Candy' was greater than for 'Texas Grano 1015 Y'. Yield of both cultivars increased as density increased, and yield of 'Texas Grano 1015 Y' was higher in 2006 than in 2007. 'Candy' had higher numbers of large-sized bulbs and 'Texas Grano 1015 Y' more small bulbs. Bulb nutrient content was affected by year with nitrate-N, potassium, sodium, and SO 4 being higher in 2006 and nitrite-N, calcium, magnesium, PO 4 , and soluble solids higher in 2007. 'Candy' had a higher soluble solids (°Brix) content than did 'Texas Grano 1015 Y'. In 2007, precipitation was higher than in 2006. This may have contributed to the year response and it appears that 'Candy' was better able to respond in a more uniform manner to the changed environmental conditions. For plants developed from greenhouse-grown transplants, the recommended rate of fertilizer and the highest plant density are beneficial to improved marketable yield.