Evaluation of Nitrogen Sources and Rates on the Yield and Quality of Sweet Onion

Abstract

During the 1980s, research was conducted mainly for long-day onion, with limited research on cultural practices for short-day cultivars, in Uruguay. Sweet onion production became important in Uruguay in 1992. Research was conducted on cultivar adaptation, sowing time, plant population, transplanting and direct-seeded methods, irrigation, and plant protection. Onion fertilization criteria were established for long-day cultivars in the southern region in the 1980s. National Research Inst. of Agriculture started a study on sweet onion fertilization using four N rates, 0, 60 120, and 180 kg/ha, and four N sources, urea, ammonium nitrate, potassium nitrate, and calcium nitrate. Nitrogen was applied into the soil 40% before transplanting and the remaining 60% in two applications in the spring. Granex 33 cultivar was transplanted on 27 June 1997 into a soil with the following characteristics, pH 6.4, P (Bray 1) 44.5 ppm, organic matter 3.3, and K 0.64 meq/100 g. Beds were separated 1.5 t, with four rows and plants 12 cm apart. Plant height and leaf color were evaluated. Lack of nitrogen and 60 kg N/ha showed lighter green colored leaves. Leaf, total plant, and soil samples were collected to determine nutrient status and dry matter production. Bulbing ratio was measured in 10 plants in each plot. Sweet onion quality was done by pyruvic acid analysis.