Vol. 69 No: 6

Title:
Effects of Source, Rate, and Frequency of N Application on Yield, Marketable Grades and Rot Incidence of Sweet Onion (Allium Cepa L. cv. Granex-33)

Authors:
K.M. BATAL, K. BONDARI, D.M. GRANBERRY and B.G. MULLINIX

pp: 1043-1052

Abstract:
In a field experiment in the 1988–89 season, fertilizer formulations of NH₄NO₃, Ca(NO₃)₂, NaNO₃, NaKNO₃, and KNO₃ as N sources were applied at 84 and 168 kg N ha^-1 to onion plots direct seeded in the fall. A second experiment in the 1990–91 season tested the same N sources, except KNO₃, at rates of 168 and 224 kg ha^-1. Application strategy involved both splitting the total amount of fertilizer over two periods of the growing season (October-December and January-April) and the application frequency. With medium and high application rates (168 and 224 kg ha^-1), NH₄NO₃, NaNO₃, and NaKNO₃ increased high-value jumbo and large onions (premium marketable grade). Increased premium grades was due to increased bulb size and weight. Only NH₄NO₃ and Ca (NO₃)₂ increased total onion weight when N rate was increased from 84 to 168 kg ha^-1. Less frequent applications of split amounts of 84 kg N ha^-1 reduced marketable weight in the 1988–89 season, but doubling the rate to 168 kg ha^-1 restored the higher yields. At 224 kg N ha^-1 in the 1990–91 season, differences in onion grades were more pronounced among the different N sources, and NH₄ NO₃ was superior in producing jumbo and large size onions. High N rates (224 kg ha^-1) and more frequent applications of split portions also increased the weight of jumbo onions. Split applications, providing 33% of the total N in the first 12 weeks of the growth period plus three applications of 22% each in the second 12 week period, increased bulb size and maximized yield of premium marketable grades. Effect of N rate on onion rot was dependent on split methods of applying the N during early and late growth periods. However, reduction in onion rot by the split application strategy was dependent on N source. Bulb decay was highest with NH₄NO₃ and least with Ca(NO₃)₂ and NaNO₃.

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