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George E. Boyhan, Reid L. Torrance, David E. Curry, Pamela M. Lewis, Donna O. Linton and C. Randy Hill

Preplant levels of 5N-4.4P-12.4K (-5S or -9S) and sidedress applications of CaNO3 were evaluated in onion (Allium cepa L.). In addition, high phosphorus fertilizers 18N-20.1P-0K (diammonium phosphate) and liquid 10N-14.8P-0K were evaluated on sites with and without high residual phosphorus levels as well as their interaction with onion cultivars. Sidedress applications of CaNO3 had a significant effect on plant height and an interaction with preplant 5N-4.4P-12.4K fertilizer. There was a linear increase in plant height with increasing applications of 5N-4.4P-12.4K from 0 to 1569 kg·ha-1 with the CaNO3 applications. Neither 5N-4.4P-12.4K nor CaNO3 applications affected stand count. 5N-4.4P-12.4K fertilizer had significant linear effects on tissue potassium and sulfur. Tissue nitrogen and calcium increased with CaNO3 applications while phosphorus, potassium, and sulfur decreased. CaNO3 also had a positive effect on suitability for transplanting. There was an interaction effect between 5N-4.4P-12.4K and CaNO3 for tissue phosphorus levels. There was a linear decrease in tissue phosphorus levels with increasing amounts of 5N-4.4P-12.4K fertilizer with the sidedress CaNO3 treatments. High phosphorus fertilizers applied directly after seeding had no effect on plant stand or plant height either on soils with or without high residual phosphorus in 1998. In 1999, 10N-14.8P-0K fertilizer had a significant effect on plant height while 18N-20.1P-0K did not. Based on this study, we conclude that additional applications of high phosphorus fertilizers applied post seeding are not required due to the relatively warm conditions found in southeast Georgia in September. There were differences between cultivars, but cultivar× high phosphorus fertilizer interactions were nonsignificant.

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George E. Boyhan, William M. Randle, Albert C. Purvis, Pamela M. Lewis, Donna O. Linton, Reid L. Torrance and David E. Curry

A 3-year study on the effects of growth stimulants on yield, bulb size, bulb quality, and storability of short-day onions (Allium cepa L.) was conducted at three locations. Treatments included 2-hydroxypropanoic acid, humic acids, humic acids in conjunction with micronutrients, and two formulations of cytokinin applied as a transplant dip and/or plant spray. There were no differences between 2-hydroxypropanoic acid and an untreated check at two different farm locations for onion yield, equatorial bulb diameter, or percent jumbos [≥3 inches (≥7.6 cm)] in 1997. Comparisons between untreated checks, 2-hydroxypropanoic acid, humic acids as a transplant dip or plant spray, and humic acids with micronutrients, all applied as transplant dip or plant spray, indicated there were no differences among treatments for yield, pungency, soluble solids, equatorial bulb diameter, or percent marketable bulbs after 6 months in controlled atmosphere storage in 1997-98. In a final experiment, these treatments were evaluated in a factorial arrangement using the short-day onion cultivar Pegasus and a mixture of cultivars WI-609 and WI-3115, which are referred to as Wannamaker cultivar mix. `Pegasus' displayed higher yield and lower soluble solids than the Wannamaker cultivar mix. Treatment with humic acids and micronutrients, or cytokinins resulted in greater percent marketable bulbs after 4.5 months of controlled atmosphere storage compared to the untreated check. No differences were observed among the treatments for pungency or bulb size. In addition, there was no treatment by cultivar interaction.