Short-day onion production in southeast Georgia, however, relies on transplant production within the production region. This is done because the currently used irrigation systems (center-pivot or cable tow) are not able to irrigate whole fields sufficiently during the high temperatures of September to insure stand establishment for direct seeded crops. High-density seedling production can be more efficiently irrigated with these systems.

In addition, transplanted onions are believed better protected during cold weather, since they are set 2.5 - 5.1 cm deep; conversely, direct seeded onions are seeded very shallow (0.6 - 1.3 cm). Consequently, meristematic tissue is more exposed and susceptible to cold injury. Finally, transplant onions don’t form seedstems in the spring as readily as direct seeded onions.

The objective of this study was to evaluate current transplant production practices with short-day onions in southeast Georgia. The ultimate goal of this study was to develop soil test recommendations for transplant production in this region.

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 x high phosphorus fertilizer interactions were nonsignificant.