Onion production in the Vidalia production region of southeastern Georgia has traditionally used transplants to produce dry bulb onions. Transplants are grown on-farm in high-density plantings, which are then pulled and transplanted to their final spacing (Boyhan et al., 2001a). All of this relies on hand labor, which adds to the cost of production. Current University of Georgia Cooperative Extension Service fertilizer recommendations for onions includes 130 lb/acre N for transplant production and an additional 150 lb/acre N for dry bulb production (Boyhan et al., 2001a). The total N requirement of 280 lb/acre is the highest for any vegetable in Georgia, which might be reduced with direct-seeded onions (Kissel, 2003). Furthermore, the Texas Agricultural Extension Service recommends 120 lb/acre N to produce direct-seeded onions, which further supports the possibility of reducing fertilizer requirements (Hall et al., 2000).
A variety of studies have been conducted to evaluate direct seeding, transplanting, and using sets to produce onions. Comparisons of direct-seeded, bare root transplants and 228-cell flat production has been conducted where plants from cell flats with one plant per cell produced the greatest percentage of jumbo onions (≥3 inches diameter) compared with bare root plants or cell flats with three plants per cell (Leskovar et al., 2004).
Sowing date has been shown to affect yield with transplanted onions. Onions sown on 10 Aug. had greater yield with ‘Agrifound Dark Red’ in Junagadh, India, compared with 25 Aug. or 9 Sept. sowing dates (Movalia et al., 1999). In a study in Egypt evaluating direct-seeded onions, it was found that those sown on 20 Sept. had higher yields compared with those sown on 23 Aug. or 18 Oct. (Gamie et al., 1996). Transplanted onions were found to have greater yields and increased bulb size compared with direct seeding in a study in India among different varieties (Khokhar et al., 1990). In a comprehensive study of onion varieties and sowing dates in New Mexico from 9 to 30 Sept., it was found that delayed sowing resulted in less bolting, greater yield, and delayed maturity (Cramer, 2003). Bolting resistance in ‘NuMex Mesa’ played a greater role than sowing date on having lower numbers of seedstems regardless of sowing date.
Transplant age and days after transplanting have been investigated for their effect on yield. In Nasik, Maharashtra, India, ‘Agrifound Light Red’ was found to have the greatest yield from 8-week-old transplants harvested 125 d after transplanting compared with 7- or 9-week-old transplants and harvest dates of 110 and 140 d after transplanting (Bhonde et al., 2001).
Fertilizers and sowing date have been evaluated with variety Al-Hassawi in Saudi Arabia (Al-Abdulsalam and Hamaiel, 2004). It was found that a 20 Oct. sowing date with fertilizer formulation 14N–16.6P–8.3K gave the best yields compared with 20 Sept. or 20 Nov. sowing dates and fertilizers 20N–8.7P–16.6K, 19N–12.7P–9.1K, or 16N–3.9P–21.6K. Brewster (1990) found in the United Kingdom that earlier sowing, greater plant density, and various fertilizer rates accelerated bulb development across locations and years. This was attributed to larger leaf area index and accumulation of thermal time (degree days).
Texas is the closest region to southeastern Georgia in terms of environment for onion production. However, Texas has several regions of production, including the Lower Valley on the Mexican border, the Winter Garden northwest of the Lower Valley, the Trans-Pecos in western Texas, and the High Plains in northern Texas (Hall et al., 2000). Their recommendations for sowing dates extend from October to March, with short-day, intermediate-day, and long-day onion varieties, depending on the region.
The studies cited above indicate that geographic location is important in determining the optimum sowing date with different varieties evaluated at each location. In addition, fertilizer interaction with sowing date is an important factor in onion development.
Because of the relative higher cost of transplant production, primarily because of greater labor requirements, compared with direct seeding, coupled with the potential lack of labor, this study was undertaken to evaluate effects of sowing date, variety, and fertility on direct seeding short-day onions in southeastern Georgia with the aim that this might lower overall production costs.
Al-Abdulsalam, M.A. & Hamaiel, A.F. 2004 Effect of planting dates and compound fertilizers on growth, yield and quality of Hassawi onion under Al-Hassa oasis conditions Scientific J. King Faisal Univ. (Basic Appl. Sci.). 5 65 79
Bhonde, S.R., Chougule, A.B. & Singh, N.B. 2001 Studies on the effect of age of seedlings and date of harvesting on yield and quality of onion during late kharif season Nwsl. Natl. Hort. Res. Dev. Foundation 21 27 30
Boyhan, G.E., Purvis, A.C., Randle, W.M., Torrance, R.L., Cook, M.J.I., Hardison, G., Blackley, R.H., Paradice, H., Hill, C.R. & Paulk, J.T. 2005 Harvest and postharvest quality of short-day onions in variety trials in Georgia, 2000–03 HortTechnology 15 694 706
Boyhan, G.E., Torrance, R.L., Curry, D.E. & Hill, C.R. 2001b Preliminary results of direct-seeded Vidalia onions Univ. Georgia Coop. Res. Ext. Publ. No. 3-2001:12–13
Brewster, J.L. 1990 The influence of cultural and environmental factors on the time of maturity of bulb onion crops Acta Hort. 267 289 296
Gamie, A.A., El-Rhim, G.H.A., Imam, M.K. & Abdoh, A.E. 1996 Effect of sowing dates on yield and bulb quality of some onion cultivars grown by direct seeding Assiut J. Agr. Sci. 27 101 110
Khokhar, K.M., Kaska, N., Hussain, S.I., Qureshi, K.M. & Mahmood, T. 1990 Effect of different sowing dates, direct seeding and transplanting of seedling on maturation, bulb weight and yield in onion (Allium cepa) cultivars Indian J. Agr. Sci. 60 668 671
Leskovar, D.I., Cantamutto, M., Marinangelli, P. & Gaido, E. 2004 Effects of direct-seeded, bareroot, and various tray seedling densities on the growth dynamics and yield of long-day onion Agronomie 24 35 40
Movalia, A.G., Kaneria, B.B., Khanpara, V.D., Jadav, K.V. & Mathukia, R.K. 1999 Response of direct seeded and transplanted onion (Allium cepa L.) to dates of sowing and nitrogen levels Gujarat Agr. Univ. Res. J. 25 90 93
U.S. Department of Agriculture 1995 United States standards for grades of Bermuda-Granex-Grano type onions U.S. Dept. of Agriculture Washington, DC