Onion (Allium cepa L.), is an important vegetable crop belonging to the family Alliaceae. It is the most widely grown as a popular crop among the alliums. Onion is considered the second most important vegetable crop grown in the world after tomato. It is popularly referred to as “Queen of Kitchen.” Recently onion is being used by processing industry to a greater extent for preparing foods with vegetables, meat, fish...etc 1.

In the Sudan it ranks the first vegetable with regard to the area grown and quantities produced. It grown in different states in the Sudan (Naher El -Neil, Gezira, Darfur States, Kassala, Northern State and Khartoum) 2. Total area devoted for onion (212.9 thousand feddan) with production of 167.5 thousand tons 3.

Onion is grown by one of three methods: direct sowing, transplanting and sets 4. Sets are small bulbs, typically weighing 2–3 g when fresh, produced by growing a crop from seed sown at very high density of 1000–2000 plants /m². They are < 25 mm in diameter and replanted to develop into larger bulbs. Because of their size, sets make a more robust plant at emergence than seeds, and do not need such meticulous seedbed preparation. It also easier to grow successfully and are widely used by amateur and small-scale growers. Sets also have a shorter growing season than plants from seeds and transplants are used where rapid, early-season production is important 5.

The present study is conducted to find a suitable combination of seed bed, cultivar and seed rate for the production of sets for onion off-season production.

The experiments were carried out during three successive winter seasons (2010/11, 2011/12 and 2012/13), at Shambat Research Station Farm on clay loam soil pH 7.8 (lat. 15° 39’N long. 32° 32’ and 381m above sea level).

The experiments were designed to test the effect of two seed bed (flat vs. 60 cm ridges), three seed rates 4, 8 and 12 g /m^² (40, 80 and 120 kg /ha) on the sets yield and quality of the two onion cultivars, Kamleen Yellow and Baftaim (S) Red. The experimental units were 2*2*3 Factorial in split-split plot design with four replications. The planting methods were assigned to the main plots, onion cultivars in the sub-plots and the seed rates in sub-sub plots. The total net area of each sub-sub plot was 10.44m^² (1.8 m. * 5.8 m.).

Before laying out the experiments, the field was disc ploughed, well leveled and divided to flat and 60 cm ridge plots. The seeds were drilled in rows 20cm apart (9 rows/plot) in flat and 3 rows/ridge on ridged plot.

The experiments were sowing in 6, 11 and 14-15 Januarys, and all agronomic practices (fertilization, irrigation and weeding… etc) were done as recommended in the three seasons.

All the experimental plots were fertilized with nitrogen (43 kg N/ha) in the form of Urea (46%N) in two equal doses.

At harvesting, an area of 1m^² was harvested randomly to evaluate yield as set number and weight and yield/h and quality (percentage of different set size). Harvested sets were cured and graded large (2.9 – 2.0 cm) and medium (1.9 – 1.0 cm) according to the diameter, the yield per hectare was calculated as follow:

Yield (t/ha) = (Yield/m^2*10000)/1000

The data were analyzed using GenStat (Computer Program) Version4 and the means were separated using Duncan Multiple Range Test (DMRT) at P≤0.05 6.

The results reflected that the set yield was significantly affected by cultivars, while there was no affect either due to seed bed or seed rate. These results agreed with 7, who recorded high onion yield of the cultivar Baftaim (S) compared to other onion cultivars. Moreover, the increase in yield on ridge sowing and moderate seed rate could be attributed to suitable plant population with ridge bed and moderate seed rate, which could not be obtained on flat sowing by lower or higher seed rates due to low plant population or higher competition for nutrients at higher seed rates, respectively. Similar results were obtained by 8 who reported that high plant population resulted in competition for nutrients and light thus resulting in short plants, while low plant population provided adequate space for growth and development.

Increasing of seed rate showed significant negative effect on set size, whereas the highest percentage of large set size was obtained by the lowest seed rate. The highest seed rate, however, gave the highest percentage of medium sets size (considered the optimum set size for off-season onion production). Similar results were also obtained by 9,1011 who found that medium set size could be considered suitable for onion off-season production.

The single set weight affected significantly by cultivars and seed rate, this result confirmed with 7 who recorded high onion yield of the cultivar Baftaim (S) compared to other onion varieties and 12 who reported low plant population result in high set weight.

It can be concluded that in order to achieve high yield and quality of onion sets; sowing on ridge (60 cm) and seed rate 12 g/m² (120 kg/ha) irrespective of cultivars for high onion sets yield an quality for off-season production.