Effects of plant density and cultivar on yield responses in onions (Allium cepa L.) grown from seeds

Two field experiments were conducted to study the effect of plant density on yield, size grading and maturity of onion bulbs grown from seeds. In the first experiment carried out during 1991-1993, three onion cultivars (Hysam F1 , Mercato F1 and Sochaczewska) were sown for intended densities of 20, 40, 60, 80,100 and 140 plants m-2, whereas in the second one, in 1996, six onion cultivars (Spirit F1, Summit F1, Hyduro F1, Armstrong F1, Renate F1 and Robusta) were sown for intended densities of 40, 60 and 80 plants m-2. The onions were grown on beds, 1,35 m wide, in 4 rows per bed (27+27+27+54 cm). Marketable yield increased with plant density, and depending on year was highest at 80 or 100 plants m-2. The average marketable yield of the 1991-1993 experiment increased from 20.5 t·ha-1 at 20 plants m-2 to 32.8 t·ha-1 at 80 plants m-2, whereas that of the 1996 experiment increased from 48,9 t-ha-1 at 40 plants m-2 to 59.0 t·ha-1 at 80 plants m-2, respectively. Yield of large bulbs decreased with density and was highest at 20-40 plants m-2, oposite to the yield of small bulbs, which was highest at the highest density of 140 plants·m-2. The medium bulb yield increased with density, at the some way as compared the total marketable yield. No greater effect of cultivar on bulb size grades was found and the existing differences were proportional to the total marketable yield . Plant density hastened maturity of onions, and at density of 140 plants m-2 the leaf fall-over occurred 9-10 days earlier as compared at density of 20 plants m-2. The cultiwars used. can be placed in the following order of decreasing productivity: 1 . Mercato F1, 2. Hysam F1 and 3. Sochaczewska, - in the first expeiiment (1991-93) and 1. Annstrong F1, 2. Spirit F1, 3. Robusta, 4. Renate F1, 5. Hyduro F1 and 6. Summit F1 - in the second experiment (1996), respectively.