Onion yield and bulb conservation as affected by rates and splitting of side-dressed nitrogen

Yield and conservation of onion bulbs are influenced by nitrogen (N) availability in the soil, which is required in large amounts. This study aimed to evaluate the effect of N application rates and splitting on the plant nutritional status, yield and conservation of onion bulbs after harvest. Three field experiments were carried out in Southern Brazilian Haplumbrepts. Treatments consisted of a factorial combination (4 x 3) involving four N rates (0, 50, 100, and 200 kg ha-1) and three times of sidedressing (only 45, 45 and 75, and 30, 60 and 90 days after transplanting). Of each rate, 25 % were applied at planting and the remaining was sidedressed all at once or equally divided in two or three times. Seedlings were always transplanted in the second half of July and the harvest occurred approximately 115 days later. Bulb yield increased quadratically with increasing N rates. The best economic yield varied from 249 kg ha-1 in 2006/07, in sandy soil, to 116 and 142 kg ha-1 respectively in 2008/09 and 2009/10, in clayey soils. Maximum bulb yields were 38, 46 and 30 t ha-1 respectively in 2006/07, 2008/09 and 2009/10, and N levels corresponding to the best economic yield led to increases of 42, 10 and 17 %, respectively, compared to the treatment with no N. Splitting N rates had no effect on yield and bulb quality, regardless of the year. In sandy soils with low organic matter content, higher N rates are required to achieve high onion yields than in clayey soils with medium organic matter content. In rainy years, N applications may have negative effects on bulb conservation.

Allium cepa L.; nitrogen fertilization; bulb quality