Abstract
This experiment was carried out at horticultural research fields, Mosul University, Mosul, Iraq, during 2004-2005 growing season to investigate the influences of polyethylene mulching, supplementary irrigation and rainfall incidences on the production of dry bulbs of three onion cultivars grown in spring seasons. Results showed that supplementary irrigated onions resulted in significant increases, bulb fresh weight, bulb size, bulb bulk density, number of storage leaves per bulb, leaf water potential and yield of dry onion bulbs, as compared to these of rainfalls onions. However, inadequate rainfalls tended to reveal significant increases in percentage of unbolted plants and bulbing ratio. Production of dry onion bulbs on bare soil under rainfall incidences in Mosul are impossible in spring season. Polyethylene mulching substantially improved growth and yield of onions, particularly these grown under rainfalls. They confirmed the ability of producing dry yield of onions under rainfalls in spring season. Clear polyethylene mulching appeared to be the most effective treatment, as it displayed significant increases in bulb size, single bulb fresh weight, plant height, leaf numbers per plant, leaf area index, bulbing ratio, dry matter percentage of storage leaf, plant dry weight, leaf area per plant and dry yield of onion bulbs. Moreover, it significantly lessen the water requirements and weed eradication labor cost. Local Red was the paramount cultivar. It showed the highest responses to supplemental irrigation, rainfalls and polyethylene mulching, Since it gave the highest, bulb fresh weight, percentage of unbolted plants and the yield of dry onions. Furthermore, it resulted in the lowest stalk numbers per plant, leaf water potential, fresh and dry weights of flowering stalks. On the other hand Local White cultivar displayed controversial results. The highest yield (1.07 kg‾¹) was confined to supplementary irrigated Local Red cultivar grown on clear polyethylene mulched soil.
