Abstract
This study 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 bulb of three onion cultivars grown in spring season. Results showed that supplementary irrigated onions resulted in significant increases bulb fresh weight, bulb size, bulb bulk density, number of storage leaves per bulb, plant dry weight and yield of dry onion bulbs, as compared to these of rainfalls onions. Production of dry onions on bare soil under rainfall incidences in mosul are possible in fall season. Polyethylene mulching substantially improved growth and yield of onions, as compared to un-mulched treatment, particularly these grown under rainfalls. Therefore the ability of producing dry yield of onions under rainfalls was confirmed. Clear polyethylene mulching appeared to be the most effective treatments. It displayed significant increases in area per plant, leaf area index, individual bulb size, single bulb fresh weight, bulb bulk density, and dry yield of onion bulbs. Moreover, it significantly lessen the water requirements and weed eradication labor cost. However, it increased onions bolting. Local Red was the paramount cultivar. It showed the highest responses to supplemental irrigation, rainfalls and polyethylene mulching, as it showed the highest values in bulb size, bulb fresh weight, , and yield of dry onion bulbs. Furthermore, it resulted in the lowest stalk numbers per plant, and dry weights of flowering stalks. On the other hand local white cultivar displayed controversial results. Bashiqi cultivar manifested moderate responses as it occupied the gap spared between Local Red and Bashiqi cultivars. Finally, the highest yield (3.59 kg.m‾²) and yield quality of dry onion bulbs was concomitant to supplementary irrigated Local Red onion cultivar grown on clear polyethylene mulched soil.
