Sprouting in bulb onions (Allium cepaL.) as influenced by nitrogen and water stress

SummaryBecause of increasing concern about the use of chemical growth retardants in crop production, alternative approaches are required. An environmental friendly alternative to the use of maleic hydrazide for preventing sprouting in bulb onions is to prolong the natural dormancy by altering the pre-harvest growing conditions. Onions were grown at various N supplies or subjected to drought stress conditions just prior to harvest. After harvest the bulbs were stored at 1˚C until April, May or June the following year. During a 40.d shelf-life period at 15˚C or25˚C the rate of sprouting was recorded. In plants grown at low N supply, the harvest date was postponed and the yield reduced. A surplus supply of nitrogen did not influence the harvest date or the yield. In contrast, drought stress during the final growth forced the onions to mature earlier. Drought stress reduced the yield and increased the dry-matter percentage of the bulbs. Onion bulbs cold stored until April started to sprout after 20.dat15˚C shelf life. Bulbs stored until May started to sprout about 10.d after removal from storage. In bulbs stored until June, sprouting was already initiated at the end of cold storage. The onset of sprouting was postponed if plants had been grown at low N supply or harvested in dry soil. Compared with the 158C shelf-life condition, the rate of sprouting at 258C was higher at the beginning, but lower at the end of, the shelf-life period.