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

Because of increasing concern about the use of chemical growth retardants i n crop production, alternative approaches are required. An environmental fr iendly alternative to the use of maleic hydrazide for preventing sprouting in bulb onions is to prolong the natural dormancy by altering the pre-harve st growing conditions. Onions were grown at various N supplies or subjected to drought stress conditions just prior to harvest. After harvest the bulb s were stored at 1 degreesC until April, May or June the following year. Du ring a 40 d shelf-life period at 15 degreesC or 25 degreesC the rate of spr outing 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 influ ence the harvest date or the yield. In contrast, drought stress during the final growth forced the onions to mature earlier. Drought stress reduced th e yield and increased the dry-matter percentage of the bulbs. Onion bulbs c old stored until April started to sprout after 20 d at 15 degreesC shelf li fe. 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 be en grown at low N supply or harvested in dry soil. Compared with the 15 deg reesC shelf-life condition, the rate of sprouting at 25 degreesC was higher at the beginning, but lower at the end of, the shelf-life period.