Salt Effects on Germination, Emergence, and Seedling Mortality of Onion
Good stands of furrow irrigated onion (Allium cepa L.) are difficult to obtain in saline areas of the Southwest. This study examined salt effects on seed germination, emergence, and seedling mortality of five onion cultivars in a series of greenhouse experiments at diurnal temperatures of 15 to 25 °C. Germination exceeded 80% within 10 d at solution salinity of 20 dS m−1 or less. Cultivar effects on germination appeared initially, but diminished after approximately 1 wk. Seedling emergence from potted and subirrigated loamy sand declined significantly when salinity of irrigation water exceeded 4.9 dS m−1. This decline was apparently caused by hypocotyl mortality when the cotyledon came into contact with the salts accumulated at the soil surface, but not by reduced seed germination. Soluble salts accumulated mostly within the top 5 mm of the soil and the accumulation below 5 mm was minimal. The removal of the salted surface layer improved seedling emergence. Leaching of the surface-accumulated salts into the seedling root zone 3 wk after seeding resulted in seedling mortality of significant magnitude; 12 and 20% in seedlings previously subirrigated with solutions of 2.8 and 4.9 dS m−1, respectively. A significant increase in seedling mortality was also observed when seedlings were sprayed twice after emergence with saline solutions of 28 and 39 dS m−1. The ability of cotyledons and seedlings to tolerate salinity, rather than the ability of seed to germinate in highly saline solutions, may be a limiting factor for obtaining good stands in furrow-irrigated onion in saline areas.
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