Seedling mortality of several crops induced by root, stem or leaf exposure to salts

Summary

Seedling mortality caused by excessive salinity is common in establishing furrow-irrigated crops. This study was conducted to evaluate the processes involved and salinity levels leading to seedling mortality in guayule (Parthenium argentatum Gray cv. 593), carrot (Daucus carota L. cv. Imperator-58), chile pepper (Capsicum annuum L. cv. New Mex. 6–4), and tomato (Lycopersicon esculentum Mills cv. Rutgers). Salt accumulation patterns were also evaluated in soil columns subirrigated with waters of 0.8 and 3.9 dS m⁻¹. Seedlings were first grown for 10 to 16 days in greenhouse pots with water of 0.8 dS m⁻¹. Upon emergence of the first true leaf, seedling roots, leaves and stems were independently exposed to different levels of salinity (0.8 to 59 dS m⁻¹) under two diurnal temperature regimes (22–32°C and 24–40°C). When seedling roots were exposed to the saline solutions, mortality was sub stantially greater under the high temperature, and increased greatly at salinity levels of soil solutions exceeding about 5 dS m⁻¹ in guayule and carrot, and 15 dS m⁻¹ in tomato and pepper. Mortality caused by leaf exposures to saline spray was greater under the low temperature with higher relative air humidities, and increased greatly when salinity levels of spray solutions exceeded ap 5, 10, 15 and 20 dS m⁻¹ in guayule, carrot, tomato and pepper, respectively. Physical abrasion of seedling leaves prior to saline water spraying significantly increased mortality. Stem exposure to a thin layer of salted sand having the saturation extract salinity of up to 58 dS m⁻¹ caused no significant increase in mortality. Soluble salts were accumulated mostly in a soil depth of 0 to 0.5 cm at a rate of 35 dS m⁻¹ in 3 weeks when subirrigated with water of 3.9 dS m⁻¹. Under furrow-irrigated conditions, seedling mortality may be induced mainly through leaf and/or root, but not stem, exposure to the salts accumulated at soil surfaces. Leaf-induced mortality can be the most significant process when wind-damaged seedlings are exposed to saline splatters during light showers common to the semi-arid region.