Effect of saline irrigation water composition on selenium accumulation by wheat

Trace amounts of selenium (Se) are essential for animal and human nutrition . However, the optimum concentration range is very narrow and outside of th is range deficiencies or toxicities can occur. Potentially harmful levels o f Se in soils and irrigation waters have been reported in regions where sal inity is also a hazard. This study was conducted to determine the effects o f irrigation water composition and salinity level on Se accumulation in lea ves and grain of spring wheat (Triticum aestivum L. cv. 'Yecora Rojo'). Pla nts were grown in greenhouse sand cultures and irrigated with complete nutr ient solution. Salinity treatments were initiated 4 days after planting by irrigating the seedlings with either chloride-dominated waters or with wate rs containing both chloride and sulfate salts. Compositions of the mixed sa lt waters were designed to simulate saline drainage waters commonly present in the San Joaquin Valley of California. The experimental design was a ran domized complete block with two salinity types (Cl- or mixed salts), eight salinity levels (osmotic potentials=0.07, 0.16, 0.21, 0.30. 0.36, 0.44, 0.5 2, and 0.63 MPa), and, three replications. Four weeks after planting, Se (1 mg L-1 as sodium selenate) was added to all irrigation. waters. In the chl oride system, the molar ratio of SO42-:SeO42- was approximately 110 across all salinity levels, whereas in the mixed salt system, the SO42-:SeO42- rat io in solution increased from about 300 to 4,700 as salinity increased. Sel enium concentration was determined in fully-expanded flag leaf blades and g rain. Salinity type, and to a lesser extent, salinity affected Se accumulat ion. In the Cl--sysrem, wheat accumulated Se to levels that may be potentia lly harmful to livestock and humans, e.g., blade-Se ranged fi om 435 to 295 mg kg(-1) dry wt; grain-Se ranged from 81 to 54 mg kg(-1) dry wt. Under th e saline conditions of the mixed salt system, the inhibition of selenium up take by sulfate reduced both blade- and grain-Se to levels that would minim ize the health risk to consumers.