Effect of saline irrigation water composition on selenium accumulation by wheat

Abstract

Trace amounts of selenium (Se) are essential for animal and human nutrition. However, the optimum concentration range is very narrow and outside of this range deficiencies or toxicities can occur. Potentially harmful levels of Se in soils and irrigation waters have been reported in regions where salinity is also a hazard. This study was conducted to determine the effects of irrigation water composition and salinity level on Se accumulation in leaves and grain of spring wheat (Triticum aestivum L. cv. ‘Yecora Rojo'). Plants were grown in greenhouse sand cultures and irrigated with complete nutrient solution. Salinity treatments were initiated 4 days after planting by irrigating the seedlings with either chloride‐dominated waters or with waters containing both chloride and sulfate salts. Compositions of the mixed salt waters were designed to simulate saline drainage waters commonly present in the San Joaquin Valley of California. The experimental design was a randomized 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, 0.52, 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 chloride system, the molar ratio of SO₄ ^2‐:SeO₄ ^2‐ was approximately 110 across all salinity levels, whereas in the mixed salt system, the SO₄ ^2‐ SeO₄ ^2‐ratio in solution increased from about 300 to 4,700 as salinity increased. Selenium concentration was determined in fully‐expanded flag leaf blades and grain. Salinity type, and to a lesser extent, salinity affected Se accumulation. In the Cl‐system, wheat accumulated Se to levels that may be potentially harmful to livestock and humans, e.g., blade‐Se ranged from 435 to 295 mg kg⁻¹ dry wt; grain‐Se ranged from 81 to 54 mg kg⁻¹ dry wt. Under the saline conditions of the mixed salt system, the inhibition of selenium uptake by sulfate reduced both blade‐ and grain‐Se to levels that would minimize the health risk to consumers.