Foliar Selenium Application Promotes Arsenic Reduction and Selenium Enrichment in Highland Barley

Foliar selenium (Se) application can mitigate arsenic (As) toxicity and enhance Se accumulation in highland barley; however, the optimal dose, Se type, and application stage remain unclear. Field surveys across the Tibetan Plateau have revealed a widespread Se deficiency in grains. Therefore, pot experiments were conducted using sodium selenite and nanoselenium at three concentrations (12, 24, and 48 mg/L) under three As levels (20, 40, and 60 mg/kg), applied at the booting, filling, and booting + filling stages. The results showed that sodium selenite reduced grain As by 2.1–54.2% and increased grain Se by 197.1–2352.4 times, outperforming nanoselenium. Application of 24 mg/L Se at the filling stage achieved the greatest reduction in the amount of grain As. Tissue Se accumulation increased with the application dosage, particularly at the filling stage. Moreover, foliar Se application inhibited As translocation while promoting Se translocation. These findings support foliar Se application as a practical strategy to reduce As accumulation and alleviate Se deficiency in crops.