Effects of Different Forms of Selenium Fertilizers on Se Accumulation, Distribution, and Residual Effect in Winter Wheat–Summer Maize Rotation System

Foliar Se fertilizers were applied to investigate the effects of Se forms on Se accumulation and distribution in the wheat-maize rotation system and residual concentration of Se in subsequent crops. Sodium selenite, sodium selenate, selenomethionine, chemical nano-Se, humic acid + sodium selenite, and compound fertilizer + sodium selenite were applied once at the flowering stage of wheat (30 g ha⁻¹) and at the bell stage of maize (60 g ha⁻¹). Compared with the control treatment, foliar Se applications significant increased the grain Se concentration of wheat and maize by 0.02-0.31 and 0.07-1.09 mg kg⁻¹, respectively. Wheat and maize grain Se recoveries were 3.0-10.4 and 4.1-18.5%, respectively. However, Se concentrations in the grain of subsequent wheat and maize significantly decreased by 77.9 and 91.2%, respectively. The change of Se concentration in soil was a dynamic process with Se depletion after harvest of maize.