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 h(-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.