Selenium accumulation in wheat (Triticum aestivum L) as affected by coapplication of either selenite or selenate with phosphorus

The objectives of this pot experiment were to study the effects of P fertilizer applied with either selenate or selenite on (1) selenium (Se) uptake and translocation in wheat (Triticum aestivum L) and (2) Se fractions in calcareous soil. The experiment consisted of three factors: (1) amount of phosphorus (P) fertilizer (0, 1 and 2 g kg(-1)); (2) type of Se fertilizer (selenate and selenite); and (3) amount of Se fertilizer (0, 1 and 2 mg kg(-1)). The results indicate that P fertilizer significantly increased wheat biomass. Selenite significantly reduced wheat biomass, whereas the effects of selenate were not significant. In the selenite treatments, P fertilizer significantly reduced soil pH, causing declines in soluble soil Se and exchangeable Se and increases in iron (Fe) oxide-bound Se and organic matter-bound Se. The Se accumulation coefficient, the Se translocation coefficient and the Se content of wheat roots, stems, leaves and spikes all declined when P was applied to selenite-fertilized soil. In the selenate treatments, P application significantly reduced soil exchangeable Se, Fe oxide-bound Se and organic matter-bound Se. The wheat Se content, Se accumulation coefficient and Se translocation coefficient all increased when P fertilizer was applied to selenate-fertilized soil. In conclusion, P fertilizer activated Fe oxide-bound Se and organic matter-bound Se, resulting in an increase in wheat Se concentrations in selenate-fertilized, calcareous soil. In selenite-fertilized soil, however, P fertilizer reduced soil pH, thus promoting the transformation of soluble Se and exchangeable Se to either Fe oxide-bound Se or organic matter-bound Se. These changes inhibited Se absorption and translocation in selenite-fertilized wheat, thus reducing Se uptake by wheat.