Selenium concentration in spring wheat and leaching water as influenced by application times of selenium and nitrogen

Selenium (Se) deficiency in Scandinavian soils is a common problem, and crops generally contain inadequate amounts to meet human need. This study shows a relationship of the Se concentration in spring wheat (Triticum aestivum L., c.v. 'Helena') and leaching water with timing of nitrogen (N) [as ammonium nitrate (NH4NO3)] and Se [as sodium selenate (Na2SeO4)] application. Ammonium-nitrate was applied by two methods (i) whole amount at sowing and (ii) in split application as 75% at sowing and 25% at stem elongation. Selenate was applied at cereal growth stages after sowing, e.g., tillering, stem elongation, head emergence, and milking. Split N application in comparison to one N application increased the grain protein content from 12.1 to 13.7 mg g(-1), and grain Se was increased from 0.8 to 1.1 mg kg(-1) when Se was applied at stem elongation and from 0.6 to 0.9 mg kg(-1) when applied at heading. The highest Se concentration in plant was achieved with the split N application and Se application at stem elongation or heading. Selenium leaching losses increased with increasing selenium concentration in the wheat grains. No differences in Se leaching losses were obtained with split N application. Applying selenate and ammonium-nitrate together after tillering increased the grain Se concentration, but did not affect the potential leaching of Se, and thus could be considered as an appropriate time of application of these elements.