Effect of selenium fertiliser formulation and rate of application on selenium concentrations in irrigated and dryland wheat (Triticum aestivum)

Abstract

Field trials were carried out on two wheat (Triticum aestivum) crops (one irrigated, one dryland) in Canterbury, New Zealand during the 2005–06 growing season to evaluate the effectiveness of two selenium (Se) fertilisers in raising grain Se levels. Both contained sodium selenate: “AgSel” is a fast release formulation (100% water‐soluble Se) whereas “Selprill Double” (76% water‐soluble Se) has been formulated to slow the release of Se. The fertilisers were broadcast in spring (Zadoks growth stage 32) at rates of 5 to 20 g Se/ ha. Grain Se increased linearly with application rate, but concentrations were higher with the fully‐soluble formulation. Mean Se concentration was significantly lower in irrigated (grain yield 9.1 t/ha) than dryland (yield 7.4 t/ha) wheat (0.17 versus 0.25 mg Se/kg), possibly owing to yield dilution. For the fully‐soluble Se fertiliser, grain Se increased by 0.018 mg/kg in irrigated wheat for each g/ha of applied Se. an application of 4–5 g/ha would raise grain Se to 0.1 mg/kg (approximate concentration in imported australian wheat), assuming natural levels in Canterbury wheat are c. 0.02 mg/kg. The water‐insoluble component of Selprill Double made little or no contribution to Se uptake when the fertiliser was applied in spring and therefore application rates should be c. 30% higher than those of the fully‐soluble fertiliser.