Uptake competition between selenium and sulphur fertilizers in sequential harvests of ryegrass: A stable isotope study

Recently, the demand for sulphur (S) fertilizers has increased due to declining S emissions from coal burning and subsequent deposition on agricultural land (Webb et al. 2016). However, application of sulphate promotes competition between selenate and sulphate for crop uptake, as both share the same transporters in plant roots (Terry et al. 2000). In our experiment, enriched selenium (Se) isotopes ⁷⁴Se^VI and ⁷⁷Se^IV were used to trace the fate of Se in (1) sequential rye-grass harvests, (2) the soil pore water, and (3) soil sorbed Se fractions. Treatments tested included a series of slow- and fast-release S fertilizers (i.e. polyhalite).