Potential Availability of Fertilized Selenium Species in Field Capacity and Submerged Soils as Measured by An Isotopic Dilution Technique.

A laboratory study was conducted to investigate the potential availability and partitioning of selenium (Se) in three soils kept under different moisture regimes, when added as elemental Se (Se (0)), sodium selenite (SeO₃^-2(IV)) and sodium selenate (SeO₄^-2 (VI)). The aim of the research was to understand the behaviour of fertilized Se in submerged rice soils to increase phyto-availability and thereby improve the nutritional benefits of rice to human and animals. The treated soils were kept at either submerged or 80% of their water holding capacity (aerobic) for 15 and 60 days. The changes in partitioning coefficient (K_d) and potential availability for plant uptake,  measured using isotopic dilution (E value), were determined using either ⁷⁵SeO₃^-2 or ⁷⁵SeO₄^-2. Both K_d and E values were controlled by the type of Se fertilizer, soil moisture content and time after application.  The potential availability of Se was found to increase with time in aerobic soils amended with SeO₄^-2 and Se (0). In contrast, E values decreased when SeO₃^-2 was added to aerobic soils and all Se treatments in submerged soils. , Elemental Se is therefore likely to be unsuitable as a fertiliser to improve the nutritional benefit of Se for lowland rice as it will fail to provide adequate concentrations of potentially available Se for rice uptake, whereas SeO₃^-2 and SeO₄^-2 fertilizers are likely to be more suitable for this crop. However Se availability was low for both SeO₃^-2 and SeO₄^-2 fertilizers in submerged soils. Therefore, more research is currently being undertaken to find best application methods and time of application in order to increase Se content in rice grains for improved human and animal health.