Selenium enrichment, partitioning and leachability along semi-arid soils of NE Punjab, India

Selenium (Se) bioavailability is largely governed by its fractionation in soil constituents which is yet an unaddressed issue of severely seleniferous agricultural soils of NE Punjab, India. Five selective soils with Se content up to 6.2 mg kg −1 were examined to understand Se partitioning in different soil constituents and fraction of exchangeable soil Se. Its mobilization behavior under oxygenated and anaerobic conditions was also examined and role of NO 3 − and PO 4 3− on it. Soil from Barwa, Nawanshahr with C T of 1.3% is found to be enriched in Se, Zn, Cr, Mn, Cu, Cr, Co, U and Th, while Ramgarh soil, Hoshiarpur with C T of 1.0% is least contaminated. Selenium leaching is favored under anoxic condition with rapid initial release, while no leaching has occurred in oxygenated condition. The presence of competitive anions, i.e., NO 3 − or PO 4 3− , has facilitated slight greater Se leaching after 9 days, whereas leaching decreased continuously in normal milli-Q water reactors. Generation of CH 4 is insignificant, whereas CO 2 production increased with time in anoxic medium. Easy bioavailability of Se around the agricultural field is inferred from the extractability of soil Se through ligand exchange, phosphate exchange and water extraction. The hard bound soil Se, i.e., crystalline phase, organic matter and iron–manganese oxide-bound fractions are nil that further supports its easy bioavailability.