Source: Soil Science Society of America

Approximately 1 billion people worldwide suffer from a deficiency of selenium, an essential nutrient for liver, heart, thyroid and immune function. Since selenium deficiency is prevalent in Southeast Asia, researchers are studying the best biofortification for lowland rice production.

In a study funded by the Commonwealth Government of Australia, the soil retention of three types of selenium was tested. The research appears in the September-October issue of the Soil Science Society of America Journal.

According to researchers at the University of Adelaide, biofortification of rice with selenium is most easily performed by adding selenium-enriched fertilizers to rice either as a spray or as a fertilizer amendment to the soil. Lowland rice soil is usually flooded, unlike upland rice soil which served as the control variable in the experiment.

Lakmalie Premarathna, University of Adelaide, and the author of the paper, measured the availability of selenium in rice crops when a pre-plant fertilizer was added.

"Elemental selenium is unsuitable as a pre-plant fertilizer for lowland rice as it is not readily oxidized in the soil to soluble forms that crops can absorb," she said. Selenite and selenate were also ruled out because they became poorly available forms of selenium when subjected to flooding.

Adding selenium in foliar sprays is more labor intensive than adding selenium-enriched fertilizers to the soils at planting, but the fate of various forms of fertilizer selenium in flooded (lowland) rice soils is not well understood, according to Premarathna.

However, lowland rice paddies are drained a few weeks before harvesting. She suspects that levels of selenium could potentially return to suitable levels for crop absorption. Research is ongoing at the University of Adelaide to find the best biofortification for lowland rice production systems.