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Effects of Soil Flooding on Selenium Transformations and Accumulation by Rice

Nat. Fertilizer Development Center, TVA, Muscle Shoals, AL 35660

Duane S. Mikkelsen

Dep. of Agronomy and Range Science, Univ. of California, Davis, CA 95616

Akbar Abshahi

Farms of Texas, P.O. Box 1305, Alvin TX, 77512

* Corresponding author.

ABSTRACT

The fate of Se in flooded soil is not well known. This greenhouse study was conducted to determine the fate of Se in flooded soil and to determine the effects of Se on plant growth. Rice plants (Oryza sativa L. cv. M101) were grown in pots containing Panoche loam soil (fine-loamy, mixed, calcareous, thermic Typic Torriorthents) to which 0, 1.5, 3, and 6 mg Se kg^–1 as Na₂SeO₄ was added. Rice was grown in continuously flooded or nonflooded (upland) soil. The flooded treatments were amended with organic matter (OM) at concentrations of 0, 2.5, and 5 g cellulose kg^–1. Soil solution samples were taken weekly from the flooded treatments and analyzed for pH, Eh, EC, and Se concentration and Se oxidation state. Plants were harvested and analyzed for Se at three plant growth stages. Selenate soil solution concentrations were reduced 95% after 6 and 10 wk following flooding for the 5.0 and 0 g OM kg^–1 treatments, respectively. Selenite in solution reached a maximum concentration (340-1920 µg Se[IV] L^–1) 5 to 8 wk after flooding and then decreased to trace levels (<0.5 µg L^–1). Selenium accumulated in all rice plant parts in direct proportion to the added Se. Plants grown in flooded soil with added OM had tissue Se concentrations <20% that of rice grown without added OM or in upland conditions. Selenium phytotoxicity symptoms were observed in plants grown in flooded soil without OM and in the upland soil when Se was added. Tissue Se concentrations associated with a 10% reduction in shoot dry matter were 160 and 81 mg Se kg^–1 for upland and flooded rice (without added OM). No Se-induced yield loss occurred when OM was added to flooded soil. Flooding those soils containing Se[VI] may be an effective way to reduce soluble Se concentrations in soil to nontoxic concentrations.

Received for publication April 19, 1988.