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SELENIUM IN SELENIFEROUS ENVIRONMENTS 25 Hamilton and Beath (1964) grew vegetable plants in soil-pots contain- ing either 3 mg Se/kg as selenate or 20 mg Se/kg as finely ground powder of the Se accumulating plants, Astragalus bisulcatus or A. preussii. Vege- table plants grew satisfactorily and most accumulated higher concentrations of Se from the organic Se source, probably because a greater amount of Bio- available Se was produced by the larger application. The absorbed Se was stored in soluble organic and inorganic forms. selenate, but not selenite, was detected in these test plants. selenite, selenate, and organic Se at several rates were included in another study (Hamilton & Beath, 1963) of Se uptake involving rangeland fortis and grasses. Selenium from the selenate form was generally absorbed more effi- ciently than that from the selenite form. Selenium from the seleniferous plant source was absorbed least efficiently. However, plants identified in Groups 1 and 2 (see above) absorbed comparatively large amounts of organic Se from the soil. Plant uptake of selenate-Se occurs at higher rates than that of the selenite- Se. Peterson et al. (1981) suggested that selenate may be taken up actively by plants, whereas selenite may be absorbed passively and in lesser concen- trations. Nevertheless, it is the selenate source that is subject to competition from S04- and other anions. Plant Response to Low Bioavailable Selenium Of plants growing on moderately low-Se soil, alfalfa accumulates more Se than does red clover, timothy (Phleum pratense L.) or brome grass (Bro- mus inermis Leyss.) (Massey & Martin, 1975). Differences in Se uptake may occur, because some plants like alfalfa are deeply rooted and may access more Bioavailable Se in the deeper, more alkaline subsoil horizons. No definite differences in Se accumulations have been noted among species growing on very low levels of available Se. Crops growing on neutral or acid soil absorb very little Se, and any attempt to increase crop Se uptake by shifting to some other species has been viewed with some skepticism (Ehlig et al., 1968). However, small but sig- nificant differences have been noted among selection of tall fescue growing on soil having moderately low levels of available soil Se (preliminary work by D. Sleper and H.F. Mayland, 1987). Therefore, some opportunity may exist to breed forage grasses that would take up greater concentrations of Se and could be planted in areas now considered to be Se-deficient for animals. Davies and Watkinson (1966) reported that a marked difference in Se concentration between species was apparent under New Zealand conditions of low-Se soil. The Se concentration was greatest in a native grass (Agrostis tenuis Sibth.) and least in white clover (Trifolium repens L.), reflecting pos- sible genetic control of Se absorption and transport to the plant tops. The Se values for orchardgrass (Dactylis glomerta L.) and ryegrass (Lolium perenne L.) fell between these extremes.