PLANT SELENIUM FROM SOIL AND THE ATMOSPHERE

Transfer of selenium (Se) to pasture is important for prevention of Se deficiency in livestock, yet little is known about the relative impor tance of inputs to pasture from soil and the atmosphere. An isotope di lution method was used to assess quantitatively the importance of thes e inputs to ryegrass. Soil was labelled with Se-75 and subjected to tw o field treatments that were untreated (pH 6.0) and limed (pH 7.0). Af ter an initial period of equilibration, the specific activity of Se as sociated with unwashed leaves became lower than that of soil. This ind icated that atmospheric Se had been deposited onto and possibly incorp orated into the ryegrass. The percent contribution of (75) in pasture leaves derived from the soil was 47% (pH 6.0) and 70% (pH 7.0), with, by inference, the remainder coming from the atmosphere.