CS-137 UPTAKE IN SPRING WHEAT (TRITICUM-AESTIVUM L-CV TONIC) AT VARYING K SUPPLY .2. A POTTED SOIL EXPERIMENT

Spring wheat (Triticum aestivum L. cv. Tonic) was grown for 16 days in a sandy loam soil which was contaminated with Cs-137. The soil was fe rtilised with K at three rates (0,1 and 2 mmol K per 950 g dry soil) a nd with NO3--N at two rates (0 and 2 mmol per 950 g dry soil) in a fac torial design. The Cs-137 Activity Concentration (AC) in the shoot tis sue significantly reduced 8.2-fold (nil N treatment, p<0.001) and 9.3- fold (highest N dose, p<0.001) with increasing K supply. In contrast, the K application increased the Cs-137 AC in soil solution 1.7 fold (n il N treatment) or had no significant effect (highest N dose). At simi lar K application, the application of N increased the Cs-137 AC in the shoot compared to the control. This effect is most probably due to th e increased NH4+ concentration in soil 4 solution which increased the Cs-137 AC in soil solution. The soil solution composition (Cs-137 and K concentration) in the rhizosphere was estimated from the average soi l solution composition at day 16 and solute transport calculations. Th e Cs-137 AC in the shoot tissue was predicted from the estimated soil solution composition in the rhizosphere and the relationship between K concentration and Cs-137 uptake derived from a nutrient solution expe riment. The predictions of Cs-137 AC'S in the shoot are qualitatively correct for the fertiliser effects but underestimate the observations between 1.4 and 9.9 fold.