17 



Barley, buckwheat, and cowpeas grown on an Evesboro sand gave a cesium/ 

 potassium DF of 0. 02, based on the amount of radioactive cesium added to the soil 

 and the acid-soluble potassium (66). The range was from 0. 06 to 0. 77 for wild 

 plants and corn grown in a radioactive disposal area (6). Upland rice, wheat, and 

 beans grown on a Japanese soil gave much lower DF values — 0. 002 to 0. 003 (41). 

 Discrimination factors of 0. 02 for barium/calcium and 0.4 for rubidium/potassium 

 were also found for the barley, buckwheat, and cowpeas grown on the Evesboro 

 sand (66). 



Discrimination in plant uptake of strontium and calcium is usually slight in 

 pot experiments, except for roots, but apparent discrimination against either stron- 

 tium or calcium can occur in the field. The strontium- 90 is normally concentrated 

 near the soil surface, or in the plow layer, the distribution of exchangeable calcium 

 in the profile usually is nonuniform, and the root zone varies with the plant species 

 and with soil conditions. 



D. Effects of Clays and Anions 



Twice as much strontium is taken up from illite clay suspension as from 

 bentonite clay (63), which indicates that bentonite holds strontium more strongly than 

 illite. Clays have more of an effect than just as an anion, for the aluminum concen- 

 tration affected calcium uptake from calcium sulfate but not from calcium clay (64). 



Anions have differential effects on various species. In tobacco, calcium uptake 

 is nearly the same from the carbonate, sulfate, or phosphate salt, but alfalfa seems 

 to prefer carbonate to sulfate or phosphate as a calcium source (102). Strontium up- 

 take by bean plants in one soil was reduced 40 per cent by calcium carbonate but only 

 15 per cent by calcium sulfate (105). Bicarbonate in nutrient solutions (32) reduced 

 strontium uptake by 70 per cent, rubidium by 43 per cent, ruthenium by 24 per cent, 

 and cerium by 19 per cent. Cesium was the only ion studied in which the uptake was 

 not adversely affected. Thus, the reduced strontium uptake from alkaline calcareous 

 soils may be due to a bicarbonate ion effect as well as to a calcium effect. 



Strontium added to soils as the sulfate, oxalate, hydroxide, fluoride, carbonate, 

 or phosphate was one tenth as available to plants as strontium added as the chloride 

 or nitrate (132). Also, calcium sulfate and calcium carbonate were more effective 

 than calcium chloride in reducing strontium uptake. This indicates an effect of solu- 

 bility, since all unavailable strontium salts are of low solubility. Massive doses of 

 phosphate have reduced strontium uptake 50 per cent on alkaline soils but have given 

 no reduction on acid soils (132). Other studies (14, 53) report conflicting results 

 from the addition of phosphate. Hydroxyapatite and fluoroapatite are insoluble calcium 

 phosphates that exist under alkaline conditions. The strontium analogs of these 

 compounds are expected to be similarly insoluble (26). 



