The uptake of calcium and strontium by plants from some Australian soils

Abstract

Calcium and strontium in eastern Australian soils and their uptake by plants have been examined in pot culture and under field conditions. The ratio of calcium to strontium in the plant material was closely related to the ratio of exchangeable calcium to exchangeable strontium in the soil, although the plants always contained a higher proportion of calcium. This was probably due to the difference in the adsorption of calcium and strontium by the soil colloids, and to small differences in the relative movement of calcium and strontium from the roots to the plant tops. The proportion of calcium to strontium in the plant material was similar to that in a water extract of the soil; this suggests that the two ions are taken up through the soil solution without any marked discrimination between them. While the proportion of calcium to strontium in the plant roots of oats and cocksfoot was generally similar to that in the plant tops, the roots of subterranean clover and Erodium botrys contained an appreciably higher proportion of strontium. However, since less than 20% of the total calcium and strontium uptake by these two species remained in the roots the effect of this on the proportions in the plant tops was small. Decreases in exchangeable calcium and strontium in soils following the growth of subterranean clover plants in pots were sufficient to account for almost 80 % of their total uptake by the plants. The amounts of calcium and strontium taken up by the clover in pots were related to the amounts of the exchangeable ions in the soil but the smaller uptake of calcium by oats was more closely related to the water-soluble calcium. When soluble calcium and strontium were added to soils in pot culture the ratio Ca/Sr (plant tops) in oats was closely related to the ratio Ca/Sr (exchangeable + added). The addition of calcium carbonate to the surface of three soils in pots markedly increased the ratio of calcium to strontium in the plant tops of subterranean clover in each case. Under field conditions the uptake of calcium and strontium by subterranean clover appeared to be related to the exchangeable forms in the surface 4 in. of soil. With wheat, however, other factors seemed to Influence their uptake including the soil calcium and strontium at depths below 4 in. The accumulation of calcium from superphosphate in the exchangeable form under subterranean clover pastures increased the ratio Ca/Sr (exchangeable) in the surface soil.