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Differentiation of Sr-Ca Supply Mechanisms to Roots Growing in Soil, Clay, and Exchange Resin Cultures¹

ABSTRACT

The ratio of Sr/Ca taken up by soybean roots growing in soil, clay, and exchange resin media was used to evaluate the mechanisms supplying these cations to the root surface. When mass-flow supplied more than uptake, the Sr/Ca ratio of uptake was similar to the Sr/Ca ratio in the soil solution. This is the ratio for the mass-flow supply mechanism. When mass-flow supplied a minor proportion of uptake, the Sr/Ca ratio of uptake corresponded to the Sr/Ca ratio of the exchange cations rather than the solution cations. This indicated that the supply by contact of the media with the root and by diffusion was in the ratio of Sr/Ca found on the exchange sites.

¹ Paper no. 4056, Purdue University Agr. Exp. Sta., Lafayette, Ind. Contribution from the Department of Agronomy. This study was supported in part by the US Atomic Energy Commission under contract AT(11-1)-1495.

² Formerly graduate assistant, Purdue University, now soil scientist, Canada Dept. of Agriculture, Lethbridge, Alberta, Canada, and Professor of Agronomy, Purdue University, respectively.

Received for publication October 9, 1970. Accepted for publication June 25, 1971.