Possible Relationships of Cation‐Exchange Capacity of Plant Roots to Cation Uptake

<jats:title>Abstract</jats:title> <jats:p> The K, Ca, and Mg contents of different plant species grown under similar conditions could be related in a majority of cases by CEC <jats:sub>1</jats:sub> /CEC <jats:sub>2</jats:sub> = K <jats:sub>2</jats:sub> /K <jats:sub>1</jats:sub> = (Ca <jats:sub>1</jats:sub> + Mg <jats:sub>1</jats:sub> /Ca <jats:sub>2</jats:sub> + Mg <jats:sub>2</jats:sub> ) <jats:sup>1/2</jats:sup> , where the subscripts 1 and 2 represent different species. It was shown that K <jats:sub>1</jats:sub> /K <jats:sub>2</jats:sub> should be expected for single‐salt solutions while K <jats:sub>2</jats:sub> /K <jats:sub>1</jats:sub> is expected when K is mixed with divalent cations. Data on root CEC and plant contents of K, Ca, and Mg obtained from a large number of citrus, corn, and soybeans grown in soil gave correlation coefficients as follows: <jats:disp-formula> <jats:graphic xmlns:xlink="http://www.w3.org/1999/xlink" position="anchor" xlink:href="graphic/saj2sssaj195803615995002200050007x-math-0001.png"> <jats:alt-text>urn:x-wiley:03615995:saj2sssaj195803615995002200050007x:equation:saj2sssaj195803615995002200050007x-math-0001</jats:alt-text> </jats:graphic> </jats:disp-formula> Even though the correlations were significant, the relations appeared to be far from simple and in some cases did not hold. For example, plants grown in sand corresponded less in the divalent ratios because of high Mg contents in corn. In some cases CEC ratios corresponded well with K <jats:sub>1</jats:sub> /K <jats:sub>2</jats:sub> rather than K <jats:sub>2</jats:sub> /K <jats:sub>1</jats:sub> . </jats:p>