ROOT CEC MEASUREMENT BY LI-EXCHANGE

A method to more accurately determine fresh root CEC was developed, using 0.1 N LiCl as the exchange cation under a 30-minute anaerobic exchange period, followed by distilled water rinses to remove occluded and diffusible portions of Li from the roots. The roots were then dried, weighed, ashed and Li was determined on an atomic absorption spectrophotometer. Studies on root CEC assay methodology revealed extreme difficulties in measuring root CEC by estimating the root exchangeable H-. It is impossible to H+-saturate the roots because of cations moving out of root cells, and it is difficult to select an end point of the titration. The Na-exchange method is not quantitatively accurate because of native and metabolically absorbed Na-contamination. Barley root CEC values, determined by the Li-exchange method, increased with increasing nitrogen level up to 2.5 m M of NH4NO3 in the nutrient solution, being 10.2, 13.1, and 14.0 me/100 g dry roots for 0, 1, and 2.5 m M of NH4NO3, respectively. © 1969 Martinus Nijhoff.