A new approach for estimating the labile aluminium fraction in soil solutions, through batch experiments, using cationic (Amberlite IR 120) or non ionic (Amberlite XAD 2) resins.

Aluminium fractionation was tested on two types of resin. The first approach was based on the selective sorption of cationic forms on a strong cation exchange resin (Amberlite IR 120) which is commonly used. Using a defined contact time (1 hour) between solution and resin (batch technique) it was possible to obtain separation between different aluminium species. The second approach was based on the sorption of organic matter, especially complexes between organic matter and aluminium, onto a non ionic resin (Amberlite XAD 2), batch reactors containing the solution and the resin were stirred for 16 hours. Some tests were carried out to compare the different techniques using samples containing various complexing molecules (salicylic acid and purified commercial humic acid). Aluminium fractionation was then carried out on different soil solutions with the two different types of resin. Horizons A and S from acid brown soil under chestnut and Douglas fir were used in order to compare the influence of the type and the content of organic matter on the released aluminium forms. It appears that A layers release more total aluminium than the S ones but only a small part is in cationic forms. The S layer presents Al essentially under reactive cationic forms.