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Because of experimental difficulties, few authors have studied the dynamics of aluminium in the rhizosphere. The aim of this paper is to present a suitable method for studying rhizosphere AI dynamics. It is based on the use of agarose as a substrate for plant growth. Agar and agarose gels are often used in rhizosphere studies, but most are poorly characterized and occasionally give rise to experimental artefacts, especially with low mobility elements like A1. The results reported here show that agarose is a relatively pure substrate, nearly devoid of phosphorus and other Al-complexing substances. Aqueous extracts of agarose also exhibit AI phytotoxicity equivalent to that of a nutrient solution. Since this substrate has the properties of a variable charge exchange complex, it can be considered as a physico-chemical model for organic matter. Finally, its A1 adsorption capacity is high enough for the A1 reserve in the substrate not to exert a limiting effect on plants and low enough to allow accurate measurement of A1 depletion in the rhizophere.

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