Aluminium contamination and other changes of acid soil solution isolated by means of porcelain suction‐cups

Abstract

Comparison was made between the chemical composition of soil solutions isolated by means of a suction method using porcelain cups and by centrifugation. The soil solutions were isolated from three depths of field plots, where the soil (Typic Haplohumod) had been subjected to various pretreatments. The cups were made of mullite and corundum as shown by X‐ray diffraction analysis. The material when powdered had a cation exchange capacity of about 10meq kg−1. Solutions with similar ionic strengths were obtained by the two methods, but the cups were found to release substantial amounts of Al and to adsorb H, Ca, K, Na and organic matter. After the cups had been placed in the soil for more than 7 months, calculations suggested that the Al activity in cup solutions was controlled by amorphous gibbsite. This amorphous material was probably produced by proton‐induced decomposition of part of the cup material. It is concluded that such cups are improper for isolation of soil solution from acid soils. Copyright © 1989, Wiley Blackwell. All rights reserved