Characterization of Aluminum in Volcanic Ash Soils

Abstract

AbstractBuffered and unbuffered salt solutions were used to characterize Al in acid volcanic ash soils of Costa Rica. The results presented show that the exchangeable Al in the Andosols studied are relatively low as determined by successive extractions with unbuffered salt solutions. When different soils were compared, exchangeable Al seemed to increase as weathering of the soils increased. Buffered 1N NH4OAc at low pH's releases considerable amounts of nonexchangeable Al. In a well developed Andosol, part of nonexchangeable Al seems to be released from organically complexed forms. In more weathered soils, the inorganic forms of Al seemed to be the main source of nonexchangeable fractions.The method of successive extractions with unbuffered salt solutions appeared to provide a reliable measuremnt of exchangeable and nonexchangeable Al. Both 1N KCl and 1N NH4Cl generally extracted similar amounts of Al from soils, and both methods are very sensitive to detect differences due to lime treatments or organic matter destruction.