ChileanJAR

A research project was carried out at the Soils Dept. of the University of Concepción, Chillán (Chile) on allophane determinatian in sails af the Ñuble province by the cation-exchange capacity Delta value.
As proposed by Aomine, S. and Jacksan M. L. (1) one sample of H₂O₂ - treated, ironextracted soil is treated with 2% Na₂CO₃ solution for 60 minutes and another sample with boiling NaOAc of pH 3,5 for 15 minutes. Both samples are washed with neutral NaOAc and the catian-exchange capacity is determined with K replaced with NaOAc. The difference obtained between the two samples is referred to as the "cation-exchange capacity Delta value" and averages 100 me/100 g. far allaphane.
"Trumao soils show high values for cation-exchange capacity Delta value because. the amorphous callaids present in these soils have a pH dependent charge.
Accarding to the propased method allaphane ranges from 41,64% to 45,35% far the Arrayán soils and from 57,03% to 64,08% (mineral fractian basis) far the Santa Bárbara soils.
Other soils as Cauquenes, Mininca, Collipulli and San Carlos, shaw low values for the catian-exchange capacity Delta value, which confirms findings by Besaain, 1964 (3) and· Espinoza, 1969 (6) indicating that these soils do not cantain structures like allophane but cristalline structures like halloysite. The cation-exchange capacity. Delta value presented by these soils is 13,73; 8,99; 12,65 and 10,00 me/100 g. for Cauquenes, Mininco, Collipulli and San Carlos sails, respectively, which can not be used as a basis far the allophane determinatian.
The trumao soils present distinct physical and chemical characteristics compared to those presented by the other sails of Ñuble province.