Abstract

Soil organic matter destruction by hydrogen peroxide (H2O2) treatment used in clay samples preparation of allophanic soils leads to oxalate formation which can be adsorbed on clay surfaces or precipitated as calcium oxalate (CAC2O4), when calcium (Ca) saturation is involved. Oxalate precipitation is detected through differential thermogravimetric (DTG) analysis. The DTG curves of Vilcun soil, a Chilean Andisol, potassium (K) or Ca ion homoionized show only the characteristic continuous weight loss of allophanic soils. After H2O2 treatment, the Ca homonized sample shows three more peaks attributed to CaC2O4 which remain even after iron oxide removal by the citrate-dithionite-bicarbonate treatment. However, they are not shown if water washings are applied after the H2O2 treatment.