engleski

The influence of Fe-oxides and organic matter on aggregation and surface physico-chemical properties of Terra rossa and Leptosol

Terra rossa and Leptosol developed on hard limestone in Istria, Croatia, were investigated in order to evaluate the influence of Fe-oxides and organic matter on their aggregation and surface physico-chemical properties. The mineral composition and the morphology of soil samples were investigated using X-ray diffraction (XRD) and field emission scanning electron microscope (FE-SEM), respectively. The SSA was determined by BET method, the CEC by ammonium selective electrode and the surface charge by EPM measurements. Kaolinites (KlD and Kl), illitic material and Fe-oxides are the main mineral phases in the clay fraction of terra rossa while leptosol enriched in organic matter contains kaolinites, chlorite and vermiculite as main mineral phases in the clay fraction. To resolve the influence of coating substances on solid soil particles, samples were selectively dissolved. Particle size distribution, specific surface area (SSA), cation exchange capacity (CEC) and electrophoretic mobility (EPM) were measured on the following soil subsamples: original samples, samples treated with H2O2, samples treated with H2O2+NH4-oxalate and samples treated with H2O2+NH4-oxalate+Na-dithionite-citrate-bicarbonate. The morphology of samples and size of aggregates and particles were examined by field-emission scanning electron microscopy (FE-SEM). Differences were observed between the surface properties of terra rossa and leptosol that are the result of particle-size distribution, mineral composition and different share of organic matter. The distribution of CEC values among subsamples of terra rossa and leptosol is different. On the contrary, the trend of SSA is same in the first three subsamples of analysed soils. The SSA increased proportionally to the amount of the removed organic matter in both soils. Following the dissolution of amorphous Fe-oxides, the SSA decreased. After the removal of well crystallized Fe-oxides the SSA decreased in leptosol and highly increased in terra rossa due to major soil aggregate decomposition and accordingly, increased fine clay content. The EPM measurements of investigated samples were diverse, which exemplified the significance of organic and inorganic coatings on the formation of surface charge at the surfaces of investigated solids.

Fe-oxides; organic matter; aggregation; surface physico-chemical properties; Terra rossa; Leptosol

nije evidentirano