Quantification of Soil Aggregates Treated with Bituminous Emulsion and Other Organic Amendments by Using Scanning Electron Microscope

Abstract

ABSTRACT Several organic amendments have been used for recovering soil physical properties that become worse when losses in soil organic matter take place. Bituminous emulsion has proved to be quite effective for improving aggregates, but the mechanisms involved are still unknown. This research aims to extend current knowledge about bituminous emulsions by using scanning electron microscopy in the quantification of aggregates. Two different soils (clay and sandy-loamy) were amended with emulsion bituminous and other organic amendments. Total and partial numbers (different-size fractions) of aggregates after 60-days of treatment, obtained by scanning electronic microscopy (SEM), were compared to aggregates percentages obtained by analytical methods. Water-soluble and EDTA-extractable fractions of the elements most likely involved in the aggregation processes were also determined. Better results in aggregate stability were obtained in the clay soil amended, which is probably due to a greater clay-organic matter interaction in this soil. While treatments having bituminous emulsion increased aggregate size and water-stability in both soils, treatments having organic matter caused formation of small low-stable aggregates in sandy soil and formation of stable aggregates in clay soil as showed the number of large aggregates, mean diameter, and total aggregated area. Bituminous emulsion seems to exert two effects in both soils: an hydrophobic effect which increases aggregate stability, and a colligating effect, favored by the clay content, which increases aggregate size. Organic matter seems to act by forming new aggregates from silt + clay particles, which are joined together by cation bridges.