Aggregate formation in salt-affected soils of the Baer mounds

Abstract

Particle-size and microaggregate-size distributions and the morphology of aggregates <1 mm have been studied in soils of the Baer mounds. It is shown that the soil aggregates contain specific clayey-salt microaggregates and coatings. The type of the clayey-salt pedofeatures (microaggregates and/or coatings) depends on the clay content in the soils, and the size and shape of the clayey-salt microaggregates depends on the concentration and chemistry of salts participating in their formation. The clayey material of the micro-aggregates is mainly represented by smectitic minerals. Calcareous (calcitic, dolomitic, and iron-bearing) clayey-salt microaggregates have been found in all the horizons of investigated soils, except for the Ap horizon of the soil of the former rice paddy in the hollow between the Baer mounds. Clayey-salt microaggregates with simultaneous participation of several different salts (chlorides and sulfates of Na, Mg, and Ca) have been detected in the solonchakous soil at the foot of the Baer mound. For the first time, quasicrystalline formations—pentagonal NaCl crystals of up to 3 μm in size with participation of phyllosilicates and sulfates of Na and Mg—have been described under native conditions in the B2 horizon of the solonchak. It is argued that the formation of clayey-salt aggregates contributes to the good microaggregation of the soils and to the stability of the Baer mounds under conditions of the arid climate.