Comparative Characteristics of the Physical Properties of Freshly Collected and Dried Soil Samples

Abstract— Soil as a colloidal system is characterized by the phenomena of peptization and coagulation. Drying of soil samples can promote coagulation and hydrophobization, whereas wetting promotes peptization. The aim of this work is to assess the effect of drying on the physical properties of freshly collected soil samples. The objects of study are the humus-accumulative horizons of soddy-podzolic soil, gray forest soil, and leached chernozem. For freshly collected and air-dry samples, the following were determined: particle-size distribution (laser diffractometry), water retention curve (capillarimetry), water stability of aggregates (vibrosieving under vacuum), paste viscosity (vibrational viscometry), and stabilty to wedging of water-saturated aggregates (blade method). It was found that the viscosity of pastes from freshly collected samples is 5–16 times higher than that from air-dry samples. The water retention curve in the capillarimetric region showed that at the same pressure, the water content of dried samples is 2–4% (by volume) lower than that of freshly collected samples. According to laser diffractometry data, in dried chernozem samples, aggregates and microaggregates are larger: the distribution peak is shifted to the range of 1 and 10 μm compared to less than 1 μm in freshly collected samples. The strength of aggregates increases upon drying: in soddy-podzolic soil, 50 aggregates remained after drying compared to 13 in freshly collected samples; in gray forest soil, 28 versus 6. The aggregate-forming effect of polymers (polyacrylamide, polyvinyl alcohol) on freshly collected chernozem samples reached 19% and 45%, respectively, whereas on air-dry samples, the effect was negative or absent (–2% and –12%). The obtained results confirm the hydrophobization of soils upon drying.