Decreased water mobility when the hydrological moisture constant of the point of limited availability of water (PLAW) is reached is attributed to the presence of film forms of water formed under the influence of the solid phase. Existence of such forms of water is known to be limited by the concentration of electrolytes. The aim of the work was to clarify the mechanism of water stabilization by the solid phase of soils at the point of limited availability of water, taking into account the colloidal component of soils. We studied samples of sod-podzolic and gray forest soils and chernozem. In this study, the value of the PLAW was determined by plotting the secant on the curve of the main hydrophysical characteristic obtained by centrifugation. Scanning electron microscopy, vibrational viscometry, and a technique for extracting gels from soils were also used. It was found that adding 1 N potassium chloride solution to the soil that compresses the double electric layer on the surface of the particles does not affect the PLAW. This suggests that the film forms of water at PLAW are stabilized by soil organomineral gels, since at such concentrations of salts water films cannot exist in free form. It was also found that increasing the amount of gels in soils by their introduction increases the PLAW of the soil sample, and decreasing the volume of soil gels leads to a decrease in the PLAW. Thus, it is shown that water at PLAW is part of the colloidal component of soils, i.e., soil organomineral gels, and the value of PLAW in soils depends on the amount and volume of these gels.
Fedotov et al. (Sun,) studied this question.