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New synthetic soil conditioners for anti‐erosion protection of soils in the form of microgel copolymers of N‐isopropylacrylamide and acrylic acid (PAA#) and their interpolyelectrolyte complexes (IPEC#) with different surface charges are tested for optimization of water retention and porous structure in two samples of soil substrates. Water retention curves (WRCs) are used as a fundamental thermodynamic indicator of water holding capacity in soil substrates treated by new polymeric materials. Soil‐hydrological constants, as well as specific surface parameters and pore distribution curves are calculated from the WRCs using the van Genuhten model and the Voronin method in the author's modification. PAA# and anionic IPEC# with high swelling degree at a dose of 1% (by weight) increase field water capacity, available soil water range and specific surface area by 5–6 times for quartz sand, along with reorganizing its structure towards micropore dominance. For loamy sand, the same treatment was less effective with a twofold increase in field moisture capacity, double or triple increase of specific surface area, and an almost constant range of available soil water due to the strong increase of wilting point parameter. Weakly swelling linear polyacrylic acid and cationic IPEC# did not significantly affect properties of both mineral substrates.

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Chernozems or mollisols/black soils are 'reference soils' with a high content of organic matter, which ensures a high level of crop yield. In the article, we describe the structural characteristics of a typical medium‐thick Chernozem taken from Kursk region and their improvement via treatment by a 1 wt% aqueous solution/suspension of interpolyelectrolyte complex (IPEC), a product of electrostatic interaction between anionic potassium humates and cationic poly(diallyldimethylammonium chloride). The native Chernozem and polymer‐treated chernozem were characterized by laser diffraction, dry and wet sieving methods, transmission electron microscopy, soil washoff in a hydraulic erosion tray, gravimetry, visual control, and vegetation miniaturization in Petri dishes with the following main conclusions: (a) Deposition of a positively charged IPEC over the Chernozem sample led to an increase in a total amount of agronomically valuable 0.25–1 mm aggregates up to 28% in comparison with a 3% content of aggregates in the native Chernozem. (b) An average diameter of the air‐dry aggregates, treated by a cationic IPEC, was of 5.5 mm (cf. with 2.5 mm for the untreated). (c) An average diameter of the IPEC‐treated water‐resistant aggregates was of 2.1 mm (cf. with 0.5 for the untreated). (d) The Chernozem pretreated by the cationic IPEC showed a minimum removal of soil during several cycles of rewatering/drying. (e) All IPEC formulations, stimulated the growth of plants. The results are of interest for preparing low‐toxic polymer formulations capable of effective stabilizing fertile Chernozem soils.