The research objective was studying the influence of saponite-containing by-products of the tails of enrich- ment received as a result of processing of kimberlite rocks on Diamond Deposit named after M.V. Lomo- nosov on the properties of soils and the crop of potatoes on alluvial soils in Arkhangelsk Region. The experiment on studying the influence of saponite as mineral fertilizer was made in 2017 together by PС"Severalmaz" and FSBI Station of agrochemical service "Arkhangelskaya" on the production site of SEC "Breeding Farm Holmogorsky" of Holmogorsky area, Arkhangelsk Re- gion. To lay out field experiment, the site with floodplain sod and gley soil, sandy loamy, formed on modern allu- vial sandy sediments, was chosen. It was established that when adding into the soil at cultivation of agricultur-al production saponite-containing materials had impact on the properties of soil and productivity of cultures. The nature of manifestation of their soil-improving properties was influenced by weather conditions, initial properties of the soil, the dose of introduction of clay materials. On neutral soils additional alkalifying did not occur. The most noticeable manifestations in the change of soils fertility affected the level of the content of mobile potas- sium (up to 12 %) and organic substance. By options of the experiments the gain of organic substance in the soil made 17.4-0.9 %, and with the increase in the dose of introduction of saponite-containing materials the accu- mulation of organic substance decreased. Potatoes crop increase at introduction of saponite-containing materials made 9-18 c/hectare. The application of saponite in the doses higher than 7 t/hectare lowered the content of nitrates in tubers by 18-33 %.