The roots of plants absorb silicon from the soil in the form of silicic acid. It is translocated through the plant until it settles in the intercellular spaces of its tissues. Silicon forms solid structures in the plant tissue (phytoliths), which provide greater strength to the cell walls without a direct role in plant metabolism. The purpose of this study was to study the material and phase composition of the tailings of gold-bearing and manganese ores of some deposits located in Kazakhstan. A silicon-containing component for obtaining silicon-phosphorus fertilisers (SPF) comprised of the tailings of the gravity concentration of gold-sulphide ore with a silicon dioxide content of 79.1 wt% was selected. Using the mechanical activation (MA) and mechanochemical activation (MCA) of Karatau phosphorites with selected silicon-containing tailings, a number of silicon-phosphorus fertilisers have been synthesised and their composition and properties studied. It has been found that the dependence of the content of assimilable forms of P2O5 and the available silicon in the MA products on the grinding time is extreme with a maximum achieved at a grinding time of 10 min. The study of the fertilising properties of the as-synthesised SPFs has shown that the content of mobile phosphorus in soil with the added SPF is 4.6 times higher than that observed in the soil without fertiliser and 3.7 times higher than soil with added superphosphate. This creates a substantial reserve of the assimilable forms of phosphorus in the soil and prevents them from binding to insoluble compounds comprised of aluminium and iron.