ObjectiveSoils and their functions are under threat from acidification. Phosphorus(P) and silicon(Si) mobility and their interactions in soils are sensitive to soil pH. Although Si fertilizer application has been reported to efficiently increase P availability in soils, the responses of Si mobility and availability to soil P enrichment are not well understood, especially in areas of intensive agriculture where soil P accumulation is significant.MethodThis study investigated the effects of P addition and artificial soil acidification on Si sorption and mobility in two typical farmland soils with different available silicon levels(the lower available silicon level, LASi and the higher available silicon level, HASi) using P and Si competitive adsorption experiments and soil incubation experiments.ResultWhen Si and P were simultaneously added at equimolar concentrations between pH 3.5 and 8.0, the presence of P decreased Si adsorption by 26%-74% and 31%-84%, respectively, in LASi and HASi soils at the corresponding pH, suggesting that P had a greater affinity to soil solids than did Si. Si sorption by the soil generally decreased with decreasing pH in the pH range of 3.5 to 8.0, and the reduction of Si sorption due to P addition was more significant under higher pH conditions.ConclusionSoil acidification and P addition decreased Si sorption and the soil HOAc-NaOAc-extractable Si content. The responses of soil CaCl₂-extractable Si content to soil acidification and P addition were different between the two farmland soils, and further studies are needed to understand the mechanisms.