Dynamic changes of soil pH as influenced by ammonium sulfate (AS), monocalcium phosphate (MCP), potassium chloride (KCl) and their interaction in soils were evaluated in incubation experiments. Applying these fertilizers significantly reduced soil pH values in all cases and followed sequences of AS > MCP > KCl, MCP > KCl > AS and KCl > AS > MCP for the paddy, calcareous and red soils, respectively. The AS-induced reduction of pH in the three soils followed the sequence of red soil > paddy soil > calcareous soil, while in MCP and KCl systems the reduction of pH followed the sequences of calcareous soil > paddy soil > red soil and red soil > calcareous soil > paddy soil, respectively. The interactions of the NPK fertilizers on pH were significant. MCP plus KCl or MCP plus AS reduced pH values more than the fertilizers applied solely in the paddy soil, but AS partly counteracted the effect of MCP on pH in the 1 d sample of the calcareous soil. The effect of MCP on pH was trivial when MCP was applied in com Dynamic changes of soil pH as influenced by ammonium sulfate (AS), monocalcium phosphate (MCP), potassium chloride (KCl) and their interaction in soils were evaluated in incubation experiments. Applying these fertilizers significantly reduced soil pH values ​​in all cases and attended sequences The AS-induced reduction of pH in the three soils followed the sequence of red soil> paddy soil> MCP> KCl, MCP> KCl> AS and KCl> AS> MCP for the paddy, calcareous and red soils, calcareous soil, while in MCP and KCl systems the reduction of pH followed the sequences of calcareous soil> paddy soil> red soil and red soil> calcareous soil> paddy soil, respectively. The interactions of the NPK fertilizers on pH were significant. KCl or MCP plus AS reduced pH values ​​more than the fertilizers applied solely in the paddy soil, but AS partly counteracted the effect of MCP on pH in the 1 d sample of the calcareous soil. The effect of MCP on pH was trivial when MCP was applied in com