Effects of potassium, calcium and magnesium fertilizers applied to soils on rice growth, nutrient migration and nutrient uptake by rice plants in soils with low base content in southern regions of China were investigated. Results showed that on the basis of NP fertilizers with the increase of K, the rice growth was retarded and its biomass decreased, Applying Mg on the basis of NPK fertilizers increased the rice biomass. Applying Ca, Mg on the basis of NPK fertilizers resulted in the synergistic effect to make the biomass remarkable increase. It is suggested that the triangular interactions of K-Ca-Mg are positive interactions. Simulation experiments using ion-exchange resin showed the positive interactions between K-Mg, K-Ca and Mg-Ca in the process of nutrient migration to roots. Pot culture experiment showed an antagonistic effect between K-Mg and Mg-Ca in the process of nutrient uptake by rice plant. However, combinative use of K-Ca-Mg increased the total uptake of nutrient, showing a synergistic effect It is mainly due to the promotion of rice root growth. In addition, the possibility of decreasing the requirement of K by the triangular interaction of K-Ca-Mg was also discussed.