Paddy soils in the granitic area,basaltic area and the Pearl River Delta of South China were used in pot experiments,their potassium potential PK-1/2p(Ca+Mg),equilibrium potassium activity ratio AR₀^k labile or exchangeable potassium -ΔK⁰ and potential buffering capacity PBC^k were determined according to Beckett's method.Correlation analysis was made between the data obtained and the grain yield and potassium uptake of rice of the first crop and the continuous four crops.