The point of zero net charge (PZNC) for the meadow brown soil in northeast of China with structural negative charges was measured by three methods: potentiometric titration, mass titration and inert electrolyte titration, showing that for the meadow brown soil which possesses structural negative charges, a PZNC independent of electrolyte concentration exists, and the values of pH_PZNC obtained by the above three methods are 2.9, 5.0 and 3.3, respectively. It was found that the values of pH_PZNC determined by potentiometric titration and inert electrolyte titration were very close while that determined by mass titration was relatively high. The estimating method of the total density of surface proton-active sites (N_s) in literatures was improved to obtain the N_s value of the meadow brown soil in northeast of China, which is 2.5 mmol• g^－1. According to the values of pH_PZNC, N_s and structural negative charge density (σ_st) measured, the intrinsic surface reaction equilibrium constants, pK of 1-pK model, pK_a1^int and pK_a2^int of 2-pK model, were directly calculated to be 3.37, 2.42 and 4.32, respectively, for the meadow brown soil in northeast of China.

Key words: clay, point of zero charge, interface reaction model, meadow brown soil in northeast of China