Abstract: In order to study the interference of matrix effect on the measurement of soil and plant potassium content by flame photometer, the electrical signals of the K⁺ test solutions and K⁺ standard solutions with same matrix were measured. The K⁺ test solutions consisted of water soluble potassium, rapidly available potassium, slowly available potassium, total potassium of soil and total potassium of plant. The interference of different types of matrixes and different dilution factors of matrixes were studied. It was shown that the K⁺ content of standard samples had a high recovery rate when the matrixes of test solutions and standard solutions were the same. It caused a negative error, especially for total potassium of soil and total potassium of plant, when the matrix of K⁺ standard solutions was deionized water. The effect of matrix could be reduced by dilution of matrix. However, within the commonly adopted dilute times of soil or plant sample, the measured electrical signals of K⁺ standard solutions with different matrixes still varied. In order to eliminate the interference caused by the differences of matrixes, the matrixes between K⁺ test solution and K⁺ standard solution should be kept consistently when the potassium contents of soil and plant samples were measured by flame photometer.

Key words: agro-chemical analysis, measurement of potassium, matrix effect