Mehlich 3 (M3) reagent is applicable to a wide range of soils for the determioration of both available macro- and micro-nutrients, perhaps to serve as an universal.soil extractant. However correlation between M3 value of soil nutrient and plant response to nutrient in field or pot experiment of calcareous soils was scarcely studied. Using the micronutrient uptake of tomato and sugar beet seedlings cultured in a mico-pot experiment and the relevant conventional soil test values as reference terms, the correlations between M3-ICP values of the calcareeous soils in Beijing and Hebei and the reference terms were studied in the present work. The results indicated that there were significant correlations between the values of M3-B、-C、-Fe、-K、-Mn、-P and -Zn and the values of corresponding conventional methods. Significant correlations were also found between the values of M3-B、-Cu、-Mn, -M o、-Zn、-A1、-Mg and-Na and the corresponding nutrients uptake of the seedlings for both the two plants; and between the values of M3-Ba,-Ca,-Cd,-Co,-Cr and -Ni and the corresponding uptake of the seeding for one plant; but no statistically significant correlation was obtained for values of M3-Fe,-Pb and -Ti. Furthermore, M3-ICP method had many other advan tages when it served as an universal soil extractant. Mechanisms and the several relevant problems are also discussed. The concept of acidic extractant being not used as a good soil extractant on calcareous soil should be questioned, and M3 reagent possibly could be used as an universal extractant of acid, neutral and alkaline (calcareous) soils in China.