The effect of buffer pH on soil phosphomonoesterase activity was carried out in laboratory conditions in vertisols using modified universal buffer with a pH range from 3-12. The pH of the MUB was adjusted to respective pH levels using 0.1 N HC1 or 0.1 N NaOH respectively. The substrate p^_ nitrophenyl phosphate of 0.025 M concentration was prepared in MUB of corresponding pH and analyzed for phosphomonoesterase activity. The soils were also analyzed for the physicochemical properties like pH, EC, available nutrients, texture and organic carbon. The results indicated that there was significant increase in the activity of phosphomonoesterase in the pH from 3 to 11.0 and later a steady decrease at pH 12. Thus all the vertisols exhibited a single peak for phosphatase activity at pH 11.0. On the other hand, two peaks of phosphomonoesterase activity at pH 6.5 and pH 11.0 was registered by the soil S-2, S-3, S-4, S-5 and S-6. The mean activity of phosphomonoesterase at pH 11.0 was found to be 231.3 µg of 4-nitrophenol released g^-1soil h^-1.

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