Page 122 - Enzymes in Tropical Soils

110 Enzymes In Tropical Soils

the decrease was attributed to the inactivation of urease by amorphous CaCO 3 .
The effect of CaCO 3 on the increase in soil pH was also possible to affect the the
urease activity. As mentioned previously, the changes in soil pH may change the
dominant microorganisms, especially fungi and bacteria; fungi prefer acid soil
environment while bacteria prefer neutral or alkaline soil environment. This
phenomenon may affect also the populations and activities of the urease producing
microorganisms.

120
Phosphatase Activity (in %) 80 Acid Soil
100

(Indonesia)
60
Acid Soil (US)
40
20
0 Alkalie Soil (US)
3 4 5 6 7 8 9 101112
Soil pH

Fig. 7.3. The differences in the optimum pH between acid and alkaline soils
(Redrawn from Rojo et al., 1990 and Salam et al., 1998d).

7.2 Optimum pH and pH Levels for Analysis of Soil
Enzymes

As previously described in this book, the analysis of phosphatases developed
by Tabatabai and Bremner (1969) is conducted as follows. A 4 mL of a modified
universal buffer (MUB) of a particular pH is added to a 1 g of soil sample (oven-dry
equivalent) after the soil microbial activities are stopped by using several drops of
toluene. A substrate in the form of 1 mL of 0.025 M p-nitrophenyl phosphate (p-
NPP) dissolved in MUB solution of the same pH is then added. After being

Abdul Kadir Salam - 2014