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64 The Chemistry and Fertility of Soils under Tropical Weeds

The forest conversion was also reported to affect the shifting in the optimum
pH for phosphatases (Salam et al., 1998; Salam, 2014). Optimum pH is a particular
pH at which the activity of phosphatase is highest. Land-use conversion from the
primary forest to the secondary forest, coffee plantation, and cultivated lands
shifted the optimum values for phosphatases to higher values (Fig. 4.2). The value
of the optimum pH in the primary forest was the lowest i.e 5.0 and that in the
coffee plantation was the highest i.e 6.3 (Salam et al., 1998b). Geiger et al. (1998)
also observed such phenomenon; Cu caused a shift in the optimum pH of -
glucosidase towards lower pH values.

7

6.5

6
Optimum pH 5.5

5

4.5

4
3.5
3
Primary Secondary Cultivated Coffee
Forest Forest Land Plantation

Fig. 4.2. The shifting of optimum pH by forest clearing and
land-use conversion (Salam et al., 1998b).

Soil researchers suggest that soil pH may greatly affect the soil enzymatic
activities, particularly more important for phosphatases. Soil pH determines the
magnitude of their activities and types in soils (Malcolm, 1983; Nakas et al., 1987;
Rojo et al., 1990; Reddy et al., 1991; Trasar-Cepeda et al., 1991; Salam et al., 1998b;
1998e; Sarapatka et al., 2004). Sarapatka et al. (2004) document that acid
phosphatase activity in the root zones of various species and cereal cultivars was
negatively correlated with increasing pH and available phosphorus level in the

Abdul Kadir Salam and Nanik Sriyani – 2019