Page 121 - Enzymes in Tropical Soils

Enzymes in Tropical Soils 109

As shown in Fig. 7.2, the activity of phoshatase is low at low pH, probably
+
due to the ionization of H ion on the functional groups of enzyme proteins. As the
soil pH increase, the ionization of enzyme functional groups progresses and so does
the activity of phosphatase. At this range of soil pH, the activity of phosphatase
increases with the increase in soil pH. After an optimum pH, in which the activity of
phospatase is maximum, the activity declines to an asymptotic value at high pH.
The cause of this phenomenon is unclear. The negative effect of high pH on the
populations and activities of particular enzyme producers is probable.
The pattern of increasing phosphatase activities at low pH and decreasing at
higher pH above the optimum pH were also previously reported by several workers
(Frankenberger and Johanson, 1982; Malcolm, 1983; Trasar-Cepeda and Gol-Sotres,
1988; Rojo et al., 1990; Trasar-Cepeda et al., 1991). Rojo et al. (1990) reported
that, by using two series of soils from The United States of America i.e. Aridic
Calcixeroll and Umbric Dystrochrept, they varied the pH and measured the
phosphatase activity. However, these soils showed different optimum pH values.
Aridic Calcixeroll showed an optimum pH at about pH 10.5 while Umbric
Dystrocherept showed an optimum pH at pH 5.5, similar to those reported by
Salam et al. (1998d). Rojo et al. (1990) concluded that the alkaline phosphatase
dominated alkaline soils like Aridic Calcixeroll whose pH was 8.4 and acid
phosphatase dominated acid soils like Umbric Dystrochrept whose pH was 4.3.
Differences in the optimum pH of these soils and also of Indonesian soils are
depicted in Fig. 7.3. A similar pattern was also reported for urease (Gianfreda et
al., 1992). The activity of urea increased with the increase in soil pH until the pH
value reached 7.0 and then decreased.
The degree of phosphatase activity with respect to soil pH is differect from
one soil to another, depending on the types of land-use systems and on the
sampling locations. The activity of phosphatase in soils collected from the pimary
and the secondary forests were in most cases higher than those collected from the
coffee plantation and the cultivated lands. Observation showed that the difference
was closely correlated with the contents of organic C and total N. The activity of
phosphatase was also higher in soils collected from Bukit Ringgis and Sekincau than
those collected from Tri Mulya, Tri Budi Syukur, and Pura Mekar. However, the
pattern of phosphatase activity with respect to soil pH was similar for all soils,
independent of land-use systems and sampling locations (Fig. 7.2).
Kumar and Wagenet (1984) also reported the effect of CaCO 3 addition on
the activity of urease. As seen from Fig. 7.4., the activity of urease decreased
significantly upon CaCO 3 addition. The decrease in the urease activity reached a
value of 29 -68% at CaCO 3 addition of 8%. Kumar and Wagenet (1984) argued that

Abdul Kadir Salam - 2014