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The Chemistry and Fertility of Soils under Tropical Weeds 83

2011) bacteria may live better in neutral and alkaline soils, while fungi may live
better in acidic soils. Therefore, the decrease in soil pH may lower the populations
and activities of bacteria and increase those of fungi. It has been reported recently
that liming at 0-5 cm top-layer of Typic Hapludox in Brazil increased not only the
soil pH but also the population, activity, and bacteria/fungi ratio (Garbuio et al.,
2011).
As discussed previously, soil researchers also 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 nutrient medium. Frankenberger and Johanson (1982) also
show the dependence of other enzymes i.e. urease and phosphodiesterase
activities on soil pH. The activities of soil enzymes may change accordingly as a
result of ionization and deionization of the functional sites of the enzyme proteins
with the increase in soil pH.
This behavior was clearly demonstrated by phosphatases in tropical soils.
Salam et al. (1998b) treated tropical soil samples of some deforested locations in
West Lampung, Indonesia, at a series of buffered pH of 3 to 12. The results are
shown previously in Fig. 4.3. Similar patterns were also documented by Trasar-
Cepeda et al. (1991) and Nakas et al. (1987). Ekenler and Tabatabai (2003) suggest
that acid phosphatase was the most sensitive and arylsulfatase the least sensitive
to changes in soil pH.
Salam (2014) argues that the lower activity of phosphatase at low pH is
+
probably due to the ionization of H ion on the functional groups of enzyme
proteins. As the soil pH rises, 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 until the related
optimum pH, in which the activity of phosphatase is the highest, the activity
declines to an asymptotic value at higher 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 increasing pattern of phosphatase activities at low pH and decreasing
pattern at higher pH above the optimum pH were also previously reported by
several workers (Frankenberger and Johanson, 1982; Malcolm, 1983; Trasar-

Abdul Kadir Salam and Nanik Sriyani – 2019