Page 75 - Ilmu Tanah

62 The Chemistry and Fertility of Soils under Tropical Weeds

microorganisms then somehow became more limited. Consequently, as shown in
Fig. 4.1, the activity was lower at water contents higher than 40%. This
phenomenon is also documented by some other workers (Klein and Koths, 1980;
Tabatabai, 1982; Baligar et al., 1988; Yusnaini et al., 2002).

160
150
140
Activity of Phosphatase (g p-Nitrophenol g -1 h -1 ) 120
130

110

100
90
80
0 20 40 60 80 100 120
Water Content(%)

Fig. 4.1. Effect of soil water on the phosphatase activity
(Salam, 1998a).

A great deal of researches demonstrate that the changes in the soil enzymatic
activities were well-correlated with the changes in the soil organic C and total N.
These observations clearly indicate the importance of soil C and N for soil
microorganisms, that produce most of the soil enzymes. Organic C is an energy
source for soil microorganisms and macroorganisms like earthworms while N is
needed to form proteins. Therefore, the presence of lower C and N in the
degraded lands may cause lower populations and activities of soil microorganisms
and macroorganims and, thereby, produce less amounts of enzymes. Several
experimental data support this thesis (Salam et al., 1998; Brzostek et al., 2012).
The results indicate that the soil enzymatic activities can be enhanced by addition
of organic C (Klein and Koths, 1980; Nannipieri et al., 1980; Harrison, 1983; Trasar-

Abdul Kadir Salam and Nanik Sriyani – 2019