Page 119 - Ilmu Tanah

106 The Chemistry and Fertility of Soils under Tropical Weeds

shrubs and alang-alang (I. cylindrica) lands compared to that of coffee plantation,
that is intensively plowed with low organic matter content (Yusnaini et al., 2002).
Higher population of earthworms then causes higher activities of soil enzymes. Jha
et al. (1992) also report that the activities of enzymes including dehydrogenase,
urease, and phosphatase in North East India were higher in the undisturbed regions
than those in the regions that had been degraded due to higher populations of
fungi and bacteria in undisturbed regions.
The relationship between the soil enzymatic activities and the soil organic C
had been investigated (Klein and Koths, 1980; Nannipieri et al., 1980; Harrison,
1983; Trasar-Cepeda and Gil-Sotres, 1987; Bonmati et al., 1991; Tate III et al., 1991;
Martens et al., 1992; Salam, 1996; Deng and Tabatabai, 1996; Salam et al., 1998b;
1999a; 1999b). In general, it is reported that the activities of soil enzymes are
positively correlated with the organic C and soil organic matter content (Soil
organic matter content = 1.5 – 2.0 times soil organic C). Bergstrom et al. (1998b)
report a strong spatial relationship between organic C and the activities of
phosphatase and arylsulfatase. Salam et al. (1999b) show that the organic C
content in soils with various length of cultivation showed positive correlations with
the activities of all investigated soil enzymes (acid phosphatase, alkaline
phosphatase, -glucosidase, and arylsulfatase) irrespective of the types of the
cultivated plants, with r = 0.605* – 0.898**in the cassava fields, r = 0.351 – 0.527**
in the sugarcane fields, and r = 0.419* – 0.542** in the pineapple fields,
respectively. Yusnaini et al. (2007) report a good relationship between soil organic
C and the activities of acid phosphatase (r = 0.790**) and alkaline phosphatase (r =
0.880**). Salam et al. (1998b) also previously report that the activities of soil acid
phosphatase, alkaline phosphatase,glucosidase, and urease were positively
correlated with soil organic C as shown in Table 6.10. The increase in soil organic C
or organic matter content raises the activities of soil enzymes. Salam et al. (1999b)
also show good correlation between organic C and some soil enzymes in cassava,
sugarcane, and pineapple plantations (Table 6.11).
Some experimental facts show that the populations and activities of soil
microorganisms are positively correlated with total N contents in soils (Salam et al.,
1998b; 1999a; 1999b). The relationship is logical because N element is very
important for the synthesis of proteins in microorganims. This relationship drives a
linear relationship between the activities of soil enzymes and the total soil N
contents because soil microorganisms are the main producers of soil enzymes. This
relationship is depicted previously in Fig. 6.6.

Abdul Kadir Salam and Nanik Sriyani – 2019