Page 91 - Enzymes in Tropical Soils

Enzymes in Tropical Soils 79

The presence of soil organic C is closely related to cover vegetation
(Handayani and Prawito, 1998; Handayani, 2001; Salam et al., 2001; Pujiyanto et
al., 2003), therefore, the activity of soil enzymes may correlate with the types of
vegetation grown on the soils. Some workers reported differences in enzymatic
activities in soils with different vegetations (Duxbury and Tate III, 1981; Jha et al.,
1992; Salam, 1996; 1997c; 1998d). Duxbury and Tate III (1981) reported that
activity of acid phosphatase significantly increased in soil covered with grasses.
Salam et al. (1998d) also reported that land-use conversion from primary and
secondary forest to agriculture lands drastically decreased the soil enzymatic
activities Jha et al. (1992) also reported that the activity of phosphatase was higher
in undisturbed forest soils compared to those in soils that had been disturbed. All
these data indicate that the activities of soil enzymes are related to the contents of
soil organic C controlled by plant covers.
Therefore, it is obvious that addition of organic C into the soil system may
enhance the activities of soil enzymes. Salam et al. (1998i) reported that an
addition of organic C (cassava leaf, alang-alang leaf, chicken dung, or goat dung)
into the soil system of Ultisol from Tanjungan, South Lampung, Sumatra, Indonesia,
clearly increased the activities of acid and alkaline phosphatases for incubation
times of up to 4 weeks. However, at incubation time of 16 weeks, addition of the
organic matters indeed decreased the enzyme activities in soil.

5.4 Relationship between Soil Total N and Enzymatic
Activities

Some experimental facts show that the populations and activities of soil
microorganisms are positively correlated with total N contents in soils (Salam et al.,
1998d; 1999d; 1999e). 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 previousy in Fig. 5.6.
The above linear relationship has been repeatedly reported by some other
researchers (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;
Salam et al., 1998d; Salam et al., 1999e). Salam et al. (1998d) reported that the
activities of soil enzymes, including acid and alkaline phosphatases, urease, and

Abdul Kadir Salam - 2014