Page 88 - Enzymes in Tropical Soils

76 Enzymes In Tropical Soils

Organic C in soils is a substrate for enzymatic activities. The more the
substrate, in this case organic C or organic matters, is available in soils, the higher
the activities of soil enzymes will be measured in the soil system. Direct
relationship between the activities of some soil enzymes and soil organic C or
organic matter contents has been reported (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. (1998d)
reported that the activities of acid phosphatase, alkaline phosphatase, urease, and
arylsulphatase in several land-use systems decreased in the order of primary forest,
secondary forest, and agriculture lands, in a accordancce with the decrease in the
contents of organic matter in the respective land-uses. Tate III et al. (1991) also
reported that the activitities of soil microorganisms and phosphatases in soil
Horizon O rich in organic matter were 2 – 25 times higher that those in soil Horizon
A with low content of organic matter. The enzymatic activities involved in the
cycles of C, N, P, and S in the soil – plant systems in soil enriched with organic
matter were shown to significantly higher than those in the control soils (Martens
et al., 1992). This relationship is related to the roles of organic matters as energy
sources for microorganisms producing soil enzymes.

100
90
mg p-Nitrophenol g -1 h -1 60 Organic C
80
70

50
40
30
Total N
20
10
0
0 1 2 3
0.5 1.5 2.5 3.5
% C or % N

Fig. 5.6. The relationship between the soil enzymatic
activities vs Organic C or Total N.

Abdul Kadir Salam - 2014