Page 86 - Enzymes in Tropical Soils

74 Enzymes In Tropical Soils

Medonca and Rowell (1996) reported that the quantity of humic acids in an
Oxisol from Brazil was lower than that of fulvic acids. The quantity of humic and
fulvic acids were higher in topsoils and decreases with soil depth. A simple
comparation of these humic substances is shown in Fig. 5.5.

5.3 Relationship between Soil Organic C and Enzymatic
Activities

A great deal of researches have been conducted to devise the relationship
between the soil enzymatic activities and the soil organic C (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., 1998d; 1999d; 1999e). In most cases, 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) reported a strong spatial
relationship between organic C and the activities of phosphatase and arylsulfatase.
Salam et al. (1999e) showed 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
arylsulphatase) 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)
reported 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.
(1998d) also previously reported that the activities of soil acid phosphatase,
alkaline phosphatase, -glucosidase, and urease were positively correlated with soil
organic C as shown in Table 5.9. The increase in soil organic C or organic matter
content raises the activities of soil enzymes. This relationship is shown in Fig 5.6.

Abdul Kadir Salam - 2014