Page 125 - Enzymes in Tropical Soils

Enzymes in Tropical Soils 113

other land-uses. They showed that this phenomenon was demonstrated more
clearly by soils from Bukit Ringgis, West Lampung, Indonesia. The optimum pH for
the primary forest was about 5.0, shifted to about 5. 5 for the secondary forest,
and to 6.3 and 6.0 for the coffee plantation and the cultivated land, respectively
(Table 7.4). The pattern of shifting was also observed in soils from Sekincau, Tri
Mulya, and Tri Budi Syukur (Salam et al., 1998d). A similar pattern was previously
observed in in soils of Galicia, Northwest Spain (Trasar-Cepeda and Gil-Sotres,
1988).
The above phenomenon is negatively corelated to the changes in several
chemical properties by forest clearing and land-use conversion such as organic C,
total N, available P, and Cation Exchange Capacity (CEC) (Table 7.4). For example,
the conversion of primary forest to secondary forest, coffee plantation, and
cultivated land changes the topsoil Organic C contents from 60.4 to 41.4, 28.5, and
-1
15.8 cmol c kg , respectively. This data shows that forest clearing and land-use
conversion and the decrease in soil organic C content drive the Optimum pH to
higher values.

Table 7.4. Effect of land-use conversion on some chemical properties of soils from
Bukit Ringgis West Lampung*.

Land-Use Op. pH Org. C Total N Av. P CEC
-1
-1
-1
-1
pH (H 2 O 1:1) (g kg ) (g kg ) (mg kg ) (cmol c kg )
Primary 5.0 4.4 60.4 5.5 4.0 43.2
Forest
Secondary 5.5 5.4 41.4 3.4 2.1 18.5
Forest
Coffee 6.3 4.9 28.5 2.3 1.5 11.4
Plantation
Cultivated 6.0 4.4 15.8 1.7 1.5 12.4
Land
*Adapted from Salam et al. (1998d)

7.4 Effects of Acidification on Soil Enzymatic Activities

Soil acidification progresses through several mechanisms. As previously
mentioned, the soil acidification may be intensified by several reactions in soils that

Abdul Kadir Salam - 2014