Page 183 - Enzymes in Tropical Soils

Enzymes in Tropical Soils 171

coping with the environmental problem by the accumulation of organic residues
and also organic wastes particularly in big cities, the presence of soil enzymes is
beneficial. It may decompose the organic matters into their constituents, parts of
it may be utilyzed by plants as plant nutrient elements. On the other hand, in the
case of organic soils, of which the organic matter is the major constituents, the
presence of soil enzymes may be destructive. The faster decomposition of organic
matters may quickly lower the thickness of organic soil layers and may cause their
subsidence (Tate III, 1994). The presence Urease in soils is also shown to waste the
use of Urea-N in agricultural fields because this soil enzyme accelerates the
ammonification process leading to the nitrification and denitrification processes
that may increase N losses through leaching and volatilization (Kissel et al., 2012).

12.2 Enzyme Degradation and Stimulation

The soil enzymatic activities may be degraded. Similar to the soil chemical,
physical, and biological properties, land-use conversion also significantly affects the
soil enzymatic activities. As previously shown, the observation in five sites in West
Lampung, the southern tip of Sumatra, Indonesia, showed with a few exception
that forest clearing and conversion to secondary forest, coffee plantation, and
cultivated lands significantly decreased the soil enzymatic activities including the
acid and alkaline phosphatases, urease, and -glucosidase. The activities of these
soil enzymes in the primary forest were the highest, followed by those in the
secondary forest and those in the coffee plantation, and those in the cultivated
lands were the lowest (Salam et al., 1998d).
The changes in the soil enzymatic activities were well correlated with the
degradation in organic C and total N contents. These data indicate the importance
on C and N for soil microorganisms, that produce most of the soil enzymes. As
discussed previously, organic C is an energy source for soil microorganisms while N
is needed to form proteins. Therefore, the presence of lower C and N in the
degraded lands may cause lower populations and acivities of soil microorganisms
and, thereby, produce less enzymes. Several experimental data support this thesis.
For example, as cited previously, Jha et al. (1992) showed that the activity of soil
phosphatase was higher in undisturbed forests than those that had encountered
deforestation. The results indicates that the soil enzymatic activities may be
degraded by lowering the soil organic C and N contents (Klein and Koth, 1980;
Nannipieri et al., 1980; Harrison, 1983; Trasar-Cepeda and Gil-Sotres, 1987;

Abdul Kadir Salam - 2014