Page 181 - Enzymes in Tropical Soils

Enzymes in Tropical Soils 169

soil factors and the soil enzymatic activities may be utilized to manage the soil
enzymatic activities For example, as previously mentioned, the phosphatase
activity can be stimulated or hindered by manipulating the soil pH. We can also
use these relationships to develop organic fertilizers and also biological fertilizers.

12.1 Roles of Enzymes in the Soil Environment

The role of enzymes is actually to decrease the energy of activation so that
they can accelerate the biochemical reactions in the soil system. The Arrhenius
equation (Eq. 2.2 and Eq. 2.3) clearly shows that the rate of any biochemical
reaction transforming the reactants into products is controlled by the Energy of
Activation, which is a measure on the magnitude of all forces that must be
surmounted during a reaction process (Sparks, 1989). This energy barrier separates
the reactant states from the product states. To form the products, the reactants
must have sufficient energy to overcome this energy barrier (Castellan, 1983).
Without sufficient energy to surmount the energy barrier, the reactants will stay at
their orgininal states and the products will never exist. A higher Energy of
Activation may result in a lower rate of reaction. An enzyme as a catalyst may
effectively lower the Energy of Activation and, therefore, fasten the biochemical
reactions.
According to Tabatabai (1982), an enzyme may then efficiently enhance the
rate of a biochemical reaction to several orders of magnitude. In addition, every
enzyme works on a specific substance and does not work on any other substances.
The reaction rates at high concentration of substrate follow the zero order
reaction; independent of the substrate concentration. In contrast to that at high
concentration of substrate, the rate of an enzymatic reaction at any time at lower
concentration of substrate is dependent on the concentration of substrate. The
rate of a reaction increases with the increase in substrate concentration following
the first order reaction as shown in Fig. 2.3. Both types of reactions may occur in
the soil environment, depending on the concentrations of organic matters as the
substrate.
The presence of soil enzymes is of importance in availing plant nutrient
elements of organic sources in the soil – plant system. As mentioned previously, in
addition to the inorganic forms (soil minerals), nutrient elements in the soil system
are also present in the forms of organic forms (organic matters). These elements
are incoorporated as the structure of organic matters that can be absorbed by

Abdul Kadir Salam - 2014