Page 46 - Enzymes in Tropical Soils

34 Enzymes In Tropical Soils

nutrient elements that are readily available for plant root absorption. Unlike that
in an open system, in a close system this process may help the preservation of
nutrient elements in the soil system and, hence, may preserve the soil fertility due
to the containment of nutrient elements in the system. This role also enables an
incoorporation of external organic matters into the soil systems to enrich the soil
nutrient status. If managed properly, this will reduce the need for commercial
nutrient sources for plant growth and production.
Out of the various enzymes found in soils, only some that are important for
nutrient element management in agriculture will be discussed in this Chapter.
These will include those involved in the cyclings of C, N, S, and P, i.e. urease,
phosphatases, arylsulfatase, and -glucosidase. Understanding the behaviours of
these soil enzymes with respect to the environmental properties will, of course,
help us to complete our understanding on the behaviours of their related nutrients.
These may include their producers, their forms, and their responses to the changes
in the soil parameters such as soil water, temperature, pH, nutrient contents, etc.

4.1 Production of Soil Enzymes

Soil enzymes are produced by soil organisms. In conducting their activities
to obtain energy from organic matters, soil organisms including microorganisms,
macroorganisms, and plant roots produce some enzymes. These enzymes work on
the biocycles of some nutrients in the soil – plant system (Tabatabai, 1982; Tate III,
1987). These enzymes are called soil enzymes. Like any other enzymes, soil
enzymes act as biocatalysts, that accelerate the soil biochemical reactions that
change reactants to form new products without themselves involve in the
reactions. Therefore, after the reactions are completed the soil enzymes return to
their original forms and may re-participate in the same biochemical reactions. A
simple expression of this role is previously shown in Fig. 2.1.
In the soil system, there are several enzymes produced by microorganisms,
macroorganisms (for example earthworms), and plant roots (Hayano, 1973;
Alexander, 1977; Ross and Cairns, 1982; Frankenberger, Jr. and Dick, 1983; Baruah
and Mishra, 1984; Satchell et al., 1984; Satchell and Martin, 1984; Nasution, 1986;
Tate III, 1987; Park et al., 1992; Sakai and Tadano, 1993; Joner et al., 1995; Joner
and Jakobsen, 1995; Dharmakeerti and Thenabadu, 1996; Vinotha et al., 2000;
Supriatin et al., 2007). Some of these enzymes live in soils for several days, and
some may live for several weeks or months, depending on their forms and

Abdul Kadir Salam - 2014