Page 22 - Enzymes in Tropical Soils

10 Enzymes In Tropical Soils

minerals such as Olivin may weather and release its structural elements relatively
quickly. However, most soil minerals weather relatively slowly. Among these soil
minerals are Feldspars, which are abundant in soils.
However, different from those of Decomplexation, Dissolution, and
Desorption, soil mineral weathering releases great amounts of nutrient elements,
higher than those from exchangeable form. For example, the amounts of structural
K reaches 100 – 3000 times higher than the concentration of exchangeable K.
Therefore, the use of weathering of soil primary minerals contained in sand and silt
fractions of soils will provide significant amounts of free ions. This practices will
decrease the amounts of nutrient elements of fertilizer origin. The use of this
practice will be more significant in young soils containing great amounts of rich
primary minerals.

1.3 Supplying Nutrient Elements from Non-Mineral
Sources

In addition to the inorganic forms (soil minerals), nutrient elements in the
soil system are also present in organic forms (organic matters). These elements are
incoorporated as the structure of organic matters that can be absorbed by plant
roots after being detached through decomposition processes involving soil
microorganisms and soil enzymes. Part of the organic matters, particularly with
low C/N ratios, will decompose relatively fast; the rest will decompose slowly or
very slowly. The presence of soil enzymes produced by soil microorganisms,
earthworms, and plant roots will accelerate the decomposition process.
The organic matters in soils are also nutrient element reserves available in
great amounts. These compounds are the results of physiological accumulation of
nutrient elements by plants originated from the soil system. Therefore, the
decomposition of organic matters will provide considerable amounts of free ions.
The decomposition of organic matters in general will proceed as Eq. 1.4 follows:

CH 2 O + O 2  H 2 O + CO 2 + Energy ..... Eq. 1.4

This process involves a redox reaction (reduction-oxidation process). In this
reaction, organic matters (CH 2 O) are oxydized by using O 2 as an electron acceptor;
the oxydation number of C increases from 0 to +4; while that of O decreases from
0 to -2. At the time of the decomposition process, there is a release of nutrient

Abdul Kadir Salam - 2014