Page 182 - Enzymes in Tropical Soils

170 Enzymes In Tropical Soils

plant roots after being released 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 decompost slowly or
very slowly. The presence of soil enzymes produced by soil microorganisms,
earthworms, and plant roots will accelerate the decomposition processes.
As discussed previously, the organic matters in soils are also the 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 great
2-
2-
amounts of free ions. For example, it is true for the release of HPO 4 and SO 4
through the decomposition of organic P and organic S, which are catalyzed by
phosphatase and arylsulfatase, respectively
The use of organic matters to provide some nutrient elements for plants
means that we conduct a reverse process from that occurs in plant tissues. In
plants, nutrient elements are chemically combined to form some organic
compounds such as sugars, proteins, and fats. Conversely, in soils the organic
compounds (sugars, proteins, and fats) are chemically decomposed back into the
+
inorganic nutrient elements. Examples of inorganic nutrient elements are NH 4 ,
- - 2- + 2+ 2+
NO 3 , H 2 PO 4 , HPO 4 , K , Zn , Mg , etc. The organic compounds can not be
absorbed by plant roots, but the inorganic nutrient elements can be easily
absorbed. Therefore, inorganic nutrient elements previously transformed into
organic compounds are finally decomposed back to form inorganic nutrient
elements.
Organic matters may probably accumulate in the soil environment. The
accumulation is accelerated by plant residues during harvest time. Generally,
farmers harvest only a very small part of plants. The rest are usually left or burned
in the fields. The amounts of the accumulated organic matters are probably huge.
In big town or cities with high populations and high level of life-styles, the
accumulation of organic wastes may also cause significant problems. The
accumulation of organic waste are indeed sometimes threatening, particularly
related to selection of where these wastes are to be safely disposed. Several sites
are finally used as disposal sites. However, most of the time in many cases the
accumulated organic matters or organic wastes cause social, health, and
environmental problems. Therefore, if managed properly, the presence of
enzymes may partially solve this problem.
However, as mentioned in the previous chapters, the faster decomposition
of organic matters by the presence of soil enzymes may cause a beneficial effect as
well as a destruction effect in the soil environment. In some cases such as in

Abdul Kadir Salam - 2014