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Enzymes in Tropical Soils 11

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elements in the form of free ions. For example, the release of HPO 4 and SO 4
through the decomposition of organic P and organic S, which are catalyzed by
phosphatase and arylsulphatase, respectively. These soil enzymes are produced by
soil microorganisms and/or macroorganisms. The activities of these enzymes in
general increase with the increase in soil content of organic matters, which serve as
energy sources for soil macroorganisms and microorganisms.
However, the decomposition of organic matters in general proceeds
relatively slowly. The rates of the organic matter decomposition are controlled by
several important factors, among which are C/N ratios, partial pressure of O 2 ,
enzymatic activities, soil moisture content, soil temperature, and pH. Organic
matters with low C/N ratios will decompose faster. Decomposition will proceed
faster in the presence of O 2 which functions as an oxydator (a compound that
enables organic matters to be oxydized and accepts electrons). Therefore, the
supply of O 2 into the soil system must be maintained, among which by providing
good soil porosity so that it may enable O 2 to diffuse easily from the atmosphere to
soil air through soil pore system. Oxygen is also needed by soil microorganisms to
grow and develop, including producing soil enzymes. As discussed previously, the
decomposition of organic matters may proceed more quickly in the presence of soil
enzymes. Indirectly, the soil moisture content will affect the rates of organic
matter decomposition because soil microorganisms also need water for their
growth and development. An optimum combinaiton of water and O 2 in the soil-
water system may enhance the production of enzymes and the decomposition of
organic matters. Because the lives of soil microorganisms are also greatly
influenced by soil temperature and pH, these two factors are also very important in
the process of organic matter decomposition.

1.4 Scopes of Enzymes in Tropical Soils

This book deals with enzyme behaviors in soils revealed by researches
conducted in the Tropics, particularly in Indonesia. Some enzyme behaviors
revealed by researches conducted not in The Tropics are also used to strengthen
some theoretical justification through a critical discussion. By this method,
understanding on enzyme behaviors in soils becomes more incoorporated.
This book is organized into 12 chapters. Each chapter deals with a very
specific topic. Chapter I (Introduction) emphasizes the importance of soils as the
suppliers of nutrient elements for plants. It is not imaginable how plants are able
to grow and produce foods without the supplies of nutrient elements from soils.

Abdul Kadir Salam - 2014