Page 16 - Enzymes in Tropical Soils

4 Enzymes In Tropical Soils

By the above reasons, the presence of soil enzymes in soils is of great
importance (Fig. 1.1). Soil enzymes catalyze the decomposition of organic matters
in the soil system. By the presence of soil enzymes, the changes of unavailable
forms of nurients in the structure of organic matters to be the inorganic elements
easily absorbed by plant roots will occur much faster. Understanding the
behaviours of soil enzymes in relation to the internal and external factors that
influence the rates of nutrient release from the structural elements in organic
matters is very important. This book will in the most part deal with the relationship
between these factors.

1.1 Roles of Soils in Supplying Nutrient Elements

It is agreed that almost all nutrient elements for plant growth and
development are originated from the soil system. The essensial elements
originated from the soil system are Hydrogen (H), Oxygen (O), Phosphorus (P),
Potassium (K), Calsium (Ca), Magnesium (Mg), Sulphur (S), Iron (Fe), Manganese
(Mn), Copper (Cu), Zinc (Zn), Boron (B), Molibdenum (Mo), and Chlor (Cl). The
nutrient elements originated off-soil system are Carbon (C) and Nitrogen (N).
Carbon is obtained by plants from CO 2 , which is present in the air in the amount of
0.03%. Nitrogen is obtained by plants from the air (N 2 ), which is present in the air
in the amount of 78%. However, plants may obtain N indirectly after N 2 is fixed and
+
released into the soil system in the form of NH 4 or after encountering nitrification
-
to be NO 3 . We can conclude that soils are the suppliers of nutrient elements for
plants. Therefore, it is logical to make a statement that: No Soil No Food.
As explained previously, the supplies of nutrient elements by soils are from
two main sources. The first source is soil minerals and the second is organic
matters. The most obvious difference between these sources is their chemical
composition. Soil minerals are inorganic, composed mainly of Silicon (Si),
Aluminum (Al), and O, together with various metal and non-metal elements; while
organic matters are composed mainly of C, H, and O, together with various metal
and non-metal elements. The supplies of the nutrient elements are originated
from the labile and non-labile forms. The labile forms are the most easily released.
It can be exchangeable or fixed elements by soil minerals or exchangeable
elements on organic matter surfaces. The non-labile forms are structural nutrient
elements; a part of it is easily detached and the rest is relatively slowly released.
The categories of the nutrient sources and their release rates are described in Fig.
1.2.

Abdul Kadir Salam - 2014