Page 133 - Enzymes in Tropical Soils

Enzymes in Tropical Soils 121

+
3+
The chemical weathering of Albit produces three constituents i.e. Na , Al , and
Si(OH) 4 . As long as the soil is moist and acid, the weathering of Albit progresses
producing its constituents to reach an equilbrium.
The above reaction will normally stops at equilbrium. However, the reaction
+
will progress faster whenever: (a) the concentration of H ion increases or the soil
+
pH decreases, (b) the concentration of Na decreases by plant root absorption,
3+
leaching, adsorption, or precipitation, (c) the concenctration of Al decreases
through adsorption or precipitation, and (d) the concentration of Si(OH) 4 decreases
through leaching or precipitation. The faster reaction by the above stimulants is
called mass action law or common ion effect.
+ 3+
On the other hand, the presence of high concentration of Na , Al , and/or
Si(OH) 4 may hinder the reaction. The high concentrations of these constituents can
be caused by the absence or little adsorption, precipitation, plant root absorption,
and/or leaching. This phenomenon is also called mass action law or common ion
effect.
The above phenomena are not exclusive and may happen to various
reactions including the biochemical reactions. Some research reports are found in
current literature related to this phenomenon, particularly for the decomposition
of P and S (Juma and Tabatabai, 1977; Pang and Kolenko, 1986; Fox and Comerford,
1992). The role of mass action law may be employed to control chemical reactions
in the soil water system, both to hinder or to stimulate the progress of a reaction.

8.2 Effects of P on the Activity of Phosphatases

As shown in Eq. 4.1, the decomposition of organic P produces
- 2-
orthophosphates (H 2 PO 4 and/or HPO 4 ). The production of ortophosphates is
faster with the increasing amount of organic P and phosphatase. However, with
equal amounts of organic P and phosphatase activity, the production of
orthophosphases may be hindered if the concentrations of orthophosphates in the
soil solution are relatively high. Appiah et al. (1985) reported that the activity of
phosphatase was inhibited by cocoa pod ash and they argued that the inhibition
was attributed to the high contents in available P in cocoa pod ash in addition to
those of Mn and Zn, which were much higher that those in soils.
Several researchers reported that the presence of high concentration of
orthophosphatse as a result of P-fertilization decreases the production of
ortophosphates as represented by the decrease in the activity of phosphatase

Abdul Kadir Salam - 2014