Page 128 - Enzymes in Tropical Soils

116 Enzymes In Tropical Soils

Table 7.5. The effect of lime on the activity of acid phosphatase in
the root zones of several weeds*.

IC** CK AS AT
mg p-Nitrophenol g h
-1
-1
Control 177 152 111 175
Limed 140 125 76 125

*Adapted from Salam et al. (1997a); ** IC = Imperata
cylindrica, CK = Cyperus kyllingia), AS = Amarannthus
spinosus), and AT = Amaranthus tricolor)

The effect of soil acidification on the activities of soil enzymes is definitely
dependent on the optimum pH. In the case of phosphatase, the activity decreases
with soil acidification at pH below the optimum pH. Conversely, the activity of
phosphatase increases with soil acidification above the optimum pH. Therefore, to
understand the pattern of soil acidification effect, knowledge on the optimum pH is
of great importance. The complete profile of the relationship of soil enzymatic
activity as a function of soil pH such as shown in Fig. 7.2 must be devised.

7.5 Manipulating and Regulating Soil pH

The depencence of soil enzymatic activity on soil pH suggests that soil pH
might be manipulated and regulated at particular pH values to obtain maximum
values of enzymatic activities. The particular pH values are the optimum pH values
of the related soils.
Soil pH can surely be manipulated and regulated to a higher or lower values
through liming (alkalination) or acidification. As discussed previously, liming may
increase the soil pH. The lime requirement to increase the soil pH is determined by
some soil properties such as pH buffering capacity and also the kinds of liming
materials. Each liming material has its own neutralizing capacity.
Conversely, the pH of alkaline soils may need acidification to attain a
particular pH so that the activity of soil enzymes is higher or maximum. To do this,
several materials are used for soil acidification, but the most commonly used
material is sulphure (S). The S powder in soils may be oxidized to produce sulfuric

Abdul Kadir Salam - 2014