Page 126 - Enzymes in Tropical Soils

114 Enzymes In Tropical Soils

+
produces carbondioxydes. Carbondioxyde molecules may generate H ions after
their reactions with water molecules. Rhizosphere soil acidification may also occur
+
by a massive excretion of H in exchange of various cations that are absorbed by
plant roots. Soil acidification is also intensified by by-products of industrialization
through acid rains and the spread of acid wastes. All of these acidification
processes may greatly affect the activity of soil enzymes.
Some workers reported the effects of soil acidification and alkalination on
soil enzymatic activities (Reddy et al., 1991; Salam et al., 1997a; 1997e; Salam et al.,
1998c). Salam et al. (1997c) observed a pattern in which the addition of Urea in
no-tillage soils caused lower pH in correlation with the decrease in soil acid
phosphatase. A plot of relationship between the activity of soil acid phosphatase
and soil pH of data reported by Salam et al. (1997c) is shown in Fig. 7.5. It is clear
from this plot that the activity of acid phsophatase is lowered by the decrease in
soil pH caused by long-term Urea treatment. The decrease of 0.75 pH unit lowered
-1 -1
the activity of soil acid phosphatase activity by 47 mg p-Nitrphenol g h or about
25%. This phenomenon clearly indicates the role of pH in controlling the acid
phosphatase activity.

200
Activity of Acid Phosphatase (mg p-Nitrophenol g -1 h -1 ) 160
180

140

120
R² = 0.3257
100 y = 42.975x - 44.609
4 4.5 5 5.5
Soil pH

Fig. 7.5. The effect of Urea driven acidification in no-tillage system on
the soil acid phosphatase activity.

Abdul Kadir Salam - 2014