Page 135 - Enzymes in Tropical Soils

Enzymes in Tropical Soils 123

However, different from that of organic P, the decomposition of organic S
can be fastened by two methods. The first is by decreasing the concentration of
2-
2-
SO 4 and the second is by increasing the soil pH (Eq. 4.5). The decrease in SO 4
concentration may happen through: (1) plant-root absorption and (b) leaching.
Increasing soil pH can be done for example by liming. Liming may produce OH -
+
ions that neutralize H ions.

Pri.Mineral Sec. Mineral Organic-P
Weathering

H 3PO 4

More Acid - Decomposition
H sPO 4
More Alkaline HPO 4 + Phosphatase
s-

3- Phosphatase
PO 4
Producers

Fig. 8.2. The suggested inhibition of soil Organic P transformation
to inorganic P.

8.4 Effects of Other Elements on the Activities of Soil
Enzymes

Some other inorganic elements other than P and S may also affect the
activity of soil enzymes. One most important variable affecting the soil enzymatic
activities is the electrical conductivity (EC). Frankenberger and Bingham (1982)
reported that increasing EC inhibited the soil enzymatic activities of amidase,
urease, acid phosphatase, alkaline phosphatase, inorganic pyrophosphatase,
arylsulfatase, rhodanase, -glucosidase, -galactosidase, dehydrogenase, and
catalase. Dehydrogenase was the most severely inhibited by EC (Fig. 8.3) and
hydrolases showed a much lesser inhibition effect. For the same level of EC, the

Abdul Kadir Salam - 2014