Page 136 - Enzymes in Tropical Soils

124 Enzymes In Tropical Soils

effectiveness of salt inhibition followed the following order: NaCl > CaCl 2 > Na 2 SO 4 .
According to Frankenberger and Bingham (1982) the inhibiting effect of salinity was
probably attributed to the osmotic dessication of the microbial cells releasing
intracelluar enzymes which become vulnerable to soil protease attacks.

40

35
(mg Formazan g -1 h -1 ) 20 Na-Sulfate
30
Activity 25

Ca- Chloride
15
10
5 Na-Chloride

0
0 4 8 12 16 20 24
o
-1
EC (mmho cm at 25 C)

Fig. 8.3. The effect of salinity on soil dehydrogenase activity
(Redrawn from Frankenberger and Bingham, 1982).

One other group of elements influencing the soil enzymatic activities is
heavy metals. Heavy metals are special because this group of elements are
currently present at increasing concentrations in the soil environment mostly due
to industrial contamination. Heavy metals are accumulated not only from non-
agricultural sources such as factories, metal industries and mines, transportation,
etc., but also from agricultural sources such as fertilizers, insecticides, fungicides,
and herbicides. A great deal or researches found that increasing heavy metal
concentrations in soils in general lowered the activity of soil enzymes (Juma and
Tabatabai, 1997; Mathur and Sanderson, 1980; Mathur et al., 1980; Stroo and
Jencks, 1982; Dick and Tabatabai,1983; Stott et al., 1985; Reddy and Faza, 1989;
Reddy et al., 1987; Park et al., 1992; Sakai and Tadano, 1993; Joshi et al., 1993;
Salam et al., 1997a; 1997e; 1997f; 1997n; Salam et al., 1999h).

Abdul Kadir Salam - 2014