Page 20 - Enzymes in Tropical Soils

8 Enzymes In Tropical Soils

2-
2+
CaSO 4 (s)  Ca + SO 4 ....... Eq. 1.3

Table 1.2. Some free ions and their complex ions in the soil – water system.
Cations In Acid Soils In Alkaline Soils
+
+
0
+
Na Na Na , NaHCO 3 , NaSO 4 -
+
+
+
K K K , KSO 4 -
0
2+
0
0
2+
2+
Mg Mg , MgSO 4 , Org* (Ex. Fulvic Cu) Mg , MgSO 4 , MgCO 3
0
2+
0
+
+
2+
2+
0
Fe Fe , FeSO 4 , FeH 2 PO 4 FeCO 3 , Fe , FeHCO 3 , FeSO 4
0
2+
2+
+
Cu Org*, Cu CuCO 3 , Org*, CuB(OH) 4 ,
0
CuB[(OH) 4 ] 4
2+
0
+
0
2+
2+
Ca Ca , CaSO 4 , Org* Ca , CaSO 4 , CaHCO 3
2+
2-
2-
Cr CrO 4 CrO 4
2+ 2+ 0 + 2+ + 0 +
Cd Cd , CdSO 4 , CdCl Cd , CdCl , CdSO 4 , CdHCO 3
0
0
4+
Si Si(OH) 4 Si(OH) 4
* Fulvic; Adapted from Sposito (1989)

Table 1.3. Composition of free and complex ions in
soil water* (Salam, 2012).

MAJOR ELEMENTS HEAVY METALS
2+
2+
+
2+
2+
+
2+
2+
2+
Forms Na , K , Ca , Mg Cu , Cd , Zn , Fe , Co
2+
Composition 70 - 90% of total soluble Zn 40% of Zn T
2+
in Soil-Water Cu 2% of Cu T
*Elliz and Knezek (1982); Zn T = Total Dissolved Zn; Cu T = Total Dissoved
Cu

2-
2+
In the soil water system, CaSO 4 will dissolve and produce Ca and SO 4 . As long as
2-
2+
the solubility product, which is [Ca ][SO 4 ], is lower than K sp , this compound will
2+ 2-
always dissolve to form Ca and SO 4 ions. However, whenever, because of one
2+ 2-
reason or another, the solubility product raises up higher than K sp , Ca and SO 4
will combine to form complexes and/or precipitates. Because in the soil water
2+ 2-
system Ca and SO 4 are always decreased by plant root absorption, the
2+
probability is that CaSO 4 will continue to dissolve to satisfy the decrease in Ca and
Abdul Kadir Salam - 2014