Page 153 - Ilmu Tanah Book

140 The Chemistry and Fertility of Soils under Tropical Weeds

root absorption or leaching, the heavy metals in complexes, chelates, adsorbed
sites, or precipitates will be released to compensate the respective equilibrium
constants through equilibrium processes. On the other hand, if the concentrations
of free ionic heavy metals in soil water are high enough due to external addition
such as waste and fertilizer applications, parts of the free ionic heavy metals in soil
solution will be complexed, chelated, adsorbed, or precipitated, depending on the
pertaining conditions to reach new equilibrium values.

Wastes
Organics Plants
Fertilizers
Minerals
Pesticides
Adsorbed

Complexes Free Ions Chelates

Leaching
Precipitates

Fig. 8.1. The relationships between forms of heavy metals in the soil environment
(Adapted from Salam, 1997a; Salam, 2017).

2+
Cavallaro and McBride (1980) reports that the free ionic Cu concentration in
the soil system was greatly pH-dependent, but the concentration was below the
levels needed for the precipitation processes to occur. Abd-elfattah and Wada
2+ 2+ 2+ 2+ 2+ -7 -
(1981) also suggest that Zn , Pb , Cu , Co , and Cd at concentrations 10 to 10
2 -3 -2
M in 10 to 10 M CaCl 2 were not precipitated as hydroxides but were adsorbed
by cation-exchange sites. Salam and Helmke (1998) also report that the logarithmic
2+
of Cu concentration was linearly related to the soil pH and was controlled by
adsorption-desorption process (Fig. 8.2). The importance of each chemical

Abdul Kadir Salam and Nanik Sriyani – 2019