Page 157 - Enzymes in Tropical Soils

Enzymes in Tropical Soils 145

shown by Fig. 9.12, in which the solubility of Cu originated from industrial waste
are decreased by the addition of lime and/or cassava leaf compost (Salam et al.,
1998a).
Bendfeldt et al. (2001) concluded from their 16 years research that organic
matter incoorporation into soils was good to improve the properties of abandoned
mine soils as long as the organic matter is long-lasting. Smolders et al. (2012)
reported that the toxicity of added Cu was significantly lower in amended soils
(with organic matters, sewage sludge, manure, and/or compost) than in control
soils. However, the decomposition of added or in-situ organic matters through
oxidation by soil microorganisms may eventually release the adsorbed heavy
metals in the future. A laboratory experiment by Stietiya and Wang (2010)
indicated that oxydation using dilute H 2 O 2 significantly decreased Cu and slightly
decreased Zn adsorbed by organic substances, but increased exchangeable Cu and
Zn. In general, organic matter oxydation increased the mobility and availabilities of
Cu and Zn, and gave no effect on Pb and As. However, Sukkariyah et al. (2005)
reported from their experiment that despite a significant reduction in organic
matter content 17 years after application, the DTPA extractable Cu and Zn
decreased by 58 and 42%, respectively.

Low Organic Matter
Heavy Metal Solubility

High Organic Matter

Low Lime High Lime

Fig. 9.11. The decrease in heavy metal solubility by lime and organic matters (Adapted
from Salam et al., 1998a; 1998f).

Abdul Kadir Salam - 2014