Chemical kinetics under controlled redox potentials of some inorganic constituents of Bang Pakong [acid sulfate] soil upon the plant behavior
1985
Jiraval Pechayapisit
The results showed that rice plants died 2 days after transplanting on all of the untreated Bang Pakong soil regardless of the moisture condition, while in case of leached and limed soil, rice plants survived for 10 days after transplanting. The chemical analyses revealed the high concentration of electrolyte (7.5 mmho/cm) and very low pH (2.6) for the untreated Bang Pakong soil. In case of leached and limed soil, although some of the salt content was removed by leaching thus, it was too high for the normal growth of the rice plants thus symptoms of salt injury and iron toxicity at the later stage were shown and died eventually. The reduction of the soil was hastened by organic matter incorporation. The pH of the treated soil was brought about 6.5 by 0.4N NaoH addition at 80 days incubation. The soil was monitored to be reduced further to -5, -55, -105 and 145 mv Eh respectively. At each Eh level, free sulfide and acid soluble sulfide were trapped by 1% CdC12 solution, and the resulting Cds was determined. The results showed that acid soluble sulfide were first detected at Eh of -55 mv and increased markedly at Eh -145 mv indicating that sulfate reduction began at about -55 mv Eh and increased greatly upon further reduction. The extractable sulfate showed the reversing trend at the corresponding Eh value. Water soluble sulfate showed a slight decrease meanwhile the free sulfide was undetected as the Eh decrease from -5 to -145 mv
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