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Effect of salt, alkali and zinc on iron equilibrium in submerged soils
Published online by Cambridge University Press: 27 March 2009
Abstract
In a pot experiment the effect of salt (EC 5, 10 and 20mmhos/cm at 25 °C), alkali (ESP 10, 20 and 40) and Zn (lOmgZn/kg soil) on Fe equilibria in submerged soils was studied. The required salt and alkali concentrations were obtained by adding calculated amounts of NaCl and NaHCO3 respectively to Rohi sandy loam (Typic Ustifluvent). The soil solutions drawn anoxically by gravity were analysed for pH, pE, EC and Fe. As the EC increased, pH and pE of the soil solution decreased and Fe concentration increased at all the stages of submergence. ESP had the opposite effect. Addition of ZnSO4 in combination with EC and ESP treatments further decreased pH and pE and increased Fe concentration; however, its effect was more pronounced in the former treatments. In spite of wide variation in pH, pE and Fe concentration in soil solution, the values of the expressions pE – pFe2+ + 3pH, pE – 1·5 pFe2+ + 4 pH and pE + pH were nearly constant and close to the standard values of 17·9, 23·3 and 7·3 for Fe(OH)3 – Fe2+, Fe3(OH)8 – Fe2+ and Fe(OH)3 – Fe3(OH)8 systems after 1, 14 and 14 days of submergence, respectively. Addition of ZnSO4 did not have an appreciable effect on these systems in salt- and alkalitreated soils.
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