Influence of Salt and Alkali on Ionic Equilibria in Submerged Soils

To clarify the effects of salt and alkali on Fe 2+ and Mn 2+ equilibria in submerged soils, Maahas clay (a Haplustalf) was amended with NaCl and NaHCO 3 to give initial electrical conductivities of 5, 10, 20, and 25 mmhos/cm at 25°C and exchangeable Na percentages of 5, 10, 15, 20, and 25, respectively. The amended soils and an untreated control were kept submerged in 16‐liter pots in a greenhouse at 25–30°C. The soil solutions, drawn anoxically by gravity, were analyzed fortnightly for Eh, pH, CO 2 , and the major ions. As the salt level increased, pH decreased and the concentrations of all cations increased. As alkalinity increased, the concentrations of all cations except K + and Na + decreased. In spite of wide variations in pH, Eh, ionic strength, and the concentrations of Fe 2+ and Mn 2+ in the soil solutions, the values of the expressions, pE − pFe 2+ + 3 pH, pE − 1.5 pFe 2+ + 4 pH, pE + pH, and pH − 0.5 pMn 2+ − 0.5 pCO 2 were nearly equal to 17.9, 23.3, 7.3, and 4.1, respectively, indicating that even in the salt and alkali treated soils, the Fe(OH) 3 ‐Fe 2+ and Fe 3 (OH) 8 ‐Fe 2+ systems controlled the solubility of Fe 2+ while the MnCO 3 ‐H 2 O‐CO 2 system regulated the solubility of Mn 2+ .