Ionic Equilibria in Submerged Paddy Soils—The Iron Hydroxide Systems

To obtain a preliminary knowledge of the dominant solid phase of iron controlling its availability in submerged soils, Habbelkher loam, Saleempur sandy loam and Heir loam were kept submerged in earthen pots in the greenhouse. The soil solutions were drawn anaerobically by gravity and analysed fortnightly for pE, pH and major cations. In spite of wide variations in pH, pE and the concentration of Fe²⁺ in the soil solutions, the values of the expressions, pE−pFe²⁺ + 3pH, pE−1.5pFe²⁺ + 4 pH and pE + pH were constant and close to the theoretical values of 17.87, 23.27 and 33, respectively, indicating that Fe (OH)₃−Fe²⁺, Fe₃(OH)₃− Fe²⁺ and Fe₃(OH)_$$$-−Fe(OH)_$$$ systems controlled the solubility of Fe²⁺.