Published online by Cambridge University Press: 27 March 2009
A pot experiment studied the effect of gypsum and green manuring on equilibrium soil solution pH, pE, Mn concentration and Mn equilibrium in three sodic soils. Submergence decreased soil solution pH and increased Mn concentration in all the soils. Addition of gypsum with green manure further decreased soil solution pH and increased Mn concentration. Maximum Mn concentration in all the treatments was observed at 4 weeks of submergence in Kaheru soil and at 6 weeks of submergence in Jagjitpur and Langrian soil followed by a decline up to 12 weeks. In spite of wide variations in pH, pE and Mn concentration in soil solutions, the solubility of Mn after peak values appeared to be mainly controlled by the MnC03-Mn2+ system irrespective of the treatments, and the Mn2O3-Mn3O4 system appeared to operate after 2 weeks of submergence in the control and gypsum-treated soils.