EXTRACTION OF MANGANESE FROM SOILS WITH POTASSIUM-SALTS

Application of KCI usually increases the solubility of soil Mn and its bioavailability, yet the mechanisms of the phenomenon are not fully u nderstood. The purpose of this study was to investigate the effects of KCI and salts such as KBr, KI, KNO3, K2SO4, K2CO3, K2HPO4, KH2PO4, Ca (NO3)(2), Ca diethylenetriamine pentaacetic acid, and Cu(NO3)(2) on th e amount of Mn extracted from soils as affected by ionic strength, aci dity of soil or extractant, and extraction time. The formation of anio nic complexes of Mn and CI in aqueous solution, using cation-anion-exc hange resins, was also investigated, Amounts of Mn extracted by KCI fr om soils increased with increases in ionic strength and extraction tim e but decreased with increases in pH. The salts usually extracted more Mn from the noncalcareous than from the calcareous soils. The KI was capable of reducing MnO2 at normal soil pH, whereas Mn extracted by KC I was similar to Mn extracted by other neutral salts, The KCI-extracta ble Mn was highly correlated with readily soluble [Ca(NO3)(2)-extracta ble] Mn and weakly adsorbed (CaDTPA-extractable) Mn fractions, but not to the specifically adsorbed [Cu(NO3)(2)-extractable] Mn fraction. Th e Mn2+ in KCl solutions was shown to form anionic Mn-CI complexes. The se complexes, along with ionic strength effects, were most likely resp onsible for the increases in solubility of soil Mn.