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Extraction of Manganese from Soils with Potassium Salts

Dep. of Soil Science, Univ. of Manitoba, Winnipeg, MB, Canada R3T 2N2

*Corresponding author (racz{at}bldgagric.lanl.umanitoba.ca).

ABSTRACT

Application of KCl usually increases the solubility of soil Mn and its bioavailability, yet the mechanisms of the phenomenon are not fully understood. The purpose of this study was to investigate the effects of KCl and salts such as KBr, KI, KNO₃, K₂SO₄, K₂CO₃, K₂HPO₄, KH₂PO₄, Ca(NO₃)₂, Ca diethylenetriamine pentaacetic acid, and Cu(NO₃)₂ on the amount of Mn extracted from soils as affected by ionic strength, acidity of soil or extractant, and extraction time. The formation of anionic complexes of Mn and Cl in aqueous solution, using cation-anion-exchange resins, was also investigated. Amounts of Mn extracted by KCl from soils increased with increases in ionic strength and extraction time 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 KCl was similar to Mn extracted by other neutral salts. The KCl-extractable Mn was highly correlated with readily soluble [Ca(NO₃)₂-extractable] Mn and weakly adsorbed (CaDTPA-extractable) Mn fractions, but not to the specifically adsorbed [Cu(NO₃)₂-extractable] Mn fraction. The Mn²⁺ in KCl solutions was shown to form anionic Mn-Cl complexes. These complexes, along with ionic strength effects, were most likely responsible for the increases in solubility of soil Mn.

Received for publication March 25, 1994.