Dynamics of Potassium Chloride Induced Manganese Release in Different Soil Orders
- G. S. R. Krishnamurti and
- P. M. Huang
The salt-induced Mn release from soils has been known for more than two decades; its kinetics and mechanism still remain obscure. Manganese release from selected soils of different taxonomic orders was studied as a function of the concentration of KCl (0, 0.01, 0.1, and 1.0 M), reaction period (0–216 h), and temperature (277, 298, and 317 K) to understand the influence of KCl on the dynamics of the release of soil Mn. The soils were sampled from six countries located in temperate and subtropical regions. Total Mn contents of the soils varied from 2.9 to 32.5 mmol kg−1; Mn was generally concentrated in the <2-µm size fractions. At the end of a 24-h reaction period at 298 K, Mn release increased consistently by 12 to 161 times as the concentration of KCl increased from 0 to 1.0 M. The amount of Mn released from the calcareous Vertisols by 1 M KCl was very low (12–20 µmol kg−1) during the reaction period of 0 to 24 h, even though the total Mn content was among the highest (25.1–32.5 mmol kg−1). Manganese release from selected soils, an Oxisol (Pakua), two Alfisols (Hyderabad and Waitville), and a Mollisol (Oxbow Orthic) by 1 M KCl followed parabolic diffusion kinetics. The activation energy of Mn release, calculated from the overall diffusion coefficients, varied from 10.9 to 16.5 kJ mol−1 among the soils, indicating diffusion as the predominant process in limiting the rate of Mn release. Ionic-strength effect coupled with complexation was mainly responsible for the enhanced Mn release by KCl from the soils in the common soil pH range.
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