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This article in SSSAJ

  1. Vol. 44 No. 1, p. 41-45
     
    Received: June 25, 1979
    Published: Jan, 1980


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doi:10.2136/sssaj1980.03615995004400010010x

The Chemistry of the Reclamation of Sodic Soils with Gypsum and Lime1

  1. J. D. Oster and
  2. H. Frenkel2

Abstract

Abstract

Sodic soil reclamation was theoretically evaluated assuming equilibrium chemistry and piston movement of soil solution. The effective solubility of gypsum when mixed with a sodic soil is increased because the exchange phase acts as a sink for Ca2+ until both the gypsum dissolution and exchange reactions reach equilibrium. The electrical conductivity of a soil solution in equilibrium with both gypsum and an exchangeable sodium fraction (ENa) of 0.0 and 0.43 is 2.3 and 14 dS m−1. Thus, mixing gypsum into the soil hastens reclamation and provides higher solution concentrations for the maintenance or improvement of the soil hydraulic conductivity. The amount of gypsum dissolved, expressed in moles of charge (equivalents), is a linear function of the moles of exchangeable Na+ replaced; r2 values typically exceeded 0.98. The slope of the regression line decreased with increasing final ENa. Typical values were 1.40, 1.27, and 1.20 moles of charge gypsum dissolved per mole of exchangeable sodium replaced at final ENa's of 0.05, 0.10, and 0.15. The inclusion of lime equilibrium reduces these slopes by 3, 6, and 9% for PCO2's of 1, 4, and 10 kPa (1, 4, and 10% CO2). Gypsum requirements for calcareous, sodic soils based on quantitative replacement of exchangeable sodium should be increased by factors of 1.3 to 1.1 depending on the desired final levels of exchangeable sodium.

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