Sodic soils swelling

Hydration swelling, 108-115 Layer charge and CEC, 113-115 Structure, 111 Sodic soils, 407 Dispersion, 414 Exchangeable Na+, 409, 412 Toxicity to plants, 407-408 Sodium, 411... 

Remediation of sodic soil is far more difficult than reclaiming a saline soil. The condition of sodicity (ESP > 15%) requires the addition of calcium amendments, time for them to react with the soil, and percolation of water through the soil to remove excess sodium. Whether or not this can even be done depends on the degree of dispersion and swelling. 

Sodium Adsorption Ratio. Because of the swelling effects of Na+, the relative amount of sodium (sodicity) in the water quality especially in the irrigation water quality is an important measurement in soil science. Decreased permeability can interfer with the drainage required for normal salinity control and with the normal water supply and aeration required for plant growth. The relative sodium status of irrigation waters and soil solutions is often expressed by the sodium adsorption ratio (SAR)... 

Studies on soils have shown that there is a nexus between saturated permeability [zero suction], sodicity and electrolyte concentration.The concentration, obtained by diluting the electrolyte, at which there is a first discernible decrease in permeability, called the threshold concentration, corresponds to the start of the swelling of the day domains. 

The increase of soil volume from clay swelling in the field has important practical consequences, particularly in soils containing smectites. The extent of this problem depends very much on the nature of the exchange cation, as illustrated by the swelling volumes of smectites reported in Table 8.3. These results emphasize the management problems likely to be encountered with soils that are sodic. 

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