Saline and sodic (alkali) soils can significantly reduce the value and productivity of affected land. By estimation, slightly more than one-fourth of irrigated farmland in the United States is affected by soil salinity. Ions most commonly associated with soil salinity include the anions chloride (Cl– ), sulfate (SO4 = ), carbonate (HCO3 – ), and sometimes nitrate (NO3 – ) and the cations sodium (Na+ ), calcium (Ca++), magnesium (Mg++), and sometimes potassium (K+). Crops differ in ability to tolerate salt accumulation in soils, but if levels are high enough (more than 16 mS/ cm), only tolerant plants will survive. As salts accumulate in soil, the soil solution osmotic pressure increases. Reclamation of sodic soils is different; excess sodium must first be replaced by another cation and then leached. Sodic soils are treated by replacing the sodium with calcium from a soluble source.