Alkali
In chemistry, an alkali (; from Arabic: "al-qaly" "ashes of the saltwort") is a basic, ionic salt of an alkali metal or alkaline earth metal chemical element. An alkali also can be defined as a base that dissolves in water. A solution of a soluble base has a pH greater than 7.0. The adjective alkaline is commonly, and alkalescent less often, used in English as a synonym for basic, especially for bases soluble in water. This broad use of the term is likely to have come about because alkalis were the first bases known to obey the Arrhenius definition of a base, and they are still among the most common bases.
Alkali soil
Calcium Chloride is also used to reclaim alkali soils. CaCl converts NaCO into NaCl precipitating CaCO. NaCl is drained off by leaching water. Spent acid (HCl, HSO, etc.) can also be used to reduce the excess NaCO in the soil/water.
Where urea is made available cheaply to farmers, it is also used to reduce the soil alkalinity / salinity primarily. The NH (Ammonium) present in urea which is a weak cation releases the strong cation Na from the soil structure into water. Thus alkali soils absorb / consume more urea compared to other soils.