An alkali soil must have pH value of

An alkali soil must have a pH value of above 8.5.
Alkali soils are clay soils with high pH, a poor soil structure, and a low infiltration capacity. They also have a hard calcareous layer at 0.5 to 1 metre depth.
Alkali soils owe their unfavorable physio-chemical properties mainly to the dominating presence of sodium carbonate, which causes the soil to swell and is difficult to settle.