Which formula is applied to calculate gypsum requirement (meq/100 gm)?

• The correct formula to calculate gypsum requirement (GR) is:
GR = (ESP(initial) – ESP(final)) / 100 × CEC

• where:
-GR = Gypsum Requirement (meq/100g soil)
-ESP(initial) = Initial Exchangeable Sodium Percentage
-ESP(final) = Desired or Final Exchangeable Sodium Percentage
-CEC = Cation Exchange Capacity of the soil (meq/100g soil)
This formula is based on the principle that gypsum (calcium sulfate) provides calcium ions (Ca2+) which replace sodium ions (Na+) on the soil's exchange complex, thereby reducing ESP and improving soil structure.