Equivalent Acidity:The amount of CaCO3 required to neutralise  the acid residues caused by acidic fertilizers in the soil e.g:100kg(NH4)2SO4 produces acidity which needs 110kg of CaCO3 to neutralise it.Therefore equivalent acidity of(NH4)2SO4 is 110;Anhydrous NH3 has more equivalent acidity than other fertilizers.

Equivalent Basicity: Residual basicity caused by application of basic fertilizers ,expressed in terms of CaCO3 equivalent of basic residues left by a fertilizer material(in kg/100g of fertilizer salt).

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