Lime
The lime you apply to a lawn is limestone or chalk. The main component is calcium carbonate. Lime with a high calcium content is referred to as calcitic lime and has the added benefit of adding calcium to the soil. Some limestone contains a significant amount of magnesium and is referred to as dolomitic lime. Dolomitic lime adds magnesium to the soil and could be used if soil tests indicate a magnesium deficiency.
The need to lime will be determined by soil tests. Working towards an ideal pH level will help bring the soil into balance and allow for optimum nutrient uptake.