Question

what is a common use of limestone in agriculture

Answer 1

The information that you need is here:
http://en.wikipedia.org/wiki/Agricultural_lime

Answer 2

simple .it increases the pH of acidic soil (the higher the pH the less acidic the soil); in other words, soil acidity is reduced and alkalinity increased
it provides a source of calcium and magnesium for plants
it permits improved water penetration for acidic soils
it improves the uptake of major plant nutrients (nitrogen, phosphorus, and potassium) of plants growing on acid soils........................ and it is as well used in fertilizers .. a medal please/.