You need one ton of lime per acre to raise the PH one point.
It's a logarithmic calculation, so a ph of 5 is ten times more acidic than a PH of 6.

If you can work the lime in to the soil 6-8 inches (think root zone) then you will be better off. It will take 6 months to get the soil to integrate the lime in to its composition. Lime helps the plant uptake nutrients and make them available for the plants.

Iron clay peas if I am not mistaken only require a PH of 5.5 to 6. so if you were at 4.7 you need one tone per acre to bring it to 5.7, which should be good for IC peas.