Netix, it doesn't have to be broad beans - any type of legume plant will do the same thing and it's only of benefit if your soil is deficient in nitrogen anyway. It would probably be a good idea to buy yourself a little soil PH test kit before you start planting anything so you know what acidity your soil it and you know what to plant that will suit it or what you need to do to fix it because some will prefer acid soil, some alkaline and others neutral.