Since lime can only affect pH of soil that it contacts, it's better to disk it in. It will eventually do the same thing though if you don't. In some cases, such as liming a pasture, you can't disk it in or you would kill the pasture so you have to just broadcast and let the rain wash it into the ground. For a food plot though, if you are disking anyway, why not wait and put the lime out 1st.