Good example of why Biologists go broke Farming. What a moron...

Where are your plants roots going to be at maturity? That is the zone that needs to have the proper pH.

Lime is water soluble...so over time it will leach into deeper areas of the soil so NO you dont have to put it 20 inches deep but this is pure garbage to leave it on top and not work it in...working in just a little bit will actually speed the process of making a difference.