Answer: The amount to use would depend on the pH change you are trying to achieve. In general, it is best to make the change gradually to avoid shocking the lawn and trees. The amount to apply depends greatly on the type of soil you have. Your county extension should be able to help you develop a long term schedule. The pelletized lime is cleaner to apply but the powder gives a more even coverage and is less expensive; which to use is a matter of personal preference.
There are other reasons why a lawn may be mossy, besides a pH problem. Excess shade precluding grass growth, overall lack of fertility, poor drainage, excess compaction and so on can all contribute to moss growth in a lawn. You may want to trouble shoot this with your county extension as well.
Q&A Library Searching Tips