Psalm 72

With the closing of this psalm is the note indicating the end of David's prayers. The location of this message at the end of this psalm is confusing. What I find most interesting to the statement that at least this psalm was noted as a prayer. I could see the reference of this and most psalms as songs. Though I recognize the elements of prayer in this psalm I would still not mark it as a prayer. So now I'm wondering how many of these psalms should be viewed as prayers rather than songs?
Stuart