RE: well i got it back!
Like everyone said 5.1 is quite acidic. Haystack is on the right track except every pointon the pH Scaleis 10 times less or more acidic than the previous/next number.
For Example-
5.0pH is 10 times more acidic than 6.0pH and 5.0 pH is 100times more acidic than 7.0pH
(at least your pH wasn't 4.1!)
The soil test should have have told you How many units of Calcium Carbonate. Rest assured -its a lot. In fact most places suggest to not try to correct the pH all in one year - if its a serious amount.Some of my plots in the low 5's were suggested 8 tons/acreAg Lime.
3-4 tons/acre might only get you up close to 6.0ph (Depends on the Buffer - Light soils pH correct easier (less lime) than Heavy Soils (more lime) - If you soil is clay-like - clumps, holds moisture well, - you'll probably want to spread it out over two or more years. If its sand like - you can probably correct it with One Application).
Good luck -
FH