Hi
Before you go to the expense of buying fertiliser, you should get a soil analysis - from a few different parts of the land.
This will tell you the pH of the soil and give you an idea of the levels of the various important chemicals such as potassium (K) and phosphorus (P). Depending on the results you may need to increase the pH (by liming) and/or improve the K & P levels by adding the right sort of fertiliser.
If your pH is too low, adding fertiliser is a waste of time and money as it will not be properly utilised by the soil, so you should lime first and then add the fertiliser later.
We do this in the spring, before the grass starts to grow. Up here, we used Scotgrain Agriculture for the soil analysis, and then used them to buy the lime and arrange for the spreader - can't use an ordinary fertie spreader for lime. The fertie we get in 600kg sacks from a large commercial farmer friend - he buys in bulk for his own holding and is happy to add a few bags onto his order for us - much cheaper than buying elsewhere.
Hope this helps
Sue