I almost never add fertilizer to my vegetable garden, relying almost solely on compost and occasional green manure. I have not noticed any deficiencies in the growing plants.
This year, however, two of my experiments involve using just compost as the growing medium. I will be growing carrots and potatoes in 12 inch deep wooden frames filled with compost. I would expect that the nutrients available to the carrots and potatoes would be limited, especially early in the growing season, since the compost in essentially sterile. To remedy this I will be adding green sand (for potassium), bone meal (for phosphorus) and blood meal (for nitrogen). My supplies are from Lee's Feeds.
The bags do not each provide the exact amount for 100 sq ft, although the bone meal does. I added the recommended amount of green sand and blood meal for 100 sq ft to the bag of bone meal and ended up with a mixture of about 34 cups (presumably 22 1/2 cups of bone meal - I didn't measure but relied on the bags statement that one pound was 2 1/4 cups - 6 2/3 cups of green sand and 4 1/2 cups of blood meal). Since this is the recommended amount for 100 sq ft then I would add the 34 cups to 100 sq ft. For the first carrot frame, which is 1.5 ft by 3.5 ft, or about 5 sq ft, I will add around 1.7 cups of the mixture.
We will see what happens.