My soil is naturally acid (pH typically 6.0 to 6.5 mostly the low end), so lime is a necessity. Soil pH greatly affects a plant's ability to take up various nutrients. The ideal pH is different for each nutrient but the "sweet spot" that is acceptable for most nutrients is between about pH 6.7 to 7.2.
The best strategy is to sample the top 8 inches or so in your plot in a number of places, thoroughly mix in a bucket, and send a fist-sized sample of that to a soil lab. They can tell you about pH but also provide much more information about your soil. They can tell you how much lime to add per area of soil. I normally add dolomitic lime which includes magnesium (from mineral dolomite).