Your Lawn & Lime
The ideal soil pH is slightly acidic, between 6.0 and 7.0. When the soil pH drops below 6.0 (becomes more acidic), certain nutrients needed for proper grass growth, such as nitrogen, phosphorus, potassium, and calcium, become unavailable to certain nutrients for proper growth and other plants. Lime can be applied to the soil to help increase the soil pH above 6.0.
However, unless you have a soil test done by a professional soil lab, don't bother applying lime to your lawn. A soil test kit or pH probe available at your local garden center will tell you your soil's pH, but will not tell you how much lime is needed to correct the problem. The amount of lime needed to correct the soil pH is dependent on soil type (how much sand and/or clay is present in the soil). Results from a professional soil lab will tell you how much lime to apply to your soil as pounds of pure calcium carbonate.