Forage Management: Why Soil pH and Lime Matter in Tennessee Forage Systems

By Dr. Bruno Pedreira

One of the best sights in April is seeing tall fescue green and growing across Tennessee. This is also a great time to assess your pastures and decide if any areas need renovation. If so, start with a soil test to identify nutrient gaps and check soil pH.

Soil pH is a key indicator of the chemical environment in the soil, influencing nutrient availability. Many soil test reports show pH levels between 4.7 and 5.3, which is below the optimal for our forages. Liming acidic soil is essential because most nutrients become more available when soil pH is between 6.0 and 7.0. Thus, this is the recommended range for common Tennessee forages like tall fescue, orchardgrass, crabgrass, and sudangrass. If you’re growing legumes, such as alfalfa or clovers, keeping the pH above 6.5 is even more important to support their growth.

One thing to remember: changing soil pH takes time. Lime needs moisture (rainfall) and from three months to a year to fully react in the soil. If your soil test shows low pH, apply lime as soon as possible. If you’re planning to renovate a pasture this fall (which is the best time to plant cool-season forages like tall fescue and orchardgrass), applying lime now will improve soil conditions in time for seeding. By September, soil pH will have increased enough to create a better environment for seedling establishment.

When checking your soil test report, pay attention to the lime recommendation. At the University of Tennessee’s Soil, Plant, and Pest Center, lime recommendations are based on 65% Relative Neutralization Value (RNV), which is the average for Tennessee. However, not all lime products have the same RNV. Some farmers have applied lime but didn’t see the expected pH increase, often because the lime had a lower RNV. Always ask for the RNV when purchasing lime and adjust your application accordingly. For example, if your soil test recommends 2 tons per acre of lime at 65% RNV, but you buy lime with 50% RNV, you’ll need to apply 2.6 tons to achieve the same effect (2 * 0.65 ÷ 0.50).

Lastly, be cautious about liquid calcium products. Some companies are marketing liquid calcium (sometimes called liquid lime) as a quick fix, but research trials carried out by my forage colleagues at the University of Kentucky have shown that these products do not increase soil pH. Agricultural lime is still the only proven way to correct soil acidity.

So, let’s stick to the basics: test your soil, apply the right amount of lime, and set your pastures up for success. A well-managed pH will keep your forage systems green and healthy for the seasons ahead!