Many of our surrounding soils are acid soils and certainly almost all East Texas soils are acidic.  If you remember your basic chemistry class from high school, acidic soils have a soil pH that is less than 7.0. More technically, acidic pH is a measure of hydrogen ion (H+) concentration in the soil solution.

Soil acidity is caused by various environmental, climatic, and cultural factors. The most common of these factors are the following three factors. First is the parent material from which the soil is derived. The rocky subsoil gets the entire process started.

Second is leaching by rainfall or irrigation which removes some elements and leaves others that contribute to the soil’s pH level. Interestingly, rainfall is about 5.6. Researching the internet, you’ll find some variability from 5.0 to a neutral 7.0, but most agree on 5.6. 

Lastly, cultural practices such as nitrogen fertilization, removal of harvested crops and associated basic elements, and soil erosion, which results in a loss of basic elements.

Digging further into some chemistry, a low (acidic) pH measurement indicates that there is an excess of H+ ions and a high (basic) pH is the presence of -OH anions. To correct low/acidic soil pH, the acidity must be neutralized. Ground limestone is a smart choice for this. Lime is typically made from crushed limestone and is primarily composed of calcium carbonate. The addition of lime is important as it is the carbonate ions that neutralize the soil acidity.ac

So while the addition of lime is done primarily to reduce acidity, it can also provide some nutrients- primarily calcium, and in some scenarios, magnesium. 

Limestone man contains small amounts of clay, silt, and dolomite. Dolomitic limestones come from natural deposits which contain both calcium and magnesium carbonates. The magnesium content of limestone is especially important where soils are deficient in this essential plant nutrient. If a soil test indicates low magnesium, dolomitic limestone can be used to correct both the magnesium nutrient deficiency and pH.

The biggest value of limestone is in its ability to neutralize soil acidity. It’s an often-forgotten fact that all limestone is not created equal.  Limestone’s properties differ considerably, and these differences influence the limestone’s ability to neutralize soil acidity. 

Its effectiveness depends on the purity of the liming material and how finely it is ground. Pure limestone has a calcium carbonate equivalence (CCE), or neutralizing value, set at 100%. When you purchase any limestone product, you should always look for the CCE.  

All other liming materials are compared with this standard and buyers should look for this percentage. The CCE of commercial liming products should be available through the retailer. The bulk agricultural lime that we’ve used in hay meadows and pastures for years in Angelina County was somewhere around 65% CCE. Recently, the more frequently used “super fine lime” is up closer to 90% CCE.

Yet with your knowledge of the need for lime, the question remains, “just how much should I put on my garden, lawn, or pasture?” 

For an accurate recommendation you’ll need a soil test. For a $15 test from a university soil lab, you’ll find out your pH, the amount of limestone needed (if any), and the availability of nutrients such as nitrogen, phosphorus, and potassium, calcium, magnesium, and sulfur.

The time to take a soil sample is long before you need it.  Ideally, several months in advance of crop growth provide time for pH adjustment. Fall is a great time to test and apply lime.