Understanding the role of limestone in soil acidity management

Many Texas soils are acidic, and this is certainly true of almost all of the soil found within the east Texas land for sale you might be seeing on the market (or that you recently purchased). If you remember some of the basics from your high school chemistry class, you probably can recall that acidic soils have a pH amounting to anything less than 7.0. Anything 7.01 and beyond is considered basic - and no, I don't mean what your teenage son or daughter may have used to describe a stuck-up kid in one of their classes. In this context, pH constitutes the measure of hydrogen ion concentration in the soil.

Soil acidity is caused by various environmental, climatic and cultural factors. The most common of these are as follows:

  • First is the parent material from which the soil is derived - the rocky subsoil that's permeated by acid and gets the entire process started.
  • Rainfall or irrigation that causes leaching - removing basic elements such as calcium, magnesium and sodium from the soil profile - also increases acidity by leaving behind hydrogen, aluminum and manganese.
  • Lastly, cultural practices such as nitrogen fertilization, the removal of harvested crops and associated basic elements, and soil erosion, all of which engender the removal of basic elements, further contribute to acidity.
Understanding the role of limestone in soil acidity managementExcess acidity can be significantly detrimental to the quality of your soil.

We care about soil acidity because of the way it affects plants and their growth. Some plants thrive in acidic soils, while others cannot tolerate acid and will prefer a basic environment. As a result, it is important to understand which species are more sensitive to soil acidity. To reduce soil acidity and help neutralize its negative effects, you can add natural limestone, in a fine granular or powder form.

Limestone is primarily composed of calcium carbonate, but many contain small amounts of clay, silt and dolomite. Dolomitic limestones come from natural deposits filled with both calcium and magnesium carbonates. The magnesium content of limestone is especially important if soils are deficient in this essential plant nutrient. If a soil test indicates low magnesium, dolomitic limestone can be used to correct the deficiency and properly adjust pH. In a nutshell, the addition of limestone is done primarily to reduce acidity but may also provide some nutrient value!

Not all limestone is created equal. The mineral's properties vary considerably from piece to piece, and these differences influence its 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, of 100 percent. When you purchase any limestone product, you should always look for the CCE.

All other liming materials are compared with the 100 percent standard. The CCE of commercial limestone products should be available through the vendor. The bulk portions of agricultural limestone used in hay meadows and pastures for years in Angelina County were somewhere around 65 percent CCE. By contrast, the "super fine lime" that's more frequently used these days is closer to 90 percent CCE.

For those looking to buy land in Texas and start a farming operation of any size, it's important to remember the following: At a pH below 5.5, the concentration of soluble aluminum increases and becomes toxic to plant root growth. Furthermore, optimum nutrient uptake by most crops occurs at a level of low acidity close to 7.0. In a perfect world, you would want soil pH to be 6.5 on the dot, but if you're off either way by a decimal point or two, it shouldn't be a big deal - just be mindful of the issue.

I hope I've convinced you of the need for limestone, but the question likely remains: "Just how much should I apply on my garden, lawn or pasture?" Well, I must say that I can't speak to specific needs of your lawn without any data handy, but I know how you can easily find out for yourself!

For specific determinations, you'll need a soil test to be conducted. For just $13, you can find out your soil's exact pH, the amount of limestone needed (if any) and the presence of nutrients such as nitrogen, phosphorus, and potassium, calcium, magnesium, and sulfur. Remember that soil pH fluctuates during the year, becoming lowest in the fall. With that in mind, be sure to take a soil sample several months before you plan to begin crop growth, to provide time for pH adjustment.

Cary Sims is the County Extension Agent for agriculture and natural resources for Angelina County. Contact him via phone (936-634-6414, ext. 0) email (cw-sims@tamu.edu).

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