Shaniqua Davis

Shaniqua Davis

Many Texas soils are acid soils and certainly, almost all East Texas soils are acidic. Acidic soils have a soil pH that is less than 7.0.

Soil acidity is caused by various environmental, climatic and cultural factors. The most common of these 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 that removes basic elements such as calcium, magnesium and sodium from the soil profile leaving acidic hydrogen, aluminum and manganese.

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.

We care about soil acidity because of the way it affects plants and their growth. Some plants thrive in acidic soils and others cannot tolerate and will prefer a basic soil.

Since plants are more sensitive to acid soil conditions than others, it is important to understand which species are more sensitive to soil acidity. And to reduce soil acidity and help neutralize soil acidity, we add the natural stone limestone in a fine granular or powder form.

Limestone is primarily composed of calcium carbonate but may contain 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 nutrient deficiency and pH.

To be clear, the addition of limestone is done primarily to reduce acidity but may also provide some nutrients!

The value of limestone is in its ability to neutralize soil acidity. It is a little-known 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, of 100%. When you purchase any limestone product, you should always look for the CCE.

All other liming materials are compared with this (100%) standard. The CCE of commercial limestone products should be available through the vendor. The bulk agricultural limestones that we have used in hay meadows and pastures that have been used for years is somewhere around 65% CCE. Recently, the more frequently used “super fine lime” is up closer to 90% CCE.

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 soil pH near 7.0. Honestly, in a perfect soil, pH would be at 6.5.

For specific recommendations, you will need a soil test. For a $12 test you will 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. Soil pH fluctuates during the year, becoming lowest in the fall.

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— Shaniqua Davis is the Extension agent for agriculture and natural resources for Gregg County. Email: Shaniqua.Davis@ag.tamu.edu .