High calcium soil is typically characterized by high alkalinity, meaning the soil pH level is above 7.0. This elevated pH creates a challenging environment for turfgrass health. When the soil is too alkaline, the chemical availability of several plant nutrients is severely restricted. This condition, known as nutrient lockup, prevents the grass from absorbing essential elements and impedes robust turf growth.
Recognizing the Signs and Confirming High Calcium
The first noticeable signs of high alkalinity are visual symptoms of nutrient deficiency. Turfgrass may appear pale green or yellow (chlorosis), even with adequate nitrogen fertilization. This yellowing is frequently interveinal, meaning the veins remain green while the tissue between them turns yellow, which is a classic sign of iron or manganese deficiency.
The high pH environment makes these micronutrients insoluble and inaccessible to the grass roots, resulting in poor growth. These visual cues are only suggestive, so confirming the issue requires a professional soil test. A reading of soil pH above 7.0, and particularly above 7.5, indicates an alkaline condition that benefits from correction.
Understanding the Source of Excess Soil Calcium
Excessive soil calcium and the resulting alkalinity often originate from the natural geology of the region. Many areas are situated over limestone or chalk bedrock, which is rich in calcium carbonate, and the weathering of this material naturally raises the soil’s pH over time.
Another common source is irrigation water, especially in arid or semi-arid regions. Hard water contains high concentrations of dissolved minerals like calcium and magnesium carbonates, adding alkaline salts to the soil with every watering. Over many seasons, this repeated application contributes significantly to rising soil pH. Historical soil management practices, such as the over-application of lime (calcium carbonate) years ago, can also leave a long-lasting alkaline legacy.
Practical Steps for Reducing Soil Alkalinity
The most effective strategy for lowering soil pH and reducing calcium’s influence is the application of elemental sulfur. Sulfur works through a slow, biological process carried out by soil bacteria. These microorganisms oxidize the sulfur, converting it into sulfuric acid, which neutralizes the soil’s alkalinity.
Because this is a biological process, it requires warm soil temperatures, ideally above 55°F, and consistent soil moisture for the bacteria to be active. General application rates range from two to five pounds of elemental sulfur per 1,000 square feet per application, with a maximum yearly total of 10 to 20 pounds per 1,000 square feet.
If a large pH reduction is needed, the total amount of sulfur must be split into multiple, smaller applications spread over several months or years. Aluminum sulfate is a faster-acting alternative because it immediately releases acid into the soil, but it is often more expensive and requires approximately six times the weight of elemental sulfur for the same effect. Organic amendments, such as sphagnum peat moss, can also be incorporated for a slower, milder, and more temporary reduction in pH.
Ongoing Monitoring and Prevention
Lowering the soil pH is a gradual process that requires patience, especially when using elemental sulfur. It can take anywhere from six months to a full year to see the maximum effect of an application, as the microbial conversion takes time. Continuous monitoring is necessary to ensure the treatment is effective and to prevent over-acidification.
It is advisable to re-test the soil every one to three years to track the progress of the pH reduction and determine if further sulfur applications are necessary. For long-term prevention, switch to acidifying fertilizers, such as those containing ammonium sulfate. As the ammonium component of this fertilizer is converted in the soil, it releases hydrogen ions, which naturally contribute to lowering the pH over time. Homeowners should avoid using lime or any calcium-based treatments unless a subsequent soil test indicates an acidic condition has developed.