Agricultural limestone (ag lime) is a naturally occurring soil amendment composed primarily of calcium carbonate. Its principal function is to neutralize soil acidity, a process known as liming. By raising the soil’s pH level, ag lime corrects chemical imbalances to promote better plant health and maximize the availability of essential nutrients.
The Role of Soil pH and Acidity
Soil pH measures acidity or alkalinity on a scale from 0 to 14; below 7 is acidic, and above 7 is alkaline. Most plants thrive in a slightly acidic to neutral range, typically between 6.0 and 7.0, with 6.5 being ideal for many crops. When soil pH falls below 5.5, it creates problems for plant health.
In highly acidic soils, elements like aluminum become more soluble and toxic to plant roots. This aluminum toxicity inhibits root growth and reduces the plant’s ability to absorb water and nutrients. Low pH also “locks up” essential nutrients like phosphorus, calcium, and magnesium, making them unavailable. Applying lime counteracts this acidity, reducing aluminum toxicity and increasing nutrient availability.
Essential Variables for Determining Application Rates
Calculating the precise amount of limestone needed requires more than just knowing the current soil pH. The first factor is the soil’s existing pH, which measures the “active” acidity in a water solution. This measurement indicates if lime is needed, but not how much to apply.
The second factor is the Buffer pH, which measures the soil’s resistance to a change in pH. Soils high in clay or organic matter have a high buffer capacity, meaning they resist pH change. These soils require significantly more lime to reach the target pH than sandy soils with the same initial pH reading. A professional soil test report provides the Buffer pH reading, which is the basis for the lime recommendation.
The third factor is the Calcium Carbonate Equivalent (CCE) of the liming material, which indicates its purity and neutralizing capacity. CCE is expressed as a percentage, comparing the product’s effectiveness to pure calcium carbonate (100% CCE). A product with a lower CCE requires a higher application rate to achieve the same result. The fineness, or particle size, of the lime also affects its reaction speed and overall effectiveness.
Calculating the Limestone Need
The most reliable way to determine the exact amount of limestone to apply is through a professional soil test report. These reports provide a specific recommendation, often listed as pounds of limestone per acre or per 1,000 square feet. This recommendation factors in the initial soil pH, the buffer pH, and the target pH for the crop being grown.
If a soil test is unavailable, a general maintenance application is far less accurate and risks over- or under-liming the soil. General guidelines suggest applying about 25 to 50 pounds of ground agricultural lime per 1,000 square feet for minor pH adjustments, but this is only an estimate.
When applying limestone, avoid applying more than 50 to 100 pounds per 1,000 square feet in a single application. Applying excessively high amounts at once can shock the soil and cause nutrient issues. For large application rates, the total amount should be split into two or more applications spaced several months apart, allowing time for the lime to react.
Understanding Different Types of Agricultural Lime
Agricultural lime is categorized into two main types based on mineral composition. Calcitic limestone is primarily calcium carbonate and is used when the soil has sufficient magnesium levels. Dolomitic limestone contains both calcium carbonate and magnesium carbonate.
Dolomitic lime is beneficial for acidic soils deficient in magnesium, addressing both issues simultaneously. Choosing the correct type is important, as applying dolomitic lime to magnesium-rich soil can cause an imbalance.
Forms of Lime
Both calcitic and dolomitic lime are available as pulverized or pelletized products. Pulverized, or finely ground, lime reacts quickly due to its small particle size, providing a faster pH adjustment. Pelletized lime is compressed into granules, making it easier to spread and reducing dust. The pelletized form breaks down when exposed to moisture, allowing the material to neutralize soil acidity.