Agricultural lime (ag lime) is a soil amendment primarily composed of calcium carbonate or magnesium carbonate. Its purpose is to neutralize soil acidity by raising the soil’s pH level. Correcting soil acidity optimizes the availability of nutrients like phosphorus and molybdenum, which become unavailable in highly acidic conditions. Applying lime correctly is necessary for soil management, ensuring crops can access the resources needed for healthy growth.
Preparation: Determining Need and Application Rate
The process of applying agricultural lime begins with a current soil test, which is the only reliable way to determine if liming is required and how much material is needed. A soil test report provides two pH values: the soil pH and the buffer pH (BpH). The soil pH indicates the current active acidity and shows if the soil is acidic (below 7.0), typically falling below the optimum range of 6.0 to 7.0 for most crops.
The buffer pH is used to calculate the actual lime requirement. This measurement reflects the soil’s capacity to resist a pH change, measuring the total acidity that must be neutralized. Soils high in clay or organic matter are more “buffered” and require a larger amount of lime to achieve the target pH compared to sandy soils.
Soil testing laboratories translate the BpH reading into a recommendation, usually expressed in tons of lime per acre, targeting the top seven inches of soil. Once the recommendation is received, the rate must be accurately calculated for the specific area being treated, especially for smaller applications like gardens or lawns. This involves converting the per-acre recommendation into pounds per 1,000 square feet. Applying the correct amount is important, as over-application can waste material and potentially cause nutrient imbalances, while under-application will fail to fully correct the acidity.
Selecting the Right Spreading Equipment
Selecting the appropriate equipment depends on the scale of the operation and the type of lime used.
For large agricultural fields, commercial truck or trailer-mounted spreaders with spinner discs are the standard choice for broadcasting bulk, loose lime. These high-capacity machines cover significant acreage efficiently but require careful calibration to ensure an even spread pattern.
For medium-sized areas, such as large lawns or gardens, a rotary or broadcast spreader is commonly used. These models distribute material in a wide swath, speeding up the application process. However, the fine, dusty nature of agricultural lime can make it challenging to use with standard rotary spreaders, as the material is prone to drift in the wind.
Drop spreaders offer the highest precision for small, defined areas, such as borders or narrow garden beds. They release the material directly below the hopper, minimizing overspray onto paths or non-target zones. Drop spreaders are less suited for spreading fine lime over large areas due to their limited width and capacity.
The Application Process and Timing
The optimal time for applying lime is in the fall or early spring, ideally well before planting. Lime works slowly, often taking three to six months for the pH to change significantly, and up to two or three years to reach its full effect. Applying lime in the fall allows the material to react with soil moisture over the winter, benefiting the next season’s crop. Avoid applying lime to wet or saturated soil, which can lead to soil compaction from heavy equipment.
Before spreading, the equipment must be properly calibrated to match the calculated application rate. Calibration involves determining the spreader’s output by measuring the material collected over a known distance or by conducting a pan test to assess the spread pattern and uniformity. Accurate metering is controlled by adjusting the feed gate height and the belt or chain speed on commercial spreaders.
During application, maintaining a consistent ground speed is necessary because changes in speed alter the rate of material discharge. To achieve uniform coverage, use a perimeter driving method, ensuring slight overlap between passes to prevent untreated strips. Spreading should be avoided during windy conditions, as the fine lime dust can easily drift, leading to uneven coverage and material loss. Personnel should wear protective gear, such as a mask and goggles, to protect against inhaling the fine dust.
Post-Application Management
Once the agricultural lime has been broadcast, incorporation often follows for maximum effectiveness. Tillage operations like disking or plowing mix the lime throughout the root zone, typically the top six to ten inches of soil. This mechanical mixing accelerates the neutralization process and helps achieve the target pH throughout the plow layer.
In no-till or reduced tillage systems, the lime is surface-applied and relies on natural processes to move downward into the soil profile. This movement is very slow, progressing at about a half-inch per year, meaning it takes several years to neutralize acidity below the surface. No-till systems may require more frequent, smaller applications of lime to manage surface acidity.
Lime should be applied and incorporated at least one month before applying other fertilizers, as it can temporarily interfere with the availability of certain nutrients, particularly phosphorus. The soil pH should be re-monitored with another soil test after two to three years to assess the change and plan for future applications.