Fact Sheets And Publications

Calculating the Lime Recommendation Using the Adams-Evans Soil Buffer

The University of Delaware Soil Testing Lab uses the Adams-Evans buffer pH test to determine lime requirement for a field based on soil test analysis of an 8-inch composite soil sample. In this quick reference guide, we will walk through the steps for determining the lime recommendation using the Adams-Evans buffer pH. Other regional soil testing laboratories may use a different soil buffer pH test to determine lime requirement (Table 1). If the lime requirement test was performed by laboratory using a different buffer method, refer to the University of Delaware fact sheet Measurement and Management of Soil pH for the appropriate lime tables.

Table 1. Methods for water and buffer pH tests used by regional soil testing laboratories.

Making a Lime Recommendation

Follow these steps to make a lime recommendation:

Step 1: Determine the target pH of the crop and select the appropriate lime table.

The University of Delaware groups crops into six different soil target pH values. Crop specific listings of target pH are available in the University of Delaware Nutrient Management Recommendations (Shober et al., 2018; Taylor et al., 2018) or the Mid-Atlantic Commercial Vegetable Production Recommendations (Wyenandt and van Vuuren, 2019). Note: If soil organic matter (OM) is greater than 6% (based on the soil test report), use a target pH of 5.6.

Target pH 5.2  -- Blueberries;  non-scab resistant potatoes

Target pH 5.6  -- Acid loving plants;  black high organic matter soils

Target pH 6.0  -- Most Delaware crops

Target pH 6.2 -- Many commercial vegetable crops

Target pH 6.5  -- High Calcium demand crops, golf course turf,

Target pH 6.8 -- Alfalfa

All Lime Tables -- This file contains copies of all six lime tables for commercial crops.

Step 2: Obtain the water pH and buffer pH values from the soil test report. Determine the base lime rate from the lime table by selecting the value where the water pH row (shown along the left side of table) and the buffer pH column (shown across the top of the table) intersect. Note: the base lime rates are for agricultural grade lime, which is assumed to have 67% effective calcium carbonate content.

Step 3: Determine whether a lime credit is necessary. The lime credit (reported in tons/ac) is used to account for any lime that was applied in the past 18 months that has not had a chance to react, as calculated using the equation:

Lime credit (ton/ac) = Previous lime rate (ton/ac) × Lime availability factor

Where the previous lime rate (tons/ac) is the amount of any liming material applied within 18 months of the soil sampling event and the lime availability factor is based on the length of time since last application (Table 2).

Table 2. Availability factor used to adjust lime rates when liming materials were applied within 18 months of the current soil test.

Step 4: Determine the net lime requirement by subtracting the lime credit from the base lime recommendation, as determined from the current soil test by the following equation:

Net lime requirement (tons/ac) = Base lime requirement (ton/ac) ×Lime credit (ton/ac)

Step 5: Determine the type of lime recommended (e.g., calcitic or dolomitic agricultural-grade lime) based on Mehlich-3 (M3) soil test calcium (Ca) and magnesium (Mg) values obtained from the soil test report as outlined in Table 3.

Table 3. Recommended type of lime as a function of Mehlich 3 soil test Ca and Mg concentrations as reported in University of Delaware fertility index value (UD-FIV).

*Soil test Mg value of 50 UD-FIV is equivalent to 131 lb/ac (65.5 ppm) and 100 UD-FIV is equivalent to 262 lb/ac (131 ppm).

Adjusting the Lime Recommendation based on Tillage System

The lime recommendation may need to be adjusted for fields managed under conservation tillage or no-till. The University of Delaware recommends submitting a 2-inch composite sample from fields managed under conservation tillage or no-till to the soil testing to determine the need for lime. If the soil pH of the 2-inch composite sample is below the critical pH, we recommend also that the soil test laboratory run the lime requirement test on an 8-inch composite sample. If lime is recommended for the 8-inch composite sample, determine the appropriate base liming rate for conventional tillage systems. If lime is not recommended for the 8-inch composite sample, surface apply 1.5 tons/ac of agricultural grade limestone.

Example Lime Recommendation

The following example illustrates how to make a lime recommendation for conventionally-tilled grain corn grown on a field that received 0.5 tons/ac of agricultural grade calcitic lime 15 months ago. Collection of the soil sample occurred in the fall prior to the crop to a depth of 8 inches.

Information Obtained from the Soil Test Report

The target pH for grain corn is 6.0 based on the University of Delaware Nutrient Management Recommendations for Agronomic Crops.

Determine the base lime rate using the Adams-Evans Lime Recommendation Table for target pH 6.0 (excerpt shown here). The base lime rate is reported in tons/ac based on neutralization of pH to a depth of 8 inches using agricultural grade limestone with 67% effective calcium carbonate content (ECCC).

The base lime rate for this corn crop is 0.75 tons/ac.

Calculate the lime credit using the information provided by the grower (0.5 tons/ac of calcitic lime applied 15 months ago) using the equation:

Lime credit (ton/ac) = Previous lime rate (ton/ac) × Lime availability factor (from Table 2)

Lime credit (ton/ac) = 0.5 tons/ac × 0.25

Lime credit = 0.125 tons/ac

Determine the net lime requirement by subtracting the lime credit from the base lime recommendation:

Net lime requirement (tons/ac) = Base lime requirement (ton/ac) ×Lime credit (ton/ac)

Net lime requirement = 0.75 tons/ac – 0.125 tons/ac

Net lime requirement = 0.625 tons/ac

We recommend using dolomitic lime because the Mehlich 3 soil test Mg value (78 FIV) is between 50 and 100 FIV AND is less than the Mehlich 3 soil test Ca value (184 FIV).

Final lime recommendation = 0.625 tons/ac of dolomitic lime