Determination of Soil Lime Requirement by the Adams-Evans Buffer
Gobena Huluka
Application and Principle
Most soils of the southeastern US are acidic, and amelioration by applying ground
limestone has been a common cultural practice for agriculturalists. The sources of soil acidity are
acidrain, dissolution of acid generating clay minerals and oxides, organic matter and oxidation of
nitrogen and sulfur containing fertilizers. Many rapid and accurate methods of measuring
potential soil acidity and making appropriate lime recommendations have been designed to
remedy the deleterious impacts of excessive soil acidity. A rapid method of using chemical
solution indicators to determine the amount of lime needed to raise soil pH to a targeted value
was developed by Morgan (1930), Mehlich (1938), Woodruff (1948), Shoemaker et al. (1961),
and Adams and Evans (1962).
Lime requirement determination by a buffer solution is defined as a rapid laboratory
procedure that measures the soil acid saturation, and determines the amount of lime needed to
neutralize the potential acidity. The amount of lime required depends on the initial soil water pH,
acid buffering capacity of the soil and targeted pH for optimum plant growth. In addition, the
amount of lime needed is affected by the neutralizing power of the liming material and the depth
of soil under consideration.
The Adams-Evans lime determination solution was developed for low clay activity and
coarse-textured soils that are dominated by kaolnite and sesquioxide soil minerals (Adams and
Evans, 1962). These soils relatively have low cation exchange capacity that is less than 13 cmolc
kg-1, and usually need less than 5 tons A-1 ground limestone. Soil and Plant Analysis Council
(1980; 1999), and Sims (1996) have provided the amount of lime needed at a given water pH and
buffer pH measurements for different target pH values by the Adams-Evans buffer solution. Both
of these data were based on the simple equation presented by Adams-Evans (1962), and cautions
must be exercised to make lime recommendations.
Equipment and Apparatus
1. 2-mm opening sieve
2. 10 cm3 scoop and leveling rod
3. 50-mL cup, glass, plastic or waxed paper
4. pH cup holding racks and glass rod for mixing
5. Automated deionized water and buffer solution dispenser
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6. Automated Labfit AS-3000 Dual pH Analyzer using a TSP WP-80D Dual pH meter or a
pH meter with glass electrode paired with a calomel reference electrode and suited with a
stirrer
7. Analytical balance
Reagents
1. Deionized water
2. Standard pH 4.00 and 7.00 buffer solutions
3. The following reagent grade chemicals are dissolved per one L of solution.
a.
b.
c.
d.
74 g potassium chloride, KCl (FW=74.56)
20 g para-nitrophenol, C6H5NO3 (MW=139.11)
15 g boric acid, H3BO3 (MW=61.83)
10.5 g potassium hydroxide, KOH (MW=56.11)
Weigh each chemical using an analytical balance. Mix chemicals A and D from above in about
700 mL of water until all are dissolved. Add chemicals C and B to the solution and mix until it is
completely dissolved. Adjust to pH 8.00+0.01 of the buffer solution using either dilute KOH or
HCl, and make total volume to 1 L with deionized water.
Procedure
1. Soil-water pH is measured by scooping 10 mL of soil sample into 50 mL cup, and by
adding 10 mL of deionized water. The samples are mixed manually or by mechanical
shaker for 30 seconds, and allowed to stand for 30 minutes. Just before reading the pH,
each sample is mixed/stirred, and the pH reading is taken to the nearest 0.1 unit while
stirring with automatic stirrer.
2. After soil-water pH is taken, 10 mL of the Adam-Evans buffer solution is added to each
sample. The solution is manually/mechanically stirred for 30 seconds. The pH of the
control solution (1:1 H2O to buffer) must be adjusted to pH 8.0+0.01 or a correction
value should be used. The soil buffer pH is read to the nearest 0.01 pH units after 10
minutes while stirring.
Calculations
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1. The Adams-Evans based is based on soil water and buffer measurements. Soil pH and
target pH are related to acid saturation according to the following equations:
a. Measured pH = 7.79 – 5.55(H-sat1) + 2.27(H-sat1)
b. Target pH= 7.79 – 5.55(H-sat2) + 2.27(H-sat2)
2. H-saturation is a measure of the fraction of soil CEC that is acidic saturated. The soil
acidic saturation is calculated as:
a. Soil H = 8(8.00 – buffer pH)
For a 1:1:1 soil, water and buffer solution, a linear relation exists between pH 7:00
and 8.00.
3. The CEC of the soil is calculated as:
a. CEC = Soil H/H-sat1
b. CEC = 8(8.0 – buffer pH)/Hsat1
4. The Adams-Evans used the following relationship to calculate lime requirement:
a. (Soil H)/Hsat1 X (Hsat1-Hsat2)
5. When a 2/3 effective neutralizing power for agricultural limestone and an 8 inch of soil
depth is considered, the amount of limestone needed is given as:
a. Ag limestone (lbs/A) = (8000(8-buffer pH)/Hsat1) x (Hsat1-Hsat2) x (3/2) x (8/6)
b. Ag limestone (lbs/A) = (8000(8-buffer pH)/Hsat1) x (Hsat1-Hsat2) x 2
Analytical Performance
Range and Sensitivity
1. The Adams-Evans buffer is used for soils with less than 8 cmolc H+/ kg (8 meq/100 g
soil). The buffer solution provides a fair degree of accuracy for estimating lime
requirement to reach pH 6.5 or less.
2. Recommendation made by this method is within 500 lb limestone sensitivity.
Precision and Accuracy
1. Buffer pH measurements can be made to 0.01.
Interference
3
1. No known interference.
Interpretation
1. Lime requirement is calculating from soil water and buffer pH measurements for target
pHs, for example, for pH 6.00 and 6.50 (see Table 1). For soils with high concentration
of acidity (water pH less than 4.5), less than 10 mL of soil can used and lime
recommendation will be made taking into consideration the dilution factor (Soil and Plan
Analysis Council, 1980). Auburn University recommends limestone for farmlands by
rounding to half unit in tons A-1.
Table 1. Ag-lime needed to raise soil pH to 6.0 and 6.5 for Adams-Evans buffer solution.
Target pH 6.0
Hundreds of pounds of Ag-ground limestone*
SoilWater
pH
5.9
5.8
5.7
5.6
5.5
5.4
5.3
5.2
5.1
5.0
4.9
4.8
7.9
7.8
7.7
Buffer pH
7.6
7.5
1
2
3
4
4
5
6
6
7
7
8
8
2
4
6
7
9
10
11
13
14
15
16
17
3
6
9
11
13
15
17
19
20
22
24
25
4
8
11
15
17
20
23
25
27
29
31
33
5
10
14
18
22
25
28
31
34
37
39
42
7.4
7.3
7.2
7.1
6
12
17
22
26
30
34
38
41
44
47
50
7
14
20
25
31
35
40
44
48
51
55
59
8
16
23
29
35
40
45
50
55
59
63
67
9
18
26
33
39
45
51
56
61
66
71
75
Target pH 6.5
Hundreds of pounds of Ag-ground limestone*
SoilWater
pH
6.4
6.3
6.2
6.1
7.9
7.8
7.7
Buffer pH
7.6
7.5
0
2
3
4
0
5
7
9
0
7
10
13
0
10
14
17
0
12
17
22
4
7.4
7.3
7.2
7.1
0
15
21
26
0
17
24
30
0
20
28
35
0
22
31
39
6.0
5
10
15
20
26
5.9
6
12
17
23
29
5.8
6
13
19
26
32
5.7
7
14
21
28
35
5.6
8
15
23
30
38
5.5
8
16
24
32
40
5.4
9
17
26
34
43
5.3
9
18
27
36
45
5.2
9
19
28
37
47
5.1
10
20
29
39
49
5.0
10
20
30
40
51
4.9
10
21
31
42
52
4.8
11
22
32
43
54
*Calculated for CaCO3 1.5 and tillage to 8 inch depth
31
35
39
42
46
48
51
54
56
59
61
63
65
36
41
45
49
53
57
60
63
66
68
71
73
76
41
47
52
56
61
65
68
72
75
78
81
84
86
46
52
58
63
68
73
77
81
84
88
91
94
97
Effects of Storage
1. Air-dry soil can be stored for many months without significant effect on soil buffer pH
measurement. Instruments used in this procedure must be maintained according to
manufacturer’s instructions and frequently checked for accuracy and precision.
Safety and disposal
1. The para-nitrophenol used in this procedure should be contained according to applicable
Federal, State and local laws for appropriate disposal.
References
Adams, F.; Evans, C.E. A Rapid Method for Measuring Lime Requirement of Red-yellow
Podzolic Soils. Soil Sci. Soc. Amer. Proc. 1962, 26, 355-357.
Mehlich, A. Use of TEA-OAc-Ba(OH)2 buffer for the determination of some base exchange
properties and lime requirement of soil. Soil Sci. Soc. Amer. Proc. 1938, 3:162-166.
Morgan, M.F. Factors affecting the estimation of lime requirement from pH values. Soil
Sci. 1930, 29:163-180.
Shoemaker, H.E.; McLean, E.O; Pratt, P.F. Buffer Methods for the determination of lime
requirement of soils with appreciable amount of exchangeable aluminum. Soil Sci. Soc. Amer.
Proc., 1961, 25, 274-277.
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Sims, J.T. Lime requirement. In Methods of Soil Analysis, D.L. Sparks, Editor; Part 3,
SSSA Book Series, 5, Soil Science Society of America, Madison, WI, 1996; 491-515.
Soil and Plant Analysis Council, Inc. 1980. Handbook on Reference Methods for Soil Testing
(Revised Edition). University of Georgia, Athens, GA. 1980; 130.
Soil and Plant Analysis Council, Inc. 1999. Handbook on Reference Methods for Soil Analysis.
Boca Raton, Florida, CRC, Press; 247.
Woodruff, C.M. Testing soils for lime requirement by means of a buffered solution and the glass
electrode. Soil Sci. 1948, 66, 53-63.
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