A modification to the Soil Lime Requirement Determination by the
Adams-Evans Buffer Solution
Gobena Huluka
Application and Principle
Many soil analysis labs routinely determine lime requirement of acidic soils using
different buffer solutions for optimum plant growth. The Adams-Evans lime determination
solution was developed used for non-montmorillonitic, low activity clay, low organic matter and
poorly buffered Alabama soils (Adams and Evans, 1962). The solution was adopted by many
labs with similar soils, especially those in the southeastern US with less than 13 cmolc kg-1 (13
meq/ 100 g soil) and relatively small requirement.
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
amount of soil (depth, area, volume and/or weight) under consideration.
The Morgan (1930), Mehlich (1938), Woodruff (1948), Shoemaker et al. (1961), and
Adams and Evans (1962) buffer solution contain para-nitrophenol because it provides a good
buffering capacity for most acidic soils. But para-nitrophenol is determined to be a hazardous
chemical (US EPA, 1980), and efforts were made to replace it without changing the AdamsEvans procedure and the other non-toxic chemicals (Huluka, 2005; Sikora and Moore, 2008).
The modified Adams-Evans buffer solution was developed by replacing the paranitrophenol with monobasic potassium phosphate (KH2PO4) that has similar buffering capacity
but with any known toxicity. Monobasic potassium phosphate is cheaper, environmental
friendly and easy to dissolve in water compared to p-nitrophenol. The linear regression between
the buffer pH values and lime recommendations made by the Adams-Evans and the modified
Adams-Evans solutions were highly significant. Thus, the modified Adams-Evans buffer
solution can be used without loss of established recommendation criteria as the original buffer
solution.
Equipment and Apparatus
1. 2-mm opening sieve
2. 10 cm3 scoop and leveling rod
3. 50-mL cup, glass, plastic or waxed paper
1
4. pH cup holding racks and glass rod for mixing
5. Automated deionized water and buffer solution dispenser.
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.
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. 74 g potassium chloride, KCl (MW=74.56)
b. 31.73 g monobasic potassium phosphate, KH2PO4 (MW=136.08)
c. 17 g boric acid, H3BO3 (MW=61.83)
d. 16.19 g potassium hydroxide, KOH (MW=56.11)
Weigh each chemical using an analytical balance and mix A, B and D in about 700 mL of
water until dissolved. Add chemical C and mix until it is completely dissolved. Adjust the pH
of the solution to 8.00+0.01 using either dilute KOH or HCl, and make the total volume to 1
L using 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 modified Adam-Evans buffer solution is added
to each sample. The solution is stirred for 30 seconds. The pH of the control solution (1:1
H2O to buffer) must be adjusted to 8.0+0.01 pH units or a correction should be applied.
The soil buffer pH is read to the nearest 0.01 pH units after 10 minutes.
Calculations
2
The modified Adams-Evans uses soil acidity measured in water solution and in buffer
solution to determine soil lime requirement. Since there is a linear change in the buffer solution
from 8.00 to 7.00, a relationship is established between change in buffer pH to amount of lime
needed for a target soil pH. Both measured pH and desired/targeted pH are related to acid
saturations as Hsat1 and Hsat2, respectively as shown in the following equations:
1. Measured soil pH=7.60 - 5.71Hsat1 + 2.99(Hsat1)2,
2. Desired soil pH=7.60 - 5.71Hsat2 + 2.99(Hsat2)2,
3. Soil H = 8(8.00 - buffer pH)
4. CEC = Soil H/Hsat1 or CEC = 8(8.0 – buffer pH)/Hsat1
5. CaCO3 (labs/A) = (8000(8-buffer pH)/Hsat1) x (Hsat1-Hsat2) x 1.5 x 1.3333
Analytical Performance
Range and Sensitivity
1. The modified Adams-Evans 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 A-1 limestone sensitivity.
Precision and Accuracy
1. Soil buffer pH measurement can be made to 0.01.
2. Interference: Clayey and highly buffered soils may reduce its effectiveness.
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, less than 10 mL of soil can used and lime recommendation will be made
taking into consideration the dilution factor. 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 the modified Adams-Evans buffer
solution.
Target pH 6.0
Hundreds of pounds of Ag-ground limestone*
3
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
7.4
7.3
7.2
7.1
1
2
3
4
5
6
7
7
8
9
10
10
2
5
7
8
10
12
13
15
16
17
19
20
4
7
10
13
15
17
20
22
24
26
29
30
5
9
13
17
20
23
26
29
32
35
39
40
7
14
20
25
30
35
39
44
48
52
58
60
8
16
23
29
35
41
46
51
56
61
68
70
10
18
26
33
40
46
52
58
64
70
77
80
11
21
30
38
45
52
59
65
72
78
87
90
7.4
7.3
7.2
7.1
17
24
30
35
39
44
47
51
54
57
60
63
65
68
72
73
20
28
35
41
46
51
55
59
63
67
70
73
76
79
84
85
23
32
40
46
53
58
63
68
72
76
80
83
87
91
96
97
26
36
44
52
59
65
71
76
81
86
90
94
98
102
108
110
6
11
16
21
25
29
33
36
40
44
48
50
Target pH 6.5
Hundreds of pounds of Ag-ground limestone*
Buffer pH
Soil7.9
7.8
7.7
7.6
7.5
Water
pH
6.3
3
6
9
11
14
6.2
4
8
12
16
20
6.1
5
10
15
20
25
6.0
6
12
17
23
29
5.9
7
13
20
26
33
5.8
7
15
22
29
36
5.7
8
16
24
32
39
5.6
8
17
25
34
42
5.5
9
18
27
36
45
5.4
10
19
29
38
48
5.3
10
20
30
40
50
5.2
10
21
31
42
52
5.1
11
22
33
44
54
5.0
11
23
34
45
57
4.9
12
24
36
48
60
4.8
12
24
37
49
61
*Calculated for CaCO3 1.5 and tillage to 8 inch depth
Effects of Storage
4
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 chemicals used in the modified Adams and Evans buffer solution have no known
safety risk and hence can be stored and disposed following routine laboratory protocols.
References
Adams, F., and C.E. Evans. 1962. A Rapid Method for Measuring Lime Requirement of Redyellow Podzolic Soils. Soil Sci. Soc. Amer. Proc. 26, 355-357.
Mehlich, A. 1938. 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. 3:162-166.
Morgan, M.F. 1930. Factors affecting the estimation of lime requirement from pH values. Soil
Sci. 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.
Sikora, F. and K.P. Moore. 2008. The Moore-Sikora Buffer for Lime Requirement
Determinations. Soil Sci. Soc. Am. J. 72:1163-1173.
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.
U.S. Environmental Protection Agency. 1980. Title 40, Protection of Environment, Part 261 –
Identification and Listing of Hazardous Wastes. Washington: Government Printing Office,
revised as of July 1, 2004.
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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