The Effect of Drying and
Drying Temperatures on Soil
Test Values
Andrew Mueller, Hailin Zhang, Jackie Schroder
Department of Plant and Soil Sciences, Oklahoma
State University
Mark Payton
Department of Statistics, Oklahoma State University
Robert Miller
Soils and Crop Sciences Department, Colorado State
University
Introduction

Dried soil samples are thought to be relatively stable and have many advantages for testing.
State
Drying
Duration
Hr.
Temperature
Celcius
AL
AR
FL
GA
KY
LA
MS
NC
OK
PR
SC
TN
TX
VA
24
72
Until dry
12
16-40
16-40
24
Until dry
Overnight
72
Overnight
Until dry
16-18
Overnight or Until Dry
57
67
40.5
43
38
38
38-40.5
38-40.5
65.5
30.5
46
65.5
43
Ambient Max=40C
Introduction

Many studies about drying on test results
with various findings

Factors that potentially change test values
are: moisture, temperature, soil type, soil
mineralogy, and soil sampling procedures

Initial nutrient concentrations of the soil
Introduction

Drying Effect on Potassium (K) Test Values

Wetting-drying, Freezing-thawing cycles have an
effect on the transformations of K between
exchangeable and nonexchangeable soil K fractions
(Mallarino et al., 2011);

Mallarino et al. (2011) also found that soils initially
high in exchangeable K may fix K upon drying while
those with initially very low exchangeable K levels tend
to release K upon drying.
Introduction

Drying is known to alter soil pH and nutrient
extractability (Van Erp. Houba et al., 2001; Turner
and Haygarth, 2003; Bartlett and James, 1980;
Gelderman and Mallarino, 1998).

Air drying has been observed to increase
extractable organic matter (Lundquist et al., 1999;
Bartlett and James, 1980).

Drying also increases particle surface acidity,
which may affect the solubility of many nutrients,
particularly micronutrients (Bartlett and James,
1980; Dowding et al., 2005).
Introduction




Large differences in bicarbonate-extractable P (organic and
inorganic) have been found between field-moist and air-dried soil
samples (Turner and Haygarth, 2003).
No significant change in extractable sulfate content.
Generally, there is an increase in extractable Mn upon drying,
caused by the reduction of insoluble manganese oxides to a soluble
form (Bartlett and James, 1980).
Venterink et al. (2002) showed that extractable nitrate increased
from almost zero in the initial soil cores to an average of 120 mg N
m−2 in rewetted soil cores and 690 mg N m−2 in the dried soil cores.
Objectives
1. To determine if drying temperature has a
significant impact on soil test values.
2. To determine if soil texture causes differences in
soil test values.
Material and Methods

Twenty-seven different soil samples from
major agricultural regions of the US were
obtained to study if soil pH, and concentrations
of K, P, ammonium-N, nitrate-N, and plant
available Ca, Mg, S, Cu, Fe, Zn, Mn, B,
organic C, and total N are affected by 5 drying
temperatures compared with the results of field
moist samples.
Material and Methods

Twenty-seven soils from various locations in the states.
Soil Characteristics
Soil I.D.
BAD
Elkorn
HAR-B
LIN
MAR-2
ATH
CLE2
DEG
TAY
W-8
TAY2
JUS-OH
CHA
HAR
USI
ON2
JMLF
BUR
DRI
TAB
LGE
GUY
SP1
LAH
STIL
HASK
CRE
State
IA
IA
IA
IA
IA
AL
SC
WI
WI
WI
IN
OH
NY
IL
IL
NE
NE
NE
ID
ID
OR
WA
SD
OK
OK
OK
MT
pH
7.5
5.9
5.3
6.8
5.6
5.9
4.8
6.9
4.8
7.1
6.9
7.5
5.2
5
4.7
4.7
5.1
3.8
6.5
7.7
6.1
7.1
4.7
6.9
4.8
7.5
7.8
Clay
31
30
10
13
20
33
15
18
20
13
25
34
15
28
15
10
30
5
20
13
28
5
15
26
20
13
14
OM
5.1
3.0
1.1
1.4
1.9
0.6
0.6
2.6
0.9
1.8
1.2
1.3
3.6
3.1
1.4
1.2
1.8
0.8
0.5
0.9
3.5
0.5
2.1
1.1
0.7
1.3
3.3
K
125
232
77
251
136
172
45
95
120
66
165
154
139
119
77
197
191
248
163
894
868
354
78
282
133
85
338
P
34
54
57
57
36
28
15
33
39
27
9
4
38
51
11
69
13
83
89
153
68
209
47
34
42
52
63
Mg
502
835
159
284
261
66
108
663
391
624
547
740
225
479
97
122
513
69
647
359
987
187
310
522
244
99
322
Ca
11351
4573
829
1770
2121
1175
480
2310
1328
1939
1700
2517
1837
2930
256
739
2629
413
2252
4031
4414
1764
2043
2412
919
2412
6610
Methods

Received frozen soils from Agriculture Laboratory
Proficiency Program

Thawed

Crushed by hand, and sieved with 2mm sieve

Each sample was separated into 6 temp. groups and
dried

Field Moist, 25, 45, 65, 85, 105 degrees Celsius

Tested for 14 analytes
Methods







pH: 1:1 soil to water suspension with a pH meter
and a combination electrode
NO3-N and NH4-N: 1.0 M KCL: Flow injection
analyzer
K, Ca, Mg, and P: Mehlich 3, ICP
Micronutrients: DTPA-Sorbitol, ICP
Sulfate (SO42-): 0.008 M calcium phosphate, ICP
Soil organic carbon and total nitrogen, LECO
TruSpec CN Analyzer
Texture: hydrometer method
Results
Soil pH as Affected by Drying Temperature
6
5
pH
4
3
2
1
0
Field Moist
25
45
65
Temperature, ˚C
85
105
Results
1200
Potassium(K)
1000
800
K(ppm)
FM
25
600
45
65
85
400
105
200
0
1
2
3
4
5
6
7
8
9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27
Soil I.D. Number
Potassium
K Increasing
600
400
ba
c
d
ab a a
c bc
25
c
45
200
65
100
aa
bbbb
a
bc
d dd
1500
Field Moist
K(ppm)
bb
a
aa
Field Moist
25
1000
a
500
45
bbc
cc
65
85
0
1: 31% clay
2: 30% clay
3: 20% clay
85
0
105
1: 13% clay 2: 13% clay 3: 28% clay
Soils
Soils
K No Change
400
a a a
a aa
a a a a a a
300
K(ppm)
K(ppm)
2000
aaa
500
300
K Decreasing
a
a a a
a a
Field Moist
25
200
45
100
65
0
85
1: 33% clay
2: 25% clay
Soils
3: 34% clay
105
105
Phosphorus and Sulfur
Phosphorus
120
P(ppm)
a
a
ab
80
60
a
a
100
c
c
c
b
bc
b
b
b
bc
c
bc
bc
ab
Field Moist
25
45
40
65
20
85
105
0
1: 18% clay
2: 20% clay
3: 13% clay
Soils
Sulfur
30
SO4- (ppm)
25
FM
20
25
15
45
10
65
5
85
0
105
1: 15% clay
2: 26% clay
3: 20% clay
Soils
4: 13% clay
5: 14% clay
Ammonium and Nitrate
Ammonium-N
30
a
NH4-N (ppm)
25
b
20
15
b
cd
cd
d
25
b
a
10
5
Field Moist
a
c
e
de cd
d
c
cd
45
c
65
85
e
105
0
1: 13% clay
2: 18% clay
3: 28% clay
Soils
NO3-N
NO3-N(ppm)
100
60
Field Moist
a
80
a
a
a
a
a
a
a
a
a
a
a
a
a
a
a
a
a
25
45
40
65
20
85
105
0
1: 20% clay
2: 33% clay
Soils
3: 15% clay
Micronutrients
Manganese
Iron
50
60
a
a
30
b
a
b
20
c
e de
d
e
decd
dd
c
c
65
e
0
1: 31% clay
25
45
b
10
Field Moist
2: 13% clay
Fe(ppm)
Mn(ppm)
40
50
a
30
85
10
105
0
3: 34% clay
Field Moist
b
40
20
a
c
25
a
c
d
d
bc
cd
b
ab
a
aa
b
bb
2: 13% clay
85
3: 34% clay
Soils
Zn
Boron
b a
e d
b
f
b
c
d
c
d
c c
25
45
65
85
105
1:13% clay
2
Field Moist
a
b a
a
2: 30% clay
Soils
3: 26% clay
B(ppm)
Zn(ppm)
2.5
c
65
105
1: 31% clay
Soils
4
3.5
3
2.5
2
1.5
1
0.5
0
45
c
1.5
1
b
a
c
a
ed
dd
f
e
0.5
b
c
bb
Field Moist
25
45
aaa
65
85
0
105
1: 31% clay
2: 13% clay
Soils
3: 34% clay
Summary

Soil pH was not affected by soil moisture or drying temperatures.

The impact of drying on K was inconsistent; some were
increased, no changes and decreased by drying temperature

Phosphorus concentrations were affected by drying slightly but
significantly

SO4-S concentrations were increased as drying temperature, but
Mg and Ca concentrations were not affected by drying
temperature.

NH4-N were changed drastically at 85 and 105 degrees, but NO3N, total nitrogen, and total carbon concentrations were not
impacted by drying temperature

Micronutrients were significantly increased by drying temperature
except for Cu
Summary
 Soil
texture did not show any direct effect on test
values
 Clay
mineralogy may be contributing some of of the
temperature effects, but remains to be studied
Acknowledgements



Dr. Hailin Zhang
Dr. Brian Arnall
Dr. Chad Penn
Dr. Jackie Shroder
Dr. Mark Payton
Dr. Robert Miller
Questions?