DISPLACEMENT OF SOIL SOLUBLES THROUGH PLANT
ROOTS BY MEANS OF AIR PRESSURE AS
A METHOD OF STUDYING SOIL
FERTILITY PROBLEMS

by

C AWpLAURITZEN

A THESIS
PRESENTED TO THE FACULTY
OF THE
MICHIGAN STATE COLLEGE
OF
AGRICULTURE AND APPLIED SCIENCE
IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS
FOR THE
DEGREE OF DOCTOR OF PHILOSOPHY

East Lansing
19 2 4

ProQuest Number: 10008493

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ACKNOWLEDGMENT
The writer wishes to express his appreciation to
Dr. C. H. Spurway for his invaluable guidance and interest
shown during the course of this investigation; also to Dr.
C. E. Millar, Dr. J. W. Crist, and Dr. E. H. Morse for their
kindly interest in the
i work and the helpful suggestions and
criticisms they have offered from time to time.

97255

—

1

*—

INTRODUCTION
The intake of dissolved substances by plant roots
growing in nutrient media is a subject of much scientific
interest, but the many investigations on this subject have
failed to satisfactorily explain the processes by which soil
solubles are taken in by plant roots and the relation which
the nature and concentration of these soil solubles bears to
soil conditions and the growth of plants.

What is believed

to be a new method of procedure for investigating the plant
nutrients of the soil and the selective power of the living
plant root is described in the following paper.

The data

presented and obtained by the use of the method seems to
justify its consideration as a means of investigating soilplant nutritional problems.

It is hoped that by its use some

of the difficulties connected with research in this field may
be in some way lessened.
Acknowledgement is due Paul J. Kramer as the idea for
devising this method as a means of studying soil-plant problems
resulted from the reading of his article "The absorption of
water by the root systems of plants" (3).
Briefly the procedure followed consisted of growing
plants in soil, some in soil which was not fertilized and some
in fertilized soil.

Subsequently to the growing of the plants

the tops were cut off and solution forced from the soil through
the plant roots by means of air pressure and collected as it
emerged from the stem stubs.

In some cases the plant roots

were killed with heat before the soil solution was forced
through them.

The solution was collected in consecutive

portions, 2 to 4 in number usually distributed over a period
of 48 hours.

Each portion of solution collected was measured

and later analyzed for phosphorus, potassium, and calcium,
Determinations were also made for these elements in the soil,
and the soil moisture content was determined at the time the
collection of the solution from the stem stubs was completed.
Greenhouse procedure
Bean plants were grown in the greenhouse in two-gallon
glazed crocks, each containing the equivalent of 8 kilograms
of oven-dry soil,

A Brookston loam soil from the vicinity of

Unionville, Michigan, was chosen for the experiment.

It has

been subjected to field tests on bean fertilization for a
period of two years.

Under field conditions beans did not

respond to moderate applications of the fertilizers used.

This

fact does not seem unusual when it is known that the soil is
very fertile, producing high yields of corn, wheat, beets, and
alfalfa, as well as beans, without the use of fertilizers al­
though some of the crops mentioned do respond to fertilizer
applications.

This soil was tested for soluble plant nutrients

using Spurwayfs method (7).

It gave low tests for both phos­

phorus and potassium, indication that a plant response could be
expected from an application of these elements in commercial
fertilizers.

- 3 In order to determine, if possible, the amounts
of these elements which would be necessary to apply to
the soil to make them available in such concentrations
as it is expected they should exist in the soil solution
of fertile soils, 100-gram samples of the soil were weigh­
ed out and increments of phosphorus as CafHgPC^ )g*HgO add­
ed in solution with sufficient water to make the soil up
to optimum moisture content when the solution was thor­
oughly mixed with it.

The soil thus treated was allowed

to stand for one day and then tested for phosphorus ac­
cording to Spurway’s method (7).

The procedure was

repeated adding increments of potassium as KOI and test­
ing for tbis element (7).

Applications of Ca(HgP0 4 )g-HgO

equivalent to 750 pounds of PgOg per 1,000,000 pounds of
soil gave a high test for phosphorus, and KC1 equivalent
to 1£00 pounds of KgO gave <Just a positive test for po­
tassium as shown in tables 1 and £.
Fertilizer was added to the soil in one-half
the number of crocks in which beans were to be planted,
in the form and at the rate given above.

The application

was made by mixing the air-dry soil on an oilcloth with
a sufficient quantity of a solution of CafElsjPC^ )g *HgO and
KCl, to bring the soil to the optimum moisture content.
The quantity of potassium added to the soil, as will be
seen, based on the tests made on the samples of soil
receiving the trial applications, was not great enough
to bring the concentration up to what might be considered

Table I

goil Tests for Phosphorus and Potassium resulting from
Phosphorus Applications

Ca(H£P04 )2 .H20
Solution
Soil Water
Grams ml* 26.8819 grams
per liter
ml.

Pounds per
acre
enuivalent

Phosphorus

Potassium

P. P. M.

P. P. M.

i

.....

- 1 -

----

100

EG* 0

0.0

------

100

19.5

0.5

150

3

100

19.0

1.0

500

l-ir- 2

----

100

18.5

1.5

450

4-5

----

100

18.0

E.O

600

High

----

100

17.5

2.5

750

High

3

Table II

Soil Tests for Phosphorus and Potassium resulting from
Potassium Applications
M
" ■—^•

,
.
,
— 5

•

Soil Water
Grams ml*

KC1 Solution
9.5939 grams
per liter
ml*

Pounds per
acre
enuivalent

Phosphorus

Potassium

P. P. M.

P. P. M.

100

20.0

0.0

—_ _

1
2

_—

100

19.5

0.5

150

2

1

-----

100

19.0

1.0

300

#

2.

-----

100

18.5

1.5

450

1

5

100

18.0

2.0

600

2
1
2

100

17.5

£.5

750

2"

5

100

17.0

3.0

900

i

5

100

16.5

3.5

1050

5

100

16.0

4.0

1200

1
2
1
2

5

5

Table III
Outline of Sreenhou.se Work

Date of
Planting

Unfertilized
Crock No.

Dry Weight
of
Plant Tops

Fertilized
Crock No.

Dry Weight
of
Plant Tops

8 /12/23

1A

8.90

2A

15.90

8/14/23

IB

13.32

2B

18.04

8/16/32

1C

16.61

2C

23.38

8/18/32

ID

19.65

2D

18.40

8/20/33

IE

15.62

2E

23.74

9/25/22

3A

10.25

4A

14.20

9/29/32

3B

9.25

4B

19.50

10/3/33

3C

15.05

4C

15.40

10/7/33

3D

13*90

4D

16.60

lO/n/22

3E

12.30

4E

14.65

- 5Apparatus and Technique for Displacing
Soil Solubles through Plant Roots
In order to force the solution from the soil
into the plant roots and out through the cut' stem, it
is necessary to subject the solution to a force sufficr
iently great to overcome the resistance offered to the
passage of the solution through the root system plus
the force necessary to overcome the retaining force ex­
erted by the soil itself on the solution contained.

To

affect this condition a chamber capable of holding air
under pressure was used.

The pressure chamber, as it will

be called, was made from a steam pressure cooker, not es­
pecially because it was considered the most suitable, but
because it was available.

Its construction was altered

in such a way as to make it as effective as possible in
serving in its new capacity.

A safety valve and outlet

valve in combination were installed in the lid.
pressure gauge was left as it was originally.

The
Three holes

about 1 cm. in diameter were bored through the lid, equally
spaced in the line of a semicircle, and threaded so that
they could be closed by screwing in metal plugs.

The cham­

ber was tested and found capable of holding at least 30
pounds per snuare inch of internal pressure.

The safety

valve was set to release the air at pressures slightly
higher to insure against too much pressure being attained
accidentally.

The steam entrance was fitted and connected

through a needle valve to an air line which was held at a

pressure of SO pounds per snuare inch by means of a reduc­
ing valve.
Connections were made to the stem studs of the
plants left after the tops were cut off by means of fit­
tings made from rudder tuding.

Two pieces of tubing, each

adout 5 centimeters long dut of different sizes, were used.
The smaller sized tuding was pulled part way through the
larger sized tuding.

The smaller and more flexible tubing,

which protruded from the end of the larger tuding, was
started on to the stem stud which had previously been
greased with vaseline and forced on until the stud extended
well up into the heavier tuding.

The sizes of the pieces

of tuding were usually close to two-eighths and threeeighths inches, respectively, inside deameter, depending
on the size of the plant stems.

After the connections

were made on the stem studs the crock was placed in the
pressure chamber.

This being done, delivery tubes made

from glass tuding having a diameter of adout one-half
centimeter were inserted through the holes in the lid of
the chamber.

The rudder seals, made by boring a hole in

rubber cushions used for centrifuge tubes, were placed on
the tubes with their concave sides next to the lid.

The

ends of the delivery tubes were then inserted in the rud­
der connections, attached to the plants, and the rubber
seals on the tubes adjusted so that when the lid to the
pressure chamber was in place they were just flush with
the surface of the lid.

Compressed air, when admitted

to the chamber after the lid was secured in place, exerted

a force on the rubber cushions, pressing them against the
lid and forming effective seals around the delivery tubes
and around the holes in the lid through which the delivery
tubes entered the chamber*

Stopcock grease was placed on

the ground surfaces of the lid and chamber to facilitate
a better seal*

The ends of the delivery tubes protruding

from the holes in the lid of the pressure chamber were
fitted into receiving flasks by means of two-hole rubber
stoppers.

One of the holes in the stopper held the end

of the delivery tube and the other served as an opening
to prevent any back pressure accumulating.

(Diagram 1

and Plate IV*)
Bean plants which had reached the stage of matur­
ity when

they were setting pods were used to obtain the

solution from the soil by the air pressure method.

The

crock and soil containing the plants were weighed, the
tops cut off about 5 cm. above the surface of the soil
and the connections made as described previously.

Follow­

ing the period in which the crock containing the soil and
roots remained in the pressure chamber, the crock and soil
were weighed in order to determine the loss of weight not
accounted for by the material removed.

A core of soil

was removed -through the center of the crock and its mois­
ture content determined.

The plant tops which were cut

off were weighed and left to dry.

The per cent moisture

and dry weight were then calculated on an air-dry basis.
This soil solution forced through the plant
roots by means of air pressure, designated in the future

- 8 for the sake of convenience as the solution, was collected
over consecutive periods of time, the length of the periods
being varied.

Usually the total period was 48 hours.

The

solution collected from each plant during each of these
periods was measured and the volume recorded after which
it was returned to the flask in which it was collected,
two or three drops of toluene added, and the flask stop­
pered and set aside.
The roots of the plants in some crocks were killed
before the solution was forced through them.

This was done

by placing the crocks containing the growing plants in a
water bath, which was at a temperature of between 80° and
90°C., until the soil at the center of the crock near the
surface was at 70°G. (4).

After this temperature was at­

tained the crocks were removed from the bath and the soil
allowed to cool at room temperature.
conditions took about 8 hours.

Cooling under room

As soon as the soil in the

crocks attained room temperature, or as soon afterwards as
was convenient, the tops were cut off, the connections made,
and the solution obtained in the same way as when the soil
was not heated.
In an attempt to see if the changes in the con­
centrations of the solutions obtained as a result of heat­
ing the soil could be affected in another way twenty-five
ml. of ether were added to the soil in one of the crocks
about 12 hours before the crock was placed in the pressure
chamber.

- 9 Methods of Analysis
Phosphorus, potassium, and calcium, three elements
which have been proved to be necessary in nutrient mediums
for growth of plants, were determined in the soil and in
the solutions.

Determinations for these elements in the

soil were made according to the method of Spurway (7).
Phosphorus was determined in the solutions by the
colorimetric method described by Truog and Meyer (8) except
in cases where the soil had been heated and the concentra­
tions in the solutions were very small.

From 1 to 2 ml.

of solution, depending on the expected concentration, were
diluted to 50 ml. the color developed and the concentration
of the solution determined.

Phosphorus determinations on

the solution obtained from heated soil were made according
tothe method of Spurway for testing soils (7).

One ml.

of the solution obtained by means of the plant roots was
used in the determination, instead of the 1 ml. of soil
extract as used in the soil tests.
Potassium was determined according to the method
of Kramer and Tisdall (2), with some modification.

Two

ml. of solution or, in some cases, 1 ml. of solution and
1 ml. of water were added to a 15 ml. centrifuge tube.
Two mis. of 95 per cent alcohol were added and the cobaltinitrite reagent added with stirring.
precipitation immediately.

Centrifuging followed

The precipitate was washed once

with 4 ml. of 50 per cent alcohol, recentrifuged, drained,
and allowed to dry following which it was titrated in the

Table IV

Soil Tests for Phosphorus, Potassium, and Calcium on Soil
in Crock when Removed from Pressure Chamber

Unfertilized
Reaction

Basic

Fertilized
Basic

Phosphorus

i

High

Potassium

Low

5

Calcium

150

200

- 10 usual manner.
Calcium in the solution was determined according to
the method of Clark and Collip (1).
Phosphorus, potassium, and calcium were determined
in the soil at the time it was removed from the pressure
chamber (7).

Results of tests for these elements in the soil,

after growing the crop, were the same as before the crop was
planted.

Compare table 4 with tables 1 and 2.
Experimental Results

Phosphorus and potassium applied to the soil produced a
marked increase in the growth of the bean plants, (pia.tes
II, and III) especially in the early stages.

I,

Plants that

grew on the unfertilized soil, however, tended to overcome
their initial disadvantage as they approached maturity, but
never overcame their slower start completely as can be seen by
noting the relative differences in the dry weights of the plant
tops grown on the unfertilized and the fertilized soil. (Table
3)
The amount of solution collected by means of a plant
root over a given period of time, as a result of air pressure
being applied to the soil, varied greatly with the period con­
sidered and the individual plant root, as with plant roots in
the same crock, and to an even greater extent with the plant
roots grown in different crocks, ranging from a few ml. to
more than 100 ml. over a 12 to 24 hour period.

(Tables 5, 6, 7,

Table V
Soil moisture, dry weight of plant tops, ml. of solution collected,
and the concentration of phosphorus, potassium, and calcium in the
solutions forced through plant roots from unfertilized soil by means
of air pressure over consecutive periods of time.
Plant
No.

Dry Wt.
of Plant
gnu

Period

Solution
PhosphorusPotassium Calcium
Collected
Hours
ml.
P. P. M.
P. P. M. P. P. M
Crock 1A
Per Cent Soil Moisture — 15.67

1

Total

0-24
24- 48

141
24

6.21
9.65

42.05
33.11

30. 36
50.73

Three

0-24
24- 48

147
28

5.68
7.86

41.37
38.41

27.32
42.45

3

8.90

0-24
24- 48

90
5.00
35.80
156.33*
16
3.50
Crock IB
Per Cent Soil Moisture — 13.70

1

4.95

0-24
24- 48

29
7

14.16
11.49

214.50
480.78*

145.44
136.09*

2

3.12

0-24
24- 48

24
5

14.10
11.92

180.13
448.59*

'82. 73

3

5.25

0-24
24- 48

36
15.25
176.38
7
10.83
337.06*
Crock 1C
Per Cent Soil Moisture — 17.06

1

3.67

0-12
12- 24
24- 48

38
29
48

6.38
6.37
5.68

94.71
60.28
69.40

59.21
17.76
17.76

2

6.65

0-12
12- 24
24- 48

13
17
19

9.09
17.50
16.06

193.60
145.58
290.26

120.38
30.59
25.66

3

6.29

74
6.64
107.08
45
3.94
29.15
76.41
56
7.56
Crock ID
Per Cent Soil Moisture — 13.39

56.25
24.67
33.55

1

8.05

0-12
12- 24
24- 48

36
6
5

17.86
11.42
8.96

96.59
232.03*
431.47*

65.13
55.26*
67.10*

2

5.40

0-12
12- 24
24- 48

20
3
3

9.56
4.25
4.19

113.25
172.53*
799.14*

97.69

3

6.20

0-12
12- 24
24- 48

28
6
5

14.37
7.32
3.25

87.34
104.67
401.82*

65.15
45.39*
49.34*

of
2

0-12
12- 24
24- 48

17.60
25.88

91.08
54.44*

Table V
(Continued)
Plant
No.

Dry Wt.
of Plant
. gm.„

Period

Solution
phosphorus Potassium
Collected
Hours
P. P. M.
ml.
P. P. M.
Crock 3B
Per Cent Soil Moisture — 17.84

Calcium
P. P. M.

1

S. 55

0-12
12— 24
24- 48

92
54
35

5.68
4.89
9.49

67.56
21.34
64. 76

14.85
11.84
30.59

2

o
1
—I
03

0-12
12- 24
24- 48

31
17
9

10.55
11.03
10.75

118.34
111.13
321.23

25.66
17.76
33.55

3

3.60

0-12
12- 24
24- 48

7.14
46
63.48
23
8.23
53.88
197.22
9
6.70
Crock 5d
per Cent Soil Moisture —— 17.30

16.78
19.76
35.55

1

3.95

0-8
8-24
24— 48

37
38
19

10.12
11.52
10.72

93.39
36.78
133.01

30.51
26.30
49.44

2

5.90

0-8
8-24
24— 48

47
53
26

9.93
12. 36
7.97

56.18
19.70
106.01

21.04
14.73
41.02

3

4.05

0 — 8
8-24
24- 48

59.48
16.71
70.72

17.88
15.78
25.24

1

3.70

0 — 8
8-23
23- 48
48- 72

35
45
41
21

9.56
6.37
8.01
6.89

116.57
66.56
137.57
134.37

38.92
29.45
41.02
54.70

2

3.75

0-8
8-23
23- 48
48- 72

42
71
104
71

9.58
5.33
4.37
3.44

132.88
78.88
60.49
59.94

43.13
28.40
17.88
31.56

3

4.85

0-8
8-23
23- 48
48- 72

58
75
122
90

6.33
5.08
3.52
2.87

95.35
49.73
33.55
36.11

30.51
26.30
13.68
16.83

46
9.17
54
12.36
7.39
35
Crock &E
Per Cent Soil Moisture — 21.55

* Single determination

Table VI
Soil moisture, dry weight of plant tops, ml. of solution collected,
and the concentration of phosphorus, potassium, and calcium in the
solutions forced through plant roots from unfertilized soil by means
of air pressure over consecutive periods of time. Roots killed by
heating soil in crock containing plants to 70°C.
Plant
Wo.

Dry Wt.
of Plant
gm.

Period

Solut ion
Phosphorus Potassium
Collected
Hours
ml.
P. P. M.
P. P. M.
Crock 3A
Per Cent Soil Moisture — 17.37

Calcium
P. P. M.

1

4.30

0-4
4-16
16- 40

54
60
10

0.50
0.50
0.50

4.28
4.71
9.43

152.37
152,37
134.79

2

3.10

0-4
4-16
16- 40

36
45
5

0.50
0.50
0.50

3.95
6. 22
----

157.25
183.62
189.48

5.04
5.51
9.23

141.63
145.53
171.90

4.16
3.46
8.15

159.88
161.98
168.30

3

2.85

1

5.30

2

5.10

0-3
3-12
12- 36

53
67
38

0.50
0.50
0.50

4.23
2.95
3.66

135.69
161.99
146.21

3

4.65

0-3
3-12
12 -36

41
49
26

0.50
0.50
0.50

2.91
3.27
8.45

161.99
161.98
164.09

0-4
4-16
16- 40

0.50
38
0.50
60
0.50
18
Crock 3C
Per Cent Soil Moisture — 17.42
'
— .. ■ " 1"■"A" 1 "■
0-3
35
0.50
42
0.50
3-12
0.50
12- 36
15

Table VII
Soil moisture, dry weight of plant tops, ml* of solution collected,
and the concentration of phosphorus, potassium, and calcium in the
solutions forced through plant roots from soil fertilized with 750
pounds PgOg and 1200 pounds of KgO per 1,000,000 pounds of oven-dry
soil by means of air pressure over consecutive periods of time.
Plant Dry Wt.
Period Solution
Phosphorus Potassium
No.
of Plant
Collected
_________ gm.
■ Hours______rrO.______ P. P. M.
P. P. M.
Crock 2A
Per Cent Soil Moisture — 16.58
*

•

a

•

*** «

.

*

«

*•* •

Calcium
P. P. M.
*

»

*

«

1

Total

0-24
24- 48

127
17

18.22
16.20

72.56
172.71

62.81
83,85

2

of

0-24
24- 48

104
15

16.50
19.50

63.71
150.74

51.65
97.36

88.94
102
18.15
239.87
13
14.41
Crock SC
Per Cent Soil Moisture — 16.79

45.55
86.96

** •

Three
3
15.97

0-24
24- 48

1

9.39

0-12
12- 24
24- 48

91
44
24

16.86
21.41
22.10

157.05
148.31
330.21

47.11
35.59
66.11

2

7.00

0-12
12- 24
24- 48

36
17
14

32.15
34.72
30.40

276.58
308.44
436.47

82.73
57.26
77.95

3

6.99

16.56
125.88
84
93.92
44
17.76
231.13
20.16
25
Crock 2D
Per Cent Soil Moisture — 17.50

49.20
22.70
55.26

1

6.15

0-12
12- 24
24- 48

59
23
15

13.89
18.15
11.17

59.18
151.65
446.20

29.66
58.61
85.95*

2

6.55

0-12
12- 24
24- 48

57
23
6

13.93
13.05
20.49

127.44
114.92
467.89

41.03
48.83
115.25*

3

5.70

0-12
12- 24
24- 48

18
8
6

30.70
26.88
15.67

442.17
524.96
642.09

67.40
56.65*
97.67*

0-12
12- 24
24— ,48

Table VII
(Continued)
Plant
No.

Dry Wt,
of plant
m.

P. P. M.

0-12
12- 24
24- 48

68
46
42

18.52
14.81
23. 68

90.49
42.25
105.19

37.87
27.35
28.40

CJI

»

Calcium

6.60

0-12
12- 24
24- 48

32
37
32

33.76
15.24
19.35

91.45
48.35
96.17

44.18
30.51
17.88

3

5.25

113.64
22. 36
38
21,26
95.25
22
200.77
32. 30
25
Crock 4Dl
Per Cent Soil Moisture — 18.36

43.13
27. 35
56.80

1

5.95

0-12
12- 24
24- 48

39
17
7

15.90
14.95
14.47

84.10
72.67
307.22

116.76
117.81
112.55

2

7.70

0-12
12- 24
24- 48

91
58
42

12.68
12.60
24.46

72.00
55.66
87.40

114.65
98.87
66.27

3

2.95

0-12
12- 24
34- 48

28
15
16

13.51
16.82
23.02

105.97
193.62
211.14

225.09
82.05
19.99

•

2

W

U1

1

Phosphorus ;Potassium
Solution
Collected
ml
Hours
P. P. M.
P. P. M.
Crock 4C
Per Cent Soil Moisture — 17.03

Period

0-12
12- 24
24- 48

1- 25 oc. of ether added to soil

Table VIII
Soil moisture, dry weight of plant tops, ml. of solution collected,
and the concentration of phosphorus, potassium, and calcium in the
solutions forced through plant roots from soil fertilized with 750
pounds PgOg and 1300 pounds of KgO per 1,000,000 pounds of oven—dry
soil by means of air pressure over consecutive periods of time. Hoots
killed by heating soil in crock containing plants to 70°C.
Plant
No.

Dry Wt.
of Plant
gm.

Period

Solution
Phosphorus Potassium
Collected
Hours
ml.
P. P. M.
P. P. M.
Crock 211
per Cent Soil Moisture — 15.70

Calcium
P. P. M.

GO

o

96
52
33

1.00
1.00
1.00

8.47
9.78
18.92

359.06
334.99
353.83

7.47

0 - .3
3-7
7 -25

85
46
29

1.00
1.00
1.00

9.84
8.64
12.20

324.52
315.10
341.27

7.47

87
51
33
Crock 4B
Per Gent Soil Moisture

1.00
1.00
1.00

11.27
13.24
25.35

362.20
330.80
359.73

00

0-3
3-7
7 -24

1

2

3

0-3
3-7
7 -25

—

16.80

1

7.05

0-4
4 -12
12-36

46
37
34

0.50
1.00
1.00

11.24
10.34
10.06

250.34
239.82
234.56

2

6.85

0-4
4 -12
12-36

39
35
33

0.50
1.00
1.00

11,50
11.14
11.91

247.18
249. 29
269.27

3

5.60

35
28
20
Crock 4E
Per Cent Soil Moisture

0.50
1.00
1.00

12.01
11.59
12.07

250.34
247.18
249.29

0-4
4 -12
12-36

—

16.87

1

5.65

0-3
3 -12
12-36

34
51
40

1.00
1.00
1.00

18.52
17.49
23.91

295.57
310.30
334.94

2

4.40

0-3
3 -12
12-36

29
40
35

1.00
1.00
1.00

17.44
17.34
27.07

315.55
344.05
390.23

3

4.60

0-3
3 -12

22
34
28,

1.00
1.00
, „ 1.00

17.40
16.24
17.03

312.40
330.28
397.10

- 11 and 8,)

Heating the soil resulted in a much increased rate

of flow and also shortened the time in which the flow was
decreased to zero.

This fact is evident when the amounts of

solutions collected over a given period of time, as is recorded
in tables S and 8, are compared with the amounts recorded in
tables 5 and 7.

The solutions obtained by means of roots in

soil which was not subjected to heating; were perfectly clear
and colorless at the time of collection, but some of the
solutions collected, after standing for from 12 to 24- hours,
became somewhat turbid.

Solutions obtained by means of roots

in soil subjected, to heating were clear but slightly yellow.
Much variation in the concentrations of phosphorus,
potassium, and calcium in the solutions are evident from the
data in tables 5 and 7.

Nevertheless, it will easily be seen

that the phosphorus'concentrations in the solutions obtained
from unfertilized soil are, on the average, not quite half as
high as they are in the solution obtained from soil which
received fertilizer applications.

Potassium and calcium in

the solutions varied more than did phosphorus and were less
consistent in any respect.

On the average, the concentrations

of both pota,ssium and calcium were greater in the solutions
obtained by means of the plant roots in fertilized soil than
they were in the solutions obtained by means of the plant roots
in unfertilized soil.

However, the inconsistency was so marked

that it does not seem plausible to attach any significance to
the average condition*

- 12 An inspection of the data in the same tables, however,
reveals a certain consistency in some respects.

The con­

centrations of phosphorus, potassium, and calcium in the
solutions obtained by means of plant roots in the same crock
were in closer agreement than the concentrations of these
elements in the solutions obtained by means of plant roots
in different crocks.

When the concentration of these elements

in the solutions procured by means of a given plant root are
followed through the consecutive periods in which these solu­
tions were collected, it is evident that considerable variation
exists.

However, a change in the concentration of an element

in the solution obtained by means of one plant root in a given
period was usually accompanied by changes in concentration in
the same direction although not necessarily of the same magni­
tude in the solutions obtained by means of the other plant
roots in the same crock in that period.

The more or lees

parallel fluctuations in the concentrations of phosphorus,
potassium, and calcium in the solutions obtained by means of
plant roots in the same crock during the time the solutions
were being collected were not consistent with regard to the
direction the changes in concentration would take.
Collecting the solutions in portions over consecutive
periods rather than as a composite lot was done with the idea
of distinguishing between solutions in the roots at the time
the tops were removed and that forced in by air pressure later.
The data obtained did not indicate any consistent differences
in the concentration of phosphorus, potassium, and calcium in

- 13 the first and subsequent portions collected.

(Tables 5 and 7.)

The potassium content increased in the latter periods, but this
was not equally true of phosphorus and calcium.
phosphorus, potassium, and calcium in the solution
obtained by means of roots subjected to heating differed greatly
from the concentration of these same elements in the solution
obtained by means of roots not subjected to heating.

Compare

the concentrations of these elements recorded in tables 5 and
7 with those in tables 6 and 8.
soil having been
potassium

As a result of the roots and

heated, the concentration of phosphorus and

in the solution is greatly reduced and the concentra­

tion of the calcium is much increased.
General Discussion
Since the method makes use of plant roots in the dis­
placement of soil solubles, plants must be grown; and the nature
of the method apparently assigns their growth to the more or less
artificial conditions coincident with plants which are grown in
a limited

amount of nutrient medium in a container.
Being

employed on a Purnell assistant ship in which

bean fertilisation had been designated as the problem of investi­
gation, it was logical for the writer to choose the bean plant
as the plant to be used in this research.

Furthermore, it

seemed logical to use soil as the nutrient medium, since its
use approximates, as nearly as possible, natural conditions
concurrent with the growing of the crop.

- 14 Regardless of what may be the opinion concerning the
method for determining the choice of composition and rate of
fertilizer applications, the results obtained were gratifying,
increasing the concentration of the phosphorus in the soil
solution or, more exactly, in a dilute acid extract of the soil,
to that considered sufficient, and increasing the potassium
slightly, resulted in a markedly increased growth of the bean
plants.

Whether or not it is due to the greatly increased con­

centration of phosphorus in the soil solution or to large addi­
tions of potassium, or both, cannot be discerned without further
experiment.
Plants from seed sown in August produced a somewhat
higher dry weight per plant than did those from seed sown later.
This is probably due to the more favorable growing weather in
the early fall.

The smaller differences between the plants

grown on the fertilized and unfertilized soils at maturity than
in the early stages of growth may possibly be accounted for,
partially at least, by the fact that as the plants increased in
size crowding resulted, slowing up the growth of the larger

plants.
The exact nature of the solution forced from the cut
stem stubs of the plants by the application of air pressure is
not known.

There can be no doubt that it is not soil solution,

unaltered; nor can it be root sap entirely, squeezed out by
the pressure applied, inasmuch as the amount obtained in many
cases is equivalent in weight to several times the weight of
the green plant too cut from the root.

While a table is not

- 15 included which gives the green weight of the plant tops, the
green weights were determined.

Moisture content of the green

plant tops ranged with small variation around 85 per cent,
thus the green weight of a plant top can easily he determined
from the dry weights of the plant tops given in tables 5, 6,
7, and 8.

To say that the solution obtained is soil solution

which is altered as a result of being forced through the plant
roots is probably as complete and accurate a statement as can
be made.

The solution is altered more by living roots than

by dead roots.
Planting was spread over a period of time in order
to have the plants as near the same age as possible when the
roots were used to displace solution fro# the soil.

Two

crocks were planted at a time, one containing fertilized soil
and the other unfertilized soil in order to determine, also,
the effect of fertilizer on plant growth.

The apparatus al­

lowed the use of only one crock at a time and since each crock
usually remained in the pressure chamber 48 hours, there would
have been considerable difference in the age of the plants
when they were used to displace soil solution if the planting
had been done all at one time.

Possibly this would not have

permitted comparison of the soil solution displaced through the
plant root on the same basis.
Any difference in the rate of flow of solution through
different plant roots in the same crock would appear at first
thought to be entirely a function of the absorbing surface of
the root in contact with the solution in the soil.

One would,

- 16 with this in mind, expect more solution to be obtained through
the roots of large plants than through small ones, however, this
is not always true.

Evidently some structural property peculiar

to the individual plant interferes with the passage of the solu­
tion into or through the roots.

However, a greater dry weight

of top may not necessarily be associated with a correspondingly
larger root system, especially the surface area of the root
system.
Differences in the rate of flow through plant roots
in different crocks may be accounted for in several ways, be­
sides differences due to the individual plant root.

The mois­

ture content of the soil seems to be a very important factor
governing the rate of flow.

Soil moisture contents below a

certain minimum value did not allow any solution to be forced
from the soil into the plant roots.
crock 2B (Table 3.)

This was the case with

The soil had a moisture content of 13.47

per cent when the crock was removed from the pressure chamber,
no solution having been obtained.

Also when crock 2D (table 7)

was placed in the pressure chamber no solution was obtained, due
to the dryness of the soil.

But when crock 2D was removed

from the pressure chamber, water added to the soil, and the
crock replaced in the pressure chamber after a short time was
allowed for the soil to absorb the water, solutions were forced
from the soil through the plant roots and collected in the
receiving flasks.

Other soil having a moisture content which

approached the minimum made possible the collection of only
small amounts of solution by means of plant roots.

(See table

-

5, crocks IB and ID.)

17 -

The moisture content in the soil in crock

ID is seen to have been lower than it was in crock 2B from which
no solution was obtained.

However, the moisture content of the

soil in crock ID was determined after the soil was removed from
the chamber.

Eighty ml. of solution is equivalent to the re­

moval of 1 per cent moisture from the soil and since 112 ml.
were removed through the plant roots and as there is always a
small loss of weight which was not accounted for, it is evident
the moisture content was well above the minimum at the time the
crock was placed in the chamber.

Moisture contents of around:

2 per cent above the minimum seemed to be sufficient to allow
a maximum rate of flow.

A higher water content than this, as

near as can be judged from the variable results, does not in­
crease the rate of flow materially in the first period but does
seem to reduce the rate at which the flow falls from its max­
imum to zero.

This becomes apparent when the amounts of solu­

tion collected in the successive periods in tables 5 and 7 are
compared with the amounts of solution collected in the succes­
sive periods under crock 3E, table 5.
It is evident that the rate of flow decreases rather
rapidly from the beginning of the flow.

This decrease, as

has been seen, takes place rega.rdless of a high soil moisture
content.

There seem to be only two ways to account for this—

clogging or collapsing of the root systems of the plants or
the removal of solution by the roots in the immediate vicinities
of the roots faster than it is replaced by the soil.

Clogging,

it would seem, would necessarily account for the less raoid

18 decrease in the rate of flow coincident with a high moisture
content and, apparently, both clogging and a deficient replace­
ment of solution in the vicinities of the root surfaces may
be responsible for the decrease in the rate of flow through
plant roots in soil having lower moisture contents.

The in­

creased rate of flow which resulted from subjecting the soil
containing the root systems of plants to heating is in accord­
ance with the results obtained by Kramer (3) when he applied
suction to the cut stem stubs of plants, some of which were
in soil which had been heated from 56° to 60°C. and others in
soil which was not heated previously to applying suction.
Considering the protoplasm in the roots to be killed as a
result of heating, the greater porosity noted in the dead
roots is in keeping with the known facts regarding the effects
of killing the protoplasm on the porosity of living membranes.
No explanation is apparent as to why the rate of flow decreases
so much faster in the case of dead roots than in the case of
living roots unless it can be attributed to greater clogging
of the system or the collapse of the root hairs.
Differences in the relative concentrations of phos­
phorus, potassium, and calcium in solutions obtained by means
of living and dead roots are attributed to a property associ­
ated with the living protoplasm of the root cells often referred
to as selectivity.

The concentration of these elements in the

solution obtained by means of dead roots, approaches the concen­
tration in which these elements exist in the soil extract.
This can be seen by comparing the concentration of these elements

-

19 -

in the soil, table 4, with the concentration of these elements
in the solutions in tables 6 and 8.

Higher concentrations of

phosphorus and potassium in the solutions obtained by means of
living roots than in solutions obtained by means of dead roots
apparently must be attributed to some power peculiar to the
living protoplasm enabling it to concentrate these elements
as they are taken in through the living root membranes from
the less concentrated soil solution which surrounds the roots.
The soil solution as a term used to designate the solution in
the soil at optimum moisture conditions is not comparable to
the solutions obtained by the air pressure method used here as
it has never been obtained unaltered.

No doubt concentrations

in the soil solution as it exists in soil are different from
those in a dilute acid extract of the soil, with which the com­
parison is made, or in solutions forced out of the soil at
moisture conditions sufficiently high to make expulsion possible.
This appears more probable when we consider the several forms
of soil water and the surface energy connected with these forms.
To what extent plant roots are able to remove these various
forms of water is little known.

Regardless of this, the premise

that soil solubles are concentrated as the solution from the
soil passes into the plant roots by some force as yet not under­
stood does not seem illogical.

Higher concentration of potas­

sium, especially, tends to correlate with a small rate of flow.
>1n cases where very little solution was obtained, it will be

seen that the concentration of potassium is usually extremely
high, a condition which accounts for the extreme variability

-

20 -

of the concentration of this element in the solutions.

This

is the case, whether or not the small rate of flow is due to
a low moisture content of the soil or some peculiarity of the
individual plant.
fact at present.

There seems to he no way to account for this
It would he interesting to study the effect

of producing a lower rate of flow by decreasing the amount
of pressure applied to the soil, on the concentration of potas­
sium in the solution obtained.

Associated with this ability

to concentrate appears one of differentiation.

Phosphorus

and potassium were much more concentrated in the solution ob­
tained by means of living roots.

Calcium, on the contrary, was

much more concentrated in the solution obtained by the dead
root s.
The low concentration of phosphorus and potassium and
the high concentration of calcium in the solution obtained from
the soil by means of dead roots indicates that when the plant root
is killed it acts merely as a filtering device for the removal
of solution from the soil, the concentration of these elements
in the solution removed being of about the same order as in the
soil solution.

The living root, on the contrary, serves as

more than a filtering device being able to concentrate in the
solutions to a marked degree some elements which apparently are
desirable and to repress the intake of others.
Pierre and pohlman (5) in their w;ork with exuded plant
sap from corn, sorghum, and Sudan grass plants report a similar,
although a more marked concentrating of phosphorus, in the ex­
uded plant sap over the concentration of phosphorus in the dis-

- 21 placed, soil solution as well as in the soil extract.

Silica

was similarly concentrated while calcium and chlorides were
found in the exuded plant sap. in less concentration than in
the soil solution.
Better correlation of the concentration of phosphorus
in the solution with applications of this element to the soil
than existed between the concentration of potassium and cal­
cium and the application of these elements is as would be ex­
pected since the addition of phosphorus to the soil increased
its concentration in the soil extract to a much greater extent
than did the addition of potassium and calcium increase the
concentration of these elements in the soil extract.
Pohlman and Bierre (6) found in their work with exuded
plant sap that applications of phosphorus to the soil resulted
in an increased concentration of phosphorus in the exuded sap
and that the concentration of phosphorus in the exuded sap
correlated well with the water soluble phosphorus and with the
available phosphorus in the soil as determined by the Truog
method.

The concentrations of phosphorus in exuded sap reported

in their article as well as those reported in the previous art­
icle (5) are much higher than any found in the solution obtained
by means of bean plant roots using the air pressure method.
Calcium, though only added to the soil in association
with phosphorus, increased materially in amount in the soil
extract and in the solution obtained by means of dead roots as
a result of the applications of phosphorus and potassium salts
to the soil.

Whether this is due to the actual amount of

-

22 -

calcium added or to the fact that the treatment may have re­
sulted in making the calcium already present more soluble is
a matter of conjecture.

However, the soil treatment resulted

in a slight decrease in the pH of the soil which no doubt has
some effect on the solubility of calcium.
The addition of 25 ml. of ether to the soil in crock
4 D , table 7, was made to see if it might result in increasing
the porosity of the root membranes as did killing the roots by
heating.

The odor of ether was evident in the solutions forced

through the roots, but the analysis of these solutions did not
show any marked differences in the concentrations of phosphorus,
potassium, and calcium from those in the solutions forced through
roots in soil to which ether was not added, although the calcium
content of the solution was higher, especially in the first
period.
The use of air pressure as a means of forcing solution
from the soil through plant roots appears to offer a profitable
means of investigating soil-plant nutritional problems, and
although the investigation using this method has not been suf-'
ficient to prove its value conclusively or to define its scope
and limitations it may not be out of place to point out some
of the general ways in which it apoears to be aoplicable to inves­
tigations of this nature.
Thus far the air pressure method has only been applied
to plants grown in potted soil but there appears to be no reason
why it cannot be aoplied to plants grown in the field if the
soil containing the roots is removed intact and placed in a

- 23 pressure chamber.

The method could be applied equally well

using plants growing in sand or water cultures, and it appears
that this procedure offers an unlimited opportunity for study­
ing the effects of the various solubles common to nutrient media
in regard to their individual and relative concentrations on
the intake of the separate elements from solution.

Toxic and

other unhealthy conditions could be studied from a standpoint
of solubles removed from the nutrient media by the roots.
It is possible that this method offers a means of
studying the habits of plant feeding relative to the age of
the plant and the kind of plant considered.

Therefore, it

may be possible through this method to account for the adapt­
ability of certain plants to certain soil conditions in the
different periods of growth, and of the adaptability of certain
plants to certain soils and their characteristic conditions.
There is little doubt but that there is an explan­
ation for the processes of plant feeding if only we can learn
the basic principles on which these are dependent.

Possibly

this method through its proper application may lead to a better
knowledge of the physical and chemical processes involved in
the intake of solubles from nutrient media by plant roots and
the effect of various environmental factors on these processes.

24 Summary
Air pressure applied to soil containing plant roots
displaced solutions from the soil through the cut stems of
the plants.

Solutions were obtained by this means from soil

over a range of moisture conditions, both above and below the
apparent optimum value.

The amount of solution collected

varied greatly with soil moisture conditions and individual
plant roots, but under optimum conditions a weight of solution
equal to several times that of the green plant top was often
obtained in from 12 to 24 hours.

Solutions so obtained were

clear and colorless.
Killing the plant roots by subjecting them to heat
resulted in an increased rate of flow of solution from the
cut stems as a result of the apolied air pressure.

The sol­

ution obtained in contrast to that obtained by means of livingroot s, although clear, was slightly yellow.
The rate of flow of the solution from cut stems de­
creased with time.

This decrease was fastest in the case of

dead roots and evident in the case of both living and dead
roots regardless of tbe soil moisture content.
Analysis of the solutions obtained showed a wide
variation in the concentration of phosphorus, potassium, and
calcium among individual plant roots,in the same crock, also
a wide variation of the concent rat ion? of' the solutions obtain­
ed by means of plant roots in different crocks.
On the average the concentrations of phosphorus,
potassium, and calcium in the solutionsobtained by means of

plant roots grown in fertilized soil were higher than the
concentrations of these elements in solutions obtained by
means of plant roots grown in unfertilized soil, however,
the only element to be consistent in this respect was phos­
phorus.

The concentration of phosphorus in the solution ob­

tained by means of plant roots in unfertilized soil was about
one-half that obtained by means of plant roots in fertilized
soil.

A good deal of variability is evident, but in general

the highest concentration of phosphorus in the solutions
obtained by means of the roots in the unfertilized soil is
below or nearly equal to the lowest concentration ootained
by means of the roots in the fertilized soil.
The better correlation of phosphorus in the solution
with fertilizer application that was obtained with potassium
and calcium was to be expected inasmuch as the fertilizer
application increased the concentration of the phosphorus in
the soil extract to a much more marked degree than it did the
concentration of potassium and calcium.
Solutions obtained from soil by means of living roots
contained phosphorus and potassium in much greater concentra­
tions than in the soil extract.

Calcium, on the contrary,

existed in the solution in less concentration theft in the soil
extract. (7)

The concentration of these elements in the solu­

tion obtained from soil by means of dead roots approached
closely the concentration of these elements in the soil extract,
the concentration of phosphorus and potassium being low and
the concentration of calcium high.

- 26 In consideration of the relative concentrations of
phosphorus, potassium, and calcium in the solutions obtained
from the soil by means of living and dead root systems and the
concentrations of these elements in the soil extract, it ap­
pears that the living protoplasm in the root membrane has the
power to concentrate certain desirable solubles as they are
taken into the roots from the less concentrated solution sur­
rounding the roots and to repress the intake of other elements.
Solutions obtained from the soil by means of dead roots have
a phosphorus, potassium, and calcium content similar to that
in a dilute acid extract of the soil, indicating that the
roots when dea.d act similarly to a mechanism for filtering
off the solution contained in the soil.
The method used in this investigation for displacing
solution from the soil by means of the root systems of plants
grown in the soil is suggested as one which may be of value
in the study of soil—plant nutritional problems.

LITERATURE CITED

Clark, E. P . , and Collip, J. B. 1925 A study of the
Tisdall method for the determination of blood
serum calcium with a suggested modification. J
Jour. Biol. Chem. 63: 461-464.
Kramer, Benjamin, and Tisdall, Frederick F. 1921 A
clinical method for the quantitative determin­
ation of potassium in small amounts of serum.
Jour. Biol. Chem. 46: 339-349.
Kramer, Paul J. 1932 The absorption of water by the
root systems of plants. Amer. Jour. Bot. 19:
148-164.
Miller, Edwin C. 1931
Plant Physiology. Page 370.
McGraw-Hill Book Company, New York.
Pierre, W. H . , and Pohlman, G. G. 1933 Preliminary
studies of the exuded plant sap and the relation
between the composition of the sap and the soil
solution. Jour. Amer. Soc. Agron. 25: 144-160.
Pohlman, G. G., and Pierre, W. H. 1933 The phosphorus
concentration of exuded sap of corn as a measure
of the available phosphorus in the soil. Jour.
Amer. Soc. Agron. 25: 160-170.
Spurway, C. H. 1933 Soil testing.
Tech. Bui. 132.

Mich. Agr. Exp„ Sta.

Truog, E . , and Meyer, A. H. 1929
Improvements in the
Deniges colorimetric method for phosphorus and
arsenic. Ind. and Eng. Chem., Anal. Ed., 1:
136-139.

i-*
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Plate I

Received 75° pounds of P2O5 and. 1200 pounds of K20 per 1,000,000 pounds of oven-dry
Untreated.

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