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Q!

EFFECT OF SOIL WATER CONTENT AND OXYGEN DIFFUSION RATE

ON GROWTH OF POTATO SETS

By

Lloyd. Peter .Lackson

A THESIS

Submitted to the College of Agriculture of Michigan State
University of Agriculture and. Applied Science
in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE

Department of Soil Science

Year 1956

*1»st 6L

ACKNOWLEDGEMEETS

The author wishes to express his gratitude to Dr..A. E. Erickson
for direction and guidance during the course of this investigation.

He is also greatly indebted to Dr. R. L. Cook and other members
of the Soil Science Department for guidance and encouragement.

The author is grateful to Dr. J. F. Davis for photographic work.

The leave of absence granted by Canada Department of Agriculture

is gratefully acknowledged.

 

 

 

«Mr
:Lv-

 

S‘lbmf

EFFECT OF SOIL WATER CONTENT AND OXYGEN DIFFUSION RATE

ON GROWTH OF POTATO SETS

By

Lloyd Peter Jackson

AN ABSTRACT
Submitted to the College of Agriculture of Michigan State
University of Agriculture and Applied Science

in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE

Department of Soil Science

Year 1956

Approved: Q? _ Lines—J

 

Lloyd Peter Jackson

ABSTRACT

Potato sets were planted in Oshtemo sand soil columns of eight
different heights. They were sub-irrigated. The soil water content
at the surface were inversely proportional to the height of the soil
column. Oxygen supply in the shorter columns was limited because of
excess water.

The platinum microelectrode method for'measuring oxygen
diffusion in soil was used to determine the rate of oxygen supply in
the various treatments. Oxygen diffusion rate increased and moisture
in the surface decreased with height of soil column above the free
water-surface.

Sprouting and growth of the sets as measured by emergence rate
and dry matter production were materially affected.by the water
content and oxygen diffusion rate in the soil.

Cut potato sets were also held in water saturated soils for
periods of one to six days and at temperatures of 50°, 65°, 70°, and
above 85°F. The detrimental effects of flooded soils on potato sets

increased with increases in temperature.

lt._-_..._..- ..

III. RPS-1R]
Aera

Gr

So

Po

De

Se

P11

Du]

Pl:

801

Lab

Tempe

IV . RESULTS

TABLE OF CONTENTS

CHAPTER PAGE
I. INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . .
II. LITERATURE REVIEW . . . . . . . . . . . . . . . . . . . .
Plants in general . . . . . . . . . . . . . . . . . . .
Potatoes . . . . . . . . . . . . . . . . . . . . . . .

Laboratory investigations . . . . . . . . . . . . . .

a: O\ Ox t' t' 0‘

F1.ld 1nv.st1gat10nn I O O O O O O O O O O I O C O O .
Irrigation investigations . . . . . . . . . . . . . . lO
Aeration measurements . . . . . . . . . . . . . . . . 11

III. EXPERIMENTAL STUDIES . . . . . . . . . . . . . . . . . . . 16

Aeration experiment . . . . . . . . . . . . . . . . . . 16
Greenhouse . . . . . . . . . . . . . . . . . . . . . 16
Soil . . . . . . . . . . . . . . . . . . . . . . . . l6
Pots . . . . . . . . . . . . . . . . . . . . . . . . . 16
Design of experiment . . . . . . . . . . . . . . . . . 1?
Seed stock . . . . . . . . . . . . . . . . . . . . . . 17
Planting . . . . . . . . . . . . . . . . . . . . . . . 17

Duration 0 O O O O O O O O O O O O O O O O O O O O O O 17

Plant measurements . . . . . . . . . . . . . . . . . . 18
Soil measurements . . . . . . . . . . . . . . . . . . 18
Laboratory measurements . . . . . . . . . . . . . . . 19
Temperature experiment . . . . . . . . . . . . ... . . . 19

IV 0 msst AND DI$USSIOH O O O O O O O O O O O O O O O O O O 21

CHAPTIB PAGE
Aerationexperiment.................. 21
Temperature experiment . . . . . . . . . . . . . . . . 37

V.SUMMARY......................... 1+2

BIBLIOGR-APHY O O O O O O O O O O O O O O O O O O O O I O O O O “3

TABLE

LIST OF TABLES

The Effect of Height of Soil Column Above the Water Table
on the Eon-Capillary Porosity and the Moisture Content
the Surface Soil . . . . . . . . . . . . . . . . . . .

The Effect of Height of Soil Above the Water Table on
Oxygen Diffusion Rate Pre—Emergence and Post-Emergence

The Effect of Height of Soil Column Above water Table on
the Time Required for Potatoe Sets to Emerge . . . . .

The Effect of Height of Soil Column Above Water Table on

the Rate of Growth of Potato Plants . . . . . . . . .

The Effect of Height of Soil Column on the Number Stems and

Yi.1d Per Plant 0 O O O O O O O I O O O 0 O O O O O I O O

The Effect of Height of Soil Column on the Yield Per Stem

Summary of Data on Soil Measurements and Yields . . . .

of

Results of Submerging and Holding Potato Sets in Saturated

Soil at Four Temperatures for Periods of From One to Six

Days Duration. Conditions Immediately on Removal From

submergence, and Result of Green Sprouting One Week Lat

er

PAGE

23

25

28

29

31

32
34

LIST

PLATE
1. Figure l . . . . . .
Figure2......
2. rigure3......
Figure“......

3. Figure 5 . . . . . .

F191r.60 . O. O O
1». Figure7......

rigur. 8 . . . O O 0

OF ILLUSTRATIONS

PAGE

................... 1h
................. lb
. . . . . . . . . . . . . . . . . . . 15
. . . . . . . . . . . . . . . . . . . 15
. . . . . . . . . . . . . . . . . . . 22
. 36
................... hl
. bl

I . INTRODUCTION

Air, with its accompanying oxygen content is essential to the well
being of higher forms of plant life.

The indispensable function of oxygen in plant life has been pro-

posed by Bonner et al (7) who point out that vital growth processes
such as water uptake and nutrient accumulation proceed with an expendi-
ture of energy which is dependent on aerobic metabolism. They have
concluded that the energy consuming processes within living organisms
cannot proceed when oxygen is not available to assist in respiration
and metabolism which provides the energy necessary for the discharge of
vital body work functions. Heald (33) states that when the oxygen
supply to living plant tissues is reduced or withheld they are likely
to smother with progressive death of various parts of the tissues.
This sub oxidation and the accompanying anaerobic respiration doubtless
contributes to the activity of certain plant diseases (33). Under
limited oxygen supply the damaged or dead tissues are susceptible to
putrefactive decay and consequently are invaded by rot producing
organisms (33). A. typical example of such condition is potato blackheart.
This disease is believed to be the result of derangement of normal
physiological processes because of unfavorable environmental conditions
and has been shown to occur when tubers do not obtain oxygen to supply
respiratory demands (4) .

Because deficiency in soil aeration is frequently suggested as an

agricultural problem, and is advanced as a reason for the failure of

certain species to grow, this series of trials was set up to determine,
quantitatively, the amount of oxygen required for statisfactory growth
during the early life of the cr0p'being studied. The crap chosen for
observation was the white, or Irish potato, (sp. Solanum tuberosum).

The potato is grown under a rather wide variety of soil conditions
but does best on a moist soil with ample aeration (54). Loam, fine
sandy'loam, or silt loam soils with especially good.under-drainage are
most desirable (5h). Detailed experimental studies of the soil air
requirements for potato growth have emphasized the fact that 'a considp
erable volume of air is required for the well being of the potato'I (55).

Space occupied.by air in a given soil increases or decreases in-
versely with moisture fluctuations and it is believed that many problems
of limited aeration are bound up with the problems of soil water (2).
In these experiments depth to water table was used to develop the
variations of air pore space in the soil.

The physical process of diffusion is considered the most important
means by which interchange of air in the soil is brought about (8).
A convenient and relatively rapid technique for the determination of
oxygen diffusion within the soil was recently developed (39. 1+1) and
this method was used to determine the optimum soil oxygen diffusion
rate for satisfactory sprouting and growth of the potato.

In a supplementary trial the result of submerging potato sets in
water saturated soil at four levels of temperature and for periods of
one to six days was studied. Appearance on removal from.submergence

and in a subsequent green sprouting test were the criteria used to

3‘

 

evaluate the effects of these treatments.

II. LITERATURE REVIEW
A. Plants in General

The dependence of root develOpment on soil air and its oxygen con-
tent has been the subject of many research problems. The vital role of
soil aeration in the life of plants has been demonstrated in the work
of such investigators as Livingston and Free (14), Cannon (l3, l4, l5,
l6), Cannon and Free (17) and Clements (19). Their findings have been
confirmed in greater detail in the more recent investigations of
Hutchins (36), Loehwing (45), Henderson (34), Boynton (6), Kramer (38),
Erickson (27), and Hepkins (35). The texts published by Raver (2),
Miller (50) and.Meyer and.Anderson (49) are also most enlightening

with regard to the essential nature of soil oxygen in the life of

plants. .

Cannon (13) demonstrated that total root growth, and rate of root
growth, decreased with low oxygen supply and concluded that composition
of the soil air was of less significance in aeration than was the rate
at which air flowed through the soil.

In seed germination studies Hutchins (36) observed that some weeds
germinated well with a slow oxygen supply while others required a very
rapid supply.

Loehwing (45) found that for optimum growth most roots depended on
free soil oxygen, and the improper cemposition of soil air resulted in

delay or failure of growth processes.

A close correlation between water absorption and respiration rate
in maize seedlings was shown by Henderson (34) who concluded that the
retarding effect of poorly aerated soils upon absorption of water may
be due in part to the toxic effect of carbon dioxide accumulation on
the root cells. Kramer (38) also concluded that rapid reduction of
water uptake by plants in poorly aerated media was probably caused'by
a high concentration of carbon dioxide which he found had an unfavor-
able effect on the protOplasm and protOplasm membranes.

Boynton (6) in his studies with apple tree growth found that higher
oxygen levels might be necessary for the production of new rootlets than
for the maintenance of'life in existing roots. Erickson (27) working
with tomato plants found that insufficient oxygen rather than excess
carbon dioxide was responsible for the characteristic differences
observed between aerated and non—aerated solutions.

The overall growth response of several plants to low partial
pressures of oxygen in the soil atmosphere was observed by Hopkins (35).
He feund that root growth ceased at an oxygen content below 0.5 per-
cent in the air surrounding the roots and suggested that quantitative
studies of soil aeration would be more desirable than the present qual-
itative studies.

The recent research work of Lemon (39), and Lemon et al (41) has
resulted in the deve10pment of apparatus by means of which quantitative '
soil oxygen determinations may be obtained. Using this apparatus Lemon
and Erickson (40), Archibald (1), Cook et al (20) and Wiersma and Mort-

land (60) have determined the soil oxygen requirements for several plant

species. They have also shown that plant growth is dependent on and
closely correlated with oxygen movement within the soil. Reduced growth
was noted in all trials when oxygen was in limdted supply. The use of
calcium peroxide as an oxygen supplier for three types of soil in which
sugar beets were grown was effective in raising the oxygen status of

the soils and the improved plant growth was attributed to the beneficial

effect of the oxygen released from the peroxide (60).
B. Potatoes

1. Laboratory investigations. Researches into the life and growth
habits of the potato (Solanum tuberosum) have resulted in an extensive
amount of literature covering all phases of the ontogeny and development
of this important plant species and the texts of’Burton (9), Stuart (56),
and Hardenburg (29) supply good reference material.

The potato is recognized as a type of plant storage tissue unable
to endure confinement which restricts or limits the air supply (55).
It is known that the end result of limited. aeration is the appearance of
the disorder called blackheart followed.by soft rot resulting from the
invasion of damaged or diseased tissue by putrefactive organisms (33).

Bartholomew (4) recognized the diseased condition known as black»
heart and determined that overheating was responsible for the damage
discovered in potatoes shipped in heated railway cars. In laboratory
trials he showed that heating tubers to 38° to 50°C for 14 to 18 hours
brought about changes in the respiration rate necessitating more oxygen

than was available (4).

Stuart and.Mix (55) confined potato tubers in hermetically sealed
Jars and.were able to develop blackheart symptoms in 10 to 12 days at
30°C. Their work demonstrated that the air supply, as well as tempera—
ture is a factor in the production of blackheart. Bennet and.Bartholo-
new (5), and Davis (23), as well as Singh and.Mather (53), all concluded
that blackheart of Irish potatoes is a good example of the detrimental
effects that may be initiated by conditions of anaerobic respiration.
Their general conclusion was that an accumulation of carbon dioxide and
a depletion of oxygen in potato tissue preceded the appearance of black»
heart. They suggested that the disease is attributable to high.respirap
tory activity and the failure of gas exchange to keep pace with
respiration rate.

Hardenburg (30) submerged dormant potato tubers of the Sebago and
Kathadin varieties for periods up to 10 days at temperatures of 40°,
50°, and 70°F, followed by green sprouting tests. Normal sprouts
developed on tubers submerged 10 date at 50° and 40° but at 70°F dead
eyes were general after three or four days. He considered temperature to
be the critical factor in damage caused'by flooding.

Ross and Robinson (52) also observed the effect of immersion of
potato tubers. Using sea water as well as fresh water they immersed
potatoes for periods up to three days. At 56°F the dormancy period was
shortened, while prolonged immersion resulted in soft rot of the tubers
and injury to the sprouts. When fresh water was used, severe rot was

observed in two days at 50°F.

Injury to and death of seed pieces at various temperatures and in
controlled or limited atmospheres was also demonstrated by Denny (24).
In his tests severe injury resulted when seed pieces were held in
closed containers at 35°C for 24 hours. Temperatures between 20°C and
30°C caused less injury. ‘A high respiration level and accumulation of

carbon dioxide were said to account for death of the tubers.

2. Field investigations. Growth failure because of seed piece decay is
known to be the cause of weak and.unthrifty stands of potatoes. Various
factors are assigned as reasons for this and many observations and
studies have attributed the trouble to physical conditions of the envir-
onment.

Jones (37) found little variation between varieties so far as seed
piece decay was concerned. He found the causative organisms to be
putrefactive bacteria which, generally speaking, are incapable of.in-
footing the tissues of sound healthy tubers. Preventive measures
suggested are those of soil sanitation through good drainage and aeration.

Reduced yields of potatoes in some Ohio experiments have been
attributed.by Bushnell (11) to the unfavorable physical conditions of
the soil brought on by faulty rotation methods. Yields were increased
following the adoption of a rotation which included sod crops and which
resulted in improved physical conditions of the soil (11).

Clark (18) conducted experiments to determine to what extent, if
any, tuber growth is influenced by soil type. He planted seed on a very

heavy clay (Billings clay loam), a clay loam (Fort Collins loam), and a

9
sandy loam (Colorado fine sandy loam). The lowest production of tubers
with.respect to both number and weight per hill was on the heaviest
soil, while the highest numbers and yield were produced on the lightest
soil.

Dunn (25) planted potatoes in soils containing 50, 60 and 70 per—
cent moisture and within temperature ranges of 140 to 15°C and 18° to
20°C. The most noteworthy result reported was that cold temperature
retarded sprouting.

McLeod (48) suggested that both soil and weather may be responsible
for conditions which favor tuber rot. He observed instances where total
or partial rotting of tubers appeared to be caused by soil that was too
wet or too dry. In a previous report (47) he stated that planting in
cold wet soil should be avoided.because such conditions favor the
rotting of the seed pieces.

Nbrking on Wooster silt loam, Bushnell (10) laid tile lines in the
ground Just below the root zone. Increased root deveIOpment and yield
obtained on that area were attributed to the improved aeration status
of the soil because of air movement through the tiles and into the
surrounding soil. In other yield trials on Wooster and. Canfield silt
loams (12) satisfactory yields were reported with an average pore space
of 49 percent, while considerably lower yields were reported when pore
space was only slightly less than 49 percent. Bushnell concluded that
this might be the minimum pore space requirement for potato growth on

those soils (12).

10
3. lipigation investigations. Water requirements for Optimum potato
production are quite high and a study of yields from irrigated and non-
irrigated plots illustrated the advantages of increased water supply
in locations of low or moderate rainfall (9). There is also a limited
amount of information on the harmful effect of excessive amounts of
irrigation water.

Harris (31) conducted experimental work on irrigation at various
stages of growth and at several rates of watering. The lowest yields
were obtained when the land was watered after the potatoes were planted
and before the plants had emerged. His conclusion was that water applied
at that time was injurious and that the period just after planting may
be quite critical in the life of the plant.

Edmunston (26) obtained good yields from irrigation at planting
time when he supplied considerable moisture to the soil that came in
contact with the seed piece but left the top 3 or 4 inches above the
seed.piece as dry as possible. He observed that the soil was not flood-
ed.

Hardenburg (28) in greenhouse experiments and Clark (18) and Werner
(59) in field trials concluded that irrigation during the growing
season is favorable to potato growth. Additional yields were obtained
as water supply was increased; however, Clark found too frequent waters
ing harmful and suggested the possibility of reduction in yield.because
of excessive irrigation.

In investigations of optimum and minimum requirements Harris and

Pitman (32), in Utah, found that low yields of potatoes were obtained

11
with less than 10 inches of water and that more than 25 inches also re-
duced yields. 0n the other hand.McGillvray (46) reported that 30 to 35
inches of water produced maximum yields under the soil conditions of
his trials. Cykler (22) obtained high yields of potatoes when the soil
water content was maintained at a high level throughout the growing
season. He pointed out that the water content of the soil was never
below one half the difference between moisture equivalent and the wilt-

ing point.

4. Aeration measurements. Many previous measurements of aeration have
been based on instantaneous determination of the air or oxygen status of
the soil. The inadequacy of this type of measure is freely admitted,
and the importance of rate of oxygen diffusion rather than original
supply has been.rec0gnized in the recent literature of Cannon (l3),
Hutchins (36), Taylor (57), Raney (51), and Lemon and Erickson (40).

The investigations of Lemon and Erickson (40) provided a very
efficient and practical method for the measurement of oxygen diffusion.
Using atrelatively simple and easily manipulated platinum electrode
they succeeded in measuring oxygen diffusion rate and obtained a good
correlation between rate of oxygen movement and growth of tomato plants.
It was found that a diffusion rate in the liquid phase of less than 30
grams x 10"8 per square centimeter per minute at the 8 inch depth may

be critical for tomato plants.

In tests with sugar beet Wiersma and.Mortland (60) found that a

8

diffusion rate of between 20 and 30 grams x 10" per square centimeter

per minute may be the critical range for sugar beet growth.

12

Cook et a1 (20) showed that a minimum of 45 to 50 grams x 10".8 per
sqare centimeter per minute is necessary for the growth of snapdragon
plants.

Archibald (1) using a similar technique to that of Lemon and Erick-
son pointed out the effect of limited aeration on the growth of sugar
beets and oats as successive craps in the same soil.

Erickson1 observed recently that the water content of field soil can
be related to the vigor and growth of potato plants growing in that
soil. On June 16, 1955. he found that potato plants on one section of
an experimental plot at Michigan State University were wilted while
plants farther along in the same row appeared quite normal. Tests made
on the two areas indicated that the wilted plants were in soil contain-
ing 20 to 21 percent water while the soil on which the plants appeared
normal was found to contain only 15 percent water. The aeration rates
for the two soils were respectively 37 x 10'“8 grams and 56 x 10‘8 grams
of oxygen per square centimeter per minute.

About six weeks after this observation the mature plants were
examined. Plate 1 shows representative plants growing on the two sec—
tions of the same plot. On Plate 2, Fig. 3 shows the growth of the tops
and yield of small tubers for plant number 1 which grew on the wet soil
and this is in sharp contrast to the plant in Fig. 4 with more luxuriant

growth and much larger tubers developed on the somewhat drier soil with

 

1Unpublished data, collected on an experimental plot area, Michi—
gan State University. Data on file with Dr. A. E. Erickson, Associate
Professor, Soil Science Department, Michigan State University.

13
improved aeration. It seemed that the critical aeration.va1ue for

potatoes growing in this Michigan field in the year 1955 was between 37

and 56 x 10"”8 grams of oxygen per square centimeter per minute.

PLATE 1

PLANTS.AT HARVEST

Fig. 1.
Note the stunted plants because of excessive soil water during

the growing season.

Fig. 2.
Plants of normal size, soil conditions were more favorable to

growth than in Fig. 1.

 

PLATE 2

YIELD OF PLANTS.AT HARVEST

July 18, 1956

Fig. 3.
Stunted plant and small tubers. The results of excessive soil

water during the growing season.

Fig. 4.
NOrmal sized plants with good tuber growth. The result of more

favorable soil conditions than for those plants shown in Fig. 3.

 

..
'-
x
. .
o
co

 

III . EDERDEENTAL STUDIES
A. Aeration Experiment

1. Greenhouse. This experiment, designed to study the related effect
of soil water and soil aeration on the establishment and initial growth
of the common potato was set up in the Sugar Beet Greenhouse at Michi—
gan State University, East Lansing, Michigan. The cr0p was grown

during the summer months when extremely hot weather conditions prevailed.

House temperatures were almost daily above 100%) for several hours.

2. Soil. The soil used for this experiment was Oshtemo sand, obtained

 

from a farm in the Rose Lake Conservation Area, located in Clinton
County, Michigan. The soil was passed through a quarter inch mesh
screen to remove all coarse material, then was thoroughly mixed and

placed in pots .

3. £933. Glazed tile eight inches in diameter were cut into 1+, 6, 8,
10, 12, 16, 20, and 24 inch lengths. The tile were made into pots by
covering one end (to be the bottom) with cheesecloth and placing them
in galvanized pans 2 inches in depth. The screened. sand Was packed
uniformly in each of the pots and as packing proceeding the soil was
thoroughly saturated with a complete nutrient solution. Each pot was
filled to within one half inch of the upper rim. The galvanized pan
was filled with water, thereby providing constant level sub-irrigation

and a source of capillary water for each soil column.

17

h. Design of experiment. The experiment consisted of eight replica—

 

tions of the eight pot heights with a total of sixty—four pots in all.
The pots were arranged in the greenhouse in an eight by eight Latin

square design.

5. Seed stock. Sebago seed potatoes grown in the fields at Michigan
State University in the crop year 1954 were obtained from the common
storage facilities of the Farm Crops Department, Michigan State Univer-
sity.

Pieces of uniform size each having at least two eyes and weighing
45 (2 2), grams were cut and placed in a cool cellar for fortyatwo hours

before being planted.

6. Planting. On June 24, 1955, the sets were planted, one to a pot,
at a depth of two inches. Sets were covered with about one inch of
soil.

It was thought that surface watering would be unnecessary during
the trial, but because of the high atmospheric temperature and associated
excessive evaporation, top watering was begun after the two-week emer—
gence period and was continued at twoaday intervals until the completion

of the experiment.

7. Duration. The eXperiment ran for thirtyhfour days with the main
interest centered on the reaction of the mother set to the various con—
ditions established within the soil of each treatment. Pro—emergence

effects were observed for fourteen days after planting and growth of

18
those plants which came through the ground was noted for a further

twenty days in the poet-emergence period.

8. Plant measurements. The experiment was terminated when the more
advanced plants had reached the full bloom stage.

Individual emergence dates were noted for all replicates of each
treatment. The date of emergence was recorded as the day on which fifty
percent of the plants were expanding their first leaves.

Individual height measurements were taken at two—day intervals
following the date of total emergence. The average length, in centi-
meters, of all stems on each plant was used as the index of growth for
that plant. The plants were harvested on July 28, at which time total
growth was determined by weighing the above ground portion of all living
plants. Measurement of root growth was also attempted but owing to
their fragile nature s considerable portion of the smaller rootlets
were broken sway in washing out the soil. For this reason, the root

measurements were considered unsuitable and are not included in this

report.

9. §gi;_peasurements. The platinum.microelectrode method, designed and
used.by Lemon (39), Lemon and Erickson (#0, #1), and recently modified
by Vsn.Doren (58) was used to obtain the oxygen diffusion rate in each
set of pots. Determinations were made at weekly intervals.

rive electrodes inserted in the soil of each pot to s depth of 2
inches were used to obtain initial and final current readings. From

these readings the rate of oxygen diffusion toward the surface of the

19
electrodes was calculated. As there seemed to be a steadily decreasing
resding in each treatment as the experiment progressed, the average
readings were calculated separately for the pre-emergence and post-

emergence periods.

10. ‘ngoratory measurements. Moisture retention and non—capillary
porosity were determined in the laboratory using the Leamer and Shaw
tension table (he). Metal cores one inch deep and.having a diameter
of three inches were filled with the same soil. After saturation with
water the losses in weight at tension increments corresponding to the
heights of the eight pots were used to calculate percent sir filled
pores in the surface layers of the soil in each treatment. The per-
cent moieture retained in the various porosity ranges was calculated

on an oven dry basis.

11. Tgmperature experiment. In addition to the previous experiment s
test was performed to determine the length of time before breakdown

of tissue occurs when potato tubers are immersed in saturated soil at
various constant temperatures.

Twentysfour lots of four out tubers each were placed in separate
pots containing Oshtemo sand. The soil in all pots was completely
flooded.with wster immediately after the sets were planted. Six lots
were placed in each of four locations having the following constant
temperatures (1) 50°F, (2) 65°F, (3) 70°F and (h) in the greenhouse where
the temperature varied with the normal daily fluctuation‘between 75° and

8501* st night to a maximum greater than 100% during the daytime.

20
Starting one day after planting one pot was removed from each tempera-
ture location every day for a period of six days. Two of the tubers in
each of the four pots were taken from the soil, examined, and placed
on a covered tray in a basement location for further observation and
green sprouting while the other two tubers were left in the soil. At
the same time a plug in the base of each of the four pots was removed
to permit drainage of_excess water. Each day thereafter a pot was taken
from each of the four temperature locations, two sets were removed and
placed on trays for the sprouting test, and.then the pots were drained
and placed on a bench in the greenhouse for observation of the two sets
remaining in the soil.

Emergence of sprouts from the sets in the soil held under the
greenhouse conditions was noted over a period of two weeks. This time
was considered adequate for any living tubers to sprout and send up
shoots.

The growth of sprouts, and the occurrence of decay on the sets

stored in the bamement were observed for one week.

IV. RESULTS AND DISCUSSION

A. Aeration Experiment

The pots shown on Plate 3 were arranged to illustrate the compara-
tive size of the soil columns. The shortest pot extended two indhes
above the free water surface while the top of the highest column was
twentybtwo inches above the water in the pans. The pots in Treatments
1 to 5 inclusive increased in.height by two inch increments while those
in Treatments 6, 7, and 8 changed by four inch treatments.

Plate 3 also shows some of the plants which were grown. Growth
was practically non-existent in Treatments 1 to h and the two plants
shown were the only ones living from the thirtyatwo sets planted in this
group. It is clear that the soil condition in the first four treatments
was decidedly unfavorable to the sprouting and growth of the potato sets.
On the other hand, the plants shown in pots 5 to 8, Plate 3, were chosen
as representative of the good stand of plants obtained. In columns 5
to 8 only three of the thirty-two sets in this group failed to produce
living plants and from this we may conclude that soil conditions in
these four treatments were favorable to sprouting and growth.

Certain soil conditions in the eight treatments are given in Table
l. The data relating to laboratory determinations of non-capillary
porosity, and tests of surface moisture at tensions corresponding to
those in the various soil columns are presented. The moisture content
as determined from samples of soil taken in the greenhouse at the con—

clusion of the experiment are also given. The almost complete filling

PLATE 3

Fig. 5.
Showing heights of the pots and plants from the treatments.
There were no plants in Treatments 1 or 3.
The plants shown in pots 2 and 4 were the only ones surviving in
these two treatments.
The plants in Treatments 5, 6, 7 and 8 are representative of the

growth obtained in these four soil columns.

 

WI

23

m MT 03‘ HEIGHT OF SOIL COLIMN ABOVE THE EASIER TABLE
ON THE HOB-OAPILLARI POESI'I'I m m MOISTURE

CONTENT 01' THE SURFACE SOIL

 

 

Soil Measurements I

 

 

 

1 Greenhous pot
Treatment Soil Laboratory cores soilsa
number column lion-capillary Moisture Moisture
inches porosity content content
42 i
l 2 2.4 25.# x
2 1+ 1+.8 23.8 x.
3 6 7.1 22.1! x
1+ 8 9.1 21.0 19.0
5 10 12.2 19.0 14.1
6 1'4 16.? 16.1 8.9
7 18 20.7 13.0 8.1
8 22 22.9 12.0 6.8

 

 

 

 

 

lDetermined on Leaner and Shaw tension table.

2

:30 sample.

Soil samples obtained from surface soils of each treat-
ment at the conclusion of the experiment.

2h

of soil pores with water in Treatment No. 1 is indicated. In this case
the low value of 2.4 percent non-capillary porosity is brought about
by a moisture content very near the saturation point. Progressive in-
creases in non-capillary porosity and at the same time a reduction in
soil moisture were obtained with increasing heights of the soil columns
above the water line.

The increases in porosity are indicated in the laboratory deter-
minations of pore space which ranged from 2.“ percent in Treatment No.
1 to 22.9 percent in Treatment No. 8 and are associated with a decrease
in water content from 25.“ percent to 12.0 percent. Data in Table 1
show that the moisture content of the soil under greenhouse conditions
was somewhat less than for the ideal conditions as calculated in the
laboratory. The difference was b.9 percent for Treatment No. 5 while
for Treatments No. 6, 7, and 8 the respective differences were 7.2, 4.9,
and 5.2 percent. These lower values obtained in the greenhouse were no
doubt caused by the excessive temperature and associated high evaporation
rate which prevailed during the time of the experiment and the fact that
the plants were extracting moisture from the soils in which they were
growing. Tabulated data presented later in this discussion reveal that
the relatively low soil moisture contents found in Treatments No. 7 and
No. 8 impose some limitations on the interpretation of the oxygen
diffusion data.

The rates of oxygen diffusion within the soils of the various treat-
ments were determined for the two-week pre-emergencs and the three-week

post-emergence periods and are shown in Table 2. All treatments showed

TABLE 2

THE EFFECT OF HEIGHT OF SOIL ABOVE TEE WATER TABLE ON
OXYGEN DIFFUSION RATE PRE—H-IIERGENCE AND
POST-EMERGENCE

 

Grams of oxygen x 10’8/cm2 per minute

 

 

 

 

Treatments __
l; 2 3. 4 5 6 7 8
Pro-Emergence
June 28 26.3 23.9 17.7 35.9 58.6 69.5 85.3 56.9
July 2 35.3 28.;1-_30.7 33.2 67.3 93.4 79.Lfi6fi.3
Average 30.8 26.0 2h.2 739:5 62.9 81.5 82.3 61g;_
Post-Emergence
July 9 25.8 26.0 30.7 29.5 64.9 103.8 110.5 67.6
July 16 11.2 9.3 12.8 19.6 140.1 76.2 61.7 33.5
July 23 7.4 621? 9.1 14.2 99.0 58:1» b7.1 26.5

 

Avegage 14.8 11.8 17.5 2’13; 51.3 79.4 73.1 142.5

26
differences in the rate of oxygen movement between the two periods with
a higher rate obtained in the pre-emergence period. In addition it was
observed that the differences between periods were of greater magnitude
in the short columns than in the higher columns. For example, the
average diffusion rate in the soils of Treatment No. 1 (the shortest
column) were reduced from 30.8 x 10"8 grams per cm? per minute to 19.8
x 10"8 grams per on2 per minute, the difference being 16.0 x 10'8 grams
per cmz. The diffusion values for Treatment No. 6 (an intermediate
height column) dropped only 2.1 x 10--8 grams per cm? per minute from
the pre—emergence to the post-emergence period. The moisture content
in Treatment 1 was 25.b percent while that of Treatment 6 was 16.1 per-
cent, (Table 1). The greater decrease in the shorter and wetter columns
is thought due to the reduction in effective pore space because) of sett-
ling and consolidation of particles and.because of an increase in oxygen
consumption due to multiplication of micro-organisms within the soils.
Under the conditions of heat and moisture the rapid reduction of organic
matter would also have a significant effect on soil conditions.

The number of days from planting to emergence are presented in Table
3. In Treatments 1 to h only two of the 32 sets grew and of these only
one made any appreciable amount of growth. Because of the very poor
growth obtained a crop failure is recorded in this group of treatments.
It is indicated that the condition of the soils in Treatments 1 to h

inclusive was entirely unfavorable to the maintenance of life processes

in potato sets.

2?

Satisfactory rates of sprouting and plant development were obtained
for the sets planted in the soils of Treatments 5 to 8 in which the
calculated emergence was 90 percent of the sets planted. The most rapid
rate of emergence was obtained in the soils of Treatment No. 5 for
which the average emergence rate was 11.3 days as compared with 12.9,
11.9, and 1h.“ days for Treatments 6, 7, and 8 respectively. In the
case of Treatment 8 the longer average time required for emergence was
probably due to the low amount of available moisture in the surface soil.
Table 1 shows the moisture content of the surface soil in Treatment 8 was
6.8 percent which.was less than one—half that measured in Treatment 5
for which the most rapid emergence rate was recorded.

In connection with the failure of growth in pots it should be menp
tioned that during the pre-emergence period a glazed (slick) appearance
was noticed on the soil surface in.most of those pots where plants did
not emerge. An examination of the sets following the two week pre-
emergence interval revealed that they were completely decayed. Inade-
quate rate of oxygen supply is suggested as the reason why the sets
failed to grow. The opinion is in agreement with ideas put forth by a
number of workers (a, 7, 2h, 33, 55) all of whom concluded that the
residues of metabolism under limited oxygen supply act as poisons
capable of disrupting the normal process on which the life of cells

depends.

The average growth rates for the individual plants in Treatments 5

to 8 are presented in Table 4. The plants in Treatment No. 5 made the

most rapid growth with an average increase of 1.9? centimeters per day,

TABLE 3

THE EFFECT OF HEIGHT OF SOIL COLUMN ABOVE WATER TABLE
ON THE THE REQUIRED FOR POTATOE SETS TO MERGE

 

 

 

 

.-

Number of days after planting

 

 

 

 

Treatment
1 2 A_3 # .5 6 7 8
Replicate
1 x x x . x 8 12 x 15
2 x x x 13 8 x 10 17
3 x x x x 12 12 12 15
4 x x x x x 12 15 19
5 x 8 x I 15 10 15 15
6 x x x 8 11 10 10 11
7 x x x x 13 17 10 13
8 x x x x 12 17 ll 10
Average8_* A
days 11.3 12.9 ,:11;9 19.9

 

x No emergence because of set decay.

28

TABLE 4

THE EFFECT OF HEIGHT OF SOIL COLUMN ABOVE HATER.TABLE ON
THE RATE OF GROWTH OF POTATO PLANTS

 

 

Height in Centimeters

 

 

 

Treatment .
5 6 7 8
Date

July 13 9.6 7.1 9.h 6.#
15 12.7 9.3 10.8 9.0
17 15.0 11.8 11.5 12.3
19 17.9 14.1 15.5 19.5
21 21.3 16.4 17.9 17.1
23 24.9 19.1 20.2 20.2
26 29.3 23.2 23.9 23.1
28 31.6 25.9 25.9 24.9
Average per day A 1.97 1.22 1.10 1.23

 

30
while in Treatments 6 and 8 the daily height increases were 1.22 and 1.23
centimeters respectively. Plants included in Treatment F0. 7 with an
increase of 1.10 centimeters per day made the slowest growth in the
experiment.

The data recorded in Table 5 present the numbers of stems on each
plant and the total dry weight of each plant. There was considerable
variation in the numbers of stems per plant as well as in the total
weight of stems produced by each plant. For example, the yield of
replicate 2 in Treatment No. 5 was 9.60 grams while only 0.52 grams
was obtained in replicate 7 in the same treatment group. In the case of
Treatment 6 the variation in yield was also very wide with the yield of
the heaviest plant being 7.3M grams and the lightest 0.90 grams of dry
matter. The variations within Treatments 7 and.8 are somewhat less
extreme than those obtained in the other treatments. Statistical analya
sis of the data indicated no significant difference between the treat-
ments in the test. The value obtained for the standard error serves to
point out the fact that there is as much variation within as between the
treatments.

With.the idea of bringing the individual plant values to a more
uniform basis for comparison of the total growth the average weight of
each stem was determined. The average weights for individual stems are
presented in Table 6. The values obtained continue to indicate the un—
even pattern of growth as pointed out in the discussion of Table 5. The
general trend, however, is to a heavier growth of Treatment 5 in.which an

average weight of 2.00 grams per stem was recorded as compared.with 1.23

{BABIES

31

TEE EFFECT OF HEIGHT OF SOIL COLUMN ON ME HUBER SEEMS
AND YIELD PER PLANT

 

-:
—:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Number of Stems and Yield per Plant
Treatment 5 6 7 8
ems Wei t Stems Weiét tems We t Stems Weight
Replications no. gm. no. a. no. gm. no. gm.
1 2 1.28 5 7.34 - - 2 1.52
2 u 9.60 - - 1 1.118 3 1.61
3 3 1+.1I0 3 3.35 2 3-25 5 3.04
u - - 2 6.00 1 1.20 2 0.48
5 1 2.13 2 1.116 1 1.06 5 3A6
6 2 8.64 2 1.60 5 6.89 1 3.60
7 1 0.52 2 1.15 1|: 3.94 1 0.75
8 L 2.50 1 0.90 3 2.03 1 2.1-I8
Average 1+.15 y 3.11 2.98 2.12
Analysis of Variance: Table 5
DJ'. S.S. H.511.
Total 31 195.1060
Replicat ions 3 39 .0870 13 . 162 l . 90
Treatments 7 10 . 0278 1 . [+33 0 . 21
Error 21 l . 12 6.933

 

 

 

 

 

 

TABLE 6

THE EFFECT OF HEIGHT 0F SOIL COLUMN ON THE
YIELD PER STEM

 

 

Weight per Stem

 

 

 

 

 

 

 

 

 

 

 

Treatment
5 6 7 8
Replication gm. gm. gm. $11.
1 0.64 1.1+? - 0.76
2 2.1-+0 - 1.148 0.514,
3 1.“? 1.12 1.63 0.61
a - 3.00 1.20 0.20
5 2.13 0.73 1.06 0.69
6 0.32 0.80 1.38 3.60
7 0.52 0.58 0.99 0.75
8 2.50 0.90 0.68 2.48
Average 2.00 1.23 1.20 1.21
Analysis of'Variance: Table 6
D.F. S.S. E.Sq. F .05
Total 31 33-3015
Replications 3 9.6053 3.202 3.177 3.07
Treatment 7 2 . 5367 0 . 362
Error _g;: _§;;1595 1.008

 

 

 

 

 

 

33

grams for Treatment 6. In Treatments 7 and 8 the average weight per
stem is 1.20 and 1.21 grams respectively. Statistical analysis of this
modified comparison once again has shown there is no significant diff-
erence between the treatment means. Comparing the analysis with that of
Table 5 the most obvious difference is the smaller error variance here,
showing that a variation between replications is responsible for a large
part of the total dispersion. Because of this wide variation between
replicates it seems appropriate that a suggestion be offered as to
causes contributing to this variation. The variable soil condition
because of freshly packed soil columns no doubt contributed considerably
to the variation and probably was responsible for an uneven moisture
distribution, particularly in the higher columns. In trials where
dependence is placed on capillary rise in the soil columns it would seem
the most uniform condition would be obtained if undisturbed cores were
obtained directly from the field. If this plan were not feasible the
next best would be to prepare the pots considerably in advance of the
time they were to be used thereby providing opportunity for consolidation
of the packed.material and possibly a development of more uniform con-
ditions within the soils of each pot.

Table 7 presents a summary of data and affords an Opportunity for
comparison of the various factors which were measured or observed during
this trial.

The results have pointed to the essential nature of soil oxygen and
the harmful effects which may occur when this material is in minimum

supply. It is indicated that unfavorable growth conditions existed in

TABLE 7

SUMMARY OF DATA ON SOIL MEASUREMENTS AND YIELDS

 

;—_

 

 

—___

 

 

 

 

 

Soil Surface Of 5°11“ Average Oxygen di fusign rate
T;::::;nt height Porosity Moisture yield gm. 1 10‘ /cm. /min.
inches § % Agrams P.E. p.e.
1 2 2.4 25.4 0 30.8 14.8
2 4 4.8 23.8 0 26.0 13.8
3 6 7.1 22.4 0 24.2 17.5
4 8 9.1 21.0 0 34.5 21.1
5 10 12.2 19.0 4.15 62.9 51.4
6 14 16.7 16.1 3.11 81.5 79.4
7 18 20.7 13.0 2.98 82.3 73.1
8 22 22.9 12.0 2.12 61.1 42.5

 

 

 

 

 

 

3h

35

Treatments 1 to h inclusive while in Treatments 5 to 8 growth was ob-
tained.whsn the soil water reactions were improved. By changing the
height of soil columns the porosity was increased from 9.1 percent
(Treatment 4) to 12.2 percent (Treatment 5) and the oxygen movement in,
creased from 34.5 x 10"8 to 62.9 x 10'8 grams per square centimeters

per minute which provided conditions favorable to the life and growth of
the potato sets.

The findings of this trial are in accord with results reported by
Cannon (16) who found that maize seedlings would not grow when soil
oxygen was less than 3 percent while Optimum growth was obtained in his
experiment when oxygen content had‘been increased to 8 percent of soil
volume. Baver and.Farnsworth (3) have also pointed out the essential
nature of soil aeration to crop growth and in their tests a total air
capacity of 8 percent gave good stands of sugar beet but when air
capacity fell to 2 percent about half the beats perished and.yie1ds de-
clined.

Figure 6 shows the relation between the various observations as
listed in Table 7. It is shown in Figure 6 that decreases in soil water
content were accompanied.by increases in non-capillary porosity. For
example, reductions in soil water from 25 to 12 percent were accompanied
by increases in non-capillary porosity (air space) from 2.4 to 23.0
percent. The oxygen diffusion rate increased with the increases in
porosity until a point was reached at which the instrument was incapable
of functioning efficiently. Then a decrease in reading was observed.

In this trial the decrease was noted at about 20 percent porosity and 14

36

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aseoaem eaoamaoz anew.
93 99 «.3 93 oém {an Tau {we
. _ _ J . . . a on
m a m m a n u H
L u on
\
\
\
..m , — \\ . 0.:
\
- \
\
II: \ \ I on
\
\\
Um \ T 8
\
In 3.3 u E
somewnoaonaaem
\ sonata samba O O I u om
\\ somewaoaeleam a. u m “n
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1w...”

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ION

LB IS 01106: WORSE

37
percent soil moisture. It is believed that at this soil water content
there was insufficient moisture in the soil to adequately moisten the
surface of the electrode and allow for optimum operation of the instru—
ment. Lemon and Erickson (#1), and.Van Doren (58) explained that the
effectiveness of the platinum electrode is dependent upon a complete
moisture film on the exposed electrode surface. The lack of this
moisture film causes errors in the observed values. They have pointed
out that under these conditions a measure of oxygen diffusion is mean-
ingless'because soil porosity and aeration are improved and are no long-
er a limiting factor to plant growth.

In Figure 6 the diminishing yield values are believed related to
the lower moisture content of the soils as the height of soil column in-

creased from 10 inches for Treatment 5 to 22 inches for Treatment 8.
B. Temperature Experiment

The data in Table 8 show that when submerged for only one day sets
retained a natural appearance and the tissue was firm and quite normal
regardless of temperature. There was a slight indication of sprout
growth taking place. In two days the sets submerged at 50°! and 60°!
retained a normal appearance but those held at a temperature of 70°F and
above seemed to have some softening of the tissue on the cut surfaces.
0n the third and successive days a softness or sponginess of the tissues
was quite noticeable in all except those held at 50°F temperature. In
the 50° treatment the tissue of the sets appeared to be not greatly

affected'by the unusual conditions of the six day test.

TABLE8

38

RESULTS OF SWERGING AND HOLDING POTATO SETS IN SATURATED SOD; AT
FOUR W8 FOR PERIODS OF FROM ONE TO SIX DAYS DURATION.

BISULT OF GREEN SPROUTING ONE WEEK LATER

CONDITIONS IMMEDIATELY ON REMOVAL FROM SUBMERGENCE, AND

 

 

 

 

 

 

 

 

 

 

 

 

 

Mnmpera fire if m
Days 0 65‘y 20° 816 - 105U
ubmerged 0n 1 week On 1 week 0n 1 week 0n 1 week
rflval later reggvg later removal later removal later
1 1' S F S F S F D
2 1' S I D D D
3 1' 8 SP D SP D Sp. D
4 1' D - Sp D Sp D Sp D
5 l' D Sp D Sp D Sp D
6 1' D Sp D ’ Sp D Sp D
F = Firm Sp = Sponsy
S = @routing D 1' Decay

 

39

The observations in the greenpsprouting test were made one week
after each lot of sets had been placed on the trays. These results are
also set out in Table 8. The tubers submerged for one and two days at
50°F were alive and grew sprouts. They seemed to be relatively unaffect-
ed by the period of confinement under water. Those tubers submerged for
three days at the 50° temperature also developed a good sprout but
typical blackheart symptoms such as contraction and discoloration of
tissue in the center of the tuber was observed. There was, however,
enough firm and living tissue under the skin to permit sprouting. These
tubers were not completely harmed and would doubtless make some growth
if placed in soil but they could not be classed as good material for
seed purposes. The tubers submerged for periods longer than three days
at the 50° temperature did not grow in the sprouting test but were in an
advanced stage of decay after the end of one week, Table 8.

The sets submerged for one day at 65oF and 70°F were still alive
as indicated‘by growth in the sprouting test. Those submerged.at these
two temperatures for periods of two days or longer failed to sprout
when placed on the trays and were in an advanced stage of decay at the
end of one week, Table 8.

There was no indication that tubers submerged at the greenhouse
temperature (85°F or above) were alive after being immersed for only one
day. Extensive tuber damage was easily observed in all sets held at
this temperature and no growth was obtained when the sets were placed on

the trays.

140

Further evidence of the comparative damage to potato sets when sub-
merged in saturated soils at various temperatures is illustrated on
Plate 4. The sets in Figure 7 are typical of those which had been sub-
merged for five days and putrefactive decay had taken over in all
pieces. Somewhat less damage is indicated in Figure 8, the specimens
having'been submerged at the indicated temperatures for only two days.
At 50°F no serious tissue injury was observed and sprouts grew in a
normal manner. The sets from the other temperatures were not living and
the tissues were considerably contracted as observed when blackheart is
present, and decay is active.

The possibility of using blackheart potatoes for seed purposes has
been investigated by Coons (21). He found affected tubers undesirable
for seed purposes, even though only partly damaged by the disease and
reported that germination, vigor, and yield under field conditions were
inversely pr0portional to the degree of blackheart developed in the seed
piece. Heald (33) stated that potatoes affected.by blackheart sprout
feebly, or not at all, and are unfit for seed purposes but it is possible
that slightly affected tubers may be strong enough to make a good seed.

The findings of this test agree very well with those reported by
other workers. Potato sets kept at 50°F or below may not‘be greatly
affected‘by short periods of anoxia caused.by unusual soil conditions
such as flooding but serious physiological dissorders occur at tempera—
tures of 60°F or greater when air (oxygen) supply is reduced if only for

a brief time as in the case of soil flooding.

41

PLATE 4
SPECIMENS FROM THE SOIL FLOODING AND GREENSPROUTING TEST

Fig. 8

Sets submerged two days at four temperatures then held one week in
the greensprouting test.

Very slight decay shown on sets submerged at 50°F and sets had
begun to sprout.

At temperatures of 60°F and higher all specimens were rotting

and had no sprouts.

Fig. 7

Sets submerged five days at four temperatures and held one week in
the greensprouting test.
Soft rots have invaded all the specimens and no sprouts were

visible indicating complete suffocation of the sets.

 

 

 

 

”....ko
no ..- Men

 

V. SUMMARY

Oshtemo sand in eight different heights of soil columns was pro-
vided with constant level sub-irrigation as a source of capillary water
supply. Depth to water level developed variations of water content and
air pore space. The related effects of soil water and soil aeration on
the germination and growth of potato sets planted in the soil were
studied.

1. Differences in vegetative growth were obtained and the close
relationship between soil air supply and the health of potato sets was
demonstrated.

2. Increases in soil moisture above 19 percent reduced soil air supply
to a critical level at which death and decay of practically all sets

was observed.

3. In an.immersion test potato sets were held in soil under water for
periods from one to six days and at various temperatures. The results
obtained suggest that in appraising possible damage due to prolonged
flooding in the field the temperature appears to be a very important
consideration.

4. Nonpcapillary porosity and soil moisture content of the seed bed are
very important factors in the starting and growth of strong healthy
potato crops.

5. In locations where infiltration is slow and water ponding or excess
soil moisture is a problem, the effect on potatoes because of the accom-
panying reduction in soil aeration is doubtless a limiting factor in

successful potato growth.

 

1.

7.

9.

10.

11.

12.

13.

l“.

BIBLIOGRAPHY

Archibald, J. A. Effect of soil aeration on germination and
development of sugar beets and oats. M. S. Thesis, Michigan
State College, 1952.

Baver, L. D. 8011 Physics, 2nd Ed. John Wiley and Sons, Inc..
New York, 1998.

Baver, L. D. and R. B. Farnsworth. Soil structure affects in the
growth of corn and sugar beets. Soil Sci. Soc. Amer. Proc. 5:
its—148 , 19140.

Bartholomew, E. T. Blackheart of potatoes. Phytopath. 3: 180-
182, 1913.

Bennett, J. P. and E. T. Bartholomew. The respiration of potato
tubers in relation to the occurrence of blackheart. California
Agr. Exp. Sta. Tech. Paper 14: 1.35, 1924.

Boynton, Damon. Soil atmosphere and the production of new rootlets
by apple tree root systems. Proc. Amer. Soc. Hort. Sci. 37: 19—
26, 1939.

Bonner, J., Robert S. Bandurski, and Adele Millard. Linkage of
respiration to auxin-induced.water uptake. Physiol. Plantarum 6:
511-522. 1939.

‘Buckingham, Edgar. U.S.D.A. Bureau of Soils Bul. 25, 1904.
Burton, W. G. The Potato. Chapman and Hall Ltd. London.

Bushnell, John. Sensitivity of the potato plant to soil aeration.
Jour. Amer. Soc. Agr. 27: 251-253. 1935-

Bushnell, John. Reasons for the low average yields of potatoes in
Ohio. Amer. Potato Jour. 16: 67—70, 1939.

Bushnell, John. Sensitivity of potatoes to soil porosity. Ohio
Agr. Exp. Sta. Bul. 726. 1953.

Cannon, W..A. Root growth in relation to a deficiency of oxygen
or an excess of carbon dioxide in the soil. Carnegie Inst. Wash.
Pub. 368, 1925.

Experimental studies on roots. Carnegie Inst. Wash.
Yearbook 22: 56-62, 1923.

 

15e

16.

17.

18.

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20.

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27.

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29.

44

The influence of the temperature of the soil on the
relation of the roots to oxygen. Science 58: 331-332, 1923.

 

Experimental studies on roots. Carnegie Inst. Wash.
Pub. 24, 1925.

 

and E. E. Free. The ecological significance of
soil aeration. Science N. S. 45: 178—180, 1917.

 

Clark, Charles 1. Development of tubers in the potato. U. S. Dept.
.Agr. Bul. 958, 1921.

Clements, Frederick E. Aeration and air-content; the role of
oxygen in root activity. Carnegie Inst. wash. Pub. 315: 183 pp.,
1921.

Cook, R. L., A. E. Erickson, and P. R. Krone. Soil factors affecting
constant water level sub-irrigation. Amer. Soc. Hort. Sci. 62: 491-

496. 1953-

Coons, G. H. The use of blackheart potatoes for seed. Michigan
Agr. Exp. Sta. Quart. Bul. 6: 182-184, 1924.

Cykler, John F. Effect of variations in available soil water on
yield and quality of potatoes. Agr. Eng. 27: 363-366, 1946.

Davis, Ward.B. Physiological investigations of blackheart of potato
tubers. IBot. Gazette 81: 3239338, 1926.

Denny, F. E. The importance of temperature in the use of chemicals
for hastening the sprouting of dormant potato tubers. Amer. Jour.

Bot. 15: 395-404, 1928.

Dunn, Stuart. Effect of soil moisture and fertilizer placement on
vitality of the potato seed piece. New Hampshire Agr. Exp. Sta.
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