 

THE mama-ma OF LEGHT, YEMPEkﬁT‘JRE
AND NUTMTiGN 0N- TEE SﬁOWﬂ-é
RESPONﬁE OF SKAPDRAGON

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Timrs for ﬂu Degree of M. S.
MECHIGAN SHE WHERSIW
Donaid Daniel Juchartz

1958

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This is to certify that the
thesis entitled
The Influence of Lig'jht, Tysrzln-rL-gture, and

lfutri‘tien on the GI‘<_:1‘.'tl1 Response
of Slagsdrugnn imtirrlinum maju: L.

presented by

Donald Du iel Ju e :chz

has been accepted towards fulfillment
of the requirements for

0- 8. degree in IlOrto

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Date ,1?!) 19 VANS?

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THE INFLUENCE OF LIGHT, TEMPERATURE AND NUTRITION
ON THE GROWTH RESPONSE OF SNAPDRAGON

ANT IRRHINUM MAJUS .11“

 

By

DONALD DANIEL IUCHARTZ

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 Horticulture

1958

Approved W" . -" i. ”5 .. J,

DONALD DANIEL JUCHARTZ ABSTRACT

The interaction of three light intensities, three minimum night
temperatures, and four fertility levels on the growth rate of hybrid snap-

dragons (Antirrhinum majus if) by the criteria of fresh weight, dry weight,

 

and leaf area, was determined at five time intervals.

Growth rate by each criterion was significantly influenced by
light intensity, temperature and fertility. Although the interactions lacked
significance, optimum fertility levels at low light intensity increased leaf

area and minimized differences in dry weight due to low light intensity.

THE INFLUENCE OF LIGHT, TEMPERATURE AND NUTRITION
ON THE GROWTH RESPONSE OF SNAPDRAGON

ANTIRRHINUM MAJUS I:

 

DONALD DANIEL JUCHARTZ

ATHESIS

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 Horticulture

l 958

ACKNOWLEDGEMENTS

Grateful appreciation is extended to Dr. W. J. Haney, Department
of Horticulture, who as the major professor and personal friend of the
author, did so much to bring this study into being. His readiness and willing-
ness to take time from a busy schedule to explain or assist with some of the
actual work, meant much to the author. Also, without the assistance of Dr.
G. J. Hogaboam, U. S. Department of Agriculture, Sugar Beet Research
Section, in the matter of unraveling some of the complexities of the statistical
analysis used herein, this study would have been much more difficult. Thanks
also belong to Dr. F. W. Snyder, U. S. Department of Agriculture, Sugar
Beet Research Section, and Dr. Haney, for suggesting the problem.

The author sincerely appreciates the assistance given by Dr. R. L.
Cook, Head of the Department of Soil Science, for making available the
assistantship under which this study was performed. The advice given dur-
ing the course of the experiment and the reviewing of the manuscript is
acknowledged with thanks.

However, the greatest debt of appreciation and thanks belongs to
the author's wife. Doris, whose constant encouragement and patience meant
much to the author. The many hours she spent assisting in obtaining meas-

urement data and keeping records will always be gratefully remembered.

Part

1::

IV

TABLE OF CONTENTS

Page
Introduction........ ..... ........ 1
Review of Literature . . . . . . . . ....... . . 3
Objectives...................... 11
Materials...................... .12
A.PlantMaterial.................. 12

RSoilMixture................... 13
C. Greenhouse and Physical Equipment . . . . . . . . 16
1.Pots..................... 16
2.Benches................... 16
3.Temperature................. 17
4.LightIntensity................. 18
D.NutrientSolutions................. 20
1. Basis for Nutrient Solution Composition . . . . . 20
2. Solution Composition. . . . . . . . . . . . . . 23

E. MeasuringInstruments. . . . . . . . . . . . . . . 26

v. MethOdS O O O O O O O O O O O O O O 0 O O O O O O I O O O O 30

A. Experimental Methods . . . . ...... . . . . . 30
1. Preliminary Investigation . . . . . . . . . . . . 30

2. Plot Design and Physical Set-up for Principle Inves-
tigation....................34

TABLE OF CONTENTS CONT'D
Part Page
3. Nutrient Application. . . . . . . . . . . . . 36
4.HarvestingMethod.............. 39
RAnalyticalMethods................ 40
1.PlantMateria1................ 40
a. FreshWeight. . ...... . . . . . . . 40
b.LeafArea................ 40
c.Dry.Weight................41
2. Soluble Salt Content of the Soil . . . . . . . . . 42
C.StatisticalAnalysis.. .. . .... .. .. 43
VI ResultsandDiscussion-. . . . . . . . . . . . . . . . . . 44
A. Effect of Light Intensity on Optimum Fertility Level. . 44
B. Effect of Temperature on Qatimum Fertility Level. . . 50

C.‘ Interaction of Light and Temperature on Optimum Fer-
tility Level O O O O C O O I O I O O O I O O C O C O 54

D. General Discussion of Results. . . . . . . . . . . . 60
VII Summary........................66

VIII Bibliography.......................69

Figure

LIST OF F EURES

Area-photometer wiring diagram ...... . . . .

The effect of full light intensity and optimum fertility
levels on leaf area at 50, 60 and 70° Fahrenheit . .

The effect of two-thirds light intensity and optimum fer-
tility levels on leaf area at 50, 60 and 70° Fahrenheit

The effect of one-third light intensity and optimum fer-
tility levels on leaf area at 50, 60 and 70° Fahrenheit

The effect of light and fertility interaction on the ratio of
increase in yield on a dry weight basis at 70°F in
33 ays O O O O O O O I O O O O I O 0' O O O O O O

The effect of light and fertility interaction on the ratio
of increase in yield on a dry weight basis at 60°F in
33 days 0 O O O O O O O O t O O O O O O O O O O O

The effect of light and fertﬂity interaction on the ratio of
increase in yield on a dry weight basis at 50°F in 33

days 0 O .0 O O O O O O O O O O O O O O O O O O O

The interaction of light, fertility level, and temperature
on the basis of dry weight yield in grams, in 62 days

Page

27

45

46

47

51

52

53

55

LIST OF TABLES

Table 1 Page
I - Potency of a Single Plant Nutrient in Terms of Baule Units
and Percent of Maximum Crop Yield, all other Plant
Growth Factors at the Optimum . . . . . . . . . . . 21

II Equivalency of Fertility Levels with Baule Units . . . . . 22

III Ratio of Increase of Fresh Weight of Snapdragon Plants -
SummerCrop................... 32

IV Ratio of Increase of Leaf Area and Dry Weight of Snapdragon
PlantS'SummeI'Cl‘Op.......o......o 32

V Nutrient Application Rates and Conversions . . . . . . . 37
VI Baule Unit Equivalency Table. . . . . . . . . . . . . . 38
VII Effect of Light Intensity and Fertility Level on the Overall
Ratio of Increase in Yield on a Fresh Weight, Dry Weight
andLeafArea,in33Days............. 48

VIII Significance of the Differences in Averages of Fertility Level
Values, for Dry Weight Yields. . . . . . . . . . . 56

1X Significance of Differences in Averages of Temperature
Values, for Dry Weight Yields. . . . . . . . . . . . 57

X Significance of Differences in Averages of Fertility Level
Values, for Leaf Area Yields. . . . . . . . . . . . 58

XI Significance of Differences in Averages of Temperature
Values, for Leaf Area Yields. . . . . . . . . . . . 58

I. INTRODUCTION

The relationship of a plant to its environment is a complex system,
with mutually inﬂuencing interdependent factors affecting the photosynthetic
process of the plant as well as the other functions involved in its physiolo-
gical processes. Hoagland and Arnon (19) felt that the most complex biolo—
gical process known is the nutrition of a plant in soil, with three factors
being taken into account: the plant, the soil system, and the above ground
environment. Under natural conditions of environment, the external appear-
ance of plants is determined by genetic and physiological factors, as they
are modified and inﬂuenced by the prevailing ecological conditions. Accord-
ing to Thomas (55), some of the principal ecological factors to be evaluated
are: light intensity, temperature, soil moisture, age of the leaves, general
nutritional level, and concentration of particular nutrients, such as nitrogen,
phosphorus, or potassium.

The variation of individuals within one species is set within certain
limits by genetic factors. Physiological factors determine the morphological
and formative expressions within these limits. Investigations by Wassink
and Stolwijk (60) have indicated that the boundaries set by these genetical
limits are not as confining as formerly believed, and can be altered provided

the physiological treatment is adequately differentiated.

Since one of the principal functions of plants is that of photosyn-
thesis, any condition inﬂuencing this process is important. The photosyn-
thetic rate inﬂuences the growth rate and ultimate fresh and dry weights of
the plant. Thomas (56), has demonstrated that the growth rate and weight
of a plant provide indirect and approximate measures of the photosynthetic
rate.

Spurway (53) has shown that optimum plant nutrition depends on
the supply of available plant nutrients in the soil, in conjunction with the
environmental and soil conditions which control the utilization of the nutrients
in the growth of plants.

In order to compare soil fertility or fertility level with quantita-
tive crop yield, a standard measure of plant nutrients as required by crops
or plants is necessary. The classical work of Mitscherlich and his co-
workers (34, 35), who discovered certain plant-nutrition relationships, has
had a great influence on yield predictions and soil fertility diagnosis.

The purpose of this investigation was to determine the inﬂuence
of light, temperature, and nutrition levels on the growth response of plants,

using for this study, the snapdragon (Antirrhinum majus 1.1.).

 

II. REVIEW OF LITERATURE

The growth of plants in a natural condition is one that is ever-
changing as the development of the plant is inﬂuenced by its variable en-
vironmental surroundings. When a plant is taken out of its natural habitat
and subjected to varying cultures, the interactions brought about assume
significant proportions.

Many areas of inﬂuence on plant growth have been investigated,
some of which are: plant nutrition, effect of light, soil moisture, and
temperature. One of the earliest attempts to relate the interaction of
plant nutrients and other factors affecting plant growth and the growth or
yield of a plant was expressed by Liebig with his "Law of the Minimum"
(46, 62), which states that the amount of plant growth is regulated by that
growth factor present in minimum amount and varies according to whether
this minimum factor is increased or decreased. Growth will increase
with additions of the limiting factor until it no longer is limiting, at which
point plant growth becomes independent of this factor. With a further in-
crease, a point is reached when it becomes toxic and causes plant growth
to decrease. It was upon this foundation that all future work was based.

Unfortunately, this law has a limited validity, for if several factors are

low, increasing any one will increase the yield.

Beginning work with this premise, Mitscherlich (35) undertook
to express the exactness of the experimental curves in mathematical
terms, and the formula he derived is widely known. He assumed that a
plant should produce a maximum yield if all conditions were ideal, but
with any essential factor limiting growth there would be a corresponding
shortage in the yield. Also, the unit increase in the plant produced by
a unit increment of the limiting factor is proportional to the deduction
from the maximum, or expressed mathematically: 5311;; = (A - y) C, where
y is the yield obtained when x is the amount of the limiting factor present,
A is the maximum yield obtainable if K were present in an optimum amount,
and C is a constant. Mitscherlich claimed that the proportionality factor
C was a constant for each nutrient, independent of the crop, the soil, or
other conditions. He used this formula to predict yields (35) and in other
ways (33), such as estimating the amount of available nutrients in a soil
through direct pot experiments.

Many workers have tried to improve on this equation, as may be
seen in the work of Baule (4), Bondorff (8, 9), Balmukand (3) and Spurway
(53). However, the interest in a more exact equation has abated, as shown
by Gregory (15) in his review of the work of plant physiologists on this sub-
ject, inasmuch as the response of a plant or crop to a nutrient depends on

many factors, such as the environmental conditions and the levels of the other

nutrients present.

The necessity for an adequate water supply with fertilizer applications
was shown by von Seelhorst (50) in 1898 at Gottingen. Lundegardh (25) reviewing
work of Mitscherlich on the influence of soil-moisture percentage in terms of
moisture capacity, indicates that the yield of potatoes varies from 16 percent
with 20 percent saturation to 100 percent with 80 percent saturation, and is
decreased to 62. 5 percent yield with 100 percent saturation.

Under favorable growing conditions, the period of rapid vegetative en-
largement is often characterized by increasing increments of total amounts of
inorganic elements, carbohydrates, and proteins. Boresch (7), Maksimov (26)
and White (61) have shown that many annual type plants have a tendency toward
absorption of the major portion of their total mineral supply in early stages of
growth.

Gregory (16) has drawn attention to the fact that over 90 percent of the
nitrogen and phosphorus taken up by a developing cereal plant had been accumu-
lated when the dry weight was only 25 percent of the final value. This store of
accmnulated nutrient was the reserve on which all later growth and develop-
ment depended, and its level determined the final yield. Loehwing (24) has
stated that the early absorption of these minerals is generally in excess of
actual needs when the external supply is adequate. Anderson and others (1)
have shown that with balanced conditions or constant supply, nitrogen, phosphorus
and potassium increase faster in the plant than calcium, iron, magnesium and

sulfur.

Goodall and Gregory (14) have demonstrated that the rate of absorp-
tion of a particular ion is determined not only by its availability in the sub-
strate but by the concentration present in the plant. Blackman and Rutter
(5) have concluded, as a result of their investigations, that the beneficial
effects of fertilizer applications are due primarily to an increase in foliar
area and of assimilative tissue rather than to an increase in the efficiency
of assimilative processes.

The three elements needed in largest amounts in plant nutrition
are nitrogen, phosphorus and potassium. Many investigations have been
made on the inﬂuence of these elements on plant physiological processes.
Ballard and Petrie (2) studied the effects of varying nitrogen supply on the
ontogeny of plants. Mason and Phillis (30) observed the inﬂuence of boll
formation on the redistribution of nitrogen in cotton plants after the external
nitrogen supply was removed, showing that nitrogen migrated from vegeta-
tive areas to the reproductive tissues. Williams (64) has presented data
for amounts of protein, nitrogen and for total and nucleic acid phosphorus

in Phalaria tuberosa leaves, suggesting that unduly rapid, short growth can

 

accelerate the senescence of more mature tissues by inducing the hydrolysis
of the nucleic acids.

Nightingale (37) has shown that certain plants can utilize ammonium-
nitrogen equally well or better than nitrate-nitrogen. For many plants, pro-

vided the growing conditions are optimum, ammonium ions may be a better

source of nitrogen than nitrate ions. If the relative efficiencies of the two forms
of nitrogen depended solely on the conservation of energy by the plant, ammonium-
nitrogen would be the preferred form, since nitrate absorbed by plants must go
through a reduction process prior to being assimilated into organic nitrogen com-
pounds. This reduction process requires energy. Nitrogen in the ammonium
form is already in a highly reduced form and immediately available for assimi-
lation. The energy necessary for nitrate reduction appears to be obtained at

the expense of carbohych‘ates which have been synthesized and stored by the

plant.

According to Nightingaleplants do not grow nearly as well on nitrogen
in the ammonium form at low as at high light intensities, which may be the re-
sult of forced utilization of carbohydrates for protein synthesis. With low light
intensities carbohydrate synthesis and reserve storage are low. Forced utili-
zation may deplete the reserves markedly and derange the growth pattern of
the plant. Ammonium-nitrogen can be utilized for protein synthesis and growth
at a rapid rate with high light intensities and the maintaining of carbohydrate
reserves.

Hewitt (18) cites evidence to indicate that plants grow as well or
better on a mixture of ammonium and nitrate nitrogen than on either form a-
lone. In a general statement, Miller (32) indicates that young plants may more
effectively utilize ammonium-nitrogen and older plants nitrate-nitrogen, although

this is not true for all plants.

Wagner (57) has shown that in cats the amount of phosphorus rose
to an early maximum in the leaves, later in the stems, and still later in the
inﬂorescence, with over 70 percent of the leaf phosphorus translocated.

Sommer (52) indicates that limited supplies of both nitrogen and phosphorus
will hasten senescence when other nutrients are in adequate supply. Williams
(63) found that the net. movement of nitrogen from the leaves was delayed by
phosphorus deficiency. He also found the rate of intake of nitrogen and phos-
phorus to be governed by the external concentration or supply of the nutrient,
and by the demand for the nutrient set up by the growth and normal function-
ing of various plant parts, including the roots. However, he considered
nutrient intake to be most often subject to the controlling inﬂuence of growth
factors other than concentration.

Eaton (12) has demonstrated the interference of potassium with nitro-
gen metabolism. The inhibitory effect of potassium deficiency upon the formation
of cell walls has been shown by Mulder (36). Investigations by Rathje (43) have
shown that the potassium level of the cell controls the processes of photosyn-
thesis and respiration to a high degree, and that conversely, the extent of
these metabolic processes is important for the uptake of potassium. Pirson 239.1:
(40) worked with algae of the Chlorella type to demonstrate the effect of potas-
sium deficiency and the inﬂuence of light on reversibility and recovery. O'Rourke

and Marshall (38) investigated the stimulation of inhibited growth in tung trees

caused by a lack of potassium. Schwabe (49) demonstrated an increased
sensitivity to strong light in bracken, with the effective range of light inten-
sity considerably narrowed by potassium deficiency. Russell (45), working
at the Rotham sted Experiment Station, found that applications of potassium
fertilizers were particularly effective in weak light.

Blackman and Wilson (6) grew sunﬂowers with and without shade
and later transferred them to other light intensities. They found that re-
gardless of early lighting conditions, the net assimilation (grams of dry
matter per 100 square centimeters of leaf surface per week) in the second
period was the same linear function of the logarithm of the light intensity
during the second period, even though some of the plant characters, like
leaf area, were modified by the early lighting. Previous exposure did not
appreciably modify the subsequent response of the plants to light. Pirson
(39) has collected evidence on the recovery of plants from a mineral defi-
ciency and its effect on photosynthesis and respiration, which shows that
an adequate level of potassium in the plant allows utilization of the shorter
wave lengths of light.

Withrow (68), in his review article, sums up the known inﬂuences
of light on the mineral nutrition of plants, as do Wadleigh and Richards (56)

on the relation of soil moisture to the mineral nutrition of plants. The effect

10.

of light intensity and light duration on woody plants has been reviewed by
Wareing (59), and the further effect of light quality on plant growth by
Wassink and Stolwijk (60).

Of more particular interest to snapdragon culture, is the work
of Flint and Asen (13), in which they conclude that the snapdragon was
injured by a high nutrient intensity. Earlier work by Post and Bell (42)
in 1936, showed that an excess of a single salt could also be injurious.

A summation of all the interactions of the many growth
factors on a plant, can be depicted in a growth curve, similar to that
of Kreusler, Prehn and Hornberger (21), whose slope can be modified

by adequately differentiated physiological treatment.

11.

n1. OBJECTIVES

In setting up this study, three main objectives were in mind.
Inasmuch as light intensity, temperature and fertility rates can be some-
what manipulated in the average greenhouse range, it was desirable to
determine the effect of the interactions of light, temperature,and fertility
upon the growth rate of plants and to plot the results as growth curves.

The effect of light, temperature, and the interaction of light and tempera-
ture on optimum fertility level, are the three main sections of investigation
undertaken.

The original study was to carry through a snapdragon crop for
each of the three main growing seasons, summer, fall and spring. We were
not able to maintain the crop in the fall, giving only a summer and early spring
crop. The summer crop, using MSC No. 16 snapdragon seed, was used as a
crop for investigation purposes.

During the summer months, the solar radiation reaches its highest
intensity and is accompanied by higher temperatures than at other times of the
year. Snapdragon crops grown at this time have often produced poor quality
while demonstrating a capacity for rapid growth. These characteristics might
indicate inadequate fertility. The first investigation was designed to determine
levels of fertilizer application snapdragon plants would tolerate. The second in-

vestigation utilized these results in conjunction with varying light and temperature.

12.

IV. MATERIALS

A. Plant Material

 

The plant material chosen for this study was the snapdragon
hybrid, designated experimental MSC No. 16, produced by crossing a true
breeding early deep bronze F6 from the cross Scarlet O'Hara x Lady Dorothy
times a homozygous pink F6 from the cross Helen Tobin x Armstrong's White.
For the purposes of this experiment, plants exhibiting uniformity, reproduc-
ibility, and maximum genetic growth potential were desirable. In repeated
bench trials this hybrid had been consistently excellent in vigor and unifor-
mity (17). The snapdragon plants used in this study were grown from seed.
Cuttings were not utilized, nor considered, from this or other plants because
of the lack of uniformity in the resulting plants. Robbins (44) has stated that
"any increase in the genetic uniformity of plants permits the use of a smaller
number of replicates of cultural treatments without loss of statistical signi-
ficance of the data than is possible with plants produced from the seeds of
parents of markedly dissimilar genetic constitution. " An ample source of
seed, produced under controlled conditions, was available from the Depart-

ment of Horticulture, Michigan State University.

13.

B. Soil Mixture

 

The soil mixture utilized in these experiments was of the follow-
ing composition by volume: (1) three parts of Miami loam soil, (2) two
parts of local, fine sand, and (3) one part of German peat". .This soil was
thoroughly mixed, shredded and steamed for approximately three hours,
with the equipment in use at the Michigan State University Plant Science
greenhouses. The three-inch pots utilized in this study were filled with
approximately equal weights of this soil mixture, to equalize the moisture-
holding capacities of the pots, seven days after steam sterilization of the
soil mixture, at which time the 15-day-old snapdragon seedlings were
transplanted into the pots.

Preliminary investigations indicated that seedlings transplanted
within 24 hours of steaming into "sterilized" soils were apparemly bene-
fitted greatly by the amount of nitrogenous nutrients immediately available.
Russell and Hutchinson (47) have found that a primary cause of this stimu-
lation comes from the ability of microorganisms in the soil, surviving
this partial sterilization, to produce more ammonia and nitrates than did
the original population, and also to increase to greater numbers due to the
reduced number of antagonistic or competitive organisms.

Chemical tests run by the Spurway method (54) indicate that im-

* Purchased from Cottage Gardens, Lansing, Michigan.

14.

immediately after steaming, high ammonia values were found coupled with

high nitrites. This was to be expected, as was the fact that the presence of
nitrates was not apparent until most of the nitrites had been oxidized. It has
been shown by Schloesing and Muntz (48, 58) that the transformation of ammonia
to nitrates is largely biological in nature, and is accomplished in two steps.
Winogradsky (65, 66, 67) isolated an ammonia oxidizing and nitrite producing

bacterium, which he called Nitrosomonas, and a nitrite oxidizing and nitrate

 

producing bacterium, which he called Nitrobacter. Martin gt 3.1: (28, 29) have

 

produced direct evidence to show that nitrate formation in soils occurs through
the nitrite stage. Therefore, with steaming, the ammonia released is oxidized

to nitrites by Nitrosomonas bacteria, and this nitrite is further oxidized to

 

nitrates by Nitrobacter bacteria. The immediate effect of steam sterilization

 

on soils appears to be similar to that of an addition of nitrogen fertilizer.

For this reason, the soil was leached twice daily for seven days with
distilled water before using, thus removing much. of the additional nitrates pro-
duced as a result of steaming. I

By actual test, the weighing of 256 soil-filled 3-inch pots, it was deter-
mined that the weight of soil in these pots varied less than one percent. By
assuring constant weight of soil and complete mixing, it was possible to

assume that the moisture-holding capacity and the soil moisture would be

relatively equal in all units of the experiment.

The soil volume had been so adjusted in each pot that, with the
addition of a seedling, there were approximately 50 cubic centimeters
of volume remaining after the soil had been settled. This allowed the

same amount of water to be applied to each plant at each watering.

16.

C. Greenhouse and Physical Equipment

 

1. Pots

The pots used in these experiments were new 3-inch porous clay
pots, not painted or treated. * Before being used they were steamed with
the potting soil and were set aside for seven days before the seedlings
were transplanted into them. To assure that all water and nutrient solu—
tion applied to the pots would remain in the soil, aluminum foil cups were
made and placed over the bottom of each pot. After each application of
nutrient solution, allowing time for percolation and drainage, these cups
were inspected for any liquid and if present it was placed on the top of
the pot again to be absorbed by the soil. Generally speaking, it was not
necessary to do this because all of the 50 milliliters of solution applied

remained within the pot in the soil.

2. Benches

The three benches employed were cement sided and bottomed, with
a tile drain extending down the center of the V-bottom, set approximately
two and one-half feet above ground level. The benches were filled to an ap-

proximate depth of six inches with fine, sharp, white silica sand. Four

* Purchased from F. W. Ritter and Sons, South Rockwood, Michigan

17.

lines of steam heating pipe ran directly beneath the benches and the south
glass walls of the greenhouses extended below the level of the benches.

Access could be gained to the plots only from the north side.

3. Temperature

For purposes of this study it was desirable to grow plants at vari-
ous temperatures to affect the structural development and physiological
reactions of the plant. According to Meyer and Anderson (31) the optimum
temperature for the elongation or enlargement phase of growth is seldom
the optimum for other portions of the growth cycle. Each stage in the plant's
development usually has a different optimum temperature. In many instan-
ces, the optimum temperature for seed germination is higher than that for
vegetative growth which may be lower than that required for ﬂowering or
fruiting.

In the case of the snapdragon, it has been commercial practice to
grow this crop at a temperature of 48 to 50°F, night temperature, as advo-
cated by Post (41).

Snapdragon seedlings, grown at 55°F until they were 29 days old,
were placed into three greenhouse compartments, each completely separated,
where the temperatures were governed by means of Minneapolis-Honeywell
thermostats controlling the ﬂow of steam through the four lines of pipe be-

neath the benches.

18.

Temperatures employed were 50, 60 and 70°F, night temperatures.
During the day the temperature varied in accordance with commercial prac-
tice for bright and cloudy days. Close control was maintained of the night
temperatures.

Each greenhouse was ventilated by two rows of manually operated
continuous roof ventilators running the entire length of the roof on both sides

of the ridge. No side ventilation was available.

4. Light Intensity

An extremely important part of the environment necessary for plant
growth is light, including its quality, duration and intensity. Various mani-
pulations have been made of all three to determine the effect on plant de-
velopment. The light source used in the majority of instances for crop
growth is that of the naturally occurring solar radiation. This radiation
varies in quantity daily and with the time of the year, as shown by Crabb
(10).

It is this variation in light conditions that makes it possible for a
grower in one section of the country to have a cultural advantage over
another in many cases. In an attempt to define the interaction of fertility
level and temperature with light intensity, three levels of light intensity

were employed with each temperature and fertility level.

19.

For purposes of controlling the light intensity, each bench used
was divided into thirds, with one section left unshaded and one section
covered with approximately twice as much shading material as the third
section. Those portions shaded were completely enclosed with the shad-
ing material.

The shading material used was No. 240 bleached-white cheese-
cloth. An average of about 100 light readings, using a Model 756 Weston
light meter, indicates that, compared with unrestricted solar radiation
through the greenhouse glass, the nonshaded portion had 100 percent
light, one section had 30. 8 percent shade - 69. 2 percent light, and the
remaining section had 59. 6 percent shade - 40. 4 percent light, or approx-

imately 0 shade, 1/ 3 shade, and 2/3 shade, at plant height.

20.

D. Nutrient Solutions

1. Basis for Nutrient Solution Composition

On the basis of the Mitscherlich-Baule theory, the ultimate yield
of any croup would be realized, all other growth factors being at the opti-
mum, with the following amounts of N, P205 and K20 per acre: N - 2250
pounds; K20 - 820 pounds. This would be equivalent to about a 5-1-2
formulation.

However, while agreeing in theory with the ideas of Mitscherlich
and Baule, Spurway (53) disagrees with the amounts of the three important
nutrients. According to him they become: N - 1, 000 pounds; P205 - 200
pounds; K20 - 370 pounds. For purposes of this study the values of Mitscherlich
were used. In Mitscherlich and Baule's thinking, these values were considered
to be the maximum amount of fertility required and are referred to as ten
Baule units of fertilizer, with one Baule unit being equal to one-tenth of these
values. Soil fertility is balanced then, quantitatively, when the same number
of Baule units of all plant nutrients are available to a crop.

In calculating possible yields on the basis of these Baule units,
Mitscherlich devised a universal yield formula: Y = 100-(0. 1 x 2(10 - X) ), in
which Y is the percent of maximum crop yield, and X is the plant nutrient in

Baule units per acre. Using this formula, the following values are apparent

as taken from Spurway (53):

21.

TABLE I

Potency of a Single Plant Nutrient in Terms of Baule Units and Percent of
Maximum Crop Yield, all other Plant Growth Factors at the Optimum

‘ L J.
—-—————r :—; J t—

 

 

 

Baule Units Percent of Maximum Crop Yield

 

a;

.4

OOOOOOOOOO

OWONrFmQNhh-OO

O\O\O\O\O\O\O°°

.—
p...

 

Inasmuch as the unit volume of soil concerned here was that con-
tained in a 3 -inch pot, the N-P-K values of Mitscherlich were converted
from pounds per acre to grams per 3-inch pot. To reduce the number of
variables, superphosphate was added, in a dry form, to the soil mixture
prior to planting, in an amount equivalent to at least ten Baule units of phos-
phorus. The levels of nitrogen and potassium were varied. To introduce
continuity with standard commercial practices of fertilizer applications,
the basic unit of commercial fertilizer recommendations was converted to

‘ grams per 3 -inch pot, and this used in making up the fertility levels.

22.

Preliminary investigations showed that with the following rates of
application, the solution concentration for further studies could be selected,
inasmuch as the No. 1, 2, 6 and 7 levels were definitely not optimal, under

the environmental conditions imposed.

TABLE II

Equivalency of Fertility Levels with Baule Units

 

 

 

 

 

 

 

Calculated ' Applied
Ba‘fle Mg. per 3-Inch Pot Fertility Mg. of Nutrients
Units
N K20 Level N K20
1 47 17 1 - -
2 95 35 . 2 22. 8 8. 5
3 142 52 3 45. 7 l7. 0
4 189 69 4 91. 3 33. 9
5 236 86 5 182. 6 67. 9
6 283 103 6 365. 2 135. 7
7 330 120 7 730. 5 271. 4
8 377 137
9 424 154
10 471 171

 

Employing the concept of a 5-1-2 formulation it was determined that
the Baule unit of nitrogen would be equal to 47. 0 mg of nitrogen per 3-inch
pot. Post (41)’ and Laurie and Kiplinger (22) recommend that ammonium
nitrate be applied at the rate of one-half pound per 100 square feet. Upon
converting to a nitrogen value, for purposes of this study, the unit application

of nitrogen was considered to be one-half pound per 100 square feet or 45. 7 mg

23.

per 3-inch pot. The amount of K20 to be applied was adjusted to this value
with the Baulic ratio recommended by Mitscherlich. The unit application
of K20 is equal to 0. 19 pounds per 100 square feet or 17. 0 mg per 3-inch
pot.

Upon this basis the solution composition for the actual experiment

was formulated.

2. Solution Composition

In making up a nutrient solution to use in these studies, it was neces-
sary to include only two nutrients, nitrogen and potassium. To obtain a
solution such as this, ammonium nitrate (NH4NO3), and potassium nitrate
(KNO3) were employed. The ammonium salt was Baker's Analyzed and
the potassium salt Fisher Reagent grade. Distilled water was used through-
out.

These two chemical compounds were chosen because of the absence
of other nutrients and because of the high amounts of nitrogen and potassium
contained therein: NH 4N03 - 35. 0 percent nitrogen; KNO3 - 13. 9 percent

nitrogen and 46. 6 percent K O. In addition, the fact that NH NO3 contains

2 4
ammonium ions may have an important effect as far as a continuous supply

of nitrogen is concerned. The results of many experiments have shown

that with autotrophically fed green algae, nitrate and ammonium salts can

24.

serve as practically equivalent sources of nitrogen, as has been demon-
strated by Pirson, Tichy and Wilhelmi (40). It is very difficult to estab-
lish the biochemical equivalence of ammonium and nitrate nutrition even
if indications can be obtained from the visual appearance of plants; as
determined by Pirson (39), the plants used for comparison can show dif—
ferences within the range of physiological tolerances.

The work of Lees and Quastel (23) has demonstrated that the site
of soil nitrification is on the adsorption surface of the soil complex. Rela-
tively little nitrification takes place in the soil solution compared to that on
the .soil where the ammonium ions are adsorbed. The nitrifying bacteria
in the soil preferentially oxidize the adsorbed ammonium ions as opposed
to those in solution. Thus, by supplying a source of ammonium ions, a
continuous source of nitrogen was assured, even after the initially added
nitrates were taken up.

As a result of the findings of the preliminary investigations, the
range of solution concentrations was reduced so as to consist of only four
fertility levels, (1) 0, (2) . 5X, (3)1;X, and (4) 2X.

The basic stock solution was made up to 10 liters of a one-fifth
strength solution and applied to the plants in five weekly 50 milliliter incre-
ments. This was done so as to make the nutrients available in less quantity

to reduce the chance of injury to the plant, and allowed the plant to utilize

a portion of the total nutrient supply over weekly portions of the experi-
mental period. Fertility level "1" received 50 milliliters of distilled

water at nutrient application time.

25.

26.

E. Measuring Instruments

 

During the course of these studies various types of measuring
instruments were employed for which descriptions and nomenclature
follow:

Thermo-Humidigraph: Continuous temperature readings were taken

 

in each greenhouse through the use of Bristol Thermo-Humidigraphs,

1
Model 4069TH. These instruments, through a 24-hour period, recorded
the temperature and humidity.

Area-Photometer: The measurement of leaf area, in square centimeters,

 

was made while the leaves were in a fully turgid condition, by means of

an Area Photometer, 2 which, when calibrated with a Keuffel and Esser com-
pensating planimeter, gave area in square centimeters. The area photo-
meter is sensitive to the optical density of the plant material being
measured, and it is necessary to make individual calibrations for each

type of material. The wiring diagram is shown in Figure l. The D. C.
circuit is actuated through light from the lumiline bulbs passing through

an aperture and striking the photronic cell. Plant material being measured
is placed on a glass tray over the aperture and the amount of light prevented

from passing through to the photronic cell is a measure of the area of the material.

1Purchased from the Bristol Company, Waterbury, Connecticut.

2Manufactured by the Agricultural Instrument Company, R. D. 1, State
College, Pennsylvania.

L} 4— Pilot light

 

 

 

 

 

V0”. LOAD
[/0 v (’99-

 

 

 

 

 

 

 

 

/ 3 - Amp. fuzed \
disconnect switch

Type 20 powerstat
automatic xmfr.

LOAD: Eight 40-wott GE lumiline bulbs

VOLT. REG.= Sorenson regulator, mod. 500 S, KVA 0-5,
freq. 50-60.

A. C. CIRCUIT

 

W 0 -250ﬂ Rheosfaf

-- Normally closed ®

micro - switch

 

 

._v—

Weston mod. 856 RR

Weston mod. 30/, 0.0.
photronic cell

microammeter, 200 [2,
0-200 ,u amps.

D. C. CIRCUIT

AREA-PHOTOMETER
WIRING DIAGRAM

Figure 1

27.

28.

M Two types of balances were used to obtain the fresh and dry weights
of the plants. Fresh weight was determined on all plants harvested by means
of a Shadowgraph, Model 4104-A, l calibrated to tenths of grams. Weights
of individual plants were estimated to hundredths of grams. Dry weight was
obtained through the use of a Torsion Balance, 2 calibrated in grams with
estimation to tenths of grams.

Solu-Bridge: In some soils, such as greenhouse or truck garden soils and

 

in some alkali areas in the western United States, the concentration of sol-
uble salts may be so great as to injure plants or prohibit germination or
growth, which has been shown by Markle and Dunkle (27). The concentra-
tion of soluble salts in a soil, resulting from a given application, is deter-
mined, to a large extent, by the exchange-capacity of the soil involved. The
greater the exchange-capacity of the soil the smaller the amount of soluble
salts generally found.

One method of determining the soluble salt content in soils is by the
electrical conductivity of soil extracts. This property is dependent on the
number and kinds of ions. Measurements are accomplished by means of the

3
Solu-Bridge Soil Tester, Model RD-15, which is a modified form of the
1Manufactured by the Exact Weight Scale Company, Columbus, Ohio.
2Manufactured by the Torsion Balance Company, Clifton, New Jersey.

3Manufactured by Industrial Instruments, Inc.

29.

Wheatstone bridge with a lOOO-cycle alternating current to avoid polari-
zation. To standardize the current, a vacuum tube oscillator is employed
with an amplified current-detector connected to a graduated scale through
a cathode-ray tube used for making the readings.

With the use of the Solu-Bridge, the units of conductivity of soil
solutions are expressed in mho's, which is a measure of electrical
conductance and is defined, according to the Handbook of Chemistry and
Physics (20), as the conductance of a body through which one ampere of
current ﬂows when the potential difference (between the ends of a con-
ductor) is one volt. The conductance of a body in mho's is the recipro—
cal of the value of its resistance in ohms. Since this conductivity is

so small, the readings are amplified and expressed as mho's x 10-5.

30.

V. METHODS

A. Experimental Methods

 

1. Preliminary Investigation

MSC No. 16 snapdragon seeds were sown in a bench watered by
constant water level on July 7, 1955. The seedlings were above ground
by July 10. They were potted into 3-inch pots on July 29 in sterilized
soil consisting of three parts loam soil, one part Canadian peat, and one
part sharp sand, to which a 4-inch pot of superphosphate had been added
per wheelbarrow of soil. The plants were selected for uniformity in
size and shape on August 8 and reselected, on the same basis, on August
10.

The experiment was set up to utilize seven levels of nitrogen and
potassium, with phosphorus remaining constant. Four pots of each fer-
tilizer level were randomized in each plot, giving 28 pots per plot. Fifty
milliliters of nutrient solution (composition outlined in Part III. section D)
were applied at weekly intervals. Five replicates of the above plots were
maintained.

To establish a starting point, one replicate was harvested on August
15. The mean dry weight of the plants harvested was 0. 0785 grams, with a

standard deviation of 0. 0078 grams. The mean leaf area of the plants was

31.

25. 2 square centimeters with a standard deviation of 0. 61 square centi-
meters.

The fertilizer levels used were: 0, . 25X, . 50X, 1X, 2X, 4X and
8X. The ”0" treatment received only distilled water. The "1X" treatment
was equivalent to 1. 9 Baule units, Table II. All remaining plots, after the
first harvest, were fertilized on 15, 22 and 29th of August and September
19th, with subsequent harvests on August 25 and September 12, 19 and 23.
Tap water was used in the watering of the pots. Guard rows of plants
were set up completely surrounding the plots to prevent undue water loss
from occurring from plants in the actual experiment.

The differences in the fresh weight, leaf area and dry weight of
these snapdragons, when harvested, indicates the growth rate. The data
in Tables III and IV show the ratio of increase of the plants from the zero
point of the experiment, or the mean point of the first harvested replicate.
Each harvest figure is listed in terms of increase over the preceding
harvest figure with a cumulative figure given for the entire harvest period.

The absence of values for fertility level "7" beginning with September
12 resulted from the death of the plants because of too high a nutrient con-
centration. Fertility level "7" was equivalent to more than 15 Baule units,
Table II. Progressive decline of growth rate at successive harvests is

demonstrated, Tables III and IV.

TABLE III

Ratio of Increase of Fresh Weight of Snapdragon Plants - Summer Crop

 

 

—— _
—_7

 

 

 

 

 

Fertility Harvest Periods

Levels 8/15-8/25 8/25-9/12 9/12-9/19 9/19-9/23 8/15-9/23

l (0) 5. 842 1. 168 2. 025 0. 747 10. 3

2 (. 25X) 6. 656 2. 445 1. 381 1. 047 23. 6

3 (. 50X) 6. 355 2. 995 1. 225 1. 228 28. 6

4 (1X) 7. 474 2. 859 1. 235 l. 158 30. 6

5 (2X) 5. 889 3. 488 1. 195 1. 245 30. 6

6 (4X) 4. 490 3. 754 1. 406 l. 031 24. 4

7 (8X) 1. 010 4. 154 — - -
TABLE IV

Ratio of Increase of Leaf Area and Dry Weight of Snapdragon Plants -
Summer Crop

‘ J
__L -’

 

 

 

 

 

Fertility ‘ Harvest Periods

Levels 8/15-8/25 8/25-9/12 9/12-9/19 9/19-9/23 8/15-9/23

Leaf Area
1 3. 9 1. 1 l. 1 0. 7 4. 8
2 4. 2 1. 8 1. 0 0. 9 6. 5
3 3. 5 2. 1 1. 1 1. 0 8. 0
4 4. 9 2. 2 1. 0 0. 9 9. 5
5 4.1 2.6 1.1 1.0 11.2
6 3. 2 3 2 l. 2 0. 8 9. 8
7 0. 4 - - — -

Dry Weight
1 6.7 2.1 1.6 0.7 15.7
2 6. 9 3. 8 1. 3 1. 0 32. 1
3 6.5 4.2 1.2 1.2 41.2
4 7. 5 4. 1 1. 1 1. 1 43. 0
5 6.2 4.7 1.2 1.2 42.4
6 5.3 3.4 1.0 1.0 29.9

‘ 7 1. 7 4. 9 - - -

 

CA.)
0.)
0

It is apparent that for all practical purposes leaf expansion has
ceased about midway through the experiment and remains at a constant
figure after September 12. This corresponds‘roughly with the data in
Table III. These plants had not reached the anthesis stage at this time
but many of them were approaching bloom. The values for dry weight
follow closely the leaf area values, although some increase is recorded
after the plant comes into bloom. This can be contrasted with the
apparent cessation of leaf expansion at a comparable stage.

Using visual appearances as well as fresh weight, leaf area,
and dry weight data, it was determined to discard the following nutrient
application levels, . 25X, 4X, and 8X, and to use the remaining levels,

0, ‘LSOX, IX, and 2X, in succeeding studies.

34.

2. Plot Design and Physical Set-Up for Principle Investigation

Seeds of the snapdragon MSC No. 16 were sown in ﬂats on January
17, 1956 at 60°F night temperature, in a mixture of equal parts by volume
of sterilized sand, soil, and acid peat. When 15 days old, the seedlings
were potted into 3-inch clay pots. .On February 7, the seedlings were
selected for uniformity in height and leaf development, and reselected
again, on the same basis, on February 14, at which time they were
placed into randomized, replicated split plots at the three temperatures
employed in this study. These plants were grown at 55°F from the time
of potting until moved into the various temperature chambers; during
this time they were watered with tap water. Treatments were started
on February 14, 1956.

This, the main experiment, was set up to utilize four levels of
nitrogen and potassium, with phosphorus remaining constant. Phosphorus
was thoroughly mixed, as 20 percent superphosphate, into the potting
soil at the rate of one 4-inch pot per three cubic feet of soil prior to
planting. In addition to the four levels of fertility there were three tem-
peratures and three light intensities employed. The greenhouses and
physical equipment used are detailed in Part 111, Section C. In each tem-
perature chamber (50, 60 and 70° F) the benches were divided into equal

thirds. Each one of the thirds was fitted for one of the light intensities

listed in Part III, Section C, 4. These light intensities were randomized
within the three chambers. Within each light chamber in each tempera-
ture chamber four pots of each fertility level employed were randomized
in one replicate consisting of 16 pots. There was a total of five repli-
cates within each light chamber in each temperature chamber. These
replicates were randomized within the various chambers. There was
a total of 80 3-inch pots in each light chamber, 240 in each temperature
chamber, for a grand total of 720 plants in the experiment.

The Thermo-Humidigraphs, listed in Part III, section E, were
placed in each temperature chamber, under the shade making the one-
third light intensity chamber. Night temperatures were regulated accord-

ing to the readings obtained from these instruments.

36.

3. Nutrient Application

The nutrient solutions used in this study were made up in keeping
with the Mitscherlich—Baule theory as outlined in Part III, section D, 1.
Stock solution was made up to ten liters with distilled water. The appli-
cation rates are found in Table V. The first nutrient application was
made on February 14, 1956, with subsequent treatments on February 22
and 29, and on March 7 and 10, 1956. Fifty milliliters of nutrient solu-
tion, in the appropriate strength, were applied to each pot individually
through the use of a calibrated beaker. All fifty milliliters were allowed
to percolate into the soil in each pot. The plots were watered with ordin-
ary tap water in the morning hours and the nutrient solution applied in
the afternoon.

Table V gives the cumulative total of the amounts of nitrogen and
potash (1(20) applied per pot and also converts this total to Baule units and
to pounds per 100 square feet. For comparison, Table VI lists the Baule
units and their equivalents in pounds per 100 square feet, as well as grams
per 3-inch pot. These values were derived from the Baule unit value ex-

pressed as pounds per acre six inches.

TABLE V

Nutrient Application Rates and Conversions

 

Fertility Weekly Applications of 50 m1 Nutrient Solution/3-inch Pot
Levels Ml Stock Mg N Mg“ K n

per Pot per Pot per ot

 

 

 

 

l (0) - - -
2 (. 5X) 3. 91 29. 8 11. l
3 (1X) 7. 81 59. 4 22. 1
4 (2X) 15. 63 118. 9 44. 2
Fertility Five Applications of 50 ml Nutrient Solution/3-inch Pot
Levels (During Experimental Period)
Ml Stock Mg N Mg K 0 Baule Unit Lbs/ 100 Sq. Ft.
per Pot per Pot per t per Pot N K20
1 .. .. - - - ..
2 19. 55 148. 8 55. 3 3. 2 1. 6 0. 6
3 39.05 297. 2 110. 6 6.4 3.2 1.2
4 78. 15 594. 6 221. 0 12. 5 6. 5 2. 2

1 ml stock solution contains - 19. 330 mg NH4N03

- 6.068 mg KNO3

NH 4N03 = 35. 0 percent N
KNO3 = 13. 9 percent N, 46. 6 percent K20

37.

38.

 

 

 

 

H: .0 mm .H 0% :v .o S .m 82 OH
«.2 .o mo 4 m2. vmv .o no .v mNoN m
>2 .o B .H owe Rm .0 2 .w 003 w
02 .0 mm. .H Em 25 .o No .m 2.3 n
mod .o ma 4 Nov mwm .o 3 .m ommé c
owe .o g .0 oz. 0mm .0 mm .N mm: m
moo .o mp .o mam m2 .0 so .N com v
«mo .0 .3 .o ova NE .0 mm .H who m
mmo .0 mm .o #2 mac .o mo 4 omv N
:o .o a .o Nw 55 .0 mm .o mNN H
Homnoawrmi 8.0 .E .vm ooqmnd angina..— uom 205-280 JR .vm COHEQA oHonmﬁ 3 ED
ammuom cowohnz 25mm

 

 

”I

II

 

III|I‘
'lHl

llHl

II

oEdH. zonoﬁisum BED 35mm

5 mung

 

39.

4. Harvesting Method

Plants were harvested by cutting the stem off even with the
surface of the soil in the pot and using the entire upper structure of the
plant. Fresh weight was obtained immediately upon cutting of the stem.
To prepare for harvesting, the plants were watered in the forenoon and
harvested in the afternoon. Since all of the pots held 50 milliliters of
liquid, it was assumed that the relative turgidity of the plants was approx-

imately equal when harvested.

B. Analytical Methods

 

1 . Plant Material

a. Fresh Weight

Fresh weight is an important measure of growth in the case of
those crops whose value is determined on a fresh weight basis. As a
scientific measurement it is subject to much variation and external inﬂu-
ence. However, fresh weight was determined on all plants harvested by
means of a ShadOWgraph, described under Part III, Section E, and recorded
to hundredths of grams.

The plants were harvested weekly beginning with the first day
of treatment, February 14, 1956. This first harvest established the zero
point for future measurements. At weekly intervals thereafter, four repli-
cates, under each light condition and at each temperature, were harvested,
with the exception of the last harvest, which went ten days from the pre-
ceding harvest. There was a total of five harvests. These periodic samp-
lings enabled the data taken to be utilized in the construction of growth rate

CUI'VG S.

b. Leaf Area

After obtaining the fresh weight the individual plants were placed

between wet paper towels to keep them in a turgid condition until the leaf

40.

41.

area could be measured. The measurement of leaf area was done by means
of the Area-Photometer, described in Part III, Section E. Individual leaves
were removed from the stems and the petiole of the leaf severed at the base
of the blade. This gave a measurement of only the blade or leaf area in
square centimeters. In the early stages of growth all of the leaves of one
plant were placed on the glass tray of the Area-Photometer at the same
time. However, as the number and size of the leaves of individual plants
increased, it was necessary to make several measurements to obtain the
total area of all of the leaves of one plant.

For these measurements all leaves on the plant were used with
the exception of the small bracts subtending the immature inﬂorescence

in the later stages of growth.
c. Dry Weight

Reducing plant material to a condition where the volatile and liquid
substances have been removed, allows the resulting plant weights to be com-
pared directly, without including the varying proportions of the above substances.

After measuring the leaf area, all portions of the plant, with the ex-
deption of the roots, were placed in individual two -pound Kraft paper bags.
These bags were placed in a forced-draft oven at a temperature of 97° Centi-
grade for 24 hours. Upon removal the contents were weighed with a Torsion

balance, weights recorded to tenths of grams, after which they were discarded.

42.

2. Soluble Salt Content of the 3011

To determine the soluble salt content of the soil in each exper-
imental condition, the four replicates of each treatment, at each har-
vest, were thoroughly mixed and a representative sample chosen for
each treatment, for a total of 180 samples. The sample was then
diluted at the rate of 50 grams of air-dry soil to 100 m1 of distilled
water. The resulting mixture was stirred for two minutes, allowed
to settle for five minutes, and the supernatant liquid poured off and
the conductivity of this liquid measured with a Solu-Bridge, readings

being recorded in mho's x 10-5.

43.

C. Statistical Analysis

 

Although visual observations can readily attest that there are obvious
differences in appearances in the plants treated in this experiment, it is another
thing to state that these differences are sufficiently significant to warrant new
cultural methods. The greater the difference the easier to see that the ex-
periment has succeeded. The smaller the difference the more difficult it is
to establish the experimental result.

As most experimental data are obtained in numerical form, they
lend themselves readily to analysis by means of statistical methods. With
this in mind the results of this experiment were subjected to analysis of
variance, as outlined by Snedecor (51). Realizing that the complete growth
response of the plants, under the varying cultures and as obtained through
this experiment, would be represented in the fifth and final harvest, the
data obtained from this harvest were analyzed statistically.

Data from the three temperatures, 50, 60 and 70° F, and for the inter-
actions of light and fertility, light and temperature, fertility and temperature,
and light, fertility and temperature, for both dry weight and leaf area were
analyzed for the significance of their variations, using the multiple range

and F tests of Duncan (11).

44.

VI. RESULTS AND DISCUSSION
A. Effect of Light Intensity on Optimum Fertility Level

The slope of the growth curve is modified by changing environ-
mental conditions. In comparing the effect of varying light intensity on
optimum fertility levels, in the growth of snapdragons in this study, it
can be seen from Figures 2, 3 and 4 that the slope of the growth curve
when plotted as leaf area expansion at the highest level, changes as the
light intensity varies. In full light the growth curves for all three tem-
peratures are approximately equal in slope, while a decrease in light
causes a steepening of the slope.

The data in Table VII show the overall ratio of increase in yield
on a fresh weight, dry weight, and leaf area basis. For example, at a
temperature of 70° F, full light intensity, and No. 2 fertility level, these
data show that plants in this particular replicate increased their fresh
weight 33. 7 times over the weight established as the "zero" point when
they were 29 days old.

The differences in yield, on a dry weight and leaf area basis,
due to the interaction of light intensity and fertility, within a temperature
group, were not significant.

Although not significant here, the effect of light on optimum fertility

 

—— 70°; "2" fertility level

  
  
  

300 b — — 60°; "3" fertility level I.
----- 50°; "2" fertility level /
250*
o
I
I
I
I
200+ ,’
I
l/ I
’I
I50 "- I,

Leaf area in square centimeters

IOOr- .
/ ,
I;

50 +- / 1’

 

 

25 35 45 55 65
Age of Plants in Days

Figure 2. The effect of full light intensity and optimum fertility level on
leaf area at 50, 60 and 70° Fahrenheit.

 

45.

 

— 70°; "2" fertility level

  
  
  

300 - — — 60°; "3" fertility level I.
----- 50°; "2" fertility level /
250 r
o
I
I
I
I
P I
200 ,
I
l/ I
I,
I50 *- I’

Leaf area in square centimeters

IOOr- .
/,
l.’

50‘-

 

 

i . . r ,

25 35 45 55 65
Age of Plants in Days

Figure 2. The effect of full light intensity and optimum fertility level on
leaf area at 50, 60 and 70° Fahrenheit.

 

45.

 

 

— 70°; "2" fertility level /

300F- -- —'- 60°; "3" fertility level /

  

-- -_- 50°; "2" fertility level /
250-

U)

H

d.)

3

g 200..

a ’O

c

U

23

5- I50r

u:

.5

co

8

<1

E

G)

.4
looL
50—

 

f 1 . . L

25 35 45 55 65
Age of Plants in Days

Figure 3. The effect of two-thirds light intensity and optimum fertility level
on leaf area at 50, 60 and 70° Fahrenheit.

 

46.

 

 

— 70°; "2" fertility l
o

300— — — 60°; "3" fertility

----- 50.; '13" fertility

I
I

O I I
I
I,
/ I
g ' i
E 200‘ I I,
§ I
a) I
3 I50 III
a F I
z: [I
- I
“a I ’
3 ' '

I
[I
I

 

 

 

 

, .“
IOOP 'I
/ ,
.'
’I.-----
50r- ’
’I
i 1 1 l J
25 35 45 55 65

Age of Plants in Days

Figure 4. The effect of one-third light intensity and optimum fertility level
on leaf area at 50, 60 and 70° Fahrenheit.

48.

 

 

m.oH m.m~ m.vH o.HH o.w~ >.mH m.HH >.0N v.5H w
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shows some trends or directions. On the basis of ratio of increase of
fresh weight, a decrease in light intensity, at all fertility levels, brought
about a decrease in the ratio of fresh weight increase at 70°, while at 60°
and 50° the fresh weight ratio remained relatively the same or increased.
A reduction in growth can be noticed at 50° with the number 4, or highest,
level of fertility. With decreasing light intensity and increasing fertility

levels the height of the plant was less and stems were larger in diameter,

until the optimum fertility level was reached.

There is an increase in dry weight ratio due to decreasing light
and increasing fertility levels, except at the highest level where there
was a marked reduction in growth.

Leaf expansion was different, in that with decreasing light there
was an indication that the ratio of increase was greater, especially in the
lower temperatures. This would indicate that when light becomes limiting,
one of the benefits of soil fertility may be found in an increase in foliar

area.

50.

B. Effect of Temperature on Optimum Fertility Level

 

The inﬂuence of temperature on the effect of level of fertility can
be seen in Figures 5, 6 and 7, which show the ratio of increase in dry weight
during the period of this study. At a temperature of 70° F, fertility level "2"
produced the greatest increase regardless of light intensity, while at 60° F,
the plants made more growth at the higher level of "3". When the light in-
tensity was cut to one-third, the plants did not respond to nutrients in level "3"
as well as to those in level "2". This indicates that at 60°F a greater growth
rate can be expected with a higher fertility level than level optimal for a tem-
perature of 70°F, as shown in Figures 5 and 6.

Reducing the temperature to 50°F will delay snapdragon ontogeny
when compared to 60 or 70°F. Data in Figure 7 show a decided advantage in
growth rate at level "2" in full light, which did not hold for the other two light
intensities. As light was decreased, the higher fertility rate (3) produced a higher
ratio of growth. Plants in the 50°F group were much shorter than those in either
the 60 or 70°F group, and the ratio of increase in both fresh weight and leaf area
data paralleled this.

Data from Table VII indicate that the growth curves for leaf area and
fresh weight follows the slope of the dry weight curve. The rate of stem elonga-
tion increases with temperature as did dry weight, indicating that even though
growth rate was accelerated, soil fertility was not primarily responsible for the

increases in fresh and dry weight.

53.

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54.

C. Interaction of Light and Temperature on @timum Fertility Level

The interaction of temperature on the level of fertility varies with
each light intensity. At 70°F, and with all light intensities employed, fertility
level "2" produced the highest yields in fresh and dry weights and leaf area.
Figure 8 shows graphically dry weight yield in grams on the basis of interaction
of fertility, light and temperature. As temperature decreased to 60° F, ferti-
lity level "3" produced the highest yields in both full light and two-thirds light,
but did not do so with the lowest light intensity, where level "2" produced the
greatest weight, both dry and fresh. At this light intensity and temperature,
the greatest expansion in leaf area was produced by a level of "3".

Decreasing the temperature to 50°F and decreasing the light inten-
sity, allowed a higher level of fertility to produce the greater yield, not only
in dry weight, but in fresh weight and leaf area, also.

With the exception of the value of the low light intensity at 60° F, as
the temperature and light intensity decrease, the optimum fertility level tends
to increase, indicating that increased fertility might substitute partially for a
lack of light.

Using an integrated statistical analysis of variance, values for the
least significant difference of yields, and for those differences between yields,
on a dry weight basis, attributable to varying temperature and fertility rates,
were analyzed with the procedure advocated by Duncan (11). Varying degrees of

significance were present.

55.

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56.

 

 

TABLE VIII
Significance of the Differences in Averages of Fertility Level Values, for Dry
Weight Yields
Fertility Averages Significance
Levels
1 1. 09
2 l. 48 Significantly larger at the 1% level than all other
values
3 1. 26 Significantly larger at the 1% level than level "4"
and larger at the 5% level than level "1"
4 l. 02

 

 

On the basis of values in Table VIII. it can be seen that the differences
in yield between fertility levels are all significant with the exception of the dif-
ferences between fertility level "1" and "4". Level "1" received only distilled
water and "4" had nutrients in excess. Dry weight increases brought about by
application of fertility level "2" were significantly greater at the 1 percent level
than values received from levels "1", "3" and "4", while "3" was significantly
larger at the 1 percent level than "4", but only greater at the 5 percent level
than "1".

In the same manner, values were derived for differences brought about

through variation in temperature. They are shown in Table IX.

57.

 

 

TABLE IX
Significance of the Differences in Averages of Temperature Values, for Dry
Weight Yields
Temperature Averages Significance
70°F 1. 417
60°F 1. 327 Significantly larger at the 1% level than 50°
50° F 0. 885
============r r

 

No significance was found for the differences in yield brought about
through the effect of variation in temperature between 70 and 60° F. How-
ever, differences between 70 and 50°F were highly significant. No signifi-
cance was found for the changes in yield values brought about by light inten-
sity, the interactions between light and temperature, light and fertility, and
light, temperature and fertility.

Beside dry weight values, the other measurement of value here is
that of leaf area in square centimeters. Data collected has been subjected
to statistical analysis, the results of which are seen in Tables X and XI.

All differences in leaf area yields due to variation in fertility level
are highly significant with the exception of the differences between fertility
level "2" and "3" which are not significant. Table XI shows the significance

of leaf area yield difference due to variation in temperature.

58.

 

 

 

 

 

 

 

TABLE X
Significance of the Differences in Averages of Fertility Lwel Values for Leaf
Area Yields
Fertility Averages Significance
Levels
1 180. 5
2 267. 6
3 255. 8 Significantly larger at the 1% level than levels
"1" and 0'4"
4 214. 7 Significantly larger at the 1% level than level
"1"
m
TABLE XI
Significance of the Differences in Averages of Temperature Values for Leaf
Area Yields
Temperature Averages Significance
70° F 340. 5 Significantly larger at the 1% level than all
other values
60°F 260. 3 Significantly larger at the 1% level than 50° F
50° F 173. 6

All yield differences due to variation in temperature are highly signifi-
cant. No significance was found for the changes in yield values brought about

by light intensity, the interaction between light and temperature, light and

59.

fertility, and light, temperature and fertility.

No toxic levels of soluble salts were found in any of the soils tested
with the Solu-Bridge as outlined in Part IV, Section B, 2. The highest level
of salts was found in those soils treated with fertility level "4". Using a
reading of "70" as the lower limit of injury to snapdragons, the highest
reading recorded was "36", which was not high enough to cause injury. It
was, therefore, concluded that most of the fertilizer had been absorbed
by the plants, even though they may not have been able to efficiently utilize

all of it, as in the case of fertility level "4".

60.

D. General Discussion of Results

 

In subjecting the snapdragon plants in this study to varying combina-
tions of light, temperature and fertility, the slope of the growth curve can
readily be seen. Using as measurement-data, increase in dry weight in
grams, and expansion in leaf area in square centimeters, trends can be
established for the interactions of light and fertility, temperature and fer-
tility, and light, temperature and fertility.

The first investigation into the highest level of fertility, under full
light intensity and high temperature, revealed that the highest level of
nitrogen and potassium fertility, that could safely be applied in the Baulic
ratio of 5-1-2, was equivalent to approximately four (4) Baule units. This
would equal about two (2) pounds of nitrogen per 100 square feet. This was
considerably more nitrogen than was recommended for optimum growth of
snapdragons by Post (41), and Laurie and Kiplinger (22). However, this
level fell far short of the theoretical Mitscherlich-Baule level of ten (10)
units, which would be equal to about five (5) pounds of nitrogen and two (2)
pounds of K20 per 100 square feet (Table VI). The application of about 15
Baule units brought almost instant necrosis, while eight Baule imits reduced
growth so markedly that it obviously was not optimal. Phosphorus level
was not a factor in that it was kept constant.

The greatest amount of growth made during this summer period was

61.

made in the early stages, and those plants making the greatest increase in
growth finished with the largest overall ratio of increase. This would lend
support to the theory of Gregory (16) that over 90 percent of the nitrogen

has been accumulated when the dry weight has reached 25 percent of its

final value, and it is upon this erserve that later growth and development
depend. After this early spurt, leaf expansion, and fresh and dry weight in-
crease remain at a constant rate (Tables III and IV). Upon the basis of this
full intensity summer study, it can be said that -

(1) Optimum nitrogen and potassium level is in excess of
that now commercially recommended per single application
for a summer period comparable to the conditions of this
study;

(2) Optimum nitrogen and potassium level on the basis of applied
fertility rates in this study is less than the theoretically optimal
Mitscherlich-Baule ratio of ten units; and

(3) The greatest ratio of increase in dry weight, fresh weight, and
leaf area, was in the earlier stages of growth, and thereafter
growth was at a smaller, constant rate.

In the second investigation four fertility levels, three light intensities,

and three temperatures were used to determine effects on the growth curve.

With a decrease in light intensity, the slope of the growth curve

62.

steepened, with a noticeable lag in the early stages in leaf area expansion
and a corresponding decrease in dry weight increase. The interaction be-
tween light intensity and fertility level did not prove significant, indicating
that the optimum fertility level would depend more upon the temperature
than upon light. .This was shown by the fact that differences in dry weight
yield between temperatures of 70 and 50, and 60 and 50°F were highly
significant, but with no significance found in yield differences between

70 and 60° F. Leaf area differences, due to temperature, were all highly
significant.

As the light intensity decreases, there is a tendency for leaf area
ratio of increase to become greater, especially with decreasing tempera-
ture. This could indicate a partial substitution of soil fertility for light
intensity in the lower temperature range.

Leaf area expansion increases in the early stages faster at the
higher temperature of 70°F than at 50°F under all light intensities, but
there is an almost equal increase at the two-thirds light intensity between
70 and 60° F. Decreasing the light intensity to one-third brought about a
leveling off, or plateau, in leaf area expansion at both 60 and 50° F, fol-
lowed by a very steep slope to the growth curve. This plateau was not
noticeable at higherlight intensities or at 70°F within this light level.

There was no significant interaction between temperature and

63.

fertility. However, differences in dry weight yields brought about by varia-
tion in fertility level, were highly significant, with the exception of the dif-
ferences between fertility levels of "1" and "4", which were not significant.
Differences between levels of "1" and "3" were significant at the 5 percent
level. Using leaf area data, all differences due to fertility rates were
highly significant, except that no significance was attached to yield differ-
ences between levels "2" and "3". Here again, the interaction of light and
fertility, temperature and fertility, and light, temperature and fertility,
produced no significant yield differences. This would indicate that fertility
will make great differences in yields within a temperature and that the tem-
perature will largely govern the maximum yield obtainable.

The fertility level that produced the greatest yield on both a dry
weight and leaf area basis was either level "2" or "3"; levels "1" and "4"
did not produce optimal growth. In most cases the higher level depressed
growth. On a dry weight comparison, the yield differences produced by
these two levels were highly significant, but there was not a significant
difference in leaf area. This can be correlated with the growth curve which
shows that the ratio of increase in leaf area levels off and remains relatively
constant while there is an increase in the late stages of growth in dry weight.
This comes about through stem elongation and ﬂowering which will produce

additional weight, but not necessarily leaf area.

64.

On conversion to pounds per 100 square feet and Baule units, fertility

level "2" contained 1. 6 pounds of nitrogen and 0. 6 pounds of K 0 per 100 square

2
feet and was equal to 3. 2 Baule units; fertility level "3" contained 3. 2 pounds of
nitrogen and 1. 2 pounds of K20 per 100 square feet and was equal to 6. 4 Baule
units. It was thought that possibly a greater number of Baule units than 6. 4
and less than the 12. 5 units in level "4", would give better growth. Each appli-
cation of "4” put 2. 5 Baule units on per pot. Therefore, one application was
.equal to 2. 5 units, two applications to 5. 0 units, three applications to 7. 5 units,
and four applications to 10. 0 units, the theoretical optimum. At none of these
points in the growth curve did ratio of increase measure up to levels ”2" or
"3". Leml "4", equivalent to 12. 5 units, was not optimal, nor were 10. 0

or 7. 5 Baule units. Under the conditions of this study, the steepest slope to

the growth curve varied between either 3. 2 or 6. 4 Baule units, depending upon
the temperature. In growing this crop for dry weight production, a fertility
level of 3. 2 units would give maximum yield at a temperature of 70° F, while

at 50 and 60°F an application 6. 4 units would produce the greatest yield. This
would not be true for leaf area yield, where the lower rate would bring the
greater economic return, since there are no significant differences in yields
between the two.

Under the conditions of this experiment, there were no significant

interactions between light intensity and fertility rate, nor between temperature

65.

and fertility. Regardless of light intensity, one fertility rate was usually
optimal for a temperature group. With decreased temperature, dry weight
and leaf area yields declined except at one-third light intensity, Table VII.
Simultaneously, fertility optima shift upward from the "2" to the "3" levels.
This unexpected trend indicates possible substitution of fertility for light
which may well be a function of greater leaf area at higher fertility levels.
Additionally, as shown by Russell (45), higher levels of potassium increased
photoperiodic efficiency at low light levels.

There is an indication that decreasing light intensity may be compen-
sated for by an increase in leaf area, with a tendency toward increasing
dry weight, provided an adequate fertility level is maintained. Selection of
a greenhouse snapdragon adapted to low light intensity conditions would be
economically practical in that low temperature and low light intensity are
conditions that are found in Michigan in the winter. Also, a snapdragon
adapted to high temperatures and high light intensity would find a use in the
summer period. Adjusting the fertility level to match growth potential is
easily done. A comparison of dry weight yields at the various temperatures,

light intensities, and fertility rates are presented in Figure 8.

66.

VII. SUWARY

During the months of January through March, 1956, snapdragon
plants were grown at three light intensities, three temperatures (50, 60
and 70° Fahrenheit), and four fertility levels, in all possible combinations,
in a randomized split-plot design. The phosphate level was constant through-
out, while nitrogen and potash were varied, using ammonium and potassium
nitrate. Nitrogen and potash were combined in ratios determined by the
Mitscherlich-Baule theory of optimum plant growth. Ten Baule units are
equal to 5. 17 pounds of nitrogen and l. 82 pounds of potash per 100 square
feet.

Under optimum growing conditions, as approached in commercial
culture, optimum fertility levels, in this study, did not approach ten Baule
units of either nitrogen or potash. Optimum yields, on both a dry weight
and leaf area basis, although varying with temperature and light intensity,
were obtained with fertility levels not in excess of 6. 4 Baule units, which
contained 3. 2 pounds of nitrogen and l. 2 pounds of potash per 100 square
feet.

Hybrid snapdragons, designated MSC No. 16, were grown in 3-inch
clay pots, to which liquid nutrient solutions were added at weekly intervals
for five applications. Weekly harvests, obtaining fresh weight, dry weight,

and leaf area data, enabled the slope of the growth curves to be determined.

67.

Through manipulation of temperature levels, light intensity, and the four
fertility levels, the inﬂuence, or interactions of environmental factors on
optimum fertility level were determined. All measurement data was sub-
jected to analysis of variance and tested for significance. The light inten-
sities used were full light, two-thirds light, and one-third light. Fertility
levels were based on levels determined in a preliminary investigation to
bracket the observed optimum fertility level. Fertility level "4" was ob-
tained by application of 12. 5 Baule units of both nitrogen and potash, "3“
by 6. 4 Baule units, "2" by 3. 2 Baule units, and "1" had no added nutrients,
being only distilled water. One-fifth of the total nutrient supply was applied
weekly giving the total supply after five applications.

No significant yield differences were produced by the interactions
between light and fertility, temperature and fertility, and light, temperature
and fertility. Yield differences due to variation in fertility levels were
significant, with the exception of the differences between levels "2" and "3"
which were not significant. Significance at the one percent level was also
found with dry weight yield differences due to temperature, except that dif-
ferences between 70 and 60° F were not significant. Differences due to
fertility were all highly significant, except there was no significance between
levels "1" and "4", and between "1" and "3" the differences were significant

at the five percent level.

68.

The greatest ratio of increase in yield, both dry weight and leaf
area, occurred early in the ontogeny of the plant, later becoming constant,
and increasing again in dry weight as plants attained ﬂowering status.

No significance was found in yield differences brought about by variation
in light intensity. There is an indication that decreasing light intensity
may be compensated for by an increase in leaf area, with a tendency
toward increasing dry weight, provided an adequate fertility level is
maintained. (mtimum fertility level, under the conditions of this study,

was found to be greater‘than commercial fertilizer recommendations.

10.

11.

12.

13.

14.

15.

69.

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