• TABLE OF CONTENTS
HIDE
 Front Cover
 Title Page
 Introduction
 Part I. General discussion
 Part II. Procedures for growing...
 Back Cover














Group Title: C.R.E.A. news letter
Title: Growing plants without soil by the water-culture method
CITATION THUMBNAILS PAGE IMAGE ZOOMABLE
Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF00089091/00001
 Material Information
Title: Growing plants without soil by the water-culture method
Series Title: C.R.E.A. news letter
Physical Description: 39 p. : ill. ; 23 cm.
Language: English
Creator: Hoagland, D. R ( Dennis Robert ), 1884-1949
Arnon, D. I ( Daniel Israel ), 1910-
Florida -- Dept. of Agriculture
California Committee on the Relation of Electricity to Agriculture
Publisher: Issued by Committee on Relation of Electricity to Agriculture ;
Issued by Committee on Relation of Electricity to Agriculture
State of Florida, Department of Agriculture
Place of Publication: Chicago Ill
Tallahassee Fla
Publication Date: 1950
Edition: Repr. Sept. 1950 / -- State of Florida, Department of Agriculture.
 Subjects
Subject: Hydroponics   ( lcsh )
Plant growing media, Artificial   ( lcsh )
Nutrient film culture   ( lcsh )
Plants -- Nutrition   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
non-fiction   ( marcgt )
 Notes
Statement of Responsibility: by D. R. Hoagland and D. I. Arnon.
General Note: "August, 1950."
 Record Information
Bibliographic ID: UF00089091
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: ltuf - AFJ1869
oclc - 79005509
alephbibnum - 001096214

Table of Contents
    Front Cover
        Page 1
        Page 2
    Title Page
        Page 3
    Introduction
        Page 4
    Part I. General discussion
        Page 5
        Page 6
        Page 7
        Page 8
        Page 9
        Page 10
        Page 11
        Page 12
        Page 13
        Page 14
        Page 15
    Part II. Procedures for growing plants by the water-culture method
        Page 16
        Page 17
        Page 18
        Page 19
        Page 20
        Page 21
        Page 22
        Page 23
        Page 24
        Page 25
        Page 26
        Page 27
        Page 28
        Page 29
        Page 30
        Page 31
        Page 32
        Page 33
        Page 34
        Page 35
        Page 36
        Page 37
        Page 38
        Page 39
    Back Cover
        Page 40
Full Text
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FI jl iuB!i'yzzinmiigia^^jii


RelPrinled Orlober, 1953
C. R. E. A. News Letter No. 17


June, 1938


I


Growing Plants Without Soil

By the Water-Culture

Method



By
D. R. HOAGLAND and D. I. ARNON
Division of Chemistry and Plant Nutrition
College of Agriculture, University of California
Berkeley, California


Issued by
COMMITTEE ON RELATION OF ELECTRICITY
TO AGRICULTURE


58 East Washington Street
Chicago, Illinois






STATE OF FLORIDA
Department of Agriculture
NATHAN MAYO, Commissioner
Tallahassee


lf1g~J~d











C R. E. A. News Letter No. 17


Growing Plants Without Soil

By the Water-Culture

Method



By
D. R. HOAGLAND and D. I. ARNON
Division of Chemistry and Plant Nutrition
College :f Agriculture, University of California
Berkeley, California


Issued by
COMMITTEE ON RELATION OF ELECTRICITY
TO AGRICULTURE
58 East Washington Street
Chicago, Illinois






STATE OF FLORIDA
Department of Agriculture
NATHAN MAYO, Commissioner
Tallahassee


October, 1953
























INTRODUCTION


The original development of technique for applying tle
water-culture method to commercial crop production is a-
tributed solely to W. F. Gericke. This independent report
was prepared at the request of the Director of the Agricul-
tural Experiment Station. Ihe cultural technique described
is based largely on the experience of the authors.

rhis report is divided into two parts: I. General Dis-
cussion; II. Procedures for Growing Plants by the Water-
Culture Method. The second part is presented in response
to many insistent requests for specific information. HoW-
ever, because of wide variations of conditions (climate, water,
etc.) affecting plant growth, modifications of the directions
given may be needed on the basis of local experience.











PART I.

General Discussion
DURING the past few years, the popular press has given
an immense amount of publicity to the subject of com-
mercial growing of crops in "water-culture"; that is,
growing plants with their roots in a solution containing
the mineral nutrients essential for plant growth. The solu-
tion takes the place of soil in supplying water and mineral
nutrients to the plant. This method of growing plants is
also described under such names as "tray agriculture,"
"tank farming," and the recently coined term "hydro-
ponics." Frequently, popular accounts of recent experi-
ments on growing plants by the water-culture method leave
the reader with the impression that a new discovery has
been made which bids fair to revolutionize our present
methods of crop production, and indeed promises to pro-
duce in the future far-reaching social dislocations by dis-
pensing with the soil as a medium for growing many crops.
In commenting on views of this kind, it should be
stated at the outset that some of the popular articles on the
water-culture method of crop production are grossly in-
accurate in fact, and misleading in implication. Widely
circulated rumors, claims and predictions about the water-
cultire production of crops often have little more to com-
mend them than the author's unrestrained imagination.
Erroneous and even fantastic ideas have been conceived,
betraying a lack of knowledge of elementary principles of
plant physiology. For example, we have been told that in
the future most of the food needed by the occupants of a
great apartment building may be grown on the roof, and
that in large cities "skyscraper" farms may supply huge
quantities of fresh fruit and vegetables. One Sunday sup-
plement article contained an illustration showing a house-
wife opening a small closet off the kitchen and picking
luscious tomatoes from vines growing in water-culture,
with the aid of electric lights. Then, there has arisen a
rumor that the restaurants of a large chain in New York
City are growing their vegetables in basements.
Stories of this kind have gained wide currency and
have captured the imagination of many persons. Many
factors have doubtless contributed to arousing the surpris-
ingly wide interest in the water-culture method of crop
production. The psychological effect of current discussion









DEPARTMENT OF COMMERCE


of the wastage of soil resources through soil erosion and
depletion has made the public mind especially receptive to
new ideas relating to crop production. Some people have
been impressed by the assumed social and economic signifi
chance of the water-culture method of growing crops.
Others, moved by the common delight of mankind in grow-
ing plants, even though the garden space is reduced to a
window sill, have sought directions which would enable
them to try a novel technique of plant culture. The conse-
ouence of the discussion of this method has been the cre-
ation of a great public demand for more specific infor-
mation. Should this newly aroused interest in plant growth
lead to a greater diffusion of knowledge of certain general
principles of plant physiology, this would be a salutary
effect of the publicity regarding the water-culture method
of crop production. Growing plants in water-culture has
sometimes been considered by popular writers as a "marvel
of science." The growth of plants is indeed marvelous, but
not more so when plants are grown in water-culture thar
when they are grown in soil.
Sometimes two entirely distinct lines of investigation
at the California Agricultural Experiment Station, in which
the water-culture technique was used, have been confused
in popular discussions. One of these concerns the method
of crop production referred to above, the other the study
for scientific purposes of plant growth in specially con-
trolled chambers artificially illuminated. It is economi-
cally impossible at the present time to grow crops commer!
cially solely under artificial illumination, even if there
were any reason for doing so. At several other institu
iions considerable attention has been devoted to study o
the effects of supplementing daylight with artificial light
during some seasons of the year, to control the flowering.
period or to accelerate growth of certain kinds of plants
(particularly floral plants) in greenhouses, but this prac-
tice has mainly been applied so far to plants developed in
soil and has no essential relation to the water-culture method
of growing crops.
That plants could be grown without soil in solutions
containing the necessary nutrient salts has been widely
known to plant physiologists for over three-quarters of a
century, and the water-culture method has been employed
by hundreds of investigators throughout the world. Our
own interest at the University of California Experiment
Station, in the water-culture method, is centered primarily
on its utilization as a laboratory tool for the determination









GROWING PLANTS BY WATER-CULTURE


of the factors affecting plant growth and the laws by which
they operate, with the ultimate objective of aiding in the
solution of important agricultural problems of soil and
plant interrelations. About ten years ago, however, W. F.
Gericke suggested that plants might be grown in water-
culture on a large scale for the purpose of commercial crop
production, and he carried out a series of experiments in
Berkeley to determine what technique would be applicable.
Recently the general method he devised has been tested
commercially in large greenhouses in several different locali-
ties.
The growth of plants in water-culture for commercial
purposes does not rest on any recently discovered principle
of plant nutrition. It involves, rather, the application of
a new, large-scale technique, developed on the basis of an
understanding of plant nutrition gained in previous in-
vestigations conducted on a laboratory scale. The funda-
mental physiology of the plant is the same whether it is
grown in an artificial nutrient solution or in a soil. In
either case, suitable temperatures and illumination, and all
adequate supply of water, of essential salts, and of oxygen
to the roots, must be provided. Apparently the impression
has sometimes been gained that by using the water-culture
method, plants can be grown successfully in dimly lighted
places, like basement rooms, or under otherwise adverse
climatic conditions, where they would not grow in soil.
This impression is, of course, completely fallacious.
The purpose of this article is to give a brief, non-tech-
nical account of the water-culture method. The reader,
however, should remember that the absorption of nutrient
salts and water is only one of the physiological processes
of the plant. In order to evaluate the possibilities and
limitations of any special technique for growing plants,
one has to understand the significance of other interrelated
processes, especially photosynthesis, respiration, transpira-
tion, and reproduction.
Comparison of Yields by Soil and Water-Culture
The understanding conveyed by most of the popular
discussions of the water-culture method is that the inherent
productive capacity of a given surface of nutrient solution
far surpasses that of an equivalent surface of soil. even under
the best soil conditions feasible to maintain. Often quoted
is the yield of tomatoes grown for a twelve months' period
in a greenhouse water-culture experiment in Berkeley. This









8 DEPARTMENT OF COMMERCE

yield is compared with average yields of tomatoes under field
conditions in California, and the yield from the water-cul-
ture plants is computed to be many times greater. But closer!
analysis shows that erroneous inferences may be drawn from!
this comparison. It is of doubtful validity to make predictions
concerning yields in large-scale commercial produc-
tion, based on yields obtained in small-scale experiments
under laboratory control. In any event, there is little profit
in comparing an average yield from unstaked tomato plants
grown during a limited season under all types of soil and
climatic conditions in the field, with yields from staked plants
grown in the protection of a greenhouse for a full year. It
is true that in one series of outdoor experiments the
yields of tomatoes under water-culture conditions were
reported to be much higher than from good soil on a unit
surface basis, but again, the general cultural treatment of
the plants (spacing, staking, etc.) was so different that com-
parisons of yields are of very limited value. Furthermore,
the equipment for an acre of water-culture plants would be
very costly, and technical supervision of the cultures and
labor of staking vines would necessitate large expenditures.
A real test of the inherent relative producing capacities
of soil and water-culture media requires that the two types
of culture be carried on side by side with similar spacing
of plants, with soil of suitable depth, having nutrient!
supplying power and physical condition as favorable as pos-
sible, and with the same cultural treatment for plants
grown in soil and water-culture. An experiment of this
kind was initiated in Berkeley, late last summer, with the
tomato as the test plant. The experiment is not complete
and only tentative conclusions can be drawn, but present
indications are that, over the course of a year, the yield
of fruit per unit area, or per plant, of plants grown in
fertile soil, will not be significally different from that of
plants grown in water-culture. (The yields were con-
sidered high for the winter season in which the plants
were grown.) Data have also become available on yields
of tomatoes grown in soil in a California commercial green-
house. It appears that on an annual basis, the yields were
of the same magnitude as those obtained in a successful
commercial greenhouse employing the water-culture pro-
cedure.
Published pictures of tomato plants grown in water-
culture show impressive height, and this growth in length
of vines is frequently the subject of popular comment. As









GROWING PLANTS BY WATER-CULTURE 9

a matter of fact, the ability of tomato vines to extend is
characteristic of the plant and not peculiar to the water-
culture method. Staked plants grown for a sufficiently
long period in a fertile soil, under favorable light and
temperature conditions, can also reach a great height. In
commercial greenhouse practice, growers usually "top"
the vines. Fruit developed at higher levels is likely to be
of inferior quality, and relatively expensive to produce be-
cause of labor required to attach supports to the vines and
the inconvenience of harvesting.
There is no magic in the growth of plants in water-
culture. This is only another way of supplying water and
essential mineral elements to the plant. Land plants have
become adapted to growing in soils during their evolution-
ary history, and it is not reasonable to expect some ex-
traordinary change in their potentialities for growth as
a result of the substitution of an artificial medium for a
soil. Assuming that no toxic conditions are present and
that a fully adequate supply of water, mineral salts, and
oxygen is provided to the root system, either through an
artificial nutrient solution or a soil, then in the absence
of plant diseases and pests, the growth of a plant is limited
by its genetic constitution and by climatic conditions.

Nutritional Quality of Plant Product

Modern research on vitamins and on the role in animal
nutrition of minute amounts of chemical elements like
iron, copper, manganese, zinc, and iodine, has justly aroused
great public interest, but unfortunately one of the results
is much popular discussion of diets and their influence on
health, which is without scientific basis. It is, therefore,
not unexpected that claims have been advanced that food
produced by the water-culture method is superior to that
produced by soil. In evaluating these claims, the point
should not be overlooked that plant products vary in com-
position, according to the particular soil or water-culture
condition under which they are grown, the climatic en-
vironment, and time of harvest. No generalization is war-
ranted at the present time. The whole subject is one re-
quiring further investigation. Claims of unusual nutri-
tional value of food products from certain sources should
not be accepted unless supported by results obtained in re-
search institutes of reputable standing.









DEPARTMENT OF COMMERCE


Present Status of Development of Commercial
Water-Culture Method
What is the justification for considering the water-
culture method as a means of commercial crop production?
The answer to this question is that the method has certain
possibilities in the growing of special high-priced crops,
particularly out of season in greenhouses, in localities where
good soil is not available or when it is found too expensive
to maintain highly favorable soil conditions. Soil beds
in greenhouses often become infected with disease-produc-
ing organisms, or toxic substances may accumulate. In-
stallation of adequate equipment for sterilizing soils and
operation of the equipment may involve considerable ex-
pense. Also, in theory at least, a water-culture medium,
when expertly supervised, should be subject to more exact
control than a soil medium.
Present information does not warrant a prediction asi
to how widely the water-culture method will find practical
application in greenhouses. One firm in California re-
ported success last year with this method in the production
of tomatoes; another California firm which invested a
large sum in equipment, stated last fall that such serious
difficulties had arisen that the equipment was not then
being utilized. It is suggested that those who contemplate
installation of the water-culture method for commercial pur-
poses, make a preliminary test with a few tanks of solu-
tion to compare the yields from soil and water-culture
media, and to learn some of the requirements for control
of the process. However, without some expert supervision,
commercial success is unlikely. Indispensible to profit-
able crop production by the water-culture method is a gen-
eral knowledge of plant varieties, habits of growth and
climatic adaptations of the plant to be produced, pollination,
and control of disease and insects; in other words, the same
experience now needed for crop production in soils. Con-
trary to some statements, it is not true that plants grown
by the water-culture method are thereby protected against
disease (except soil-borne disease), or the attacks of insects.
The above discussion is primarily based on experiments
with greenhouse crops. Conceivably in regions highly fav-
ored climatically, but where soil conditions are adverse,
some interest may arise in the possibilities of growing
crops outdoors, commercially, by the water-culture method.
What crops, if any, could be grown profitably by this
method would depend on the value of the crop in the market









GROWING PLANTS BY WATER-CULTURE 11

served, in relation to cost of production, which would in-
clude a large outlay for tanks and other equipment and
materials, as well as special costs of supervision and oper-
ation. Thus far, no evidence is available on which to base
any prediction as to future development of the water-cul-
ture method of crop production under outdoor conditions.
Before planning any investment in this field, the most
careful consideration should be devoted to the economic
and technical factors involved.

Growing of Plants in Water-Cultures by Amateurs

Most numerous among the inquiries for information
about the water-culture method are those from persons
who wish to grow plants in this way as a hobby. Those
persons usually seek exact directions as to how to proceed
to carry on water cultures. For reasons which, it is hoped,
have already been made clear, it is not possible to describe
a general procedure insuring success. Many technical diffi-
culties may be met, related to character of water, adjust-
ment of acidity of the solution, toxic substances from tanks
or beds, uncertainty as to time for replenishing salts in
the nutrient solution, or for changing the solution, and
the like.
Why, it may be asked, do not most of these technical
difficulties of water-culture method arise in growing plants
in soil? Because in a naturally fertile soil, or one which
can be made fertile by treatment, there occurs an auto-
matic adjustment of many of the factors determining the
nutrition of the plant.
Some amateurs have recently reported results satis-
factory to themselves, with certain kinds of plants grown
in water-culture, and similar success can presumably be
achieved by others, through a fortunate combination of
nutritional and climatic condition. Yet without knowl-
edge of the factors involved, no assurance can be given
that success with one kind of plant at one season can be
consistently repeated with other kinds of plants, or at
other seasons. It is true that not every successful gar-
dener has a thorough training in plant and soil science,
nor that such training, by itself, can always insure suc-
cess in gardening. However, since the growing of plants
in soil is one of the oldest occupations of mankind, the
gardener can often obtain guidance based on a rich store
of accumulated experience. Such experience is lacking









DEPARTMENT OF COMMERCE


for the growth of plants by the water-culture method.
Growing of plants as a hobby, in either soil or culture
solution, without regard to cost of labor and materials,
is of course a very different matter from producing crops
for profit.
Many amateurs have been interested in the purchase
of mixtures of nutrient salts ready for use, and various
individuals and firms have offered for sale small packages
of salt mixtures. Clearly a prepared salt mixture does
not obviate the difficulties mentioned above, which may
be met in growing plants in water-culture. Recently,
some firms have made highly misleading claims for the
salt mixtures they sell. The California Agricultural Ex-
periment Station makes no recommendation with regard
to any salt mixture, and the fact that a mixture is regis-
tered with the California State Department of Agricul-
ture, as required by the law governing sale of fertilizers,
implies no endorsement for use of the product. The direc-
tions given in Part II will, it is hoped, help the amateur
to prepare his own nutrient solutions.
Brief Outline of the Technique of Water-Culture
Production of Plants
The usual equipment for the commercial water-culture
method consists essentially of long, narrow, and shallow
tanks, which may be constructed of wood, cement, black
iron coated with asphalt paint, or other sufficiently cheap
materials which do not give off toxic substances. These
tanks contain the nutrient solution in which roots of the
plants are immersed. Wire screens are placed over the
tops of the tanks, or inside, above the solution. The screens
support a layer of bedding of varying thickness (often
three or four inches), according to the kind of plant grown.
The bed may be prepared from a number of inexpensive
materials-for example, pine shavings, pine excelsior, rice
hulls. Some materials, such as redwood shavings or saw-
dust, may be toxic. Seeds are planted in the moist beds,
or young plants from flats set in them with their roots
in the nutrient solution. It is to be noted that roots may
later develop not only in the solutions in the tanks, but
also in the beds. The shallowness of the tanks and the
porous nature of the beds facilitate aeration of the root
system-an essential factor-although it has not been dem-
onstrated that such aeration unsupplemented by an addi-
tional oxygen supply, would be optional for all kinds of
plants.









GROWING PLANTS BY WATER-CULTURE


Chemically pure salts commonly employed in making
nutrient solutions for scientific experiments would be too
expensive for commercial practice, and a number of ordi-
nary fertilizer salts can serve in large-scale production
of crops. Recent developments in the fertilizer industry
have made available cheap salts of considerable degree of
purity. Some commercial salts, however, contain impuri-
ties (fluorine, for example, is commonly found in phosphate
fertilizers) which may be toxic to plants under water-culture
conditions.
Temperature Relations

In general, air temperatures suitable for growing
plants in soil will also be suitable for growing plants in
water-culture. Under natural conditions, the temperature
of the soil fluctuates but slightly from day to night, except
close to the surface of the soil, whereas air tempera-
tures are usually lower during the night than during the
day. When tanks of culture solution are utilized for grow-
ing plants and night temperatures are low and days are
cool the solution may not maintain a sufficiently high
temperature to produce the most rapid growth of the
plant permitted by other conditions of the environment.
Heating the solution would then be effective. However,
existing knowledge of temperature effects is altogether in-
adequate. Certainly it is not possible to specify any one
best solution temperature since this will vary with the
kind of plant, the amount and duration of sunshine, and
with day and night air temperatures.
If the nutrient solution is to be heated, one way of ac-
complishing this is by the use of insulated electric cables
laid in the bottom of the tank; but much care must be
exercised to select a proper type of installation to avoid
corrosion of the cables and difficulties with thermostatic
controls. Also, the cost of electric heating should be care-
fully investigated and compared with the cost of heating
by other means. One commercial firm heats the culture
solution in a boiler tank, very economically, with natural
gas. The heated solution is circulated through the tanks
in which plants are grown. The particular method of cir-
culating solutions has been patented by the firm which
developed it.
The heating of solutions will not take the place of gen-
eral heating of the greenhouse, except in localities in which
there is assurance against frost injury, or unfavorably low









DEPARTMENT OF COMMERCE


air temperatures. Provision for heating the greenhouse
may be found desirable even when this danger is absent,
in order to control humidity and plant diseases.
Most amateurs who try the water-culture method will
grow plants in warm seasons and probably will not wish
to complicate their installation by the addition of heating
devices. Anyone who desires to test the influence of heat-
ing the culture solution should make comparisons of plants
grown under exactly similar conditions, except for the differ-
ence of temperature in the solutions.

Composition of Nutrient Solutions

Thousands of requests have been received by the Col-
lege of Agriculture for formulas for nutrient salt solutions.
It is often supposed that some remarkable new combination
of salts has been devised and that the prime requisite for
growing crops in solutions is to use this formula. Now
the fact is that there is no one composition of a nutrient
solution which is always superior to every other composi-
tion. Plants have marked powers of adaptation to different
nutrient conditions. If this were not so, we should not
have plants growing in varied soils in nature. Within
certain ranges of composition and total concentration, fairly
wide latitude exists in the preparation of nutrient solutions
suitable for plant growth. Many varied solutions have
been used successfully by different investigators. Even
when two solutions differ significantly in their effects on the
the growth of a particular kind of plant under a given
climatic condition, this does not necessarily mean that the
same relation between the solutions will hold with another
kind of plant, or with the same kind of plant under another
condition.
Another point concerning nutrient solutions needs to be
stressed. After plants begin to grow, the composition of
the nutrient solution changes because the constituents are
absorbed by plant roots. How rapidly the change occurs
depends on the rate of growth of the plants and the vol-
ume of solution available for each plant. Even when large
volumes of solutions are provided, some constituents
may become depleted in a comparatively short time by rapid-
lv growing plants. This absorption of nutrient salts causes
not only a decrease in the total amounts of salts available,
but a qualitative alteration as well, since not all the nutri-
ent elements are absorbed at the same rates. One second-









GROWING PLANTS BY WATER-CULTURE


ary result is that the acid-base balance (pH) of the solu-
tion may undergo changes which in turn may lead to precip-
itation and loss of availability of certain chemical ele-
ments (particularly iron and manganese) essential to the
plant. Also to be considered are the effects of salts added
with the water (discussed later). For these various reasons,
the maintenance of the most favorable nutrient medium
throughout the life of the plant involves not merely the
selection of an appropriate solution at the time of plant-
ing, but also continued control, with either the addition
of chemicals when needed or replacement of the whole
solution from time to time. Proper control of culture solu-
tions is best guided by chemical analyses of samples of
the solution taken periodically and by observations of the
crop. Only further investigation will determine if suc-
cessful standardized procedures requiring only limited con-
trol and adjustments can be developed for a given crop,
locality, and season of the year.
The plant physiologist in his experiments, prepares
his solutions with distilled water, for the purpose of ex-
act control. The commercial grower, or the amateur, is
usually limited to the use of domestic or irrigation water
which contains various salts, including sodium salts, such
as sodium chloride, sodium sulfate, and sodium bicarbon-
ate. Most waters suitable for irrigation or for drinking
can be utilized in the water-culture method, but the ad-
justment of the reaction (pH), in the nutrient solution,
depends on the composition of the water. Some waters
may contain so much sodium salt as to be unfit for mak-
ing nutrient solutions. Even with a water only moder-
stely high in salt content, the salt may concentrate in the
nutrient solution with possibly unfavorable effects on the
plant, if large amounts of water have to be added to the
tanks and the solutions are not changed.
As already indicated, the successful growth of a crop
is dependent on sunlight and on temperature and humidity
conditions, as well as on the supply of mineral nutrients
furnished by the culture medium. Complex interrelations
exist between climatic conditions and the utilization of
these nutrients. The relation of nitrogen nutrition and
climatic conditions to fruitfulness has often been stressed.
In :'ome localities, deficient sunshine may prevent the pro-
duction of profitable greenhouse crops of many species, in
winter months, no matter what nutrient conditions are
present in the culture solution.









DEPARTMENT OF COMMERCE


PART II.
Procedures for Growing Plants by the
Water-Culture Method
The description of the technique for growing plants in
water-culture, which follows, has been adapted for pre-
sentation in popular form from information now available
to us.
Tanks and Other Containers for Nutrient Solutions
Various kinds of tanks and containers have been util-
ized for growing plants in water culture. Tanks of black
iron, well painted with asphalt paint (most ordinary paints
cannot be used, because of toxic substances), have proved
satisfactory for experimental work. Galvanized iron may
give trouble, even when coated with asphalt paint, if the
paint scales off.
Concrete tanks have been tried, but they may require
thorough leaching before use. Painting the inside of the
tank with asphalt paint is advisable. Wooden tanks will
serve the purpose, if made watertight. Redwood may give
off toxic substances and therefore may require preliminary
leaching to remove these substances. Finally, coating with
asphalt paint is desirable. For small-scale cultures, 2- or
4-gallon earthenware crocks may be serviceable. A wire
screen to hold the bedding material can be bent over the
sides of the crock. For demonstrations in schools, Mason
jars covered with brown paper, to exclude light, can be
employed. The jars are provided with cork stoppers in
which one or more holes have been bored. Plants are fixed
in the holes with cotton. Wheat or barley plants are very
suitable for these demonstrations.
The dimensions of tanks must be selected in accord-
ance with the objective. One kind of tank, of large size,
adapted to many purposes, has dimensions of 10 feet in
length, 21/. feet in width, and 8 inches in depth. A smaller
tank, 30 inches long, 12 inches wide, and 8 inches deep, is
convenient for use in many experiments. In general, shallow
tanks will be found suitable. The length and width may be
determined by consideration of convenience.
A heavy chicken-wire netting (1-inch mesh), coated
with asphalt paint, is fastened to a frame and placed di-
rectly over the tank to provide support for the porus bed.
In constructing a frame, it is desirable to leave several
narrow sections not covered with wire netting but with









GROWING PLANTS BY WATER-CULTURE


wooden covers which can be conveniently removed for in-
spection of roots, or for adding water or chemicals. The
wire netting should be stretched immediately above the sur-
face of the solution when the tank is full. Cross supports
may be placed under the netting to prevent it from sagging.
A carpenter or mechanic can design and build suitable
tanks and frames, which may take many forms, and fur-
ther detailed description here is unnecessary.
Nature of Bed*
The wire screen is covered by a layer of porous bed-
ding material several inches thick-thicker when tubers
or fleshy roots develop in the bed. Various cheap bedding
materials have been suggested: pine excelsior, peat moss,
pine shavings or sawdust, rice hulls, etc. Some materials
.re toxic to plants. Redwood should usually be avoided.
One type of bed which has produced no toxic effects in
experiments carried on in Berkeley, with tomatoes, consists
of a layer of pine excelsior two or three inches thick, with
a superimposed layer of rice hulls about one or two inches
thick. For plants producing tubers or fleshy roots, some
finer material may need to be mixed with the excelsior.
This is also essential when small seeds are planted in the
bed, to prevent the seeds from falling into the solution and
to effect good contact of moist material with the seed. In
all cases, the bed must be porous and not exclude free access
of air.
If seeds are planted in the bed, it must, of course, be
moistened at the start and maintained moist until roots
grow into the solution below. The bed should also be main-
tained in a moist state, by occasional sprinkling for the
development of tubers, bulbs, fleshy roots, etc. Great care
should be observed to prevent waterlogging of the bed,
which leads to exclusion of air and to undesirable bacterial
decompositions.
Planting Procedures
Seeds may be planted in the moist bed, but often it is
better to set out young plants chosen for their vigor, which
have been grown from seeds in flats of good loam. Cereal
-eeds may be conveniently germinated between layers of
moi,,t filter paper if plants are to be fixed in corks and
grown in jars of solution. In transplanting from a flat
*The general arrangement of this type of bed was first described by W. F. Gericke
and J. R. Tavernetti, Agricultural Engineering 17: 141-43. 1936.









DEPARTMENT OF COMMERCE


of soil, the soil is thoroughly soaked with water so that
the plants can be removed with the least possible injury
to the roots. The roots are then rinsed free of soil with
a light stream of water and immediately set out in the
Beds, with roots immersed in the solution. If young plants
are set out, the roots are placed in the solution, and at the
same time the layer of excelsior is built up over the screen.
Then the layer of rice hulls is placed on top of the excelsior.
If seeds are to be planted in the bed, the whole bed must be
installed and moistened before the seed is planted.
Spacing of Plants
In the experiment with tomato, plants were set close
together, in some instances 20 plants to 25 square feet of
solution surface. No general advice can be offered as to
the best spacing. This depends on the kind of plant and
on light conditions. Individual experience must guide the
grower.
Addition of Water to Tanks
In starting the culture, the tank is filled with solution
almost to the level of the lower part of the bed. As the
plants grow, water will be absorbed by plants or evapo-
rated from the surface of the solution, and the level of the
solution in the tank will fall. The recommendation has
generally been made that after the root system is well
developed, the level of the solution should remain from
one to several inches below the lower part of the bed, to
facilitate aeration. However, since the solution level should
not be permitted to fall very far, regular additions of water
are required.
As pointed out in Part I, when large amounts of water
have to be added to a tank, excessive accumulations of
certain salts contained in the water may occur, especially
if the salt content of the water is high. To avoid this diffi-
culty, the entire solution is changed whenever the salt con-
centration becomes high enough to influence the plant ad-
versely. Because of the wide variation in the composition
of water from different sources, no specific direction to
cover all cases can be given. For some waters, special
modifications of the directions given later for preparation
of nutrient solutions may be required.
Nutrient Solutions
It is well to emphasize again that there is no one nu-
trient solution which is always superior to every other
solution. Among many solutions which might be employed,









GROWING PLANTS BY WATER-CULTURE


those described below have been found to give good results
with various species of plants in experiments conducted in
Berkeley, with a source of good water. Other solutions, no
doubt can also b(e used with good results.
The composition of the solutions is given in two forms:
(1) by rough measurements adapted to the amateur with-
out special weighing or measuring instruments, and (2)
in more exact terms for those with some knowledge of
chemistry, who have proper facilities for more accurate
experimentation.
Preparation of Nutrient Solutions: Method A,
for Amateurs
Either one of the solutions given in Table V may be
tried. The "T.C." solution may often be preferred because
the ammonium salt delays the development of undesirable
alkalinity. The salts are added to the water, preferably in
the order given.
To either of the solutions add the elements iron, boron,
manganese, zinc, and copper, which are required by plants
in minute quantities. There is danger of toxic effects if
much greater quantities of these elements are added than
indicated later in the text.
With the exception of iron, the elements of this group
are added only when the solution is first prepared or when
the whole solution is changed.

TABLE V. COMPOSITION OF NUTRIENT SOLUTIONS*
(The amounts given are for 25 gallons of solution)
Approx. Approx.
Grade Amount in Amount in
Salt of Salt Ounces Tablespoons
"P. N." SOLUTION**
Potassium phosphate Technical 1/2 1 level
(monobasic)
Potassium nitrate Fertilizer 2 4 level (of
powd. salt)
Calcium nitrate Fertilizer 3 7 level
Magnesium sulfate Technical 11/2 4 level
(Epsom salt)
*The University does not sell nor give away any salts for growing plants in water
culture. Chemicals may be purchased from local chemical supply houses, or possibly
may be obtained through fertilizer dealers. Some of the chemicals may be obtained
from druggists. If purchased in fairly large lots, the present price of the ingredients
contained in one pound of a complete mixture of nutrient salts is approximately 5-10
cents for either solution described above.
**To either of these solutions, iron, boron, manganese, zinc, and copper must be
added in minute quantities: see directions in the text.









20 DEPARTMENT OF COMMERCE

"T. C." SOLUTION**
Ammonium phosphate Technical 1/ 1 heaping
(monobasic)
Potassium nitrate Fertilizer 21/, 5 level (of
powd. salt)
Calcium nitrate Fertilizer 21/2 6 level
Magnesium sulfate Technical 12 4 level
(Epsom salt)
It may be necessary to add the iron solution at frequent
intervals; for example, once or twice a week. If the leaves
of the plant tend to become yellow the reason may be lack
of iron, although a yellowing or mottling of leaves can also
be due to other causes.
1. Iron Solution.
Dissolve a level teaspoon of iron tartrate (iron citrate
or iron sulfate can be substituted, but the tartrate or citrate
are often more effective than the sulfate) in a quart of
water. Add half a cupful of this solution to 25 gallons
of nutrient solution each time iron is needed (once weekly,
or more frequently if the plants are pale.)
2. Boron Solution.
Dissolve a level teaspoon of powdered boric acid in a
gallon of water. Use a pint and a half of this solution for
each 25 gallons of nutrient solution.
3. Manganese Solution.
Dissolve a teaspoon of crystalline, chemically pure man-
ganese chloride (MnCl, 4 H,O) in a gallon of water.
Manganese sulfate can also be used. Dilute one part of
this solution with two parts of water, by volume. Use a
pint of the diluted solution for each 25 gallons of water.
4. Zinc Solution.
Dissolve a level teaspoon of crystalline, chemically pure
zinc sulfate (ZnS04 7H20) in a gallon of water. Use four
teaspoons of this solution for each 25 gallons of nutrient
solution.
5. Copper Solution.
Dissolve a teaspoon of chemically pure copper sulfate
(CuSO, 5 HO) in a gallon of water. Dilute one part of
this solution with four parts of water; use one teaspoon
of the diluted solution for each 25 gallons of nutrient so-
lution.









GROWING PLANTS BY WATER-CULTURE 21

Testing and Adjusting the Acidity of Water and
Nutrient Solutions
The chemicals required are:
1. Brom thymol blue indicator. This can be obtained,
with directions for use, from chemical supply houses, in
the form of solutions or impregnated strips of paper.
2. Sulfuric acid. Purchase a supply of three per cent
(by volume) acid of chemically pure grade. (Concentrated,
chemically pure sulfuric acid may be purchased and diluted
to three per cent strength, but the concentrated acid is dan-
gerous to handle by inexperienced persons). This three per
cent acid may be further diluted with water if a preliminary
test indicates that only small additions of acid are required
to bring about a desirable reaction.
Adjust the acidity of the water before adding nutrient
salt according to directions given.
Test the degree of acidity of a measured sample of the
water (a quart, for example) by noting the color of the
added indicator or test paper immersed in the solution.
A yellow color indicates the desired slight acidity (with
no further adjustment necessary), green a neutral reaction
blue and alkaline reaction.
Add the dilute sulfuric acid (three per cent or less)
slowly with stirring until the original green or blue color
just changes to yellow. Do not add more acid beyond this
point, since the yellow color will also persist when exces-
sive amounts or acid are added. Record the amount of
acid required.
Finally add a proportionate amount of the acid to the
solution in the culture tank or vessel, having first deter-
mined how much it holds.
The reaction of the culture solution should be likewise
tested from time to time and, if found alkaline, corrected
by ihe addition with stirring of dilute sulfuric acid. If
strips of indicator paper are used, the test may be performed
directly in the tank, or on a small sample of the culture
solution.
Preparation of Nutrient Solutions: Method B, for
Special Experimentation by Schools, etc.
The use of distilled water and chemically pure salts
is recommended. Molal stock solutions (except when other-
wise indicated) are prepared for each salt, and the amounts
indicated below are used.









DEPARTMENT OF COMMERCE


C.c. per liter of
"P. N." Solution Nutrient Solution
M 1 KH,PO, potassium acid sulphate 1
M 1 KNO. potassium nitrate 5
M/1 Ca(NO3)2 calcium nitrate -- 5
M/1 MgSO, magnesium sulfate ---- 2
"T. C." Solution
M/1 NH4H2PO, ammonium acid phosphate --- 1
M/1 KNO, potassium nitrate ---- 6
M/1 Ca(NOs)2 calcium nitrate --- 4
M/1 MgSO, magnesium sulfate 2
To either of these solutions add the following:
(a) Iron in the form of 0.5 per cent iron tartrate solu-
tion or other suitable iron salt, at the rate of 1 cc. per liter,
about once weekly or as indicated by appearance of plants
(more if pale).
(b) Prepare a supplementary solution which will sup-
ply boron, manganese, zinc, and copper, as follows:
Grams Dissolved
Compound in 1 liter of HO
H,B03 2.86
MnCI, H20--- 1.81
ZnSO, 7 H20 -- ----- 0.22
CuSO, 5 H O -- 0.08
Use 1 cc. of this solution for each liter of nutrient solu-
tion. This will give the following concentrations:
Parts per Million
Element of Nutrient Solution
Boron --------- 0.5
Manganese --------- 0.5
Zinc ---------- 0.05
Copper ------- -- 0.02
Adjustment of Reaction During Growth of Plants
If the culture solution should become alkaline (pH
greater than 7) as a result of growing plants, make the
solution slightly acid (about pH 6) by adding N/10 H,SO,
(or some other suitable dilution).
Changes of Nutrient Solution
As the plants begin to grow, nutrient salts will be
absorbed and the acidity of the solution will change. More
salts and acid may be added, but to know how much,
chemical tests on the solution are required. When these









GROWING PLANTS BY WATER-CULTURE


cannot be made, an arbitrary procedure may be adopted
of draining out the old solution every week or two, im-
mediately refilling the tank with water, and adding salts
and acid, as at the beginning of the culture. The number
of changes of solution required will depend on size of
plants, how fast they are growing, and on volume of solu-
tion. Distribute the salts and acid to different parts of
the tank. In order to effect proper mixing, it may be well
to fill the tank at first only partly full (but keep most
of the roots immersed) and then after adding the salts and
acid, to complete the filling to the proper level with a
rapid stream of water.
Plant Diseases
In Part I, attention has been called to the fact that
growing plants in water-culture does not render them
immune from disease or from insect pests. In fact, the
conditions of the water-culture method may sometimes even
be conducive to attacks of mildew. The control of diseases
and insects is described in publication of the California
Agricultural Experiment Station.
Varieties of Plants and Pollination
Knowledge of varieties and their adaptation to general
climatic conditions, or to greenhouse conditions, is just
as important for the water-culture method of crop produc-
tion as for production in soil. Experienced gardeners or
greenhouse men, farm advisers, or others with special
knowledge, should be consulted on this point.
Special procedures may be required to insure pollina-
tion of some kinds of plants, under greenhouse conditions.
Consult an expert or a publication describing the culture
of the plant to be grown.


CROP PRODUCTION WITHOUT SOIL

W. E. TOTTINGHAM
Department of Agricultural Chemistry
University of Wisconsin
Madison, Wis.

The nutrient solution must be made within a range
favorable to uptake of salts but without sufficient concen-
tration to injure the plant. In general terms, this range
is from 0.1 to 0.3 per cent, which is more than ten to
thirty times the average concentrations of the solution in









24 DEPARTMENT OF COMMERCE

the soil. Obviously, it becomes necessary to restore both
water and mineral salts as these are removed by the crop.
It may be desirable also to correct either acidity or alkalin-
ity, which tends to develop as the basic or acidic element
respectively is assimilated from the salts. This applies
particularly to the salts which supply nitrogen. In the
assimilation of nitrate from nitrate of soda, for example,
a residue of carbonate of soda is left in the nutrient solu-
tion and this eventually becomes injurious by its alkalinity.
This effect is partly due to rendering iron unavailable, as
indicated by chlorosis or the bleaching of leaves from their
normal green color.
The optimal reaction of the nutrient solution is in a
slightly acid range for most species of plants (namely,
4 to 6 in the pH scale, of which 7 is the neutral point).
This range is well covered by the indicator methyl-red,
which is fully red at 4.2 and fully yellow at 6.3 pH. Sim-
ilarly, resorcin-blue changes from red at 4.4 to blue at
6.2 pH. These indicators are best used in the form of
absorbent paper slips (test paper) in which the indicator
has been deposited from solution and dried. Electric equip-
ment is available for very accurate determination of acidity,
but it is rather expensive for the present purpose. Lit-
mus paper, a very common indicator, should be useful in
this connection. It is fully red at 4.5 and fully blue at 8.3
pH, the latter being a seriously injurious alkaline reaction.
If the nutrient solution imparts even a trace of blue to
the color of litmus paper wetted by the liquid, sulfuric
acid should be added with stirring until the reaction gives
a fully red color. This may be done in a pilot portion of
one gallon, using a solution of about 10 per cent acid. In
computing the needs of a tankful of solution, consider one
cubic foot equivalent to eight gallons. In the case of much
assimilation of ammonia the solution may become too acid.
In that event it may be adjusted to change the reaction of
litmus from red to faintest pink, by the addition of a solu-
tion containing about 10 per cent sodium hydroxide. It
will be necessary to use a burette for adjusting the control
test and a graduated cylinder for treatment in the tank.
The necessary acid or alkali, as well as supplementary sup-
plies of salts, may be added through standpipes erected at
intervals on the bottom of the tank. Some device for stir-
ring the added chemicals into the nutrient solution without
injuring the roots may be desirable, as unaided diffusion
acts very slowly. It might be advantageous to aerate the
solution, as this also stimulates respiration and the uptake









GROWING PLANTS BY WATER-CULTURE 25

of mineral elements. This would serve also to mix the solu-
tion with added materials. It could be provided for through
displacement of air by water in a closed vessel, from which
tubes lead to the bottom of the culture tank.
The requirements for nitrogen and potassium are high,
relative to other mineral elements, curing rapid vegetative
development. Some species do not assimilate nitrate well
early in this stage, but this is not true of the tomato. Where
the requirement is not known in this respect, at least 20
per cent of the nitrogen should be supplied by sulfate of
ammonia. The total concentration of the more abundant
nutrients should not be allowed to decrease excessively.
One might set the minimum at about one-fifth that of the
original sample. The best test for need of this reinforce-
ment is the determination of electrical conductivity, but
the equipment and experience required seem prohibitive
to its use. Certain color tests may be more generally prac-
ticable. These will require special chemicals and some in-
struction in technique. Nitrate may be determined on
evaporated portions of the solution by the color formed
through reaction with a reagent produced from carbolic
and sulfuric acids. A simple form of the instrument called
colorimeter will be required for comparing the used with
unused nutrient solution. A pilot determination on a small
sample should show the amount of nitrate required per tank
if the contents were previously mixed. Ammonium and
potassium require more complicated reagents. The former
may be estimated by use of Nessler's solution, as commonly
practiced in analysis of drinking water. Potassium may
be determined by a procedure commonly applied to plants
and soils.
In recent years it has become apparent that beyond the
seeding stage, plants commonly require several rarer min-
eral elements for complete development. It thus becomes
necessary to provide for minute amounts of boron, copper,
manganese and zinc, in addition to nitrogen, sulfur (of
sulfates), phosphorus (of phosphates), potassium (or pot-
ash), calcium (or lime) and magnesium (or magnesia).
Still rarer essential elements are quite likely to be supplied
in the minute amounts necessary by the commercial grade
of salts available through drug stores.
On the basis of personal experience the following for-
mula is proposed. It is necessary to dissolve the citrate
or tartrate of iron as one or two per cent solution in
boiling water. On account of its organic character it is
quickly destroyed by microorganisms and must be prepared









DEPARTMENT OF COMMERCE


quickly. The more abundant salts can be made into con-
centrated stock solutions (above 25 per cent), with the ex-
ception of the calcium salt. This must be kept separate
because of the tendency to formation and precipitation of
calcium sulfate. It is probably best to add the rarer ele-
ments when preparing the diluter nutrient solution. Still
rarer elements will probably be adequately supplied if the
salts used are generally of commercial grade.
WISCONSIN SOLUTION
Per Cent
COMPOUND by Weight
Ammonium sulfate 0.01
Calcium dihydrogen phosphate 0.04
Ferric citrate -- 0.001
Magnesium sulfate _- -- 0.03
Potassium chloride 0.04
Potassium nitrate 0.08
To each liter of the above solution should be added one
cubic centimeter of a solution containing per liter (quarts
may be substituted for liters) 0.01 gram copper sulfate,
0.05 gram each of borax and zinc and 0.5 gram manganous
chloride or sulfate. At first signs of chlorosis, test for
alkalinity or deficiency of nutrients. Even in acid solu-
tions it may be necessary to repeat the additions of ferric
citrate, unless iron tanks are used. The solution here
recommended has a total salt concentration of 0.2 per cent,
which is twice that of Gericke's formula (1 lb., in water
25 sq. ft. x 7 in., or about 900 lbs.). The 300 pounds of
tomatoes which he produced per year on such a tank should
have contained about 1.5 pounds of minerals (as ash), in
comparison with the 7 pounds of salts which he supplied.
It may be possible to provide iron more simply where
iron tanks are not used. Trelease and Trelease substituted
for ferric citrate 0.0014 per cent ferrous (iron) sulfate
and 0.0016 per cent potassium citrate with favorable re-
sults in short term cultures. Their proportions between
nitrate and ammonium salts served also to regulate the re-
action of the culture solution for young wheat plants.









GROWING PLANTS BY WATER-CULTURE


Indiana Nutrient Solution Methods of
Greenhouse Crop Production*

Only the subirrigation method of culture and certain
nutrient solution formulas are presented in this abstract as
both sand and water culture are discussed in other articles
of this bulletin.

Subirrigation Method of Culture

The subirrigation method of culture is the most recent
system of nutrient solution culture of the three methods
that appear to have practical possibilities. The details of
the system were developed at Purdue for the more accurate
control of the nutrition of large numbers of plants growing
under various experimental conditions. This system con-
sists essentially of a waterproofed bed, such as may be used
in the water culture method, filled with fine gravel or
cinders. The nutrients are supplied from the bottom of the
bed by means of a centrifugal pump connected to a cistern
placed at a lower level than the bed. The pump is operated
by a time clock for three periods each day, so that at each
period of operation the benches of gravel or cinders are
flooded with the nutrient solution. At this stage the pump
is turned off and the solution drains by gravity back through
the pump into the cistern. If a centrifugal pump is used
the solution starts to drain back as soon as the motor stops
operating, and no valves or traps are needed.
The solution is forced into the benches at the end
through a short nipple. It flows from the end of the nip-
ple throughout the whole length of the bed, which may be
a distance of 100 or 200 feet, if proper precautions are taken
with regard to leveling. The trough through which the
solution flows consists of a double beaded four-inch roof-
ing gutter thoroughly coated with asphalt and turned up-
side down on the bottom of the waterproofed benches,
The eaves trough forms a channel through which the solu-
tion may flow by gravity, and should fit the bottom of the
bench loosely enough so that the solution can flow out
under the bottom edges. All of the pipe connections must
be of black iron pipe. Galvanized iron pipe may cause
toxicity due to the presence of zinc. The eaves trough
*Abstract from Circular 232, Nutrient Solution Methods of Greenhouse Crop Pro-
duction by R. B. Withrow and J. P. Biebel. (November, 19371. Published by Purdue
University, Lafayette, Ind. Messrs. Withrow and Biebel are members of the staff of
the Department of Horticulture, Purdue University.









DEPARTMENT OF COMMERCE


may be readily painted with an asphalt paint or emulsion
to protect the solution from the zinc, but it is not so readily
possible to protect the solution from the galvanizing of the
pipe.
The centrifugal pump should have a minimum capacity
of 20 gallons per minute per 1,000 square feet of bench
space. A 1/4-horsepower pump is capable of handling 20
gallons per minute against a 10-foot head and will flood
1,000 square feet of bench space containing five inches of
gravel in 40 to 60 minutes. It takes about twice that time
for the benches to drain.
The gravel serving as the growth medium should be
well sifted to include only particles ranging from 1/20- to
1/4-inch in diameter. Sand in large quantity will tend to
clog the pump and pipes of the system and also will pre-
vent the thorough aeration of the roots. If cinders are
used to fill the bed they should be sifted first through a
1/.-inch sieve to remove the larger pieces, and then washed
through a 1/16-inch sieve to remove the finer particles.
In this system the chemical composition of the gravel
or cinders is rather important. In general, it appears that
gravels containing more than five per cent acid soluble
material calculated as calcium carbonate are unsuitable for
most work. Possibly ten per cent would do for plants not
requiring a pH below 6.5.
After being placed in the benches the cinders should be
thoroughly leached with acid water for at least one week.
The water should be changed every other day. Crude sul-
phuric acid added at the rate of one gallon per 1,000 square
feet of bench space will effectively neutralize small quanti-
ties of alkalies. The acid should be added to the leaching
water at each change until the pH of the solution stays at
five or less for several days at a time.
The cistern used as the nutrient solution reservoir
should have a capacity of at least one-fourth the cubic
content of the bench, figured on the basis of a five-inch
depth of material.
The subirrigation method offers several advantages
over the other systems of culture. It makes possible the
accurate control of the nutrients and keeps the roots in con-
tact with fresh nutrient solution and air and at the same
time offers a convenient means of support, as is offered in
soil or sand, and the elimination of the labor involved in
watering. Such a system can be made wholly automatic









GROWING PLANTS BY WATER-CULTURE 29

by means of time switches so that little attention need be
given it except to keep the nutrient solution level in the
cistern constant with tap water.
Sufficient data have now been accumulated on the cost
of installation and operation of the subirrigation system
to make possible a rough estimate of some of the various
items of cost. The waterproofing of existing wooden
benches with asphalt is estimated to cost between two and
three cents per square foot. The various other items in-
cluding the roofing gutter, piping, pump, motor, and cistern
are estimated to total about 15 cents per square foot for
large systems of 5,000 square feet or more, and 20 cents
for small experimental systems of 500 to 1,000 square feet.
The pump operates for only a few hours per day so
that the cost of electricity is not a large item. With elec-
tric energy costing three cents per kilowatt hour, the oper-
ating cost would be about 0.2 cent per square foot per year.
Depreciating all of these costs over a ten-year period,
adding the cost for electricity, plus 0.3 cent per square
foot for interest on the investment, the total yearly cost
per square foot amounts to only two cents.

Nutrient Solutions

Regardless of the method of application in the particu-
lar system used, the primary requisite of any nutrient
solution is a proper balance as to total concentration and
proportion of the various inorganic elements. Plants re-
quire potassium, calcium, magnesium, nitrogen, phosphorus,
and sulfur in relatively large quantities. Besides these
elements they need small quantities of iron and traces of
manganese, boron, copper, zinc, and other elements. When
cinders or gravels containing a wide variety of minerals
are used for growing the plants, and commercial fertilizers
are used as salts for the nutrient solution, it is generally
necessary to supply only the six major elements mentioned,
with possibly the occasional addition of iron.
In Table VI is presented a series of nutrient solution
fertilizers. These fertilizers are based upon the use of
magnesium sulphate, double superphosphate, potassium sul-
phate, potassium nitrate, ammonium sulphate and calcium
sulphate. All of these are available from fertilizer con-
cerns.









DEPARTMENT OF COMMERCE


Commercial fertilizer salts contain considerable insolu
ble impurities and possibly one-quarter of the material may
fail to dissolve, but the impurities appear to have little
detrimental effect upon the growth of the plants if the
proper grades of salts are selected. The highest analysis
fertilizer salts should always be selected for nutrient solu-
tions. The purer grades of magnesium sulphate, potassium
sulphate, potassium nitrate and ammonium sulphate appear
to contain no impurities which are toxic to plants. The
fertilizer grades of phosphate salts, however, all contain
some fluorine as an impurity which varies from 1 to 3.5 per
cent. It appears essential that only those grades be used
which contain less than one per cent fluorine. Higher
values man result in root injury to some plants.
The nutrient solutions are prepared by dissolving the
necessary fertilizer chemicals, as given in Table VI, in
small quantities of water before adding to the large tanks
of water. The pH of the solution should be adjusted with
crude sulphuric acid until it is in the correct range, which
is between 4.0 and 6.5 for most crops growing in nutrient
solutions.
For example, gardenias should be kept at between pHI
4 and 5. Roses grow best at between 4.5 and 5.5. Other
commercial crops such as sweet peas, which in soil grow
best under alkaline conditions, should be kept at between 5
and 6 when grown in nutrient solution culture. A dropper
bottle of .04 per cent brom cresol green, a porcelain test
plate or glass vial, and a color chart, are a useful combinai
tion for this pH range.
Once each month or oftener the solution is changed or
the depleted nutrients replenished. Between these inter-
vals the solution is kept at a constant level with tap water,
Plants remove water more rapidly from the solution than
they do nutrients. Therefore, water must be added many
times as often as the fertilizer salts.
Three solutions of Table VI contain three levels of
nitrogen in relation to the other elements. Solution 1D
contains the least nitrogen and tends to promote the hard,
est type of growth. It is especially valuable during the
winter months. 2D is intermediate in composition, and
3D contains the highest level of nitrogen. 3D is especially
valuable during the spring and summer months when there
is plenty of sunlight available. This solution tends to pro4
mote the softest type of growth. These three solutions
make possible a wide range of control of the type of growth,









GROWING PLANTS BY WATER-CULTURE


Intermediate control of the growth can be readily
obtained by controlling the total concentration of the nu-
trient solution. If the growth tends to be a little soft
with any particular solution, it may be hardened slightly
by adding more nutrient solution fertilizer. Possibly 50
per cent increase in concentration will bring about the
proper degree of hardness. If this is not enough the con-
centration can be doubled.
The nutrient solutions given in Table VI cost between
forty and sixty cents per 1,000 gallons of solution. With
the exception of the phosphate, none of the chemicals
should cost more than three and one-half cents per pound
in small quantities. The food grades of monocalcium phos-
phate cost about eight cents per pound as compared to two
cents for the fertilizer grades of superphosphate. The
latter, however, must be chosen very carefully to avoid
fluorine injury.
The salts (Tables Nos. VI and VII) may be mixed,
powdered, and added as a mixture at the rate of approxi-
mately one-half pound per 1,000 gallons of solution.
While it is frequently not necessary to add iron and
the micro elements to nutrient solutions for sand or sub-
irrigation culture, deficiencies of the elements may oc-
casionally appear. This is especially likely where pure silica
gravels are used. Table VII presents a formula that will
adequately supply iron and the more important micro ele-
ments. The dry salts should be dissolved in tap water be-
fore being added to the nutrient solutions.
This discussion is not intended to imply that any of
these nutrient solution methods are yet ready for large
scale commercial introduction. The difficulties pertaining
to their application to the commercial range are not all
solved by any means. For the grower who likes to ex-
periment they offer a very interesting and fascinating field.
It is only as growers experiment with nutrient solution
methods and cooperate with the experiment stations that
the final difficulties will be overcome and the practicability
of these methods be definitely determined.









32 DEPARTMENT OF COMMERCE


TABLE VI. COMPLETE NUTRIENT
FERTILIZERS


No. Fertilizer Salt
1D "Magnesium Sulphate (anhydrous)
**Monocalcium Phosphate (food grade,
0-55-0)
Potassium Nitrate (13-0-44)
Ammonium Sulphate (20-0-0)
Calcium Sulphate (agri. gypsum)

Total ... .
2D *Magnesium Sulphate (anhydrous)
**Monocalcium Phosphate (food grade,
0-55-0) .. .
Potassium Nitrate (13-0-44)
Ammonium Sulphate (20-0-0)
Calcium Sulphate (agri. gypsum)

Total... ....
3D *Magnesium Sulphate (anhydrous)
"*Monocalcium Phosphate (food grade,
0-55-0)
Potassium Nitrate (13-0-44)
Ammonium Sulphate (20-0-0)
Calcium Sulphate (agr. gypsum)

Total


TABLE VII. MICRO ELEMENT


Fertilizer salt
Iron Sulphate (Copperas)
Manganese Sulphate.. .
Copper Sulphate (Blue Vitriol)
Zinc Sulphate (Zinc Vitriol)
Sodium Tetraborate (Borax)


SOLUTION

Per 1,000 Gals.
Water
Lbs. Ozs.
1 2


22 0
0 8


0 8


19 10


SUPPLEMENT
Ounces per
1,000 Gallons
Solution


*Epsom salts may be substituted for the anhydrous magnesium sulphate by doubling
the quantity indicated.
**A fertilizer grade of double (treble) superphosphate may be substituted for the
monocalcium phosphate provided the fluorine content is less than one per cent. Grades
of superphosphate containing higher levels of fluorine are unsuitable. This also applies
to other phosphate salts. The fluorine comes from the original phosphate rock from
which the phosphates are prepared.









GROWING PLANTS BY WATER-CULTURE 33

Important Points Regarding the Subirrigation System
1. The benches must be level to within one inch and in
good repair.
2. Avoid unknown grades of asphalt. Use only petroleum
asphalts free of tars and fluxes. A good asphalt for
this purpose does not discolor water in which it is boiled
and produces no oily film on the surface. This also
applies to mulsified asphalts.
3. Use only gravels containing less than five per cent lime.
Such a gravel will not boil vigorously on applying dilute
hydrochloric (muratic) acid. The soils departments
of Agricultural Experiment Stations are generally
equipped to determine the percentage of lime in gravel
samples.
4. Cinders should be leached for at least one week before
using with water kept at a pH of less than four. The
acid water should be changed at least every two days.
Crude sulphuric or hydrochloric (muratic) acid may
be used to keep the water acid.
5. Do not use sand or very fine cinders as a benching
medium. They are too fine to allow proper aeration.
6. Do not use galvanized iron pipe or fittings. Zinc is toxic
to plants at low values of pH. Use black iron pipe and
cast or malleable iron fittings. Paint the surface of all
galvanized eaves, troughs and tanks with asphalt paint
or hot asphalt.
7. Use only high analysis fertilizer salts.
8. Use a double (triple or treble) superphosphate low in
fluorine. One per cent fluorine represents the upper
safe limit and lower values are preferable. The food
grades of monocalcium phosphate (which is a pure
grade of double superphosphate) are safest.
9. Follow the pH of the nutrient solution with a test kit.
Brom cresol green is a very useful indicator for this
purpose. Keep the pH between 4.0 and 6.5 for most
plants. If it tends to rise rapidly from day to day, it
is likely that the cinders or gravel contain appreciable
quantities of lime.
10. Do not try out any nutrient solution method on a large
scale, at first. Confine the first tests to less than 500
square feet and maintain adequate soil check plots.









34 DEPARTMENT OF COMMERCE

New Jersey Methods of Growing Plants
In Solution and Sand Cultures*

This abstract shall be devoted primarily to the sand
culture method and such formulas for preparing nutrient
solutions as are recommended by the authors.

The Sand Culture Method
The method of sand culture is essentially solution cul-
ture in sand, and employs the same type of nutrient solu-
tions. With slight modification, the continuous flow appar-
atus may be used with sand cultures where the solution isi
permitted to fall upon the surface of the sand in pots, perco-
lators, wooden boxes, or other containers. Although the sand
itself is chemically inert and can supply nothing to sustain
plant growth, it does provide a solid substratum which
gives effective support to the plant. Another feature is the
fact that the sand culture provides a very efficient aerating
system for the plant roots-a most important factor in the
growth of many species.
The sand culture method is being developed for the pro-
duction of superior seedlings for transplanting to the spring
garden. It has reached such a point of practicability that
it may become generally available for the growth of good
house plants and greenhouse plants for ornamental pur-
poses and for the greenhouse production of ornamentals;
and vegetables in general.
Many types of culture vessels have been used with the
sand culture method of growing plants. They consist of
glazed pots of various sizes and shapes with drain holes:
in the bottoms, stoneware crocks, percolators, wooden boxes,
and even greenhouse benches. Good drainage must always
be provided from the bottom of the vessel.
If the plants are not grown for experimental purposes,
ordinary construction sand may be employed. It need not
be washed if it is known to be free from materials which
might be toxic to the plants. If the sand is too fine it
does not allow adequate aeration, and if too coarse it does
not retain enough solution to supply water and nutrients
at optimum rates to the plants.
*Abstract of Bulletin 636, Methods of Growing Plants in Solution and Sand Cultures,
by J. W. Shive and W. R. Robbins (November, 19371. Published by Rutgers Univer-
sity, New Brunswick, N. J. Drs. Shives and Robbins are staff members of the
Division of Botany, Rutgers University.









GROWING PLANTS BY WATER-CULTURE 35

For best results, the solution is supplied to the sand
by the continuous flood method.
Where less control of the nutrient supply is permis-
sable, the solution may be poured on the surface of the sand
intermittently at regular intervals. The degree of possible
control in this procedure is determined by the frequency
with which the solution is applied to the culture. An oc-
casional thorough flushing of the sand with the solution
or with water is desirable in order to prevent the con-
centration of salts in the sand through water loss by
evaporation and transpiration, which might materially
alter the solution composition and unfavorably affect plant
response.

The Culture Solutions

No culture solution is complete unless it contains the
six major elements-potassium, calcium, magnesium, nitro-
gen, phosphorus, and sulfur-and the trace elements-
iron, boron, manganese, zinc, and perhaps copper and
some others. All these essential elements must be pres-
ent in adequate proportions and concentrations and in ap-
propriate combinations. They must also be in aqueous
solution form, since salts and salt combinations cannot
be supplied to plants except in water solutions, from which
alone a plant can absorb its nutrient supply, whether it is
growing in the soil or in a solution culture.
The formulaes for several culture solutions which have
produced excellent growth of several species of vegetables
and ornamentals in water culture and in sand culture under
average greenhouse conditions are given here. To complete
these solutions, minute quantities of the trace elements-
iron, boron, manganese, and zinc, must be added. These
are usually supplied in the following forms:
Iron as ferrous sulfate --- FeSO, 7H..O
Boron as boric acid H.BO,
Manganese as manganese sulfate MnSO, 4H.,O
Zinc as zinc sulfate ZnSO. 7H,O
The necessity of including other trace elements in a
general formula for the growth of plants has not yet been
demonstrated.
The solution characterized by formula I, tested over a
series of years, has produced uniformly excellent growth
of agricultural plants of a number of species.









36 DEPARTMENT OF COMMERCE

The solution designated by formula I may be prepared
as follows: For five-gallon quantities, the required amount
of each salt as given in the formula is weighed out, and
each salt is dissolved separately in a pint or more of water
to avoid precipitation. The four solutions are then mixed
together, and water is added to make a volume of five
gallons. To this five gallons of solution are now added
not more than ten cubic centimeters (2 teaspoonfuls) of
a stock solution of trace elements prepared by dissolving
together in a pint of water 0.8 gram (about 1/4 teaspoon-
full) each of boric acid (crystals), manganese sulfate, and
zinc sulfate. Since iron slowly precipitates in the culture
solution, it should not be added until just before the solu-
tion is supplied to the plants. A stock solution of iron is
prepared by dissolving 0.8 gram (about 1/ teaspoonful)
of ferrus sulfate in a pint of water. To each quart of
culture solution are added about five cubic centimeters (1
teaspoonful) of this iron solution. The iron requirement
varies greatly for different species and for the same species
from time to time with variation in light intensity and
other factors.
FORMULA I. SOLUTION FOR THE GROWTH OF
PLANTS IN WATER-CULTURE AND IN
SAND-CULTURE.


0



Salts l g a


Volume molecular concen-
tration 0.0023 0.0045 0.0023 0.0007
Grams per 5 gallons of so-
lution ---- 5.9 20.1 10.7 1.8
Teaspoonfuls per 5 gal. of
solution (approximate) 114 4 21/. 1

It will be observed that in formula I, ammonia sulfate
is present as a constituent of the solution, and is intro-
duced, because its presence has a stabilizing effect upon
the hydrogen-ion concentration of the nutrient medium.









GROWING PLANTS BY WATER-CULTURE 37

FORMULA II. SOLUTION FOR THE GROWTH OF
PLANTS IN WATER-CULTURE AND IN
SAND CULTURE







o3 4 1 3 -
Salts ) 'a .


Volume molecular concen-
tration 0.0015 0.0040 0.0022 0.0015
Grams per 5 gallons of so-
lution 3.9 6.4 10.3 3.2
Teaspoonfuls per 5 gal. of
solution (approximate 1 1 21/. 1


The solution indicated by formula II is prepared and
used in precisely the same manner as that described for
the solution designated by formula I. The trace elements:
boron, manganese, and zinc, are added immediately from
stock solution of these elements prepared as described and
in the quantity designated. Iron from stock solution is
added just before the culture solution is applied to the
plants.
This culture solution contains, in addition to the six
major elements, two additional elements-sodium (in so-
dium nitrate) and chlorine (in calcium chloride). These
two elements are not ordinarily considered essential for
growth, yet there is no experimental evidence to indicate
that they are toxic to plants in the concentrations pre-
scribed in the formula, and under certain conditions they
may even show beneficial effects.
The solution designated by formula II has produced
excellent growth of certain species such as tomato, tobacco,
cotton, and radish. If salts of technical grade are employed,
this solution can be prepared at somewhat less expense
than solutions of formula I.









DEPARTMENT OF COMMERCE


Excellent plants may be grown in both sand-culture
and water-culture with solutions prepared from crude
salts of the grade of commercial fertilizers, such as are
used in large-scale fertilizer practice in the field. The
description of such a solution is given in formula III. These
solutions when properly prepared are equal in plant-pro-
ducing value to solutions prepared from salts of highest
purity, and they are less expensive than the refined salts.
Usually these solutions may be used for the growth of
plants without the addition of trace elements since the
fertilizer salts ordinarily contain, as impurities, minute
quantities of the trace elements as well as other ingredients
not required for growth. No harm can result to the plants,
however, from the addition of very low concentrations of
the trace elements boron, manganese, and zinc, and indeed
the addition might be beneficial in certain cases, but trace
elements should then be added in quantities not greater
than approximately one-half those previously specified for
solutions prepared from chemically pure salts. For certain
species, iron must also be added to these solutions as re-
quired by the plants. The solution characterized by formula
III has given excellent results with several species.


FORMULA III. SOLUTION FOR WATER-CULTURE
AND SAND-CULTURE PREPARED FROM
SALTS OF THE GRADE OF COM-
MERCIAL FERTILIZERS














solution (approximate 2 1 2 1
Salts -4 '


Grams per 5 gallons of solu-
tion 5.8 6.4 10.3 3.9
Teaspoons per 5 gallons of
solution (approximate 2 1 21.) 1









GROWING PLANTS BY WATER-CULTURE 39

In the preparation of this solution in five-gallon quan-
tities, the specified amount of each salt is dissolved sep-
arately by shaking in a pint or more of water. Any in-
soluble material, such as is always present in superphos-
phate in particular, is allowed to settle out completely.
The clear supernatant liquid is then decanted, and this
only is used, the sediment being discarded. The four single-
salt solutions are then mixed together and made up to
volume by the addition of water. For certain species of
plants it may be necessary to add iron to this solution as
specified for the solutions prepared according to formulas
I and II.








































































































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