DOCUMENT RESUME SE 016 035 AUTHOR INSTITUTION D.C. …€¦ · DOCUMENT RESUME ED 077 678 SE 016 035 AUTHOR Blankendaal, M.; And Others TITLE Growing Plants Without Soil for Experimental

DOCUMENT RESUME

ED 077 678 SE 016 035

AUTHOR Blankendaal, M.; And OthersTITLE Growing Plants Without Soil for Experimental Use.INSTITUTION Agricultural Research Service (DOA), Washington,

D.C.REPORT NO Misc-Pub-1251PUB DATE Dec 72NOTE 20p.AVAILABLE FROM Superintendent of Documentsi-GWernment Printing-

Office, Washington, D.C. 20402 (Stock No. 0100-02657,$0.30)

EDRS PRICE MF-$0.65 HC-$3.29DESCRIPTORS Biological Sciences; *Controlled Environment;

*Culturing Techniques; Experiments; *Guidelines;Instructional Materials; *Methods; *Plant--Growth;Plant Science

ABSTRACTMuch of the current research in experimental plant

biology requires highly uniform plants. To achieve this, many plantsare grown under conditions in which the environment is carefullymanipulated. This pamphlet has been prepared, therefore, to presentand describe growth procedures which will produce vigorous, healthy,uniform plant material in regulated environments for experimentalpurposes. The publication is intended for those with some knowledgeof plants who want to grow one or-more species for experimentalpurposes, for demonstrations in schools, Cr for science projectswhere limited facilities are available. Topics discussed include: (1)

control of environmentgreenhouses, growth chambers, and seedgerminators, (2) factors for plant growth--light, temperature,relative humidity, growth'media, and nutrition, (3) germination ofseed - -two methods, (4) transplanting, (5) culturetechniquescontainers, aeration, subirrigation, and nutrientsolution, and (6) techniques for specific plants. An index tc morethan 50 plants mentioned in the text is also given. The techniquesand equipment described a:e those used at the Metabolism andRadiation Research Laboratory, Fargo, North Dakota. (BL)

GROWING PLANTS WITHOUT SOILFOR EXPERIMENTAL USE

US OERARTMENT oF HEALTH.EDUCATION & WELFARENATIONAL INSTITUTE OF

EDUCATIONTHIS DOCUMENT HAS SEP* R FPROOUCED EXACTLY AS RECE'RED tROvTHE REASON OR ORGANIZATIVRORIDt%ATH40 IT POINTS Or .*EA, OR OPINIONSSTAYED DO NOT NECESSARILY REPRESENT OFFICIAL RATIONAu INSTITUTE OFroucTatoN POSITION OR POLICY

Miscellaneous Publication No. 1251

Agricultural Research ServiceUNITED STATES DEPARTMENT OF AGRICULTURE

Contents'Page

Control of environment_ 2Greenhouses 2Growth chambers 3Seed germinators 4

Important factors for plant growth 4Light 5Temperature 6Relative humidity 6Grivrth media 6Nutrition__ 6

Germination of seed 8Method 1 8Method 2 8

Transplanting 11Culture techniques 12

Containers 12Aeration 12Subirrigation 13Nutrient solution 13

Techniques for specific plants 14Literature cited 16Index of plants 17 -

Trade names and names of commercial organizations are used in this publication solely forthe purpoie of providing specific information. Mention of a trade name or manufacturer doesnot constitute a guarantee or warranty of the product by the U.S. Department of Agricultureor an endorsement by the Department over other products not mentioned.

WASHINGTON, ISSUED DECEMBER 1972

For sale by the Superintendent of Documents, U.S. Government Printing Office

Washington, D.C. 20402 - Price 30 centsStock number 0100-02667

a

GROWING PLANTS WITHOUT SOIL

FOR EXPERIMENTAL USEBy M. BLANKENDAAL, R. H. HODGSON, D. G. DAVIS, R. A. HOERAUF, and R. H. SHIStABUKURO, Metabolism and RadiationResearch Laborelory, North Central Region, AgriculturalResearch Serrice, United States Department of Agriculture, Fargo, N. Dak.

Crop plants have been grown in soil for cen-turies. With the discovery of the many chemicalsubstances in the soil, methods were developed forgrowing plants _without soil. They were grown insuch media as cracked rock, vermiculite, andcoarse sand-- alt inherently very low in essentialplant nutrients. The nutrients were supplied dis-solved in water. This allowed researchers to regu -.late the kinds and amounts of nutrients availableto the plant. However, because of the adhesivepropetties of the supporting media and becausethey could not always be relied on as purelyinert materials, it was often necessary to usehydroponics or nutrient solution culture.

The original technique of growing plants hydro-ponically (11)' is still widely used (7) and hasproved satisfactory in many instances. Many.plants can be grown from seed to seed withoutever coming in contact with soil. Some of thetechniques used to grow plants without soil aredescribed in detail (5, 7, 8, 9, 12). For a historicalsketch of the development of the water culturemethod, see references 8, 9, and 11.

Plants grown in soilless culture have the advan-tage of a consistent supply of moisture andnutrients, resulting in steady growth (2). How-ever, plants grown in solution culture may requiremore intensive care than those grown in soil toinsure adequate moisture and to prevent develop-ment of nutrient toxicity or deficiency symptoms.

Much of the current research in, experimentalplant biology requires highly uniform plants. Thisquality of plant material is best grown under con-ditions in which the environment is 'carefullymanipulated. Some research groups have centered

1 Italic numbers in parentheses refer to Literature Cited,p. 16.

their efforts on determining the environmentalconditions under which maximum plant growth isachieved, with a view toward understanding thefactors that limit plant growth, determining maxi-mum growth rates, and exploring the potential foreconomical production of plants under controlledconditions_

In contrast, our objective has been to producevigorous, healthy, uniform plant material inregulated environments for experimental purposes.

This publication is intended for those with someknowledge of plants who want to grow one or morespecies for experimental purposes, for ,demonstra-tions in schools, or for science projects wherelimited facilities are available. Techniques andequipment are described that are used at theMetabolism and Radiation Research Laboratory,Fargo, N. Dak., to raise crop and weed species inthe absence of soil for experiments in which pesti-cides and their metabolites are applied to plants orplant parts, often in radioactive form. Some of thetechniques have been adapted specifically for usewith radioactive tracers, where consideration mustbe given to the absorptive properties of thecontainers and -their disposability or ease ofdecontamination.

The growth procedures described here can bemodified considerably to meet the facilities andbudget of others who attempt to use them. Theequipment is described here in some detail, butthis degree of sophistication is not essential forgrowing plants, even for experimental purposes.The ingenious experimenter may have to modifythe described techniques for his particular situa-tion. For example, instead of a growth chamber, aconverted room or part of a laboratory may suffice.We use vermiculite in many instances, but otherinert supports such as "Jiffy Mix" may have to be

1

2 MISCELLANEOUS PUBLICATIONS

used, and commercially available fertilizers mayhave to be substituted for the pure reagents we use.This is entirely dependent on the purpose forwhich the plants are grown.The growth conditions described here for each

species will produce vigoroui plants and can serve

CONTROL OF

Since there are only four frost-free months in ayear at Fargo, facilities to control the environmentire required in order to grow plants throughout theyear. We use greenhouses and controlled environ-ment chambers for this purpose to duplicategrowth conditions at different times.

Greenhouses

Many types of greenhouses are available. Com-mercially they -vary considerably in size, shape,and construction materials (15). The covering maybe glass or translucent plastic. Glass is more trans-parent, but it is susceptible to breakage and in-creases heat retention. Regardless of the type ofgreenhouse available, certain featurEs are neces-sary to insure its usefulness for growing plantsthroughout the year. Provision must be made forwinter heating, and some type of supplementallighting is often needed during the winter. Neces-sary cooling is usually provided in the summer by acombination of some type of shading, cooling, andappropriate ventilation.

Temperature is controlled in the winter bythermostatically actuated steam heat. In mildclimates proportional heat control may be desir-able, but it is not necessary under severe winterconditions where greenhouse heat losses are high.The radiators are located around theTerimeter ofthe greenhouse where they are most effective.

Shading of greenhouses in the summer is essen-tial to prevent excessive heat buildup. It is gen-.erally accomplished either by painting the houseswith 'a lime-linseed oil shading compound or byusing a shade screen. One of the types availablemay be obtained from the Chicopee Manufactur-ing Co., Lumite Division, Cornelia, Ga. Shadescreen can be installed on rollers near the green-house ridge and raised or lowered as needed. Al-though shade screen may be expensive to installinitially, it will last forS to 10 years. In contrast, ashading compound has to be applied each spring

1251, U.S. DEPT. OF AGRICULTURE

as guidelines. Deviations from these conditionscan be used, but one must expect some variationin plant development. Generally this variation willnot be of concern, particularly if the plants are tobe used for demonstration and not for criticalexperiments.

ENVIRONMENT

and removed by scrubbing each fall. These opera-tions require considerable labor if the greenhousearea is extensive. In addition. the shading com-pound will weather during the summer, often pro-viding inadequate shading during the last part ofthe summer, and over the years it will etch thegla.s-s and thus reduce the transparency of thegreenhouse during the winter.

Temperature is further controlled by using ridgeor side vents, which may be hand or electricallyoperated. These vents are often used in conjunc-tion with forced-air evaporative coolers, whichbring air into the greenhouse. A high degree ofsummer temperature control can be achieved ifboth the evaporative coolers and r lotorized ventsare thermostatically activated. The covering ofvent openings with a fine screen such as Nitex 263,available from Smico Sales Co., Minneapolis,Minn., will exclude birds and most insects andthereby reduce plant damage .and the need tofumigate more frequently for insect control.

The temperature in the greenhouse during thesummer fluctuates between 21° and 35° C. Duringthe rest of the year one of the sections of the green-house is kept at approximately 21° and the othersections at 27° during the day. Temperature is de-creased about 6° in all sections at night. Thisprovides a selection of temperature regimes forgrowing different types of plants.

Supplementary light controlled by timeclocks isbest supplied by fluorescent lamps without reflec-tors. These provide minimum shading of theplant benches when the sun is shining and can beleft in place permanently. We commonly use four244-cm. fluorescent lamps (F96T12/CW 1,500ma.) over each 122- by 244-cm. table. They supplyfrom 300 to 600 foot-candles (ft.-c.) of illumina-tion, which controls day length and is sufficient tomaintain many species above the compensationpoint during the winter. These lamps have anaverage life of approximately 7,500 hours andcan be used in the greenhouse for at least two win-

GROWING PLANTS WITHOUT SOIL FOR EXPERIMENTAL USE

ters. Since they primarily supplement natural day-light in the greenhouse, we employ old lamps thathave been used in growth-chamber illumination.

With an overcast sky during the day the naturalillumination in the greenhouse is 900 to 1,100 ft.-c.,and on a bright day it may reach 5,000 to 7,000ft.-c.

The ideal situation is to grow each species ofplant under the specific conditions in which itgrows best. However, each species has require-ments different from the next. Because of limita-tions in cost, space, and time, it is necessary at theFargo laboratory to grow several species in thesame greenhouse section or growth chamber.Therefore compromises have to be worked out. Forexample, peas= and barley may have to be grownnext to each other. Peas grow best with cool temz_peratures and short days, uhereas barley requireshigher teinperatureiand longer days. When thesetwo crops are groWn side by side year around weexpect thatTheither will respond optimally le-acompromise growth condition. The plants lookhealthy under these comproMise conditions eventhough better growth could be obtained. We makeevery attempt to grow plants together that havesimilar-growth requirements. For example, only ifabsolutely necessary do we attempt to grow peasand corn under the same conditions.

Under varying environments the water andnutritional requirements of plants will differ.During the summer it may be necessary to waterthe plants twice daily, whereas once a day maybe satisfactory iithe winter. The same is truewhen nutrient solution is applied two or threetimes a week, alternating with water only. If thegrowth rate of the plants increases, additionalnutrients are necessary. A decreased growth rate isaccompanied by reduced nutrient requirements.As the plants approach maturity, their nutrientrequirements gradually decrease.

For certain species of plants, the floweringstage may be delayed or hastened according tothe photoperiod they receive (4). The growthrates of the .plants discussed here and that arelisted in table 2 were obtained under averageconditions in the greenhouse. The photoperiods,light intensities, temperatures, and humiditieslisted in tables 2 and 3 are those found to besatisfactory in growth chambers or incubators.

For scientific names, see the index.

INN

Growth Chambers

3

Many tyt'es of controlled environment systemsfor raising plants are available commercially andtheir use in research is increasing. The systemsvary considerably in size and capability, rangingfrom simple lighted cabinets to those providingrigorous control of several environmental pa-rameters._ Growth chambers are used primarily(1) to obtain uniform plant material, (2) to permitselection of environmental conditions appropriatefor a given plant species without regard to season,and (3) to permit environmental manipulation asan experimental variable. If more than one typeof growth chamber is available, the selection ofthe most appropriate one will depend on itsintended use.

In general, all growth chambers contain me-chanical, electrical, and perhaps electronic com-ponents and controls, all of which are subject tobreakdown and require maintenance. The moresophisticated chambers generally provide greaterflexibility of operation but often require morefrequent or more complicated maintenance.Usually the simplest chamber that will meet therequired environmental. conditions is the bestand often the least expensive.

Several kinds of growth chambers are used fordifferent types of experiments at the Fargolaboratory. Since all the environmental factorsare 'interrelated in their effect on plant growth(10, 16), none can be considered independentlyof the others. However, satisfactory control of afew major parameters will result in uniform andreproducible plant growth.

Temperature control is usually achieved throughthe combined use of refrigeration and heatingsystems that are thermostatically controlled.It is most useful- to have two thermostats, oneto control day temperature and the other fornight temperature, with a timeclock to switchfrom one to the other. Switching need not coin-cide with the light-dark cycle. Temperaturecontrol of +2.0° C. is adequate for many pur-poses. Continuous temperature programing isprovided in some growth chambers, but it isnot needed for most experimental work. Thedegree of temperature control provided in anordinary laboratory or classroom may be adequatefor many purposes, and the on-off cycling of

7,1". V`i


adequately ventilated banks of lights will providesome day-night temperature differential.

The lighting for growth chambers is commonlyprovided by a combination of fluorescent andincandescenFilltimination, banks of which com-monly occupy the entire ceiling. The quality ofthe light from artificial ramps is not equal tosunlight (14). However, a satisfactory light qualitymay be achieved by using approximately 4 wattsof cool-white fluorescent illumination per wattof incandescent illumination. The incandescentlamps need not be larger than 60 watts, although100-watt lamps are sometimes used.

Control of day length is an essential part ofenvironmental regulation.- Timeclocks that canbe set to turn the lights on or off at any 15-minuteinterval are satisfactory for most purposes. Regu-lation of light intensity is most commonly achievedby a combin'ation of varying the distance betweenthe plant bed and the light bank and by varyingthe number of lamps lighted at any given time.Most growth chambers contain a mechanismfor adjusting the plant- bed height and severaltimeclocks, each controlling a part of the lights.Although illumination as low as 400 ft.-c. maSi bedesirable for some purposes, most plants willgrow- satisfactorily in a white-walled chamberunder a measured illumination of 1,000 to 2,500ft.-c.

Many growth chambers can provide. illumina-tion considerably in excess of 2,500 ft.-c.; how-ever, the literature reveals -that 1,600 -to 2,000ft.c. is usually sufficient for vigorous growth.Achieving maximum -growth rates may requirehigher illumination.

The lamp bank and associated electrical ballastsgenerate a considerable amount of heat and thismust be dissipated if temperature control is tobe achieved. One of the better growth-chamberarrangements has the ballasts in a compartmentinsulated from the plant. growth space and thelamp bank itself isolated from the plant growthspace by a transparent barrier. If open lampbanks are used in a laboratory or classroom,


adequate ventilation must be provided. to pre-vent excessive heat buildup on the plant bedand in the room itself. -

Some degree of humidity control is commonlyprovided many growth chambers. Such cham-bers have a humidity sensing apparatus, whichcontrols the operation of a refrigeration coil totrap unwanted water vapor, Ahd-a-steam_genera-tor, wet pad, or aerosal generator to increase mois-ture in the air. In closed growth chambers withouthumidity control, precautions must be taken toinsure- adequate ventilation and thereby preventthe excessive moisture -buildup that results fromtranspirational water logs from plants held inan enclosed space. Increased humidity maypromote mildew development. If plants aregrown under a light bank in a laboratory, orclassroom, humidity control is not practicaland normal watering of the plants should besufficient. A fresh-air change every 2 hours inthe chamber is desirable to prevent excessivecarbon dioxide buildup at night and a depletionduring the day.

Since there is so-much variety in growth cham-bers depending on the manufacturrer and on thepurpose of the chamber, the reader is referred tomanuals and specifications of the manufacturers'.Anyone planning to purchase new chambersshould consult with those who have had practicalexperience with several types.

Seed Germinators

At the Fargo laboratory a temperature-con -trolled incubator is used for seed germination.Most seeds are germinated in the dark, although-sonie require light. If a dark incubator is notavailable, any dark cabinet in which the temper-ature remains fairly constant between 21° and27° C. can be used, and reasonably uniform andreproducible seed germination of the specieslisted here (p. 17) will , occur. Other specieshaving special germination requirements oc-casionally may be encountered.

IMPORTANT FACTORS FOR PLANT GROWTH

Illumination and quality of light, photoperiod,temperature, relative humidity, and nutritionall interact to affect plant growth. If any one

of these factors is less than optimum, poor plantgrowth can result (4, 5, 14)-

Good plant growth usually can be obtained

,- ." 0"7


by selecting environmental conditions approxi-mating those under which the plant flourishes innature. Once established, species from arid regionsoften grow well under dry conditions and thosefrom nonacid regions often grow well underhumid anditions. When the environment canbe controlled at least partially, these conditionscan often be met and the results are usuallygratifying.

Because there are so many different speciesand varieties of plants with differing needs foroptimum growth; the grower should ,experimentto find the optimum conditiOns for eatli speciesor variety.

Light

Light is required for plant growth. The illumi-nation, light quality, and photoperiod require-ments vary among species (14). A number ofdifferent instruments may be used to measureillumination. In biological research a foot-candlemeter is often used to measure illumination.The illumination on a surface that is everywhere1 foot from a uniform point source of light of onecandle intensity is equal to 1 lumen per squarefoot or 1 ft.-c. Although inexpensive foot-candlemeters can"-be obtained, photographic lightmeters are more generally available and arepractical for light measurement. Photographiclight-meter readings can be converted to foot-candles by the following formula:3

B =20(f )2TS

Where

B = illumination in foot-candlesf =aperture in f stopT =shutter speed in secondsS = film speed in ASA units

To measure illumination with a photographiclight meter, reflected rather than incident lightmust be measured. To do this, place a large sheetof white paper on the surface to be measured, setan appropriate ASA film speed on the meter, and

* We are indebted to John A. Witz, Department of Elec-trical Engineering, Oklahoma State University, Stillwater,for supplying this formula.

5

read the shutter speed required for proper exposureat a given f stop. Values for ASA speeds of 64 to100 at various f stops and shutter speeds are givenin table 1. Values for-other meter settings may beobtained by solving the equation. The results willbe approximate depending on the accuracy of themeter and the cone of light it accepts. For example,false low readings may result if the meter acceptslight from an area greater than that of the whitepaper at which it is directed. Nevertheless the.readings can suffice to determine whether illumina-tion is adequate for good plant growth. About1,200 ft.-c. of light in a growth chamber is satis,factory for many plants such as cabbage,, carrots,peas, and tobacco, whereas other plants such ascorn, cotton, rice, and sorghum grow better whensupplied with 1,600 to 1;800 ft.-c.

TABLE 1.Relationship between photographic lightmeter readings and foot-candles

Film speed(ASA)

Aperture Shutterspeed

Illumination

F stop Seconds Fl. c.

100 16 1/2 10264 16 1/2 160100 16 1/5 256100 11 1/15 36364 16 1/5 400100 16 1/10 512100___- 11 1/25 605100 16' 1/15 76864 16 1/10 800100_ 16 1/2.0 1,02464 16 1/15 1,200100 16 1/25 1,280100 11 1/60 1,45264 16 1/20 1,60064 16 1/25 2,000100 16 1/50 2,560100 16 1/60 3,072100 11 1/150 3,63064 16 1/50 4,00064 16 1/60 4,800100 16 1 /100 5,120100 16 1/125 6,40064 16 1/100 8,00064 16 1/125 10,000100' 16 1/200 10,240

3 Measure light reflected from a white paper or othershnilarly textured surface.

1

6 MISCELLANEOUS PUBLICATIONS 1251, U.S. DEPT. OF AGRICULTURE

The quality or spectral composition of lightaffects the growth and development of plants (4).An improper balance of lightquality can result inabnormal growth. r

Different plant species vary in their photoperiodrequirements for best growth. For example, barleyrequires a photoperiod greater than 12 hours forgood flowering, whereas soybeans can matureunder a 12-hour day. The photoperiod can beregulated to hasten or delay flowering (4). In thegrowth chambers the plants can be given what-ever photoperiod is required for optimum plantgrowth. Some suggested photoperiods are given intable 2.

In the greenhouse many different species ofplants are grown. Some of these may require longdays for flowering and others short days. It isimpossible to provide the optimum light require-ments for each species, but many plants can begrown satisfaCtorily. During the winter a 12-hourphotoperiod is generally used as a compromise daylength under which reasonable vegetative growthcan be maintained. The short natural photoperiodin the winter is supplemented with fluorescentlight.

Temperature

During the summer it is often difficult to main-thin cool enough temperatures in the greenh'usesfor certain species of plants. For example, ueadlettuce and peas will often grow poorly in mid-summer. It is not recommended to grew thesespecies until conditions are more favorable.

Relative Humidity

When moisture supply to the roots is adequate,the degree of water vapor saturation in the airexerts a major effect on the rate of transpiration ofmany plants. An average of 50-percent relativehumidity is satisfactory for many species.

A relative humidity of 100 percent is oftenneeded to germinate very small seeds such as thogeof tobacco or bluegrass or to root sugarcane stemsections. The required humidity can be obtainedby covering the plant containers with plastic bags.If mildew infection is a problem under highhumidity, a light dusting with, sulfur may besufficient to control it.

Growth Media

At the Fargo laboratory the plantsare notgrown in soil but in either vermiculite or deionizedwater. Vermiculite of a medium fine texture. some-times called-horticultural grade, is readily obtainedfrom local dealers. Local tapwater may be toosaline or alkaline for use in nutrient culture. It isusually deionized by passage through a commercialmixed -bed deionizer. The resins remove. cationsand anions such as potassium and chloride ionsfrom the tapwater.

Nutrition

Environmental conditions affect the amount andrate of nutrient uptake by individual plants. Ifmany different kinds of plants are to be grown,considerable variation in nutrient requirementscan be expected. By careful observation, earlydeficiency or toxicity symptoms can be diagnosedand readily cured (2, 13). If fairly exact nutrientrequirements are not known for a given species.is best to use a standard solution, such as th,given on pages 13 and 14, taking care not to ove.fertilize, for it is easier to correct a nutrient defi-ciency than a toxicity. Many plants seem totolerate wide variations in nutrient supply. It isnaturally desirable to supply nutrients at theoptimum level.

Nutritional guidelines for several species arelisted in table 3. These have proved very satis-factory at the Fargo laboratory. One should notexpect that these methods are optimum for othergrowth conditions, and some alterations may be re-quired. In this respect nothing replaces commonsense, careful observation, and a little "tender,loving care."

In the Fargo laboratory we use a modificationof one basic nutrient solution (9), in which achelated form of iron is substituted for the ironsalt originally reported. This is satisfactory formost of the plants. The full-strength solutionis made up and the concentration varied simplyby- diluting to three-fourths, one-half, or one-third strength with deionized water. Tapwatermay be substituted for deionized water in somelocalities. We find that generally the full-strengthsolution, is too ,concentrated for many species,partiellarly in early stages of growth.


TABLE 2.-Light, temperature, and humidity requirements and derelopment of selected planis

Species 2

Conditions used in growth chambers Plant development under averagegreenhouse conditions

IlluminationTemperature

Photoperiod (day-night) HumidityHeight in-

Bloom Maturity4 weeks 8 weeks

Alfalfa -BarleyBarnyardgrams... _____Bean 'Black Valentine'BeetBermudagrassBluegrass ....... ...BroadbeanBroccoliBuckwheatCabbageCarrotCornCotton

CucumberDillEndiveFall panicumFlaxHad lettuceJohnsongrassLeaf lettuceLimabeanMelon --- . - - - - ...Millet

OatOkraParsnipPeiPeanutPepperPigeongrassPintobeanPlantainPotatoRed clover_RiceSorghumSoybeanSpinachSquashSudangrassSugarbeetSugarcaneSunflowerSweetpotatoSwiss chard

11.-c.

1,5001,6002,2001.500

T,12001.2001,2001,2001,4001,4001,4001,2001,6001,8001.4001.2001,2001,2001,4001,6001,6001.6001,5001,4001.8001,4001,6001,5001,2001,2001,6001,4002,2001,5001,2001,4001,2001,6001,8001,6001,4001,4001,8001,2001.8001,6001,4001,400

Hours

1416141212121214121212121414141212121214141412141412161412121414141212121214

.14121214'141214141212

° C. 3

26-2030-2030-2520-1525-2026-2026-2020-1023-1826-2023-1823-1530-2530-2530-2330-2323-1623-1630-2023-1630-2325-1820 -15.

30-2330-2323-1830-2030-2023-1520-15'30-2530-2030-2520-1525-2021-1621-1630-2530-2330-2025-2030-2330-2325-2030-25

30-25-2025-20

Percent

4040506050504050555055507040505560

40506060

604050405540505050405050604040507040405540405050305060

Cm.

20253036..88

30201515107620..1510152012

122

.30

20152530363615..2536-.15

302036__

..20108

7615

-10

Cm.

366155._3015207036553630

18351..81._

61

--86507061.. ._ .

3630

--15612076865625

ii

3638

178

ii

Days

76605030

757545__35__

ii503560.. -4045-40__

40356060705030304260

-4030

705080756035503560

Days

1009070

365120909085

412070

412085

1059060

100470

708570

ii

7560

100

10-- 0

806060

1008565659075

11010510980

60-

10012014010085

See footnotes at end of table.


TABLE 2.Light, temperature, and humidity requirements and derelopment of selected slants' --- Continued

Species

Conditions used in growth chambers

TemperatureIllumination Photoperiod (day - nights Humidity

4 weeks 8 weeks

Plant development under averagegreenhouse conditions

Height inBloom Maturity

Ft.-c. Floras * C. I'crcott Cm. Cm. Days Pays

Tobacco 1,200 14 30-25 60 1 10 120_ .

140Tomato 1,400 14 25-25 50 20 61 50 100

Turnip 1,200 12 25-20 60 10 35 65Wheat 1,600 16 30-20 40 .,-5 61 70 100Wild buckwheat 1,200 12 25-20 50 30 50 65Wild mustard 1.400 12 23-18 55 30 28 60Wild at 1,600 16 3C-20 40 25 70 60 90

Plant development is similar for a given species whether raised under growth-chamber conditions listed or average green-house conditions.

*See index for scientific names.s Edible pods in 45 days.

Harvested heads.

GERMINATION OF SEED

The plants described here are primarily cropspecies and their seeds are easy to germinate.However, problems do exist with seed germinationof certain plant species. An extensive text onplant propagation (6) has been published andshould be very useful if problems are encountered.The germination methods used in the Fargolaboratory will be discussed here. Additionalcomprehensive information on seed germinationhas been published by Andersen (1) and Barton(3)

Method IA small flat, 30-by 20 by 10 cm., is filled with

5 cm. of vermiculite. The seed is placed on topof the vermiculite and covered with 1.3 cm. ofvermiculite for such seeds as alfalfa and 2.5 cm.for pea seeds. Very small seeds such as those oftobacco are mixed with sand to increase the volumefor better distrib it ion. Theite seeds are not coveredafter seeding. The-vermiculite is wetted from thebottom. An enamel tray is placed under the flatto maintain the moisture level. The flat withtray is 'placed in an incubator at the desiredtemperature for the required length of time.If the seedlings are kept in the flat foi an ex-

tended period of time, a dilute nutrient solutioncan be used in place of water. Metal slats shouldbe of stainless steel, or if galvanfiled they shot'-Idbe coated with an asphaltic material to preventtoxic levels of zinc from leaching into the germi-nating medium.

This method is generally the easiest and moatsuccessful for many types of seeds. The advantagesof using vermiculite for germinating seed are asfollows: (1) It has adequate moisture-holdingcapacity and aeration. (2) It contains virtuallyno nutrients or toxic materials. (3) Roots developwell in it. (4) It is light weight and easy to handle.Although peat may be nixed with verimiculitefor some purposes,ts high absorptivity may in-terfere with subsequent chemical treatmentsapplied to the roots.

Method 2

Two pieces of absorbent paper toweling ap-proximately 20 by 30'cm. are wetted thoroughlyand laid on a sheet of waxed paper of the samesize. The upper paper is folded back 5 cm., seedis placed on the second paw along the fold,and the upper paper is folded back over the seedsagain. The absorbent papers are rolled loosely


TAME 3.--- Germination, transplanting. and nutrient requirements for selected Plants

Germination Period between seeding invermiculite and-

Species Transplant- Applying nutrienting in st.lution at- -

Method 3 depth Temperature Time nutrientsolution One-third One-half

strength strength

Seeding

Cm. Days Days Days Days

Alfalfa...... ......... .. 1 1.3 6 6 61, 2 2.5 30 6 6 21

Barnyardgrass..._.. _ . - 1 1.3 30 6 14 6Bean 'Black Valentine'. -. 1, 2.5 27 6 . ... 6

1 2.5 25 7 21 7Ittrinudagrass 1 0 26 7 21 7Blueoass 1 0 26 7 21 7Broadbean ...... ... 1,2 3.8 24 10 10Broccoli... -. __ . 1 1.3 23 6 21 6 21Buckwheat, _ 1,2 2.5 30 5 5Cabbage_ .. _ - 1 1.3 23 6 21 6 15Carrot._ 1 1.3 23 7 28 7 ...Corn.. , _ 42 2.5 30 5 s 21Cotton 1,`2 2.5 30 5 0 21Cucumber-- . - . .... 1,2 2.5 30 5 ... 5 21Din_ ____ ... 1 1.3 30 7 28 7 28Endive... __ . _ 1 1.3 23 5 28 5Fall panicum... 1 2.5 3 8 21 sFlax- _ .. ...... . _ . 1 1.3 30 4 21 4Head lettuce 1 1.3 23 0 14 5Johnsongrams... _ -__ 1 35.0 30 7 .. -Leif lettuce.. _ _ - 1 1.3 5 5 14 5 ..Limabean _ . _ _ . 1,2 2.5 21 6 .. 6Melon 1, .5 30 5 5 21Millet. - . - - - I, 2 1.3 30 5 14 5 14Mustard 1 1.3 23 6 21 6 21Oat -1, 2 2.3 30 6 s 21Okra ...... _ ... _ .. - _ 1,2 .5 30 s sParsnip 1 1.3 23 10 iii 10Pea 1,2 2.5 24 5 ... 5Peanut 1,2 3.8 30 7 -_ 7 42Pepper 1 1.3 30 10 28 10Pigeongrass 1 1,3 30 6 14 6

_Pintobean - 1, 2 2.5 2 7 6 __ - 15

Plantain 1 0 25 7 49 7Potato....... -. - - - 1 35.0 21 310 10Red clover, I 1.3 21 6 28 6Rice. 1,2 2.5 30 7 ... 7Sorghum_ ..... _ . _- 1, 2 1.3 30 5 14 5 14Soyboln 1, 2 2.5 30 5 . _ 5Spinach. 1 1.3 25 5 28 5 -_Squash 1, 2 2.5 30 5' .. 5 21Sudangrass. __.=, 1,2 1.3 39 5 14 5 14Sugarbeet 1 2.5 25 7 21 7 21Sugarcane 1 1.9 30 7 35 7 35Sunflower, 1, 2 2.5 30 4 _ 4 28

See footnotes at end of table.

1.10 MISCELLANEOUS PUBLICATIONS 1251, U.S. DEPT. OF AGRICULTURE

TABLE 3.Germination, transplanting, and nutrient requirements for st lected plantsContinued

Species 1

Germination

SeedingMethod 2 depth Temperature Time

Period between seeding invermiculite and

Transplant- Applying nutrienting in solution at

nutrientsolution One-third One -halt

strength strength

Cm. C. Days_ Days Days DaysSweetpotato 1 42.5 25 5 14 14Swiss chard 1 2.5 25 6 ... 6Tobacco 1 0 30 7 40 7 60Tomato 1 1.3 25 7 21 7 21Turnip 1 2.5 25 4 . 21 4Wheat 1,2 2.5 30 6 ... 6 21Wild buckwheat 1 2.5 25 10 10 _ _Wild mustard 1 1.3 23 6 21 6 21Wild oat 1,2 2.5 30 6 6 21

See index for scientific names.2 Method 1 = vermiculite; method 2 = paper roll (see pp. 8-11).'Rhizome sections.Tuber or fleshy root.

5 Shoot emergence from tuber or fleshy root.

-- inside the waxed paper, _placed in a beaker orjar with 5 cm. of water, and incubated at thedesired temperature, usually in the dark (fig. 1).The absorbent paper keeps the seeds moistand the waxed paper prevents the toweling fromdrying out. Generally 4 to 5 days' incubation isrequired.

When the seedlings are removed from a darkincubator, they are colorless or etiolated andcannot be exposed to bright illumination withoutfirst hardening them for a day in room light (100-200 ft.-c.). If the seedlings are directly exposedto sunlight or bright illumination in a growthchamber, the hypocotyl or cotyledons may bedamaged and the seedlings may die. For example,it has been our experience that unhardenedsoybean seedlings become scalded if transferreddirectly from a dark incubator into a growthchamber with an illumination of 1,600_ ft.-c.In contrast, hardened seedlings can be trans-planted and placed in an environment with anyrequired illumination.

Seed germination by the "pane' roll" methodmay require more time and care than directseeding in flats. However, distinct advantages

make the method worthwhile. Seedlings germi-nated by the paper roll method may be selectedfor uniformity of root and shoot developmentand may be transferred to nutrient or othersolutions with minimum root damage and withoutparticulate matter adhering to them.

FIGURE 1.Germination of cucumber seed on moist papertoweling.

GROWING PLANTS WITHOUT SOIL FOR EXPERIMENTAL-USE

Some precautions to be taken when using paperrolls are as follows: (1) If the seed is too small.the wet paper toweling will seal off the oxygensupply and cause poor germination. (2) Seedmay mold if spores are present unless treated with

11

a mild fungicide, or the rolls can be checkedafter 48 hours and the 'bad seeds removed. (3)Chemicals toxic to certain seeds might be presentin the paper and inhibit grthvth.

TRANSPLANTINGWhen seedlings have been germinated in a paper

roll, they can be transplanted easily into nutrienttroughs (fig. 2) or individual solution containers(fig. 3).When plants are uprooted from vermiculite or

soil, some root damage may occur. The plant willcontinue to transpire and may wilt if little mois-ture can be absorbed by the damaged roots. Wilt-ing can be minimized by reducing transpiration.This can be accomplished by keeping the plantmoist, lowering the temperature, and diminishingthe airflow around the plants. When uprootedplants are handled in this manner, they can bekept without harm for 12 to 24 hours until trans-planted. Exposing plants -to direct sunlight andhigh temperature immediately after transplantingcauses an enormous stress oti them. They shouldbe kept at 15° to 21° C. for 48 hours to slow thetranspiration rate and to prevent wilting.

The size, age, and type of plant being trans-planted often determine success or failure. In gen-eral, younger plants are more successfully trans-planted. Selection of uniform seedlings is essentialto obtain uniform subsequent growth. The rootsshould be inserted vertically into the solution or

:11111111womr:si--

mq.2924FIGURE 2.Nutrient culture trough: Plastic frame insert

with nylon screen bottom, metal cover, and stainless-steeltrough with drain (top to bottom).

rs-2925FIGURE 3.Corn and pea seedlings growing in aerated

nutrient solution, with capillary tubing 9.25 mm.) in-serted into air line for each culture jar.

vermiculite without bending or leaving them ex-posed. A little extra care at the time of transplant-ing will give improved results throughout thegrowing season. The transplanting medium suchas soil or vermiculite should be saturated withwater or dilute nutrient solution to restore themoisture that the plant may have lost. Care mustbe taken not to have the nutrient solution too con-centrated when transplanting directly into it. orsalt- injury and desiccation may occur. It is advis-able to increase the concentration of the nutrientsolution gradually as the plant grows. If seedlingsare transplanted to container§ of vermiculite 30cm. or more in diameter, some of the nutrient saltsare adsorbed on the vermiculite and are-not avail-able to the plant. This can be avoided by using aslightly stronger nutrient concentration.

If transplanting into specialized containers is notrequired, seed may be planted directly into potswith vermiculite and grown in that manner.


Containers

CULTURE TECHNIQUES

When plants are grown in jars. the jar lids,tinfoil, waxed cork. Masonite, or other materialscan be used for plant support. However, we havefound paper cups most satisfactory for support.They can be used in different ways dependingon the species of plant to be grown. For example.when pea plants are grown-, two cups are glued-together on the bottom (fig. 4). The lower cupslips over the outside of the jar; the upper cup isused for plant support. One small hole is punchedthrough the bottom of each cup for the seedlingand another small hole through the lower cupfor the aeration tube.

Reasons for using this technique are as follows:(1) The cups are chemically unreactive. (2) Theyare cheap enough to be discarded after a singleuse. (3) Sharp cutting edges are eliminated thatmay injure the hypocotyl, stem, or roots. (4)Girdling can be prevented by gradually enlargingthe hole as the plant stem increases in diameter.(5) Cups can be easily lifted so that nutrientsolution can be added. (6) Plants can be easily,transferred to other jars. (7) There is more'stem support for certain plants than with manyother types of lids.

The plant container must be of sufficient size topermit adequate root grotith; otherwise the de-velopment of the plant may be restricted. Forexample, a pea plant can be grown to maturity ina 10-cm. plastic pot filled with vermiculite or in a500-m1. jar filled with nutrient solution. A cornplant grown in a 10-cm. pot or 500-ml. jar becomesrootbound after 5 to 6 weeks of growth and ab-normalities will occur. Corn plants require an18-cm. pot or 2-liter jar to grow to maturity. Forthis reason various types and sizes of containersare used, such as jars, stainless-steel troughs withlids, and plastic pots with saucers. Milk cartonscan also be used as dispilsable containers. Theywill often last for 6 to 8 weeks. Glass jars arecovered with a coat of black paint followed by acoat of aluminum paint. The black paint excludeslight, inhibits growth of algae in the nutrient solu-tion, and prevents abnormal root pigmentation.Since the aluminum paint reflects sunlight, thejars remain cool.

When many plants are to be grown together inthe same container in nutrient solution for experi-mental purposes, we use a stainless-steel trough,66 by 15 by 10 cm., with a stainless-steel lid (fig. 2).The plants are placed in holes in the lid, whichserves as a support and-keeps out the light. Softplastic collars may be used for additional stemsupport. The size of the holes should be adequateto prevent stem girdling. Alternatively the flatsteel trough lids may be replaced by wood or plas-tic frames with nylon screen bottoms. Theseframes are supported within the troughs, 3.8 cm.above the bottom (fig. 2). The screen is filled withvermiculite. The plants can be grown directly fromseed-or transplanted. Nutrient solution is added towet the vermiculite. The plant roots grow throughthe screen and into the nutrient solution. Manyplants grow well in this manner. The screen givesgood root support, and most of the roots can beharvested.

Plexiglas framing is preferred to wood to avoidleaching of chemicals from the frame. If in an ex-periment it is necessary to treat the roots by add-ing a chemical to the nutrient solution, a woodenframe might become contaminated and should bediscarded.

Aeration

When plants are grown directly in liquid cul-ture, air usually must be supplied to the nutrientsolution. A small electric pump such as a fishtank aerator can force air through rubber or-plastic tubing to the jar or troughs. Glass capillarytubing is inserted in the solution. A well-regulateduniform flow rate can be obtained for severalaerators on the same line by inserting a 2.5-cm.

1%-2926

FIGUREt 4.Paper cups and Iid supports for plants grownin culture jars.


length of 0.25-mm. bore capillary tubing intothe air line for each aerator tube (fig. 3). Aeratingcan be done continuously or at regular intervals.such as 2 hours on, 2 hours off, by using a time:clock.

If compressed air is available, this may bemore economical than using many small pumps,which require frequent maintenance. Oil vaporsfrom a rotary-type compressor must be trappedout with a charcoal filter before the air reachesthe plants.

SubirrigationAt the Fargo laboratory the plants grown in

,vermiculite-filled pots or flats generally receivewater and nutrient solution by subirrigation.Saucers or shallow pans are used under the potsand enamel trays under, the flats. The amount ofwater or nutrient solution added is dependenton the plant and growing conditions. Commonsense and experience are often required to de-termine how often and how much to water. Itis not so easy to overwater plants grown invermiculite as it is in soil. However, plants thatrequire well-aerated media can become water-logged if the vermiculite is watered excessively.Care must be taken to avoid this. Waterloggedplants will often wilt, although for differentreasons than when they are desiccated. When indoubt, consult those who have previously grownthese plants, or refer to literature on the specificplant (2).

Some salt accumulation may occur on the sur-face of the vermiculite after a period of time,and this should be leached out once a month.This is done by applying excess water at thetop and letting it drain through the container.Then subirrigation can be resumed on the usualschedule. Salts are leached away very rapidlyfrom vermiculite by this method (2). The potsand flats are watered from the top only at seedingtime. When very small seed is placed in flatsand left uncovered, subirrigation is used. If theyare watered from the top, a fine spray must beused to prevent the seed from being carried toodeep into the vermiculite to emerge.

The following methods can be used to applynutrients to plants: (1) Mix the nutrients directlyinto the watering system. (2) Add nutrient solutiontwo or three times per week and water at other

13

times. (3) Supply a nutrient solution every daywithout mixing it in the, watering-system; theconcentration can then be *varied as needed.When using method 2, tapwater can often besubstituted for distilled or deionized water ifthe plants are not going to be used for a criticalexperiment in which nutrition should be carefullycontrolled. The use of tapwater several times perweek has the advantage of reducing the volumeof deionized water required. However, it mustbe employed with caution, since some domesticwater suppliFs are apt to contain levels of saltsthat will damage plants. -Soft water is not neces-sarily low in salt content since the softeningprocess usually only exchanges highly solublesalts for less soluble ones.

The acidity or alkalinity of the water used ma,-also affect plant growth adversely. Some of theadverse pH effects probably result from changesin the availability of nutrient salts. For example,excessive watering of corn with alkaline (pH 9)tapwater can cause the leaf margins to becomechloroth and torn. These _symptoms are remi-niscent of certain nutrient deficiencies! Theaddition of dilute acids, bases, or buffering saltsto the tapwater or nutrient solution can helpovercome these difficulties. Care must be taken,however, to insure that neither the 'nutrientsolution nor the tapwater used between additionscontains too much salt.

We emphasize again that it is necessary toexperiment in order- to determine the optimumamounts of nutrient for individual species.

Nutrient Solution-

The formula of Hoagland and Anion (9) is usedwith a slight modification; Preparation is asfollows:

Preparation of Stock Solutions

Major Elements. Individual 1 M stock solu-tions of each major element are made with de-ionized water.

Chemical

Potassium dihydrogenphate

Potassium nitrateCalcium nitrateMagnesium sulfate

Ph9s-

Formula

ICH:PO41002Ca(14103)14H10Mg804.71110

Gramsper liter

131.1101.1236.2246.6


Iron Solution.Chelates of iron in ethylenedia-mine tetraacetic acid are commercially available,often as Vetsene or Sequestrene. Dilute thecommercial product to obtitin a ,5-percent wjvsolution. Dissolve 200 ml. of this solution indistilled water and make to 1 liter. This stocksolution contains 10,000 p.p.m. of iron. One ml.of stock solution will give an iron concentrationof 10 p.p.m. when diluted to 1 liter.

Micromitrients.The microelements or traceelements are dissolved together- in 1 liter ofdeionized water to make a stock solution. Themicroelements should be added to the waterthe order listed and each dissolved before thenext is. added. This prevents precipitates fromforming.

ChemicalGrams

Formula per liter


Preparation of Nutrient Solution Front StockSolutions

The following volumes of the six stock solutionsare then individually added to about 500 ml. ofdeionized water with stirring. After all stocksolutions have been added, the nutrient solutionis made to 1 litmwith deionized water to obtaina full-strength solution. This solution is usuallydiluted to one-third. one-half, or three-fourthsstrength.

Boric acid 1131303 2.50Zinc chloride ZnCI: .50Cuprous chloride CuC12-11:0 .05Molybdenum oxide Mo03 .05Manganese chloride MnC12.411:0 .50

TECHNIQUES FOR

Tables 2 and 3 summarize the methods usedfor growing several plant species. In table 2 arelisted the light, temperature, and humidity re-gimes used for these species when raised in growthchambers and also some growth characteristicsobtained under average greenhouse conditions.These characteristics also closely approximatethose obtained in growth chambers as listedfor each species. In table 3 the germinationmethod, germination period, and nutrient re-quirements are listed.

For many of the species-additional precautionsand comments are to be noted if good plantgrowth is to be insured. These species are listedalphabetically by common name. Some plantsare grouped together since their specific growthrequirements are nearly identical. For plantsnot in alphabetical order, see the index.

Alfalfa.This species may be propagatedvegetatively as well as from seed. Five-cm. stemsections, each bearing one or two trifoliate leavesnear the apical end of the cutting, are removedfrom well-established plants and rooted in moistvermiculite or aerated water for 3 weeks. During

Chemical Formula Milliliters

Potassium dihydrogen phosphate__Potassium nitrate....___ ______ KNOX 5

Calcium nitrate_ Ca(NO3). 5Magnesium sulfate. MgSO4 2Iron 1

Micronutrients 1

SPECIFIC PLANTS

this period a 12-hour photoperiod with an illumi-nation of 1,000 ft.-c., day-night temperaturesof 21° and 16° C., and a relative humidity of75 percent can be used. Flowering can b' inducedby interrupting the dark cycle for 1 hour nearthe middle of the night or by increasing theillumination to about 2,200 ft.-c. 1 or 2 weeksafter transplanting.

-Barley, Oat, Wheat, and W ild Oal. The barleyvariety larker' is susceptible to mildew. Thisdisease may be controlled by lightly dustingthe plants with sulfur. It may be desirable toadd potassium bicarbonate at a final concentrationof 2 X 10-3M to the nutrient solution to preventleaf tipburn of `Larker' barley. Other barleyvarieties may notrequire this treatment. Tohasten maturity of barley, oat, wheat, and wildoat grown under Ahort-day conditions, it is neces-sary to interrupt the dark period with light for1 hour near midnight.

Barnyardgrass, Pigeongrass, and Rice.Whenthese species are grown in liquid culture, noaeration is required. These grasses may be trans-planted directly into one-third strength solution


supplied continuously, or they may be directlyseeded into vermiculite-filled screen frames (fig. 2)and moistened with one-third strength solutionto obtain a dense stand.

Bean 'Black Valentine,' Broadbean, Limabean,and Pintobean.These species have a widenutritional toleraree. The first symptom ofdeficiency is a reduction in leaf area of newlyexpanding leaves that may be readily correctedbefore any leaf injury becomes apparent Pollina-tion of broadbean flowers_ is best done by handor by using an oscillating fan near the plants for afew hours each day. The relative humidity shouldbe kept low for maturing limabeans to preventseed from sprouting while still in the pod.

Beet and Sugarbeet.If these species are to beraised in vermiculite without transplanting, theymay be supplied with one-half strength solutionat time of seeding.

Bermudagrass and Bluegrass. Vegetative prop-agules of bermudagrass may be obtained fromsections of runners. Freshly harvested bluegrassseeds are often dormant. Good germination of2- to 4-year-old seed can be obtained by moisten-ing with nutrient solution under high humidity.Once germinated, the seedlings should be grownunder low humidity to prevent mildew infection.Bluegrass may be vegetatively propagated bysubdividing the crowns.

Buckwheat.This species requires hand orinsect pollination to insure seed set.

Cabbage, Mustard, and Wild Mustard.Somestem injury to cabbage may occur if youngplants are not well supported in liquid culturesor if nutrient salts' are allowed to accumulateon stems. Mustard grows better in vermiculitethan in liquid culture. Wild mustard has lownutrient requirements and leaf burn may occurif solutions more concentrated than one-thirdstrength are used. Mature plants are large enoughto tip solution culture jars if they are not wellsupported.

Carrot.Roots of this species are abnormallybranched and short when grown in solutionculture.

Corn. - -This species is sensitive to nutritionalchanges during the first 4 to 6 weeks and requires

..a plentiful iron supply at all .times. If grown insolution culture, best results are obtained whenthe solution pH is maintained near 7. Plants willbe severely stunted if grown in 500-m1. containers.

15

Two-liter solution containers or 18-cm. pots arerecommended if corn is to be grown to maturity.

Cotton.Seed should be moistened with one-half strength solution if started in vermiculite orwith one-third strength solution or 1 x 10-4 Mcalcium chloride if started in a paper roll for bestseedling root development. Leaves may becomemottled if plants are grown under high humidity.

Cucumber, Melon, and Squash.Vines of theseplants will occupy a great deal of space unlessstaked up, and pruning is recommended to preventexcessive branching. When foliage is removed bypruning, the nutrient requirements are correspond-ingly reduced. When these plants are grown in-,doors, hand pollinating is required to obtaingood fruit set, and thinning to control fruit sizemay be required. The squash variety 'GoldenNugget' is determinate and suitable for growingin a restricted space. It remains bushy with thefruits at the base of the plant. These species areall susceptible to mildew if grown under highhumidity.

Endive.This species develops a very extensiveroot system as compared with other species whengrown hydroponically.

Flax and Red Clover.Stem cuttings rooted inaerated water may also be used to propagatethese species. After rooting, the cuttings aresupplied with one-third strength solution. Whengrown in vermiculite, flax should be given smallamounts of nutrient solution at any given time.Excess moisture will cause yellowing of lower-leaves and nutrient stress will cause yellowing ofupper leaves. Red clover can be grown well inscreened frames (fig, 2) when one-fourth strengthsolution is used continuously.

Johnsongrass.This species is easily grownfrom rhizome sections. Plant development isnormal in vermiculite, but poor rhizome develop-ment is obtained when grown in liquid culture.

Millet, Sorghum, and Sudangrass.Rust-coloredblotches will occur on leaves of these speciesunder high humidity.

Okra.--This species has low nutritional re-quirements, and older leaves will become senescentif the nutrient solution is allowed to become tooconcentrated.

Peanut.This species grows well to maturity invermiculite. Large containers should be used topermit normal fruit development. Young plants--


should be watered sparingly to prevent rootrot: Seed viability is much reduced after 1 year.

Plantain and Sunflower.These species havevery low nutritional 'requirements and are sus-ceptible to mildew when grown under highhumidity.

Potato.When greenhouse-grown tubers arereplanted in the greenhouse, the resulting vinesmay be spindly and tuber production poor.

Soybean.When illumination is insufficient,internodes become greatly elongated, leaves be-come enlarged and. the plants will fall over. At ahigh nutrient concentration the young leavesbecome cupped.

Sugarcane.Solution culture of seedlings introughs for more than 30 days is difficult becausetrough covers (fig. 2) will interfere with stemthickening. If seedlings are grown in fertile soil,little nutrient addition may be required in thefirst 4 weeks. Then, one-half strength solution canbe supplied three times per week for the next 4weeks, followed by a full-strength solution onthe same schedule for the remainder of the growthperiod. In vermiculite use one-half strengthsolution three times per week. For further propa-gation, 10-cm. stem sections of mature plants,each bearing a node, may be layered in, moistvermiculite, covered, and incubated for 5 to 7

days at 32° C. The sprouted sections will growrapidly when transplanted to vermiculite andsupplied with one-half strength solution. Sugar-cane forms more tillers in vermiculite than insolution culture.

Sweetpotato.This species is easily propagatedby layering a vine and transplanting the vinesections that sprout at each internode. Newsprouts 15 to 20 cm. long also may be removedfrom the root and planted. When sweetpotato isgrown in liquid culture, the fleshy roots do notdevelop well.

Tobacco.Reduce moisture stress for 48 hoursafter transplanting by lowering the temperatureto about 18° C. and increasing the humidity.

Tomato.Uneven watering of plants in ver-miculite will result in ovary rot of developingfruit. Pollination can be promoted by tappingthe plants or by using a fan. A determinatevariety such as 'Sheyenne' is especially suitablewhere compact plants are desired.

Turnip.This species has lOw nutritional re-quirements. Roots enlarge rapidly, in solutionculture.

Wild Buckwheat.Newly harvested seed mayremain dormant. Vines should be staked upadequately and spaced to prevent tangling.

LITERATURE CITED

(1) ANDERSEN, R. N. (7)1968. GERMINATION AND ESTABLISHMENT OF WEEDS

FOR EXPERIMENTAL PURPOSES. 236 pp.W. F. Humphrey eSs, Inc.;Geneva, N.Y.

(2) BAKER, K. F.1957. THE U.C. SYSTEM FOR PRODUCING HEALTHY

CONTAINER-GROWN PLANTS. 332 pp. Calif.Agr. Expt. Sta. Ext. Serv., Berkeley, Calif. (9)

(3) BARTON, L. V.1967. BIBLIOGRAPHY OF SEEDS. 858 pp. Colum-

bia Univ. Press, New York.(4) DOWNS, R. J., BORTHWICK, H. A., and PIRINGER, A. A.

1961. LIGHT AND PLANTS. U.S. Dept. Agr. Misc.Pub. 879, 26 pp.

(5) EVANS, L. T., ed.1963, ENVIRONMENTAL CONTROL OF PLANT GROWTH.

449 pp. Academic Press, New York.(6) HARTMAN, H. T. (12)

1968. PLANT PROPAGATION: PRINCIPLES AND PRAC-

TICES. Ed. 2, 702 pp. PrenticeEnglewood Cliffs, N.J.

(8)

(10)

(11)

HEWITT, E. J.1966. SAND AND WATER CULTURE METHODS. Ed. 2

(rev), 547 pp. Commonwealth Agr. Bur.,Farnham Royal (Bucks), England.

HOAGLAND, D. R.1948. INORGANIC NUTRITION Op PLANTS. 226 pp.

Chronica Botanica Co., Waltham, Mass.and ARNON, D. I.

1938. THE WATER-CULTURE METHOD FOR GROWINGPLANTS WITHOUT SOIL. Calif. Agr. Expt.Sta. Cir, 347, 39 pp.

HUDSON, J. P., ed.1957. CONTROL OF THE PLANT ENVIRONMENT. 240

pp. Butterworth's Sci. Pub., London,England.

Sams, J. VON.1887. LECTURES ON THE PHYSIOLOGY OF PLANTS.

836 pp. Clarendon Press, Oxford, England.SCHWARZ, M.

1968. GUIDE TO COMMERCIAL HYDROPONICS. 136pp. Israel Univ. Press (Daniel Davey andCo., Inc., Hartford, Conn.).


(13) SPRAGUE, H. B.1964. HUNGER SIGNS IN CROPS. Ed. 3, 461 pp.

David McKay Co., New York.(14) U.S. DEPARTMENT OF AGRICULTURE, AGRICULTURAL

RESEARCH SERVICE.1966. PLANT LIGHT-GROWTH DISCOVERIES FROM

PHOTOPERIODISM TO PHYTOCHROME. ARS

17

(15) VAN WIJK, W. R.1966. PHYSICS OF PLANT ENVIRONMENT, 382 pp.

North Holland Pub. Co., Amsterdam,Netherlands.

(16) WENT, F. W.1957. THE EXPERIMENTAL CONTROL OF PLANT

GROWTH. 343 pp. The Ronald Press Co.,Spec. Rpt. 22-64, 17 pp. New York.

INDEX OF PLANTS

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Alfalfa (Medicago sativa L.) 7, 8, 9, 14 Parsnip f.Pastinaca saliva L.) 7, 9Barley (Hordeum vulgare L.)_ 3, 6, 7, 9, 14 Pea (Piston sativum L.) _3, 5, 6, 7, 8, 9, 12Barnyardgrass (Echinochloa crus-galli (L.) Beauv.) 7, 9, 14 Peanut (Arachis hypogaca L.) 7, 9, 15Bean (Phaseolus vulgaris L., `Black Valentine')__ .. 7, 9, 15 Pepper (Capsicum frulcscens L.) 7, 9Beet (Beta vulgaris L.) 7, 9, 15 Pigeongrass (Selaria viridis (L.) Beauv.) 7, 9, 14Bermudagrass (Cynodon dacfylon (L.) Pers.)_-_ 7, 9, 15 Pintobean (Phaseolus vulgaris L.) 7, 9, 15Bluegrass (Pea pratensis L.) 6, '4, 9, 15 Plantain (Planlago major L.) 7, 9, 16Broadbean (Vicia faba L.)_ _____________ 7, 9, 15 Potato (Solanum tuberosum L.) 7, 9, 16Broccoli (Brassica olcracea L. var. italica Planck)._ 7, 9 Red clover (Trifolium pratense L.)___._.... 7, 9, 15Buckwheat (Fagopyrum csculentum Moench). _ _ 7, 9, 15 Rice (Oryza saliva L.)_ 5, 7, 9, 14Cabbage (Brassica oleracea L. var. capitala L.).,..5, 7, 9, 15 Sorghum (Sorghum bicolor (L.) Moench). 5, 7, 9, 15Carrot (Daucus carola L.) 5, 7, 9, 15 Soybean (Glycine max (L.) Merr.) 6, 7, 9, 10, 16Corn (Zea mays L.) 3, 5, 7, 9, 12, 13, 15 Spinach (Spinacia olcracea L.) 7, 9Cotton (Gossypium hirsuturn L.),_ 5, 7, 9, 15 Squash (Cucurbita maxima Duchesne) 7, 9, 15Cucumber (Cucumis sativus L.) 7, 9, 15 Sudangrass (Sorghum sudanense (Piper) Stapf)_. 7, 9, 15Dill (Anethum graveolens L.) 7, 9 Sugarbeet (Bela vulgaris L.) 7, 9, 15Endive (Cichorium endivia L.). 7, 9, 15 Sugarcane (Saccharum officinarum L.)* 6, 7, 9, 16Fall Panicum (Panicum dicholomiflorum Michx.) 7, 9 Sunflower (Helianthus annuus L.) 7, 9, 16Flax (Linum usitatissimum 14_ 7, 9, 15 Sweetpotato (Ipomoca balatas (L.) Lam.)_ . 7, 10, 16Head lettuce (Lactuca saliva L.). 6, 7, 9 Swiss chard (Bela vulgaris L.)_ _ ________ 7, 10Johnsongrass (Sorghum halcpense (L.) Pers.) 7, 9, 15 Tobacco (Nicotiana labacum L.). 5, 6, 8, 10, 16Leaf lettuce ( Lactuca saliva L.) 7, 9 Tomato (Lycopersicon esculentum Mill.) 8, 10, 16Limabean (Phaseolus lunalus L.) 7, 9, 15 Turnip (Brassica rapa L.) 8, 10, 16Melon (Cucumis melo L.) 7, 9, 15 Wheat (Triticum aestivum L.) 8, 10, 14Millet (Panicum miliaccum L.) 7, 9, 15 Wild buckwheat (Polygonum convolvulus L.) 8, 10, 16Mustard (Brassica juncca (L.) Coss.) ..._ 7, 9, 15 Wild mustard (Brassica kaber (DC.) L. C. WheelerOat ( Arena saliva L.) 7, 9, 14 var. pinnatifida (Stokes) L. C. Wheeler)_ 8, 10, 15Okra (Hibiscus esculents L.) 7, 9, 15 Wild oat (Arena falua L.) 8, 10, 14

*U.S. GOVERNMENT PRINTING OIPICE I 1m 0-114.451