Studies on the absorption of nitrogen by citrus from foliar applications of urea

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Studies on the Absorption of Nitrogen by Citrus
From Foliar Applications of Urea

By

WILFRED CHING-CHING CHEN

A DISSERTATION PRESENTED TO THE GRADUATE COUNQL OF

)

THE UNIVERSITY. OF FLORIDA

IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE
DEGREE OF DOCTOR OF PHILOSOPHY

UNIVERSITY OF FLORIDA
January, 1953

ACKMQwLiaXg^tiHT

» . i

The author is sincerel7 appreciative of the guidance and
enccauragetaent of Dr. I. W. Wander* Soil Chaaist* Citrus £xperin»nt

Statim* Lake Alfred* Florida* under whose direction and supervision

*

this investlgati(m was made. He is also grateful to Dr. J. W. Sites*
Horticulturist* Citrus fixpezlment Station; Dr. H. S. Wolfe* ilead Pro-
feesor* Depairtment of Horticulture; Dr. T. W. Steams* Associate Pro-
fessor* Department of Agricultural Chemistry; and Dr. F. B. Smith*

Head Professor* Department of Soils* University of Florida* for their
Invaluable advice* suggestions* and criticisms of this work. Apprecia-
tion is expressed to the University of Florida Citrus Ssq^eriment
Station at Lake Alfi^* Florida* for facilities used throughout these

studies

TABLE OF CONTEKTS

Page

I. INTRODUCTIQII 1

U. REVIEW OF LITERATURE 3

A* The Uee of Urea as a Source of Mltrogea in

Plants 3

B* Foliar Application of Nitrogenous Compounds. «•••• 10

III* METHODS AND PROCEDURES 17

A* Dipping Trials with Individual Branches of

Mature Trees..**. ..*...* *•*• 17

B* Field S^rizoents...... ..••*•*. IB

C. Greenhouse Pot Cultures* •.....* 19

D* Analytical Methods ••*•*..** •**......* 22

E* Saapling Procedure and E]^ressian of Results***.* 23

IV. PRESENTATION OF DATA AND RESULTS 25

A. The Effect of the Concentration of Urea Spray

on Citrus.*...**..** ••*..*.. 25

B. Effect of the Concentration of Urea Sprays on
Leaf Injury of Hvne Connercially Isportant

Species of Citrus*. 36

C. The Use of Sxicrose in Eliminating Leaf Injury

Caused High Concentration of Urea Spray* ...... 43

0. The Effects of Sucrossji Magnesium Sulfate and

Lime on the Absorption of Nitrogen 47

£. The Effects of Stickers and a Wetting Agent on

Nitrogen Absorption***** * 48

F. The Effects of Wetting Agent-Sucrose Coid>in&-

tions in Urea Spray on the Absorption of Nitrogen 53

G. The Efficlenoy of Nitrogen Absorption in Rela-

tion to the Initial Nitrogen Content of the
Leaves**.. 61

H. The Effect of the Acidity of the Spray Solution

on the Nitrogen Absorption by Citrus Leaves...... 66

1. Coiparative Stxidies of Foliar and Soil Appli-
cations of Nitrogen ..*..**. 68

J. The Rapidity of Nitrogen Absorption by Citrus

Leaves... .*...*...... 78

V. DISCUSSION 83

VI. SUMMARY 92

VII. LITMIATURE CITED 94

Vm. APPENDIX 99

I

imoDUcnoM

Foliar applications of sdnor elanmts have been used success-
fully to correct deficiencies in some fruit trees. Recent reports (54)

t . f ‘ I *' • * f

indicate that a satisfactory level of {Bosphorus nxitrition can be
nnintained In certain vegetable crops by foliar applioatiaa of o-pho»>
phorlc acid. Tha current widespread applications of Insocticidesa
fungicides, and growth regulators to crops have caused ccnsiderable
Interest in the possibilities of applying najor nutrient elooents to
the leaves of plants.

Nitrogen, being one of the major elooenta or "energy olements",
has long been used in agricultural prootioes. Iiowever, its use as a
nutrient applied to the foliage of plants was not known until recent

t , ^ , i T

years. Apples, tomatoes, and soras ornamental plants are found to be

responsive to oltrogiBa, sprays, while peach trees and other stone fruits

were not benefited by foliar application of nitrogen. The factors

idiich control the absorption of materials sprayed on the foliage are

not yet fully understood, but it seems that the efficiency of absori>>

tion of a spray application varies among different kinds of plants,

probably because of morphological differences in the leaves.

\

Due to the waxy nature of their leaves, several (pestions arise
concerning citrus and the use of foliar fi^splication of nitrogen. First
is the question of whether citrus treds are reeponsive to nitrogen
spraysj second, what concentration may be ueed; third, henr rapidly is
nitrogen absorbed} and fourth, does urea affect the plant in ways
other than those related to the supply of nitrogen?

ICxiMrinmite of Jones and Parker (36)« ,and Haas (30) pazi^ially
answered cne of these questioos since they found that both Washington
navel orange trees and lemon cuttings were responsive to foliar a|^)Ll->
cation of nitrogen in the font of urea*,

Since little is known about using foliar application of nitro-
gen on citxuSf the work included in this thesis was designed to study
the following j^iasesi

A* The Effect of the conc«itration of urea spray on oitxtie*

B* The use of sucrose in elininating leaf injury caused by
hi^ concentrations of urea sprays*

C* The effects of stickers and a wetting agent <m nitrogen

t

absorption by the leaves*

D* The effect of the acidity of the spray solution on nitrogen

' J

absorption*

S* Comparative studies of foliar and soil applications of
nitrogen*

F« The rapidity of nitrogen absoz^stion by the leaves*

2

ii» immi OF LrriaL\TURfi

A. The vuf of itf»a ag a sourc# of nitrogen in vHmU

Urea is found in higher plants OTly 1& small quantities (25)
and is present in maxl.nmn amounts in seedlings^ in young buds and
leaves, and other actively growing tissues* Urea In young plant tissues
is to a large extent combined with aldehydes (3^)* In terns of per>
centage of total amide, it amounted to 2d»50S^ of the total amides in
the seedlings of Dollchos biflorus and Phaseolus lamigo according to
Oamodaran and Venketesam (16)*

The foniffition of urea within the jdnnt body has been fairly
well deanonstrated by different investigators. A general agreement is
established that urea in plants is not derived wholly from a single
source, but from two or more different substanoee* In a series of studies
(15, 16), it was found that a part of the urea amide in the seedlings
SL* hiflorus arose from the hydrolysis of arginine and arginine^like
compounds hy the action of arginase* Another study by Fosse (25), showed
that urea is derived from uric acid in the following steps t

urioase allantoinase AUantoin d

Uric acid - AUantoin ^

AUantoin 1

— •» Allantoic acid Urea 4 OlyoKylic acid

The urea thus formed is not the result of a synthesis but is set free
from uric acid and the nucleins* MetaboUam of nitrogen is continued by
hydration of urea to anmonia* These studies demonstrate the fact that
the formation of lurea is one of the in^rtant biochemical changes taking
place in the course of jnrotein regeneration in plants* As Gilbert (26)

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stated^ <^ho nltrogenoue compounds elixoinatad by animals are chleHy
urea« uric aeid> and amnonia^ vhich« alcoig with other coiz^jounds, result
froa the breaking down of proteins and protoplasm* The same coiqpounds
are apparently formed la the life processes of the plant cell, but are
again directly utilized in the formation of new protein coo^wunds and
are not eliminated as in animals”*

It has not been demonstrated that molecular urea can be absorbed
and utilised directly by plants* However, Bltcover and Wander (6) re-
ported that the urea fom of nitrogen can be absorbed by citrus trees*

In their experiment, a knom cpiantity of urea nitrogen in a known volume
of nutrient solutiim was passed through the pot in idtieh the tree was
growing, and the solution was collected in a flask for quantitative
deteminatian of nitrogen* The process toc^ about 10 minutes to be com-
pleted* The amount of nitrogcm lost was calculated by difference from
the ocHicentration in the original nutrient solution* Results indicated
that this value of nitrogm loss ranged from 10*6 to 26*5^* Based on an
aasuiqjtion that in such a ehort time (about 10 minutes) the changes or
transformation of urea caused by microorganisms would be miniuasa, they
considered that the changes in concentration of nitrogen in the solution
would be solely die to absorption by the tree*

In the soil, urea is rapidly transfoxmed into ammcmia, and
subaequaatly into nitrates* The process includes both ammonifieetion and
nitrification, and it goes through the following reactions t

The ammonium carbonate in solution partially reacts with the base ax-

change and the pti of the laedlua goes up* The aanonlun e&z^

bonate is nitrified according to the following reaction: t

♦ 4O2 — ► 2HHO3 ♦ CO2 ♦ 3H;P
As the ananoniiim carbonate is oxidised to nitric aeid^ the hydrogen of
the acid is dissociated as ions and gives the loeer pH value at this
point* The NO3' 1(» is associated eith other bases axul the nitrifies^
tion process is cosqpleted* Hoeever« under certain circumstances, Mihm
the oQcygen supply is insufficient to cosqplete the oxidation of the
nitrogsi to the nitrate fom, the following reactions will occur:

(NH2>;^ t ► ^2

+ 3O2 ► 2HO2” ♦ 4 2H*^

In this case nitrite accumulation may be considerab3.e* Bitcover and
Wander (6) reported that relatively hi^ temperature is a factor in
nitrite accuaulation, and it seems that this hi^ tec^rature may de-
press the ^ Activity of the nitrite-oxidising microorgaxd.sms which
ordixiarily would convert the nitrite to nitrate* . .

Pascour, according to Wasksman {6k) t was the first to recognise
that the transformation of urea to aciaonia is brought about by a living
organism, Torula aiaaoniacale* However, it was later discovered that
organiama capable of decooQweing urea are found in most families of
bacteria, actinosyeetes, and fungi* Migael (64) found that the urea
organisms of tbs surface soil were Ir-SSi of the total bacteria, and that
manure and urine contain IQ^ of their flora as urea bacteria*

The rate of urea decomposition to ansonia is dependmit on the
soil type, soil ooistxm) and temperature* In general, this process is
very rapid in coo^mirlson with other sources of nitrogenous materials*

-5*

Kleberger (37) "The speed of decos^sitlon of urea varies vith

the pb^^cal teactuire of the soil; the lighter the soil, the qiiieker the
decoB$)Osition''« While Borders (7) found that certain soils possess only
a sli^t ability to transfonc urea into cmsonla, he also found that the
addition of an anaonification factor, such as fresh zaanure or soy-bean
urease, favors this transformatim. Turchin (62) claimed that uz^ is
qid.ckly trsnsforced in most soils* This was especially true for podzols

I

and the slightly degrede<i chernozems, but very little transfonaation vae

I

noted in sandy soils ajnd in caxtxnate soils* Eotini (52) had etxpeirl-
mental evidence that the decomposition of urea in arable soils into

I

ammonia takes place only in certain soils; he noted that practically no

f

decomposition occured in soils sterilized by heat or in artificial soil*
Prince and tfinsor (46) investigated the rate of decat$x>sition of iirea

in cultures containing different percentage of soil and sand, about 1Q$^

<

moisture being used in sand cultures and 15^ in HaI f aand and half soil.
The cultures mre maintained at room tes^serature* !nie index for deters
mining the rate of dec<»^)osition of urea vas the amount of «n»Min1e pre-
sent in the cultures at different periods of tims* After 5 days thiy

found that on]y 3% of urea was c(»iverted to atnraonia in the sand cultures,

♦

6?^ in half sand and half soil, and 90^ in soil alone*

A correlation was found to exist between the soil moisture con-
tent and the rate of tranaformaticn of urea to aumonla and subsequently
to nitrate in Norfolk sand (35)* The rate of anaaonia accuiaulatiaa from
urea decreased with an increase in the soil moisture in the early period
of Incxibatlon* Later, idien nitrification began, the quantity of AwmoniA
accumulated from urea decreased with an increase in soil moisture up to

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13»95% of tha dxy wight of the soil. At 15«S5Jt and 17*9552 aoleture the
ansBonla accumulation again increaeed. At 20*55^ moisture, which ro-
presents an anerobie condition of the soil, very little anminn^a^ accunu-
lated from urea. Littauer (41) observed that although drought retarded
the rate of urea transformation, increasing the soil moisture above 50^
of its maximum watex^holdlng capacity did not cause any significant
change in the rate of decomposition. Smith (56) reported that the optimum
soil moisture content for nitrate production from various nitrogenous
materials was between 50 and 60^ of tbs msytmum water>holding capacity of
Norfolk sandy loam soil. However, he obtained a larger nitrate aceunaaa-
tion from urea at 7052 of the water^holdlng capacity of the soil
from ammonium sulfate, dry ground fish meal, or alaughteiwhouse tankage*

Many investigators have observed that tenQ)erature is a factor
which controls, in a great measure, the quantity of nitrate produced in
unit tine. Schlosing»e observaticn, cited by Greaves (27), showed that
nitrification is very slow at 7*5® C., qjuite marked at 11® C., reaches
its maximum at 37® C., and inhibited entirely at 55® C. In Jones*
study, found that over an average daily tei^rature range varying
between 10® arwi 30^ C., the fluctuations in the production of nitrates
troa. urea seemed to vary directly with temperature. Other findings (46)
reported that the optimum temperature for nitrification in soil cul-
trues is about 35® C. or slightly higher, although the process take
place between 15® and 40® C.

Because of its rapidity of transfonaation to and nitrates,

which are generally considered to be the forms of nitrogen absorbed
and utilized by plants, urea is one of the iaportant nitrogwi ferti-

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Users for plants. Various e^qperiiaents in cel!^}aring the efficiency of
urea and other soluble nitrogen-oontaining materials^ such as anEomium
and nitrate corpounds^ have bean reported in the literatxire. Hi^ier
yields of sugar cane (17, 8), rice (61), spy-bean (2), mstard (40),
and cotton (5) have been obtained by the application of urea. Appreci-
able growth produced by the urea-injected branches of pear (58) wd
apple seedlings (53) has been recorded. The jnaexeion of iris bulbs up
to 24 hours in 1$ urea induced longer st«a, deeper green foliage, and
earlier and nore abundant bloom (i!i4)* In a "orop-producing capacity”
test, Anderson (1) found that 175 lbs. nitrogen as urea applied per
acre of tobacco is approximately equivalent to 200 lbs. of nitrogen as
cottonseed meal. However, Lewis (40) found no significant difference
between the effects of ammonium and urea salts in pot cultures of
barley plants.

Detrimental effects of also have be«i reported. Urea at a
concentration of 1,000 p.p.m. showed 75^ inhibition of growth on cress
seedlings (4). Haas (29) stated "Urea-containing (xmipounds when used in
excess on citrus in soil sonetimes cause yellowing of the leaf tip, or
a Qottljng near the apex of the leaves”. Wilting of young citrus trees
was noted during the wannest pezdod of the year when the source of ni-
trogen in the nutrient solutions was in the form of urea (6). There is
also evidence that when urea was applied in direct contact with the seeds
of cotton and beet, gemination was eonsldersbly decreased (3). This
injurious action of urea seems to be cloeely related to its conversion
into ammonium ecurbonate, which dissociates with the liberation of free
ammonia.

•e 0 «m

An «3q)«riBMnt has besn reported fagr Skok (55)# found that
the ai^pearanee of calolum deficiency syB^taoas in the bean plant eas
noticeably delayed In plants that received urea as a source of nitrogen
as coBfiared vith those that received nitrate nitrogen. He interpreted
these results to be in suj^rt of JSckerson*s findings (19) that' oalciuia
is essential for the assimilation of nitrates^ by being necessary for
the successful catalysis of the reduoti«a of nitrates to nitrites by
the so-called jreduetase en«yn». His plants receiving urea \nre thus
supplied with a reduced form of nitrogen and the necessity for nitrate
reduction was eliminated* He suggested that since other elmoants—
potassium, phosphorus# and sulphux*— were also found to be necessary
for normal reductase activity by Hekerson (19)# their deficiency syap~
toms nay also be lessened in severity by the use of urea*

Similar eoq>eriiaHats have been reported by Breon# CiUom# and
Tendam (10)* Th<^ found that tonato plants utilising urea as a source
of nitrogen# when deprived of their normal supply of phosphorus# did
not eodiibit the usual signs of phosphorus deficiency as soon as did
deficient plants growing in a medium containing nitrate nitrogen* Chemi-
cal analyses of the plant tissue showed that the plants utilizing urea
ccKitained much more phosphorus per unit of dry weight than did the
plants receiving nitrate nitrogen* Furthermore# during phosj^rus stax^
vatiMi it to<^ the plants growing in a medium containing urea longer
to deplete this reserve store of phosphorus* They eiaimixi that the delay
in the appearance of deficiency syii^tams by the plants furnished urea
ml^t be due to a greater accumulation of phosphorus and not to the
removal of the necessity for nitrate reduction by the substitution of

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urea for nltirate in the nutrient solutioa*

B> Foliar applicatioa of nitrogenous cogapounde

lu 1939> while Haniltonf PaLsiter and Itfearer (32) of Kew York
State Agricultural S3q)eriment Station were woiicing on the eraluation
of fenoate, ferric-dimetfayl-dithio-carbaaate for the

control of apple scab and cedaivapple rust fungi« th^ found that the
compound caused considerable increases in the grewi coloring of the

leaves, and th^y thought it was possible that the greening of the leaves
was due, at least partly, to the nitrogen idiich is contained in formate.
This possibility that nitrogen may be assimilated through the leaves in

appreciable (Quantities suggested its application in foliar sprays as a
means of controlling the supply of nitrogen to fruit trees.

In 1942, Hamilton, Palmiter and Anderson (31) commenced experi*
ments to determine the effects of various nitrogenous compounds applied
with the regular sulfur scab sprays on apple trees. They found that urea
sprays at a concentratiai of 5 lbs. to 100 gallons of water caused a
vexy rapid Increase in the green color and chlorophyll c«itent of the
leaves without apparent injuxy to the foliage. Their experiments have
suggested the usefulness of urea sprays in solving special problmos of
nitrogen fertilization where a control of amount and timing aiay be of

paramount importance.

Because one of the major problems in the production of apples
la the northeastern United States was the regulation of the nitrogen
level to obtain satisfactory yields of well colored and high (quality
fruit, and because of Hamilton and his co-woricers* discovery that

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nltrog«n sprays odLght possibly control ths nltzogen level of Amlt
trees^ such woric along this lias has been done by various ixxvestiga>-
tors. However^ this woxk was limited only to apple trees until 1948^
when Weinberger* Prince and Havis (65) started to use urea sprays on
the foliage of st<«ie fruits. Sven though they found that application
of urea on the foliage of peach trees was not effective* other workers
followed them in trying foliar application of nitrogen on many other
fzuit trees* field crops* and ornamental plants. Qrapes (24)* apricots*
Japanese plume* almonds* and other stone fruits (50) receiving up to
three applications of 5 lbs. of urea to 100 gallons of water were not
benefited by the nitrogen sprays* while figs* olives* walnuts (50)*
cotton (59)« roses* and chrysanthemums (47) semned to assimilate the
nitrogen applied as urea sprays. <

Work done by Cook. and Boynton (13) has confirmed earlier
evidmice that the lower surface of the leaf takes in urea much more
readily than the upper surface and that young leaves absorbed it more
efficiently than old ones in the case of young apple trees. On the other
hand* Rodney (51) found that the amount of nitrogm entering through
the upper surface was similar to that entering through the lower surv
face when sprays were applied in July. However* he believed it may be
that a sli^itly greater amount of material entered through the lower
surface tr<m sprays applied in September. This was evidence that the
nitrogen compounds entered directly through the leaf cuticle* since the
upper surface of apple leaves contains no stomatee. Co<^ and Boynton

also found that there was a direct relationship between hi£^ urea absor|>-

♦

tion and high initial nitrogen level in the leaves when the values were

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•xpressed as ths psrcsnt of tbs applied urea irfhlch was absorbed by the
leaves. Also high absorption seeioed to be associated with low tempera^-
ture^ while the inclusion of a wetting agent in the spray solution
more than doubled the percent absorption. Under all conditions there
was a cmtinuing movement of urea troa. the surface to the inside of
the leaf over a period of three or more days following spray appUcm-
tlonSf and the urea was converted to protein nitrogen or moved out of
the absorbing leaf over more than three days.

The eocperience with apples has stimulated interest among citrus
growers in the use of nitrogen sprays in Callfomia. This work was
started in 1947 sod is still being continued. at the Citnis fi}Q)erimKxt
Station in Riverside. Jcxies and Parker (34)^ spraying urea on Washing*
ton navel orange trees« found that the sprayed trees showed a marked
increase in green colors a slight increase in vegetative growth^ and
an Increase in fruit production over the unsprayed trees. Haas (30),
in a study with lemon cuttings, carried out imder greenhouse conditions
to avoid possibls effects of rain, found that spr^ysd loaves showed a
marked inqprovement in the green color and some new growth in a few days.
Tip and marginal bum aeooo$>anied the increased color in the older
leaves, but this c was eliminated by the addition of 2.5 lbs. of
hydratod lime in 100 gallons of the spray solution. He suggested that
with citrus trees, urea may be included with the varltms types of n»i-
tritional and Insecticidal sprays which are being applied throughout
the year.

During the period from 1939 to 1948, various organic and inor-
ganic nitrogen-containing materials v#sre tested as foliar sprays.

« 12

Eosults ixidioatad that among all kinds of nitrogen carrler8« materials
vhlch eontain nitrogen in the form of ^lrea (for exacqple^ Uramcm) seamed
to be the beet for foliar applications (22, 23, 33)* Based on the
suceessfulness of a great volume of woxic with urea apreys on apple
trees in hew York State and in the northMostexn United States^ DuPont
Chemical CompensT developed in 1949 a concentrated nitrogen fertilizer
especially for application of foliar sprays^ and named it *%iGre<m*«

It is a light green-coloredf semi-granular material containing
nitrogen in the tom of urea along with conditioning agents which pre*
vent caking and assure free flow and yet maintain high solubility*
y The valxxe of foliar applloation of urea results from the rapid

absolution and utlllzati(»i of the urea nitrogen by the leaves. Tests
with apple leaves showed that a large proportien of the spray was
absorbed during the first few hours and further absorption oecured
later (12)* This nitrogen which is absorbed by the leaves starts to be
assimilated in a short period of time« and this enables growers to
regulate the supply of nitrogen for optimum effects on early growth
and bloom, fruit set, fruit developmmat, and fruit coloration at
maturity* Nitrogen ap;dJ.ed to the soil may require considerable time
to reach the leaves where it is used* It may take only a few days under
good conditions, or many weeks if cold, wet soil conditions or dry
weather prevail* In some cases the nitrogen applied to soil is called
below the root zone by heavy rains, or it may remain above the princi-
pal root zone for prolonged periods because of lack of rain or irrig^
tion* Coopetitlcm fr<»i cover crops or deflcien<qr of functional roots
may limit nitrogen absorption. Thus, under good condititms the nltrogma

- 13 -

may reach the leaves at the proper time, but under adverse conditions
sufficient nltrogm may not becone available when the nitrogen require-
ments of the tree are great.

Foliar applications of urea have also benefited pest control.

In one experiment (45), the amount of fruit infected apple scab
increased from 17 to 30^ a> the rate of soil nitrogen was Increased,
while the urea-sprayed trees showed little increase in fruit scab over
that on unfertilised trees. Palmiter (45) thought that the better scab
control in the urea-sprayed trees may have been due partly to a bettor
nitrogen balance in the trees, but the results also indicated a direct
increase in fungicidal effectiveness %dien the urea was used in coadalna-
tion with sulfur and arsenate of lead. As the amount of urea added to
the spray was increased, the amount of fruit scab was decreased from
17 to 13^. Stoddard (60) stated, "The fungicidal activity of sulfur plus
urea is greater than that of sulfUr alone. Against Sclerotlnia and
appl^scab conldla on glass slides, a mixture of sulfur and uxea was
approximately twice as effective as sulfUr alone". He explained that
the ii^iroved growth and color of the sprayed foliage indicated that
nitrogm is absorbed. Normally an Increase in foliage nitrogen Increases
susceptibility to scab. The improved control in these fungi is evidence
of fungicidal synergism between sulfur and urea.

Urea sprays at a concentraticsi of 5 lbs. per 100 gallons of
water caused a visible deepening in the green color of the apple leaves
(50). Hamilton (31) reported that Uraacm sprays applied three times in
early spring seemed to increase foliage color early in the season, but
the effect gradually disappeared, tdiile trees receiving an additional

14-

e^plioation 30 days after bloom showed better color of the foUa^
throughout the growing seas<si than the trees receiving three appUea-
ti<ms in the early spring* Fisher (21) reported the similar effects of
late appUeatimi of urea on apples^ stating^ "The later a spray is
applied the greater is tlM nitrogen effect following that spray* within
the Units from pre^blossom period to the tine of the second cover ^
spray"*

Other evidoace (23) showsd that spray treatments with urea
resulted in greater nitrogen and chlorophyll levels than for a given
amount of nitrogen applied on the soil* Leaves fkon vigorous trees with
a heavy crop of Aniit which were sprayed with Uramon at a c(»icentration
of 2 lbs* per 100 gallons did not have a nitrogen content appxeciably
above that of the tree receiving no fertilizer* but leaves Aram the
less vigorous trees with a U^t crop of fruit did have a significant
increase (31) •

The effects of urea sprays have been tested on a variety of
vegetable crops* Cucnunbers* celery* carrots* radishes* and tomatoes
were found to be responsive to urea sprays* whereas snap beans axKt
spinach were not affected by the sprays (49)«

In testing roses in the gremhouse (47)* begining with the third
weekly appUcatlon of huGreen at the concentration of 5 lbs* per 100
gallons* it became obvious that the sprayed bushes looked dazicer green
than the controls* By the time the fifth application was made* the
results were even more striking* In addition to better foliage* plants
treated with NuGreen averaged 10 buds whereas untreated plants averaged
only 6 buds per plant* A coo^)arable increase developed in the nufld)er

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and length of stems on the tx<eated as ecnq^ared with untreated plante*

In chzysantheiaLu&e (47)* the results were aore striking^ perhaps because
the roii^ier leaves on the plants wetted more evenly and thus enabled
more of the material to enter. As with the roaes^ the differwice in
foliage siae and color soon became obvious.

Due to the striking effects of urea spray on plants, the con-
sumption of this material has been Increasing. About 500 tons of coi»>
msrcial urea were sold in New Toxic State for the purpose of foliar
applications on apple trees in 1950 (9)« In 18d groves in the Cornell
Cost of Spraying Survey, I|3 used this as a main source of nitrogen.

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m. MKTHCiDS AJJD PROCgDURKS

A»' Dipping trials with individual branchas of mature tr— 8

Dipping trials wars mads i«ith individual shoots of maturs
tress. With the eaceepti<m of the preliminary trials in using sucrose
as a protectant against leaf tauzn caused by urea sprays and the tests
conducted to study the response of three species of Citrus to urea
spray in leaf Injuxyf the plants used were Duncan grapefruit trees
budded on sour orange rootstocks. The choice of Duncan grapefruit trees
was made because of the ready availcd>ility and the relatively larger
leaves of these trees.

The effect of the treatments upon the tip and marginal bum of
the leaves, and on the total nitrogen content after treatment, received
major attention in these studies.

Shoots uniform in age and location on the tree were selected
and tagged with numbers. Different treatments were tested by dipping
each shoot in the prepared solution of G.P. urea for about tm seconds,
fiach treatment was replicated from 3 to 5 times.

The first leaf samples were taken to measure the Initial nitro*
gen content immediately before the treatments were applied. Later
samples were taken from these same leaves, in order to eliminate the
variation of the nitrogen content due to the thickness of the individual
leaves. However, severe dropping of leaves resulted in some oases due
to the treatments with high concentration of urea; consecpiently, it was
sometimes impossible to take samples from the same leaves. In these
eases, sample disks were taken from other similarly treated leaves.

-17-

B» Field experiments

A porticm of the trees used for field experiments were ir*yeu^
old 80\ir oraiM^ seedlings located in a mirsery of tbs Florida Citrus
Experiment Station. Tbs soil cm which the trees %#ere growing was
classified as Lakeland fine sand with a low degree of fertility. Since
no fertiliser had been applied during the past two years, most of tbs
tzees showed a considerable degree of yellowing due to deficiencies of
nitrogen, magnesium, sine, iron, and perhaps other plant nutrients.

In Februaiy, 1952, when the soqjerinwits were started, fertiliser oaa-
taining all necessary elemants exespt nitrogen was applied to each
tree at a rate of on»*half pound per tz*ee of analysis. A

secc»d application of fertiliser of the same amount and analysis was
made a month later.

In some experiments, 2-year-old Ruby grapefruit on sour orange
rootstocks in the same location were used. Fertiliser treatments be-
fore experimeats wexe the same as those on the V-yeaivold seedlings.

In Harch, 1952, deficiency syi9>t<aas of magnesium, sixio, and
iron had disappeared; bowsrer, yellowing of the leaves due to nitrogen
deficiency was still presmt, and the trees showed stunted growth with-
a small amount of foliage. Treatments on these tress were started in
tiaroh, aiui the urea was supplied in the form of NuGreen.

The nursery was rectangular in shape, approodmately 40 x 600
feet, and leaf nitrogen of the sour orange seedlings varied due to loea-
ticn within the area. A preliminary survey showed that these values
ranged from 0.04 to 3*23 pllligrams nitrogm per 10 em^ of leaf area.
This gave a good opportunity to study the relationship of nitrogen^

13 <-

absorption to the initial nitrogen content of the leaves*

Applications of NuGreen spray wre made on the grapefruit trees
by using a 3-gallon hand sprayer. The rate of applications for each
treatment was 1,0 gallon spray solution per tree, Qa the sour orange
seedlings^ spr^ solutions iieze applied by means of a power sprayer*
Approadmately 1*0 gallon of spxey solution was applied to each tree at
each application*

C* Greenhouse pot jultures

Experiments were set up in the greenhouse under controlled ccn-
ditions primarily for studies of nitrogen absorption. Ten-inch clay pots
and glazed porcelain Jars of 5-gallon size were washed and sterilized
in 3% formaldehyde solution for 30 minutes* Each pot was filled with the
well-washed saiwl to about 1 inch from the top* Two-year-old Valencia
orange trees budded on zwigh lemon rootstocks and 2-year-old sour orange
seedlings were planted individually on September 26, 1951* The Ixidded
trees were cut back to about 24 inches in height* The nutrient solution
used is shown in Table 1*

In addition to the nutrients listed in Table 1, 1 ml* of the
supplementary solution was added to each liter of nutrient solution. The
Bupplouentary solution was made up with the salts listed in Table 2*

At the same time iron was added in the form of 0*5^ ircxi tartrate solt>-
tion, at the rate of 1 ml* per liter, once or twice a week or as
indicated by the appearance of the trees*

The nutrient solution was applied to the trees twice a week at
the rate of 1,000 ml* per tree* Each pot was watered with tap water a

19

Tahl* !• Nutrient Solution used for Pot Cultures in the Greenhouse

Salts

Molarity of
Stock Solution

ml* per
liter

p*D*a* of Ihitrimts
P k Hg Ca S

. >

0*50

5

195.5

80.0

MgS0^*7H20

1*00

2

46*6

64*2

Ca(H2P0j^)2.H20 . 0*05

10

31

20

CaS0j|^*2!l20

o*ca

2C0

80 64*2

Table 2* The Coa^wsition of Supplemsntaiy Solution used along with
the Nutrient Solution in Greenhouse Pot Cultures

Salts

gou/liter

Amt* hlement (p.p*m*)

it ’

l^BOj

2*36

0.50

B

MdS0j^*2H20

1*70

0*50

Hn

ZnSO^.TH^O

0*22

0.05

Za

GaS0i^»5H^0

0*08

0*02

Cu

E^oO^*H20 (85^ H0O3)

0*02

0*01

No

day or so before the nutrient a{)plicatioQ8 in order to preivmt the

•»

aecuBulati<»i of the unused salts*

The purpose of the studies made in the gz*eenhouse was to give
better control to those factors such os rain and insect damage^ as
as to the amount of urea spray solutimi put on the leaf surfaces* The
teclmiqiue in apidyixig the solution to the leaves was similar to the one

- 20 -

i^ch Cook and Boyntcn (33) and Hcmtatlaro (43) Hat* uaed, Ths aolotieii
was applied on the leaf surfaces by using a caoMl-hair brush tdiich vas
attached to a 2-al» pipette* The amount of actual nitrogen applied to
the leaves by this techni<|LLe can be calculated irLth fairly high
accuracy* Urea of C*P* grade imub used*

Sach treatment was applied to t«i leaves which were grouped in
age as closely as possible* These ten leaves for each treatinent were
selected froa five different trees, using two leaves on each tree* At
the ttstd of each absorption period, whi^ was assigned specifically for
different treatments, the leaves were washed with 2 portions of 300 lO.*
of deixmized water* The washing was dcHM by means of a paint brush
idd.ch was then thorou^ily cleaned with another portion of 300 ml* of
deionized water* TIw total volume of the washings amounted to one liter,
and the aliqeuots of this on which urea nitrogen was deterained varied,
generally, from 2 to 5 ml*

From the differences between the amount of nitsrogen applied on
the leaves and the amount of nitrogen present in the washing after a

i K ^

certain length of time of application, the nitrogen loss was calwilatsd

K A,

as percent of applied nitrogen which was absorbed during that particular
period* Since no appreciable loss of urea through the action of urease
on leaf surfaces was found on applea (13)« it was assuxced that this
lose of nitrogen after a certain period of time was solely due to the
absozptlon by the leaves*

For coiq>arative study of soil and foliar application of nitrogen^

potted 2r>^sjxild sour orange seedlings wers tised* Sach pot was oovered
tif^xtly with a metal cover to prevent any spray material from going down

21

into tho pot and being absorbed fagr the trees through their roots*

D* Analytical methods

• . . ••

The analytical Biethod used for total nitrogen detensinatioa was
mainly the one which is described by Cotton (14) • leaf saa^e was

digested in 2 ml* of concentrated sulfuric acld^ and then aoddized with
30^ hydrog«i peroxide* The mixture was diluted to 100 ml*^ and a 5-^*’
aliquot was transferred to a 50-<nl* Tolumetric flask* One ml* of 2*5 N
sodium hydroxide and 1 ml* of lOSC sodium silicate were added and the
solution ms made up to volume with deionised water* The color of a ^
5«al* portion of this diluted solution was developed by means of
Nessler's reagoit« prepared according to Vanselow (63)* The color
intmslty was cos^xired with a series of standards in a photoelectric >
eolorimster using a 425*B light filter* >

For determination of urea nitrogen^ the method deeexdbed
jamies<xi (34) was wqployed* A 2- to 5hslL* aliquot was transferred to a
12-ml* centrifuge tube* Five ml* of glacial acetic acid was added and
stirred* Then 1 ml* of 5% xantlydrol in methyl alcohol was added and
stirred again* After standing overnight in a cold room (approximately
F*)^ 1 ml* of methyl alcohol saturated with dixanthydrol-urea waa
added to the surface, and after the sdbd;ure was centrii>aged for 15
minutes, the supernatant liquid was drained off* The precipitate was
washed with 4 ml* of 3:1 methyl aleohol-watsr solution saturated with
dixanthydrol-urea* The mixture was stirred, centrifuged again for 15
minutes, aiui the supernatant liquid was drained off* The precipitate was
then dissolved in ’1 ml, of 50^ sulfuric acid* The color intensity was

22

rMd In an electrojAotonieter* using a 425^ filter^ and coc^yarsd

with a series of standards prepared simLtaneausIy.

For total chlorophyll determination of leaves ^ the method
reported hy Coc?>ton and Dpynton (12) was used. Fifty disks of 1 ca^ area
were removed from fresh leaves and placed inmediately in a 30HhL« portiem
of 95% ethyl alcohol. The tissue was left to stand in the solvent for
24 hours and then ra^vivi in a Waring blender for 5 minates* The solution
was than filtered into a 100-ml, volumetric flask using a Whatman 42
filter paper^ and up to volume by washing the pulp with portions
of solvent* The extract was read in a photoelectric colorimeter* using
a li^t filter which transmitted above 610 millimicrons* ^ value was
reported as milligrams of chloroi^U per 100 em^ leaf area for two sides*

The water-soluble portion of nitrogen in the loaves was coctraetad
according to the prooedureo given by Cook and Boynton (13}» The urea
fraction of the water-soluble nitrogen was deteimined by means of
zanthydrol reagent (34)* A group of untr^ted leaves served as a blank*
After the extraction of the water-soluble nitrogen* the residue was
dried and azudyaed for insoluble nitrogen* The results of total nitrogen
content were adjiisted for variations in leaf area and reported as mg* N
per 10 cm^»

g* 3a«al*»fi pTttnadure and eocpreesion of results

When a large nuod>er of leaf sanies has to be taken at the same
tiffls for chemical analyses* the usual procedure which involves cleaning*
drying* grinding and weighing Is too tizoe ccuiauming* Furtheznore* iaost
of the trees used Lti these studies were q^ite« email* with only limited

— • 23 **

sooun'ts of fo3.1&go^ sijtd tliio ffwte iX ijs^poosiblo to foUoif tho ususl
sampling procedure of taking several leaves from each quarter of the
treetop* Therefore^ the following nodifled pxacedure for sampling
leaves was used:

Ten coeqAratle leaves on a young tree or c» a single shoot of
a bearing tree wore ohosen# A single disk of 1 ca^ in area was removed
^he lamina of each leaf by means of leaf punch* These 10 di^s of
leaf tissue from 10 different leaves were collected as a coi!qx>site
sample* The saoqjle thus obtained waa cleaned with deionized water in
order to remove the foreign matter and tlie spray materials retained on
tl»e surfaces of the leaves, vihich mi^t interfere with the results of
the analysis* The sample was put into a 50-ml* Erlenmeyer flask

for ths determination of total nitrogen* The reeults were reported as
milligrame of nitrogen per sample of 10 cm* fresh leaf tissue*

On several occasicms, idien the troes used were comparatively
largd in size, ^diole leaves were coUeotod at random in the usual wsy*>
After the leaves were cleaned, 1 cm^ of fresh tissue was rmaoved from
each leaf for determination of dry matter* content, and the rest of the
tissues were then dried, ground, and mixed* Portions of this dry sas^tle
corresponding to 10 cm^ of fresh leaf were weighed out for determination
of nitrogen* The results were expressed as milligrams of nitrogen per
10 cm^ fresh leaf* The procedure wae used in order to give uniformity
of presentation of data*

ly. pRsaarTATioN of data ;j.T) results

A| oooQgotratiop of ur»a iprw op cltyog

»

Since urea sprasre aometijQes hare Injurioue effects <m foliage^
a study of the effect of dlffermt concentrations of urea solution
sprayed on citrus leaves was oade as the first step In these Investi-
gations.

nilrty*-five similar shoots of a 28-year-old bearing Duncan
grapefruit tree budded on sour orange rootstock were selected for
uniformity. Seven different concentrations of urea solution wsre tested
by means of dipping sach shoot In the preparsd solution. Each treatment
was replicated five times and the treatments were arranged in a random-
ized block design. different concentrations were: 0^ 5# 10^ 15» 20^
30« and 40 lbs. of iirea per 100 gallons of water. Four applieatlans of
each treatment were made at weekly intervals, begirming October 30, 1951.

Leaf saiiyjles were taken twice. The first set of samples was «

1

taken on October 30, Just before the treatments were .begun. The second
set of sai^ee was taken on Noveadoer 28, el^t days after the last
application of ths urea scdutlons.

The treated leaveo were carefully aocandned from time to time
for max'ginal taim. TI9 and marginal bums of the leaves in the treatmmts
of 30 lbs%, and even more so of 40 lbs., of ux^ per gallons of water
were noticeable 3 days after the see<»id application. This burning became
more axxi more severe, and by the time eight days had elapsed after the
fourth application, idien the leaves were saspled for nitrogm detezw
mlnatlon on Novembrr 28, 1951« some of the leaves had a burned area

- 25 -

Total Nltrogan Content of Duncan Graf)efruit Leaves before and after Four Applications
of Urea of various Concentrations* (og* N/ 10 co^)

• • • • •

o o o o o

• • • • •

o o o o o

UNvQ'O Q
u>>0 <4- >AnO

• • • • •

o o o o o

CO >0 tAtO

• • • • •

O O O O H

• • • • •

M OI CM CM <M

• • • • «

<^^<M cyj CM cj

^CM CM>OvO

o

• • • • •

CAfACM CM CM

• • • • •

CM f*>CM CM C^

CM CM CM CM CM CM CM CM CM CM

3533!^

• • • • •

CM CM CM CM CM

• • • • •

CM CM CM CM CM

e

4»

II

ll

cd •

II

i

I

OOOOO IAtf\U\IA«A

I H H

«A«A W\»A«A
rM rM H H rM

CM

H N fA

CA

CA

26

3« Total Nitrogen Content of Duncan Grapefruit Laaree before and after Four AppLicatiane
of Urea of varioue Concentrations - Continued*

r-

» .

§

V

H

d

T ' -

s

."I

ll

h.

A A A A m

m m e e e

5 o •

# # # A #

H O H O H

• e • • •

o O O H o

W w w ^ w

H H H H O

e

■P

g

* M *

# A # ^ #

# # ft # %

. s.

e!

i!

h

• ♦ # ♦ #

c»>

<*> c*^ c*^ <»% <*>

«r\ <n <»\ <n

•ri

S3

•g

m

1

•

i:

Ml

51'

B

S)

, 8l5SISe

d cv (4 H

sssas

« j • • •

(V CM CV M c3

Cl ovo v\-e

» O' -if l-l tv ff\ ‘

• • • • •

H Ci cV CM (V

1

O O Q O O
c*M»N c»> C»\

e.8

=> H

«

0

B

27

Least Significant Difference Required for Treatment ttoans:

level } 0*41 ng./lO om^, level : 0*31 mg./LO cm'

cov0ring &• nuch m OQ0^t>hlTd of tho on^ijra Xo&f* Lo&tos tirofltod vitli
loH0r eonerntratiooBt below 20 lbe« per 100 gallcsnSf shoved no burning
at anjr tine*

The total nitrogen contents of the treated leaves are given in
Table 3. The results of analysis of variance of the data are presented
in Table 3a« Appendix.

It is apparent that grapefruit leaves are able to absorbed
nitrogen in the fom of urea applied to the foliage} however, variations
in the nitrogen absorption existed between individual shoots.

Treatments with 40 lbs* of urea per 100 gallons gave consider^
able greater increase of nitrogen in the loaves than did ai^ other
treatments} however, the effects of leaf injury showed that the use of
this oonMntration is not practical*

There was little difference between treatment means of 30 and
20, and between treatment means of 15 and 10 lbs* of urea per 100 gal-
loos of water* Statistically, differences between treatment means
required 0*31 mg* nitrogoo per 10 cm^ leaf tissue at the 3% level in
order to be significant*

Treatments with 5 lbs* of urea per 100 gallons of water did not
increase the nitrogen content as cooipared with the checks* It was
thou^t that the amount of actual nitrogen in this concentration was
probably not sufficient to cause a measurable Increase in the nltrogsn
content of the leaves* If 10 lbs* of urea per 100 gallons of water
caused a noticeable nitrogm Increase whm the solution was applied 4
times, then natually the qpjestion arises as to idiether 5 lbs* of urea
per 100 gallons of water will give similar results when 8 applications

- 28 -

of this concsntratiMi are made. Other socperlBMntal trials wars eot>»
dncta^ to answer this question*

Triplioats shoots of Dunoan grapefruit tree were tested with
the solution of 5 lbs. of urea per 100 gallcms of water* Treatcmits
consisted of from one to ei^^ applications of this solution were
applied at, 2-day internals from September 7 through September 22, 1952.
Leaf saflq;>les were taken from eax:h shoot for nitrogm determinaticsi on
SepteodMr Just before the first applications of treatments were made
and two days after applieatims of the respective treatmmts* The checks
were sampled on September 7 and 24* The total nitrogen content before
and after treatments, together with the values of nitrogen increase,
are given in Table 4, idiile the results of analysis of variance of
the data are presented in Table 4a« Appendix*

Si^iifieant differences of nitrogen increase for treatmmts
were obtained* The total nitrogen content of the leaves increased as
the number of applications increased. This regression relationship of
the two is , shown in Figure 1* The increase was markedly noticeable after
the third applicatiau The difference was significant at the 5^ level
after 3 applications and it was significant at the 1^ level after 5
applications of the 5-pound concentration of urea* In the previous
eoqjeriment where 4 applications of the same concentration did not in-
crease the nitrogm content, it was apparently not solely due to the
low concentration itself* Since one of the characteristic s of nitrogm
in plants is its translocation from one part of the plant to another,
with the previous experiment where the leaf samples wsrs taken eight
days after the last application, ths cooparatively small amount of

- 29 -

Tabid 4* Sffeot of Succesalva AppUcatlcxia of Uraa (5 Iba* por 100
gaUcna) on tba Mitrogon Content oX Grapefruit Loarea
(og* H per 10 leaf area) ^

XreatBwnt

Total hitroRsn
Before After

Treatments Treatments

Nitrogen

Increase

Mean

Checke

2.64

2.72

0.08

0.15

2*40

2.64

0.24

a

2.44

2.58

0.14

One Application

2.64

2.80

0*16

0.15

2*49

2.60

o.n

2.49

2.68

0J.9

Two Applications

. 2.61

2.68

0.07

0*20

2.40

2*72

0.32

2.40

2.60

0.20

Three Applications

2.46

3.04 .•

0.58

0*46

2.55

2.84

0.29

2.70

3.20

0.50

Four Applications

2.49

3.04

0.55

0.49

2.64

3.04

0.40

2.25

, 2.76

0.51

Five Applications

2.64

2.80

0.16

0.50

2*49

3.20

0.71

. 2.58

3.20

0*62

Six ApplioatiMS

2.88

3.20

0.32

0.58

2.70

3.32

0.62

2*52

3.32

0.80

Seven Applications

2.40

3*08

0*68

0.71

2.01

2.68

0*67

2.13

2.92

0.79

Sight Applications

2.31

3.12

0.81

0.86

2.49

3.48

0.99

2*70

3.48

0.78

L*S.D. 1^ I 0*345 Bg*/10 om.^, 5^ i 0*252 iag*/lO cm^*

30

Figure la Regression of Nuober of Applieatltms of Urea at a Concen-
tration of 5 lbs. per 100 Gallons of Water on Nitrogen
Increase of Duncan Grapefmit Leaves#

31

nitrogtta absorbed by bhe leaves from 4 appUcatioos of the lower con*
ceotratian was probably translocated from the absorbing leaves to other
parts of the tree before the d-day period was up. In this experioent,
however^ leaf saoples were taken only 2 days after the application of
each treatiaent^ and it appeared that the absorbed nitrogen was still
present in the absorbing leaves when they were saiqpled.

A sindlar esqjeriioent was set up with /r'year-old sour orange
seedlings under field conditions. Treatments consisted of from one up
to eight applications of urea spray at a cmcentration of 10 lbs. per
100 gallons which were applied to duplicate trees at weekly Intervals
starting April 21« 1952. Total nitrogen and chlorophyll contents of the
leaves before the first and 72 hours after the last applications of each
treatment were measured as the index of nitrogen absorption by the
leaves. The results are summarised in Table 5*

As in the resiilts previously obtained^ there was a direct rela>
tionship between the number of applications and the total nitrogen
increase in the leaves. One or two applications of urea at a concentra-
tion of 10 lbs. per 100 gallcms did not increase the nitrogen content
in sour orange seedling leaves, howsver^ the nitrogen increase was
maxked 72 hours after the third application, and the total nitrogen
increase was progressively greater as the nuzaber of aji^zlications was
increased.

There was also a significant correlation between the number of
applioatlons end the amount of chlorophyll increase (Figure 2). The
increase of chlorophyll was not as marked as the increase of nitrogen
tdksn less than 4 i^^plications of urea were made. Ifowever, after the

32

Table 5*' Total NitrogKi and Chlorophsrll Contents of Leaves of S<Hir Orange Seedlings sprasred
with Urea at a Concentration of 10 lbs* per 100 Gallons of Water

88

88

Pii
o o

88

8

•H

a

• •

• #

O O

• •

O O

o o ■

• •

o o

o o

e

8

H

i

» »

u

• •

• •

So ^

# •

• •

S18

• •

O «q
fCNH

• •

•

< H

o o

O O

o o

o o

O H

H H

1

1

e

o

o

>^1

^ e

o o

1^8

• •

O O

• •

o o

. OO

&S;

• •

o o

0.97

0.91

e

«’

-

»

*

88

8©

Q

• •

• •

o

c> o

‘ o o

O O

<3 O

Oi

n

8

1

’

O

i

i

u ^

• •

CM C3

• •

• c«- «A
c^-e.

• •

-ewN

• •

• •

< H

H H

H H

H H

H 1-4

H H

H H

«

c

m

«

8

•g

.

e

X

cl

O 4

u

• •

>0 Q

1^8

• •

88

• •

• > •

H H

H H

rM H

H H

f-4 H

H H

i

e

»

•

§

§

•H

1

1

•H

•H

tS

1

1

"S'

q

O

O

•H

•rl '

•g

d

d

flu
. S!

i.

u

iL

w#

<

a

i

e

o.

*4

3

M

-4

«=<

.5.

4

1

1-

S

1

(4

g

O

O

«-•

tk.

b.

33

Table 5* Total Nitrogen and Chlorophyll ContenU of Leavea of Sour Orange Seedlings s]
with Urea at a Conerntratloa of 10 lba« per 100 Gallone of Water Continued

e

o

**

» »

to K-

8^

o o

• •

o o

• •

O O

»r\ w>
H H

1.75 •
1.59

• •

M H

• • • • • •

o o o o o o

(SR SS

• • • • • •

o o o o o o

.38 ^3

• • • • # f

H H CM CM H CM

3?^ 5581

# ••

H H H H H H

34

Fi|;ure 2« Regression of Number of Applications of Urea at a Concent
tretlon of 10 lbs, per 100 Gallons of Water on Chloro-
pbgrll Increase of Leaves of Sour Orange Seedlings,

35

fifth application of urea the rate of Increase in chloropbgrll content
lias similar to the rate of nitrogen increase*

B* Sffeet of y>e ooncentration P sprays on leaf Injniy
eoenereially iMDortant species of Citrus

Since leaf injury i«a8 noted on leares idiich have be<m treated
with hi^ concentrations of urea in tlie preceding experinents« similar
trials were also conducted in an attaqit to detemine this resultant
effect of urea <ai different species of the genus Citrus* Three trees of
each axmercially important species mre used^ Valencia orange for
CitaruB sinensis. Duncan grapefruit for Citrus paradisi* and Dancy
taiiigerinc for Citrus reticulata. One shoot on each tree of the three
speciee was dipped in each of the solutions of 0, $, 10, 15* 20, 30,
hO, and 50 lbs* of urea per 100 gallons of water* A sin£^ application
was made on August 14* 1952*

Observations of leaf injury at 24-hmir intervals indicated
that the first STiqptons of loaf bum were noticeable in two days with
some treatments* The severity of this leaf bum Increased as the days
passed by* until 7 days eifter the applicaticms of urea tmatmiKit the
severity of leaf bum stopped changing; however* some of the leaves
idiich had been treated with high concentrations of urea dropped before
the end of the 7‘*'day period*

Figure 3 shows the effects of \urea concentrations on leaf bum
of Dunoan grapefruit leaves* Figure 4 shows the same effects on Duncan
grapefruit leaves^ but here the leaves have bem cut by means of a leaf
punch which gave mechanical injtirles of the leaf tissue* In coqtaring
these two pictures, it should be noted that leaf bum showed up on

36

Figuro 3. Leaf Injuiy as a Result of Urea Treatoents aa Uninjured
Grapefruit Leaves*

From left to right in the upper row are leaves treated with
0# 5» 10, and 15 lbs* of urea per 100 gallons of water* In
the bottom row are leaves treated with 20, 30, I4O, and 50 lbs*
of urea per 100 gallons of water* Note that the injury starts
to appear at a 30>lb* \irea concentration*

37

Figurv 4« Leaf Injuxy as a Result of Urea Treatments on Injured
Grapefruit Leaves*

From left to rl^t in the upper ixw are leaves treated with
0« 5* lOf and 1$ lbs* of urea per 100 sa11w>» of water* In
the bottom row are leaves treated with 20, ^0, kO, and 50 lbs*
of urea per 100 gallons of %iater* Itote that the Injury starts
to appear at a 15~U>* urea ooneentratlon*

Figure 5« Leaf Injury &a a Result of Urea Treatiosnts on Uninjured
Orange Leaves*

From left to rl^t In tbe upper row are leaves treated with
0« lOj and 15 lbs* of lurea per 100 gallons of water* In
the bottom row are leaves treated with 20, 30^ 40^ and 50 lbs*
of urea per 100 gallons of water* Note that the injury starts
to appear at a 30-lb« urea cmcentraticn^ and compare the
degree of burning with Figure 3*

39 •

Figure 6* Leaf Injury aa a Result of Urea Treatments on Injured
Orange Leaves.

Fran left to rigbt in the upper row are leaves treated with
Of $f lOf and 15 lbs. of urea per 100 gallons of water. In
the bottom row are leaves treated with 20f 30, 40* and 50 lbs.
of urea per 100 gallons of water. Note that the injury starts
to appear at a 15*lb. urea concentration.

• 40 •

Figurtt 7« Ltaf Injuxy as a Result of Urea Treatoaixts oa Uziinjursd
Tangerine Leaves*

From left to ri^ in the upper vent are leaves treated with
Of 5f lOf and 15 lbs* of urea per 100 gallons of water* In
the bottom row are leaves treated with 20f 30« UO, and 50 lbs*
of urea per 100 gallons of water* Note that the injuxy starts
to appear at a 15~lb* urea c<xicentration*

- Al-

Figure d« Leaf Injury as a Result of Urea Treatments on Injured
Tangerine Leares*

Frcm left to right in the upper row are leaves treated with
0, 5t 10» and 15 lbs* of urea per 100 gallons of water. In
the bottom row are leaves treated with 20, 30^ kO, and 50 lbs.
of urea per 100 gallons of water. Note that the Injuzy starts
to appear at a 15-’lb. urea conoentratlon.

« 42

iininjurad leaves at a concentration of 30 lbs* of urea per 100 gall one
of -water^ whereas on injured leaves this effect shoMsd up at the lower
concentration of 15 lbs. Siailar resiats wsre obtained from orange
and tangerine leaves as illustrated by Figures 5« 7t aixi 8*

In eooperlxig Figures 3, 5, and 7* injuries showed up only
slightly at a concentration of 30 lbs. of urea per 100 ^Uons of water
on grapefruit leaves^ whereas on orange leaves the degree of burning
was considerably higjwr for this concentration. Tangerine leaves showed
leaf injury at a concentratioa of 15 lbs.

Under the conditions of this ecxperlinent, it seened that the
tolerance of the tree to high concentrations of urea spray varied with
different species. The difference between grapefruit and oranges >as
not great, but both seeiaed able to withstand a higher concwitration of
urea spray than the tangerine.

Another interesting point oust be mentioned here, that grape*
fruit leaves treated with a given concentratlcm, for exasqple, 30 lbs.
of urea per 100 gallons of water, did not show leaf injxuy in the first
week in the aaq^erimant reported in the preceding section when the urea
solution was applied on October 30, 1951* whereas this leaf injury
showed up in only 2 days in the eaqieriment reported here, when the urea
solution was applied on August 14* 1952.

C. Pie uae of suoroe* inifoy caused by high opftOSBr

tratjon of virea spray

Leaf tnjuzy caused by urea sprays can be elioixiated by the
addltim of certain materials in the spray solution. Haas (30) fomkl
that the leaves of leosm cuttings were injured by urea spreys at a

* 43 -

CMicontratioo of 44«d lbs« por 100 gallons of Maters but that ^dasn
2.5 lbs. of hjrdratod T-twa wore added to this oonoentration of urea
spray, the leaf injxiry was eliminated* Mack and Shaulis (42) reported
that tdien 3-3-100 Bordeaux mixture was added to a 4^100 urea spray
solution, which had been reported to damage the jOant, the leaf injuxy
of Cmcord grape was prevented* Other reports (43) indicated that
xaagnesium sulfate added to the solution reduced leaf injury resulting
from applications of urea spray to tomatoes*

According to finmert and Klinkere* restats (20), e<|aal molar
solutims of sucrose mixed with urea solutions stopped urea burning
and enabled ten times as ouch ttrea to be used on tomatoes without
burning as wh«i no sucrose was used* This has stimulated interest in
the use of sucrose on citrus for this purpose. In the first trials the
equivalent of 120 lbs* of sticrose and 20 lbs* of utrea per 100 galltms
of water was used* The shoots of a mattire Temple orange tree treated
with this mixture showed ix> burning at any time* Then a treatment of
the equivalent of 180 lbs* of sucrose and 30 lbs* of xurea per 100
gall<ars of water was used after which no burning of the shoots resulted*
Urea alone at the 20>lb* rate caused slight burning, and at the 30-lb*
rate burned so severely that most of the leaves dropped within a few
days after the application had been made*

Since these preliminary trials loc^ced promising, a more detailed
study of the use of sucrose as a protectant against urea burning was
made* Twsnty>two treatcwnts of urea-sucrose cooibinatlons were applied
on Duncan grapefruit leaves* Sach treatment consisted of two shoots,

A and B* Another set of 22 shoots of similar uniforxolty was also

selttctwl as corrbrols* Tha firet appUcation of uroa-sucroaa mixture*
va* ninri* on both shoot* k and B on January 22j 1952« while the secmd
application on January 29# the third on February 5# and the fourth on

February 13# 1952^ were made «i shoots A «3ly*

Shoots B, which were treated with the nixed solution only ono*
on January 22, at no time showed any burning except when the urea
concentration was high# 40 lbs* per 100 gallons of water, in idiich
case burning of leaf tip* was noticed 3 days after the application*
were made. The degrees of burning on shoots A are given in Table 6«

It is apparent that sucrose, when added to the urea solution
appHurt to citrus foliage, prevwated urea burning to some «xt«it. The
highest concwitration of urea used,. 40 lbs, of urea plus no sucrose
per 100 gAiiftns of water, caused moderate burning of the leaves after
only one application. This burning was noticed 4 days after the first
application, and from then on modernte and severe burning showed up
until 16 days after the fourth applicatiwi, when most of the leaves
had dropped off the shoots. When 120 or 100 lbs, of sucrose was added
to this concentration of urea, leaf injury did not appear \mtil 5 days .
after the second spplioatlon. When 40 lbs, of urea and 240 lbs, of
sucrose per 100 gallons of water were applied to the shoots, no burning
of any type was noticed at any tine.

With 30 lbs. of urea per 100 gallons of water, 240 and
100 lbs, of sucrose were added, ik> burning resulted, but when 120 and
90 lbs, of sucrose were added, burning showed up slightly and moderately,
mspectively, after the fourth application of these sucrose coneentm-
tionsj and whan no sucrose was added in the solutioa, burning of leaves

Table 6. Tb« Sffeet of Sueroae on the Beduetlon of Loaf Ihjuxy caused by Sprays cn

I

C9

I

Dm

a

I

Vi

1

A
*c H

o

■ I

g

O

&

I

IT\

i

Dm

#

•g

gr

3

►»

g|g OOH^g OOMMMy ooooooo

m ““•'M

oo

M H H ^ OOOOOOO

oooyg ooMMMjj ooooooo

«»»

O M

o H

HH

OOOOM OOMHHH ooooooo

OOOO M OOHHHM OOOOOOO

OOOO^ OOOHMH OOOOOOO

OOOH ooooo oooooo ooooooo

-st

21

I".

II

iiii

«4

o

I

t

•o

a

' m

I

oe

H

H

s

»0

o.

I

2

«

46

appeared severely after the third application*

With 20 lbs* of urea per 100 gallons of water, when 240 and
ISO lbs* of sucrose were added, no burning was noticed, but when 120,

90, and 60 lbs* of sucrose weze added, alight burning was noticed after
the second and third applications* When xu> sucrose was added to this
concentration Af urea, sli^t buxning resulted after the second
application and by the fburth application had become moderately severe*
With 15 lbs, of urea per 100 gallons of water, no leaf injury
was observed at any time*

In general, idien urea solutions were mlasd with six times as
much sucrose as urea, no leaf injupy to Duncan grapefruit was observed
uxidsr the conditions of this eacperiment*

OP the absorption

Sucrose, magnesium sulfate and lime have been found to reduce
injury is caused by hi^ concentrations of urea sprays on

plants* An atten^jt was made to detexmine the effects of these so-called
protectants against urea spray injury on the absorptim of nitrogen by
the leaves* TrsataMits consisted of t (l)-30 lbs* of urea aloiwj (2)

30 lbs. of urea plu« 180 lbs* of sucrose; (3) 30 lbs, of urea plus
34.2 lbs* of magnesium sulfate (0*05 M solution); and (4) 30 lbs. of
urea plus 3 lbs. of hydrated lime* These amounts per 100 gallons of
water ware applied to the leaves of 2*yeax'"K)ld Valencia trees tdiich
were grotdng in pots in the greenhouse*

The percent of applied nitrogen which was lost during the ab-
sorption period was termed as "percent absorption". The results of seven

- 47 -

D* Tto effects of swrose. aagpeslum sulfate and lime
of nitro/gen 6y eitrue leaves

rone are show in Table 7* The reaulta of analyais of rarlance are
presented in Table 7a« Appendix* >

The differences betveen treateient losans were all significant
at the 1$ level* Apparently^ sucrose and jaagnesium sulfate depressed
the nitrogen absorption considerably* LJjm did not depress the absorp*
tion of nitrogen fr<M foliar applications of urea; on the cmtrary^
it increased the average nitrogen absorption significantly* No leaf
injury vas observed in any case*

Table 7* The Sffects of Sxicrose« Magnesium Sulfate and Lime i«hen added
to Urea Sprays on the Absorption of Nitrogen by Valencia
Orange Leaves

Absorption Period
(hours)

Percentage of Absorption from
Urea Alcme t Sucrose t

<f Lime

4

38.S

29*9

32.2

44*4

26*7

11*8

16.2

30*1

5

46.5

32.2

40.0

46.3

2

34.1

25.8

29.4

36.5

2

30.7

21.6

28.9

34.2

3

28.3

U.3

18*3

28.3

3

26

U.3

21.8

28*3

Average

33.1

21.4

26.7

35.4

L*S*0* — IjC « 1*1$(
5%m 0*88^

fi Tht iffti ir aie«r" i| ,iiHi ■H'"* "»

The ability of stickers to hold deposits through weatlering
and the decrease in surface tensi<m« idiich gives a more even distri>
butlon of the spray droplets on the leaf surfaces^ caused by the

-48-

additi<m of a wsttlng agent to the spray solution are wsU recofTilssad*
Various stickers aiKl wetting agents are being included in spray appli/-
cations for citrus in cooDWxuial practice* It was hoped that the use
of these two oaterlals also luftrove the efficient^^ of urea sprays on

citrus* *

In a preliioinary study^ the effect of sticker and wetting agent
cn the retttitlon of spray naterlal on the leaf surfaces was tested*
Treatawits were as followsi (1)15 lbs. of urea alonej (2) 15 lbs. of
urea plus 1*5 lbs* of Anaour sticker} (3) 15 lbs* of urea plus 4 pints
of Linck W-A wetting agent} and (4) 15 lbs* of urea plus both wetting
agent and sticker* One hundred leaves for each treatment were diH>»d In
the solution In a 100-na* graduate cylinder* The amount of spray soIuf.
tion retained per unit area was measiured for the four treatments* The
resxilts are given in Table 8*

Table 8* The Effects of Sticker and Wetting Agent when added to Urea
Sprays on the Retention of Spray. Solution on Uaf Surfaces

, ' I . »

TreatmKit

< ■ *■

> ml* of Spray Solution
Retained on 1^000 cm?

• *•.

Hean >

Urea Alone

2*86

2*92

t- g

* 2*90

.

Urea ^ Sticker

V *

3.02

3.04

3.06

Urea e Wetting Agent

3.25

3.26

3.27

Urea ^ Both

3.31

3.31

3.31

L*S.D* — I5f s 0*12 nl./l000 cm? 5JS ■ 0*08 nd./lOOG cm^

- 49 -

From prolimiiuay study it waa Isainsd that the addition of

either a sticker or a netting agent to urea sprays retained more spray
material per unit area than did the urea solution alonej and %faen both
of these tno were added^ the amount of spray matexdai vhich can be
retained on leaf surfaces was even mere than when only one of the two
was used.

Further studies on the effect of these two Biaterials on the
absorption of nitrogen by the leaves were made under greenhouse condi-
tions* Treatments applied were the same ae in the preliminary study*

After various periods of time following applications (abaorptioi perioda)^
the leaves were washed and the washings were analysed for urea nitrogen*
The results from this eaqjexdjarat are presented in Table 9*

Table 9* The Sffecte of Sticker and Wetting Agent when added to Urea

Sprayo on the Absorption of Nitrogen by Valencia Orange Leaves

r

Absorptim Period
(hours)

Percenta/:e of Absoz*Dtion from
Urea A1<»m ^ Sticker •»> W*A*

* Both

3

38*1

»

48.4

53*4

66.5

3

40*4

46*6

53.4

66.5

2

41*9

48.9

50.8

53*7

2

41*9

46.9

55*3

56*0

5

51.9

• 53*4

63*7

70*2

Average

42*8

48*8 .

55*3

62*6

r '

L*s*o* — ■ 9*3;;^

m 7.12%.

Significant dif ferencee were found between some of the treat-
ment means (Table 9a, Appendix)* Highest absorption of urea by the
leaves was obtained from the treatment in which both sticker and wetting

- 50 -

agmt were added^ the percent absorption for this treatment being almost
5055 hi^er than in the treatnwnt with urea alone* According to the data
obtained here, the addition of a wetting agent to urea sprays gave a
higher value of nitrogen absorption than did the addition of a sticker
only.

Various coomercial grades of stickers and Lixwk W-A wetting
agent were added to urea spray solutions to coiqpare the effects of these
materials on the absoj^ion of nitrogen. Dipping of the Duncan grape-
ftnilt. shoots in the solutions were made cm August 22, S^«ober 1, and
Septenber 8, 1952, Leaf saaqiles were taken Innediately before and 48
hours after the third application. The' nitrogen increase due to the
treatntnats were measured and the results are sumaarisad in Table 10,

It is apparent that stickers and a wetting agent \dien added to
urea sprays increased the total nitrogen content of the leaves in a
measurable amount as conqpared with leaves treated with sdutlone con>
taining urea alone. Little difference was found between six stickers
tested except in the case of oil emulsion, which ^ve a eocqparativaly
low value. Here again Linek wetting agent gave a higher value of

4 i

nitrogen increase than ell of. the stickers. It was apparent that the
amount of spray solution retained on the leaf surface has a close
correlation to the nitrogm absorption.

In order to obtain values which aze cosapareblo with Table 9>
the amount of nitrogen applied was estimated for treatments with urea
al(»e, urea plus Anaour sticker, and xirea plus Linok W>A wetting agent.
Based on the preliminary data shown in Table 8, the amounts of nltz*ogsn
applied to the leaves for these three treatments could be calculated.

- 51

Table 10« Sffeet of Three AfqpUeations of Urea at a CoocentratloD of 15 lbs* P«r ICX) Gallcne
of Watar« plua Various Coomsrclal Stickers ai^ Linck U<-A Wetting Agent on the
Nitrogen Increase of Duncan Grapefruit Leaves* ^

(Each figure represents the average of 3 saiqples in ag* N/LO esr)

52

For ■jn the case of treatment >d.th 15 lbs* of uj?ea alcne^ the

average increase of nitrogen in the leaves after three appUcatlons was
0,34 ng./lO leaf area. Subtracting the value 0,10 ing,A0 ^

checks from this« the ranaining 0,24 mg*A0 considered as the

nitrogen increase due to the treatment itself. Since 1^000 leaf area
retained 2,92 ml, of the spray solution at a concentration of 15 lbs, of
urea per 100 gallons, then 10 cm^ leaf area retained 0,245 xag* nitrogen,
Thue 0,2/>5 X 3 or 0,735 ng* nitrogen was applied to 10 cm^ leaf area in
three applieati(»is. The percent absorption was then estimated by dividing
the net increase of nitrogen, 0,24, by the amount applied, 0,735> and
nultlplying by 100, Similar procedures were applied to treatments
ecntaining Azmour sticlnr and Linek VMl wetting agent.

As compared with the results shown in Table 9* the lower values
obtalxxed here were thought to be accounted for the translocation of
nitrogen out of the absorbing leaves during the 48»hour absorption
period. Nevertheless there was evidence that wetting agent and stickers
increased nitrogen absorption when these materials were added to urea
solution applied to the foliage of citrus trees,

F, The effects of wetting aaent^sucrose eoifrinations in uf* spray on
the absorption of n^t^^ bv 4«»year^^ sour oranuge eeedii tnge

From the results of previous aocperiaents, it is evident that
wetting agent when added to urea spray soluti(»is enables a more even
distributism and a greater amount of urea to be retained on the leaf
surfaces. As a result of this situation, a higher value of nitrogen
absorption was obtained from urea spray in which the wetting agent had
been added, Cn the other hand, nitrogen absorption by citrus leaves was

- 53 -

depressed ly the addition of sucrose to the urea sprays although sucrose
had been found to be protective against leaf Injtuy caused by high
concentration of urea spray on citrus. An attempt to detexciine the effest
of combining these two materials in ux^ spray on nitrogen absorption
was Tnart.* on, /t^year-old sour oreuige seedlings under field conditi<ms.

Yariotxs treatsttrrts are shown together with the results of leaf
analyses for total nitrogwi and chlorophyll in Tables 11 and 12# Four .
applications of treatments were made, with the first application on
Ilarch 16, the second on liarch 31# the third on June 16, and the fourth
«i June 30, 1952. Leaf samples were taken on the 15th of each month
for total nitrogen and chlorophyll detenoinatiwis starting in lla3*ch
and in October, 1952. The clrcximferonce of the tree trunks, at

a position six above the ground, was also measured on March 15

and October 15 as an index of growth responso of the trees to various
treatments.

Sour orango seedlings treated with 4 applications of urea spray
maintained a satisfactory nitrogen level throu^iout the growing seas<m
(Table 11). It is noted from Figure 9# that wt»n 2 applications of urea
sprays were made in March, the nitrogen cortent of the loaves had in-
creased markedly by April 15 when the leaves were sampled. The trees
then maintained a rather stable nitrogen level vuxtil after May 15#
when the nitzegen content decreased considerably. If no further nitrogen
was applied, the nitrogen level of the leaves would have been decreased
caitinaously at the expense of the new growth which was producwl by the
trees during that period. After two additional spray of urea had been
applied in June, the nitrogen content of the leaves increased again,

- 54 -

and fTGoi than <m tha trees maintained a fairly stable nitrogen level
until October 15 vben the last set of saoplee was taken*

Regarding the effects of various combinations of wetting agent
and sucrose on the nitrogen content of the leaves^ the highest values
were found from treatments with urea plus wetting agents the lowest'
values were obtained frcmi treatiaente with urea plus sucrose, and intexw
mediate values from treatments with urea plus wetting agent and sucrose
and from treatments with urea alone* It is apparent that ths addition
of a wetting agent to urea sprays Increased nitrogen absorption and
the addition of sucrose to urea sprays decreased nitrogen absorption
by citrus leaves, and when both of these materials are added. It seems
that the effects of the two are being neutralised ly each other as
coQ^jared with the results obtained from the treatmenbe where urea was
used alone*

SiAUar results were obtained for chlorophyll cmtent of the
leaves (Table 12 and Figure 10)* The increase of chlorophyll contmat
was maziced in the first few months of the seaswi after applications of
IjuGreen spray were made, but this remained at a rather stable level,
with little increase or decrease after July* This would suggest that
trees with low nitrogen and chlorophyll ccnatent are highly responsive
to urea sprays; however, this responso woe decreased as the nitrogm
content of the leaves was increased to a certain :polnt, srd above this
point, the increase in nitrogen content has little effect on the chloro-
phyll content of the leaves*

The increase of olrcrmiference of the tree trunks, measuzod at
the beginlng and at the end of the growing season, is recorded in

- 55 -

Table 11* The Effect of Wettiiig Agent-Sucroee Additions to Urea Sprays on the Absorption of
Nitrogen by Sour Orange Leaves* (Mg* of N per 10 cia^ of leaf sta*face)

I

•1

RSSS SI

cj i4 H pJi4f4H r4

cj cj cS cj

ciAcic^

e

CO

cj 0? H CM

• « • *

CM CM CM CM

1

<M »4 CM <4

vO P WQ

JJSP-O^O

■ c44^c4

July

fM H CM CM

c444c4

June

WNWN«0 c*

* >A'0 b-

AAAA

CMi4hH

cmMhM

CM HH c4

1

AAAA

• •if

H H H

i

H H f-l H

• if*

r1 H H

„ 8SSS

zzit zzlz

lllll tins

i$]il ijiil

s •!• I 4 I e + I + i

u\

o

«. 56 «•

OTT crt Lo^x 80*1 oz*x o*rx 9^*1

p4

S5JS3 P
444h* -4444 o"

* •

1

9PgP P

■4444 •4444'o

•

1

!!IP$8 P
•4444 -4444 '4

■|

SPPS ?)!3SS5 R
•4444 4444 -o*

1

1

PflKS 43SP P
•4444 4444 <S

P8P4 «83?J S
•44o‘4 4444 o‘

p]|«P

3oOO 'r-<OOr4 O

Apr#

StSPP P^PP P
<3S<i<S <S<loo <S

'i

8^$P P3<}P &

■4444 *4444 4

.Ilk gilli

fiiii liiii

tllll
■fiili fill!

a a 1

» 3 S

J

57

Total Nitrogtn mg./IOcm*

Figure 9* Seasonal Trend of Nitrogen Content of Leaves of Sour Orange
Seedlings Showing Effect of Wetting Agent-Sucrose Additions
on Absolution of Nitrogen fron Urea Sprays*

r

'» Wotting Agofit- Sue root

♦Wotting Agont ♦ Sucrooo

-Wotting Agont— Sucrooo

-Wotting Agont -f Sucrooo
Chock

1

58

Totol Chlorophyll
mg. / too cm*

Figur« 10* Seasonal Trend of Chloropligrll Contttxt of Leaves of Sour
Orange Seedlings ShoMing Sffeot of Wetting Ag«it-Suerose
Additions on Absox^tiGa of Nitrogen from Urea Sprays.

^ ■*> Wotting Agont - Sucroso

'tWotting AgonttSocroo#

-Wotting Agont Sucrooo
-Wotting Agont — Sucrooo
Chock

It* i

59

Table. 33.

Effect of Wetting Agent-Sucroae Additions to Urea Solution
on Absorption of Kitrogon bgr Sour Orange Leaves fjraa
Foliar Sprays^ as Indicated bgr the Increase in Trunk
Circuaferenee of Young Seedlings. (Increase in onu)

Treatoent

Replications

1' j

Ave.

15 lbs. Urea/loo gal.

^ Wetting Agent - Sucrose

2A

aa

2.7

2.5

- Wetting Agent •f Sucrose

2.6

2.3

2.6

2.7

^ Wetting Agent <t Sucx^>se

3.5

3a

3.6.

3.5

- Wetting Agent * Sucrose

2.3

2.3

2.5

10 lbs. Urea/iOO gal.

4- Wetting Agent » Sucrose

3a

2.7

3.2

3.0

<• Wetting Agent 4 ^icrose

2.2

3.0

2.3

2.5

4 Wetting Agent 4 Sucrose

3.3

2.3

2.9

3.0

>> Wetting Agent - Sucrose

3.0

2.0

2.5

2.5

Cheeks

1.6

2.4

2.0

2.0

L.S.O. 0.31 ei&.

^ X 0.22 cn.

60 ^

Table 13* No difference vas found between treatments of 15 lbs« and
10 lbe« of urea per 100 gallons of water (Table 13a, Appendix)* The
addition of both sucrose and wetting agent gave a highly significant
increase in tiuck circumference over spreya containing urea (»ily at
both concentrations of urea. Addition of sucrose only to urea sprays
gave no significant difference, and addition of watting agent alone
gave highly significant increase in trunk circumference with 10 lbs.
but not with 15 lbs. of ujrea.

G. The eff ieje^ of nitrogen ^sorpt^ by /»-yearwold sour orange seed-
lings in relation to the Initial nitrogen «mtent of the leaves

In ccnsidering the data presented in Tables 3 and 4, it was
noticed in many cases that under the same treatamt, when the results
are aoqjressed as percentage nitrogen increase relative to the initial
nitrogen contwit of the leaves, higher values were found in leaves which
had a lower initial nitrogen content. For example (Table 3), the
nitrogen contents of leaves given the 15-pound urea treatment were
2.46, 2.34» 2.49» 2.34# and 2.22] the nitrogen increases for the
respective values were 0.38, 0.?6, 0.35# 0.58, and 1.06 mg./lO cm^.

The percent nitrogen increases were calculated as 15.4, 32.5, 14.1,

24.8, and 47*7# respectively.

It was not possible to develop a relationship between these
two variables due to the limited sise of samples in the S3q)eriment,
which was not designed for this impose] however, further observation
was made on sour orange seedlings to study this matter.

Forty-two trees of 4*ysarwold sour orange seedlings which had
different leaf-nitrogen levels chie to variation in locations and

- 61 -

4irr*ront f«rtUizar praetlevs served as good materials for the study*

A

Applications of xirea spray at a cmoentration of 10 lbs* per 100 gal-
lons of water were made at weekly intezvals starting April 4 and emt-
Ing April 25» 1952* Leaf saoples were taken on April 4# just before
the treatments were made^ and on May 2, 1952f 7 d^ys after the fourth
application of lurea spray*

The results of chemical detenninatlon of nitrogen before and
after four applications of urea spray are given in Table 14* The results
in testing for significance of regression coefficient and correlation
coefficient are given together in Figure 11*

A hi£^t)ly significant correlation (r - •0*945) uas found between
the iid-tial nitrogen content of the leaves and the common logarithm
values of the percent nitrogen increase which was caused by \irea
treatments* regression coefficient was also significant at the 1J(
level (t m 17*68)* The relationship of ti» two is shown graphically in
Figure 11* From these data, an increase in the initial nitrogen content
of the leaves of 0*1 og*/10 cm^ was approocimately equivalent to a de-
crease of 0*02^ cooDxm logarithm value in the relative percentage of
nitrogen increase; in other words, the efficient^ of nitrogen absolution
of the leaves from urea spray, as measured by relative percentage of
nitrogen increase, was decreasing eocponantlally as initial nitrogen
content increased, the logarithm of the relative percent Increase de-
creasing at the estimated uniform rate of 0*442 per milligram of the
Initial nitr(^en content of the leaves*

62

Tabl« 14, Sffoot of Initial Nitrogen Content of Sour Orange Leavee
on the Increase in Nitrogen Content Resulting from
Foliar Spjraya of Urea*

Kitrojen^ a^lO
Initial l<i After

Treatment

ca*^

Nitrogen

Increase

Percent

Increase

Common
Logarithms
of % Ine,

0*84

1.44

0.60

71.42

1.854

0.92

1.57

> 0,65

70.65

1.849

0,94

1.64

0.70

74.46

1.872

0*94

1.69

0.75

79.78

1.902

0.97

1.73

0.76

78.35

1.894

0.97

1.71

0.74

76.28

1.882

0.97

1.65

0.68

70.10

1.846

0.98

1.64

0.66

67.34

1.828

0.99

1.66

0.67

67.67

1.820

0.99

1.50

0.51

51.51

1,712

1.00

1.50

0.50

50,00

1.699

1.01

1.50

0.49

48.51

1.686

1*16

1.74

0.58

50.00

1.699

.1,20

1.77

0.57

47*50

1.677

1.24

1.84

0.60

48.38

1.685

1.48

1.93

0J>5

30.40

1.483

1.60

2.03

0Jf3

26.87

1.429

1.66

2.03

0,37

22.28

1.348

1*66

2.19

0.53

31.92

1.504

-1.66

2.18

0,52

31.32

1.496

1.66

2.10

0.44

26,50

1.423

1.70

2*06

0,36

21.17

1.326

1.80

2.16

0.36

20.00

1.301

1.81

2.16

0.35

19.33

1.286 ,

1.92

2.25

0.33

17.18

1.235

1.98

• 2.31

0.33

16.66

1.222

2.04

2.37

0.33

16.17

1.209

2.16

2.33

0.17

7.87

0.896

2.23

2.41

008

8.07

0.907

2.24

2.42

0.18

8.03

0.905

2.45

2.70

0.25

10.20

1.009

2.50

2.75

0,25

10.00

1.000

2.55

2.80

0,25

9.80

0.991

2.62

2.90

0.28

10.68

1.029

2.88

3.14

0,26

9.02

63

Table 14, Effect of Initial Nitrogen Content of Sour Orange Leavee
on the increase In Nitrogen., Content Reaulting firoa
Foliar Spre^ of Urea -> Continued*

^

,, ... , . . -k

NitroiMn. ng./lO cn^ Coonen

Initial N mer . Nitrogen Percmt Logaritboe

Treatoient Increase Increase of % Inc*

2*90

3.20

0*30

10*34 <

i;OL5 >

3.00

3.25

0*25

d.33

0*921 -

3.02

3.30

0*28

0*967

3.10

3.35

0*25

8.06

0.906

^ 3.20

3M

0*28

8.75

0.942

3.20

3.AB

0*28

8.75

0.942

3.23

3.50

0.27

8.35

0.922 .

Hiiii.iiieiii I ici ^ ■ Ml I ^

•• 64 •»

Figure U« Begressioa of Iiiitlal Nitrogen Content on Relatire Percent
Increaae of Leaf Nitrogen Caused by Urea Sprays in Test->
ing tbe Efficiency of Nitrogen Absorption of Leaves of
Sour Oraxige Seedlings*

65

H> •ffeot of the acidity of the epwar ^

Tn studying iron deficiency in citrus^ Guest and Chapman (23)
found that a given iron spray was more effective if the solution was
acid. Cook and Boynton (13) found on apples that the pH of a urea
spray had a marked effect on absorption under some conditions. They
reported the percent of applied urea which was absorbed as being 61.1^
63*2« and 50.5/^ for I>H 5»U$ 6*6, 7»3« and d.O respectively. As

the result of these studies^ an eoq>erlment was set iip to determine
whether the pH of the urea spray affects the abeozption of nitrogen by
citrus iMves.

Triplicate shoots for each treatmoit from a mature Duncan
grapefruit tree were dipped in 10-lb. urea solutixxis of various degrees
of acidity. Three applications were made at weticly intervals starting
February 12f 1952. Immediately before and 7 days after each s^iplica-
tlon« leaf saoples were taken for total nitrogen determinations. The
urea solutions were buffered and the desired pH values were dtytained
by mixtures of varying proportiwis of sodium borate and hydrochloric
acid. The initial nitrogoi and total nitrogen content after each of
the three applications, together with the nitrogen differences after
treatments, are given in Table 15.

It can be seen fkom the data that the total nitrogen content of
the check leaves decreased markedly during this period. This situation
was associated with the appearance of new growth on the shoots. Since

the ejqaeriment was conducting in the early spring during the growing
season, a decrease in nitrogen «aitent of the older leavee was to be

- 66 -

Table 15* Sffect of of Urea ^ray Solution on Nitrogen Absorption by Duncan Grapefruit
Leaves* (ng*' nA^ csi^

1

s

8

*

&

8PlS

• • •

•

•

O

# # #

CVJ N Ci

CM

CM CM CM

04

rM H H

H

CM H r-4

H

8

o

•

o

ej'O'O

0 O' O'

• • •

01 H H

8

cJ

• • «

CM CM CM

' 1
CM

1.77

1.74

1*60

H

• • •

H CM CM

1

60*0

o

CM -4- CO

CM

CO

8^9

S3

SFi°J

vO

to

»o

CO

•

«0

# • •

Cl ca ci

^el

C^ CM CM

CM

• • •

H H CM

•

H

• # »

H H CM

*

H

.

o

•

• • •

H

•

O 'O >o
rH rM

• ■ •

•

as a

* • «

8

•

aas

• • •

8

•

s

r-

04 CJ CM

CM

CM CM CM

CM

04 H CM

CM

CM CM CM

CM

•

1

o

c^<?8

CM CM CM
COCO H

*n

CM

31^'^

»o

to

H COC;
CO rM O

8

>

•

• • •

CM CM 04

CM

c4 CM <4

•

CM

• • •

H H H

»

• • •

CM CM CM

•

CM

•

9

Bi

o

s

»88

u>

H

8^8

. s

883^

8

8

•

vr\

c4 H cj

#

CM

cJ CM CM

•

CM

c4h4

J

CM CM CM

8

•

O

O

:388

d

>0 'O 'O
H O' O'

A Jk A

s

8 ^ ^

lo

85S3

3

•

* # #

CM C4 CM

#

CM

V V V

CM H r-t

#

CM

H CM

r-4

c4 CM i4

8

o

<*>

m >o >0
o Htr

8

-*vO nO
CMH CO

w>

CM

8

883

8

•

<n

• • •

CM CM CM

•

CM

CM cS CM

•

CM

H f4 CM

•

H

CM 8 8

tP

CM

t

O

•

•

•

•

s

$

$

1

1

•r

■<

■<

e

sO

CM

ir\

u

5

1

Date

•

A

•

JO

ee

#

•8

•

t

1

CO

&M

hi

Cm

67

L,S«0» ^ lj( ■ 0«50 ai«/10 co^ 5^ s 0*36 ng«A0 en^

caqpacted. The shoots which had receivod urea appUcaticos showed an
increase in the nitrogen content of the leaves In all but one case« as
coB^^ared with the untreated checks*

The average increase in nitrogen content of leaves after three
applications^ cocqpared to the controls^ was significant at the 5^ level
for urea solutions at pH 3«3« 4*0, 5*0 and 9*0* At other pU values the
differences were not significant (Table 15a^ Appendix)*

1* CoBg>arstlve studies of foliar and soil appUcations of nitrogen

Duplicate trees of d-year-old sour orange seedlings growing in
pots in the greenhouse were given the following treatments t (1) Urea
spray; (2) Nitrogen fertilization with sodium nitrate to the roots;

(3) Spray plus soil applications of nltrogwni; and (4) Cheeks*

For Treatment 1^ 200 ml* of urea at a concentration of 10 lbs*
per 100 gallons were sprayed on the leaves* For Treatment Z, an eqpal
amount of nitrogen in the form of sodium nitrate was dissolved In a
liter of water and applied to the roots* For Treatment 3« 100 ml* of
urea at a 10-100 concentration were sprayed on the leaves and an
equivalent aooxmt of nitrogen in the fom of sodium nitrate was applied
to the roots* nie treatments were made at weekly Intervals starting
January 20 and ending April 3^ 1952« so that the trees received 10
applications throughout the eaq)erliocnt. The amount of nitrogen which
the trees received was identical in all cases (11*2 grams of actual
nitrogen per tree from 10 applications). Leaf nitrogma, chlorophyll
contentf and dxy wel^t of the trees (Table 16) were measured as the
lesponse of the trees to the treatments*

68

fttct of Soil and FoGLiar Applicationa of Nitrogen on the Nitrogen and Chloropbgrll
intents of the Leaves and the Dry Weight of the Trees of Sour Ch:enge Seedlings*

H

r

CM

II

e

o

d

o

g

U^

H

U

s

'll

ia

I

S3

•t *

&

•M

§

o

CM
t-

• •

o o

AA

c> o

Fig

4o*

• *

CM CM

8 cm

• •

H H

s

«

I

es

• •

O H

h*3I

oM

S4

H H

CM cT

H A

O'

O

s

l»

H O

3^

c^4

3g

4c>

CM

- ^

5 44

•c^

Hf<

O

g

4

II

3S|

4^

4c5

FiS

Rg

ii

33

44

'O o

R

3

>f\

CM

I

I'll

si

• •O'

O O'©

n H 11

CM CM
OC<>M\

00*4

e ■ It

lls

& &

fi p p

Vi M ^

• • •

aacj

a a a

69

Figure 12« Growth Bespoose of Foliar and Soil AppUcatioos of Nitrogsn
of 2-ysai>-old Sour Orange Seedlings in Pot Culture
perioent in the Greenhouse* (Photo taken April 14« 1952)

Pot A» Tree received 10 applications of urea spray at a concen-
tration of 10 lbs* per 100 gallons of water*

Pot Bt Tree received equal amount of nitrogwi In the form of
BOdium nitrate from soil applicaticne*

70

Figore 13* CoByarialon of Growth Respcsise of Foliar Sprays and Foliar
Sprays plus Soli Ap^eatlous of Nitrogen of 2-ysaj>-old
Sour Oraige Seedlings in Pot Culture S^q^erinant in the
Greenhouse* (Photo taken April 14» 1952}

Pot At Tree received 10 applioatioos of urea spray at a oanecg>>
tratlon of 10 lbs* per 100 gallons of water*

Pot Bi Tree received eqiial axsouxit of nitrogen as Pot A but hair
of the nitron was applied as urea spray and half was
a]^;GJ.ed to the roots in the form of sodium nitrate*

71

llarkei differences in nitrogen and chloroj^U increase^ and In
the dry weight of the trees between treated and untreated trees were
observed. The nitrogen increases were higher in Treataaent 3 udiere the
nitrogen had been split into soil and foliar applications, but this was
not significantly different from the other treatowits where the trees
received nitrogen from soil or foliar applications alone, liu signifi*
cant difference was found in chlorc^hyU increase between foliar and
soil apflications, but trees receiving combination applications had a
higher chlorophyll increase than trees receiving only spray applicaticms
of nitrogen, and this difference was significant at the 5^ level. As
in the case of chlorophyll increase, trees receiving nitrogen fnom the
combination applications had produced more dry matter Apnil 15# 1952,
and the higher values for this treatment were statistically oi^iifleant
at the 1^ level. Trees given soil a^plicatlcai of nitrogen produced
i ghtly sore dzy matter than trees given foliar |g>pllcatlon8 of an
equal amount of nitrogen, but the differences were not significant.
Figures 12 and 13 illustrate the growth response of the trees to foliar
and soil applications of nitrogen.

Studies coiqparing the availability of nitrogen from foliar and
soil apflicati(si8 of urea were further carried out under field condi-
tions. TwD-yeazM)ld Ruby grax)efruit trees budded on sour orange root-
stocks ^fere used for this purpose. Triplicate trees received 0.1$ S lb.
nitrogen in the form of urea applied to the roote on April 29, 1952.

In order to eliminate the time effect, four spray applications of urea
at a concmtration of 10 lbs. per 100 gallons were made to triplicate
trees at 2-day intervals starting April 29. One gallon of urea solution

- 72-

Tabl« 17. Effect of Soil and Foliar Applications of Urea on Nitrogen Content of Rulay
Grapefruit Leaves* (Mg*^0 car)

June 10

0 0 H

• - • •

CM tM CM

5

c{

3c5c!

«

CM

C*-vO U>
N cl CM

444

H

June 3

0 CM to
\r\u\^

* * f

CM CM CM

•

OJ

CM CM cl

3

cJ

444

CM

•

H

5

t

CM CM CM

CM

«

CM CM CM

s

c5

^ CM C^

444

4

If

2’

c5 cj CM

•

CM

^SR

CM CM CM

CM

81 fd ol

• -# •

H H H

c^

-#

H

•r

1

3

01

CM CM pJ

rt Hr?

^ n

Sf?8

•* • •

r-i ri H

>«

H

%

1

H Q 0
cn<M cn

c5 CM CM

n

•

cJ

53.ni

H H H

t'-

*3

H

0 0 t-

HHr?

8?

-♦

fH

1

1^1 '
H H H

, 1

i

r"

CM O'O

4hc4

vO

r

r-

0 <5^ at

H H H

n

4

•g

'«

S

i

1

1

H

1

S'

03 .

1

0

0000
II II H II

i

»•

I

Ok

CO

•4

I

••

a

CO

73

ms appLUd to each tree at each application, and so each tree had a
total of 0.1B6 Ih* of nitrogen applied. Another 3 trees served as
untreated checks. Leaf samples were taken at weekly Intervals. The
results of chemical detenalnations of nitrogen are shov® in Table !?•
Differences in level of leaf nitrogen between trees receiving
and trees receiving soil applications of urea were significant
at the level within 6 days after applicatimis h^ been itiade, trees

I

receiving sprsy applications having the higher nitrogen level. The
leaf-nitrogen level of trees receiving the seme amount of nitrogen
appUsd to the soil did not increase until 3 '‘wks after the appUesr-
tioa had been made. This would indicate that nitrogen applied to the
soil nob reach the leaves and be utilised by the tree 'antil 2 »

weeks after applicationj howenrer, once the soil nitrogen reaches ths
leaves they will maintain a sore satisfactory nitrog^ level than
from spray applications. As can be seen fr<sa Table 17, trees receiving
soil application of nitrogwi had a considerabls higher nitrogen con-
tent after May 20 than trees receiving spray applications.

Additional trials with 2-ysarM>ld budded Buby grapefruit trees
were marto under field conditions. Different treatments are sunn
marized as follows:

Treatment 1: Four spi*ay applications of urea at a concentra-
tion of 10 lbs. per 100 gallons of water. Sach tree received approxi-
mately one gallon of spray on April 29, May 6, May 13, and May 20, 1952.
A* total amount of 0.136 lb. nitrogen was applied in U applications.

Trsatmsnt 2t Cns soil application of urea at a rate of 0.4 16.
or 0.136 lb. actual nitrogen, was mads on April 29, 1952.

-74-

Treatnant 3t One soil ai^>Iicatlon on April 29# and tvo spr^ra
' ■ <81 April 29 and Kay 6, 1952* A total aiaount of 0*279 lb* actual nitro-

gen was applied.

Treatment 4t One soil applicatica on April 2), and four sprays
on April 29» May 6j Kay 13» and Kay 20* A total amount of 0*372 lb*
actual nitrogen was applied*

Treatment 5i Two soil appUcations with a total nitrogm of
0*372 lb* were made on April 29 and Kay 13* 1952*

Treatment 6t Untreated checks*

For soil applications* the material was broadcast evenly around
the tree trunk within a radius of 1*5 feet* For spray applications* one
gallon of the prepared solution was applied to tlie foliage by means of a
hand sprayer and the ground around the tree trunk was covered with a
piece of plastic cloth %rtiioh had a diameter of 5 feet to re<lace the spray
material reaching the ground to a mininum* Leaf sanies were taken
periodically for nitrogen determinations. The results are pz^ented in
Table 18* The data are also show graphically in Figure 14 for con-
venience*

Leaf-nitrogen level was significantly higher in treated trees
than in untreated checks* With equal amount of nitrogen fertilization*
trees receiving soil applications had a slightly higher leafwitrogen
level than trees receiving foliar aHjlications thrwighout the experlamt*
Also om a basis of equal amount of nitrogen* four sprays plus one soil
ai^jlicatlon were just as effective as two soil applications of urea*

In almost every case* leaf-nitrogen level of trees receiving
sprey applications dropped considerably after July 15* The nitrogen

75

Tabl« 18. Sffect of Foliar and Soil Applleatlms of Urea on the
Nltrogan Content of Leaves of Ruby Grapefruit Trees.
(Ug. M per 10 cor leaf area)

> * . «
Sampling Date

Treatment

Apr* 29

June 15 July 15

Aug* 15

Sepb, 1

Four sprays

1.71

2*80

*

2*72

2.28

2.12

1.71

2*50

2*38

208

2.00

1*48

2*20

JUIO

2,14

1.88

Ave*

1.63

2*50.

’ 2*40

2.20

2*00

One Soil AppUeatloo 1*41

2*80

2*78

2*70

2*60

1.U

2.71 .

2*69

2*60

2*60

1.29

2.3S

2.14

2.15

Ave*

1.37

2.62

2*60

2.48

2.45

Two sprays plus one

1*20

2*70

2*36

2.30

2*00

soil applioatlon

1*92

3.00

2*99

2,90

2*70

1*21

2,70

3.11

2*90

2.80

Ave.

1.44

2*80

2.82

2*70

2,50

Four sprays plus od» 1*26

3.10

2.70

2*62

2*22

soil application

1.71

3.29

3.30

3.00

2*88

1.54

3.12

3,00

3*08

2*70

Miu.

1*50

3,17

3.00

2,90

2*60

Tmo soil

1*62

3.42

3.30

3.30

3.10

appUeatioos

1*34

3.05

3.00

3.00

3.00

1.26

2.68

2.70

2.70

2*75

Ave^

1*41

3.05

3.00

3.00

2*95

Checks

1*20

1.24

1*18

1.10

1*10

1.40

1*42

i*a

1.15

1*26

1*00

1.U

1*08

1.05

i

Ave*

1*30

1*21

1.24

1*13

lao

76

Figure 34.

Nitrogen Content of Leavee of Subjr Grapefruit Trees
ReeelTlng Foliar and Soil AppUeatlone of Urea«

2 Soil 4 Spray

^pro)^ |"S^I “7 S^r “

77

oaat«nt of Isarres from trees reeelvizig soil appUoation also decreased^
but this decrease was less in eoctent than with the spregr applioations.
It is apparent that soil application of nitrogen sewasd to maintain
a satisfaetozy nitrogen level of the trees for a longer period of time
than spray applications of the same amount of nitrogen*

J* The rapidity of nitrogep, **^***TlrtOKiiil**^ leaves

It has been found that ^Iclntosh apple leaves absorb nitrogen
most rapidly in the first few hours after foliar applications of urea
(13)* Experimental trials carried under greenhouse conditions to see
whether the same is tru« for citrus leaves* In the first test^ urea
solution at a concentration of 10 lbs* per 100 gallons of water was
sprayed on the leaves of d-year-old Valencia orange trees in the green-
house* Leaf samples were taken immediately before and 1« 3* 5> 7 Ixmrs
and If 3# 5« snd 7 after application* Ho siguificant differ«iee
in nitrogen inezuase was found even after the 7-^^ period (Table 19)«
IMs finding has confirmed the results obtained in previous eoqjeri-
msntSf that (me application of urea spray did not increase the nitrogen
content of the leaves by a measurable amount*

Jh the second testf know amoimts of zzltrogen in the fora of
urea were painted on the leaves. The leaves were then thoroughly washed
with deionized water at various intervals* Chemical determinations of
urea nitrogen ware made on the washixigs* The percent of applied nitro-
gen which was absorbed by the leaves is presented in Table 20*

Immediate absorption of nitrogen by the leaves can be seen
fxum this table* Even by the end of the first hour of afplicationf as

- 78 -

ouch as 14«6^ of ths appliad nitrogen had been absorbed. Harked 1a»
czwse In the rate of absorption vras found 3 hours after application.
The absorption rate was progressively higher as the absorptlcai period

was increased with the exception of Treatment
were washed 3 days after the application. The
leaves was continuously absorbed until 7 dsTa
at which tixM 26% of the applied nitrogen was
surfaces.

where the leaves
nitrogen applied to the
after the application,
still found on the leaf

Table 19* Nitrogen Content of Leaves of Valencia Orange Trees at
Various Intervals after the Application of Urea Spray
at a Concentration of 10 lbs, per 100 Gallons of Water,
(Hg« N per 10 cnT leaf area)

Interval

-A

Dec, 25,

PH

Jan. 9. 1952

iNweii

Mar, 3. 1952

Iniiial .
Nitrogen

N After
Treat.

Initial

Nitrogen

N After
Treat.

Initial

Nitrogen

N After
Treat.

1 hour

1.53

1.52

2.22

2.22

2.52

2.50

3 hours

1.A1

1.41

2.13

202

2.40

200

5 hours

1.5^^

1.55

2.04

2.05

2.61

2,64

7 hours

1.59

1.60

2.31

2.31

2.34

2.34

1 day;

1.53

1.55

2.16

2.18

2.37

2.35

3 di^

1.60

1.60

2,30

2.30

2.52

2.54

5 days

1.26

1.25

2.29

2.30

2.70

2.73

7 days

1,29

1.31

2.40

2.37

2.54

2.55

No significant difference between treatments.

79

Tabl* 20, /Percent of Applied Nitrogen Absorbed by Valaaoia Orange-
Learee at Varloua Intexrals under Greenhouse Conditioos.

Interval

July 3# 1952

Aug. 5, 1952

SepU.27, 1952

Ave.

1 hour

17.5

14.9

H.3

14.6

3 hours

42.7

40.2

40.5

a.i'

5 hours

45.6

54U.

42.8

47.5

7 hours

46,5

64.2

50.2

53.6

1 day

64.1

73.1

56.4

65.2

3 days ’

86.3

86.4

67.6

80.1

5 days

75.5

72.5

69.7

72.6

7 days

76.8

77.1

68.2

74.0

L«S»D« for treatment meanst

m 1.26%

5% = 0.91S

Along with the absorption rate studies « an attesqpt was made to
stxidjr in some detail how rapidly the absorbed urea would be translo*
oated to the other parts of the tree from the absorbing leaves. Sets

of leaf samples were taken for initial nitrogen determinations. Know

amounts of urea nitrogen were brushed on the leaves^ and the amounts

\ -Vi. ..

of nitrogen absorbed were determined for various absorpti(»i periods.

». t *. w w

At the end of each absorption period the leaves were san^^led^ and the
water-soluble and the Insoluble portions of nitrogen in the leaves were

determined. The data of this eocperiraent are presented in Table 21.

A consistent trend of nitrogen absorption as a function of time
was observed, i.e. higher absorption rates were found with longer
absorption periods. On the other hand, the percent of absorbed urea
nitrogen which was still in water-soluble form in the leaves decreased

80

08 tbs Isngth ot tisw after application increased. The total nltrogna
content showed little increase after urea applications* This would
suggest that the oaior portlcm of the absorbed urea nitrogen is
promptloT translocated out of the absorbing leaves^ and^ that this pro-
cess is continuously tAMng place until at least 120 hours or 5 days
after application,

^ . • » •

31 •

Tranalocatlon Studies of the Absoz4>ed Urea in Valmeia Orange Leaves

i

I

i

I

af

t

8

5^

m

|i

»

i

I

8S 8^ 8d 8Sl S:8 &8

CM CM H H

hM c^4 ‘ciA

• •

H <M

H-4- -*co w>H C-vx

^ NO Q p c{

9!

to t^

• *

o o

O CM

- * •

S'-

cS6

so>n

H • • .

H H

ON

c»\

I

« •

lA WN

HH

»A»f\

C^CM

’ • •

_ . , <<x >A

r-c- NO u>

cn

S8

88

4i4

5 il fl

CM CM

• • < • •

CM r«l H H

>0-* On'CM HnO cmo cmh -*<0

» *' «• -*• •• «•' ••

^

ON so

CM CM

&

• • • •

C^CCX C*X«<X

«A «A

UMA

• •

»A«rN

<A N©

3

o t^

• •

wxux

pi

cj c5

S:^ So8 S8 Sigi 8^8
4c4' 4h h4 c^cm*’ 44 4c^ -• •

CM H

H CM ^-<^

• • • •

ONr-

1"^

83

giSr

<5o

f

u\L

to -it

• •

CACA

• •

UMA

82 «.

Percent of applied nitrogen which was still in water-soliible fomu

V. DISCUSSIOM

Posslbl* errors in sampling procedure might exist on a few

instances where high urea concentrations were applied* With the re»

«

sultant effect of leaf drop trom high concentrati<xx of urea sprays*
it was not always possible to take the second set of samples Troa. the
earns leaves from which the first set of samples had been taken* In
this case* a small variation in nitrogen content due to the variable
thickness of individual leaves is to be eoq^ected* However* since the
magnitude of leaf thickness is so small in ordinary citrus leaves
(average less than 1 mm*)* the variation in total nitrogen content of
the leaves is considered to be unijq>ortant*

Foliar applications of nitrogen in the form of urea have been
reported to be successful on some plants* The i^esults reported herein
have indicated that citrus trees are also responsive to nitrogen
sprays* The ability of plants to withstand a given concentraticm of
urea spray varies slightly even within the genus Citrus* Grapefruit
and oranges are tolerant to somewhat higher concentrations of urea
than tangerines* The factors which control the resistance of leaves
to urea injury are not known*

The response of citrus to urea spray was measured by the ni-
trogen level and chlorophyll content* as well as by the dry matter

(

produced by the trees* In one case where grapefniit shoots were treated
with urea at a concwitration of 5 lbs* per 100 galltms, the nitrogen
content of the leaves did not increase significantly when the leaves
were sampled d d^s after the fourth application (Table 3)* In another
case where the grapefruit shoots were treated with urea at the same

- $3 -

concontratifm« the nitrogen content of the leaves inczvased by a
significant amount when the leaves were sashed 2 days after the third
application (Table 4). Since one of the characteristics of nitrogen
BMtabolism in plants is its translocation frcoi one part of the plant
to another^ the lack of an increase of nitrogen in the leaves to a
measurable amount in the first case was thought to be due to the
prolonged time before sampling* Later studies demonstrated that only
7*9 * 19«7!l( of the absorbed urea still remained in a watez^soluble
form 5 days after application* and the sprayed leaves failed to show
any measurable increase in total nitrogen level (Table ZL)* These
findings suggest that a major portion of the urea taken into the leaves
and thought by Co<^ and Boynton (13) to be converted into non-soluble
protein might have bem translocated out of the leaves during the
longer absorption periods*

, Two types of experiments have been used in studying the absori>>
tion of nitrogen by the leaves* In the first type* a known amount of
nitrogen was applied to the leaves* and the leaves were then washed
with portions of deionized water at certain intervals. The difference
between the amount of nitrogen applied and the amount presmt in the
washijags was considered to be the amount of nitrogen absorbed by the
leaves in that particular period* and the results were reported as
percent of applied nitrogen which was abeozbed by the leaves* or per>
cent abeorptioa* As Cook and Bf^ton j(13) stated* "The disappearance
of nitrogen trom. the leaf surfaces was attributed to (a) absorption by
the leaves* (b) adsorption on the leaf surfaces by a force great enough
to resist the washing* or (c) release from the leaf surfaces as

— 34 —

vapor through the action of urease"* It was assuiaed that surface ad-
sorption without subsequent absorption by the leaf was not inportant*
Also no msasurable amounts of anmonia released by the action of urease
were found over a ten-day period by Cook and Boynton* Thus the loss of
nitrogen on the leaf surfaces after the applicatimi was considered to
be the amount which was absorbed by the leaves* Results froa e3q>eri-
mants of this type indicated that leaves absorbed nitrogen froa a
single application of urea (Tables?* 9* and 20)* In the second type
of experiment, the initial nitrogen of the leaves was determined
before any treatments were made, and the nitrogen content of the leaves
after treatment was also determined* Results of this type of experi-
ment showed that the nitrogen increase of leaves due to foliar appli-
cations of urea was not a measurable amount until two or three appli-
cations had been made (Tables 4 and 5)* This would lead, therefore,
to the conclusi<m that absorption of nitrogen by citrus leaves oce^lr8
idien a single application of urea spray is made, but that the amount
absorbed frua a single application at concentratiais of 10 lbs* or
less per 100 gallons is not great enough to cause a significant dif-
ference in the total nitrogen content of the leaves even in the first
day or two following application*

Injury of citrus leaves flnom urea spray can be reduced to some
extent by the addition of sucrose in the spray solution (Table 6)* Two
possibilities might help to explain this situation. The first is of a
physiological nature, while the second is purely a physical p)Mnomenon*
i!bm»rt and Klinker (20) thought that higher concentrations of carbo-
hydrates must be present in the leaf tissues to combine with the urea

9s it enters the tissue if burning is to be prevented* Results of their
esqperinents idth tomatoes shoiesd that leaves absorbed sucrose Arom
spray applicaticns and that addition of equimolar quantities of sucrose
in urea sprays permitted ten times as high ccmoentrations of urea to
be applied >rithout leaf injury as could be d<me with sprays coitaining
urea only* It is possible that the reduction of urea injury by the
addition of sucrose to the sprays is due to a better vttilisation of
urea nitrogen in the loaf tissues* Purthermoref the possible meta-
bolism of urea in plants is likely to cmisist of the following bio-
chemical changes!

Urea

W

(urease)

( 4 o(- ketoglutario acid)

V \v^

%

( <f Fumaric acid)

■" (ILutamie acid

(Krebs

cycle)

\

\

\\

Aspartic acid Oxaloacetic acid

'}

\

A>ginine

In these biochemical reactions, the required «(-ketoglutaric acid,
ftunaric acid, or possibly still other plant acids are intermediate
products of carbohydrate metabolism* Accordingly, if there is an
Insufficient amount of these reqjiired plant acids which wcmld cooibine
with the from the hydrolysis of urea to form subsequent
acids, the excess MhJ dissociates with the liberation of free antaonia,
and the injurious effect of free ammonia to leaf tissue is easily

- R6 -

recognlMd. Thus, the addition of sucrose or other oarbohydrates to
urea sprigrs to furnish sufficient amounts of the materials which are
required hgr the metabolism of urea in plants seems to be a logical
means of preventing urea injury*

Table 7 shows that sucrose depzessed nitrogen absorption by the
leaves to a certain extent* Similar results have been reported on apples
and tomatoes (13, 43)* It seems that the reduction of leaf injury
caused by the addition of sucrose to sprays might be due in part to the
direct reduction of absorption of urea ty the leaves.

In studying the effects of sucrose, magnesium sulfate and line
on the absorption of nitrogen, it was found that sucrose and magiMsium
sulfate depressed the rate of nitrogen absorption to various degrees
(Table 7)* Kreuz (39) in studying the cells of Tradescantia elongate
and Taraxacum officinale found that dextrose definitely decreased
the peroeabllity to urea, the decrease being greater as the proportion
of dextrose increased* He also found that the pexmeability of highly
permeable tissues was more reduced ly dextrose than was that of less
permeable tissues* Apparently, magnesium sulfate has a similar effect
on the permeability of cells* It has been demonstrated by Brooks (U),
that certain elements are capable of preventing or reducing the
penetration of dyes into the cell; potassium, calcium, sodium, and
magnesium chlorides all cheeked the penetration of the dye into

the living cells of Nitella* On the other haxui, hydrated lime vdien
added to urea spray did not reduce the rate of absorption by the leaves*
In five of the seven runs, lime increased the percent absorption of
nitrogen slgniTloantly* This situation might be explained by the

87

results Thowi in Table 15* The nitrogen absorption vas found to be
much higher at pH 9*0 than at 3«0. A water solution of urea has
and addition of line in this case raised the pH to 10. 5* Presumably
the higher absorption at pH 9*0 continues to be effective also at
higher pH values.

The addition of stickers and a wetting agent to the spray solu-
tion has been found to increase nitrogen absoxption by the leaves
from urea sprays (Tables 9 and 10). This Is probably due to the ability
of the sticker to hold deposits throixgh weathering and the decrease in
surface tension^ which gives a more even distribution of the spray
droplets cn the leaf surfaces^ caused ly the addlticm of a wetting
agent. Since most of the urea nitrogen applied can be absorbed ty
(^trus leaves in the first few hours after application^ as shorn in
Table 20, weathering of the spray residue Is not an iiq)ortant factor]
and It appears that the use of a wetting agent to furnish a more even
dl8tvibuti(»i of spray material on the leaf surface Is of beneficial
in this type of spray applicatlcms.

The efflcioicy of nitrogen absorption was found to be higher in
trees which had a lower initial nitrogen content (Table 1<»). !Rie tem
“efficiency of absorption" Is used in oxder to distinguish froa “percent
absorptlcn" idilch was used by Cook and Boynton (13)« In their work
with apple treeSf they found that there was a direct relationship
between high urea absorption and high Initial nitrogen level when their
restilts were eaqsreased as percent of applied nitrogen which was ab-
sorbed b7 the leaves. In tlM experiroent reported here^ the actual amount
of nitrogen applied to the leaves was not known, but the Initial

— 33 —

nitrogen content of the loaves before appUeation was determined. From
the total nitrogen content after ai^jlications of treatment and the
initial nitrogen content of the leaves^ the net increase of nitrogen
could be calculated. The percent nitrogen Increase relative to the

nitrogen , content of the leaves was then estimated by dividing
the net increase with the initial nitrogen content of the leaves. Since
different approaches were used, the results from these two types of
experiment are not comparable.

The data shown in Table 15 indicate that the pH of the sproy
solution has a definite effect on the absorption of urea by the leaves.
The treatment at pH d,0 represents closely the value of an unbuffered
urea solution. Change in pH in either direction seemed to increase
absorption by the leaves, with increases significant at the 5% level
for pH 3,3, 4.0, 5.0 and 9,0, While Cook and Boynton (13) found on
apples that there was relatively high absorption at pH 5.4 and 6,6
with little difference between them, a low value at pH 7.3, and an
intermediate value at pH 8,0, Drawert (18) in eocperimenting with the
epidermal cells of Sedum praealtvua. Triticum vulgare. Allium cepa, and
Blodea canadensis imasrsed in urea solution. He found that at a given
pH of the immersion solution, urea is taken \q> more rapidly as the
acidity of cell sap increases. Cells with sap of a given acidity take
up urea more rapidly as the alkalinity of the immersion solution ln~
creases. The effects or interactions between the acidity of the cell
sap and the acidity of the spray solution are obvious. Results obtained
here idiere the value of nitrogen increase is higher at 9.0 than at
8,0 are in accordance with Drawert* s fiiwiings; however, the increase

of nitrogan at lowr pH 3.3 and 5*0 fflist be attributed to soae other
factors idilch are not yet fully understood* Those values are aore In
agreement with the work of Cook and Beaton, cited above, but no
miwtmnm at 7*0 WHS observed*

An att«a^>t to compare the effects of foliar and soil applicar-
tions of urea in sand cultures of citrus in the greenhouse failed.
Throe pots of 2-yearw>ld sour orange seedlings had received 210 p*p*iiu
nitrogen in the form of urea froa the nutrient solution applied at
weekly intervals starting March 12, 1952. The growth of these 3 trees
was excellmit during the first 3 months of the eaqperimsnt, but about ^
the middle of July, 1952, all three trees wilted and they died within
one month* Examination of the roots showed that symptoms similar to
those caused by onygen deficiency were present* Chemical analyses
indicated that the concentration of nitrite nitrogen of the sand from
these 3 pots which had received urea from the nutrient solution ranged
from 14 to 25 p*p*m. As coQQ>ared with the concentration of nitrite
which ranged from 2 to 4 p.p*m* in pots receiving no urea from soil
applloatlon, the accuimmilatlan of nitrite in the first case was con-
sidered to be rather hi^* Biteover and Wander (6) thou^t that the
toodlc effect on the urea-supplied plants was probably due to a lack of
sufficient oKygen about the roots, but there is also the possibility
of a direct injurious effect by the high concentration of the nitrite
present*

In the soil, urea is transformed into ammonia and subsequently
into nitrates* The process includes both aomonificatlcm and nitrifi-
cation, and various laicroorganisms are involved* If the microorganisms

- 90 -

which are required for the coo^Ietlaa of nitrification are absent or
conditions are unfavorable^ as ess thought to be the case In the
veil-washed sand used in the pot cultures^ the process would not be
completed and an accuomlatlon of nitrite would result*

91

VI. SUMMARY

!• Citrus leaves absorb and assimilate nitrogen fiw sprays

of urea*

2* Concentrations of spray solution hi^r than 20 lbs* of
urea per 100 gallons of water cause injruy to citrus leaves* Tan-
gerine leaves are somewhat more easily injured than orange and
grapefruit leaves*

3* Additlcm of sucrose to tt» urea spray decreases leaf in-
jury} forty lbs. of urea plus 240 lbs* of sucrose In 100 gallons of
water caused no injury when sprayed on leaves*

4* The use of higher concentrations of urea spray made possibly
by the protective action of sucrose resulted in greater increases in
nitrogen^ although at any given concentration of urea the addi-
tion of sucrose reduced sonodiat the absorption of nitrogen ftom urea*

5* Magnesium sulfate and hydrated lime both reduced Injury to
leaves from urea spraye, the former depressing nitrogen absorption
somewhat and the latter increasing it sli^tly*

6* One and two applications of urea at ratea of 10 lbs* or less
par 100 gaTimnw produced no measurable resp<m8eBj but three or more
applications even when used at a rate of 5 lbs* per 100 gallons caused
increases in nitrogen and chlorophyll content of leaves* These increases
were progressively greater as the nuid>er of spray applications Increased*
7* Addition of a wetting agent to the spzay soluti(m maz^ed-
ly increased the abaorption of urea nitrogen by leaves* This effect
was further Increased by addition of a sticker* In sprays combining
wetting agent and sucrose the former modified the depressing effect

92

of th« l&ttor*

8« Loaves low in nltro^ showed a greater efficiency of '
nitrogen absorption from urea spirays than leaves high In nitrogen^
when efficient Is aeasured by the percent of nitrogen Increase re*
latlve to the Initial nitrogen level of the leaves.

9« Absorption from urea sprays Is significantly greater below
pH 5.0 and above pH 9*0 than at pH d.O^ which Is close to the reaction
of an unbuffered urea solution.

10. For equivalent amounts of nitrogen applied^ little dlf*
ference was found In the total Increases In leaf nltrogm and
chlorophyll contents between applications to the soli and to the
leaves. However^ during the first two weeks after appUoatlon the
response was more rapid to foliar appUeations» while soil applications
produced a note lasting effect and gave higher leaf values after *
the third week.

11. Absorption of nitrogen from xxrea sprays was readily
measured within an hour after appUcatlGn« and continued for at least
7 days at a steadily decreasing rate.

- 93 -

VII. LITmTURK CITia)

!• Anderscmy P. J. and T* R. Swanback* RalatlYe crop-producing capa-
city of ur«a and cotton oeedneal. Conn. Agrle. Rxpt. Sta, J
Bui. 229-34. 1942.

2. Andrews^ W. B. The response of soybeans to sources of nitrogen in

the field. J. Aiaer. Soo. Agron. 779-36. 1933.

3* Aslanyan^ G. Ch. Urea and its derivatives as fertilizers. Trans.

Sci. Inst. Fertilizers Insectofungicides (U.S.S.R.) 136 t
165-73. 1937. (Chea. Abst. 22* 1^3. 1939).

4. Audus, L« J. end J. H. Quastel. Toxio effects of azzdno acids and

amines seedling groirth. Nature 1^: 22:^23. 1947.

5. Belskii^ V. P. Field tests with urea. Trans. Sci. Inst. Fertili-

zers Insectofungicides (U.S.S.R.) 136> 174-31. 1937*

(Checu Abst. 22* 1363. 1939).

— 6. Bitcover^ S. H. and I. ¥. Wander. Soom observations on nitrite

formation and the absorption of nitrogen citrus. Plant ./
Physiol. 22* 461-68. 1950.

7. Bordas^ J. and G. Hathien. Action of urea upen the Quatemazy
alluvial soils of Cosobat-Venaissin. Amer. Sci. Agron. 46:

561-74. 1929.

3. Bordenj R. J. Forms of nitrogen for sugar cane. Hawaiian Planter’s

Record 81-8. 1940.

9. Boynton, 0. and S. Fisher. Nutrient foliage sprays in the apple
orchard. Hort. News 22* 2425, 2427-28, 2ii30, 2A35 and
2444. 1951.

10. Breon, W. S., W. S. Gillan and 0. J. Tendam. Influence of phos-

phorus supply and the fom of available nitrogen on the
absorption and the di8tributi<ni of phosphorus by t}» tomato
plant. Plant Physiol, l^i 495-506. 1944.

11. Brooks, M. M. Studies on the permeability of living cells. VIII.

The effect of chlorides upon the penetration of into

Nitella. Protoplasma 2i 420-27. (Biol. Abst. 2: 9334.

1943).

12. Coo9}ton, 0. C. and 0. Beynton. A rapid method for the determina-

tion of chlorophyll in apple leaves. Proc. Amer. Soc. Hort.

Sci. 45-50. 1945.

13. Cook, J. A. and 0. Bqynton. Soas factors affecting the absorption

of urea by McIntosh apple leaves. Proc. Amer. Soc. Hort.

Sci. 22* 32-90. 1952.

94

14* Cotton, R. H# Doternination of nitrogen, phosphoriie, and potaesiTan
In leaf tissue. Application of lalcromethods; Ind. £ng.

Chea,} Anal. Ed. 12.: 73V-38. 1945*

15. Daiaodaran, K. and T. R. Venketesan. Urea formaticm in genainatlaig

seedlings. Proe. Indian Sel. Congr. 2d. Paper No. 32. 1941.
(Chen. Abst, 16: 17039. 1942). .

16. Damodaran, M. and T. R, Venkatesan. Andde synthesis in plant. III.

Urea formation in seedlings. Proc. Indian Acad. Sci. See. B.

rr? (1): 26-32. 1948.

17. Decent » w. D. and K, B, Sturgis, Anhydrous anmcaiia and other

jtaterlals as a source of nitrogen for sugar cane. Sugar J.

12 (11): 16-7. 1950.

18. Drauert, H. The absorption of substances by the living plant cell,

III, The effect of the hydrogtti icsi concentration of the cell
sap and of the enviroaent upon the uptake of urea. Plants
2^1 579-600. 1948. (Chem. Abet, 5852, 1949).

19. Bckerson, S. U. Conditions affecting nitrate reduction by plants.

Contrib. Boyce Thoo^), Inst. 119-30. 1932.

20. ^icMirt. £. K, and J. S. Klinker. Spraying tomato foliage with

sucrose to increase caxtwhydrates axui protect against injury
by urea sprays. Ky. Agrle. Bxpt. Sta. Bui. 550. 1950.

21. Fisher, £. G. The principles underlying foliage applications of

urea for nitrogen fertilization of the McIntosh apple, Proc.
/uaer. Soc, Hort. Sci, 22* 91-8. 1952.

22. Fisher, E. G., 0. Boynton and K. Skodvln. Nitrogen fertilization

of the McIntosh apple with leaf sprays of urea, Proc. Amer.
Soc, Hort. Sci. 21s 23-32. 1948.

23. Fisher, £. G. and J, A, Cook. Nitrogen fertilization of the Mc-

Intosh apple with leaf sprays of urea II. Proc. Amer. Soc.
Hort. Sci, 2^: 35-40. 1950.

•

24. Fleming, K. K. and R. B. Alderfer. The effects of urea axA oil-

wax etoulsion sprays on the performance of the Concord grape-
vine under cultivation and in Ladino clover sod, Proc. Amer.
Soc. Hort. Sci. 2^: 171-76. 1949.

25* Foss, R. Urea fonaation ai^ metabolism of purine nitrogen in plants.
Conpt. rend, 208: 865-68, 1939. (Chem. Abst. 33: 4627,

1939).

26. Gilbert, F. A. Mineral nutrition of plants and animals. P. 12.
U^versity of Cklahoma Press. 1949.

- 95 -

27* Greavas^ J« £• Agricultural bacteriology* Lea & Febiger* 1922*

2B» Guest^ P. L* and U* S. Chapman* Inveotigations on the use of iron
sprays j dusts> and soil applications to control iron chlorosis
of citrus* Proe* Amer, Soo« liort. Sci* 11-21* 1949*

29* ilaaSf A* R« C* Nutriticmal aspects in mottle-leaf and other

ptK7Bi<>logical diseases of citrus* Kilgardia 6: 4$>-559«

1932.

30* UaaSf A* R* C* La^rimental applieati<m of urea to lemon leaves*
Calif. Citrog* 2^: 286 and 318. 1949.

*

31* iiomilton, J* K*j D* H* Paloiter and L* C* Anderson* Preliminary
tests with Uramon in foliage sprays as a means of regulating
the nitrogen supply of apple trees* Proc* Amer* Soc* Horb*
Sci* 123-126* 1943.

32* Hamilton^ J, H*; D* H* Palmiter and L* 0. Weaver* iivaluation of
fermate for the control of aople scab and cedaivapple rust
fungi* Phytopath* 22* 5. 1943.

33. Howard, J* Feeding trees with nltrogmi foliage sprays* Amer* Fruit

Grower 2: 24 and 43* 1951.

34. Jamieson,V* C* The detenaination of nitrate, nitrite, and

urea nitrogen in sandly soils* Unpublished* Fla* Citrus
i£xpt* Sta* Progress Report*

35* denies, H* U* Some transformations of lurea and their resultant ef-
fects on the soil* Soil Sci* 2i* 281-99* 1932*

36* Jones, K* W* and R* R* Parker* Nitrogen for orange trees, experi-
ments on the use of urea applied to the foliage as a source
of nitrogen now under stuety* Calif, Agric, 3^: 13* 1949*

37* Kleberger* The decomposition of urea in sand cultures and in soil*
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2522. 1929).

38* Krass, H* J«; V* L* Gaddy and K* G* Claxic* A direct synthetic urea
process. Ind, and aig* Ghsm* 289-93* 1930.

39* Kreuz, J* Der Mufluss von Calcium und Kalium-Salzen auf die Pe]>>
jiieabilitat des Protoplaamoe fur Hamstoff und Glycerin*
Oesterreich Bot* Zeitschr* 90(1): 1-30. 1941. (Biol* Abet.
16: 17039* 1942).

40* X/ewls, A* ii* The fertilizer value of some concentrated materials,
particularly urea and guanidine and their nitrates and phos-
phates. J* Agric* Sci* 26: 509-26, 1936*

- 96 -

41. Llttauer^ F* Dacomposition of usrea in tho soil. 2tschr. Pflan-

sonemahr. u. Dungung 2;Ai 165-79* 1924*

42. Mack, 0. L. and M. J. tihaulia. Nutritional sprays on grapes.

Phytopath. 22* 1947*

43. Montelaro, J. Nitrogen nutrition of tomatoes with foliar sprays of

urea. Unpublished. Ph. D. dissertaticm. University of Florida.
1952.

i»4. Newton, W. and J. £. Bosher. Growth stimulaticm in iris bulbs by
urea. Sci. Agric. (Ottawa) 26(7) » 300-2. 1946.

45. Palmiter, D. U. Soil and foliage applications of nitrogen for

apple scab control. Farm Research 16( 1 ) : 628.. 1950* •

46. Panganiban, S. H. Temperature. as a factor in nitrogen changes in

the soil. J. Amer. Soc. Agrm. 17 1 1-31. 1925*

47. Pirone, P. P. Now they're feeding plants through the leaves.

Popular Gardening, iiay^June. 1950.

48. Prince, A. L. and H. W. Winsor. The availability of nitrogen in

garbage tankage and in urea in comparison with standard
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49* Proceedings of the Twenty-Seventh Annual. .*{eeting of the National
Joint Coiaaittee on Fertilizer Application* 1951.

50. Proebsting, k. L. Nitrogen sprays, tests reported with fertilizer

containing 44^ organic nitrogen. Calif* Agri* 5(3)» 12 and
43. 1951.

51. Rodney, D. R« The entrance of nitrogen ccoipounds through the

epidermis of apple leaves* Proc. Amer. Soe* Hort* Sci* 59 »
99-102. 1952.

52. Hotinl, 0. T. and F. Sessa* The ureolytic action of arable soil*

Chimica e industria (Italey) 3-6. 1943* (Chom. Abst.

28: 6458. 1944).

A

53. Sen, P* K. The injectl<m of individual branches of a tree which

has not been spu]>*pruned* Progress Report. Ann. Rept. fiast
Hailing Research Sta* Kent. 171-3* 1936*

54* Silberstein, 0. and S. H. Wittwer* Foliar application of phosphatlc
nutrients to vegetable crops. Proc. Amer. Soc. Hort Sci. ^8:
179-90. 1951.

55. Skok, J. Effects of the form of the available nitrogen on the cal-
cium deficiency lymptoms in the bean plant. Plant Physiol.

16: 145-57. 19U.

- 97-

56« Smithy A* A study of tho factors influozxcing the efficiency of
different forms of nitrogen as related^ to soil type and
croplng systm in the Atlantic Coastal Plain Region^ Part !•
Soil Sci. 137-60* 1927*

57* Snedecor^ G« M. Statistical Methods. Tlie Iowa State College Press*
1950.

53* Srivastava, U. N. and tf. A. Hoach. The injection of individual
branches of a spur-piMned pear tree* Progi>ea8 Report. Ann*
Kept, i^t Hailing Reasearch Sta* Kent. 167-70. 1936*

59. Staten, G. A prellBiiixary report on spraying nitrogen fertilizer <xi

cotton* New Mexico Agric. £xpt. Sta* Press* Bui. 1048* 1950.

60. Stoddard, j£* H. Fungicidal synergism between urea and sulfUr.

Phytopath. I^Ot 27. 1950*

61* Toknoka, H* and H* Morooka* jSffectiveness of urea nitrogen for
rice. III. Comparison of urea-gypsum and anBaciiium sulfate
for varieties of rice. J. Soc* Trop. Agric. Taihoku Imp*

Univ. 8i 197-210* 1936* (Chem* Abst. 1381. 1938)*

62. Turchin, F. V. Transformations of urea in the soil. Udobrenie i /
Urazhai 2,t 555-61. 1931* (Chem. Abst. 26: 2265. 1932).

63* Vanselow, A* P. Preparation of Nessler’s reagent. Ind. £hg* Chem.
Anal. :Sd. 12* 516-17* 1940*

64. Maksman, S. A. Principles of soil microbiology* Williaiiis 6 Wilkins

1927.

65. Weinberger, J. H*j V. S, Prince and L« Haves. Tests on foliar fer-

. tllization of peach trees with urea. Proc* Amsr. Soe. Hort.

Sci* 26-28. 1949.

VIII. APPiSKDIX

Table 3e. AmOysle of Variance! Hitrogan Increaae of Duncan Grape-
fruit Loaves after Four Applications of Urea of Various
Concentrations •

Source of
Variation

Degree of
Freedom

Sum of
Squares

Mean

Squares

tipn

Value

Total

34

6.032

Treatment

6

4.740

0.7900

14.62**

Replication

4

0.002

0.0005

0.09

Error

24

1.290

0.0540

Leaert Difference Required fca* Siffiificance Between Treatment
Means: TS m 0«i»14 mg,/2X) esr

5% s 0.305 fflg./lO cm2

Table 4a. Analysis of Variance: Nitrogen Increase Of Duncan Grape-
fruit Leaves treated with Urea Solution at a Concentration
of 5 lbs. per 100 gallons of Viater.

Source of

i. ..

Degree of

Sum of

Mean

NpN

Variation

Freedom

Sqiuares

Squares

Value

Total

26

1.9245

8.52^

Treatment

8

1.4936

O.I867

Replication

2

0.0804

0,0402

1.83

Error

16

0.3505

0.2190

Least Difference Reqjuired for Significance Between Treatment
Means : 1% ^ 0.345 ag./lO cm^

5^ • 0.252 ng./lO cm2

99

Tabl* 5a

Anal^vie of Varianco: Nltrogon Inoroaso of V7«ar-old Soar
Orange Seedlings Sprayed with Urea at a Concentration of
10 U>8. per 100 Gallons of Water*

Source of

Degree of

Sun of

Kean

MfR

Variation

Freedom

Squares

Squares

Value

Total

17

1*626

Treatment

d

1.541

0.193

21.4**

Error

9

0*065

0*009

,

Least Olffermce Required for Slgnifieaoee Between Treatment
Means I 1^ r 0*33 ffig*/lO cm^

5$ ■ 0*22 og*A0 em^

Table 5b* Analysis of Variance i Chloropiiyll Increase of irTsar-old
Sour Orange Seedlings Sprayed with Urea at a Concentration
of 10 lbs* per 100 Gallcsis of Water*

Source of
Variaticn

Degree of

FreediMn

Sub of
Squares

Mean

Squares

Mp«

Value

Total

17

2.043

27.1**

Treatment

6

1.953

0.244

Error

9

0.061

0.009

«

Least Difference Required for Significance Between Treatment
Meansi « 0*28 ag*/l00 oa^

$$ s 0*19 mg*A00 <XB^

100

f

Table 7a« AxMlysie of Variance: The Bffeots of Sueroee^ Kagneslua
Sulfate and Line vhen Added to Urea SpragTS on the Absorp-
tion of Nitrogen b7 Valencia Orange Leaves.

Soiu^e of

Degree of

Sum of

Mean

npn

Variation

Freedom

Squares

Squares

Va}jue

Total

27

23.25

4.53**

Treatment

3

8.44

2.81

Brror

2U

14.80

0.62

Least Difference Required for Slgilfieanoe Between Treataent
Means: 1^ s 1«1$3 percmt

s ^*^5 percent

Table 8a.

- ■ / / >

AnaljrsiB of Variance: The Sffecte of Sticker and Wetting
Agent :dien Added to Urea Spresrs on the Retentiim of Spray
Solution on Leaf Surfaces.

Source of

Degree of

Sum of

Mean

npii'

Variation

Freedom

Squares

Squares

Value

«

Total

7

0.212

34.<f*

Treatment

3

0.2Q3

0.068

Error

4

0.009

0.002

4

•

Least Difference Required For Signifleance Between Treatownt
Ileans: 1^ s 0.12 nl./lOOO cnr

5% r 0.08 ial.A000 car^

- Id -

Table 9a« Analysis of Vazdaneei The £f foots of Sticker and Wetting
Agent irtion Added to Urea Sprays on the Absorption of Nitro-
gen by Valencia Orange Leaves.

Source of

Degree of

Sum of

Mean

i\p»

Variation

Freedom

Sqoarea

Squares

Value

Total

... --10 ~ r 2

1532.149

12.8**

Treatnent

3

1081.129

360.376

Srror

16

451.020

28.190

L.S.D.— 1^ - 9*82 percent, s 7.12 percent

Table 10a. Treatments of Different Stickers on Grapefruit Leaves.

»> ■ * ■

Sticker or Wetting Agent

Amt. Material/100 gal.

*

Good-rite Latex V.L. 600

1 pint

Good-rite p.e.p.s.

.

^ pint

Dowax 222

8 pints

Colloidal Z-1 sticker

i pound

AxDoor sticker

l| pounds

Oil emulsion

4 pints

Linck Iff-A uetting agent

4 pints

Table 10b. Analysis of Variance for Table 10c.

«*

Source of
Variation

Degree of
Freedom

Sum of
Squares

Mean

Squares

npn

Value

Total

26

0.3910

Treatment

8

0.3821

0.0478

95.6**

Krror

18

0.0089

0.0005

L.S J). — 1^ ■ 0.052 og./lO cmf x O.Q38 mg./lO ca2.

- 102

Table lOo*

Nitrogen Gontmt before and after Three Applleatlone of
Urea at a Concentration of 15 Iba. per 100 Gallons of
Water plus Various Cocanereial Stickers and Linck W-A
Wetting Agent. (Mg. U/lO em^)

Treatment

Initial

Nitrogen

Nitrogen

after

Applieatioas

Nitrogen

Increase

Heab

Checks

2.00

2.20

0.i2

0.10

1.92

2.x

O.X .

2.00

2.10

0.10

Urea alone

1.96

2.31

0.35

0.34

2.00

2.32

0.32

' 1

1*95

2.30

0.35

Good-rite Latex

1.90

2.39

o.a

OM.

V.L. 600

2.00

2.40

0.40

2.02

2.45

0.43

Good-rite p.e.p.s.

2.10

2.55

0.45

0.47

2.14

2.x

0.46

2.16

2.66

0.50

Dowax 222

2.04

2.47

0.43

0.44

2.00 ■

2.42

0.42

2.00

2.55

0.47

Colloidal Z-1

2.00

2.a

o.a

0Jt2

2.15

2.56

OJd

2.15

2.59

0.44

Armour sticker

2.05

2.45

0.40

0.39

2.x

2.36

0.36

2.10

2.51

0^

Oil enulsion

2.10

2.46

0.36

0.35

2.04

2.36

0.32

2.10

2Jt7

0.37

Linck W-A

2.10

2.66

0.56

0.56

Wetting agent

2.x

2.62

0.54

'

2.15

2.73

0.50

1Q3

Tabl« 11a.

Nitrogen Content of iv^yer^old Sour Orange Soedllnge for
; Stiic^jring the £ffects of Wetting Agent-Sucrose Combinations
in Urea Sprays on the Absolution of Nitrogen by the Leaves
——Original Data. (Mg. N/10 om^)

A. 15 lbs. Urea per 100 gallons

Sanq^ling

W. Agent

- W. Agent

4 W. Agent

- W. Agent

Date

• Sucrose

<¥ Sucrose

4> Sucrose

- Sucrose

Mar. 15. 1952.

1.28

1.21

1.42

1.45

1.36

1.20

1.46

1.37

1.26

1.28

Ave.

1.30

ra

lJU

i.Xo

Apr. 15

2.34

1.46

1.76

2.08

2.40

1.52

1.80

1.92

2.31

1.52

1.60

Ave«

2.5s

l.?0

— E75

SRS

May 15

2W^7

1.67

1.80

«

2.10

2.49

1.60

1.81

1.97

2.W

1.68

1.W

2.08

Ave*

2^5

Oi!'"""""

ftw

June 15

i;65

1.53

1.68

1.76

2.30

1.52

1.70

1.67

1.60

1.60

-

Ave.

i.55 ‘

1.66

life

July 15

2.42

1.68

2.04

2.20

2.46

1.68

2.06

•2.18

2*32

2.02

HI

Ave.

2j[o

1.70

2.04

Aug. 15

2.45

1.86

2.07

2.22

2.50

1.82*

2.10

2.11

2.40 .

2.00

2.07

2.14

Ave.

2.45

05

2*54

2.15

Sept.l5

2.53

2.00

1.98

2.20

2.60

1.97

2.00

2.12

2,52

2.06

1.93

2.16

Ave.

2.3

1.^7

CT5

Oct. 15

2.80

2.05

2.09

2.45

2.82

2,02

2.12

2.30

2*45

Ave.

2.75

2.o4

i.16

^

- lQt» -

Table Ua« Nitrogen Cwitant of 4-ywu^-old Sour Orange Seedlings for
Studying the Effects of Wetting Agmt-Sucrose Coobinations
in Urea Sprays on the Absorption of Nitrogen by the Leaves
*~Original Data. (Mg. N/10 cm^) — • Ccxxtinued.

B. 10 lbs. Urea per 100 gallons

Sampling

4 W. Agent

» w. Agent

W. Agent

• ,W. A^nt

Checke

Date

0 Sucrose

^ Sucrose

Sucrose

• Sucrose

Mar. 15

1.20 .

1.32

, 1.28

1.09

1.33

1.24

1.32

. 1.24

.1.16

1.35

1.19

1.38

1.2

hh

Ave.

.El5

Apr. 15

2.28

1.56

1.44

1.75

1.42

2.30

1.58

1.38

.1.80

1.50

2.26

1.64

1.38

2.00

Ave.

2.28

1.3

ES

- -

1I46 __

May 15

2.34 .

1.56

1.60

,1.90

IJ^O

2.38

1.55

. 1.50

.2.09

1.42

i. W

,|ao

1,38

Ave.

2.54

' ills

2.03

i.4o

June 15

2.14

1.39

. 1.40

1.60

1.08

2.20

1.39

1.32

.1.62

1.30

1.42 _

3-7?

1,22

Ave.

2T5

il4o

■^•1.54

Esc

1.20

July 15

2.60

1.66

. 1.90

.2.01

1.04

2.62 V

1.65

. 1.68

.2.04

1,10

2.SK:

.1.70 __

2.10

J.-10

Ave.

i.59

iW

EC3

Aug. 15

2.56 .

1.70

. 2.03

.1.96

1.03

2.60 .

1.66

. 2.00

.1-97

1,10

2.5a

,,.1.74

^82

2,07

1.08

Ave.

2fr-'

1,70

E^5

2.00

Sepfc 15

2.81

2.00

. 2.10

2.08

1.11

2.86

1.94

, 2.C0

'2.10

1.17

2.76 .

2.06

1.11

Ave.

2.£

2.00 *

2.05

.15.12

1.13

Oot. 15

2.82

1.93

. 2.12

,2.30

1.07

2.88

1.92

2.00

,2.32

1.15

2.79

2.00

_ 2.09

1.08

Ave.

1.95

M—

~ 105 •"

Table 12a« ChloropdQrll Content of kf-jear-^dld Sour Orange Seedlings for
Studying the Effects of Wetting Agent-Sucrose Con^inaticsM
in Urea Sprays on the Absorption of Nitrogen by the Leaves
-—Original Data^* (Mg»/l00 cnr) • •

k» 15 lbs« Urea per 100 gallons

Sampling

Date

'

4> V. Agent
- Sucrose

- W. Agent
+ Sucrose

4 W. Agent
4 Sucrose

- W. Agent

- Sucrose

Mar. 15, 1952. *

0.77 •

0.88 >

0.88

0.78

0.82

0.82 .

0.84

0.75

»

HI ’

0.82 .

0.83

0.75

*

" 0.84 ^

Os

Apr. 15

0.91

0.90 .

0.94

0.92

*

0.94

0.88 •

0.90

0.89

^91 —

0.86 •

0.S6

9',

0.90

TO

Hay 15

»

0.95 -

0.91 •

0.88

1.00

1.02

0.87 *

0.87

0.98

•

HI

- 0*0^

0.96

Ave.

6.S

—im

June 15

106

1.06 •

1.00

1.27

%

1.40

0.99 '

0.98

1.22

■-

1.23

.^TS.

i.a r

6.fe

1.24

July 15

1.94

1.77 ♦

1.56

1.52

•

*

2.00

2.00_

1.66
l^TO ‘

1.50

1.50

1.50

1.45

Ave.

: Oi

1.49

Aug. 15

«

1.94

1.74 *

1.80

1.90

-

2.01

1.68 >

1.78

1.80

.r ,

^1.70

1.76

. Ave.

1.M

05

1.82

Sept 15

A

2.20

1.66 '

1.86

2.00

2.28

1.66 ''

1.8C

1.94

t

2A ,. ,

1.94

Ave.

iM "1

\M

i.%

oot. 15

2.17

1.78

1.87

2.04

2.20

2.17

1.70 *

1.78

1.99
h3k

iSfi

106

Tabid 12a. ChloroplylL Contact of /ryeai>-old Sour Oranee Seodllnga for
Studjylng the Effects of Wetting Agent-Sucrose Conbinationa
in Urea Sprays on the Absorpticai of Nitrogen by the Leaves
— — Origitial Data. cm2) Continued.

B.

10 lbs. Urea per 100 jsallons

Sampling

Date

4> W. Agent
- Siicrose

• W. Agent
4- Sucrose

•f tf. Agent
Sucrose

•> V. Agent
•» Sucrose

Checks

Har* 15

0.77

0.8^

0.88

0.30

0.79

0.80

0.81

0.83

0.80

0.80

0.80

0.81

< 0.81

0.77

0.84

Ave.

(H75

0.82

-

Apr. 15

0.95

0.88

0.93

0.95

0.81

1.00

0.85

0.90

.0.91

0.81

0.99

0.85

0.87

0,90

0>»

Ave.

03

■r 0*90 -

9.t3.2

May 15

1.26

0.92

0.90

.1.15

0.77

1.30

0.89

0.90

1.09

0.80

1.28

0.86

o.g „

Ave.

1.2^

05

0.85 _ _

M6

0.79

June 15

1.53

1.07

1.04

1.26

0.81

1*59

0.97

1.01

1.23

0.82

1.56

0.96

1.01

1.20

Ave.

1.00

1.62

.h?l —

oTeS

J\i3y 15

2.06

1.52

1.65

1.80

0.76

2.16

1.50

1.60

1.66

0.76

2.11

1.42 ___

1.55

0.79

Aug. 15

2.18

1.68

1.90

2;oo

6.71

2.30

1.58

• 1.86

1.90

0.74

2.21

1.57 __

rV >2S -

^

,

Ave.

2.23

i.a_

tts

Q.73 _

sept 15

«. 4. -

2.20

1.80

1.90

2.07

0.72

2.26

2.20 . .

1.72

1.70

1.88

1.80

1.97

l.?6

0.80

■gf.^

Ave.

2.a >

1.74

:^.o6

Q-W

Oct. 15

2.18

1.78

1.90

2.00

0.77

2.28

1.70

1.89

1.97

0.79

2.26

1.68

9-n

Ave.

fS

— 05”

05

0.76

107

Tabl* 33a, Analyeis of Variation* Ef foot of Wotting Agont-Sucroso
Addition to Urea Solution on Absorption of Nitrogsn by
Sour Orange Leaves from Foliar SpragrSf as Indicated by
the Increase in Tnnk Circunference of Young Seedlings*

Soiaroe of

Degree of

Sum of

Mean

npH

Variation

Freedom

Squares

Sqpares

Value

Main Plot

■ w

*•

-«

0.02

Cenoontration

1

0.01

0.01

Replication

2

0*02

0.01

0.02

’ Main plot error 2 *

l«0{i.

0.52

w

Subplots

Treatment

3

2.03

0.63

22-'’^

T X C

3

0.78

0.26

8.7

Subplot error

12 .

0.35

0.03

Least Dif fersnee Re<iciired for Sl®ftificanoe Between Treatment ,
Means* 1$ s 0»31 cm*

. . 5% s 0*22 cm.

Table 15a* Analysis of Variation*' Effects of pH of Urea Spray Sola^
tion on Nitrogsn Absorption by Duncan Orapefruit Leaves*

Source of
Variation

a

Degree of
Freedom .

Sum of
Squares

Kean

Squares

NPN

Value

'• « -

Total

»■ -

23

lJi5d2 '

2.66^

Treatment

4

7 .

0.7839

0.1120

Error

«

16

0.6763

0.0421

• . - k ' *•

Least Difference Required for Significance B^wesn Treatment
Means* 1% s 0*50 ag*/10 oar
, . 5% s 0*^ ag*/lO car

103

Tabl« 16a. Analysia of Variatloni Bffact of Soil and Fbliar

tiona of Nltrogon on tha Nitrogan and Chloropfagrll C«itanta
of tba Laavaa and tha Dry Uel^ of tha Traaa of Sour
Orange Saodllnga.

Sourco of
Variation

Degree of
Froedon

' • V

Sum of
Squarea

Kean

Squarea

NfM

Va?Jie

A. Nitrogen

r

, , > . » * { r . « •

1

Totol

7

3;Q333

23.7**

Treatment

3

2.8703

0.9568

Brror

4

0.1410

B. ChloroTidnrll

0.0403

i

Total

7

lUm

106.9**

Treatment

3

1.4761

0.4920

Error , '

4 •

0,caj83

C. Dr7 Weight.

0.0046

Total

7

337665^0

-

156,^ :

Treatment.

3

334812.5

arj604.2

Error

‘4

2332.5

713.1

• t ' i' . ,

L*S*D« for Nitrogflnt

2$ z 0*92 ng./lO em^
5% m 0.56 ag*/lO oar
L*S»0* for Chloroi^U}

z 0.32 iag./l00 cr^
5% z 0,19 ng.AoO err
L.S.O. for Dry V^lgfxtt

IX s 115.1 grama ^
$$ a 69*4 grama

109

Table 17a. Axialyeie of Varlatloat Sffeet of Soil Foliar Applica^

>■ tioaa of Urea otx nitrogen Content of Subj Grapefktilt Leavee.

II ' I ■ ' * "

Source of Degree of Sun of Keen "P"

Variation Freedcm Sqjoaree Squares Value

Totcl
Treatment
Sampling Date
T X D =

Krror

62

22.137

2

12025

6.061

6

4.9©

0.631

12

4.9/A

0./42

206*^

42

0.065

0.002

L.S.D. for Treatment Means t

Ijt s 0.029 ng./lO err
5^ : O.OQLA Bg./10 oar
L.S.D. for SarpUng Date:

1% S 0.056 ng.A0 ceT
5% s 0.042 ng.Ao err

Table 19a. Analysis of Variation: Nitrogen Contert of Leaves of
Valencia Orange Trees at Various Intervals after the
Application of Urea Sprey at a Concentration of 10 lbs.
per 100 Gellono of Water.

Source of
Variation

Degree of
Freedom

Sm. ot
Squares ^

Mean

S<9iares

njfn

Value

Total

23

o;co50

-

Treatment

7

0.0016

0.00023

1.09

Error

16

O.OQ34

**' .

0.00021

No sigoificant difference betv»en treatment means.

no

Table 20a, Analysis of Tariatlcm Percent of Applied Nitrogen Ab-
sozbed by Valencia Orange Leaves at Variooa Laterrale
under GreenhMise Conditions,

Source of
Variation

Degree of
Freedom

Sum of
Squares

Mean

Squares

mfu

Value

Total

23

10520.74

Treatment

7

10508,55

1501.22

1975.3**

Error

16

12,19

. 0,76

Least Difference Required for Sigiificaaee Between Treatramt
Meanst 2$ s 1*^ peircent

... ^ at 0.91 percent

. Ill •

BIOCEAPHICAL ITaS

WUArvd Chixiie-ching Ch«n vas bom on July 3» 1924« in Poi-
ping« China. After he had finished his high school education in Toy-
Shan Middle School^ he anroUed in the Nantung Agricultural College
at Shanghai in September^ 19AO» where he spant one and a half years
with his aajor subject as Agronony. In the spring of 1942^ he trans-
ferred to the National Sun Yat-San Ibilverslty at Cantcn» China^ where
he recelTsd his B.S. degree in Horticulture in June^ 1944.

Following hie graduation from college^ he was called into
service and was s«it to India by the Chinese An^jr. Cn returning from
India in Ootober« 1945» he was appointed as Assistant in Horticulture
by the National Sun Yat-San Heaorlal Park at Nanking^ China. He was
amployed by this institution as Assistant Horticulturist from
October^ 1946« until June« 1949*

He came to the U.S. in September^ 1949» for further studies
in his field of horticulture. He received his Master of Agriculture
degree from the University of Florida in July^ 1950. Since that tins
he has pursued his studies in the University of Florida to

a degree of Doctor of Philosophy.

112

This dissertation was prepared under the direction of the
ehaizman of the candidate's supervisozy ccxnmittee and has been approved
by members of the connittee* It was submitted to the Graduate
Council and was approved as partial fulfilment of the requirements for
the degree of Doctor of Philosophy.

I

.. A