LIBRARY,
A 8n M COLLEGE»
CAMPUS.

A98-1030-10M-L180

TEXAS AGRICULTURAL EXPERIMENT STATION

A. B. CONNER, DIRECTOR
COLLEGE STATION, BRAZOS COUNTY, TEXAS

BULLETIN NO. 419  , l ’ DECEMBER, 1930

DIVISION OF HORTICULTITRTEV   <3 v

'7’ ,1» .

Citrus Production in the Lower Rio
Grande Valley of Texas

 

AGRICULTURAL AND MECHANICAL COLLEGE OF TEXAS
T. O. WALTON, President

STATION STAFFT

ADMINISTRATION:

A. B. CONNER, M. S., Director
R. E. KARPER, M. S., Vice-Director
CLARIcE MIxsON, B. A., Secretary

. P. HOLLEMAN, JR., Chief Clerk
J. K. FRANOKLOW, Assistant Chief Clerk
CHEsTER HIGGS, Executive Assistant
C. B. NEBLETTE, Technical Assistant

CHEMISTRY:

G. S. FRAPs, Ph. D., Chief; State Chemist
S. E. AsRURY, M. S.. Chemist

J. F. FUDGE, Ph. D., Chemist

E. C. CARLYLE, B. S., Assistant Chemist
WALDO H. WALKER, Assistant Chemist
VELMA GRAHAM, Assistant Chemist

T. L. OGIER, B. S., Assistant Chemist
ATHAN J. STERGES, B. S., Assistant Chemist
JEANNE M. FUEOAs, Assistant Chemist

RAY TREIcHLER, M. S., Assistant Chemist
RALPH L. ScHwARTz, B. S., Assistant Chemist
C. M. POUNDERs, B. S., Assistant Chemist

HORTICULTURE:
S. H. YARNELL, Sc. D., Chief
L. R. HAWTHORN, M. S., Horticulturist

RANGE ANIMAL HUSBANDRY:
J. M. JoNEs, A. M., Chief
B. L. WARwIcK, Ph. D., Breeding Investigations
STANLEY P. DAvIs, Wool Grader

ENTOMOLOGY:
F. L. THOMAs, Ph. D., Chief; State
Entomologist
H. J. REINHARD, B. S., Entomologist

R. K. FLETcHER, Ph. D., Entomologist

W. L. OWEN, JR., M. S.. Entomologist

J. N. RONEY, M. S., Entomologist

J. C. GAINEs, JR., M. S., Entomologist

S. E. JoNEs, M. S., Entomologist

F. F. BIBBY, B. S.. Entomologist

CECIL E. HEARD, B. S., Chief Inspector

OTTO MAcKENsEN, B. S. Foulbrood Inspector

é

. B. WHITNEY, Foulbrood Inspector

AGRONOMY:
E. B. REYNOLDS, Ph. D., Chief
R. E. KARPER, M. S., Agronomist
P. C. MANGELsDORE, Sc. D., Agronomist
D. T. KILLOUOH, M. S., Agronomist
. E. REA, B. S., Agronomist
—>——————~—-—, Agronomist _
. C. LANGLEY, B. S., Assistant in Soils

PUBLICATIONS:

A. D. JAcKsON, Chief
VETERINARY SCIENCE:

*M. FRANcIs, D. V. M., Chief

H. ScHMIDT, D. V. M., Veterinarian

F. P. MATHEws, D. V. M., M. S., Veterinaria.

W. T. HARDY, D. V. M., Veterinarian

F. E. CARROLL. D. V. M., Veterinarian
PLANT PATHOLOGY AND PHYSIOLOGY:

J. J. TAUBENHAUS, Ph. D., Chief

W. N. EzEKIEL, Ph. D., Plant Pathologist

W. J. BAcH, M. S., Plant Pathologist

B. F. DANA. M. S., Plant Pathologist
FARM AND RANCH ECONOMICS:

L. P. GABBARD, M. S., Chief

W. E. PAULsON, Ph. D., Marketing

C. A BONNEN, M. S., Farm Management

W. R. NISBET, Ranch Management Specialia

i———————, Assistant
RURAL HOME RESEARCH:

JEssIE WHITACRET, Ph. D., Chief

MARY ANNA GRIMEs, M. S., Textiles

ELIZABETH D. TERRILL, M. A., Nutrition
SOIL SURVEY:
**W. T. CARTER, B. S., Chief

E. H. TEMPLIN, B. S., Soil Surveyor

A. H. BEAN, B. S., Soil Surveyor

R. M. MARsHALL, B. S., Soil Surveyor
BOTANY:

V. L. CORY, M. S., Act. Chief

SIMON E. WOLFF, M. S., Botanist
SWINE HUSBANDRY:

FRED HALE, M. S., Chief
DAIRY HUSBANDRY:

O. C. COPELAND, M. S., Dairy Husbandman
POULTRY HUSBANDRY:

. M. SHERWOOD, M. S., Chief

AGRICULTURAL ENGINEERING:

H. P. SMITH, M. S., Chief
MAIN STATION FARM:

G. T. McNEss, Superintendent
APICULTURE (San Antonio):

H. B. PARKS, B. S., Chief

A. H. ALEX, B. S., Queen Breeder
FEED CONTROL SERVICE:

F. D. FULLER. M. S., Chief
. D. PEARcE, Secretary
. H. ROGERS. Feed Inspector
. L. KIRKLAND, B. S., Feed Inspector
. D. NORTHcUTT, JR., B. S., Feed Inspectoi
DNEY D. REYNOLDS, JR., Feed Inspector
. A. MOORE, Feed Inspector
E. J. WILsoN, B. S., Feed Inspector

w@zx~w

SUBSTATIONS

N 1, Beeville, Bee County:

o.
R. A. HALL, B. S., Superintendent
No. 2, Troup, Smith County:
P. R. JOHNSON, M. S., Superintendent
No. 3, Angleton, Brazoria County:
R. H. STANsEL, M. S., Superintendent
No. 4, Beaumont, Jefferson County:
R. H. WYcHE, B. S., Superintendent
No. 5, Temple, Bell County: _
HENRY DUNLAVY, M. S., Superintendent
B. F. DANA, M. S., Plant Pathologist
H. E. REA, B. S., Agronomist; Cotton Root Rot
Investigations _ _
SIMON E. WOLFF, M. S., Botanist;_Cotton Root
Rot Investigations
No. 6, Denton, Denton County:
P. B. DUNKLE, B. S., Superintendent
No. 7, Spur, Dickens County: _
R. E. DICKSON, B. S., Superintendent
-————————i, Agronomist
No. 8, Lubbock, Lubbock County:
D. L. JoNEs, Superintendent
FRANK GAINEs, Irrigationist and_Forest
Nurseryman _
No. 9, Balmorhea, Reeves County:
J. J. BAYLEs, B. S., Superintendent

No. 10, College Station, Brazos County:
R. M. SHERWOOD, S., In charge
L. J. McCALL, Farm Superintendent

No. 11, Nacogdoches, Nacogdoches County:
H. F. MORRIs, M. S., Superintendent

**No. 12, Chillicothe, Hardeman County:
J. R. QUINRY, B. S., Superintendent

**J. C. STEPHENS, M. A., Assistant Agronomist

N0. 14, Sonora, Sutton-Edwards Counties:
W. H. DAMERON, B. S., Superintendent
——-——————, Veterinarian
W. T. HARDY, D. V. M., Veterinarian

**O. G. BABCOCK, B. S., Entomologist
O. L. CARPENTER, Shepherd

No. 15, Weslaco, Hidalgo County
W. H. FRIEND, B. S., Superintendent _
SHERMAN W. CLARK, B. S., Entomologist
\V. J. BAcH, M. S., Plant Pathologist

No. 16, Iowa Park, Wichita County:

N C. H. McDOwELL, B. S., Superintendent
o. 17, ———————--—--

No. 18,
———-———, Superintendent

No. 19, Winterhaven, Dimmit County:

E. MORTENsEN, B. S., Superintendent
N L. R. HAWTHORN, M. S.,‘Horticulturist

0. 20, ——-—-——————

, Superintendent

—, ‘Superintendent

Teachers in the School of Agriculture Carrying Cooperative Projects on the Station:

W. ADRIANcE, Ph. D., Horticulture

W. BILSING, Ph. D., Entomology _

P. LEE, Ph. D., Marketing and Finance

ScOATEs, A. E., Agricultural Engineering
. K. MAcKEY, M. S., Animal Husbandry

*Dean School of Veterinary Medicine.
**In cooperatlon wIt

J. S. MOGFORD, M. S., Agronomy
F. R. BRIsON, B. S., Horticulture

TIN. R. HORLAcHER, Ph.-D., Genetics

H. KNOX, M. S., Animal Husbandry

TAs of December 15, 1930.

h U. S. Department of Agriculture.

Citrus fruit production in the Lower Rio Grande Valley,

‘especially grapefruit, has increased at a rather rapid rate dur-

ing the past few years. More than 5,000,000 citrus trees were
set in orchard form in the Lower Rio Grande Valley up to July,
1929. The proportion of the acreage which is being set to
grapefruit indicates that growers and shippers have found the
grapefruit to be the most profitable type of citrus fruit for this
region. Of the grapefruit varieties now available, Marsh and
Thompson are obviously the most desirable types for com-
mercial planting. Sweet oranges are apparently not as well
adapted to local conditions as are grapefruit but are being
grown to a limited extent. Until a variety of sweet orange
is developed or introduced which will combine early maturity
and good “keeping quality” with excellence of flavor and
prolific bearing capacity, this industry will not keep pace
with grapefruit production.

The problem of root stocks for citrus in the Lower Rio
Grande Valley is not a problem of major importance at the
present time. The commonly used sour-orange stock appears
to be a very desirable type for use in propagating most of the
commercial forms.

The soils on which citrus are usually grown in the Lower
Rio Grande Valley are very fertile, and experiments with fer-
tilizers on the Victoria fine sandy loam soil, up to the present
time, indicate that soil fertility has not become a limiting
factor in grapefruit production, under the conditions of these
experiments. However, these results should not be interpreted
as meaning that fertilizer should be withheld after the trees
reach bearing age. Moderate applications of fertilizer along
with other beneficial orchard practices, throughout the develop-
ment and maintenance of the orchard, will tend to keep the
original fertility of the soil unimpaired.

As citrus fruits are grown under irrigation in this region,
the physical nature of the soil must be given due consideration.
Leguminous cover cropping and mulching has been found to
exert a beneficial effect on the soil as shown by the increased
production from plats where these practices were followed.
It seems desirable to recommend a system of seasonal, legu-
minous cover cropping, rather than the usual method of clean
cultivation with only sporadic natural cover crops. Plowing
the soil to a depth of six inches once each season was not
found to be of practical value. " .

The size attained by Valley grapefruit trees makes the close
spacing practiced in some of the older citrus-producing areas
impracticable in this region. Apparently a spacing distance
of 25x25 feet is desirable with grapefruit trees in the Lower
Rio Grande Valley.

CONTENTS

 

  

PA i‘
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . l

Soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 . . . . .

Climate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Scope of Publication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..

Citrus Variety Standardization . . . . . . . . . . . . . . . . . . . . . . . . . .

Plan of Standardization Experiment . . . . . . . . . . . . . . . .. y’

Explanation of Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 9

Interpretation of Results . . . . . . . . . . . . . . . . . . . . . . . . . .. 181

Grapefruit  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 18?

Grapefruit Quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 19<

Standards for Maturity . . . . . . . . . . . . . . . . . . . . . . . . . . .. 20f

Description of Grapefruit Varieties . . . . . . . . . . . . . . . . . . 20

Sweet Orange . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 22

Sweet Orange Quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Description of Sweet Orange Varieties . . . . . . . . . . . . . .. 24

Mandarin and Tangerine Orange . . . . . . . . . . . . . . . . . . . . . . .. 26

King and Satsuma Orange . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 26

Lemon and Lime . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 26

Kumquats, Hybrids, and Miscellaneous Forms . . . . . . . . . . . . . 28

Citrus Root-Stocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Plan of Experiment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Interpretation of Results. . ~. . . . . . . . . . . . . . . . . . . . . . . . . 30

Grapefruit Orchard Management . . . . . . . . . . . . . . . . . . . . . . .. 34

Orchard Plat Technic . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 35

Cultivation, Cover Crops, and Mulches . . . . . . . . . . . . . . . . 44

Plan of Experiment . . . . . . . . . . . . . . . . . . . . . . . . . . .. 44

Interpretation of Results . . . . . . . . . . . . . . . . . . . . . .. 45

Fertilizer Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 48

Plan of Experiment . . . . . . . . . . . . . . . . . . . . . . . . . . .. 48

Interpretation of Results . . . . . . . . . . . . . . . . . . . . . .. 52

Spacing of Grapefruit Trees . . . . . . . . . . . . . . . . . . . . . . . . . . .. 55

Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 55

Literature Cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .V . . . . . . . 58

BULLETIN‘ NO. 419 DECEMBER, 1930

CITRUS PRODUCTION IN THE LOWER RIO GRANDE
VALLEY OF TEXAS

HAMILTON P. TRAUB* AND W. H. FRIEND

The preliminary experiments concerning citrus fruit produc-
tion at Substation N0. 15, Weslaco, in the Lower Rio Grande
Valley, from 1924 to 1930, are summarized in this report. It is
realized that experimentation over a much longer period will be
required to settle definitely many of the points raised in the
present report. This publication serves a double purpose: it
gives an evaluation of the work in progress, and also makes
available to the Valley citrus grower such tentative conclusions
as the results warrant up to the present.

The citrus industry in the Lower Rio Grande Valley, as shown
in Table 1, although of recent growth, takes a high rank among
the horticultural industries of the State. Nationally, the Valley
ranks among the three leading citrus-producing areas; in grape-
fruit production, it ranks second only to Florida.

From an output of approximately 15 carloads of grapefruit in
1921 the citrus industry of the Valley has expanded to a produc-
tion of more than 4,000 carloads in 1929-30. The data given
in Table 1 are conservative, since shipments by express and truck
are not included. The rapid increase shown in the table gives
an accurate indication of the trend.

The total number of citrus trees planted in the Lower Rio
Grande Valley up to July 1, 1929, as shown in Table 2, numbered
5,118,981; of these 72 per cent were grapefruit, 13 per cent of
which were 5 years of age or older (37) i‘

While the greater part of the Texas citrus acreage of bearing
age is located in the Lower Rio Grande Valley, plantings have
been made in the Laredo and Winter Garden districts and the
Upper Gulf Coast region (20). The present report is concerned
only with the industry in the Lower Rio Grande Valley.

Although experiments in citrus fruit production have been
conducted in other producing areas, it does not follow that
results obtained elsewhere are directly applicable to conditions
in the Lower Rio Grande Valley. Soil and climatic factors
differ greatly from those found in California, Florida, and
Arizona (39, 40, 42, 7, 31, 41). It is therefore necessary to con-
duct fundamental experiments under the conditions found in
the Lower Rio Grande Valley in order to determine the most
profitable practices to be followed in growing citrus fruit in
this region.

*Chief Division of Horticulture, 1928-1930; Horticulturist, U. S. Depart-
ment of Agriculture since July 1, 1930.

TNumbers in parentheses refer to literature citations, p. 58.

   

6 BULLETIN NO. 419, TEXAS AGRICULTURAL EXPERIMENT STATION
Table 1. Car-lot shipments of citrus fruits from the Lower Rio Grande Valley by i‘
Shipments by express and truck not included

1921-22 to 1929-30, inclusiveT

Car lot shipments
Year Railroad _ _ Totals on .
Grapefruit Oranges Lemons Mixed each G ¢
citrus railway, to _
1921-22. . . Mo. Pac. 7 1 0 3 . . . . . . . . .. 1 .

1922-23. . . Mo. Pac. 44 0 0 7 . . . . . . . . . . 5

1923-24. . . Mo. Pac. 107 0 1 7 . . . . . . . . . . 11

1924-25. . . Mo. Pac. 50s 1 1 11 . . . . . . . . . . 52

1925-26. . . Mo. Pac. _ 290 1 0 0 . . . . . . . . . . ' y,

1926-27. . . Mo. Pac. 706 11 0 39 . . . . . . . . . . 7 -‘
1927-28. . . Mo. Pac. 903 27 0 86 1016 .-,
So. Pac.* 140* 11 v_‘_
1928-29. . . Mo. Pac. 1311 28 0 112 1451 ,
So. Pac.* 299* 17 *5-
1929-30. . . Mo. Pac. 2898 114 0 365 3377 -- '
So. Pac.* 604* 398 ’

TData furnished by Missouri Pacific and Southern Pacific Railways.
*Reported as total carlots not classified.

 
  
  
  
   
   
      
    
    

Table 2. Citrus planting in the Lower Rio Grande Valley of Texas as of July 1, 1 1-
Totals for Cameron, Hidalgo,’ and Willacy counties (37) 

Number of growing citrus trees of different ages

i

Class Under One Two Three Four Five To 
one year year years years years years »~
and over

Grapefruit . . . . . ..1,319,103 916,334 458,232 297,084 224,662 487,3343,722,

Oranges. . . . . . . . .. 367,236 280,298 181 ,100 157,434 138,802 195,7441,320,
Other citrus . . . . . . 13,485 7,638 ' 5,717 8,923 10,580 29,275 75,
Total . . . . . . . 1 ,699,824 1 ,204,270 645,049 463,441 394,044 712,353 5,118, i’

Soils- The soils on which citrus fruits ‘are grown in the Lo i
Rio Grande Valley vary considerably as to their physical 
chemical properties, ranging from the rather light sandy lo ¢_
soils of the Brennan and Victoria series to the heavier clay 10a 1;
of the Rio Grande and Laredo series. It is generally conce‘
that the well-drained, deep sandy loam soils such as Victo
Brennan, and Hidalgo fine sandy loams, are best suited to cit
fruit production (4, 10, 11, 14, 15). However, some excelle
orchards are found growing on Victoria clay loam where natu  y
drainage is adequate. Most of the soils of the Valley which 
used for crop production compare very favorably, as regar
fertility, with the principal types used for crop production y
other parts of the state (10). i “

Climate- The climatic conditions in the Lower Rio Gran
Valley are in general favorable for crop production. The :

CITRUS PRODUCTION IN THE LOWER RIO GRANDE VALLEY OF TEXAS -7

nual rainfall amounts to approximately 23 inches, the greater
portion of which falls during the periodsfrom May to June, in-
clusive, and from September to November, inclusive (21, 38).
Because distribution is not satisfactory it is usually necessary
to supplement the rainfall with irrigation water.

The growing season is relatively long in this region, extend-
ing from February to December, and temperature favorable for
the growth and development of citrus trees is the usual condi-
tion during this period. From April 1 to November 1, the
monthly mean temperature ranges above 70 degrees. Critically
10W temperatures are occasionally experienced during the months
of December, January, February, and March.

The prevailing direction of the wind is from the southeast,
and the moisture-laden air from the Gulf usually maintains the
humidity at about 75 per cent, which is favorable for plant
growth (38).

Scope 0f Publicativn- Since the various classes oflcitrus fruits
are rather closely related genetically and the cultural require-

~ ments are similar, the experimental results concerning some

factors in citrus-fruit production in the various classes are
treated in a single publication. The subject matter is con-
veniently grouped under the following heads,—(a) Citrus Va-
riety Standardization, (b) Citrus Root-stocks, and (c) Grape-
fruit Orchard Management.

CITRUS VARIETY STANDARDIZATION

Probably the most important benefit to be derived from
standardization of citrus varieties is the elimination of various
inferior forms which make it difficult to maintain a constant
supply of a relatively few varieties of special merit which can
be grown in sufficient quantities, and which the consumer will
recognize and demand. An added advantage is that standard-
ization will simplify the problems of both the grower and the
nurseryman since it will enable them to specialize on the pro-
duction of a relatively few forms. In this connection the needs
of the industry must be given first consideration. Varieties
should be introduced or developed which mature their fruit
relatively early (prior to December 15), in order to avoid pos-
sible loss due to low temperature. Since consumers have de-
cided preferences as to the size of fruit which they purchase,
this character should receive due consideration. Also, it should
be indicated that the factors responsible for quality in citrus
fruits are probably of more importance than is generally recog-
nized. The proportion of rind and “rag,” the number of seeds
per fruit, and the quality of the juice in terms of solids to acids
ratio, or a still better measure if it can be found, must be con-

8 BULLETIN NO. 419, TEXAS AGRICULTURAL EXPERIMENT STATION

sidered. The capacity of the fruit to hold up well in transit A

and storage is also of primary importance.

The experience of growers during the past has shown that up
to the present time the grapefruit is more profitable than other
classes of citrus in the Valley. This greater relative importance
is apparently due to the wider adaptability range of grapefruit
as compared with other classes of citrus fruits. (See Table 3.)
This fact, however, does not preclude the possibility of the in-
troduction or development of forms in other classes of citrus
which will be equally well adapted.

The data presented in this section under citrus variety
standardization are concerned with (a) the systematic study of
the plant as a whole as it responds to the environmental condi-
tions of the Valley, and (b) the factors which affect quality and
other standards in citrus fruits.

Plan of Standardization Experiments

The standardization experiments, located on‘ Victoria fine
sandy loam soil, may be conveniently grouped into ecological
studies and quality studies. .

Ecological Studies- The method followed in determining the sum
total of environmental factors as affecting citrus plants consisted
in growing, whenever possible, 3 or more trees of each item
studied under the usual orchard practices in the Valley. The
trees were planted in orchard form and the following records
were taken: “ripening season,” degree of frost resistance, keep-
ing quality, and a general adaptability rating. These terms are
explained in detail under “Explanation of Terms.” Yield rec-
ords are not included in the present report, since most of the
trees are relatively young.

Quality Stlldies- In these studies it was the aim to study the

quality of citrus fruits under the conditions of normal orchard
practices as now followed in the Valley. The physical characters
of the entire fruit and the quality of citrus juice were subjected
to detailed analysis. The following determinations were made
in the case of the entire fruit: total weight in grams and the
proportion of “rag,” juice, and seeds; thickness of rind, diameter
of pulp in millimeters, and thenumber of seeds. The quality of
the juice was studied on the basis of total soluble solids, kind of
sugars, total acids, effective acidity (pH), Van Slyke buifer in-
dex, protein, and ash. The methods of procedure have been
published elsewhere (34, 35, 36). The terms used are defined
under “Explanation of Terms.”

Sampling- The constants for fruit character are based upon
random samples of commercial grade fruit. Whenever-possible,
ten or more fruits were utilized as a sample.

CITRUS PRODUCTION IN THE LOWER RIO GRANDE VALLEY OF TEXAS 9

Explanation of Terms

The experimental data have been summarized in Tables 3, 4,
and 5. The statistical analysis of the data given in Tables 4 and
_5 are presented elsewhere (34, 35, 36). The facts concerning
adaptability of cultivated forms of citrus from various sources,
grown under Valley conditions, from 1924 to 1930, are shown
in Table 3. The cultivated forms have been grouped according
to the classification by Swingle (2, 16).

The following definitions of special terms apply to the data
presented in Tables 3 and 4.

“Ripening season” refers to the period when the major por-
tion of the crop reaches maturity and may be harvested; “Early”
refers to the period between October 15 and December 1; “Mid-
season,” December 1 to January/l; and “Late,” January 1 to
March 1.

The term “Frost Resistance” is used as a measure of the
capacity of the plant to withstand temperatures below 28 degrees
F. The sign “—|-,” is used to designate varieties commonly un-
injured at 28 degrees F.; “++,” refers to varieties that are
uninjured at 23 degrees F.; “—” designates forms which are
injured at 28 degrees F. _

“Keeping quality” is a broad term used to distinguish rather
conspicuous differences in perishability as observed by packers
and shippers.

“Adaptability rating” is a general term used to indicate the
effect of the sum total of environmental factors as found in the
Lower Rio Grande Valley on citrus plants. Three degrees of
adaptability are recognized: “good,”—vigorous and prolific
forms; “fair,”—medium vigorous and prolific forms; and “poor,”
—forms not vigorous, unproductive or unable to survive.

“Rag” is that portion of the fruit remaining after the juice
has been extracted by means of a conical citrus-fruit extractor,
and after the rind and seeds have been removed.

The physico-chemical characters of citrus juice presented in
Table 5 were determined as follows: total soluble solids, by
means of a Brix spindle at room temperature, correcting for
temperature variations and expressed at 22 degrees C. ; sugars,
protein, and ash, by direct analysis; total acids, by titration
with 1/10 normal alkali solution, and expressed as anhydrous
citric acid; pH or effective acidity, on an electric hydrogen ion
apparatus to three decimal places; buffer index (Van Slyke),
based on pH determination after adding 1 equivalent of acid to
1000 cc. of juice. The procedure in each case has been described
fully in another publication (36).

The pH scale is used to measure the degree of effective acidity
or alkalinity of a given solution. On this scale the neutral value,

10 BULLETIN NO. 419, TEXAS AGRICULTURAL EXPERIMENT STATION

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11

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12 BULLETIN NO. 419, TEXAS AGRICULTURAL EXPERIMENT STATION

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13

CITRUS PRODUCTION IN THE LOWER RIO GRANDE VALLEY OF TEXAS

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CITRUS PRODUCTION IN THE LOWER RIO GRANDE VALLEY OF TEXAS

 

  

 

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18 BULLETIN NO. 419, TEXAS AGRICULTURAL EXPERIMENT STATION

when a solution is neither acid or alkaline, is 7.0. Values higher ,. »
than 7.0 up to 14.0 represent increasing degrees of alkalinity; ,
and values lower than 7.0 down to 0.0, represent increasing de- 
grees of acidity. An increase of effective acidity is therefore l

associated with a decrease in the pH value.

The Van Slyke buffer index is used as a measure of the degree ii
of protection possessed by a solution against relativelygreat .
changes in acidity or alkalinity. Plant juices usually contain 1
buffer substances, weak acids, weak bases, etc., which neutralize ;
strong acids or bases which may be added. The buffer capacity .
of citrus juice has been measured by determining the pH or j
effective acidity of the juice before, and after the addition of i1

acid.
Interpretation of Results _

While this work has not extended over a sufficient period of  "
years to warrant definite conclusions in most cases, certain facts ;,j_
have come to light in regard to dessert quality of citrus fruit and 
such characters as resistance to cold, season of maturity, keeping i
quality of the fruit, and adaptability of the plant, as a whole, to i;
local conditions. As shown in Table 3, the grapefruit and sweet 
orange varieties are relatively more hardy to cold than are com- ‘a
mercial varieties of limes and lemons. Some of the mandarin ;_
oranges such as the commercial tangerines are more hardy than "

the more common varieties of sweet orange and grapefruit.

Limequats are relatively not as hardy to frost as are kumquats "

but are more frost-resistant than green-fleshed limes.

The relative merits of the cultivated forms under the various
classes of citrus fruits, as grown in the Lower Rio Grande
Valley, are conveniently treated under the respective classes:
grapefruit, sweet orange, mandarin or tangerine orange, lemon,
lime, and other citrus fruits.

GRAPEFRUIT

This section is devoted to the particular standards for culti-
vated forms of grapefruit.

It will be seen in Table 3 that there is some variation in the
season of maturity of the various varieties. The outstanding
early forms are Duncan, Conner’s Prolific, McCarty, and
Triumph. The more important midseason sorts are Marsh,
Thompson, ‘and Foster. From the standpoint of possible ldss
of fruit due to low temperature, a part of the midseason crop
may be affected, but in this connection the quality of the fruit
must be taken into consideration, as will be pointed out later.
When varieties at present available are considered, it is un-
doubtedly advisable to set the larger portion of future plantings

CITRUS PRODUCTION IN THE LOWER RIO GRANDE VALLEY OF TEXAS 19

to midseason, “seedless” forms rather than to the early, “seedy”
sorts.

As regards keeping quality, there is little varietal difference,
except that Triumph is more perishable than the other forms.

Grapefruit of size “70” t0 “80” per box are in greatest de-
mand, for the retail fruit dealer is enabled to sell fruit of this
size to greater advantage. At ten cents per fruit, the dealer
realizes seven to eight dollars per box on 70’s and 80’s, while
larger fruit, 54’s and 643s, must either be sold at a higher price
per fruit, or at less profit to the dealer by the box. The figures
in Table 4 show that the mean weights of Marsh and Thompson
grapefruit are 466 grams and 449 grams, respectively, which
would grade about size “70.” The Duncan fruits included in
the study show that fruits of this variety weighed about 468
grams. In general, Duncan fruits average larger than size 7 O’s.

Grapefruit Quality

The composition of mature grapefruit juice is fairly constant
for the principal commercial varieties, such as Marsh, Thomp-
son, and Duncan, included in the experiment, as shown in Table
5. The outstanding difference in the fruits is apparently in the
number of seeds per fruit.

The proportion of “rag” varies somewhat, being lower in
Marsh and Thompson and higher in Duncan. Amount of “rag”
is not the only measure of the relative importance of this char-
acter, since the nature of the “rag” must also be considered.
Observations show that the “seedy” types of grapefruit have a
relatively greater proportion of fibrous tissue than is found in
the fewer-seeded types.

Palatability of citrus fruit juice is usually measured by the
ratio of soluble solids to acids, as determined by titration (36).
A completely satisfactory explanation of the principles involved
has not been discovered. Work conducted to date (34, 36) seems
to indicate that there is a decline in total solids as the fruit
matures. The amount of acids also declines relatively more

. than that of total solids, which brings about a gradual rise in
the solids to acids ratio as the season advances. It should be g

pointed out in this connection that originally the ratio of total
sugars to acids was used. The amount of sugar present is,
however, directly correlated with the total solids content of the
juice (34). It is, therefore, permissible to utilize the relatively
more simple total solids determination by the specific gravity
method (hydrometer) in place of the more expensive and cum-
bersome direct sugar determination method.

The importance of the protein and ash fractions as afiecting
palatability of grapefruit juice has not been explored. Figures

20 BULLETIN NO. 419, TEXAS AGRICULTURAL EXPERIMENT STATION

shown in Table 5 indicate that the fractions are relatively small
and are subject t0 but slight variation.

The effective acidity, as measured by the hydrogen ion con- .

centration in pH units, and the buffer capacity, as measured
by the Van Slyke Buffer Index, show that the pH rises slightly
as the season advances, giving a decrease in efiective acidity.

The buffer index decreases as the fruit matures indicating that e

the original bufiered nature of the grapefruit juice is low-

ered (36).
Standards for Maturity

Legal maturity standards for citrus, including grapefruit,
have been established in California, Florida, and Texas (6, 9,
32). The California law with reference to grapefruit requires
a minimum of 6 parts of total soluble solids to 1 part of
anhydrous citric acid (determined by titration) for District No.
1, and 5% to 1 for District No. 2; except that after June 1st,
until the crop is sold, all fruit is considered mature irrespective
of the analysis of the juice. The Florida law as applied to grape-
fruit sets up a decreasing minimum ratio of solids to acids with
increasing total soluble solids of the juice:

Per Cent Total Soluble Solids* 8.5 9.0 10.0 1
Minimum Ratio,* Solids Acids 7 :1 6&1 6:1 5.
*To1erance Factor—0.2

The Texas law regulating maturity standards for grapefruit
requires a minimum total soluble solids content of 10 per cent
and a ratio of 7 parts of soluble solids to 1 part of acid, except
for early, “seedy” varieties after October 15th, for which the
requirements are the same as those set up in the table for Flor-
ida, beginning with the second column, with 9 per cent total
soluble solids and a ratio of 6:}; parts of solids to 1 part of acid.
It will be seen that the Texas standard is the more exacting.
It should be noted that the solids to acids ratio, in the samples
of Marsh grapefruit reported in Table 5, was above 7 to 1 and
in one case reached a ratio of 9 to 1, toward the latter part of
the season. The Thompson and the Foster varieties show a
trend similar to that of Marsh.

lvlr-l ‘A

.0 12.0
:1 5:1

Description of Grapefruit Varieties

Grapefruit varieties have been grouped in two classes by
Traub (35) on the basis of effective acidity. Detailed descrip-
tions of the main varieties are given under the two classes.

Class 1. Varieties ivith relatively high efiective acidity, be-
low pH 3.5.

Marsh- This variety is planted more extensively in the Valley
than any other form of citrus. The trees are quite prolific and

CITRUS PRODUCTION IN THE LOWER RIO GRANDE VALLEY OF TEXAS 21

mature their fruits at such a time (November and December)
that they may be harvested before the frost-danger period.
Some objection has been raised to the relatively smaller size of
Marsh grapefruit, but a large part of this objection can be over-
come by proper orchard management. Specimens studied aver-
aged medium to large in size (466 grams) .* As is common With
practically all commercial forms of grapefruit, shipping quality
is good. The proportion of “rag” is approximately 20 per cent;
seeds average 4 in number; ratio of solids to acids ranges from
7 to 1 in October and 9 to 1 in February; and the effective acidity
varies from pH 3.1 to pH 3.2. Because of its relative “seedless-
ness” and delightful flavor, this is by far the most desirable ‘type
for commercial planting. Marsh grapefruit, as grown in the
Lower Rio Grande Valley, has created a distinctive demand in
the consuming centers, and it is logical that the high standards
set by this variety should be capitalized to the extent of eliminat-
ing as far as possible the inferior varieties.

Tlwmpsvn- A pink-fleshed bud mutation of Marsh (36) that is
practically identical With this excellent variety, except as regards
flesh color. This variety Will in all probability become the lead-
ing commercial sort in the Valley in years to come. The at-
tractive pink-flesh color coupled with the excellent dessert qual-
ity has an immediate appeal to the consumer.

Walters- Trees are quite prolific and are apparently Well
adapted to the region. Fruits are quite seedy; possess a rela-
tively high proportion of “rag”; and lack the appealing flavor
of Marsh. Not recommended for general planting.

Fvster- A pink-fleshed bud mutation of Walters. Trees are
prolific and Well adapted to local conditions and mature their
fruit relatively early. The fruits are large in size (521 grams) ;
With 18 per cent to 20 per cent rag; seeds average 54 in number;
solids to acid ratio reached, 8 to 1 in November, 1929; and
effective acidity ranged from pH 3.1 to pH 3.2. A character-
istic feature of the fruit is the pink blush on the outside of the
fruit.’ Because of its seedy nature Foster is not recommended
for general planting in the Valley.

Dllnwn- Probably the most Widely planted commercial form of
the early, seedy type of grapefruit. Trees are very prolific and
Well adapted to Valley conditions. The fruits are in general
larger than those of Marsh (468 grams). “Rag” averages 22
per cent; seeds are 63 in number; solids to acids ratio approxi-

*Quantitative measurements indicated in parentheses refer to data pre-
sented 1n Tables 4 and 5 for the dates indicated.

22 BULLETIN NO. 419, TEXAS AGRICULTURAL EXPERIMENT STATION l

 

mately 8 to 1 in December; effective acidity, pH 3.2. Probably .

this variety is the best of the “seedy” types.

McCarty- This variety is quite similar to Duncan.

 

C0nner’s Prolific and Innman’s Late. These varieties are similar 
to Duncan in many respects. Fruit characters have not been
studied, as trees of these varieties in the Station collection are ~

not of bearing age.

Little River Seedless, and Cecily Seedless. These are “seedless” l.
types of rather recent introduction. It is claimed that they are f

earlier than Marsh.

Class 2. Varieties with relatively low efiective acidity, above 1

pH 3.5.

Triumph (Royall A very distinct type of grapefruit that differs I

markedly from the varieties included under Class 1.

Total solids increase and total acids decrease as the season y;
advances, as shown by Porto Rico analyses (34), causing a very 
marked increase in the solids to acids ratio with increasing age. 
Solids to acids ratio was 12 to 1 in December under Valley con- ’

ditions. Effective acidity is relatively low, pH 3.6 in December.

Fruits are medium in size; have approximately 31 per cent l

“rag”; and contain on an average of 51 seeds. Flavor is almost
sweet and lacks the typical grapefruit character.

These marked differences have caused some to believe that
this variety is a grapefruit-sweet orange hybrid. This variety
is not to be recommended for commercial planting because of its
insipid flavor, and general low quality.

SWEET ORANGE

The Valencia is the most extensively planted variety of sweet
orange in the Lower Rio Grande Valley, followed by Pineapple.
Other varieties such as Parson Brown, Washington Navel, and
Temple have been planted in a limited way.

Most of the commercial sweet orange varieties grown in the t

Rio Grande Valley, as shown in Table 3, are sufficiently mature
to be marketed before there is danger of loss from frost. Varie-
ties which may be harvested without encountering frost hazards
are: Parson Brown, Pineapple, Ruby, J oppa, Washington
Navel, and similar types. Varieties such as Valencia, Lue Gim
Gong, and Temple ripen at a relatively later date and may en-
counter frost hazards worthy of consideration.

Valencia, Lue Gim Gong, and Washington Navel hold up better
in transit and storage than do varieties like Pineapple, Parson
Brown, J oppa, Ruby, and Temple.

Navel oranges, as grown under Valley conditions, are relatively

CITRUS PRODUCTION IN THE LOWER RIO GRANDE VALLEY OF TEXAS 23

larger in size than other commercial types. Ranked according
to size the other varieties would be listed as follows: Temple,
Valencia, Lue Gim Gong, Pineapple, Parson Brown, Ruby,
J oppa, and St. Michael. The relative size of the different varie-
ties of oranges according to weight in grams is shown in Table 3.

Sweet Orange Quality

The proportion of “rag,” number of seeds, and palatability of
juice are the principal factors affecting the popularity of the
different varieties so far as the consumer is concerned.

The sweet orange varieties may be conveniently grouped on
the basis of number of seeds per fruit into three classes: (a)
varieties with 2 to 10 seeds represented by Washington Navel,
Valencia, J oppa, Lue Gim Gong, and Hamlin; (b) varieties with
11 to 15 seeds represented by Ruby; and (c) varieties with 16 to
30 seeds represented by Parson Brown, Pineapple, St. Michael,
and Temple. In general, as shown in Table 3, the proportion of
“rag” is relatively less in the first class than in the other two
classes.

The legal maturity standards as they relate to oranges are
comparatively uniform where such standards are in force. In
Florida and Texas (9, 32) an unqualified solids to acids ratio
of 8 to 1 is in force. In California (6) a qualified ratio has
been set up. When the fruit is 25 per cent colored (on the
tree) the 8 to 1 ratio applies; however, fruit showing 75 per
cent color may be deemed mature when it shows a ratio of 6%

_to 1. No fruit may be artificially colored which shows a ratio

lower than 8 to 1.

Figures shown in Table 5 indicate that Valley-grown oranges,’

in so far as the solids to acids ratio is concerned, are well above
the 8 to 1 standard. The data show only one exception, this
being in the case of an immature lot of Lue Gim Gong oranges
collected December 16, 1929.

Under Texas conditions, high dessert quality in oranges is
apparently associated with relatively greater effective acidity,
commonly expressed in pH units. The commercial types have
been placed in two groups by Traub (35) on the basis of this
character. The first group represented by Lue Gim Gong,
Valencia, J oppa, Pineapple, Hamlin, and St. Michael show a pH
range of 3.1 to 3.8. The second group represented by Parson
Brown, Ruby, and Washington Navel shows a pH range of 4.2
to 4.3. The oranges of the first group having a relatively higher
effective acidity are more “tart” in flavor than those in the sec-
ond group. Oranges of the second group are, in general, rather
insipid in flavor as grown under Valley conditions. The Temple
orange, possibly a hybrid type (16), shows a pH range of 3.1
to 3.4, and should be placed with the first group.

24 BULLETIN NO. 419, TEXAS AGRICULTURAL EXPERIMENT STATION

Description of Sweet Orange Varieties

The Work on the standardization of sweet-orange varieties
may be conveniently summarized under the two classes described:

Class 1. Varieties having relatively high acidity: below pH
4.0. »

Valencia- This variety is Well adapted t0 conditions in the
Lower Rio Grande Valley. The fact that it matures late in the
season subjects the crop to some hazard from frost. Fruits are
of medium size (150 to 190 grams) and hold up Well in storage
and transit. From the standpoint of proportion of “rag” and
number of seeds (6 to 10) this variety is highly desirable.
Solids to acids ratios varied from 10 to 1 in December to 16 to 1
in February. This variety, in spite of its lateness, is of superior
dessert quality and is probably the best sort available to Valley
planters at the present time.

Lue Gim Gvng- A variety of Florida origin that is quite similar
to Valencia. The fruit is slightly more acid than Valencia.
Solids to acids ratios varied from 6 to 1 in December to 12 to 1
in February.

Pineapple- Trees of the Pineapple variety are Well adapted to
local conditions and mature their crop of fruit relatively early in
the season (November and December). Fruits are small to
medium in size (160 to 200 grams). From the standpoint of
shipping quality this variety is inferior to varieties like Valencia.
The proportion of “rag” is relatively high (23 per cent). Num-
ber of seeds varies approximately from 22 to 29, which Would
place this variety in the seedy class; dessert quality is excellent,
solids to acids ratios varying from 21 to 1 in December to 25 to 1
in March. Next to Valencia this variety is being planted more
extensively in the Valley than any other sort.

Joppa- This variety is quite similar to Pineapple.

Hamlin (Norris) The Hamlin orange Was introduced under the
name of “Seedless Pineapple” and in many respects it is similar
to Pineapple. It differs from the latter variety chiefly in the
average number of seeds (5 per fruit). The fruit shows a loW
percentage of “rag” (16 per cent) but does not hold up Well in
transit and storage. Apparently this variety should be given
preference over Pineapple. '

St- Michael- One of the blood oranges that has never been very
widely planted. Apparently, it is not suited to Valley conditions.
It is a midseason sort, small in size, and of poor keeping quality.
Dessert quality is good, being similar to Pineapple in many re-
spects. Solids to acids ratio Was 19 to 1 in December. Not
recommended for commercial planting.

CITRUS PRODUCTION IN THE LOWER RIO GRANDE VALLEY OF TEXAS 25

Temple- This apparently hybrid type from Florida shows
some promise because of its superior dessert quality. However,
it is one of the most perishable types. Sizes range from medium
to large (200 to 280 grams). The proportion of “rag” is rela-
tively low (18 to 18 per cent). The fruit is rather seedy, having
21 to 25 seeds. Solids to acids ratios ranged from 9 to 1 in
December to 15 to 1 in March. Not recommended for general
commercial planting.

Class 2. Varieties having relatively low acidity: below pH
4.0.

Parson Brown- An early, prolific type that has been rather
extensively planted in spite of its limitations. It is one of the
earliest sorts, ranking with Hamlin in this respect. The fruits
are rather small in size and quite perishable. The proportion
of “rag” is high (24 per cent), and the number of seeds is inter-
mediate, 12 per fruit. The solids to acids ratio was 11 to 1 in
December. Because of its appealing mild flavor, this variety has
enjoyed unwarranted popularity. Hamlin, a less seedy sort,
should be given preference over this variety where early sorts
are desired. l

Ruby- This variety is planted to a limited extent in the
Valley. It is one of the blood oranges, but does not show red-
flesh pigmentation as grown in the Lower Rio Grande Valley.
It is quite similar in many respects to Parson Brown.

Washington Navel- A variety apparently not adapted to Valley
conditions. Trees are not regular, annual bearers, and rank
low from the standpoint of productive capacity. Fruits are
large in size (212 grams) and are usually rather irregular in
shape. Fruits ripen later than those of varieties such as Hamlin
and Pineapple. The fruit has excellent shipping quality. The
proportion of “rag” is low (12 per cent) and the average num-
ber of seeds is the lowest of any of the cultivated forms (2 per
fruit). The flavor is insipid, which can be explained by the
relatively low effective acidity, pH 4.3, and the relatively high
solids to acids ratio. This variety is not to be recommended for

general planting.
Other Sweet Oranges

Various other varieties of sweet oranges are included in the
variety standardization collection at Substation No. 15. Most of
these varieties are of the Mediterranean type and are in general
inferior to varieties like Valencia and Hamlin. A number of
oranges of the Navel type are included in the collection, but most
of these trees are not of bearing age.

26 BULLETIN NO. 419, TEXAS AGRICULTURAL EXPERIMENT STATION

MANDARIN OR TANGERINE ORANGES

Tangerine oranges have not been extensively planted in the
Lower Rio Grande Valley. The trees are apparently well
adapted to the Valley and bear heavy crops of fruit, but the
perishable nature of the fruit has prevented the rapid extension
of this industry.

Daney- This tangerine orange is the most widely planted com-
mercial sort at the present time. The trees are well adapted,
prolific, and fairly hardy to cold. The fruits are small in size
(98 grams) and ripen during December. The seeds are rather
numerous for such small fruit (11 per fruit). The quality of
the fruit is only fair. Solids to acids ratio was 18 to 1 in
December, the effective acidity on this same date being rather
low, pH 3.8. The fruit deteriorates rather quickly after reach-
ing maturity and is subject to “drying” at the stem end.

Clementine (Algerian) A variety quite similar to Dancy in
many respects, except that the fruit matures considerably earlier
and the trees are more hardy to cold and the fruit is of higher
quality. This variety should be given preference over Dancy.

Other Tangerines- Several other varieties of tangerines are in-
cluded in the variety collection but the trees are not of bearing

 

age. Among this lot are: Willow Leaved Mandarin, Swatow,_

and Warnuco.
KING AND ‘SATSUMA ORANGE

These species, closely related to the mandarin or tangerine
oranges, are not of much commercial importance in the Lower
Rio Grande Valley.

King Orange- Trees of this variety are tender to cold and the
fruit has little commercial value except in special markets.

Satsuma Orange- As previously indicated, the growing of this
variety of orange in the Valley has been limited by the lack of a
suitable root-stock species. Due to its extreme earliness, the
Satsuma orange offers some promise from a commercial stand-

point.
LIMES AND LEMONS

Neither limes nor lemons are grown on an extensive scale in
the Rio Grande Valley on account of the relative tenderness of
these forms to cold. Trees are prolific bearers but in the case
of lemons are also quite subject to disease.

Mexican Lime (Key)- Trees of this variety are heavy producers
of fruit but are quite tender to cold. The fruits are small in
size, and mature for the most part during the season of greatest

CITRUS PRODUCTION IN THE LOWER RIO GRANDE VALLEY OF TEXAS 2'7

demand (June to December). The flesh is green in color and
quite free 0f “rag.” Seeds average few in number (4 per fruit).
The effective acidity of the juice is the highest of any 0f the
citrus fruits studied, pH 2.1. The flavor is quite distinctive,
differing rather markedly from Rangpour, and Limequats. Use-
ful for home planting.

Tahiti (Bearss Seedless) Lime- This lime is similar to Mexican in
some respects, but the fruits are too large for commercial use.
The Wood of the trees is quite brittle, and trees are therefore
subject to severe breakage.

Sweet Lime- A form cultivated to some extent in Mexico, and
used as a root stock for certain commercial sorts. The juice of
the fruit is insipid and lacks tartness. Not of any commercial
value as a fruiting plant.

Rangpur Lime- Possibly a hybrid form which partakes of the
character of the tangerines in that the nature of the rind is
similar. It is relatively largerin size than Mexican (57 grams)
and is more seedy (19 per fruit). The effective acidity is the
same as that of commercial lemons (pH 2.3). The flesh is
tangerine-colored.

Eureka Lemen- This is the most commonly propagated variety
of commercial lemon in the Valley at the present time. The
trees are not particularly Well adapted to local conditions, being
subject to frost hazards and disease. Fruits are medium in size
(106 grams); “rag” percentage is about 21 per cent; number
of seeds average 20. The effective acidity (pH 2.3) is higher
than that of Meyer. No recommended for commercial planting.

Meyer Lemon or Dwarf Chinese Lemon. A rather regent intfQduc-
tion that offers some promise as a variety for home plantings.
Trees are much more hardy to cold than are varieties like
Eureka and are about as hardy as grapefruit. Trees are more
resistant to disease than are other forms. Size is of no par-
ticular significance, as fruits may be harvested at any time after
fruit has attained minimum size for commercial use.

The shape of these lemons differ from that of types like
Eureka in that many of the fruits are round or globular. The
proportion of “rag” is 15 per cent; number of seeds, 12 per
fruit; and the effective acidity is pH 2.5. The juice is not so
acid as that of Eureka, and has ‘a very distinctive flavor. The
variety offers some promise, provided the public can be educated
to accept a round lemon instead of an oblong one.

28 BULLETIN NO. 419, TEXAS AGRICULTURAL EXPERIMENT STATION

KUMQUATS AND HYBRIDS

Kumquats- This type of citrus is Well adapted to the Valley,
but so far no commercial outlet for the fruit has been found.
The trees are hardy and very prolific. Three types have been
studied and all of them appear to be adapted to local conditions.
These are N agami, an oval-fruited type; Marumi, a round-fruited
type; and MeiWa, an intermediate form. Meiwa fruits are
largest in size (10 grams), followed by Nagami (7 grams);
Marumi fruits are smallest (2.5 grams).

Hybrids- Of the hybrids, special attention should be called to
the tangeloes, segregated individuals from grapefruit-tangerine
crosses. The trees are prolific, but are more tender to cold than
grapefruit. Like the tangerines most varieties of tangeloes are
poor keepers. It is claimed that there are varietal differences
in this respect, and other sorts are being studied in the hope that
a commercial variety may be discovered.

The Thornton tangelo bears a fruit of superior quality but
which is too perishable to be of commercial value. In size, the
fruit is nearer that of the grapefruit than that of the tangerine
(227 grams). The solids to acids ratio and effective acidity ap-
proach those of the tangerine, being 16 to 1 and pH 3.8, re-
spectively. Seeds average 16 in number.

Trees of Sampson tangelo are quite prolific but are rather

l tender to cold. The fruit is smaller in size than Thornton, and

is quite seedy. The flavor of the juice is distinctive and is not
pleasing.

Trees of other hybrid forms in the standardization orchard,—
Citrange, Citradia, Citrangequat, and Limequat,—are not of
bearing age.

MISCELLANEOUS FORMS

The following miscellaneous forms are included in the stand-
ardization collection,—

Shaddock- A form closely related to grapefruit, but used to a
very limited extent as a dessert fruit.

S0111‘ Orange- The fruit of sour orange is used to a limited
extent in certain countries in the manufacture of citrus by-
products. Not of commercial importance in the United States,
except as a root-stock plant.

Calamvndin Orange- Calamondin trees are hardy and highly
productive. The fruit is extremely acid and has a distinctive
flavor.

Ichang Lemvn- A species native to the Ichang region of China.
Has not fruited in the Rio Grande Valley up to the present.

CITRUS PRODUCTION IN THE LOWER RIO GRANDE VALLEY OF TEXKS 29

Other Types- Suen Kat, Severinia buxifolia and Citropsis
schweinfurthi are citrus types in the Station collection the
adaptability of which has not been determined.

CITRUS ROOT-STOCKS

Early plantings of citrus fruits in the Rio Grande Valley
were made 0n Poncirus trifoliata root-stock, but these attempts
were unsuccessful, probably on account of the susceptibility of
this plant to root diseases (foot-rot and cotton root-rot). Prac-

tically all of the present commercial plantings are on sour- A

orange and rough-lemon root-stocks. The trees on rough-lemon
stock were practically all imported from Florida, and in most
instances the purchaser was not aware of the fact that he Was
receiving such stock. Many of the trees propagated on rough-
lemon root-stock are now in a state of decline or have died.

Although the sour orange is apparently a most satisfactory
stock for grapefruit and sweet oranges, it is entirely possible
that other stocks may be discovered which will be better adapted
to other commercial forms like kumquats, tangerines, limes, and
lemons. It has been pointed out that inferiorities due to in-
compatibility with root-stock may not be apparent for a num-
ber of years, especially in the case of lemons budded on sour
orange (5, 43).

With such practical consideration in mind, experiments deal-
ing with root-stocks were started in 1925, and enlarged in suc-
ceeding years.

The work with citrus root-stocks was planned to include (a)
a study of the adaptability of the various root-stock plants to
the conditions in the Lower Rio Grande Valley; and (b) a study
of the compatibility between root-stock and scion.

Plan of Experiment

The plant material used in the root-stock studies, located on
Victoria fine sandy loam soil, is being grown under the condi-
tions of normal orchard culture in the Valley. Whenever pos-
sible, 10 or more individuals are used for each type of union
studied.

In the adaptability studies an attempt is being made to deter-
mine the efiect of the sum total of climatic and soil factors on
the root-stock plants. In arriving at the “adaptability rating,”
such factors as general vigor, resistance to disease, prolific bear-
ing capacity, adaptability to soil conditions as evidenced by
foliage coloration (presence or absence of chlorosis), and re-
sistance to low temperatures were considered. The facts are
presented in Table 6.

Under the second line of investigation it is the purpose to

30 BULLETIN NO. 419, TEXAS AGRICULTURAL EXPERIMENT STATION

determine the degree of compatibility between the root-stock
and scion. In determining the degree of compatibility, failure
of the scion t0 persist after a short period, dwarfing, unequal
growth of root-stock and scion, and chlorosis were used as evi-
dence. Rate of decline if any over a relatively long period of
years should be considered but has not been included in the
present report on account of the short time the experiment has
been in progress. The facts are summarized in Table 7 .

Interpretation of Results

The results are briefly discussed under the chief classes of
citrus grown in the Valley.

Root-stocks for Grapefruit As shown in Table 7, the standard
varieties of grapefruit are compatible with sour orange, rough
lemon, Cleopatra mandarin, Rusk citrange, and Citrangequat.
Since grapefruit are apparently well adapted to the commonly
used sour-orange root-stock, it would not seem advisable to
recommend any changes at this time.

Root-stocks for Sweet Oranges. Sweet Qrangeg are Qommgnly
grown on sour-orange root-stock and this combination appears
to be well adapted to local conditions. The experiments show
that the sweet orange is also compatible with sweet lime and
calamondin.

Root-stocks for Other Citrus Fruits. Tangerjneg are cQmmQnly
grown on sour-orange root-stock but are compatible with types
like Rusk Citrange and Thomasville Citrangequat. ,

Satsuma oranges are not grown in the Valley on a commercial
scale, apparently on account of the fact that no adapted root-
stock plant has been discovered. Rusk Citrange, however, ap-
pears to be a promising root-stock plant for this type. Poncirus
trifoliata stock as explained above is not successful under Valley
conditions even though the union is congenial.

Kumquats are not compatible with sour-orange root-stock and
are commonly budded on rough lemon roots. They appear to be
congenial with rough lemon, calamondin, and Rusk Citrange.

Limes and lemons, except Meyer lemon, may be grown on
sour orange and appear to be compatible with Thomasville
Citrangequat and Rusk Citrange. Meyer lemon is best grown on
its own roots. Limes budded on Calamondin show overgrowth
of scion and may develop chlorosis.

The Time Faeter- In an experiment of this nature the time
factor must be given due consideration. Work must extend over
a relatively long period of time in order that a more accurate
measure of compatibility may be obtained. Only the more



CITRUS PRODUCTION IN THE LOWER RIO GRANDE VALLEY OF ‘TEXAS 31

marked incompatibilities have come to light thus far. The suc-
cess or failure of these unions must be followed through the
development of the trees to maturity before final recommenda-
tions may be based upon the experiments.

Recommendations- At the present time the following root-stocks
are recommended for the Valley: (a) grapefruit, sweet orange,
tangerines, and limes on sour orange; (b) Satsumas on Rusk
Citrange; (c) Meyer lemon on its own roots; and (d) Kumquats
on rough lemon or Rusk Citrange.

Table 6. Citrus rootstocks: adaptability rating, 1924-30

Adapt-
Species and cultivated form HOW Date NO- 0f ability Remarks
propagated planted trees rating

SOUR ORANGE

Citrus aurantium . . . . . . . . . . . . . . l . . . . .. Seedling 1924 2 Good Vigorous-prolific
“ 1924 1015 “ Vigorous—fairly hardy
“ 1925 100 “ Vigorous-fairly hardy
“ 1929 88 “ V'igorous——fairly hardy
LEMON
Citrus limonia “ -
Rough . . . . . . . . . . . . . . . . . . . . . . . . . . . . H 1929 2 “ Tender to cold
Meyer . . . . . . . . . . . . . . . . . . . . . . . . . . . . “ 1924 200 “_ Dwarf—hardy to cold
Sweet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1927 15 Fair Tender to cold

ICHANG LEMON
Citrus ichangensis

Ichang . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  . .. 1929 4 Good Vigorous and hardy
Ichang . . . . . . . . . . . . . . . . . . . . . . . . . . .. 566611118; 1927 . . . . . . .. Vigorous and hardy
CALAMONDIN ORANGE “
Citrus mitis . . . . . . . . . . . . . . . . . . . . . . . . . . “ 1924 1  Hardy and prolific
1927 10 Hardy and prolific
SHADDOCK
Citrus mazirna u
Cuban . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1927 10 “ Vigorous but tender to cold

MANDARIN OR TANGERINE
Citrus nobilis deliciosa

Cleopatra . . . . . . . . . . . . . . . . . . . . . . . .. Clltjfllg 1924 5 “ Fairly vigorous, tender"to'cold
~ 1927 10 Fall‘ Tender to cold
LIME
Citrus aurantifolia _
Sweet lime . . . , . . . . . . . . . . . . . . . . . . .. 599511112 1929 12 “ Vigorous but tender tofcold
TRIFOLIATE ORANGE _
Poncirus trifoliata ................ .. Seedhng 1924 25 Not
adapted All trees died first season
HYBRIDS
Citrange

(Citrus sinensis a:
Poncirus trifotiata) _
R sk Cllttlllg 1924 25 Good Hardyivigorousfgrower

 

1924 24 “ Vigorous and hardy to cold
1927 15 “ Vigorous and hardy to cold
1929 1 “ Vigorous and hardy to cold
1929 15 "
Citradia
(Citrus aurantium z
Poncirus trifotiata) “
1924 6 Very
u poor Chlorotic, died 1926
1924 " Chlorotic, died 1926

5
6 “ Chlorotic, died 1926

 

32 BULLETIN NO. 419, TEXAS AGRICULTURAL EXPERIMENT STATION

Table 6. Citrus rootstocks; adaptability rating, 1924-30—Continued

 

Adapt-
Species and cultivated form How Date No. of ability Remarks
propagated planted trees rating
HYBRIDS—Continued
Citrangequai
I Citrus sinensis z }
l Poncirus trifoliata a:

Fortunella margarita) _ »
Thomasville . . . . . . . . . . . . . . . . . . . . . Seedling 1924 25 Good Fairly vigorous and hardy
Thornasville . . . . . . . . . . . . . . . . . . . . . “ 1924 25 “ Fairly vigorous and hardy
Thomasville . . . . . . . . . . . . . . . . . . . .. " 1924 5 “ Fairly lwéigorous and hardy to

c0
Thomasville . . . . . . . . . . . . . . . . . . . . . “ 1927 15 “ Fairly vigorous and hardy
Thomasville . . . . . . . . . . . . . . . . . . . . . “ 1929 2 “ Fairly vigorous and hardy
Savage . . . . . . . . . . . . . . . . . . . . . . . . . . “ 1929 10 “ Fairly wrigorous
LIMEQUAT
Eustis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1926 2 Poor Chlorotic
Eustis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cutting 1927 7 Un-
adapted
VARIOUS SPECIES
Citropsis schweinfurthi . . . . . . . . . . . . . . .. Cutting 1929 2 Unde- .
termined Died
Atalantia distascha . . . . . . . . . . . . . . . . . .. Seedling 1929 2 Unde-
termined
Sum kat . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cutt-ing 1927 10 Good Fairly vigorous and hardy
Severinia buxifolia . . . . . . . . . . . . . . . . . . . . “ 1929 5 Unde-
termined Dwarf

Table 7. Citrus rootstocks; compatibility between rootstock and cion; 1924-30

Date No. of Degree of

Species and cultivated form Rootstock planted trees compatibility Remarks
GRAPEFRUIT
Citrus paradisi
Marsh . . . . . . . . . . . . . . . . . . . . . . . . Calamondin r1924 Incompatible Overgrows stock;dwarfed
Marsh . . . . . . . . . . . . . . . . . . . . . . .. Rough lemon 1924 Compatible -
Marsh (33-3) . . . . . . . . . . . . . . . . . . Thomasville
citrangequat 1929 “
Marsh (33-3) . . . . . . . . . . . . . . . . . . Rusk citrange 1929 “
Marsh (33-3) . . . . . . . . . . . . . . . . . . Cleopatra
mandarin 1929 “
Sour orange 1926 “
“ 1925 “
“ 1929 -10 "
x 1929 6 
“ 1924 “
“ 1929 “
ll  l‘
Cleopatra 1924 “ One tree died

Rusk citrange 1929
Sour orange 1924
Rough lemon 1924

 

Duncan . . . . . . . . . . . . . . . . . . . . . . . Sour orange 1926 “

Duncan . . . . . . . . . . . . . . . . . . . . . . . “ 1926 “

Duncan . . . . . . . . . . . . . . . . . . . . . . . “ 1927 “

Conner's prolific . . . . . . . . . . . . . .. “ 1926 “

Foster . . . . . . . . . . . . . . . . . . . . . . . . . “ 1924 “

McCarty . . . . . . . . . . . . . . . . . . . . .. Rough lemon 1924 “

McCarty . . . . . . . . . . . . . . . . . . . . . . Sour orange 1926 “

Triumph . . . . . . . . . . . . . . . . . . . . . . “ 1924 "

Triumph . . . . . . . . . . . . . . . . . . . . . . “ 1926 “

Walters . . . . . . . . . . . . . . . . . . . . . . . “ 1926 “

Inman’s Late . . . . . . . . . . . . . . . . . . “ 1926 “

{OP-l <0 r-l
UIQJCAJCAJIOO-iwwLOPdUIQCrJOBUIC-OQOQCAQ-QUIKOQO©BD U10’! COCO

Little River Seedless . . . . . . . . . . . “ 1929

 

 

Warnuco . . . . . . . . . . . . . . . . . . . . . .

  

CITRUS PRODUCTION IN THE LOWER RIO GRANDE VALLEY OF TEXAS 33
Table 7. Citrus rootstocks; compatibility between rootstock and cion; 1924-30—Continued
Date .No. of Degree of
Species and cultivated form Rootstock planted trees compatibility Remarks
SWEET ORANGE
Citrus sinensis

Lue Gim Gong . . . . . . . . . . . . . . . .. Sour orange 1924 3 Compatible

Lue Gim Gong . . . . . . . . . . . . . . . .. “ 1926 2 “

Valencia . . . . . . . . . . . . . . . . . . . . . . . “ 1924 6 “

Valencia . . . . . . . . . . . . . . . . . . . . . . . “ 1926 4 “

Valencia . . . . . . . . . . . . . . . . . . . . . . . “ 1926 25 "

Joppa . . . . . . . . . . . . . . . . . . . . . . . . . “ 1926 3 “

Pineapple . . . . . . . . . . . . . . . . . . . . . “ 1924 3 “

Pineapple . . . . . . . . . . . . . . . . . . . . . “ 1926 3 “

Ruby . . . . . . . . . . . . . . . . . . . . . . . . . “ 1924 3 “

Rub . . . . . . . . . . . . . . . . . . . . . . . . . ‘i 1926 1 “

Parson Brown . . . . . . . . . . . . . . . .. " 1924 3 “

Parson Brown . . . . . . . . . . . . . . . . . “ 1926 3 “
Norris (Hamlin). . “ 1924 3 “
Norris (Hamlin) . . . . .. “ 1926 3 “

Norris (Hamlin) . . . . . . . . . . . . . . . “ 1929 5 “

Washington Navelf . . . . . . . . . . . . “ 1924 3 “

Washington Navel . . . . . . . . . . . . . “ 1926 3 “

Washington Navel . . . . . . . . . . . . . “ 1926 2 “

S. P. I Navel . . . . . . . . . . . . . . . . .. “ 1924 1 “ ,

S. P. I Navel . . . . . . . . . . . . . . . . . . “ 1924 3 “

S. P. I Navel . . . . . . . . . . . . . . . . .. “ 1924 2 “

S. P. I Navel . . . . . . . . . . . . . . . . .. “ 1924 3 “

S. P. I. Navel . . . . . . . . . . . . . . . . . . “ 1924 3 “

S. P. I. Navel . . . . . . . . . . . . . . . . .. “ 1924 3 “

Mediterranean Sweet . . . . . . . . . . . Calamondin 1924 2 “

Homosassa . . . . . . . . . . . . . . . . . . . . Sour orange 1926 3 “

Pervis . . . . . . . . . . . . . . . . . . . . . . . . . “ 1926 3 “

Raymondville . . . . . . . . . . . . . . . . . . “ 1924 3 “

Ravmondville . . . . . . . . . . . . . . . . . . " 1926 1 “

Golden Buckeye . . . . . . . . . . . . . . . " 1926 3 “

Buckeye Navel . . . . . . . . . . . . . . . . “ 1926 3 “

Malta Blood . . . . . . . . . . . . . . . . . .. “ 1926 1 “

Thompson Navel . . . . . . . . . . . . . .. " 1926 1 “

ville . . . . . . . . . . . . . . . . . . . . . . . . " 1927 1 “
Cham0udi.. Sweet lime 1928 1 “
Chamoudi. . . . “ 1928 1 “
Chamoudi . . . . . . . . . . . . . . . . . . . . . Sour orange 1929 3 “
TEMPLE ORANGE
Citrus sinensis 1:
c. nobilis deliciosa
Temple . . . . . . . . . . . . . . . . . . . . . . . " 1924 3 Fairly com-
patible . . . . . . Trees show mettle‘ leaf
‘Temple . . . . . . . . . . . . . . . . . . . . . . . Calamondin 1924 3 Fairly com- l" l
patible. . . . . . Trees showjnottle leaf
Temple . . . . . . . . . . . . . . . . . . . . . . . . Sour orange 1926 1 . . . . . . . . . . . . . .
Temple . . . . . . . . . . . . . . . . . . . . . . . . “ 1926 25 Compatible
KING ORANGE
Citrus nobilis
King . . . . . . . . . . . . . . . . . . . . . . . . . . “ 1924 3 “
King . . . . . . . . . . . . . . . . . . . . . . . . . . Rough lemon 1926 3 "
King . . . . . . . . . . . . . . . . . . . . . . . . . . Sour orange 1926 1 "
MANDARIN OR TANGERINE
Citrus nobilis
var. deliciosa
Dancy . . . . . . . . . . . . . . . . . . . . . . . . “ 1924 6 “
Danc _. . . . . . . . . . . . . . . . . . . . . . . . “ 1926 10 . . . . . . . . . . . . . . Dead
W. L. Tangerine . . . . . . . . . . . . . . . “ 1926 3 Compatible
Clementine (Algerian) . . . . . . . . .. “ 1927 8 “
Clementine (Algerian). .  “ 1926 3 “
Clementine (Algerian) . . . . . . . . . . “ 1929 7 “
Clementine (Algerian) . . . . . . . . .. Thomasville
citrangequat 1929 2 “
Swatow . . . . . . . . . . . . . . . . . . . . . . . Sour orange 1928 1 “
" 1929 3 “

34

BULLETIN NO. 419, TEXAS AGRICULTURALVEXPERIMENT STATION

Table ZECitrus rootstocks; compatibility between rootstock and cion; 1924-30—Continued

_ _ Date No. of Degree of
Species and cultivated form Rootstock planted trees compatibility Remarks
SATSUMA ORANGE
Citrus nobilis unshiu
Owari . . . . . . . . . . . . . . . . . . . . . . . . . T rifoliata 1924 3 Compatible Died, 1925
Owari . . . . . . . . . . . . . . . . . . . . . . . . . Calamondin 1925 3 “
Owari . . . . . . . . . . . . . . . . . . . . . . . . . Rusk citrange 1926 3 “
CALAMONDIN ORANGE
Citrus mitis
Calamondin . . . . . . . . . . . . . . . . . . .. Sour orange . . . . . . . . . . . . . . .. Uncongenial All died
KUMQUAT
Fortunella japonica
Nagami . . . . . . . . . . . . . . . . . . . . . .. Rough lemon 1924 3 Compatible

Nagami . . . . . . . . . . . . '. . . . . . . . . . . Calamondin 1926 3 “

Marumi . . . . . . . . . . . . . . . . . . . . . . . Rusk citrange 1927 1 “ .

Nagami . . . . . . . . . . . . . . . . . . . . . . . Sour orange 1924 25 “ Died, 1924

Meiwa . . . . . . . . . . . . . . . . . . . . . . . . Rusk citrange 1927 3 “

LIME
Citrus aurantifolium
Mexican . . . . . . . . . . . . . . . . . . . . . . . Thomasville
citransequat 1929 1 “ Killed by cold, 1930
Mexican . . . . . . . . . . . . . . . . . . . . . . . Calamondin 1926 1 Cion olvergrows
stoc

Mexican (Key) . . . . . . . . . . . . . . .. Rough lemon 1926 1 Compatible

Sweet Lime . . . . . . . . . . . . . . . . . . . Sour orange 1924 1 “

Sweet Lime . . . . . . . . . . . . . . . . . . . “ 1925 1 "

Tahiti . . . . . . . . . . . . . . . . . . . . . . . . “ 1926 1 “

Tahiti . . . . . . . . . . . . . . . . . . . . . . . . . Rusk citrange 1926 1 “
LEMON

Citrus limonia
Meyer . . . . . . . . . . . . . . . . . . . . . . . . Sour orange 1924 10 Incompatible Failed to survive
Meyer . . . . . . . . . . . . . . . . . . . . . . . . ‘Thomasville
citrangequat 1929 5 Compatible

Eureka . . . . . . . . . . . . . . . . . . . . . . . . ur orange 1929 10 “ Killed by cold, 1925

Lisbon . . . . . . . . . . . . . . . . . . . . . . . . “ 1924 10 “ Killed by cold, 1925
LIMEQUAT V

Eustis . . . . . . . . . . . . . . . . . . . . . . . . . “ 1926 10 Uncongenial Chlorotic, died
TANGELO

Sampson . . . . . . . . . . . . . . . . . . . . . . Ca1amondin~ . . . . . . . . 3 Compatible

Thornton . . . . . . . . . . . . . . . . . . . . .. Sour orange . . . . . . .. 3 “

GRAPEFRUIT ORCHARD MANAGEMENT

In the other grapefruit-producing areas of the United States
the orchard practices vary markedly (39, 40, 42, 7, 31, 41). ln
the Lower Rio Grande Valley of Texas grapefruit trees are
usually spaced 21x21 feet to 30x30 feet, and as a general rule a
combined system of cultivation, irrigation, fertilization, cover
cropping, and mulching is followed in maintaining bearing grape-
fruit orchards. The procedure naturally falls into four periods:

(a) From December to February, inclusive. Winter Weeds are
allowed to grow. Between February 1 and 15 from 8 to 20
pounds of a 5-15-5 fertilizer mixture (or its equivalent) is ap-
plied. The actual amount is determined on the basis of 1%
pounds per tree for each year of age up to a 20-pound maximum.
Irrigation water, at the rate of about 3 acre-inches, is applied
previous to the flowering period, from February 15 to 28.

CITRUS PRODUCTION IN THE LOWER RIO GRANDE VALLEY OF TEXAS 35

(b) From March to April, inclusive. Winter weeds are incor-
porated into the soil by disking to a depth of about 4 inches.
The area disked varies with the size of the trees and is usually
12 t0 14 feet wide where trees are planted 25x25 feet. During
this period it may become necessary to apply irrigation water;
the amount applied will vary from 3 to 4 acre-inches.

(c) From May to August, inclusive. Cover (grgpg are usually
grown during this period and may consist of crops such as cow-
peas or native Weeds. These crops are disked under when the
first seeds are matured, usually in July. Irrigation water at the
rate of 3 to 4 acre-inches per application is given at rather
frequent intervals, 4 to 5 applications being made per season,
depending upon the amount of rainfall. Volunteer cover crops
are allowed_to grow during August and September.

(d) From September to November, inclusive. During this rainy
season no attempt is made to keep weeds under control by disk-
ing; and in case of occasional droughts it may become necessary
to apply irrigation water.

Young Ordwrds- In maintaining the young orchard until the
bearing stage is reached, a system of intercropping is followed.
It is a common practice to grow such money crops as snap beans,
potatoes, tomatoes, vine crops, corn and root crops in rotation
with soil-improving crops such as cowpeas and yellow annual
Sweet Clover, Melilotus indica. Fertilizers are not ordinarily
used in developing young citrus orchards, since the rate of
growth is usually quite satisfactory.

300m 0f Cultural Experiments- The scope of the orchard manage-
ment investigations includes studies concerning the influence of
(a) cultivation, cover cropping, and mulching; and (b) the ap-
plication of inorganic and organic fertilizer mixtures to the soil
upon the yielding capacity of grapefruit trees.

ORCHARD PLAT TECHNIC

The orchard utilized in theseexperiments, located on Victoria
fine sandy loam soil, was planted in May, 1920. After removal

of native vegetation, chiefly Mesquite, Opuntia, etc., the virgin

soil was plowed, leveled off, and graded so as to permit the
application of irrigation water. The land was then planted to
grapefruit trees. Trees of the Marsh variety, one year old, were
purchased from a California nursery, and were set 21x21 feet
apart. The plan of the orchard showing contours is presented
in Figure 1. The trees were cared for by a tenant from the
time they were set until the property was acquired by the Texas
Agricultural Experiment Station in September, 1928. It has
been given the usual care of a commercial orchard in the Lower

36

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BULLETIN NO. 419, TEXAS AGRICULTURAL EXPERIMENT STATION

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CITRUS PRODUCTION IN THE LOWER RIO GRANDE VALLEY OF TEXAS 37

Rio Grande Valley as described above both previous to and during
the period covered by this Work, excepting where experimental
treatments required a variation in this routine.

Critically low temperatures were experienced in December,
1925, when the temperature dropped to 25 degrees F. The prin-
cipal injury to the trees was in the nature of breakage caused
by ice formation on the limbs and leaves. Only slight defoliation
followed this cold period and most of the trees recovered in

approximately two years. Critically low temperatures Were ex-

perienced also during 1929-30, when the temperature again
dropped to 25 degrees in December and to 22 degrees F. in Jan-
uary. The fruit had been removed from the trees at the time
of the January freeze and yields were, therefore, unaffected for
this season. Only slight bark injury was noted on the 11-year-
old trees and defoliation was so slight as to be negligible.

Scale activity during the season of 1926-27 caused consider-
able injury to some trees in the orchard. The gum diseases be-
came a factor of primary importance during the season of 1926
following the 1925 freeze. By using the recommended surgical
treatment for this disease and then painting the wound with a
solution of denatured alcohol, bichloride of mercury, and rosin
(12), practically all of the affected trees recovered within a
period of two years.

Normality 0f Yields- In considering the data presented in Tables
11 and 12, it should also be realized that out of the five years,
only three have been normal as to yield, primarily on account
of unusual seasonal influences in two seasons. This shows the
necessity of caution in interpreting the results. This indicates
that more weight should possibly be given to results obtained
in normal years than to a five-year mean, for instance. The
history of the orchard would indicate that the season 1929-30
is probably the most typical of the behavior to be expected
under the condition of experiment as to yields secured to date.
It has been pointed out that during the season 1925-26 the trees
were unduly affected by low temperatures during December,
which caused marked injury to some trees on account of break-
age from ice accumulation on foliage, limbs, and fruit; the
following seasons were fairly representative of what one could
expect from trees recovering from the injury of 1925-26. Dur-
ing the fourth year, 1928-29, the ravagesjof scale insects led to

‘partial defoliation of a considerable number of trees. In 1929-
30, no undue seasonal influences were encountered before the

crop was harvested.

Yields from Abnormal Trees- The yields from abnormal trees
were discarded for the purpose of this experiment on the fol-
lowing basis: yields of broken, diseased, and insect-damaged

38 BULLETIN NO. 419, TEXAS AGRICULTURAL EXPERIMENT STATION

trees, Where such damage obviously affected yields, Were omitted;
annual yields were also discarded if the trees Were unduly
affected by sporadic attacks of red scale.

Yield Records» As a measure of performance, the total yield
per tree Was taken to the tenth pound. It became apparent

later that such a measure was too refined, and the yield data_ l

have therefore been uniformly expressed as 100-lb. boxes per
tree, which is the logical measure for grapefruit. The smallest
unit used is a tenth of such a 100-lb. box, and is therefore equal
to 10 pounds.

Table 8. l Blank experiment with grapefruit, entire orchard, 1924-25
Before differential treatments were begun V

Mean Mean Mean Mean
yield yield yield . yield
Plat per tree* Plat N0. per tree* Plat No. per tree* Plat N0. per tree*
100-lb. 100-lb. 100-lb. 100~lb.
boxes boxes boxes boxes

A~1.. 0.3 B-1..... 0.9 C-  0.3 D-  0.8
2.. 0.6  0.8  0.4  0.7
3.. 0.4  1.2  0.5  0.6
4.. 0.3  1.0  0.9  0.7
5.. 0.4  1.2  1.3  0.9
6.. 0.4  1.0  1.3  0.8
7.. 0.6  1.3  1.3  0.8
8.. 0.5  1.7  1.3  0.5
9.. 0.6  1.6  1.3  0.8
10.. 0.6 10..... 1.2 10..... 1.1 10..... 0.7
11.. 0.7 11..... 1.1 11..... 1.2 11..... 0.7
12.. 0.7 12..... 1.4 12..... 1.4 12..... 0.9
13..... 1.7 13..... 1.1

14..... 1.6 14..... 0.8

15..... 1.6 l5..... 1.0

16..... 0,9 16..... 1.0

17..... 1.5 17..... 1.0

18..... 0.9 18..... 1.2

19..... 1.5 19..... 1.6

20..... 1.0 20..... 1.3

21..... 1.7 2l..... 1.2

22..... 1.7 22..... 1.0

23..... 1.0 23..... 0.8

24..... 1.6 24..... 0.8

25..... 1.2 25..... 1.1

26..... 1.5 26..... 0.8

27..... 1.6 27..... 1.1

28..... 1.8 28..... 1.0

29..... 1.3 29..... 0.9

30..... 1.5 30..... 0.9

31..... 2.0 31..... 0.7

32..... 1.5 32..... 0.7

33..... 2.0 33..... 0.8

34...... 2.1 34..... 1.6

35..... 1.5 35..... 1.2

36..... 1.7 36..... 0.6

37..... 1.4 37..... 0.7

38..... 1.2 38..... 1.0

39..... 1.4 39..... 1.4

40..... 1.0 40.. 0.8

*Yield on 5 tree plat basis, and expressed as mean per tree.

CITRUS PRODUCTION IN THE LOWER RIO GRANDE VALLEY OF TEXAS 39

Table 9. Blank experiment with grapefruit, 1334-25; continuity plats C-13 to 29,
an

d I)-13 to
Mean yield per tree,* expressed in 100-lb. boxes
Fdat P¢o.*
1924-25 1925-26T 1926-27 1927-28 1928-291 1929-30
(113 . . . . . . . . . . . . . . .. 1.67 1.45 1.91 2.28 1.01 4.38

14 . . . . . . . . . . . . . . .. 1.63 1.48 1.46 2.09 1.01 4.06

15 . . . . . . . . . . . . . . .. 1.65 . . . . . . . . .. 1.83 2.41 1.16 3.65

16 . . . . . . . . . . . . . . .. 0.88 . . . . . . . . .. 1.45 2.67 1.29 4.26

17 . . . . . . . . . . . . . . .. 1.53 . . . . . . . . .. 1.53 3.29 1.78 4.71

18 . . . . . . . . . . . . . . .. 0.92 . . . . . . . . .. 2.04 3.31 2.35 4.66

19 . . . . . . . . . . . . . . .. 1.48 . . . . . . . . .. 2.63 3.54 2.72 5.49

20 . . . . . . . . . . . . . . .. 1.02 . . . . . . . . .. 1.91 2.91 1.47 4.34

21 . . . . . . . . . . . . . . .. 1.68 . . . . . . . . .. 1.60 2.83 1.76 5.79

22f . . . . . . . . . . . . . .. 1.71 . . . . . . . . .. 1.08 3.27 2.60 5.58

23 . . . . . . . . . . . . . . .. 1.00 . . . . . . . . .. 1.05 3.11 2.56 4.91

24 . . . . . . . . . . . . . . .. 1.60 . . . . . . . . .. 1.10 4.09 1.92 6.39

25 . . . . . . . . . . . . . . .. 1.24 . . . . . . . . .. 2.06 4.09 2.94 5.79

26 . . . . . . . . . . . . . . .. 1.55 0.54 0.81 3.40 1.38 5.37

27 . . . . . . . . . . . . . . .. 1.63 0.45 1.37 3.71 1.70 6.43

28 . . . . . . . . . . . . . . .. 1.82 0.68 1.75 4.36 2.53 5.32

(129 . . . . . . . . . . . . . . .. 1.33 0.84 2.21 4.54 2.50 5.78

I)13 . . . . . . . . . . . . . . .. 1.08 1.49 1.94 2.84 2.13 4.49

14 . . . . . . . . . . . . . . .. 0.78 . . . . . . . . .. 1.85 1.96 2.03 3.74

15 . . . . . . . . . . . . . . .. 0.99 . . . . . . . . .. 1.92 2.46 2.38 4.63

16 . . . . . . . . . . . . . . .. 1.01 . . . . . . . . .. 2.34 2.45 2.28 5.40

17 . . . . . . . . . . . . . . .. 0.96 . . . . . . . . .. 1.27 2.88 2.04 4.81

18 . . . . . . . . . . . . . . .. 1.18 . . . . . . . . .. 1.37 3.03 1.42 5.13

19 . . . . . . . . . . . . . . .. 1.59‘ . . . . . . . . .. 2.45 3.11 1.59 6.46

20 . . . . . . . . . . . . . . .. 1.27 . . . . . . . . .. 2.26 2.69 1.82 3.22

21 . . . . . . . . . . . . . . .. 1.22 . . . . . . . . .. 1.84 2.45 2.10 5.73

22 . . . . . . . . . . . . . . .. 0.97 . . . . . . . . .. 0.90 2.27 1.78 5.07

23 . . . . . . . . . . . . . . .. 0.76 . . . . . . . . .. 0.82 2.42 2.07 5.81

24 . . . . . . . . . . . . . . .. 0.80 . . . . . . . . .. 2.49 3.26 1.57 4.52

25 . . . . . . . . . . . . . . .. 1.14 0.59 0.50 ’3.45 0.88 5.60

26 . . . . . . . . . . . . . . .. 0.84 0.40 1.39 3.13 1.28 5.40

27 . . . . . . . . . . . . . . .. 1.15 0.82 2.48 3.89 1.32 6.68

28 . . . . . . . . . . . . . . .. 0.98 0.49 1.19 3.17 1.37 5.29

{X29 . . . . . . . . . . . . . . .. 0.88 0.78 1.29 3.77 2.12 6.60

*Yields on 5-tree plat basis, and expressed as mean per tre_e.
TCertain plats omitted due to damage irom freezing of fruit.
IYields lowered by severe scale infestation.

EXperimental Error- In carrying ~ on experiments in orchard
management, it is necessary to give due consideration to experi-
mental error, Which makes difficult the accurate interpretation
of the results secured under any particular conditions of soil,
climate, plant material, plant pests, and cultural practices (13,
8, 27, 23, 24, 25). The scientific method requires that all other
conditions be held constant while one or a combination of two or
more are varied. The practical orchardist knows only too well
that this is not strictly possible under orchard conditions where
such factors as bud-mutation* (26, 23, 24, 25) in trees, soil fer-
tility, damage from plant pests, and low temperature may not
affect all the trees uniformly. However, when the danger from
these sources is fully realized, it is possible by the application of
proper statistical methods to determine the approximate relative
performance under the experimental conditions together with

*Possibly not of much importance from the standpoint of total yield.

40 BULLETIN NO. 419, TEXAS AGRICULTURAL EXPERIMENT STATION

some estimate of the accuracy 0f such approximations. Such

values Will serve for practical purposes.

Plat Variability- In order to secure a rational basis for inter-
preting the data secured it is desirable to determine the amount
of variation over the entire orchard. Johnston (17) in 1849,
from a theoretical viewpoint, emphasized the importance of de-
termining “the limits of variation in natural productivity of the
field,” i. e., the (comparative yields of all the plats of the experi-
mental field Without differential treatment, as a necessary step
in field experimentation, It Was not until the 90’s, however, that
extensive blank field experiments Were carried out by Larsen
(18). Anthony ( 1) in 1927 used the principle of performance
records in apple fertilizer experiments, and Batchelor, Parker,
and McBride (3) in 1928 reported on a blank experiment with
citrus trees prior to their use in a nutrition experiment.

In order to secure an index of the amount of variation over
the entire orchard, the grapefruit crop Was harvested Without
differential treatments for the season 1924-25. These yields are
shown in Table 8. As a continuous measure of variation for the
duration of the experiment, the yields from a portion of the
orchard, hereafter called “continuity plats” (Plats C-13 to 29,

Table 10. Analysis of blank experiments; plat variability as influenced by size of plats

       

lVIean
_ Number yield Coeffi-
Size of plat, feet of trees Number Season per tree Standard cient of
per plat of plats 100-lb. deviation variability
boxes
I. Entire orchard, 1924-25
21 x 21 . . . . . . . . . . .. 1 550 1924-25 1.11.01 0.58 52.7
21 x 105 . . . . . . . . . . .. 5 104 1.11.02 0.37 33.6
21 x210 . . . . . . . . . . .. 10 52 1.11.02 0.26 23.6
II. Continuity plats (C-13 to 29 and D-13-29), 1925-30
21 x 21 . . . . . . . . . . .. 1 70 1925-26 0.81.03 0.47 58.7

21x 105 . . . . . . . . . . .. 5 12 ' 0.81.06 0.36 46.0

21 x 210 . . . . . . . . . . .. 10 5 * ’ * *

21 x 21 . . . . . . . . . . .. 1 155 1926-27 1.51.06 1.12 74.6

21 x105 . . . . . . . . . . .. 5 34 1.51.06 0.59 39.3

21 x 210 . . . . . . . . . . .. 10 18 1.51.07 0.46 30.6

21 x 21 . . . . . . . . . . .. 1 169 1927-28 3.11.05 0.99 31.6

21 x 105 . . . . . . . . . . .. 5 34 3.11.07 0.69 22.2

21 x 210 . . . . . . . . . . .. 10 18 3.11.10 0.65 20.9

21 x 21 . . . . . . . . . . .. 1 168 1928-29 1.81.04 0.91 50.5

21 x 105 . . . . . . . . . . .. 5 34 1.81.05 0.53 29.4

21 x 210 . . . . . . . . . . .. 1O 18 1.81.06 0.41 22.7

21 x 21 . . . . . . . . . . .. 1 160 1929-30 5.11.08 1.44 28.0

21 x 105 . . . . . . . . . . .. 5 32 5.11.10 0.83 16.2

21 x210 . . . . . . . . . . .. 10 16 5.11.11 0.66 . 12.8

*Omitted on account of small number of plats.

CITRUS PRODUCTION IN THE LOWER. RIO GRANDE VALLEY OF TEXAS 41

and D-13 to 29), were harvested each year Without differential
treatments. These yields, from 1924-25 to 1929-30, are shown
in Table 9. A general idea of the amount of variation over the
parts of the orchard included in these blank experiments may
be secured by inspecting the data in Tables 8 and 9. However,
a more accurate and quantitative measure of the variability may
be secured by calculating the coefficient of variability (C. V.),
which indicates the amount of variation over the entire area
considered in terms of percentage of the average yield per plat.
In Table 10, the coefficient of variability has been Worked out
for the blank experiments on the basis of 1-tree, 5-tree, and 10-
tree plats.

In general, when the size of plats is increased without increas-
ing the total area, there is a decrease in the coefficient of
variability. When the yield data for the entire orchard are
expressed in terms of 1-tree plats, the variation ranges from
28 to 74 per cent of the mean or average plat yield over the
period of 5 years. This extreme variation throughout the entire
orchard is reduced to a range of 16 to 46 per cent when the same
data are expressed as 5-tree plats. Expressing the data on a
10-tree plat basis gives in general a further reduction in variabil-
ity, but the amount of reduction is not as consistently large as it
is when 1-tree and 5-tree plats are compared.

The relatively large number of trees per plat required for
experimental purposes to overcome the indicated variability
would make orchard experiments of this kind prohibitive if the
ordinary method were to be used of contrasting treatments with
check plats distributed over the entire orchard (1, 19, 30, 33).
An economical method of statistical analysis in harmony with
the facts must therefore be adopted.

Methods of statistical analysis should of course be used only
for valid biological reasons. It is imperative, on this account,
to consider carefully not only the type of plant material studied
under the particular conditions of growth as already indicated
but also the stage or stages in the development of the plant
organism in which the quantitative measurements (variates)
were secured. The pomologist, with few’ exceptions, deals with
perennial woody p1ants,—trees and shrubs. Such plant material
is often studied in the developmental stage,—the grand period of
growth, during which yields are subject to progressive increases
over a period of years. From the standpoint of statistical
analysis, when the grand period of growth is ended and the
stage of so-called maturity is reached in trees, the conditions
are probably somewhat comparable to those which obtain in the
case of annual crops. When the stage of decline or senescence
sets in the conditions are again altered.

In the present case, the grapefruit trees were 5 years old when

42 BULLETIN NO. 419, TEXAS AGRICULTURAL EXPERIMENT STATION

the experiment was begun, and have developed over a 5-year l-

period. The absolute yields have, in general, reached a higher
level with increasing age of the trees. ' Since we are not dealing
with an absolute yield level, it is erroneous to consider a fictitious
mean yield for the period on the basis of the normal curve of dis-
tribution where fluctuations about a mean value are logically con-
sidered as due to errors of random sampling. Unless each season
is considered separately, it is clear that the use of probability
tables, based upon the normal curve of distribution, are not jus-
tified. It has been shown, however, that variation in plat yields
over the entire orchard is too great to make feasible the interpre--
tation of data for single seasons on the basis of the comparison
of widely separated plats. The making of seasonal paired com-
parisons of'adjacent plats on the basis of the consistency of
differences would make it possible to escape from the difiiculty
presented in the case of plants studied as developing organisms.

Method ef Interpreting Data- It follows from the preceding dis-
cussion of plat variability that even if adjacent orchard plats
are given the same cultural treatments for the duration of the
experiment they will vary to some degree one from the other.
However, as a general rule, plats adjacent or near each other
will have a tendency to vary less one from the other than plats
distributed in distant parts of the orchard for environmental
factors, such as soil fertility, drainage, etc., will tend to be sim-
ilar for both. By considering plats adjacent or near each other
some of the variable factors affecting the trees are eliminated
(22).

Since 1908, there has been available a method, commonly
known as “Student’s” Method (28, 29, 30), which meets the re-
quirements of our problem: (a) it makes possible the use of
paired comparisons, and (b) it is applicable to small numbers.

By this method groups of contrasting pairs may be compared
on the basis of the consistency of individual gains in estimating
the significance of the average difference. When this method
is employed, in the present instance, the yields of 5-tree plats of
grapefruit trees adjacent or near each other and receiving dif-
ferent treatments may be compared, and the results interpreted
on the basis of the consistency of the gain of one plat over the-
other.

The making of paired comparisons was not original with
“Student,” and his real contribution to methods of statistical
analysis is due to the development of probability tables which
are applicable to small numbers,—-2 to 30 variates. When large
numbers are available it is possible to calculate quite accurately"
the value of the standard deviation of a mean value. In such
a case the calculated results for the purpose of determining the

CITRUS PRODUCTION IN THE LOWER RIO GRANDE VALLEY OF TEXAS 43

significance of a difierence Would naturally be referred to
probability tables based upon the normal curve of distribution.
When relatively small numbers are the only data available these
tables Would not give reliable indications of the significance of a
difference since We have, then only an estimate of the true
standard deviation. In the development of “Student’s” tables
(28, 29, 30, 19) this fact Was taken into consideration. It is
not claimed that results from small samples are as reliable as
those based upon large numbers of variates. It is true, how-
ever, that the use of “Student’s” tables eliminates the mathe-
matical error that Would enter in if probability tables based on
the normal curve Were used When mean values and their standard
deviations from the means have been calculated from relatively
small samples. The Worker in such a field of economic botany
as horticulture must assume a practical attitude, and must ex-
pect to encounter the condition of small populations When dealing
With plant materials such as grapefruit trees which are not as
cheaply produced as annual crops. So long as the due caution
is exercised in the interpretation of the results under the condi-
tions there is little likelihood of going astray.

It has been pointed out above that probability tables have
been developed by “Student” (29, 19) to Which the calculated
results, according to “Student’s” formula, from any group of
contrasting pairs may be referred for the purpose of securing an
indication of the significance of the results. The probability
tables give the odds that such differences as may be obtained are
due to a cause or causes Which affected one of the pairs and not
the other and is not the result of chance variation.

When the experiment is so conducted that the factors which
influence one side of the pairs and not the other is reduced to
the minimum, except the differential treatment required by the
experiment, then the odds indicated give a measure of the sig-
nificance of the increases secured from the differential treatment.

It is the usual practice to conclude that a certain treatment is
better than another, when the odds are 30 to 1 or higher that a
given difference is the result of differential treatment and not of
chance variation. When the odds are less than 30 to 1, further
proof is required before We may conclude that the difference
obtained is due to the differential treatment and not to chance.
This condition applies especially When one is dealing With small
numbers.

Utilization 0f Plats- Out of a total of 104 plats, containing 5
trees each, 20 Were devoted to studies in cultivation, cover crops,
and mulches; 48 Were used for fertilizer Work; and 38 Were
reserved for a continuous blank experiment as indicated in the
preceding discussion.

44 BULLETIN NO. 419, TEXAS AGRlCULlURAL EXPERIMENT STATION I

CULTIVATION, COVER CROPS, AND MULCHES

Experiments concerning cultivation, cover cropping, and
mulching in citrus orchards have been reported by workers in
California (39, 40) and Florida (31, 41). The results in gen-
eral show the necessity of maintaining the organic content of the
soil at a productive maximum. This is borne out especially by
the Rubidoux experiments with citrus in California (39, 40) , and
for crops in general by the classical experiments at the Rotham-
stead Experiment Station in England.

There is considerable variation in the season of the year when
cover crops are chiefly grown in the important citrus-producing
regions. In Florida cover crops are grown during the rainy
season, May to October; in California they are produced from
December to March, and i.n Texas, summer cover cropping, from
May to August, is the general rule. .

The present experiments Will serve as a first step in determin-
ing, on an experimental basis, the most economical methods of
cultivation, cover cropping or mulching under Valley conditions.

Plan of Experiment

The experimental work concerning cultivation, cover cropping,
and mulching as factors in maintaining the Valley grapefruit
orchard at maximum bearing capacity was planned to include
ten contrasting treatments:

(a) Modified clean culture- This system of cultivation and
cover cropping consists of disking under the weeds that appear
after each irrigation. Whenever possible, weeds are not allowed
to grow to a height of more than two feet before they are disked
under. No effort is made to keep the ground entirely free of
weed growth.

This is the method commonly followed by many Valley citrus
growers on account of the fact that it becomes difiicult to keep
Valley citrus orchards free of weeds during certain periods of
the year.

(b) Modified clean culture with 6-inch plowing. When this system
is followed, a strip about 8 to 10 feet wide between the trees is
plowed to a depth of 6 inches and then the method described
under “modified clean culture” is followed.

((3) Winter cover crops,-—non-legume. This methgd Consists of
growing a crop of oats or barley on the soil during the season
from November to April and then incorporating it with the soil.
Subsequent management is the same as that described under
“modified clean culture.” i

(d) Winter cover crvpr-legume- Crops of yellow annual Sweet
Clover, Melilotus indica, are grown during the period from

' 'm.1...;

CITRUS PRODUCTION IN THE LOWER RIO GRANDE VALLEY OF TEXAS 45

November to March and then incorporated with the soil by disk-
ing. After this, “modified clean culture” is given.

(e) Summer cover crops,-—legume. CrQpg 0f cgwpeag are grown
during the period from May to August, inclusive; followed by
“modified clean culture.”

(f) Intermittent s0d—legume and culture. Alfalfa and sweet
clover were allowed to grow undisturbed for a period of three
years and were then incorporated into the soil. “Modified clean
culture” was followed the fourth year.

(g) Continuous sodrloguino- The land is kept seeded to alfalfa
for an indefinite period. No cultural tillage is given.

(h) Mulohod basin- Natural grass and weeds are allowed to
grow and are cut down with scythes several times each season
and used to mulch around trees. No cultural tillage is given.

(i) Continuous sod,—culture about trees. Natural grass and
weeds are allowed to grow undisturbed except that a small area
around the trees is kept hoed free of vegetation. No other
cultural tillage is given.

 Continuous sod,—no culture about trees. Natural grass and
weeds are allowed to grow undisturbed. No cultural tillage is
given. '

Utilization of Plats- A total of twenty 5-tree plats were avail-
able for this work, which made it possible to replicate each of
the above ten treatments twice. Practical limitations dependent
on available irrigation laterals made it necessary to arrange the
treatments in two parallel series, Plats C-3O to 39, and D-30 to
39; C-29 and C-40, D-29 and D-40 serving as border plats. The
plat arrangement is shown in Figure 1. The treatments are
indicated in Table 11.

Duration of EXporiInoni» The experiment was conducted for a
period of 4 years, 1925-26 to 1928-29. The work had to be dis-
continued after the season 1928-29 on account of the fact that
by this time the branches of the 8-year-old trees touched in
the middle of the rows. This condition made it impractical to
grow“ cover crops as originally planned.

Interpretation of Results

The results have been analyzed by the application of “Stu-
dent’s” Method on the basis of comparing adjacent plats. This
does not make it possible to compare “Modified Clean Culture,”
for instance, directly with other treatments not adjacent. How-
ever, the comparative value of any particular plat may be deter-
mined by comparison with adjacent plats on both sides, and
these in turn may be compared with plats farther removed.

 

46 BULLETIN NO. 419, TEXAS AGRICULTURAL EXPERIMENT STATION

 

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CITRUS PRODUCTION IN THE LOWER RIO GRANDE VALLEY OF TEXAS 47

It will be noted, by referring to Table 11, that 0n the basis of
a 4-year-average loss of 0.03 box, or 3 pounds, per tree, the odds
are 1:1 that “Modified Clean Culture with 6-inch Plowing” has
caused a lesser yield than “Modified Clean Culture.” Since odds
of 30 :1 are considered on the border line of significance, we con-
clude that there is no significant difference, and that nothing has
been gained or lost by the additional 6-inch plowing.

Similarly, the 4-year-average gain of 0.2 box per tree in favor
of “Winter Cover Crop,-—Non-legume” as compared with “Modi-
fied Clean Culture with 6-inch Plowing” shows odds of only 2:1
that this gain is due to the treatment and not t0 chance varia-
tion. Clearly the gain is not significant.

When, however, “Winter Cover Crop,—Legume” is contrasted
with “Winter Cover Crop,—Non-legume,” the 4-year-average
gain of 0.4 box per tree in favor of the first treatment is shown
to be significant. The odds are 87:1 that this treatment has
caused consistent gains over a 4-year period.

The Al-year-average differences, gains or losses as the case may
be, between “Summer Cover Crop,—legume” and “Winter Cover
Crop,—legume,” between “Intermittent sod—legume and culture”
and “Summer Cover Crop,—legume,” between “Continuous sod,
—legume” and “Intermittent sod—legume and culture,” and be-
tween “Mulched Basin” and “Continuous sod,—legume” are ap-
parently not significant, since on the basis of comparison of
adjacent plats the odds that these differences were due to the
treatments received and not to chance range from 1:1 to 11:1.
We conclude therefore that these five types of treatment have
given about the same responses as far as yields are concerned
during the 4 years covered by the experiment. Further experi-
ments are necessary over a longer period of years to determine
the relative importance of the various treatments which have
given the most favorable responses so far.

When the “Mulched basin” system is compared with “C0ntin-
uous natural sod,-—culture about trees,” there is an apparent
annual average loss of 0.8 box per tree as a result of the latter
treatment. The odds are 70:1, and therefore significant that
this system of sod culture was responsible for the loss.

No significant difference was revealed between the two
methods of sod culture: the one with culture about trees, and the
other without culture about trees. The odds are only 2:1 that
the latter is better than the former.

Application of Results The four years’ results indicate that
better yield responses, a gain of approximately 0.4 box per tree,
were obtained in grapefruit culture by methods of seasonal or
continuous cover cropping with legumes, or a system of mulch-
ing, than were secured by the commonly used method of “Modi-

48 BULLETIN NO. 419, TEXAS AGRICULTURAL EXPERIMENT STATION

fied clean culture,” or systems of continuous sod culture. Al- l

though the results are quite conclusive as regards the two groups

of cultural practices, the evidence is not conclusive with refer- ‘
ence to the relative importance of the treatments which have ¢
given most favorable increases in yield. This may be due to f
the fact (a) that the experiment Was conducted on relatively ;
fertile virgin soil and covered a period of only 4 years, and (b) 
that the trees Were only 9 years old at the end of the experi- §
ment. It is possible that the natural fertility of the soil made A
it impossible to reveal differences great enough to be measured 
under the conditions. With mature trees (10 to 20 years of 

age) over a similar or longer period of years, the relative values
of these outstanding treatments may be obtained.

For the present, it Will be safe to recommend a system of
seasonal leguminous cover cropping with tillage rather than the
customary method of clean cultivation with only sporadic natural
cover crops. Deeper plowing, 6 inches once per season, does not
seem to be of practical value, when added to the system of
“Modified clean culture.”

FERTILIZER APPLICATION

It is natural that Where large crops are removed from the
land annually, even in the case of virginally fertile soils, the
plant food Will ultimately become exhausted and must be re-
placed. The question of economical fertilizer application must
therefore be considered sooner or later. Consequently, in other
citrus-producing areas fertilizer experiments have been carried
on for some time. Work carried on in California (39, 40) over a
period of year points to the fact that nitrogen is a critical ele-
ment in citrus-fruit production on the soils utilized. Similar
experiments conducted in Florida (7, 31, 41) seem to indicate
the advisability of using complete fertilizers.

Plan of Experiment

The present experiment concerning grapefruit fertilization
was undertaken With the object of determining (a) the time
required for exhausting the natural fertility of the soil to such
a point, by cropping With grapefruit, Where the application of
commercial fertilizers will become profitable, and (b) the grade
and amount of fertilizer mixture required to keep productivity
at the most profitable point When the time arrives that fertilizer
applications are profitable.

Plats Available- Exclusive of border plats, a total of forty 5-
tree plats Were available for these experiments: A-2 to 11; B-2
to 11; C-2 to 11; and D-2 to 11. The location of the plats with

 

CITRUS PRODUCTION IN THE LOWER RIO GRANDE VALLEY OF TEXAS 49

reference to the entire experimental orchard is shown in Fig-
ure 1.

Kind 0f Treatments- A total of 18 different treatments are in-
cluded in the experiment. The fertilizer formula, 4-8-4 (4 per
cent nitrogen; 8 per cent phosphoric acid; and 4 per cent potash) ,
was adopted as the standard grade or formula for the treatments
With inorganic fertilizers. Treatments were arranged to test
the three fertilizer elements, nitrogen, phosphoric acid, and pot-
ash (a) in combination as a so-called complete fertilizer
(N-P-K) ; (b) in pairs (two fertilizer elements, O-P-K N-O-K,
and N-P-O) ; and (c) alone (one fertilizer element, N-O-O,
O-P-O, and O-O-K) . In addition to these treatments, phosphoric
acid was used in one-half (4-4-4), and potash in double (4-8-8)
amounts with full amounts of the other two as required by the
standard formula. In one treatment, consisting of nitrogen
alone, one-half of the amount was applied in the spring, and
the other half in the summer. In one case cottonseed meal was
added to the standard treatment (4-8-4) with inorganic chem-
icals. The following sources of the fertilizer elements were
used: (a) nitrogen,—nitrate of soda; (b) phosphoric acid,-
superphosphate; and (c) potash,—sulphate of potash, and
muriate of potash.

Organic fertilizers (barnyard manure, bone meal, and cotton-
seed meal), hydrated lime, gypsum, flowers of sulphur, and iron
sulphate were applied alone.

The amounts and kind of fertilizers constituting the various
treatments are conveniently indicated in the first column of
Table 12.

Replication- The relatively large number of treatments, 18 in
all, precluded the possibility of much replication. As 11 plats
were reserved as checks receiving no treatment, two replications
were possible with 11 treatments; this left 7 treatments with-
out replicates. The relatively small number of replications will
necessitate carrying on the experiment over a long period of
years to make up in part for this deficiency. r

Application of Fertilizers» The various treatments have been in-
dicated in actual weight of fertilizer material applied. In or-
der to reduce the possibility of cross feeding to a minimum, the
greater part of the amount was applied to the soil between trees
in the same row, but small amounts were also applied on the
other two sides. No fertilizer was placed on the soil compris-
ing the irrigation borders between plats.

50 BULLETIN NO. 419, TEXAS AGRICULTURAL EXPERIMENT STATION

 

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51

CITRUS PRODUCTION IN THE LOWER RIO GRANDE VALLEY OF TEXAS

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52 BULLETIN NO. 419, TEXAS AGRICULTURAL EXPERIMENT STATION

Method of Interpreting Results

It has been emphasized in the discussion of cultivation and
cover cropping that in an experiment with relatively young trees
(4 to 10 years old) grown on fertile virgin soil, it may be pos-
sible to show only the marked differences over such a compara-
tively short period of 5 years. The experiment must be con-
tinued long enough to include also the behavior of maturegrape-
fruit trees (10 years or older). The analysis of the 5-year
data, however, will shed some light on the degree of natural
fertility of the soil, which is one of the purposes for conducting
the experiment. The second enquiry regarding the grade and
amount of fertilizers to apply will become of importance only
When nutrient deficiencies become apparent. The interpreta-
tion of the results at the end of 5 years, in the case of young
trees which were 4 years old at the beginning of the experiment
and are now 10 years old, under the conditions of the experiment
must be approached with due respect for these facts.

Yields without Fertilizer Application. Seasonal variations in yields
are quite marked, as would be expected in the case of develop-
ing trees. The trees, four years of age, at the beginning of the
continuity experiment as shown in Tables 9 and 10, averaged
one 100-pound box of fruit per tree. During the following years
seasonal mean yields per tree were: 1925-26, 0.8; 1926-27, 1.5;
1927-28, 3.1; 1928-29, 1.8; and 1929-30, 5.1 boxes. These yields
were secured without the use of fertilizer. It will be noted that
when the trees in this experiment had attained the age of 10
years the per tree yield was comparable to that secured from
well-cared for commercial orchards of similar, age, approxi-
mately 4.0 100-pound boxes.

Use 0f “Studenifs Method- The results have been interpreted
according to “Student’s” method, the contrasted pairs consisting
of a treated plat and a mean or average value arrived at by con-
sidering the nearest check plats on both sides of the treated
plat. Where this procedure was not possible, the nearest check
plat alone was utilized as the other member of the pair. The
complete results are presented in Table 12.

Application of Complete Fertilizers. Ag ghgwn in Table 12, a Com-
plete fertilizer composed of 2.6 pounds of nitrate of soda, 5
pounds of acid phosphate, and 0.8 pound of sulphate of potash
gave indicated increases of 0.6 and 0.1 box per tree over a 5-
year period. On the basis of the consistency of these increases,
the odds, according to “Student’s” tables, range from 1 :1 to 8:1
that these indicated differences are consistent and therefore sig-
nificant. In the light of the results from the continuity experi-
ment, where no fertilizer was applied, and the yields are appar-

CITRUS PRODUCTION IN THE LOWER RIO GRANDE VALLEY OF TEXAS 53

ently normal as judged by comparison with yields from com-
mercial orchards 0f the same age, such results as secured by the
application of a complete fertilizer would seem to indicate that
soil fertility has not as yet become a limiting factor under the con-
ditions of the experiment.

In the case of all the remaining treatments with complete
fertilizers as shown in Table 12, similar results have been se-
cured so far. The odds range from 1 :1 to 14 :1 that such treat-
ments have caused increases or losses as the case may be, and
are therefore, not significant.

Application of Two Fertilizer Elements. When two fertilizer ele-
ments are applied, as shown in Table 12, the indicated gains or
losses due to the treatments, over a 5-year period, are apparently
not significant. Two exceptions appear. A loss of 0.6 box per
tree in the case of a treatment with 5 pounds of acid phosphate
and 0.8 pound of sulphate of potash with odds of 40:1 is counter-
balanced by an indicated gain of 0.4 box in another similar
treatment with odds of 1:1 in another part of the orchard.
Similar contradictory results were secured for the treatment of
two plats with 2%- pounds of nitrate of soda and 5 pounds of acid
phosphate.

Application of One Fertilizer Element. Ag would be expected frem
the results discussed thus far, the gains or losses indicated as
associated with the treatment with one fertilizer element are
apparent rather than real. The odds range from 1:1 to 3:1
that the difierences indicated are due to the treatments, except-
ing in one instance. When 5 pounds of acid phosphate was
applied in one case the indicated gain was 0.7 box, with odds of
35:1, but another identical treatment in another part of the
orchard gave an indicated increase of 0.1 box per tree with odds
of only 2 :1 that the difference is due to the treatment and not to
chance variation.

Organic Fertilizers, Lime and Other Chemicals. When different plats
were treated at the rate of 400 pounds of stable manure, 10
pounds of bone meal, 75- pounds of cottonseed meal, 12 pounds
of hydrated lime, 12 pounds of gypsum, 1% pounds of flowers
of sulphur, and 1.1; pounds of iron sulphate per tree in eachlcase,
the oddsgthat increases or decreases indicated are significant
range from 3:1 to 20:1. In all except one case, the odds are
11:1 or below that the differences are due to the treatments and
not to chance variation. When hydrated lime was applied at

the rate of 12 pounds per tree an indicated mean anuual in-

crease of 0.5 box per tree is shown, and the odds are 20:1 that
this difference is significant, but in the absence of a replicate,

54 BULLETIN NO. 419, TEXAS AGRICULTURAL EXPERIMENT STATION

the results must be observed over a longer period before any I

reliance can be placed on the odds approaching 30:1.

Discussion of Results- The results secured over a five-year period
with fertilizer treatments seem to show that on the basis of the
application of “Student’s” method, increases or decreases indi-
cated are not significant. Several explanations are possible:
(a) soil fertility may not as yet be a limiting factor in this
orchard; (b) variation in yields due to differences in soil, plant
materials, etc., may be important; (c) the differences caused
by the treatments may not be great enough to be revealed by the
‘technic of analysis used; or (d) cross feeding may occur.

In view of the fact that consistent results Were secured by
the application of “Student’s” method in the interpretation of
data secured with varying treatments in the cultivation, cover
cropping, and mulching experiment, it would appear that the
method of analysis used is adequate, and that cross feeding has
not been an important factor up to the present.

Although there was a rather great variation in yields over the
entire orchard at the beginning of the experiment as shown in
Table 8, the yields of the continuity experiment, shown in Tables
9 and 10, indicate that this variation is becoming generally less
and less as the orchard reaches maturity. The elimination of
yields from abnormal trees, and the comparison of plats which
are adjacent or in close proximity also has the tendency to re-
duce plat variation from such causes as differences in soil fer-
tility, injury from pests, etc., to the minimum.

It appears, therefore, that the inconsistent results from the
application of fertilizers under the conditions of the experiment,
up to the present, are due to the favorable virginal fertility of

‘the soil. That the fertilizer elements applied under the experi-
‘mental conditions were apparently not limiting factors up to
the present time is borne out by the yields indicated in the con-
tinuity experiment as pointed out above. Although these trees

received no fertilizer applications, their development and yields
appear normal.

Application 0f Results The results from the fertilizer experi-
ments thus far seem to indicate that the Valley citrus grower is
favorably situated as regards natural soil fertility. These re-
sults are in essential harmony with the practice of not utilizing
fertilizers until the trees reach bearing age.

The results, however, should not be interpreted as meaning
that fertilizers should be withheld after the trees reach bearing
age since moderate applications along with other orchard prac-
tices throughout the development and maintenance of the orchard
"will tend to keep the original fertility of the soil unimpaired.

Figure 2. Spacing of grapefruit trees. Upper—10-year Marsh trees spaced 21x21 ft.,
Weslaco Station; lower—10-year Marsh trees spaced 30x30 ft., Donna, Texas.

‘56 BULLETIN NO. 419, TEXAS AGRICULTURAL EXPERIMENT STATION

SPACING GRAPEFRUIT TREES

In laying out the grapefruit orchard one should allow sufficient
space between the trees to facilitate such necessary orchard
practices as cultivation, cover cropping, orchard heating, pest
control, fruit harvesting, and the maintenance of irrigation
borders. Planting distances will depend in the main upon the
growth habits of the variety and root-stock, the fertility of the
soil, and the amount of irrigation water available, or the amount
-of rainfall. Although grapefruit trees planted relatively closer
together are better protected from wind and frost, close spacing
has the effect of crowding out the lower fruiting branches.

The spacing distances formerly used in the Valley, 21x21 feet,
as used in California (42), are apparently not suited to local
conditions of high soil fertility and favorable climatic factors
for growth. As a general rule grapefruit trees grow vigorously
in the Lower Rio Grande Valley, and after 8 years the branches
-of adjacent trees spaced 21x21 feet, usually touch. This inter-
feres seriously with cultivation and other orchard practices, and
as has been pointed out, the lower branches of the trees are
unduly shaded. Proper spacing distances for grapefruit trees in
the Valley seem to be about 25x25 feet. As shown in Figure 2,
trees of the Marsh variety in the Station orchard on Victoria
fine sandy loam soil, spaced 21x21 feet, are crowded at the end
of 10 years. Trees in a similar orchard of the Marsh variety
at Donna, Texas, on the same type of soil, spaced 30x30 feet, do
not show crowding at the end of 10 years. However, this wide
spacing will tend to reduce acre yield during the first six or
eight years of bearing.

ACKNOWLEDGMENTS

The experiments dealing with the various factors that enter
into citrus production in the Lower Rio Grande Valley, including
standardization of varieties, citrus root-stocks, fertilizer appli-
cation, use of tillage, cover crops and mulches, etc., were initiated
by W. H. Friend and A. T. Potts in 1924. Experiments on
quality in citrus were initiated by H. P. Traub and W. H. Friend
in 1928. Thanks are due Dr. G. S. Fraps for advice in planning
the fertilizer experiments and for assistance in connection with
the analytical work on citrus quality.

CONCLUSIONS

1.1 The annual citrus-fruit shipments from the Lower Rio
Grande Valley of Texas reached approximately 4000 carloads by
1929-30.

2. More than 5,000,000 citrus trees were growing in orchard

CITRUS PRODUCTION IN THE LOWER RIO GRANDE VALLEY OF TEXAS 57

form in the Lower Rio Grande Valley as of July 1, 1929; of
these, approximately 75 per cent Were grapefruit, 13 per cent of
which were 5 years of age or older.

3. On the basis of adaptability t0 local conditions, physical
character of the Whole fruit, and quality of juice, the relative
merits of various types of citrus fruits have been studied during
the period from 1924 to 1930.

4. The Marsh grapefruit and Thompson, a pink-fleshed bud-
mutation of Marsh, are recommended for general planting in
the Valley. These varieties are desirable because of their rela-
tive “seedlessness” and superior quality of juice.

5. The desired tartness in sweet oranges as grown under
Valley conditions seems to be present in late varieties like»
Valencia; early varieties like ParsonBrown are apparently lack-
ing in this respect. Of the early varieties, Hamlin is recom-

mended for general planting on account of its relative “seedless-

ness” and excellent quality. However, this variety lacks the
qualities desirable in a good “shipping” orange. Of the late
varieties, Valencia is recommended as the standard. This
xrariety possesses excellent “shipping” quality and the desired
tartness of juice.

6. The Clementine or Algerian tangerine is recommended as
the most desirable variety in this group, because of its early
maturity and superior quality.

7. Ordinary commercial forms of lemons are too tender to
frost to be profitable in this region. From the standpoint of
general adaptability, especially frost resistance, a special form,
the Meyer lemon, takes first rank in this group of citrus fruits.

8. The commercial forms of limes are too tender to frost to
be profitable in this region. A special form, Rangpur lime, al-
though quite hardy to cold, is lacking in quality.

9. The kumquat is one of the hardiest forms of citrus grown
in the Valley and is well adapted to local conditions.

10. The following citrus root-stocks are recommended for
the various" types: (a) grapefruit, sweet orange, tangerine, and
lime on sour orange; (b) Satsuma orange on Rusk Citrange;

(c) Meyer lemon on its own roots; (d) Kumquat on rough lemon;

or Rusk Citrange.

11. Four years’ results with cultivation, cover crops, and
mulches in grapefruit culture indicate that beftter yield re-
sponses, an annual gain of approximately 0.4 box per tree, were

obtained by the use of leguminous cover crops and by a system

of mulching than were secured by the commonly used method of '

“modified clean culture,” or non-leguminous cover cropping.

12. Five years’ results with differential fertilizer treatments.
in grapefruit culture indicate that the materials and amounts.
used have not produced significant increases in yield.

58 BULLETIN NO. 419, TEXAS AGRICULTURAL EXPERIMENT STATION

13. A spacing distance of 25x25 feet is apparently more
desirable for grapefruit in the Lower Rio Grande Valley than a
closer spacing. The 21x21-foot spacing used -in the early days
of the industry is too close for this region.

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