• TABLE OF CONTENTS
HIDE
 Title Page
 Credits
 Table of Contents
 Introduction
 Relation of temperature and time...
 Relation of spacing to head size...
 Other cultural factors
 Summary and conclusions
 References
 Tables














Group Title: Bulletin - University of Florida. Agricultural Experiment Station ; no. 365
Title: Crisp-head lettuce in Florida
CITATION THUMBNAILS PAGE IMAGE ZOOMABLE
Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF00027278/00001
 Material Information
Title: Crisp-head lettuce in Florida a preliminary report
Series Title: Bulletin University of Florida. Agricultural Experiment Station
Physical Description: 19 p. : ill., charts ; 23 cm.
Language: English
Creator: Beckenbach, J. R ( Joseph Riley ), 1908-
Publisher: University of Florida Agricultural Experiment Station, 1941.
Place of Publication: Gainesville Fla
 Subjects
Subject: Lettuce -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Bibliography: Bibliography: p. 17.
Statement of Responsibility: by J.R. Beckenbach ... et al..
General Note: Cover title.
Funding: Bulletin (University of Florida. Agricultural Experiment Station)
 Record Information
Bibliographic ID: UF00027278
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: aleph - 000924598
oclc - 18229903
notis - AEN5225

Table of Contents
    Title Page
        Page 1
    Credits
        Page 2
    Table of Contents
        Page 3
    Introduction
        Page 3
        Page 4
    Relation of temperature and time of planting to the heading of several strains of crisp-head lettuce
        Page 5
        Page 6
        Page 7
        Page 8
        Page 9
        Page 10
        Page 11
        Page 12
    Relation of spacing to head size and earliness
        Page 13
        Page 14
        Page 15
    Other cultural factors
        Page 16
    Summary and conclusions
        Page 16
    References
        Page 17
    Tables
        Page 18
        Page 19
Full Text

bulletin 365
Bulletin 365


December, 1941


UNIVERSITY OF FLORIDA
AGRICULTURAL EXPERIMENT STATION
WILMON NEWELL, Director
GAINESVILLE, FLORIDA





Crisp-Head Lettuce in Florida
A PRELIMINARY REPORT

By
J. R. BECKENBACH, F. S. JAMISON, R. W. RUPRECHT AND F. S. ANDREWS


Fig. 1.-Crisp-head lettuce grown under critical temperature condi-
tions. The varieties and strains are as follows: 1. Cosberg; 2. New York
No. 12; 3. Imperial No. 152; 4. Imperial No. 847; 5. Imperial No. 850;
6. Imperial No. 44; 8. Imperial No. 615; 9. New York No. 515.




Single copies free to Florida residents upon request to
AGRICULTURAL EXPERIMENT STATION
GAINESVILLE, FLORIDA







EXECUTIVE STAFF
John J. Tigert, M. A., LL. D., President
of the University3
Wilmon Newell, D.Sc., Director3
Harold Mowry, M. S. A., Asst. Dir., Res.
W. M. Fifield, M. S., Asst. Dir., Admin.
J. Francis Cooper, M. S. A., Editor3
Clyde Beale, A.B.J., Assistant Editor3
Jefferson Thomas, Assistant Editor3
Ida Keeling Cresap, Librarian
Ruby Newhall, Administrative Manager3
K. H. Graham, Business Manager3
Rachel McQuarrie, Accountant3
MAIN STATION, GAINESVILLE
AGRONOMY
W. E. Stokes, M.S., Agronomist'
W. A. Leukel, Ph.D., Agronomist3
Fred H. Hull, Ph.D., Agronomist
G. E. Ritchey, M.S., Associate2
W. A. Carver, Ph.D., Associate
Roy E. Blaser, M.S., Associate
G. B. Killinger, Ph.D., Associate
John P. Camp, M.S., Assistant
Fred A. Clark, B.S.A., Assistant
ANIMAL INDUSTRY
A. L. Shealey, D.V.M., An. Industrialist',
R. B. Becker, Ph.D., Dairy Husbandman3
E. L. Fouts, Ph.D., Dairy Technologist3
D. A. Sanders, D.V.M., Veterinarian
M. W. Emmel, D.V.M., Veterinarian3
L E. Swanson, D. V. M., Parasitologist
N. R. Mehrhof, M.Agr., Poultry Husb.3
W. M. Neal, Ph.D., Asso. in An. Nutrition
T. R. Freeman, Ph. D., Associate in Dairy
Manufactures
D. J. Smith, B.S.A., Asst. An. Husb.3
P. T. Dix Arnold, M.S.A., Asst. Dairy
Husbandman'
L. L. Rusoff, Ph.D., Asst. in An. Nutr.3
L. E. Mull, M. S., Asst. in Dairy Tech.
0. K. Moore, M.S., Asst. Poultry Husb.
ECONOMICS, AGRICULTURAL
C. V. Noble, Ph.D. Agr. Economist 1,3
Zach Savage, M.S.A., Associate
A. H. Spurlock, M.S.A., Associate
Max E. Brunk, M.S., Assistant
ECONOMICS, HOME
Ouida D. Abbott Ph.D, PhHome Econ.1
Ruth Overstreet, R.N., Assistant
R. B. French, Ph.D., Asso. Chemist
ENTOMOLOGY
J. R. Watson, A.M., Entomologist'
A. N. Tissot, Ph.D., Associate
H. E. Bratley, M.S.A., Assistant
HORTICULTURE
G. H. Blackmon, M.S.A., Horticulturist'
A. L. Stahl, Ph.D., Associate
F. S. Jamison, Ph.D., Truck Hort."
R. J. Wilmot, M.S.A., Asst. Hort.
R. D. Dickey, M.S.A., Asst. Horticulturist
J. Carlton Cain, B.S.A., Asst. Hort.
Victor F. Nettles, M.S.A., Asst. Hort.
F. S. Lagasse, Ph.D., Asso. Horticulturist2
H. M. Sell, Ph.D., Asso. Horticulturist2
PLANT PATHOLOGY
W. B. Tisdale, Ph.D., Plant Pathologist1.3
George F. Weber, Ph.D., Plant Path.3
L. 0. Gratz, Ph.D., Plant Pathologist
Erdman West, M.S., Mycologist
Lillian E. Arnold, M.S., Asst. Botanist
SOILS
R. V. Allison, Ph.D., Chemist'.s
Gaylord M. Volk, M.S., Chemist
F. B. Smith, Ph.D., Microbiologist3
C. E. Bell, Ph. D., Associate Chemist
J. Russell Henderson, M.S.A., Associate3
L. H. Rogers, M.S., Asso. Biochemist
H. W. Winsor, B.B.A., Assistant Chemist
Richard A. Carrigan, B.S., Asst. Chemist
Geo. D. Thornton, M.S., Asst. Chemist


BOARD OF CONTROL
H. P. Adair, Chairman, Jacksonville
W. M. Palmer, Ocala
R. H. Gore, Ft. Lauderdale
N. B. Jordan, Quincy
T. T. Scott, Live Oak
J. T. Diamond, Secretary, Tallahassee
BRANCH STATIONS
NORTH FLORIDA STATION, QUINCY
J. D. Warner, M.S. Agron. in Charge
R. R. Kincaid, Ph.D., Asso. Plant Path.
Elliott Whitehurst, B.S.A., Assistant An.
Husbandman
Jesse Reeves, Asst. Agron., Tobacco
CITRUS STATION, LAKE ALFRED
A. F. Camp, Ph.D., Horticulturist in Chg.
John H. Jeffries, Asst. in Cit. Breeding
Chas. K. Clark, Ph.D., Chemist
V. C. Jamison, Ph.D., Soils Chemist
B. R. Fudge, Ph.D., Associate Chemist
W. L. Thompson, B.S., Associate Ento.
F. F Cowart, Ph. D., Asso. Horticulturist
W. W. Lawless, B.S., Asst. Horticulturist
R. K. Voorhees, Ph.D., Asst. Plant Path.
EVERGLADES STA., BELLE GLADE
J. R. Neller, Ph.D., Biochemist in Chg.
J. W. Wilson, Sc. D., Entomologist
F. D. Stevens, B.S., Sugarcane Agron.
Thomas Bregger, Ph. D., Sugarcane
Physiologist
G. R. Townsend, Ph.D., Plant Pathologist
R. W. Kidder, M.S., Asst. An. Husb.
W. T. Forsee, Ph.D., Asso. Chemist
B. S. Clayton, B.S.C.E., Drainage En-
gineer2
F. S. Andrews, Ph.D., Asso. Truck Hort.
Roy P. Bair, Ph.D., Asst. Agron.
J. C. Hoffman, M.S.. Asst. Hort.
SUB-TROPICAL STA., HOMESTEAD
Geo. D. Ruehle, Ph.D., Associate Plant
Pathologist in Charge

S. J. Lynch, B.S.A., Asst. Horticulturist
E. M. Andersen, Ph.D., Asst. Hort.
W. CENTRAL FLA. STA.,
BROOKSVILLE
W. F. Ward, M.S., Asst. An. Husband-
man in Charge2
RANGE CATTLE STA., WAUCHULA
W. G. Kirk, Ph.D., Animal Husbandman
in Charge
Gilbert A. Tucker, B.S.A., Asst. An. Husb.
FIELD STATIONS
Leesburg
M. N. Walker, Ph.D., Plant Pathologist
in Charge
K. W. Loucks, M.S., Assistant Plant
Pathologist
Plant City
A. N. Brooks, Ph.D., Plant Pathologist
Hastings
A. H. Eddins, Ph.D., Plant Pathologist
E. N. McCubbin, Ph.D., Asso. Truck
Horticulturist
Monticello
A. M. Phillips, B.S., Asst. Entomologist2
Bradenton
Jos. R. Beckenbach, Ph.D., Truck Horti-
culturist in Charge
David G. Kelbert, Asst. Plant Pathologist
Sanford
R. W. Ruprecht, Ph.D., Chemist in
Charge, Celery Investigations
W. B. Shippy, Ph.D., Asso. Plant Path.
Lakeland
E. S. Ellison, Meteorologist2

'Head of Department
2In cooperation with U. S.
'Cooperative, other divisions, U. of F.









Crisp-Head Lettuce in Florida
A PRELIMINARY REPORT

By
J. R. BECKENBACH, F. S. JAMISON, R. W. RUPRECHT AND F. S. ANDREWS'

CONTENTS
Page
Relations of Temperature and Time of Planting to the Heading of
Crisp-head Lettuce -........-.........- ..... ..- ---------------- 5
Yield Response of Crisp-head Lettuce to Fertilizers......--- .............-..... 8
Influence of the Soil ....-.....-.- .... ... ... ---..... ..- ---- 8
N nitrogen ......-...--- ..-- --- .------. .......----. --------- -------- 9
Phosphates --..--.. --.... .- ...... -..- ....--------- -- --- 10
Potash ... .......... ...... .... ....-....--- ------- --- ---..-..- -- 10
Fertilizer Ratios ..........---.-- .--....... .... .. --- ...............- 11
Sources of Nitrogen ...... ---- ------...-..-............... 12
Relation of Spacing to Head Size and Earliness...---....... ..... ....- ....---. 13
Other Cultural Factors ...- .. ...--- -...----- -----... 16
Summary and Conclusions ..-._.-.. ....-...- ............. -- ..- .. 16
References -..-..- ..... -.....-----....... -- ----...--.... 17
Appendix --..- ..... ...... .... ..........-- ---- --------- ------. --18

INTRODUCTION

The lettuce industry has perhaps the most interesting history
of any vegetable crop in the United States. It has experienced
a tremendous increase in demand and consumption in the last
two decades. Several factors combined to bring this about,
among which were rapid population shifts to urban areas, the
discovery of the importance of vitamins and minerals in human
physiology, and an increased liking for salads by the bulk of the
population.

From the standpoint of the Florida growers, this increased
demand was much to be desired until the consuming public be-
gan to show a decided preference for crisp-head types of lettuce
as grown in the Far West in contrast to the butter-head types
grown in Florida. Whether or not the same tremendously in-
creased consumption would have resulted had butter-head va-
rieties alone been available will never be known. Certainly,
when the demands of a salad and vitamin conscious public in-
creased many-fold in the 1920's it was the crisp-head types that
were wanted. Varieties of this type available at that time were
not suited to Florida's climatic conditions. New York and strains
of this variety grown in the West would not head consistently in

'The authors are indebted to D. G. A. Kelbert and Victor F. Nettles
for their assistance throughout the work reported.









Crisp-Head Lettuce in Florida
A PRELIMINARY REPORT

By
J. R. BECKENBACH, F. S. JAMISON, R. W. RUPRECHT AND F. S. ANDREWS'

CONTENTS
Page
Relations of Temperature and Time of Planting to the Heading of
Crisp-head Lettuce -........-.........- ..... ..- ---------------- 5
Yield Response of Crisp-head Lettuce to Fertilizers......--- .............-..... 8
Influence of the Soil ....-.....-.- .... ... ... ---..... ..- ---- 8
N nitrogen ......-...--- ..-- --- .------. .......----. --------- -------- 9
Phosphates --..--.. --.... .- ...... -..- ....--------- -- --- 10
Potash ... .......... ...... .... ....-....--- ------- --- ---..-..- -- 10
Fertilizer Ratios ..........---.-- .--....... .... .. --- ...............- 11
Sources of Nitrogen ...... ---- ------...-..-............... 12
Relation of Spacing to Head Size and Earliness...---....... ..... ....- ....---. 13
Other Cultural Factors ...- .. ...--- -...----- -----... 16
Summary and Conclusions ..-._.-.. ....-...- ............. -- ..- .. 16
References -..-..- ..... -.....-----....... -- ----...--.... 17
Appendix --..- ..... ...... .... ..........-- ---- --------- ------. --18

INTRODUCTION

The lettuce industry has perhaps the most interesting history
of any vegetable crop in the United States. It has experienced
a tremendous increase in demand and consumption in the last
two decades. Several factors combined to bring this about,
among which were rapid population shifts to urban areas, the
discovery of the importance of vitamins and minerals in human
physiology, and an increased liking for salads by the bulk of the
population.

From the standpoint of the Florida growers, this increased
demand was much to be desired until the consuming public be-
gan to show a decided preference for crisp-head types of lettuce
as grown in the Far West in contrast to the butter-head types
grown in Florida. Whether or not the same tremendously in-
creased consumption would have resulted had butter-head va-
rieties alone been available will never be known. Certainly,
when the demands of a salad and vitamin conscious public in-
creased many-fold in the 1920's it was the crisp-head types that
were wanted. Varieties of this type available at that time were
not suited to Florida's climatic conditions. New York and strains
of this variety grown in the West would not head consistently in

'The authors are indebted to D. G. A. Kelbert and Victor F. Nettles
for their assistance throughout the work reported.





Florida Agricultural Experiment Station


Florida. The whole story of the trend to the crisp-head type is
evident from Table 1.

TABLE 1.-CARLOTS OF LETTUCE (INCLUDING ROMAINE) SHIPPED, 1916-17 TO 1939-40.1
Carlot Shipments, Carlot Shipments Percent
Year Florida Total, U.S. of Total

1916-17 1,116 5,428 20.6
1917-18 2,352 6,959 33.8
1918-19 2,134 8,018 26.6
1919-20 2,940 13,788 21.3
1920-21 2,267 18,738 12.1
1921-22 3,32N 22,240 14.9
1922-23 2,926 27,793 10.5
1923-24 2,490 29,461 8.5
1924-25 2,190 36,509 6.0
1925-26 707 41,546 1.7
1926-27 950 45,824 2.1
1927-28 880 51,420 1.7
1928-29 1,117 54,687 2.0
1929-30 560 54,529 1.0
1930-31 940 51,999 1.8
1931-32 440 46,757 .9
1932-33 465 42,859 1.1
1933-34 420 45,180 .9
1934-35 316 45,157 .7
1935-36 324 48,401 .7
1936-37 321 51,299 .6
1937-38 360 44,333 .8
1938-39 3372 51,783 .6
1939-40 5752

'Information from USDA Statistical Yearbooks.
"Includes truck shipments, information from Florida State Marketing
Bureau.

There are now indications that Florida growers are once again
breaking into the picture with head lettuce. In the past several
years new strains of crisp-head lettuce have been developed
which show considerable resistance to high temperatures, with
respect to both heading and bolting to seed. These are mostly
known as "Imperial" strains, and are the result of controlled
breeding and selection by the United States Department of Agri-
culture. The original purpose was to develop strains suitable for
special conditions in the Far West, and disease resistance was
one of the primary objects. In the course of the work several of
the new strains, while not particularly suited to Western condi-
tions, showed qualities which led to their trial in the East and
South, by both the United States Department of Agriculture and
state experiment stations. This work is being continued. It is
reasonable to assume that strains or varieties will be developed






Crisp-Head Lettuce in Florida


which will be more suitable for Florida conditions than any yet
available.

However, it is evident at this time that Florida growers are
now in a position to furnish the market with crisp-head lettuce
of excellent quality during a limited season due to the introduc-
tion of these new varieties. This fact has been established both
by commercial trial and by Experiment Station research. The ag-
ricultural agents of railroad lines serving Florida also have con-
tributed in a major way toward this conclusion. As a result,
Florida will undoubtedly become a competitor with other sec-
tions during the season in which lettuce of quality can be grown.
The purpose of the experimental work upon which this bulle-
tin is based was two-fold: first, to test varieties and strains
which might be adaptable to production in Florida; and second,
to study various cultural practices in relation to the growth of
these varieties and strains under Florida conditions. The fact that
lettuce is a cool weather crop, very sensitive to high tempera-
tures and a complete loss once it bolts to seed, makes it tre-
mendously important that some real understanding of the crop
based on Florida conditions be obtained as soon as possible. As
a consequence, in order to get essential information in the
growers' hands, this bulletin is being published on the basis of
only two years' results. Research work is being continued to
get a more complete solution of the problems involved, but it
was felt that early publication was essential to help this new in-
dustry become established in the state with the least possible loss
of time and energy.

RELATION OF TEMPERATURE AND TIME OF PLANTING
TO THE HEADING OF SEVERAL STRAINS OF
CRISP-HEAD LETTUCE
The climate of Florida varies from sub-tropical to temperate,
and since climatic factors (particularly temperatures) are of the
utmost importance in the commercial production of lettuce, it
is necessary to consider these conditions carefully in experi-
mental work with this crop.
If temperatures remain above a certain maximum level,
particularly during the period when the heads are forming, the
plants will bolt to seed, and no salable heads will be formed.
At the other end of the temperature range, it has been known






Florida Agricultural Experiment Station


that lettuce is tolerant of frosts and freezing temperatures,
particularly in the seedling stage. In the mature or heading
stage its tolerance to frost or to cold, drying winds, depends
largely upon weather conditions which precede the period of
cold weather. It has been found that a sudden, though light, frost
which follows a comparatively warm spell can do tremendous
damage to heading lettuce, particularly if the day following the
frost is also warm. On the other hand the severe freeze of late
January 1940 did comparatively little damage to mature lettuce
in the Manatee section, although ice formed as much as an
inch-and-a-half inside the head, and temperatures dropped be-
low 25" F. This physiological preconditioning to adverse tem-
perature conditions is common to many plants, may be effective
at either end of the temperature range, and is quite apt to cause
confusion where temperature relationships must be studied.
For the most part it is possible to divide Florida into two
sections on the basis of temperature effects on lettuce. Where
only occasional frosts are experienced as in the southern end of
the state and in a strip extending north on each coast, crisp-head
lettuce is a winter crop. Where freezing winter temperatures are
normally expected, lettuce can be considered as a spring or fall
crop.
This subdivision of the state should cause little confusion,
since it is based on a definite temperature, 320F. It is at the other
end of the temperature range that the tolerance of lettuce must
be determined. Studies with several varieties and strains re-
ported herein were for the purpose of finding the temperature
above which lettuce will go to seed without forming salable
heads. Other factors, such as fertilization, have been found to
affect the expression of bolting somewhat, but the factor re-
sponsible is unquestionably relatively high temperatures.
Experimental work with varieties and strains of lettuce has
been carried out at Sanford, Gainesville, Belle Glade, Bradenton,
Hastings and Homestead by staff members of the Florida Ex-
periment Station located at each of these areas. The findings
are in agreement on the major issue of importance to commer-
cial growers-that of all available commercial varieties at this
time, Imperial No. 44 has exhibited the greatest tolerance to
high temperatures, regardless of the season or location in which
the comparison was made. This is in agreement with results re-
ported by the Cornell University Agricultural Experiment







Crisp-Head Lettuce in Florida


Station in 1939 (3),2 where Imperial No. 44 had been tested
against a number of other varieties and strains. This strain, as
well as other Imperial strains on the market, was developed by
the United States Department of Agriculutre, and the history
of their development has been published recently (2).
Other commercial strains tested which proved more sus-
ceptible to bolting in warm weather, but which were in some
respects preferable to Imperial No. 44 under suitable weather
conditions, were the Imperial strains No. 487, No. 850, No. 615
and No. 152. These strains normally grow somewhat larger than
Imperial No. 44 when planted on mineral soils, and are less apt
to produce ribbyy" heads when grown under conditions of high
fertility. It is doubtful if these advantages are enough to make
up for their high temperature sensitivities. Varieties and strains
tested but found undesirable were New York No. 12, New York
No. 515, Columbia No. 1.
As stated above, results from all sections of the state have
indicated agreement on these comparisons. From this material,
one group of results has been selected and the data presented
in Table 2. These data are from the 1939-40 season of the Braden-
ton plantings. A record of weekly minimum temperatures for
the last two seasons at Bradenton is presented in Fig. 2, for com-
parison with this table and for discussion with respect to these
two seasons as they affected the commercial crop in the area.

TABLE 2.-PERCENTAGE OF MARKETABLE HEADS CUT OF VARIOUS LETTUCE STRAINS
FROM PLANTINGS MADE AT DIFFERENT DATES (1939-40 SEASON, BRADENTON,
FLORIDA).
1st 2nd 3rd 4th 5th 6th
Planting Planting Planting Planting Planting Planting
Date Seed Sown 9-25-39 10-26-39 11-25-39 12-26-39 1-25-40 2-24-40
Date of First Cutting 12-19-39 2-6-40 3-13-40 4-9-40 4-27-40 5-10-40
% % % % % %
Cosberg 0.0**** 91.0* 38.0*** 0.0** 0.7** 0.0***
New York No. 12 56.5** 71.0**
Imperial No. 152 48.7** 96.5* 70.0** 2.7** 0.7** 0.0***
Imperial No. 847 17.2*** 93.0* 84.0* 2.2** 3.2** 0.5***
Imperial No. 850 88.0* 89.0* 84.5* 3.0** 4.0** 1.0***
Imperial No. 44 89.2* 97.0* 85.0* 23.0* 8.2* 5.7*
Imperial No. 615 ...... .... 74.5* .... 1.2** 0.0***
New York No. 515 ...... ...... 35.5*** ..... 0.0*** 0.0***
Columbia ... ..... 0.0*** 0.0***
Most satisfactory strains are determined by statistical analysis of each planting.
** Poorer than those marked (*).
*** Poorer than those marked (**).
**** Poorer than those marked (***).

'Figures in parentheses refer to References in the back of this
bulletin.






Florida Agricultural Experiment Station


Some of the strains were omitted from certain plantings but
it can readily be seen that Imperial No. 44 was consistently the
most desirable strain. If it were possible to predict Florida wea-
ther from the 30-year normal curve (see Fig. 2), some of the
other strains would unquestionably dominate Florida commer-
cial plantings except in the fall and late spring crops. However,
90-
as-- _____ _________
30 Yi. MEA 1Mwu MONTI1 v TEMPERATE RES
80 939-40 Mmlmus.E aL.TLEm -P -
1940-41 ".

570 i--





350
C3 N

Q so .--



SEPT OCT. Nov. DEC. j JAN. FEB. MARCH APRIL i

Fig. 2.-Temperature records through two lettuce seasons at Braden-
ton. Critical periods are indicated by arrows.
since it is in the winter season that Florida weather is most
variable, the safest available variety for planting at any season
is unquestionably Imperial No. 44. The limits of the lettuce sea-
son at Bradenton, for the 1939-40 and 1940-41 seasons, are des-
ignated by arrows in Figure 2. At these points in each of these
seasons, mature Imperial No. 44 was bolting.
YIELD RESPONSE OF CRISP-HEAD LETTUCE TO FERTILIZERS
The Influence of the Soil.-Fertility experiments have been
conducted on a variety of soils in the state, varying from the or-
ganic soils of the Everglades to the light sandy loams of some
of the other districts. It is not yet possible to make any absolute
recommendations with regard to quantities or ratios of nitro-
gen, phosphoric acid and potash for the different sections of the
state. In general, it may be said that lettuce does best on slight-
ly acid soils with a fair to good content of organic material.






Crisp-Head Lettuce in Florida


It is certainly of importance to the lettuce grower that he con-
sider carefully the past history of his land, and that he find
out as much about its present condition as is possible. A pH read-
ing is of very real importance in planning a fertility program for
the crop. Extremely acid soils should receive applications of
dolomite or lime, in quantities which can be suggested by county
agents or the Experiment Station.
Alkaline soils of the state present a different type of problem.
On such soils it is probably more satisfactory to supplement the
fertilizer program with applications of secondary elements than
to attempt to lower the pH. Excellent lettuce has been grown in
experiments on a heavy Parkwood soil with a pH of 7.8 when
such a program was followed. The use of acid-forming fertilizers
is excellent on such soils, as will be discussed later in the section
on nitrogen source materials. On soils already acid, neutral fer-
tilizers are more suitable.
Nitrogen.-Fertilizer tests in which the amount of nitrogen
has been varied from 10 to 90 pounds per acre on sandy soils
have indicated that on such soils between 50 and 90 pounds of
nitrogen per acre must be applied for crisp-head lettuce. In
the coldest part of the season, 90 pounds per acre of nitrogen
seems necessary to keep head sizes up, whereas in moderate
weather a total of 60 pounds per acre is usually enough. For
the most part, the past history of sandy soils in Florida is of little


Fig. 3.-Effect of nitrogen on head size of Imperial No. 44. Left to
right: 10, 50 and 90 pounds of nitrogen per acre.






Florida Agricultural Experiment Station


consequence in planning the quantity of nitrogen to be used,
since relatively heavy rains apparently keep the soluble nitro-
gen leached out. When a heavy leguminous cover crop has been
plowed in previous to a crop of lettuce, some allowance can prob-
ably be made for the nitrogen such a crop returns to the soil,
but no data are available on this point. Tables 3, 4 and 5 in the
appendix and Figure 3 show the response of lettuce to nitrogen
applications at Bradenton, Sanford and Gainesville. No signi-
ficant response has been secured from the addition of nitrogen
to lettuce grown on muck soils. However, there may be areas of
muck that require the addition of nitrogen for satisfactory let-
tuce production.
Phosphates.-In tests on mineral soils, the quantity of phos-
phates was varied from 0 to 160 pounds of P2O5 per acre on
each of four areas representing three distinct soil types. On
none of the areas was there any measurable response to the ap-
plication of phosphatic materials in the fertilizers. All four of
these areas had been previously intensively farmed, and a soil
test for "available" phosphorus" showed all of these soils to be
very high in this element. The actual reliance that can be placed
upon such soil testing methods for Florida soils is open to ques-
tion, but it is possible that on similar intensively farmed soils
there has been a reserve of phosphates built up which may per-
mit a reduction in applications of this element. Because of these
factors, it is impossible to make any kind of blanket recom-
mendation with respect to the use of phosphatic fertilizers on
Florida mineral soils. The addition of phosphate increased the
yield of lettuce on the organic soils of the Everglades. However,
when the amount applied was as high as 60 pounds of P205 an
acre, yields were lowered. Results indicate that 30 to 40 pounds
an acre of P205 is the maximum quantity that should be used
on the organic soils of the Everglades.
Potash.-The same mineral soils mentioned in the sections
on nitrogen and phosphates were used to test the necessary
amounts of potash for crisp-head lettuce. There was no yield
response to added potash on either the Manatee fine sandy loam
or Parkwood fine sandy loam, but there was a decided response
on the Bradenton loamy fine sand. Increasing amounts of potash
resulted in increased yields of lettuce on Everglades muck. The
results indicate that probably 100 to 140 pounds of K20 an acre
will yield maximum returns.


"Hellige-Truog soil-testing kit.






Crisp-Head Lettuce in Florida


Fertilizer Ratios.-The application of fertilizers is an attempt
not only to add additional nutrients but also to change the
balance of those already in the soil so that it is better suited to
the crop which is to be grown. An application of superphosphate
alone would have thrown any of the above soils further out of
balance for lettuce than they were before the fertilizer was
applied, with a possible depression of yields resulting. The ex-
tent of this depression of yields is dependent upon two main
factors: (1) the buffer and exchange capacity of the soil, and
(2) the extent of the deficiencies in the soil with respect to
other nutrient or fertilizer materials. On a heavy soil (i.e. a
soil of high exchange capacity) which is in fairly good nutritional
balance, no measurable depression of yields may result. On a
light sandy soil with a definite need for both potash and nitro-
gen, an application of superphosphate alone may cause a real
depression of yields. This illustration has been used only to
emphasize the type of errors which can be easily avoided if the
grower makes a real effort to know his soil, and considers care-
fully its recent crop history. Where fertilizer is applied with
banding machines this question of balance of nutrients assumes
even greater importance. The application of fertilizer in con-
centrated bands near plant roots often results in more efficient
use of the fertilizers, but it becomes more important than ever
that the fertilizer be properly balanced.
It is probable, therefore, that only for nitrogen applications
will it be possible to make definite recommendations for lettuce
growing on mineral soils. A knowledge of the past cropping
history of the particular piece of land and pH information are
necessary for intelligent planning of the fertilizer program with
respect to phosphate and potash applications.
Crisp-head lettuce on mineral soils requires 50 to 90 pounds of
nitrogen per acre, the latter amount for cold or wet weather.
This means an application of 1,500 pounds of a fertilizer contain-
ing 4 to 6% nitrogen. Phosphate and potash requirements will
vary with the land in question. If no information is available
to the grower on this point, a fairly safe formula for moderate
weather should be a 4-5-7 at 1,500 pounds per acre, with the
quantity somewhat higher in cold weather. On muck soil an
0-6-16 or an 0-8-24 applied at the rate of 500 pounds per acre will
prove satisfactory.
For those interested in comparing actual head weights as
produced on the experimental fields, tabular material has been
included in the Appendix (see Table 3).






12 Florida Agricultural Experiment Station

Sources of Nitrogen.-Most commercial vegetable fertilizer
mixtures contain nitrogen from three or more sources. Sulfate
of ammonia and nitrate of soda are usually included, with the
balance of from 20 to 60% of the total made up from natural
organic materials, such as tankage, guano, castor pomace, cot-
tonseed meal or fish meal. The mineral sources, being soluble,
are included in order that the plant may have nitrogen avail-
able immediately from the time it establishes a root system. The
organic materials, containing the bulk of their nitrogen in in-
soluble form, remain in the soil unavailable to plants until they
are broken down by microbiological action. The decompQsition
products resulting from such action are soluble and available to
plants over a period of time.
With long-season crops grown in warm weather, such a com-
bination of nitrogen source materials has been proven excellent
by careful experimental work, particularly on light, sandy soils
in the southeastern section of the country. Crisp-head lettuce
is a crop of another type, however, since it matures in a rela-
tively short season, and since it makes its growth during colder
weather.
An experiment was therefore set up to test several different
nitrogenous materials and combinations of such materials. The
tabular material is again included in the appendix (see Table 6).
The soil upon which the test was made was a medium heavy Park-
wood series soil (pH 6.0) on the Dickman farm north of Ruskin,
Florida. The plants of Imperial No. 44 were set in the field on
November 5, 1940, and the crop was cut in January. Over five
inches of rail fell in late December.
All plots received a total of 1,500 pounds of a 4-8-8 fertilizer,
so that the only treatment differences involved were the nitro-
gen sources. Three of the treatments received half of their nitro-
gen in the original application, and the balance was applied when
the plants had been in the field one month. No beneficial effects
were secured from side-dressing but this may have been due
to the fact that no rains occurred until after the application of
the side-dressing. However, since the quality and yield of cer-
tain treatments were excellent, it is believed that a valid com-
parison of the nitrogenous sources was secured.
In general, the results indicated that organic nitrogen sources
which decompose slowly (such as castor pomace) are not suited
for lettuce. Natural organic which are more quickly decomposed






Crisp-Head Lettuce in Florida


(such as milorganite or tankage) are suitable when 40% of the
total nitrogen is derived from that source. Nitrate of soda
used as the sole nitrogen source was unsatisfactory in this ex-
periment. In direct contrast, two of the other low-cost sources
(sulfate of ammonia and uramon) proved among the best ma-
terials tested.
For crisp-head lettuce, therefore, there is a variety of suitable
nitrogenous materials to choose from, and the grower should
base his choice on his soil and on the season the crop is grown.
Both sulfate of ammonia and uramon are acid-forming and if
either of these materials is used as the sole nitrogen source, its
effect upon the pH of the soil should be watched, and lime or
dolomite added when necessary to counteract the effects of a
possible drop in pH.

RELATION OF SPACING TO HEAD SIZE AND EARLINESS
The different sections of the state all vary somewhat in their
cultural methods with most crops, and lettuce is no exception.
On tiled mineral soils and in the muck areas the crop has been
flat-planted. On untiled sandy lands the plants are set on single
or double row beds. In a few cases seed has been sown directly in
the field.
It is generally conceded that wide spacings produce larger
heads than do close ones, and in New York on muck soils it is
recommended that plants be spaced 12 inches apart within the
row, with rows 18 inches apart (3). In California (7) lettuce is
planted on double row beds, 40 inches apart from center to center,
with rows 10 to 17 inches apart and the plants 10 to 14 inches
apart in the rows. Wide spacings produce large heads; but fewer
plants can be set per unit area than when close spacings are
used. The spacing problem, therefore, is to keep the plants
as close together as possible and still maintain desirable market
sizes.
A spacing experiment using Imperial No. 44 was conducted
on a Parkwood series soil to study the effects of several differ-
ent plant spacings on head size. The area selected for the test
was not tiled; consequently the test was carried out on double
row beds 40 inches apart from center to center. The two rows
were spaced 14 inches apart on the beds. Five different spacings
between plants in the row were tested, 10, 12, 14, 16 and 18






14 Florida Agricultural Experiment Station

inches. The field design was a randomized block test with six
replications.
It was found that the largest heads (by weight) were pro-
duced at the 18-inch spacing, and that these were slightly larger
than those produced at 16 inches. These in turn were slightly
larger than the heads produced at 14 inches, and at spacings
closer than that the head size dropped rapidly. The average
weights of all heads harvested of the various sizes were as
follows:
18-inch spacing 1.36 pounds
16-inch spacing 1.25 pounds
14-inch spacing 1.23 pounds
12-inch spacing 1.09 pounds
10-inch spacing .98 pounds
The heads produced by the plots with wide spacings were not
only the largest but also the earliest. Since these records were
taken from a crop grown during good lettuce weather there were
no significant differences in the percent cut at the different
spacings. However, the heads cut from the close spacings were
small, and a large portion of them were late, but the majority
of the plants did produce hard heads. A record of the effect of
spacing upon earliness is given graphically in Fig. 4. These
data suggest that plants not be spaced too closely if satisfactory
head size is to be produced.
'5
50








I-M
J
.30
I- -______

S--



i ll .


1ST CUTTING 2ND CUTTING 3RD CUTTING


4TH CUTTING


Fig. 4.-Effect of different spacings (shown in inches at foot of each
bar) upon earliness of maturity of Imperial No. 44 lettuce.





Crisp-Head Lettuce in Florida


In an attempt to determine whether the large sizes produced
by the wide spacings made up for the few plants set per acre, the
total yields per acre were calculated for each of the spacings
tested. The average head weights were determined from com-
400-


LEGEND: CRATE
GRADE DISTRIBUTION.


F- 90's

6 DOZEN (75's)

| 5 DozEN

4 4DozEN


SPACING ON 9EDS,INCHES
Fig. 5.-Effect of different spacings of Imperial No. 44 lettuce upon
the number of crates per acre of variously sized heads produced.
mercially packed crates of the various grades of heads cut from
this field. It was then possible to calculate the number of crates
of each size produced at each spacing. The data are presented
graphically in Figure 5. Since four or five dozen heads per






Florida Agricultural Experiment Station


crate (Western lettuce crate) are preferred by the market, and
since sizes smaller than six dozen to the crate are seldom salable,
it follows that even when the number of plants per acre is taken
into account, spacings of 14 inches or more within the row were
the best in this experiment. This is in agreement with conclus-
ions reached in New York with the same variety, Imperial No.
44.

OTHER CULTURAL FACTORS
It has not been possible, as yet, to compare, in experimental
plots, drilling the seed directly in the field against setting plants
in the field from the seedbed. Observation of commercial plant-
ings leads to the conclusion that it is preferable to transplant,
especially when weed control is difficult, and particularly in rainy
weather. Seeding directly in the field is apparently suitable in a
dry season in reasonably weed-free fields. When this latter
method can be used the season from seeding to harvest can be
shortened by as much as two weeks.
The unexpected heavy rains of late December 1940 provided
a rough means of comparison of high vs. low bedding or flat
planting of sandy soils. High beds (8 to 10 inches from the top
of the bed to the bottom of the furrow) provided sufficient
drainage throughout this wet spell. Fields set on low beds or
flatplanted suffered heavily from drowning and rapid spread of
diseases.

SUMMARY AND CONCLUSIONS
Experiments on many soil types throughout the state have
proven conclusively that of all strains of crisp-head lettuce avail-
able commercially at this time, Imperial No. 44 is the least
susceptible to bolting and the surest to head under most Florida
conditions.
On sandy soils the nitrogen requirement of the crop is from
60 pounds per acre (1,500 pounds of a fertilizer analyzing 4%
nitrogen) to 90 pounds of nitrogen per acre (1,500 pounds of a
6% nitrogen fertilizer).
Fertilizer studies with respect to quantities of phosphates
and potash have demonstrated that requirements for these ma-
terials are extremely variable, and dependent largely upon the
condition and past history of the land. It is suggested that these
factors be taken into account in choosing the fertilizer program.






Florida Agricultural Experiment Station


crate (Western lettuce crate) are preferred by the market, and
since sizes smaller than six dozen to the crate are seldom salable,
it follows that even when the number of plants per acre is taken
into account, spacings of 14 inches or more within the row were
the best in this experiment. This is in agreement with conclus-
ions reached in New York with the same variety, Imperial No.
44.

OTHER CULTURAL FACTORS
It has not been possible, as yet, to compare, in experimental
plots, drilling the seed directly in the field against setting plants
in the field from the seedbed. Observation of commercial plant-
ings leads to the conclusion that it is preferable to transplant,
especially when weed control is difficult, and particularly in rainy
weather. Seeding directly in the field is apparently suitable in a
dry season in reasonably weed-free fields. When this latter
method can be used the season from seeding to harvest can be
shortened by as much as two weeks.
The unexpected heavy rains of late December 1940 provided
a rough means of comparison of high vs. low bedding or flat
planting of sandy soils. High beds (8 to 10 inches from the top
of the bed to the bottom of the furrow) provided sufficient
drainage throughout this wet spell. Fields set on low beds or
flatplanted suffered heavily from drowning and rapid spread of
diseases.

SUMMARY AND CONCLUSIONS
Experiments on many soil types throughout the state have
proven conclusively that of all strains of crisp-head lettuce avail-
able commercially at this time, Imperial No. 44 is the least
susceptible to bolting and the surest to head under most Florida
conditions.
On sandy soils the nitrogen requirement of the crop is from
60 pounds per acre (1,500 pounds of a fertilizer analyzing 4%
nitrogen) to 90 pounds of nitrogen per acre (1,500 pounds of a
6% nitrogen fertilizer).
Fertilizer studies with respect to quantities of phosphates
and potash have demonstrated that requirements for these ma-
terials are extremely variable, and dependent largely upon the
condition and past history of the land. It is suggested that these
factors be taken into account in choosing the fertilizer program.






Crisp-Head Lettuce in Florida


It has been found that sulfate of ammonia and urea (uramon)
are good nitrogen sources on slightly acid or alkaline soils. Nat-
ural organic that decompose fairly rapidly are also excellent
when not more than 40% of the total nitrogen is derived from
such sources. Milorganite and guano are examples of such sourc-
es. Natural organic that decompose slowly (such as castor
pomace) are not desirable, since lettuce is not only a short sea-
son crop but it is grown during relatively cold months when
microbiological activity is relatively slow.
Lettuce plants should not be planted closer than 14 x 14
inches, since in closer plantings the sizes are relatively small and
the bulk of the heads form slowly, thereby lengthening the sea-
son and requiring more harvests.

REFERENCES
1. Beattie, W. R. Lettuce growing. U.S.D.A. Farmers' Bul. 1609. 1940.
2. Jagger, I. C., T. W. Whitaker, J. J. Uselman and W. M. Owen. The
Imperial strains of lettuce. U.S.D.A. Circ. 596. 1941.
3. Knott, J. E., E. M. Andersen and R. D. Sweet. Problems in the
production of Iceberg lettuce in New York. Cornell Univ. Agr.
Exp. Sta. Bul. 714. 1939.
4. McGeorge, W. T., M. F. Wharton and W. A. Frazier. Fertilizer of
lettuce on alkaline-calcareous soils: soil and plant studies. Arizona
Agr. Exp. Sta. Tech. Bul. 85. 1940.
5. Schmidt, Robert. Lettuce growing in North Carolina. N. C. Agr.
Exo. Sta. Bul. 319. 1938.
6. Skinner, J. J., and R. W. Ruprecht. Fertilizer experiments with
truck crops. Fla. Agr. Exp. Sta. Bul. 218. 1930.
7. Tavernetti, A. A., and J. B. Schneider. Head-lettuce production in
California. Calif. Agr. Ext. Ser. Circ. 105. 1938.
8. Watson, J. R. Florida truck and garden insects. Fla. Agr. Exp. Sta.
Bul. 232. 1931.
9. Weber, G. F., and A. C. Foster. Diseases of lettuce, romaine and
endive. Fla. Agr. Exp. Sta. Bul. 195. 1928.
10. Wilkerson, A. E. Lettuce, Iceberg type. Conn. Agr. Ext. Serv.
Bul. 268. 1938.





APPENDIX

TABLE 3.-THE AVERAGE HEAD WEIGHTS (IN POUNDS) OF CRISP-HEAD LETTUCE AS INFLUENCED BY FERTILIZER RATIO.
Series A 1939 40 Series B 1939 40 Ser.es C 1939 40 Series D 1940 41
Treat- Block Block Block Av. Block Block Block Av. Block Block Block Av. Block Block Block Av. Grand Av.
ment A B C A B C A B C A B C 4 areas.
1-0-0 .98 .75 .53 .75 .95 1.17 .75 .96 1.17 1.10 .96 1.08 1.13 .79 .96 .99 .95
1-0-8 .90 .80 .82 .84 .78 .77 1.11 .89 .89 1.16 .92 .99 1.32 .88 1.01 1.10 .96
1-0-16 .85 .60 .81 .75 .89 1.23 1.10 1.07 1.01 1.07 1.09 1.06 1.02 .96 1.01 1.00 .97
1-8-0 .89 .63 .66 .73 .89 1.00 .82 .90 1.11 1.16 1.00 1.09 .97 .99 1.01 .99 .93
1-16-0 .76 .69 .64 .70 .99 1.05 .99 1.01 .92 .94 1.10 .99 1.15 .92 1.11 1.06 .94 *'
1-8-16 .86 .82 .59 .76 .88 1.11 1.02 1.00 1.02 .90 1.05 .99 1.22 1.14 1.03 1.13 .97 2
1-16-8 .72 .75 .68 .72 1.19 .73 .91 .94 .96 1.04 .92 .97 1.11 .99 1.10 1.06 .93
1-8-8 .97 .80 .73 .83 .91 1.29 .89 1.03 .88 1.07 1.06 1.00 1.04 .98 .94 .98 .96
1-16-16 .72 .67 .67 .69 1.03 .87 .79 .90 1.51 1.14 1.13 1.26 1.18 .91 1.12 1.08 .98 .
5-0-0 .90 1.05 .96 .97 1.02 1.19 1.33 1.18 1.29 1.63 1.50 1.47 1.15 1.05 1.16 1.13 1.19
5-0-8 .95 1.00 .91 .95 1.52 1.21 1.10 1.28 1.76 1.47 1.42 1.55 1.20 1.22 1.12 1.18 1.24
5-0-16 1.35 1.05 .88 1.09 1.00 1.75 1.21 1.32 1.97 1.61 1.71 1.76 1.16 .80 1.02 1.04 1.30 S,
5-8-0 .92 .95 .82 .90 1.47 1.39 1.31 1.39 1.58 1.21 1.71 1.50 1.12 1.11 1.10 1.11 1.22
5-16-0 1.10 .91 .83 .95 1.56 1.50 1.55 1.54 1.63 1.71 1.39 1.58 1.26 1.04 1.04 1.11 1.29 2
5-8-16 1.09 1.18 .79 1.02 1.55 1.40 1.52 1.49 1.29 1,82 1.63 1.58 1.15 1.18 1.21 1.18 1.32
5-16-8 1.07 .97 .92 .99 1.52 1.29 1.57 1.46 1.46 1.53 1.39 1.46 1.18 1.15 1.01 1.12 1.26 ti
5-8-8 1.03 .96 1.13 1.04 1.46 1.26 1.62 1.45 1.59 1.31 1.53 1.48 1.14 1.17 1.11 1.14 1.28
5-16-16 .94 1.23 .81 .99 1.19 1.18 1.41 1.26 1.55 1.21 1.26 1.34 1.23 1.12 1.20 1.18 1.20
9-0-0 1.12 .90 .84 .95 1.35 1.76 1.79 1.63 1.59 1.96 1.59 1.71 1.09 1.08 1.19 1.12 1.35
9-0-8 1.04 1.12 .83 1.00 1.65 1.89 1.60 1.71 1.60 1.96 1.63 1.73 1.30 1.03 1.21 1.18 1.40 n
9-0-16 1.35 1.25 .88 1.16 1.24 1.39 1.66 1.43 1.74 1.91 1.83 1.83 1.32 1.24 1.09 1.22 1.41
9-8-0 .80 1.05 .88 .91 1.64 1.89 1.67 1.73 1.82 1.58 1.89 1.76 1.27 1.12 1.29 1.22 1.41
9-16-0 1.07 1.07 1.02 1.05 1.70 1.77 1.83 1.77 1.97 1.88 1.59 1.81 1.21 1.17 1.04 1.15 1.44
9-8-16 1.04 .95 1.02 1.00 1.78 1.85 1.76 1.80 1.90 1.55 1.76 1.74 1.06 1.14 1.03 1.08 1.40
9-16-8 1.07 .92 1.09 1.03 1.63 1.99 1.44 1.69 1.77 1.38 1.68 1.61 1.25 1.28 1.22 1.26 1.40
9-8-8 1.25 .94 1.03 1.07 1.37 1.86 1.73 1.69 1.60 1.55 1.80 1.65 1.30 1.21 1.16 1.22 1.40
9-16-16 1.08 .96 1.00 1.01 2.01 1.90 1.76 1.89 2.04 1.90 1.61 1.85 1.22 1.10 1.30 1.21 1.49

Note: Each series was laid out in a 3 x 3 x 3 factorial design with three replications. Fertilizer applied at the rate of 1000 pounds an
acre.
Series A-Bradenton loamy fine sand (provisional) ; pH about 5.8. Significant differences between nitrogen levels (1% point),
and potash levels (5% point) only.
Series B-Manatee fine sandy loam, heavy phase (provisional); pH about 7.7. Significant differences between nitrogen levels
(1% point) only.
Series C-Manatee fine sandy loam (provisional) ; pH about 6.8. Significant differences between nitrogen levels (1% point) only.
Series D-Parkwood fine sandy loam; pH about 6.0. Significant differences between nitrogen levels (1% point) and for







Crisp-Head Lettuce in Florida 19


TABLE 4.-EFFECT OF NITROGEN UPON HEADING AND WEIGHT OF HEADS OF THREE
CRISP-HEAD LETTUCE STRAINS (SANFORD WINTER PLANTING).
10 lbs. N per Acre 50 lbs. N per Acre 90 lbs. N per acre
% Cut Wt. per % Cut Wt. per % Cut Wt. per
STRAIN Head (oz.) Head (oz.) Head (oz.)
Imperial No. 44 5.0 not determined 30.0 13.3 29.0 14.0
Imperial No. 847 2.5 not determined 33.3 15.3 45.0 17.0
Imperial No. 850 1.0 not determined 28.3 15.0 39.0 16.0


TABLE 5.-EFFECTS OF NITROGEN UPON HEADING AND WEIGHT OF HEADS OF THREE
CFISP-HEAD LETTUCE STRAINS (GALNESVILLE SPRING PLANTING).
10 lbs. N per Acre 50 lbs. N per Acre 90 lbs. N per Acre
% Cut Wt. per % Cut Wt. per % Cut Wt. per
STRAIN Head (oz.) Head (oz.) Head (oz.)
Imperial No. 44 39.5 8.2 79.2 12.1 67.0 15.3
Imperial No. 847 41.5 9.5 44.0 15.0 54.0 14.1
Imperial No. 850 5.0 10.0 14.0 14.6 23.0 14.9


TABLE 6.-THE EFFECT OF SOURCE OF NITROGEN AND TIME OF APPLICATION UPON
HEAD SIZE WITH IMPERL4L NO. 44 LETTUCE. DATA IN POUNDS PER HEAD.
Av. Wt.
Treat- per Head
Group* ment Treatment (lbs.)
I 1 Sulfate of ammonia only. 1.361
5 40% milorganite, 30% sulfate of ammonia, and 30%
nitrate of soda. 1.303
8 Milorganite only (2-8-8) followed by side-dressing of
remaining nitrogen from half sulfate of ammonia and
half nitrate of soda. 1.303
3 Uramon only 1.300
9 A 2-8-8 original application, nitrogen sources as in
Treatment 5; side-dressing as in Treatment 8. 1.277
4 Half sulfate of ammonia, half nitrate of soda 1.275
II
7 40% castor pomace, 30% sulfate of ammonia, 30%
nitrate of soda. 1.251
10 A 2-8-8 original application, nitrogen sources as in
Treatment 4; side-dressing as in Treatment 8. 1.250
6 Milorganite only. 1.244
III
2 Nitrate of soda only. 1.144
*Average head size of first treatment listed in each group found to be significantly
larger than all treatments in succeeding groups. Analysis of variance used on data.




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