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Group Title: Bulletin University of Florida. Agricultural Experiment Station
Title: Effects of soil fumigation on cigar-wrapper tobacco and on soil nitrogen
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 Material Information
Title: Effects of soil fumigation on cigar-wrapper tobacco and on soil nitrogen
Series Title: Bulletin University of Florida. Agricultural Experiment Station
Physical Description: 24 p. : ; 23 cm.
Language: English
Creator: Kincaid, Randall R ( Randall Rich ), 1903-
Volk, G. M ( Gaylord Monroe ), 1908-
Publisher: University of Florida Agricultural Experiment Station
Place of Publication: Gainesville Fla
Publication Date: 1952
Copyright Date: 1952
 Subjects
Subject: Tobacco -- Diseases and pests -- Florida   ( lcsh )
Tobacco -- Soils -- Florida   ( lcsh )
Soil fumigation   ( lcsh )
Soils -- Nitrogen content -- Florida   ( lcsh )
Nematode diseases of plants -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Bibliography: Includes bibliographical references (p. 23-24).
Statement of Responsibility: by Randall R. Kincaid and Gaylord M. Volk.
General Note: Cover title.
 Record Information
Bibliographic ID: UF00026856
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: ltuf - AEN6410
oclc - 18266375
alephbibnum - 000925754

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Full Text
MAR 5 l2

Bulletin 490 January 1952

UNIVERSITY OF FLORIDA
AGRICULTURAL EXPERIMENT STATIONS
WILLARD M. FIFIELD, Director
GAINESVILLE, FLORIDA









Effects of Soil Fumigation on

Cigar-Wrapper Tobacco and on

Soil Nitrogen

By RANDALL R. KINCAID and GAYLORD M. VOLK










TECHNICAL BULLETIN






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









BOARD OF CONTROL P. T. Dix Arnold, M.S.A., Asst. Dairy Husb.'
Leon Mull, Ph.D., Asso. Dairy Tech.
Frank M. Harris, Chairman, St. Petersburg H. H. Wilkowske, Ph.D., Asst. Dairy Tech.
Hollis Rinehart, Miami James M. Wing, M.S., Asst. Dairy Husb.
Eli H. Fink, Jacksonville
George J. White, Sr., Mount Dora EDITORIAL
Mrs. Alfred I. duPont, Jacksonville J. Francis Cooper, M.S.A., Editor
George W. English, Jr., Ft. Lauderdale Clyde Beale, A.B.J., Associate Editor 3
W. Glenn Miller, Monticello L. Odell Griffith, B.A.J., Asst. Editor
W. F. Powers, Secretary, Tallahassee J. N. Joiner, B.S.A., Assistant Editor

EXECUTIVE STAFF ENTOMOLOGY
J. Hillis Miller, Ph.D., President A. N. Tissot, Ph.D., Entomologist'
J. Wayne Reitz, Ph.D., Provost for Agr.s L. C. Kuitert, Ph.D., Associate
Willard M. Fifield, M.S., Director H. E. Bratley, M.S.A., Assistant
J. R. Beckenbach, Ph.D., Asso. Director F. A. Robinson, M.S., Asst. Apiculturist
L. O. Gratz, Ph.D., Asst. Dir., R. E. Waites, Ph.D., Asst. Entomologist
Rogers L. Bartley, B.S., Admin. Mgr.3
Geo. R. Freeman, B.S., Farm Superintendent HOME ECONOMICS
Ouida D. Abbott, Ph.D., Home Econ.1
MAIN STATION, GAINESVILLE R. B. French, Ph.D., Biochemist
AGRICULTURAL ECONOMICS HORTICULTURE
G. H. Blackmon, M.S.A., Horticulturist1
H. G. Hamilton, Ph.D., Agr. Economist F . B.amison, Ph.D., Horticulturists
R. E. L. Greene, Ph.D., Agr. Economist Albert P. Lora, Ph.D., Horticulturist
M. A. Brooker Ph.D., Agr. Economist R. K. Showalter, M.S., Asso. Hort.
Zach Savage, M.S.A., Associate R. A. Dennison, Ph.D., Asso. Hort.
A. H. Spurlock, M.S.A., Associate R. H. Sharpe, M.S., Asso. Horticulturist
D. E. Alleger, M.S., Associate V. F. Nettles Ph.D., Asso. Horticulturist
D. L. Brooks, M.S.A., Associate4 F. S. Lagasse, Ph.D., Asso. Hort.'
M. R. Godwin, Ph.D., Associate R. D. Dickey M.S.A., Asso. Hurt.
H. W. Little, M.S., Assistant4 L. H. Halsey, M.S.A., Asst. Hort.
Tallmadge Bergen, B.S., Assistant C. D. Hall, Ph.D., Asst. Horticulturist
D. C. Kimmel, Ph.D., Assistant Austin Griffiths, Jr., B.S., Asst. Hort.
W. K. McPherson, M.S., Economist S. E. McFadden, Jr., Ph.D., Asst. Hort.
Eric Thor, M.S., Agr. Economist C. H. VanMiddelem, Ph.D., Asst. Biochemist
J. L. Tennant, Ph.D., Agr. Economist
Orlando, Florida (Cooperative USDA) LIBRARY
G. Norman Rose, B.S., Asso. Agr. Economist Ida Keeling Cresap, Librarian
J. C. Townsend, Jr., B.S.A., Agr. PL T
Statistician 2 PLANT PATHOLOGY
J. B. Owens, B.S.A., Agr. Statistician W. B. Tisdale, Ph.D., Plant Pathologist'
J. K. Lankford, B.S., Agr. Statistician Phares Decker, Ph.D., Plant Pathologist
Erdman West, M.S., Mycologist and Botanist
AGRICULTURAL ENGINEERING Robert W. Earhart, Ph.D., Plant Path.2
Frazier Rogers, M.S.A., Agr. Engineer 1 Howard N. Miller, Ph.D., Asso. Plant Path.
J. M. Johnson, B.S.A.E., Agr. Eng.a Lillian E. Arnold, M.S., Asst. Botanist
J. M. Myers, B.S., Asso. Ar. Engineer C. W. Anderson, Ph.D., Asst. Plant Path.
R. E. Choate, B.S.A.E., Asso. Agr. EnRg.3 po H A t
A. M. Pettis, B.S.A.E., Asst. Agr. Eng."s POULTRY HUSBANDRY
J. S. Norton, M.S., Asst. Agr. Eng. N. R. Mehrhof, M.Agr., Poultry Husb.13
J. C. Driggers, Ph.D., Asso. Poultry Hush.
AGRONOMY SOILS
Fred H. Hull, Ph.D., Agronomist'
G. B. Killinger, Ph.D., Agronomist F. B. Smith, Ph.D., Microbiologist s
H. C. Harris, Ph.D., Agronomist Gaylord M. Volk, Ph.D., Soils Chemist
R. W. Bledsoe, Ph.D., Agronomist J. R. Henderson, M.S.A., Soil Technologist8
W. A. Carver, Ph.D., Associate J. Neller, Ph.D., Soils Chemist
Darrel D. Morey, Ph.D., Associate Nathan Gammon, Jr., Ph.D., Soils Chemist
Fred A. Clark, B.S., Assistant Ralph G. Leighty, B.S., Asst. Soil Surveyor
Myron C. Grennell, B.S.A.E., Assistant G. D. Thornton, Ph.D., Asso. Microbiologist
E. S. Horner, Ph.D., Assistant Charles F. Eno, Ph.D., Asst. Soils Micro-
A. T. Wallace, Ph.D., Assistant biologist
D. E. McCloud, Ph.D., Assistant H. W. Winsor, B.S.A., Assistant Chemist
H. E. Buckley, B.S.A., Assistant R. E. Caldwell, M.S.A., Asst. Chemist 8'
E. C. Nutter, Ph.D., Asst. Agronomist V. W. Carlisle, B.S., Asst. Soil Surveyor
James H. Walker, M.S.A., Asst. Soil
Surveyor
ANIMAL HUSBANDRY AND NUTRITION S. N. Edson, M.S., Asst. Soil Surveyor
T. J. Cunha, Ph.D., An. Husb.13 William K. Robertson, Ph.D., Asst. Chemist
G. K. Davis, Ph.D., Animal Nutritionist 0. E. Cruz, B.S.A., Asst. Soil Surveyor
J. E. Pace, M.S.. Asst. An. Husb.3 W. G. Blue, Ph.D., Asst. Biochemist
S. John Folks, Jr., M.S., Asst. An. Husb. 4 J. G. A. Fiskel, Ph.D., Asst. Biochemist
Katherine Boney, B.S., Asst. Chem. H. F. Ross, B.S., Soils Microbiologist
A. M. Pearson, Ph.D., Asso. An. Hush.3 L. C. Hammond, Ph.D., Asst. Soil Physicist a
John P. Feaster, Ph.D., Asst. An. Nutri.
H. D. Wallace, Ph.D., Asst. An. Husb.3 VETERINARY SCIENCE
M. Koger, Ph.D., An. Husbandman3 D. A. Sanders, D.V.M., Veterinarian'
M. W. Emmel, D.V.M., Veterinarian 3
DAIRY SCIENCE C. F. Simpson, D.V.M., Asso. Veterinarian
E. L. Fouts, Ph.D., Dairy Tech.'1 L. E. Swanson, D.V.M., Parasitologist
R. B. Becker, Ph.D., Dairy Husb.3 Glenn Van Ness, D.V.M., Asso. Poultry
S. P. Marshall, Ph.D., Asso. Dairy Hush.3 Pathologist
W. A. Krienke, M.S., Asso. Dairy Tech. 3 W. R. Dennis, D.V.M., Asst. Parasitologist









BRANCH STATIONS SUB-TROPICAL STATION, HOMESTEAD
Geo. D. Ruehle, Ph.D., Vice-Dir. in Charge
D. 0. Wolfenbarger, Ph.D., Entomologist
NORTH FLORIDA STATION, QUINCY Francis B. Lincoln, Ph.D., Horticulturist
Robert A. Conover, Ph.D., Plant Path.
R. R. Kineaid, Ph.D., Plant Pathologist John L. Malcolm, Ph.D., Asso. Soils Chemist
L. G. Thompson, Jr., Ph.D., Soils Chemist R. W. Harkness, Ph.D., Asst. Chemist
W. C. Rhoads, Jr., M.S., Entomologist R. Bruce Ledin, Ph.D., Asst. Hort.
W. H. Chapman, M.S., Asso. Agronomist J. C. Noonan, M.S., Asst. Hort.
Frank S. Baker, Jr., B.S., Asst. An. Husb. M. H. Gallatin, B.S., Soil Conservationist

Mobile Unit, Monticello WEST CENTRAL FLORIDA STATION,
R. W. Wallace, B.S., Associate Agronomist BROOKSVILLE
William Jackson, B.S.A., Animal Husband-
Mobile Unit, Marianna man in Charge 2
R. W. Lipscomb, M.S., Associate Agronomist
RANGE CATTLE STATION, ONA
Mobile Unit, Pensacola W. G. Kirk, Ph.D., Vice-Director in Charge
R. L. Smith, M.S., Associate Agronomist E. M. Hodges, Ph.D., Agronomist
D. W. Jones, M.S., Asst. Soil Technologist
Mobile Unit, Chipley CENTRAL FLORIDA STATION, SANFORD
J. B. White, B.S.A., Associate Agronomist W. Rupreht, Ph.D., Vice-Dir. in Charge
J. W. Wilson, Sc.D., Entomologist
CITRUS STATION, LAKE ALFRED P. J. Westgate, Ph.D., Asso. Hot.
A. F. Camp, Ph.D., Vice-Director in Charge Ben. F. Whitner, Jr., B.S.A., Asst. Hort.
W. L. Thompson, B.S., Entomologist Geo. Swank, Jr., Ph.D., Asst. Plant Path.
R. F. Suit, Ph.D., Plant Pathologist
E. P. Ducharme, Ph.D., Asso. Plant Path. WEST FLORIDA STATION, JAY
C. R. Stearns, Jr., B.S.A., Asso. Chemist C. E. Hutton, Ph.D., Vice-Director in Charge
"J. W. Sites, Ph.D., Horticulturist H. W. Lundy, B.S.A., Associate Agronomist
H. 0. Sterling, B.S., Asst. Horticulturist W. R. Langford, Ph.D., Asst. Agron.
H. J. Reitz, Ph.D., Horticulturist
Francine Fisher, M.S., Asst. Plant Path.
I. W. Wander, Ph.D., Soils Chemist SUWANNEE VALLEY STATION,
J. W. Kesterson, M.S., Asso. Chemist LIVE OAK
R. Hendrickson, B.S., Asst. Chemist
Ivan Stewart, Ph.D., Asst. Biochemist G. E. Ritchey, M.S., Agronomist in Charge
D. S. Prosser, Jr., B.S., Asst. Horticulturist
R. W. Olsen, B.S., Biochemist GULF COAST STATION, BRADENTON
F. W. Wenel, Jr., Ph.D., Chemist E. L. Spencer, Ph.D., Soils Chemist in Charge
Alvin H. Rouse, M.S., Asso. Chemist E. G. Kelsheimer, Ph.D., Entomologist
H. W. Ford, Ph.D., Asst. Horticulturist David G. A. Kelbert, Asso. Horticulturist
L. C. Knorr, Ph.D., Asso. Histologist' Robert O. Magie, Ph.D., Plant Pathologist
R. M. Pratt, Ph.D., Asso. Ent.-Pathologist J. M. Walter, Ph.I., Plant Pathologist
J. W. Davis, B.S.A., Asst. in Ent.-Path. Donald S. Burgis, M.S.A., Asst. Hort.
W. A. Simanton, Ph.D., Entomologist C. M. Geraldson, Ph.D., Asst. Hort.
E. J. Deszyck, Ph.D., Asso. Horticulturist W. G. Cowperthwaite, Ph.D., Asst. Hort.
C. D. Leonard, Ph.D., Asso. Horticulturist
I. Stewart, M.S., Asst. Biochemist
W. T. Long, M.S., Asst. Horticulturist FIELD LABORATORIES
M. H. Muma, Ph.D., Asst. Entomologist
F. J. Reynolds, Ph.D., Asso. Hort. Watermelon, Grape, Pasture-Leesburg
E. J. Elvin, B.S., Asst. Hort.
W. F. Spencer, Ph.D., Asst. Chem. C. C. Helms, Jr., B.S., Asst. Agronomist
V. L. Guzman, Ph.D., Asst. Hort. L. H. Stover, Asst. in Hort.

EVERGLADES STATION, BELLE GLADE Strawberry-Plant City
R. V. Allison, Ph.D., Vice-Director in Charge A. N. Brooks, Ph.D., Plant Pathologist
Thomas Bregger, Ph.D., Physiologist
J. W. Randolph, M.S., Agricultural Engr. Vegetables-Hastings
W. T. Forsee, Jr., Ph.D., Chemist A. H. Eddins, Ph.D., Plant Path. in Charge
R. W. Kidder, M.S., Asso. Animal Hush. E. N. McCubbin, Ph.D., Horticulturist
C. C. Scale, Asso. Agronomist
N. C. Hayslip, B.S.A., Asso. Entomologist Pecans-Montiello
E. A. Wolf, M.S., Asst. Horticulturist Pecans-Moncello
W. H. Thames, M.S., Asst. Entomologist A. M. Phillips, B.S., Asso. Entomologist*
W. N. Stoner, Ph.D., Asst. Plant Path. John R. Large, M.S., Asso. Plant Path.
W. A. Hills, M.S., Asso. Horticulturist
W. G. Genung, B.S.A., Asst. Entomologist Frost Forecasting-Lakeland
Frank V. Stevenson, M.S., Asso. Plant Path.
R. H. Webster, Ph.D., Asst. Agronomist Warren O. Johnson, B.S., Meteorologist
Robert J. Allen, Ph.D., Asst. Agronomist
V. E. Green, Ph.D., Asst. Agronomist Head of Department
J. F. Darby, Ph.D., Asst. Plant Path. 2 In cooperation with U. S.
H. L. Chapman, M.S.A., Asst. An. Husb. Cooperative, other divisions, U. of F.
Thos. G. Bowery, Ph.D., Asst. Entomologist 'On leave.









CONTENTS
Page
REVIEW OF LITERATURE ..-------... ..... ........... ------.- ..-...-....---- ..... 5
MATERIALS AND METHODS ......--...-....--..----..............-- --..----.... 7
RESULTS BY SEASONS AND TESTS ......-....----...-----..- -..--.-... ......-- 11
1946 ...-.-----. -- ------ ------....... .......-... --.---....--..- ...-- 11
1947 ...........--.. -..- ---- ----...-- ---... .. ....--.. -- ------.. -...--..- ... 11
1948 .......... ........ -- ............-........... .--.-.....- .........----- 14
1949 .......-- ..--..- ...-- ......---- ........- ............ ........ ........ .... 14
RESULTS BY CLASSES OF OBSERVATION ......--..--.....-.. --..- ---.--.....----... 16
Root-Knot Index ..-..---.--... -- -..- ...-..-- -..... -- ........--..---.. 16
Coarse Root Index .........--....------ .-------------- .. ...-- .--..--.. 17
Y ield ..-...- ....-..--.. ...... .. - -.... ... ... ..- .... ... ....... 17
Grade Index ...... .....---- ..-- ..--. -------..--...-- .. ---. -- ..... ... 17
Crop Index ...---------.--------.......-- .....----....-............---- 17
Burn Test ..-...-..---- ..-.. --..... ----------...... .........-....--...... 17
Soil pH ... --...... ...---- --...-- ------...-..--- ---...... -...... .....--... 17
Ammonia Nitrogen ..........-..... ...------....--------....-- .........- 17
Nitrate Nitrogen ..--....------ ---......... -.............. -...-... .......... ... 17
CORRELATIONS .....-- .....----- .... ..---------- ..... ...-...... .... ..--- --........ 18
Root-Knot Index and Yield --............--... ---....- --.--- ...-..--....... 18
Coarse Root Index and Yield .... --..-------- ..-..------ -......--..-- ...-.. 18
Burn Test and Yield ........--- -----... .... ..-..--- --..- .................. 18
Ammonia and Yield ................ .. ..------....--.---.... --- ..- ...- .......... ....... 18
Ammonia and Grade Index ---.......-.....-..-......---..-..--...-........ 18
Ammonia and Burn Test ....----............ .............-- ............ ..... 18
Nitrate and Yield ...... ...--- ----.....--..--........-- ....- ......--.. ... 20
MISCELLANEOUS RESULTS ......-... .... ........ -..-- .......-------- ...... -- 20
Repeated Fumigation -..-......-.--... ..... ----------------.......... ....... 20
Residual Effects ........ -...... .. .... -- --- ...... .................... 20
DISCUSSION ....... ..- .. .........---------- ------.......-...-... -..--..-..- -......... 20
SUMMARY AND CONCLUSIONS ...........-.. ....------.--. ---....--...... -- 21
Choice of Fumigant ........... ...-----....------ ... ... ......... ... ...... 21
Rate of Application -.......-.. .. ............. ... ........ .. .. ............. 22
Date of Fumigation ...---. ........ ...... .... .........--- ..................... 22
Repeated Fumigation .......-------. ----.---..............- -- ................ 22
Residual Effects ...--- ........... ......-....--... ...................... .. 23
Ammonia and Nitrate Nitrogen ......--.................----............. 23
Miscellaneous -------................. ......--------------..--- .................. 23
LITERATURE CITED ............... ....... ................ .------ ... ................ 23










Effects of Soil Fumigation on
Cigar-Wrapper Tobacco and on
Soil Nitrogen
By RANDALL R. KINCAID and GAYLORD M. VOLK

Nematode diseases have been for several years the most im-
portant diseases of cigar-wrapper tobacco1 in Florida. There has
long been a need for methods of control which would replace or
supplement those already in use. Soil fumigation for the control
of nematode diseases first appeared to have economic possibilities
for tobacco shades when comparatively inexpensive fumigants
were introduced.
Fumigation experiments conducted in 1946 gave promising re-
sults. Nematode diseases were controlled fairly well and yield
was increased substantially and economically. Acceptance of
fumigation by shade growers was rapid, with some 500 acres
fumigated in 1947 and upwards of 4,000 acres, three-fourths or
more of the crop in northern Florida and southwestern Georgia,
in all succeeding years to date.
Two types of fumigant, dichloropropene-dichloropropane mix-
ture and ethylene dibromide solution, were used in the 1946 tests.
These two materials have received about equal attention in
subsequent experimental work and in commercial usage.
It was noticed early that plants growing in fumigated soil were
often darker green in color than those in untreated soil. This
suggested that the availability of nitrogen in the soil was affected
by fumigation.
Fumigation studies conducted during the seasons 1946 through
1949 have been concerned mainly with the choice between the
two types of fumigant mentioned and with date of fumigation
and, to a lesser extent, with rate of application and frequency of
fumigation. Soil nitrogen analyses have been made and their
relationship to the characteristics of the crop studied.

REVIEW OF LITERATURE
Carter (6)2 in 1943 reported that the use of dichloropropene-
dichloropropane gave "a very real measure of control" of the
1U. S. Type 62, "shade tobacco"; a field is referred to as a "shade."
SItalic figures in parentheses refer to Literature Cited in the back of
this bulletin.







6 Florida Agricultural Experiment Stations

root-knot nematode in vegetable crops and improved the growth
of pineapples. Early reports of the efficacy of ethylene di-
bromide as a soil nematocide were published by Newhall (16)
in 1946 and Stark and Lear (19) in 1947. A large volume of
literature has appeared on the subject of soil fumigation for
various crops, but comparatively little on cigar tobacco.
Anderson (1) obtained "remarkably successful control" of
brown root rot by fumigation of the soil with nematocides. In
1950 (2, 3) he reported that fumigation with ethylene dibromide
produced increases of 11 percent in yield, 11 percent in grade
index, and 23 percent in crop value of Havana Seed tobacco in
Connecticut. Beginning about a month after fumigation, am-
monia nitrogen was higher and nitrate nitrogen lower in treated
than in untreated soil. It was thought that subsequent nitrifica-
tion produced an abundant supply of nitrate nitrogen during the
latter part of the season which might account for some of the
improvement observed. A test with dichloropropene-dichloropro-
pane on plots where nematode infestation was low showed no
differences in yield and grade between treated and untreated.
Ammonia nitrogen reached higher concentrations and nitrate
nitrogen lower concentrations with this fumigant than with ethy-
lene dibromide. Ethylene dibromide gave a slight increase and
dichloropropene-dichloropropane a decrease in fire-holding ca-
pacity of the leaves. These results with Havana Seed tobacco
were in agreement with tests on shade-grown tobacco. Analyses
showed increased bromine in samples of leaves taken from plots
fumigated with ethylene dibromide.
The Georgia Coastal Plain Experiment Station (7) reported
control of root-knot with both types of fumigant. Burn and
aroma of shade tobacco were not affected.
Three preliminary papers (12, 13, 14) have been published,
covering certain phases of the investigations reported in this
bulletin.
Other references which have a bearing on the response of to-
bacco plants to soil fumigation have been found.
Tam (20) reported that 7 cc. of dichloropropene-dichloropro-
pane per cubic foot of soil, covered with mulch paper for four
days, suppressed nitrification for eight weeks.
Thomas (21) obtained much better growth of tobacco in
sterilized sand with nitrate nitrogen than with ammonia nitro-
gen. Beaumont (5) found that tobacco plants in water culture







Effects of Soil Fumigation on Cigar-Wrapper Tobacco 7

grew better for two or three weeks with ammonium salts than
with nitrates as sources of nitrogen, suggesting assimilation of
the ammonium ion by the plant, particularly in the early stages
of growth. Afterwards, nitrates gave better growth and a
healthful green color; ammonium salts gave a dark green color
to the leaves and injury to the roots.
Nightingale (17) reviewed literature showing that a high level
of nitrate favored potassium intake and limited phosphorus in-
take. On the other hand, with soil fumigation and with am-
monium ion rather than nitrate as the chief source of nitrogen
for pineapples, very much heavier applications of potassium and
other cation-containing fertilizers were indicated.
Attoe (4) reviewed literature on factors affecting fire-holding
capacity of tobacco and demonstrated the positive effect of potas-
sium and the negative effect of chlorine and of reduced forms of
nitrogen.
Vickery and associates (22) found that as ammonia nitrogen
was substituted for nitrate nitrogen to the extent of more than
20 percent, there was a slight reduction in growth of tobacco, a
phenomenal increase in hydration and a remarkable decrease in
organic acids in the green leaves. A direct correlation between
fire-holding capacity and organic acid content has been sug-
gested by numerous investigators. LaPrade and Carr (15)
found that with each increment of fertilizer nitrogen supplied
largely from sources other than nitrate the fire-holding capacity
of cigar-wrapper tobacco was reduced.

MATERIALS AND METHODS
Fumigants consisting principally of 1, 3 dichloropropene and
1, 2 dichloropropane were D-D and Dowfume N. Fumigants con-
sisting of ethylene dibromide (dibromoethane) dissolved in
naptha were Dowfume W-40, Iscobrome D and Soilfume 60-40.
One test was made with Iscobrome, a methyl bromide solution.
Fumigants were applied with a home-made gravity feed ap-
plicator mounted on a plow stock. The reservoir was a one-pint
milk bottle graduated in tenths of a pint. The bottle was closed
with a cork stopper with a long glass tube for the air intake and
a short tube for the liquid outlet selected for diameter to give
the desired rate of flow. The fumigant was conducted through
a funnel and copper tubing and delivered at a depth of about six
inches, behind the point of a two-inch scooter.
Streams of fumigant were applied 12 inches apart. The rate







8 Florida Agricultural Experiment Stations

of delivery varied slightly with the amount of fumigant in the
reservoir, but this was partially compensated for by the return
trip of the applicator. The soil was smoothed and compacted
with a drag, usually within a few minutes after injection of the
fumigant.
Soil temperature readings at depths of 6 and 12 inches were
taken for most tests. The air temperature recorded was the
mean for the three days immediately preceding the time of
application. Soil moisture was generally moderate, always suit-
able for cultivation.
Four areas were used for tests. Areas A and B were adjacent
in the same shade and had a similar cropping history. Areas C
and D were in separate shades. The soils were classified as
follows: Area A, Orangeburg and Norfolk fine sandy loams; Area
B, Orangeburg fine sandy loam; Area C, Norfolk, Ruston and
Orangeburg fine sandy loams; and Area D, Marlboro and Norfolk
fine sandy loams.
Conditions under which the various tests were conducted are
summarized in Table 1.
Tests were conducted in duplicate on areas A and B and in
triplicate on areas C and D. Area D received surface irrigation
in dry weather.
The methods of production were similar to those in general use
on farms in the Quincy area. The soil was disked in the fall at
least a month previous to fumigation; plant residues were fairly
well decayed at time of fumigation. During the latter part of
January from 5 to 10 tons of stable manure was broadcast and
the soil disked and listed. Two or three weeks before trans-
planting 1,500 pounds of a mixture of cottonseed meal, urea,
steamed bone meal, sulfate of potash and dolomite, analyzing
approximately 6-4-6, was applied in the drill. Within four weeks
after transplanting an equal amount was applied in two side-
dressings. The crop was grown, harvested, cured and sweated
in the usual manner. The variety Rg (8), resistant to black-
shank but susceptible to nematode diseases, was used in all tests.
Shortly after harvest suitable samples of the plants were pulled
and examined for the three diseases under consideration: Black-
shank (Phytophthora parasitica var. nicotianae Tucker) ; root-
knot (Meloidogyne sp. Chitwood) ; and coarse root, a nematode
root rot apparently closely related to brown root rot. The
severity of each disease was rated in 11 categories from 0 (none)
to 100 (most severe) and the average was reported as the index











TABLE 1.--SUMMARY OF CONDITIONS FOR SOIL FUMIGATION TESTS ON CIGAR-WRAPPER TOBACCO.

Sea- Test Date Air Soil Soil Date Corn-
son No. Test Area of Fumi- Temper- Temperature Moisture Set pare
_gation ature 6 in. 12 in. Test
"F. "F. *F. I.
1946 1 November fumigation .... A 11/2/45 68 med.* 3/29
2 February fumigation ...... B 2/4/46 51 ed. 3/29
1947 3 Residual effect ................. A ** 4/10 1
4 Second year -................. B 1/10/47 51 high* 4/10 2
5 Choice of fumigant ........ C 1/9/47 '50 high* 4/6
1948 6 Choice, second year ........ C 2/5/48 57 62 62 med. 3/29 5
7E Date of fumigation ........ D 9/29/47 65 high 3/25
7M Date of fumigation ........ D 12/3/47 52 61 56 med. 3/25
7L Date of fumigation ........ D 2/5/48 57 62 62 med. 3/25
1949 8 Rate of fumigation .......... A 12/15/48 69 69 66 med. 3/24
9 Fourth year ............... B 12/15/48 69 69 66 med. 3/24
10 Alteration ....... ........ C 12/16/48 70 69 68 med. 3/11 5, 6
11 Residual effect .................. D ** 3/11 7
12E Date, second year........... D 10/8/48 68 77 73 med. 3/11 7
12M Date, second year .......... D 11/30/48 58 61 59 high 3/11 7
12L Date, second year ........... D 2/4/49 54 58 57 med. 3/11 7

Rain fell next day.
** Fumigated during the previous season.



t0








10 Florida Agricultural Experiment Stations

for the plot. The blackshank indexes are not reported because
the incidence of this disease was low in all experiments.
The fire-holding capacity or burn test was determined on
sweated leaves by the strip method. The leaf was ignited by
contact with a faintly glowing electric coil and the duration of
burn, up to 30 seconds, was measured with the aid of a metro-
nome. Five leaves taken at random from each priming consti-
tuted a sample. Each leaf was tested twice, near the middle of
a tip quarter and of a base quarter, making 10 tests per sample.
Results for the seven or eight primings were averaged to repre-
sent the plot.
Yield in pounds per acre was calculated from the weight of the
leaves after sweating.
The grade index was determined by grading a sample from
each priming of each plot. The best or "light wrapper" grade
was assigned a factor of 1.000 and to the other grades were
assigned smaller factors in proportion to their relative market
value, as judged by five local packers. A weighted average
factor was calculated and reported as the grade index.
The crop index, obtained by multiplying yield by grade index,
was a comparative measure of the value of the crop.
Soil samples were taken to a depth of six inches in the row
between plants. The soil was air dried indoors on waxed paper
and stored in paper bags in a dry room until analyzed. Soil pH
was determined by means of the glass electrode, ammonia nitro-
gen by cold aspiration (23) and nitrate nitrogen by the method
of Harper (9).
The data were subjected to statistical analysis and the least
significant difference (L.S.D.) between means at the 5 percent
and 1 percent levels3 was calculated by methods described by
Hayes and Immer (11). Differences larger than L.S.D. 5 per-
cent are referred to as "significant" and those larger than L.S.D.
1 percent as "highly significant". Significant and highly signifi-
cant differences between fumigation treatments and untreated
checks in each table are indicated by one and two asterisks,
respectively.
The means of the data for the 12 tests are given in Tables
2 to 4.
Coefficients of correlation4 with their probable errors were
Differences which could be obtained by chance alone in 5 percent (or
1 percent) of trials.
SA measure of the degree of association between two types of observa-
tion.







Effects of Soil Fumigation on Cigar-Wrapper Tobacco 11

calculated by methods described by Hayes and Garber (10) and
are given in Table 5. Correlations which may be considered sig-
nificant and highly significant are indicated by one and two
asterisks, respectively.
Coarse root indexes, yields and burn test data for all tests were
combined and analyzed in pairs by the method of Snedecor (18).
Conclusions derived are given in the text.

RESULTS BY SEASONS AND TESTS
Results varied somewhat by seasons as well as by tests. This
was particularly true of yield and burn. Since the differences
in grade index within tests were mostly small and not significant,
the crop index was approximately proportional to the yield.
Paragraph numbers correspond with test numbers.

1946
The rainfall was low in April, very high in May, and fairly
low in June. Yield was high and burn was satisfactory, but the
crop was low in grade.
1. November Fumigation.-Fumigation on November 2, 1945,
gave large increases in yield, averaging 338 pounds per acre for
Dowfume W-15 and 322 pounds for D-D at the 23-gallon (ap-
proximately normal) rate. Results with D-D at the 40-gallon
rate were not quite as good, but all three treatments gave signifi-
cant increases in yield.
2. February Fumigation.-Fumigation on February 4, 1946,
gave lower yield of fumigated plots and higher yield of checks
than did November fumigation. Yield differences in this test
were not significant.
1947
The rainfall was high in April and May and normal in June.
Low yield, high grade and good burn characterized this crop.
3. Residual Effect.-Results of plots fumigated on November
2, 1945, showed substantial, but not significant, increase in yield
as compared with checks. D-D (40 gallons) produced the largest
increase, followed closely by D-D (23 gallons). Dowfume W-15
(20 gallons) produced the least increase.5

"Iscobrome gave poorer results in 1946 in nearly all respects than did
no treatment. On the other hand, results of the residual test in 1947
showed a substantial, but not quite significant, increase in yield. No expla-
nation for this outcome can be suggested.














TABLE 2.-RESULTS OF SOIL FUMIGATION TESTS ON CIGAR-WRAPPER TOBACCO IN 1946 AND A RESIDUAL TEST IN 1947.

Sea- Date Root- Coarse Grade Crop Burn Corn- "
Test son Area Fumigant Rate Applied Knot Root Yield Index Index Test pare Q
__ __ Index Index __Test
SGal./A. lbs./A. Sec.
1 1946 A D-D ........... 23 11/2 14 67 1611* .546 880* 14.2
D-D ............ 40 17 40 1568* .566 887* 13.0
Dow. W-15 -. 20 14 39 1627** .575 935* 14.0
Iscobrome ... 20 31 77 1240 .560 694 14.7 "
Check .......... 23 68 1289 .577 744 14.6

2 1946 B D-D ............. 23 2/4 20 52** 1559 .573 893 12.7
Dow. W-15 .. 20 11 52** 1537 .555 853 12.6
Iscobrome .... 20 25 80 1336 .552 738 13.4
Check ......... - 20 73 1492 .551 822 13.8
3 1947t A D-D .............. 23 11/2t 14 61 1005 .744 748 13.7 1
D-D .............. 40 19 63 1086 .722 784 13.8
Dow. W-15 .. 20 26 65 883 .711 628 14.2
Iscobrome .... 20 7 61 1082 .745 806 12.3 .
Check .......... 23 65 773 .723 559 13.2

Significant difference between fumigation treatment and check.
** Highly significant difference between fumigation treatment and check.
t Fumigated during the previous season (residual test).












TABLE 3.-RESULTS OF SOIL FUMIGATION TESTS ON CIGAR-WRAPPER TOBACCO IN 1947 AND 1948.


Root- Coarse Soil Analyses (Days after Transplanting) Com-
"Test Sea- Area Fumigant Rate Date Knot Root Yield Grade Crop Burn pH Ammonia N I Nitrate N pare
son Applied Index Index Index Index Test 13-149- 13 -144-5-13-534- Tet
__ 21 69 21 31 41 155 69 21 31 41 55 69____
I | Gal./A. I Lbs./A, I Sec. 1 1 P .. m. 1 p. p.m.
4 1947 B D-D ................... 20 1/10 0 38* 1117 .791 884* 11.2 6.4 16.0 105 88 13 25 11 22 2 9 2
Dow. W-10........ 30 1/10 1 40* 1094 .767 839* 11.3* 5.5 5.7 25 23 18 17 25 34 28 10
Isco. D ................ 30 1/10 2 38* 1231* .776 955** 10.7* .5.8 4034 27 7 6 39 38 4
Check .................. 17 67 810 .757 613 14.8 5 .6 13 12 12 13 9 18 4
5 1947 C D-D .................... 20 1/9 4** 44** 1066** .746 796** 8.8* 5.8 5.7 49 64 33 39 18 17 26 9
Dow. N ........... 20 1/9 9** 57 1043** .735 766** 9.2 .8 5.3 37 40 29 37 14 28 28 37
Dow. W-10 .......... 30 1/9 4** 40** 1120** .746 835** 9.0 5.6 5.4 8030 32 30 18 22 30 24
Isco. D .............. 30 1/9 3** 35** 1053** .730 769** 9.8 5.7 5.8 18 19 25 15- 24 22 20 13
Check ................. 29 63 867 .743 644 10.9 5.4 5.3 6 21 18 15 8 8 1 15 -
6 1948 C IY-D .................. 20 2/5 42 63 1238 .652 807 7.4 5.7 5.2 2718 19 21 11 4 17 24 24 19 5
Dow. N ......... 20 2/5 52 67 1083* .639 692 6.5* 5.5 4.9 2625 19 17 11 5 16 28 28 27
Dow. W-40 ........ 15 2/5 17* 46* 1389 .611 849 7.3 5.3 5.0 22 11 12 11 9 10 27 28 21 18
S. 60-40 .............. 15 2/5 13** 46* 1370 .633 867 6.9 5.8 5.2 27 15 10 8 8 9 ?4 9 36 23
Check ............... 46 61 1284 .627 805 7.7 5.1 4.9 8 11 7 12 9 7 16 13 17 20
7 1948 D D-D .................. 24 9/29 8* 44 1522* .697 1061* 7.1 5.4 5.2 27 6 5 4 7 6 8 10 12 8
D-D .................. 22 12/3 13* 44 1405 .683 960 7.1 5.9 5.3 5330 9 8 8 1 8 22 26 8
D-D ..................... 22 2/5 27 46 1422 .686 976 7.4 5.95.3 53 32 18 7 8 0 6 14 227
Dow. W-40 .......... 17 9/29 10* 41 1472 .680 1001 7.6 5.1 1 10 4 4 3 5 4 4 7 12 9
Dow. W-40........ 15 12/3 21 49 1474 .678 999 7.6 5.4 52 29 8 4 5 5 2 7 11 15 7
Dow. W-40......... 14 2/5 52 56 1356 .701 950 8.0 5.4 51 30 7 5 6 8 4 8 10 111
Check ........... 39 56 1311 .677 888 8.0 .2 5.2 11 2 2 3 3 3 3 7 15 7

Significant difference between fumigation treatment and check.
** Highly significant difference between fumigation treatment and check.







14 Florida Agricultural Experiment Stations

4. Second-Year Fumigation.-In this test with fumigation
repeated, Iscobrome D was substituted for Iscobrome. Second-
year fumigation produced significant increases in yield, ranging
from 284 to 421 pounds per acre, but significant reduction in
burn. Yield and grade were both higher but burn was lower
than in Test 3, where fumigation was not repeated.
5. Choice of Fumigant.-Fumigation gave highly significant
increases in yield, ranging from 176 to 253 pounds per acre, and
slight reduction in burn, which was significant only with D-D.
About the first of May the plants in the D-D and Dowfume N
plots were smaller in size and darker in color than those in the
Dowfume W-10 and Iscobrome D plots, and yields were slightly
lower.
1948
The second month of the season was dry. Burn was poor but
yield and grade were good, especially on Area D, which was
irrigated.
6. Choice of Fumigant.-The second year of this test showed
significantly reduced yield and burn for Dowfume N. All other
burn tests were slightly below that of the check. Dowfume W-40
and Soilfume 60-40 increased yield slightly.
7. Date of Fumigation.-The three dates of application were
September 29, December 3 and February 5. The September
application was followed by a cover crop of oats. Highest yield
was obtained with D-D applied in September, followed by Dow-
fume W-40 applied in September and December. All burn tests
except one were slightly below the check.

1949
The season was dry from the latter part of April to the first
of June and generally less favorable than the preceding three.
Yield, grade and burn were all rather low.
8. Rate of Fumigation.-This test was conducted on area A,
which had been planted in 1948 in crops other than tobacco and
not fumigated. All treatments increased the yield 79 pounds
or more except the 43-gallon rate of D-D, which gave a decrease.
Burn was reduced with each increment in amount of fumigant
applied, especially so with D-D.
9. Fourth-Year Fumigation.-The plots in area B had been
fumigated in 1948, but were planted in crops other than tobacco.







TABLE 4.-RESULTS OF SOIL FUMIGATION TESTS ON CIGAR-WRAPPER TOBACCO IN 1949.


Date Root Coarse Soil Analyses (Days after Transplanting) Com-
Test Sea- Area Fumigant Rate Applied Knot Root Yield Grade Crop Burn pHI Ammonia N Nitrate N pare
son Index Index Index Index Test 25- 37- -,2- 65- 82- 37- 52- 65- 82- T'est
S_____________ ___________ 40 83 25 40 4 70 83 25 40_654 70 83
|I Gal./A. I Lbs./A. I | Sec. I p. p.. m.
8 1949 A D- ...................... 13 12/15 12** 31** 1138* .577* 657 10.9 5.4 5.2 6 8 6-- 3 5 6 6-
D-D ...................... 20 12/15 6** 25** 1127* .630 710 8.6** 5.8 5.4 31 18 9 4 8 5 6 -
D-D ................. 43 12/15 1** 27** 914 .620 567 3.9** 6.15.5 52 37 24 23 1 3 3 6 -
Dow. W-40 .......... 9 12/15 23** 32** 1058 .591 625 10.4 5.2 5.2 3 6 5 3 2 5 5 4 -
Dow. W-40.......... 16 12/15 8** 28** 1100 .558* 614 9.9* 5.45.3 6 6 7 4 3 4 7 4 -
Dow. W-40 .......... 34 12/15 4** 33* 1085 .606 658 9.3* 5.35.3 5 6 6 2 5 7 5 -
Check ................ 44 40 979 .668 654 12.0 5.35.2 34 4 6 6
9 1949 B D-D .............. 21 12/15 5* 32 1098 .603 662 7.8** 5.9 .4 2914 9 9- 4 8 8 8 2,4
Dow. W-40 .......... 16 12/15 5* 26* 1132 .599 678 9.2** .4.2 7 5 5 2 4 7 -
Mixture ............ 18 12/15 9* 34 1061 .551* 585** 8.7** 5.7 5.3 22 112 6 8 4 6 7 7 -
Check ............... 31 37 1111 .655 728 12.4 5.45.2 6 3 2 4 6 8 -
10 1949 C D-D ................... 18 12/16 27* 83 1055** .555 85* 10.4* 5.6 3 17 12 11 7 3 8 12 5 5, 6
D-D .............. 21 12/16 20** 71** 1088** .542 590* 9.0** 5.65.3 -18 13 12 2 6 8 3
Dow. W-40 .......... 16 12/16 12** 54** 1161** .593 689** 11.5 5.4 .3 5 6 2 6 8 3
Dow. W-40 ........ 16 12/16 28* 70** 1050** .551 579 11.8 5.4 5.2 4 6 5 5 2 7 9 4
Check .................. 58 89 900 .551 496 11.6 5.25.0 --5 6 4 2 8 10 5
11 1949t D D-D .................... 24 9/29t 34 49 1268* .589 747 13.7 5.4 4 2 --- -- 7
D-D ................. 22 12/3t 29 56 1191 .577 687 12.3 5.5 5 2 -
D-D .................... 22 2/5f 38 49 1213 .617 748 14.1 5.6 - 3 - 3 -
Dow. W-40 ........ 17 9/29t 37 50 1252 .597 747 13.0 5.5 5 --
Dow. W-40 ........ 1 12/3 42 64 1126** .595 670 12.6 5.5 - 4 2 -
Dow. W-40 ......... 14 2/5t 27 60 1181 .586 692 12.8 .5 4 2 -
Check ................. 40 60 1206 .594 716 12.4 .4 4 3 -
12 1949 D D-D ..................... 19 10/8 16** 47* 1362** .542 738 12.4 5. 3 4 7 7 3 3 5 7 7
D-D ............... 21 11/30 2** 46** 1226 .547 671 10.9* 5.85.4 16 10 9 5 3 5 6 5
D-D .................. 20 2/4 1** 46** 1209 .608 735 8.3** .3 5.6 52 37 23 8 1 5 6 4
Dow. W-40 ........ 15 10/8 5** 35** 1310** .545 714 13.1 5. .3 5 6 3 4 6 6
Dow. W-40 ........ 15 11/30 9** 41** 1285* .578 743 11.6 .7 .4 -15 7 8 3 2 4 6 3
Dow. W-40........ 15 2/4 5** 47* 1275* .565 721 10.8* .7 4 10 10 8 5 2 4 4 6
Check .................. 44 62 1161 .601 697 13.2 54 5.4 4 6 4 2 7 5_
Significant difference between fumigation treatment and check.
** Highly significant difference between fumigation treatment and check.
f Fumigated during the previous season (residual test).
$ Mixture of D-D and Dowfume W-40 (equal volume).
In alternation with the other type of fumigant.







16 Florida Agricultural Experiment Stations

In the 1949 fumigation a mixture of equal volumes of D-D and
Dowfume W-40 was substituted for Iscobrome D. The fumigants
gave little or no increase in yield and grade index was reduced.
Crop indexes for the two fumigants were about the same and
both were lower than the checks. Burn was significantly re-
duced by both fumigants; D-D resulted in the poorest burn and
the mixture was intermediate.
10. Alteration of Fumigants.-This test on area C previously
was the choice-of-fumigant test, involving four fumigants, two of
each type. The test was changed in 1949 to two fumigants
applied either in continuation of the same type or in alteration
with the other type. All treatments increased yield significantly,
but the highest rate of increase was from continuous Dowfume
W-40. D-D, either continuous or alternating, gave a significant
reduction in burn. Dowfume W-40, either continuous or alternat-
ing, had little effect on burn.
11. Residual Effect.-One row of each four-row plot in the
1948 date-of-fumigation test was left unfumigated in 1949.
Yields were increased slightly by September fumigation with
both fumigants but the increase was significant only with D-D.
12. Date of Fumigation.-The second year of this test gave
more striking and significant results than the first (Test 7).
Both yield and burn were lower with each successively later date
of fumigation. Yields were increased over the check by all treat-
ments. Significant increases were, in order from most to least:
D-D early, Dowfume W-40 early, medium and late. D-D gave
lower burn tests than Dowfume W-40.
Late application of D-D retarded growth and produced a dark
green color of the plants. Yield and burn were lowest of all
treatments but grade index was highest.
In comparison with the preceding test, where fumigation was
not repeated, yields were higher but grade indexes and burn tests
were lower. Crop indexes were about the same for both tests.

RESULTS BY CLASSES OF OBSERVATION
Root-Knot Index.-Incidence of root-knot was reduced signifi-
cantly by one or more of the fumigants tested in 7 out of 10
tests (not including residual tests) and substantially in the
others. Average reduction in root-knot index was about 65 per-
cent for both types of fumigant.







Effects of Soil Fumigation on Cigar-Wrapper Tobacco 17

Coarse Root Index.-Incidence of coarse root was reduced sig-
nificantly in 8 out of 10 tests, but comparatively much less than
that of root-knot. Dowfume W-40 gave significantly better
results than D-D.
Yield.-Yield was increased significantly by fumigation in 7
out of 10 tests. Considering all tests with normal rate of applica-
tion for the first, second and third years of treatment, the average
increase in yield with D-D was 145 pounds per acre and with
Dowfume W-40 (or its equivalent) 167 pounds. The difference
of 22 pounds was not significant.
Grade Index.-Differences in grade index within tests were
small and generally not significant.
Crop Index.-Crop indexes were approximately proportional
to yields.
Burn Test.-Fire-holding capacity was significantly reduced
by fumigation in 7 out of 10 tests. Considering all tests, Dow-
fume W-40 reduced burn significantly and D-D more significantly.
Reduction in burn, although somewhat consistent, was relatively
small and probably unimportant in most tests.
Soil pH.-Readings varied rather closely with ammonia nitro-
gen levels in the soil.
Ammonia Nitrogen.-Ammonia accumulated to higher levels
and persisted later in the season in fumigated than in unfumi-
gated soil. Dichloropropene-dichloropropane caused more pro-
nounced effects than ethylene dibromide fumigants, and late
fumigation with either type of fumigant produced more notice-
able differences than early fumigation. Ammonia readings re-
mained higher in fumigated plots than in checks until the sixth
week after transplanting in nearly all tests, but they fell to
nearly normal by the beginning of harvest, except in the late ap-
plication of D-D in 1949 (Test 12). In some tests relatively large
amounts of ammonia in the soil were associated with the dark
green color and retarded growth of the plants.
Nitrate Nitrogen.-The results gave some direct evidence of
delayed nitrification, especially for the February application of
D-D in 1948 (Test 7). Nitrate readings were higher in fumigated
plots than in checks until the sixth week after transplanting in
nearly all tests in 1947 and 1948. Readings in 1949 were gener-
ally lower than in previous years, and there was little difference
within tests.







18 Florida Agricultural Experiment Stations

It may be expected that the samples, which were taken in the
drill row between plants, would be affected by the uptake of
nitrogen by the plants as well as by moisture conditions in the
soil.

CORRELATIONS
Root-Knot Index and Yield.-Correlation was negative in 11
out of 12 tests (including residual tests) and significant in eight
tests.
Coarse Root Index and Yield.-Correlation was negative in all
12 tests and significant in 10 tests.
The high correlations between nematode diseases and yield
indicated that yield was considerably, perhaps predominantly,
affected by the incidence of the diseases in 10 out of 12 tests. In
the other two (Tests 8 and 9 in 1949) a depressing effect of high
ammonia on yield appeared to predominate. Coarse root seemed
to be at least on a par with root-knot in reducing yield.
Burn Test and Yield.-Correlation was negative in seven out of
12 tests and highly significant in two. This suggests that factors
favorable to high yield tended to depress burn.
Ammonia and Yield.-Correlations for 1947, a season of high
rainfall, were positive in both tests and highly significant in one
test. Correlations for 1948 and 1949, seasons with dry weather
during the second month, were negative and highly significant
in three tests without irrigation; correlations were not signifi-
cant in three other tests, two of which were irrigated. These
results suggested that during dry seasons ammonia had a de-
pressing effect on yield, which was alleviated by irrigation.
Ammonia and Grade Index.-Correlation was positive in five
out of eight tests and highly significant in one. Fourth-year
fumigation (Test 9), on the other hand, gave a significant nega-
tive correlation.
Ammonia and Burn Test.-Correlation between ammonia
nitrogen6 and burn was negative in all eight tests. It was highly
significant in five, including all but one of the tests conducted in
1947 and 1949. The effect of fumigation at normal rates on burn
was probably not serious, with the possible exception of fourth-
year fumigation (Test 9) and February fumigation with D-D
(Test 12L).

SAmmonia and nitrate nitrogen levels used for these calculations were
those occurring from 34 to 41 days after transplanting.













TABLE 5.-CORRELATION BETWEEN VARIOUS OBSERVATIONS IN SOIL-FUMIGATION TESTS ON CIGAR-WRAPPER TOBACCO.

Root-Knot Coarse Root Ammonia Ammonia t&
Season Test Experiment Index Index Burn Test Ammonia and and Nitrate and 0
No. I and Yield and Yield and Yield and Yield Grade Index Burn Test Yield

1946 1 Nov. Fum. .. -.54- .15* -.62 .13** -.24 .20 -
2- Feb. Fum. -.74 .11** -.22 .23 -.41 .20 -

1947 3 Residual ...... -.63 .13**-.54 .15* -.28 .20 --
4 Second year -.72 .12** -69 .13** -.83 .074* .11 .33 .79 .13** -.59 .22 .83 .11** Q
5 Choice ......... -.81 .06** -.67 .10** -.65 .10** .61 .17* -.20 .26 -.83 .09** .96 .02**

1948 6 Choice ........ -.69 .09** -.68 .09** .41 .15 -.73 t .13** .26 .26 -.22 .26 .03 .28
7 Date ............ -.56 .10**-.86 .04** .30 .13 .07 .15 .09 .14 -.33 .13 -.28 .13

1949 8 Rate ........... 24 .17 -.15 .18 .44 .15* -.53 .13** .06 .18 -.90 .04** .12 .18
9 Fourth year .13 .23 -.59 .16** .47 .19 -.61 .15** -.54 .17* -.79 .09** -.15 .23
10 Alternation -.87 .04**-.81 .06** -.21 .17 .22 .17 -.28 .16 -.77 .07** .00 .17
11 Residual ...... -.30 .13 -.85 .04** -.07 .15 -
12 Date ............ -.30 .13 -.50 .11** .27 .14 -.29 .13 .35 .13 -.74 .07** .07 .15
Correlations considered significant. "
** Correlations considered highly significant.
0




,0







20 Florida Agricultural Experiment Stations

Nitrate and Yield.-Correlation was significant in two out of
eight tests. Both were positive and occurred in 1947 when the
levels of nitrate nitrogen were generally higher than in 1948 and
1949. With more complete sampling of the soil a favorable effect
of increased nitrate supply on yield probably could have been
shown for more of the tests.

MISCELLANEOUS RESULTS
Repeated Fumigation.-First-year fumigation in five tests
(Tests 2, 5, 7E, 7M, 7L) averaged 11 percent increase in yield
for both fumigants. Second-year fumigation in five tests (Tests
4, 6, 12E, 12M, 12L) on the same plots averaged 10 percent in-
crease for D-D and 14 percent increase for Dowfume W-40.
Third-year fumigation in a single test (Test 10) gave 17 percent
increase for D-D and 29 percent for Dowfume W-40. Fourth-
year fumigation in two tests (Test 9 and an alternation test in
1950 not otherwise reported) averaged 3 percent decrease in
yield for D-D and 2 percent increase for Dowfume W-40; grade
indexes were higher for D-D, making crop indexes for the two
fumigants about equal but both lower than the checks.
With repeated fumigation, both fumigants gave a decline in
grade index in relation to unfumigated checks. Dowfume W-40
gave more of a decline. Both fumigants gave a fairly consistent
decline in burn in relation to checks. D-D caused a bigger
decrease.
Summarizing the results of repeated fumigation, Dowfume
W-40 maintained the better yield and burn and D-D maintained
the better grade. No explanation can be offered for the unsatis-
factory results of fourth-year fumigation.
Residual Effect.-Results of repeated fumigation were com-
pared in two seasons with the residual effect of fumigation not
repeated. In 1947 (Tests 3 and 4) repeated fumigation gave the
higher yield and grade but lower burn. In 1949 (Tests 11 and
12), with three dates of application, repeated fumigation gave
the higher yield but lower grade index and lower burn. Crop
indexes were about the same. D-D showed somewhat more
residual value in increasing yield than did Dowfume W-40.

DISCUSSION
The retarded growth and dark green color of the plants ob-
served in several instances, notably with the February applica-







Effects of Soil Fumigation on Cigar-Wrapper Tobacco 21

tion of D-D in 1949, seemed to have disappeared by the begin-
ning of harvest. Nevertheless, these symptoms probably were
related to reduced burn.
Since the accumulation of ammonia might be expected to con-
serve some nitrogen frequently lost as nitrate by leaching, it
seems likely that the amount of nitrogen applied to the crop might
be reduced. In the light of the literature reviewed, increased
amounts of potash and possibly other bases would also be indi-
cated. These adjustments in fertilization have not been investi-
gated.
Stable manure was applied after fumigation in all tests except
those where fumigation was done in February. It is not known
whether this had any effect on results.
Possible effects of the chlorine in dichloropropene-dichloropro-
pane and of the bromine in ethylene dibromide have not been
investigated. Presumably, most of the fumigant leaves the soil
in vapor form, but possibly some residues remain in the form of
slowly volatile materials or products of decomposition. Effects
of bromine on the tobacco plant are similar to those of chlorine
(24). The poor response to fourth-year fumigation may have
been related to an accumulation of halogen.
Experiments are in progress on new fumigants and on the ap-
plication of fumigants in the drill.

SUMMARY AND CONCLUSIONS
Fumigation studies with cigar-wrapper (shade) tobacco in the
field were conducted in shades at Quincy, Florida, during the
seasons of 1946 through 1949. The two fumigants used most,
D-D (dichloropropene-dichloropropane) and Dowfume W-40
(ethylene dibromide), were those which have been used for fumi-
gating a large proportion of the shade acreage beginning with the
1948 season. Observations were made on the incidence of nema-
tode diseases and blackshank, fire-holding capacity, yield, grade
index and crop index. Beginning with the 1947 season soil
analyses were made for pH, ammonia nitrogen and nitrate nitro-
gen.
Choice of Fumigant.-D-D and Dowfume W-40 controlled root-
knot equally well. Dowfume W-40 controlled coarse root signifi-
cantly better than did D-D, but neither was considered satis-
factory in this respect. Yield was inversely correlated with the
incidence of nematode diseases in most tests. Coarse root ap-







22 Florida Agricultural Experiment Stations

peared to be at least on a par with root-knot in reducing yield.
No evidence that fumigation affected the incidence of blackshank
was found in these tests.
The average increase in yield from all first-, second- and third-
year treatments was 145 pounds per acre for D-D and 167 pounds
for Dowfume W-40. The difference of 22 pounds was not sta-
tistically significant. Average grade indexes and crop indexes
were about the same for both fumigants. Dowfume W-40 gave
a slight but significant reduction in fire-holding capacity, as
compared with unfumigated checks, and D-D gave a further
slight but significant reduction as compared with Dowfume W-40.
In two years' tests D-D gave better results than Dowfume N,
another fumigant of the dichloropropene-dichloropropane type.
In one year's test Iscobrome D and Soilfume 60-40, fumigants of
the ethylene dibromide type, gave about the same results as
Dowfume W-40. Iscobrome, a methyl bromide fumigant, gave
anomalous results for which no explanation can be offered.
Rate of Application.-Twenty gallons of D-D and 15 gallons of
Dowfume W-40 (or equivalent using other concentrations of the
active ingredient) per acre were considered normal and were
used in most of the tests. These rates appeared to be about the
best which could have been selected, considering yield, grade
index and fire-holding capacity. D-D at twice the normal rate
produced yield and fire-holding capacity lower than at the normal
rate. Dowfume W-40 at twice the normal rate produced about
the same yield and fire-holding capacity as at the normal rate.
Date of Fumigation.-With successively later dates of fumiga-
tion there were trends toward lower fire-holding capacity, especi-
ally with D-D, and toward lower yield and higher grade index.
Fumigation about the first of October, followed by a planting
of oats, gave good results with both fumigants, especially with
D-D. Fumigation during November, December and January gave
slightly higher yield, grade index and fire-holding capacity with
Dowfume W-40. Fumigation early in February gave slightly
higher fire-holding capacity and yield with Dowfume W-40, but
higher grade index with D-D.
Late application of D-D in two tests was associated with re-
tarded growth and dark green color of the plants. Fire-holding
capacity and yield were low. Grade index was normal for the
season in one test and comparatively high in the other.
Repeated Fumigation.-With repeated fumigation Dowfume







Effects of Soil Fumigation on Cigar-Wrapper Tobacco 23

W-40 maintained the higher yield and fire-holding capacity and
D-D maintained the higher grade index. Fumigation should be
limited to two, or possibly three, years in succession. Fourth-
year fumigation gave unsatisfactory results, the reason for which
was not determined.
Residual Effects.-Residual effects of fumigation not repeated
were inconsistent. Results in one test were inferior and in an-
other test about equal to those with fumigation repeated. D-D
showed somewhat more residual value in increasing yield than
did Dowfume W-40.
Ammonia and Nitrate Nitrogen.-Fumigation resulted in ac-
cumulation of ammonia in the soil. D-D had a more pronounced
effect than Dowfume W-40, and late fumigation with either
fumigant produced more noticeable differences than early fumi-
gation. The amount of ammonia nitrogen was inversely corre-
lated with fire-holding capacity and, in most tests, directly with
grade index. Correlation between ammonia nitrogen and yield
was variable, depending apparently on moisture conditions.
Nitrate nitrogen was generally higher during the latter part
of the growing season in fumigated soil than in unfumigated soil.
Correlations with yield were positive and highly significant for
the 1947 season, which had favorable distribution of rainfall.
Miscellaneous.-No effect of soil temperature and moisture
was evident within the range represented in these tests. Neither
alteration nor mixture of fumigants showed any advantage over
the usual procedure.
LITERATURE CITED
1. ANDERSON, P. J. Controlling diseases of tobacco. Conn. (New Haven)
Agr. Exp. Sta. Bul. 527. 1949.
2. ANDERSON, P. J. Nematodes on tobacco. Larvacide Log 11: 16-17.
1950.
3. ANDERSON, P. J. Effect of soil fumigation and irrigation on fire-holding
capacity of tobacco leaves. Larvacide Log 11: 19-20. 1950.
4. ATTOE, O. J. Leaf-burn of tobacco as influenced by content of potas-
sium, nitrogen, and chlorine. Jour. Am. Soc. Agron. 38: 186-196.
1946.
5. BEAUMONT, A. B. The toxicity of ammonium compounds for tobacco.
Proc. 2nd Int. Cong. Soil Sci.: 65-78. 1930.
6. CARTER, WALTER. A promising new soil amendment and disinfectant.
Science 97: 383-384. 1943.
7. GEORGIA COASTAL PLAIN EXP. STA. 29th Ann. Rpt. 1948-1949. Bul.
48. 1949.








24 Florida Agricultural Experiment Stations

8. GRATZ, L. 0., and R. R. KINCAID. Tests of cigar-wrapper tobacco
varieties resistant to blackshank. Fla. Agr. Exp. Sta. Bul. 326.
1938.
9. HARPER, H. J. The accurate determination of nitrates in soils. Ind.
Eng. Chem. 16: 180-183. 1924.
10. HAYES, H. K., and R. J. GARBER. Breeding crop plants. 2nd. ed. Mc-
Graw-Hill Book Co. 1927.
11. HAYES, H. K., and F. R. IMMER. Methods of plant breeding. First ed.
McGraw-Hill Book Co. 1942.
12. KINCAID, R. R. Rapid acceptance of soil fumigation for cigar-wrapper
(shade) tobacco in Florida. Down to Earth 3: 5. 1947.
13. KINCAID, R. R., and G. M. VOLK. Soil fumigation for cigar-wrapper
tobacco fields. Fla. Agr. Exp. Sta. Press Bul. 655. 1948.
14. KINCAID, R. R., and G. M. VOLK. Soil fumigation for cigar-wrapper
tobacco in Florida. (Abst.) Phytopath. 39: 13. 1949.
15. LAPRADE, J. L., and J. M. CARR. Fertilizing type 62 shade tobacco.
Ga. Coastal Plain Exp. Sta. Bul. 39. 1943.
16. NEWHALL, A. G. Volatile soil fumigants for plant disease control.
Soil Science 61: 67-82. 1946.
17. NIGHTINGALE, G. T. The nitrogen nutrition of green plants. II.
Botanical Review 14: 185-221. 1948.
18. SNEDECOR, G. W. Statistical methods. 4th ed. The Collegiate Press.
1946.
19. STARK, F. L., JR., and BERT LEAR. Miscellaneous greenhouse tests with
various soil fumigants for the control of fungi and nematodes.
Phytopath. 37: 698-711. 1947.
20. TAM, R. K. The comparative effects of a 50-50 mixture of 1:3 dichloro-
propene and 1:2 dichloropropane (D-D mixture) and of chloropicrin
on nitrification in soil and on the growth of the pineapple plant.
Soil Science 59: 191-205. 1945.
21. THOMAS, R. P. The relation of nitrate nitrogen and nitrification to the
growth of tobacco following timothy. Wis. Agr. Exp. Sta. Res. Bul.
105. 1950.
22. VICKERY, H. B., G. W. PUCHER, A. J. WAKEMAN and C. S. LEAVEN-
WORTH. Chemical investigations of the tobacco plant. VIII. The
effect upon the composition of the tobacco plant of the form in
which nitrogen is supplied. Conn. Agr. Exp. Sta. Bul. 442. 1940.
23. VOLK, G. M. Factors determining efficiency of Cyanamid and Uramon
for weed control in tobacco plantbeds. Soil Science 69: 377-390.
1950.
24. WILSON, L. B. Effects of chlorine, bromine, and fluorine on the tobacco
plant. Jour. Agr. Res. 46: 889-899. 1933.





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