LOWER LEAF HARVESTING OPTIONS AND LEAF POSITION EFFECTS ON SOME

AGRONOMIC, CHEMICAL, AND MINERAL CHARACTERISTICS

OF FLUE-CURED TOBACCO

By

GLENN RALPH STOCKS

A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL

OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT

OF THE REQUIREMENTS FOR THE DEGREE OF

DOCTOR OF PHILOSOPHY

UNIVERSITY OF FLORIDA

1991

UNIVERSITY OF FLORIDA LIBRARIES

PRELUDE
"At the awful day of judgment, the discrimination of the good from the wicked, is
not made by the criterion of the sects or of dogmas, but by one which constitutes the
daily employment and the greatest end of agriculture. The judge upon this occasion has
by anticipation pronounced, that to feed the hungry, clothe the naked, and give drink to
the thirsty are the passports to future happiness; and the divine intelligence which
selected an Agricultural state as a paradise for its first favorite, has here again
prescribed the Agricultural virtues as the means for the admission of their posterity
into heaven."

John Taylor, 1813

ACKNOWLEDGMENTS

In this study, 30,024 tobacco leaves were used to generate 40,224 data points.
Of the 30,024 leaves used, 10,592 had the midribs removed manually. There were
3636 samples that were ground for either mineral and chemical, or total non-
structural carbohydrate analysis. To accomplish all of this work required the assistance
of many people and the author intends to duly recognize all involved who made this Ph.D
research program possible.

Gerald Durden, David Durden, and Shannon Brown's technical assistance in
harvesting and measurement of the agronomic parameters is greatly appreciated. Ernest
Terry's assistance in grinding, and processing of samples for TNC and mineral analysis
was invaluable. Chief Tobacco Technician Rick Hill's assistance in the total management
of this program is gratefully appreciated.

Much appreciation is given to Dr. D.G. Shilling and Dr. J.M. Bennett for their
advice and counsel all through the conducting of this study. Also, gratitude is given to Dr.
R.N. Gallaher for the use of his dryer for desiccating the samples used in the TNC study
and the use of his laboratory for sample preparation for mineral analysis. The use of
Dr. Bennett's lab space for the TNC analysis is much appreciated. Unfortunately, Dr.
F.M. Rhoads was stationed outside of Gainesville and interaction with him was limited by
the miles; however, his willingness to serve on the supervisory committee is
appreciated.

To all committee members, the author is grateful for the challenges presented to
him in the qualifying examinations. The diversity of this committee challenged the
author on the written and oral exams. Each and every member posed probing questions
that caused the student to question his reasoning for being in graduate school. The

iii

successful completion of such a diverse qualifying examination process no doubt was the
turning point of this student's program.

The author's parents lifelong devotion to him is greatly appreciated. Had his
father, a farmer, not involved the author with the farming operation, a career in
agriculture might not have become a reality. The author's mom basically did all the
paper work for the author to be enrolled at N.C. State. Had she not done this, the author
might well have ended up in the armed forces.

By the time the author has completed this dissertation, he will will have taken a
bride. The loving devotion of Kathleen Best has carried the author through the inevitable
low points of this graduate program. Kathleen has shared the good times and bad times
with equal vigor and picked the author up when he was feeling down. Many years of
happy marriage are looked forward to by the author.

Dr. E.B. Whitty has been a godsend to the author. As a major professor, Dr.
Whitty has provided leadership to the author. As a person, Dr. Whitty is one of the
author's best friends. As a scientist, Dr. Whitty is clearly a leader in his field, as his
recognition as 1 991 Florida Extension Specialist of the Year clearly demonstrates. In
the author's humble opinion (although some might say there is nothing humble about the
author), there is not a better major professor than Dr. Whitty. Academics aside, Dr.
Whitty has allowed the author to develop professionally by including him on extension
programs and sending him to numerous professional meetings. From a research stand-
point, whenever the author needed something for his studies, Dr. Whitty willingly
supplied the needed equipment. The author is forever indebted to Dr. Whitty for having
served as his major professor for both the M.S. and Ph.D programs. Without question,
whatever success the author experiences over his career will be directly due to his
interaction with Dr. Whitty.

The funding of the research assistantship by R.J. Reynolds Tobacco Company made
it possible for the author to obtain his Ph.D degree. R.J. Reynolds has been an intricate

iv

part of the author's academic career since he was an RJR research apprentice in 1 984.
This program got the author interested in agriculture research and led directly to him
attending graduate school at the University of Florida. The interaction with Mr. A.R.
Mitchum, Mr. R.C. Reich, Dr. D.L Davis, and Dr. C.R. Miller, all of RJR, has allowed the
author to develop friendships with industry that hopefully will continue throughout the
author's career.

Without the cooperation of R.J. Reynolds and Philip Morris Tobacco Companies in
running the leaf chemical analyses, these studies would not have been complete. The
author is indebted to both companies for their willingness to run these analyses. The
cooperation of Mr. A.R. Mitchum of RJR and Mr. D.L Connor of PM is gratefully
appreciated in arranging to have these samples processed and analyzed.

In summary, anyone who has read this dissertation recognizes the immense
amount of data that was generated. This was clearly a team project and all involved
deserve and are accorded a gargantuan thank you from the author, Glenn R. Stocks.

TABLE OF CONTENTS

ACKNOWLEDGMENTS

ABSTRACT vjj

CHAPTERS

1 INTRODUCTION •]

2 CHARACTERIZATION OF FLUE-CURED TOBACCO BY LEAF

POSITION PRODUCED UNDER NORMAL HARVESTING

METHODS OR MONITORED OVER TIME AFTER TOPPING 7

Introduction 7

Materials and Methods 1 1

Results and Discussion 1 g

Conclusions 49

3 LOWER LEAF HARVESTING EFFECTS ON AGRONOMIC

CHARACTERISTICS OF FLUE-CURED TOBACCO 50

Introduction 50

Materials and Methods '"™t 52

Results and Discussion ' 54

Conclusions 65

4 LOWER LEAF HARVESTING: THE INFLUENCE OF TIME ON

THE CHEMICAL AND MINERAL CHARACTERISTICS OF

FLUE-CURED TOBACCO LEAF POSITIONS 66

Introduction gg

Materials and Methods [""[ 68

Results and Discussion 73

Conclusions 39

5 SUMMARY AND CONCLUSIONS 93

REFERENCES 99

BIOGRAPHICAL SKETCH 104

VI

Abstract of Dissertation Presented to the Graduate School of the University of Florida in
Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy

LOWER LEAF HARVESTING OPTIONS AND LEAF POSITION EFFECTS ON SOME AGRONOMIC,
CHEMICAL, AND MINERAL CHARACTERISTICS OF FLUE-CURED TOBACCO

By

Glenn Ralph Stocks

December, 1991

Chairman: Dr. E.B. Whitty
Major Department: Agronomy

Lower leaf harvesting options are management tools of flue-cured tobacco

(Nicotiana tabacum L.) farmers that are determined by economic considerations. The

lowest leaves of the flue-cured tobacco plant are the lowest in yield and value and some

farmers choose not to harvest them because of their relatively low economic return.

There are inherent differences in the agronomic, chemical, and mineral characteristics

of tobacco leaves depending on where the leaves are positioned on the stalk. Pruning and

discarding the lowest three or four leaves has been shown in some studies to not

adversely affect total yield. However, pruning lower leaves reduced yield in another

study. The objective of this study was to evaluate the effects of five lower leaf

harvesting options on leaf position characteristics of flue-cured tobacco plants having

exactly 21 leaves prior to pruning. The responses of leaf position parameters were

evaluated under normal harvesting methods and a time after pruning study involving

acquisition of ail leaves that remained on plants at a given period of time. Not harvesting

the lower leaves reduced yield as total leaf number harvested declined, but average value

per kilogram was increased because the lowest leaves were the lowest valued . No

differences in leaf position yield or total non-structural carbohydrate concentration

were found, leading to the conclusion that lower leaf harvesting treatments had no effect

vii

on net photosynthesis of the leaves above them. Not pruning and not harvesting the lower
leaves resulted in lower lamina nicotine and P concentrations and higher concentration
ratios of N to nicotine and reducing sugars to nicotine. The reduced concentrations of
nicotine and P were associated with a dilution effect due to not pruning and not
harvesting the lowest leaves on the tobacco plants. Results from these studies describe
the influence that the position of tobacco leaves on the stalk had on leaf agronomic,
chemical, and mineral parameters and the influence of leaf maturity on the development
of those same leaf parameters.

VIII

CHAPTER 1
INTRODUCTION

Lower leaf harvesting options of flue-cured tobacco (Njcotiana tabacum L)
provide practical means of managing the yield and value per unit of the crop. Lower leaf
harvesting options have become management tools for two reasons: 1 ) the federal
program for flue-cured tobacco controls the weight of tobacco that can be sold from a
farm, and 2) there are inherent differences in value per kilogram of tobacco based on
the position of the leaves on the stalk. The value per kilogram of flue-cured tobacco
generally is lowest for the lowest leaves and increases progressively to the middle- and
upper-leaf positions on the stalk.

Because the lowest leaves on the tobacco plant are the lowest in yield and value
and improved cultivars produce high yields, some growers choose not to harvest the
lowest leaves. Data from previous studies dealing with lower leaf harvesting options of
flue-cured tobacco suggested that pruning and discarding the lowest three or four leaves
did not adversely affect total yield and improved the average value per kilogram when
compared to harvesting all leaves (Suggs, 1972; Currin and Pitner, 1980; Stocks,
1 988). However, Court and Hendel (1 989) found that if the number of leaves harvested
was reduced from 1 8 to 1 5 to 1 2, either by lower leaf pruning or topping to a lower leaf
number, total yield was progressively reduced.

In that lower leaf harvesting options reduce the total number of leaves harvested,
other methods may be used to achieve the same goal. Woltz and Mason (1 966) found that
increasing the leaf number per hectare through higher plant populations increased yield
with the response fitting a quadratic model. When leaf quality was evaluated, 296,400
leaves per hectare were found to be the optimum. Collins et al. (1 969) found a leaf

population of 444,600 per hectare increased yield and value when compared to
296,400 leaves per hectare, but value per kilogram decreased with the increase in leaf
population. They concluded that the production of the additional leaves was not
economically feasible. Kittrell et al. (1972) found a leaf population of 370,500 per
hectare increased yield and value when compared to 296,400 leaves per hectare, but
gross and net prices were reduced by the higher leaf population.

Topping height and within-row plant spacing are the most common methods used
to achieve a desired leaf population. Kittrell et al. (1972) found that with equal within-
row plant spacings a topping height of 20 leaves per plant yielded higher than that
observed when topping at 1 6 leaves per plant with equal gross prices for the respective
topping heights. Net price was higher for the 20 leaves per plant topping height. Elliot
(1 976) evaluated the effects of several within-row plant spacings and topping heights
on flue-cured tobacco. He found that increasing topping heights from 1 2 to 1 5 to 1 8
leaves per plant generally increased total yield and value per hectare for each increase
in leaf number per plant, except for a lower value per kilogram for the 1 8 leaf topping
height treatment. Lower topping did not increase the specific leaf weight of the lowest
leaves or highest leaves, but increased the specific leaf weight of the middle leaves.
Increasing within-row plant spacings decreased yield and value per hectare, but
increased specific leaf weight of all leaves. Lower topping heights and wider within-row
plant spacings increased nicotine and total N concentration, with no response of topping
height or plant spacing on reducing sugar concentration.

The objective of lower leaf harvesting options is to maximize the use of quota by
selling the highest quality leaves. By not harvesting lower leaf tobacco, the lowest
quality and value leaves are not marketed. Information in the literature suggests that
the weight, and perhaps the quality, of the lower leaves can be improved by wider
spacing of plants within the row. Lower topping did not increase the weight of the lowest
leaves, but lamina weight increases were found in the middle leaves on the stalk.

However, lower yields resulted from both options. Increasing the within-row plant
spacing or topping to a lower leaf number limits the farmer's lower leaf harvesting
options in that he probably will need to harvest all the leaves produced on the plant to
make full use of his allotted quota. Within-row spacings and topping heights that
produce good quality tobacco and that may allow a farmer to exceed his allotted quota
under favorable growing conditions would enable the farmer to decide whether or not to
harvest the lower leaves. Those decisions would be based on the expected quality and
price per kilogram for the lower leaves, as well as the expected total yield of the crop.

All the studies dealing with lower leaf harvesting options have reported total
yield and explanations for the yield responses were not fully elucidated. Yield of each
leaf position would be a useful parameter when evaluating the effects of lower leaf
harvesting options. If the studies reported by Suggs (1972), Currin and Pitner
(1980), and Stocks (1988) had included yield by leaf position, the distribution of the
total yield on the plant could have been evaluated to determine where the yield
redistribution occurred due to lower leaf pruning.

Physiologically, lower leaf harvesting options of tobacco can be viewed as a
manipulation of the source-sink relationship of the plant. In flue-cured tobacco
production, the reproductive sink is removed (topping) to increase the yield and quality
of the leaves that remain on the stalk. The topping process has been found to eliminate
the traditional source-sink relationship of the tobacco plant causing the leaves to
function as alternate sinks (Hurng et al., 1 989). Some effects of topping are increased
specific leaf weight and leaf carbohydrate concentration (Hurng et al., 1989), and
increased leaf nicotine concentration (Woltz, 1955). Given equivalent environmental
and nutritional conditions, the timing of topping has significant effects on the agronomic
and chemical properties of the tobacco crop. Early topping increased leaf yield and
nicotine concentration more than late topping (Woltz, 1955; Steinberg and Jeffery,
1957; Marshall and Seltmann, 1964; Elliot, 1966; Stocks and Whitty, 1992). Woltz

(1955), Marshall and Seltmann (1964), and Elliot (1966) found N and reducing sugar
concentrations were not affected by topping delays. As topping has such a dramatic
influence on some of the agronomic and chemical qualities of the crop, further
manipulation of the plant's source-sink relationship, i.e., lower leaf harvesting options,
might be expected to influence similar parameters. Suggs (1 972) found that when the
lowest nine leaves were pruned and discarded from flue-cured tobacco plants nicotine
concentration was increased in the remaining leaves .

Numerous studies have dealt with source-sink manipulations in other plant
species. Removal of the grain sink of corn (Zea mays L) caused dramatic increases in
the carbohydrate concentration of both upper and lower leaves (Allison and Weinmann,
1970). Pod removal from soybean (Glycine max L Merr.) increased leaf carbohydrate
concentration (McAlister and Krober,1958; Kollmann et al., 1974; Ciha and Brun,
1978; Mondal et al., 1978; Streeter and Jeffers, 1979; Crafts-Brandner et al.,
1 984), and also increased N and P concentrations in the leaves (Kollman et al., 1 974;
Crafts-Brandner et al., 1984). Kollmann et al. (1974) further reported that leaf Ca
and K concentrations were decreased due to depodding of soybean. Lawn and Brun
(1 974) found soybean depodding decreased net photosynthesis. The photosynthetic
decline was linked to an accumulation of assimilate in the leaves. Depodding of soybean
also has been found to delay leaf senescence (Hicks and Pendleton, 1 969; Mondal et al.,
1978; Crafts-Brandner et al., 1984). The effects of reproductive sink removal can be
summarized to include increased leaf carbohydrate levels with a subsequent decline in
net photosynthesis, increase in leaf N and P concentrations, decreases in leaf Ca and K
concentrations, and a delay in the onset of senescence.

Results from leaf removal studies with wheat (Triticum aestivum L) and oats
(Ayena satiya L) demonstrate that leaf area losses greater than 1 0% reduced grain yield
(Womack and Thurman, 1962). Grain yield of sorghum (Sorghum bicolor L Moench)
was reduced as defoliation increased (Stickler and Pauli, 1961). Pauli and Stickler

(1 961 ) found that increases in the percentage of leaves pruned from grain sorghum
plants decreased the total carbohydrates in the vegetative tissue and grain. Vegetative
tissue N concentration decreased and grain N concentration increased as the percentage of
defoliation increased. Weber (1955) and McAlister and Krober (1958) found soybean
seed yield and size decreased in response to defoliation. The causal mechanism of lower
grain yield with defoliation was the loss the total photosynthetic capacity of the plant.
Flue-cured tobacco is managed differently than most other agronomic crops in
that the leaves, and not the seed, are harvested. Also, leaves are removed as they mature
on the plant. Most source-sink manipulation studies with other crops have dealt with
the effects of either the removal of the reproductive sink on leaf and seed characters or
the removal of leaves on seed characters. Lower leaf harvesting option studies with
flue-cured tobacco have reported total yield and chemical effects only. To ascertain the
specific effects of lower leaf harvesting options, a study was designed and implemented to
evaluate leaf position responses to five lower leaf harvesting options of flue-cured
tobacco plants having exactly 21 leaves. The five lower leaf harvesting options were:

1) Harvest all 21 leaves in a normal manner (control).

2) Prune and discard the lowest 3 leaves, harvest remaining 1 8 leaves in a
normal manner.

3) Do not prune and do not harvest the lowest 3 leaves (leaves were left on the
stalk), harvest remaining 1 8 leaves in a normal manner.

4) Prune and discard the lowest 6 leaves, harvest remaining 1 5 leaves in a
normal manner.

5) Do not prune and do not harvest the lowest 6 leaves (leaves were left on the
stalk), harvest remaining 1 5 leaves in a normal manner.

To maintain the integrity of the leaf positions, the 21 leaves of the plants were

partitioned into seven, 3-leaf stalk positions with the lowest three leaves designated

1-3 and progressing up the stalk with the upper-most three leaves designated 19-21.

The objective of the present study was to evaluate the effects of pruning and

discarding, not pruning or harvesting, or harvesting in a normal manner, the lowest

three or six leaves on flue-cured tobacco plants on the leaves above those involved in the
the treatments. Leaf number per plant and by harvest was controlled so that any effects
due to the treatments could be reported by the position or node on the stalk where leaves
were formed. Previous work on this topic indicated positive effects on yield and value by
pruning and discarding lower leaves, but negative effects by not pruning or harvesting
the same leaves.

The present study involved the measurement of numerous properties of tobacco
leaves based on the position or node on the stalk at which leaves were formed. Data are
lacking that characterize the agronomic, chemical, and mineral qualities by leaf position
of currently-grown flue-cured tobacco cultivars. These data are reported by leaf
position for normally-harvested mature leaves and for the same leaf positions over time
after topping to maturity to contribute data on the characteristics and the development of
the leaves comprising a leaf position.

CHAPTER 2

CHARACTERIZATION OF FLUE-CURED TOBACCO BY LEAF POSITION PRODUCED UNDER

NORMAL HARVESTING METHODS OR MONITORED OVER TIME AFTER TOPPING

Introduction

Tobacco (Nicotiana tabacum L) production, unlike that of most other agronomic
crops, involves harvest of the vegetative tissue (leaves), not the reproductive tissue
(seeds). Flue-cured tobacco leaves, unlike most other tobacco types, are harvested
manually or mechanically as the leaves mature on the plant. Harvest of the flue-cured
tobacco leaves progresses with maturity from the lowest to the highest leaves on the
plant stalk. This harvest method allows for all leaves to become fully mature if proper
production practices are followed. With most other tobacco types, the entire plant is
severed in the field at a stage when a majority of the leaves on the plant are judged to be
mature. Although the progressive harvest of flue-cured tobacco results in mature
leaves, there are considerable physical and chemical differences depending on the
position or nodes at which leaves are formed on the stalk (leaf position).

Leaf position (LP) is of considerable importance to the tobacco industry. Tobacco
is marketed, graded, and sold according to LP regardless of type. Tobacco companies
purchase tobacco based on their needs for a given characteristic most often derived from
the inherent differences between LPs. The tobacco is processed and stored based on LP,
as well. Tobacco products are manufactured based on certain characteristic properties
of the cured leaf. Weybrew et al. (1 984) determined that the leaf chemical components
of tobacco are influenced most by LP. In general, the LP characteristics of tobacco
dictate what type product can be manufactured.

Because LP is such an important factor in tobacco production and manufacturing,
numerous studies over the years have evaluated a wide array of LP properties for
tobacco types. Various burley tobacco LP properties have been described by Bowman and
Nichols (1968), and Williamson and Chaplin (1981). Flue-cured tobacco LP
properties have been described over the years. Agronomic, chemical, and mineral
composition data on LPs of flue-cured tobacco can be garnered from reports by Darkis et
al. (1936, 1952), Askew et al. (1947), Walker (1968), Brown and Terrill (1972,
1973), Bowman et al. (1973), Nel et al. (1974), Neas et al. (1978), and Campbell et
al. (1980). Raper and McCants (1966), Srivastava et al. (1984), and Bruns and
Mcintosh (1988) has reported dry matter accumulation data for tobacco, but these
studies were based on whole plant sampling with no segregation of the leaves.

One of the most important production and management practices of flue-cured
tobacco (Nicotiana tabacum L.) is the removal of the apical meristem (topping). Tobacco
is topped to improve yield and quality of the upper leaves. The topping process breaks
apical dominance resulting in rapid axilary bud development and generally corresponds
to the onset of floral initiation. The axilary buds (suckers), if allowed to develop will
reduce yield and quality of the tobacco leaves. Consequently, farmers remove suckers by
hand or use growth regulators to suppress their development. The process of topping is
also associated with many important developments of the tobacco plant. Topping, for
practical purposes, eliminates the traditional source-sink relationship for a tobacco
plant. Hurng et al. (1989) found that topping tobacco plants increased leaf dry weight,
specific leaf weight, and P concentration indicating that in the absence of the
reproductive sink, the leaves acted as an alternate sink. Wolf and Gross (1937) detailed
anatomical changes associated with tobacco topping and found larger, thicker leaves
resulted due to an increase in cell size in response to topping. Steinberg and Jeffery
(1957) found topping increased root development and nicotine concentration. Nicotine
is synthesized in the roots of the tobacco plant and translocated to the leaf (Dawson and

Solt, 1959). Wolf and Bates (1964) showed that a more extensive tobacco root system
resulted in higher leaf nicotine concentrations.

Nicotine is the most unique of all the chemical components of a tobacco leaf, and
its accumulation in the leaf as a response to topping is an important event, but, other
important processes are associated with topping. Elliot (1975) reported that topping
increased, not only nicotine concentration, but also lamina weight, leaf N and reducing
sugar concentration, and quality of the cured leaf.

At topping, there is a clear and distinct gradient in leaf age on a tobacco plant.
The oldest and most mature leaves will be the lowest on the stalk, and leaf maturity will
decline as LP increases to the top of the plant. Wolf and Gross (1937) reported that
leaves that were the most mature at topping were least modified, while those that were
least mature were profoundly modified. In Florida, topping generally occurs 80 to 90
days after transplantation of seedlings. The topping process often coincides with the
first harvest of the mature lowest leaves.

Because the production of flue-cured tobacco involves the harvest of leaves as
they mature on the stalk, management of the crop becomes a science of leaf senescence.
Weybrew et al. (1984) state that "physiological maturity (of a tobacco leaf) marks the
transition from growth to senescence and is usually identified as the point of maximum
dry weight attainment." They estimated that a leaf becomes ripe approximately 12 days
after physiological maturity. Also, because the leaves emerge sequentially, they will
ripen progressively from the lowest leaf, earliest emerged, to the uppermost leaf, latest
emerged. Weybrew et al. (1984) proposed that weekly harvests of three leaves per
plant would be the optimum way to produce quality tobacco because one leaf should be
"ideally" ripe, and the other two leaves would be only two days before or past the
"ideally" ripe stage.

Moseley et al. (1963) stated that "as a tobacco leaf approaches maturity, it loses
much of its tackiness and acquires a velvety feel. It develops "grain" or mounds between

10

the small veins. It becomes more turgid, does not wilt readily, and will snap crisply
from the stalk. Both the yellow and green pigments decrease, but the green ones at a
faster rate, thus the leaf becomes less green and more yellow in appearance." Moseley et
al. (1963) studied the maturity of tobacco leaves at harvest and found chlorophyll
decreased at a faster rate than did carotene or xanthophyll. Nicotine concentration
increased with maturity. Reducing sugar, N, and K concentrations, and the N to nicotine
and reducing sugar to nicotine concentration ratios declined as the tobacco leaves
matured. Walker (1968) found that as tobacco leaves matured the Ca, Mg, and K
concentrations declined, and noted inherent concentration differences between leaf
positions.

On a more general nature, Leopold (1961) described two positive effects of leaf
senescence. As leaves become shaded, senescence allows for organic and inorganic
compounds, which had been committed to those leaves during growth and development, to
be remobilized to leaves that are actively growing in a more favorable environment.
Also, with age and shading, the photosynthetic activity of a leaf declines sharply. The
shaded leaves are not parasitic to the plant, rather they are removed through senescence.
Thomas and Stoddart (1980) suggested leaf senescence is: 1) controlled genetically, 2) a
result of competition for light, space, and nutrients, or 3) a response to environmental
factors such as light, temperature, water relations, mineral relations, and diseases.

Sinclair and deWit's (1975) "self-destruct" hypothesis suggested soybean leaf
senescence to be a result of N being transported out of the leaves to supply the developing
seed to such an extent the leaves senesce. Flue-cured tobacco leaves ripen or partially
senesce as result of N starvation. In Sinclair and deWit's (1975) hypothesis the N
demand of the developing soybean seed depleted leaf N. However, in flue-cured tobacco
production N is managed such that the plant gradually depletes the soil N supply, thereby
limiting the N availability to the leaves, progressively from the lowest leaves to the top
leaves.

1 1

In flue-cured tobacco production, proper N management is the key to quality
cured leaf. Ideally, the N management scheme would cause the soil N supply to be
depleted when all but the upper-most leaves have fully developed allowing for the
remobilization of N from mature to maturing leaves. This scheme is the objective of
every flue-cured tobacco farmer each year, however, environmental factors nearly
always make this scheme difficult to achieve.

Numerous studies have detailed nutrient and dry matter accumulation for various
tobacco types over time (Grizzard et al., 1942; Raper and McCants, 1966; Sims and
Atkinson, 1971,1973, and 1974; Atkinson and Sims, 1977; Raper et al., 1977;
Srivatava et al., 1984; Bruns and Mcintosh, 1988). In all the above mentioned studies,
composite samples were acquired and data were reported on a whole plant basis. Studies
are lacking that detail the effects of time on the development of individual LPs.

Data are lacking that describe the characteristics of leaves by position on the
stalk of currently grown flue-cured tobacco cultivars. In the present study, agronomic,
chemical, and mineral data were collected from two flue-cured tobacco cultivars
('NC37NF' and 'K-358') topped to 21 leaves. The purpose of this study was to provide
information on tobacco leaf characteristics based upon the position or node on the stalk at
which leaves were formed. Data on LP characteristics over time are presented because
changes in the characteristics of individual LPs have been described in few previous
studies.

Materials and Methods
Field experiments were conducted in 1989 and 1990 at the University of
Florida's Green Acres Agronomy Farm near Gainesville, FL. Two flue-cured tobacco
cultivars, 'NC37NF and 'K-358', were grown in an Arredondo fine sand (fine-sandy
siliceous, Hyperthermic Grossarenic Paleudult) (Carlisle et al., 1989) for both years.

12

Plants were spaced 41 cm apart in rows spaced 121 cm apart. Transplanting dates were
10 March 1989 and 2 April 1990.

Prior to transplanting in 1989, weed and soil-borne pest management consisted
of 6.73 kg (a.i.) ha1 fenamifos (nematicide) {Ethyl 3-methyl-4-(methylthio)
phenyl(1-methylethyl)phosphoramidate}, 2.26 kg (a.i.) ha1 chlorpyrifos
(insecticide) {0,0-Diethyl 0-(3,5,6-trichloro-2-pyridinyl)-phosphorothioate},
4.46 kg (a.i.) ha1 peculate (herbicide) {S-Propyl butylethylthiocarbamate}, and 0.58
kg (a.i.) ha1 pendimethalin (herbicide) {N-(1-ethylpropyl)-3,4-dimethyl-2,6-
dintro-benzenamine}. These pesticides were broadcast and then incorporated into the
soil by disking. The same pre-transplant pest management treatments were used in
1990, except that 56.0 L ha1 of 1,3 dichloropene (nematicide) was used rather than

fenamifos. Acephate (0.83 kg (a.i.) ha1) {O.S-Dimethyl acetylphosphoramidothiate}
was used as needed to control foliage-feeding insects.

Fertilization for both years consisted of 448 kg ha1 of a 6-6-18 (N, K20, P205)
fertilizer formulated for tobacco and 168 kg ha1 15-0-14 (sodium-potassium nitrate)
at transplanting, 448 kg ha1 6-6-18 at first cultivation, and 448 kg ha1 6-6-18 at
last cultivation. All fertilizer was banded to the sides of the plants. Total application of
the primary and secondary nutrients was 106 kg ha1 N, 81 kg ha1 P205, 266 kg ha1
K20, 54 kg ha1 Ca, 54 kg ha1 Mg, and 148 kg ha1 S. In 1990, due to leaching of N and
K, 112 kg ha1 of 15-0-14 was hand-applied to plots three weeks after the last
cultivation.

Leaf position (LP) will be defined as the leaves associated with a consecutive
grouping of nodes along the stem. To maintain the integrity of a designated LP, all plants
were topped to 21 leaves (each plant's leaves were counted). Suckers (axilary buds)
were chemically controlled by pouring 25 ml of a solution consisting of 20 ml L*1
flumetralin (2-chloro-N-[2,6-dinitro-4-(trifluoro-methyl)phenyl]-N-ethyl-6-
flouro-benzene-methanamine) and 40 ml L1 fatty alcohol (hexanol 0.5%, octonol 42%,

13

decanol 56%, dodecanol 1.5%) down the stalk at topping. The 21 leaves were
partitioned into seven, 3-leaf stalk positions for harvesting purposes.

A normal harvest study, so called because it most closely approximated the
normal production practices of flue-cured tobacco, was used to evaluate the responses of
the leaves when they were mature. A whole plant harvesting study was used to evaluate
the responses of individual LPs over time. These two studies will be described
separately because of the differences in design and layout in the field and the methods by
which the data were managed.
Normal Harvest Study

Ten plants comprised a plot and each plot was replicated four times each year.
Seven weekly leaf harvests were taken from 3-leaf stalk positions, beginning one week
after topping. Weybrew et al. (1984) suggested that flue-cured tobacco leaves should
mature at a rate of one leaf every two days. Based on their statement, harvesting three
leaves per week should ensure that mature tobacco was harvested each week. The lowest
three leaves were taken first, and subsequent harvests progressed up the plant until the
final harvest of the last three leaves that remained on the plants. The lowest three
leaves were designated LP 1-3, and uppermost three leaves designated LP 19-21, with
appropriate designations for the intermediate leaves.

Thirty leaves constituted a harvest on a given date (three leaves from each of 10
plants). On harvest days, 15 of the 30 leaves were measured for leaf area using a Li-
Cor 3100 leaf area meter. The 15 leaves for leaf area measurement always came from
the same five plants to minimize variation between plants and to ensure that the 15
leaves were composed of an equal number of leaves from each of the three leaf groups per
plant. To facilitate accurate leaf area measurement, individual leaves were severed
down the midrib and each leaf half was passed through the leaf area meter. Once leaf area
measurement was completed on the 15 leaves, fresh weight was determined using an
Ohaus 8000 digital scale. Fresh weight was also taken on the intact 1 5 leaves. Once leaf

14

area and fresh weight measurements were completed, the leaves were cured in the
normal flue-curing manner. The cut and intact samples were kept separate in the
curing barn so that the cured weights could be obtained on the leaf area samples for
specific cured leaf weight calculation. Once the leaves had been cured, the cut and intact
leaves were measured for cured weight. These weights were composited for the total plot
yield of cured tobacco.

Cured (intact) leaves from all samples were evaluated by United States
Department of Agriculture tobacco graders. Each sample was assigned a grade. These
grades were used to determine the value per hectare or kilogram, using the 1989 or
1990 Georgia-Florida flue-cured tobacco (Type 14) market average for the respective
grades. The numerical index for each grade (Bowman et al., 1988) was used to
determine a grade index for each LP. The grade index reported in this study for each LP
is the mean of the grade indices for the tobacco that was in the designated LP. Eight cured
leaves were selected from each sample of each LP for chemical or mineral analyses. The
midribs were removed from the lamina. The lamina was ground to 1 mm using a Wiley
mill. Total N, nicotine, and reducing sugar analyses were performed by R.J. Reynolds
Tobacco Company in Winston-Salem, N.C. For Ca, Mg, K, and P analyses, samples were
prepared by the ashing and acid digestion method described by Walsh (1971). The
resulting solutions were analyzed by Inductively Coupled Argon Plasma (ICAP) in the
University of Florida's Institute of Food and Agricultural Science Extension Soil Testing
Laboratory by methods described by Hanlon and Devore (1989).

A split-split-plot design was used for statistical analysis with years being main
plots, cultivars being sub-plots, and leaf positions being sub-sub-plots. Analysis of
variance and Fisher's Least Significant Difference (LSD) were carried out by methods
described by Gomez and Gomez (1984). For most variables, interactions were either
not significant, or were determined not to be of practical importance. No differences
between cultivars or years were found. The data reported were averaged across

days after topping

1 4 2J 28 35 42 49_

leaf positions harvested

19-21 19-21 19-21 19-21 19-21 19-21 19-21 1 9-21 x

16-18 16-18 16-18 16-18 16-18 16-18 1 6-1 8X

13-15 13-15 13-15 13-15 13-15 13-15x

10-12 10-12 10-12 10-12 1 0-1 2X

7-9 7-9 7-9 7-9x

4-6 4-6 4-6*

1-3 1-3X

***Bold type indicates that leaf area, leaf mineral and chemical components, and
total non-structural carbohydrates (TNC) were measured on those leaf positions.
x Indicates leaf positions which were harvested normally on this date.

The data discussed herein were extracted from a larger study dealing with the

effects of lower leaf harvesting options on the same characters described in this paper.

Analysis of variance revealed that three treatments: 1) harvest all 21 leaves, 2) prune

15

cultivars and years. For clarity, only the LP effects are discussed because they were of
the greatest significance for each variable.
Whole Plant Harvest Study

This study was designed to monitor changes in LP characteristics for the duration
that each leaf position remained on the plant prior to normal harvest. Seven weekly
harvests were taken of all LPs that remained on the stalk, beginning one week after
topping. A set of samples was taken at topping to establish a baseline for all LPs.
Because this study was designed to monitor LP changes over time, LPs that were
harvested in the normal harvest study were removed from all plots that were to be used
for future harvest date analysis. The progression of the LPs as they were harvested is
illustrated in Table 2-1.

Table 2-1 . The leaf positions removed per plant by harvest date in the days after
topping study.

, .

16

the lowest 3 leaves, and 3) do not prune or harvest the lowest three leaves, had few if
any differences (discussed in Chapters 3 and 4). Most flue-cured tobacco farmers
practice one of these three treatments. Because of the lack of differences between
treatments, the data from the three treatments were combined, thereby increasing
sample size from 12 to 36 observations.

Each plot consisted of two plants occupying an area of 1 square meter. All LPs
were removed from the designated plants for a given harvest date as illustrated in Table
2-1 . Each LP harvested consisted of six leaves (2 plants X a 3-leaf position). Fresh
weight was taken on all LPs using an Ohaus 8000 digital scale. Leaf area was measured
using a Li-Cor 3100 leaf area meter on LPs 1-3, 7-9, 13-15, and 19-21. To
facilitate accurate leaf area measures, each leaf was severed down the midrib and each
leaf half passed through the leaf area meter. All leaf samples were cured in the normal
flue-curing manner. After curing, the dried leaf samples were rehydrated for handling
purposes, and cured weights were taken on all LPs.

The six leaves from LPs 1-3, 7-9, 13-15, 19-21 of each plot were used for
leaf chemical or mineral analyses. The samples for chemical or mineral analyses were
processed the same as described in the normal harvest study above.

Total non-structural carbohydrate (TNC) data reported herein were derived
from separate plants than those used for leaf mineral and chemical analyses, but the
progression of harvesting LPs was identical to that indicated in Table 2-1 . The TNC
samples were obtained from a single plant that was adjacent to those used for the
agronomic and mineral analyses. Because a single plant was used, total sample size was
three leaves per LP harvested. The lamina was severed from the midrib and placed in a
paper bag. The sampling and cutting of leaves was done in the field. When the samples
were obtained, bags containing samples were placed in a large plastic bag in a cooler
containing ice. This procedure was followed so that the leaf metabolism would be slowed,
conserving as much of the leaf carbohydrate as possible. Once all samples had been

taken, samples were transported to drying facilities. A Blue M forced air dryer was used
to desiccate samples. Prior to sampling, the dryer was set to 100 C, so that the
temperature would be at the desired level upon arrival at the drying facility. The paper
bags containing the leaf lamina were quickly placed in the dryer. The temperature was
maintained at 100 C for 1 hr to arrest lamina metabolism. After 1 hr at 100 C, the
temperature was reduced to 70 C for the duration of lamina drying. This drying method
was the best alternative to freeze-drying (Heberer et al., 1985). The elapsed time
between sampling initiation and arrival at the drying facilities was generally between 1
and 2 hr, depending on the number of samples that were to be harvested. Sample
acquisition always progressed from replication 1 to replication 4, so that any effects due
to sampling time could be accounted for. There were no appreciable differences in
replications indicating samples were processed in a timely manner. The TNC was
analyzed by a modified procedure of the methods described by Smith (1974).

Leaf chemical and mineral data are reported for leaf lamina only. Midribs were
not evaluated, and previous studies indicated that their chemical and mineral
constituents were different from the lamina (Darkis et al., 1952).

The treatments were arranged in a split-split-split-plot design in the field with
cultivars being main plots, lower leaf harvesting options being sub-plots, leaf position
being sub-sub-plots, and harvest dates being sub-sub-sub-plots. Analysis of the entire
data set was not possible due to lack of balance. With each harvest date there was a loss
of one LP (Table 2-1). Consequently, for harvest date evaluation, each harvest date was
analyzed individually. The statistical model was also a split-split-split-plot design
with years being main plots, cultivars being sub-plots, treatments being sub-sub-
plots, and leaf positions being sub-sub-sub-plots. The LSD values for LP comparison
given in the tables were calculated from the individual harvest date analysis of variance.
Data from each LP were regressed separately over the time period during which the
given LP remained on the plant. The model used was the same as that used for the

17

individual harvest date analysis except that harvest dates (days after topping) were
sub-sub-sub-plots. Analysis of variance, Fisher's Least Significant Difference (LSD)
and regression analysis of LP means were carried out by methods described by Gomez and
Gomez (1984). All regression equations reported were significant at the five-percent
level or greater (p>0.05). For most variables, interactions (except for leaf position X
harvest dates) were either not significant, or were determined not to be of practical
importance. For clarity, only the leaf position X harvest date effects are discussed
because they were of the greatest significance for each variable.

Results and Discussion

Each 3-leaf LP comprises 14.3% of the 21 total number of leaves that were
evaluated per plant. Fresh weights (FW) observed at the seven LPs during the normal
harvesting scheme were similar except for those at LPs 1-3 and 19-21 (Fig. 2-1).
Fresh weight accumulation of a given LP over time was dramatically influenced by leaf
age at topping (Fig. 2-2a and Fig. 2-2b.) At topping, the oldest leaves are those nearest
the bottom of the plant (i.e. LP 1-3), and leaf age declines progressively toward the the
top of the plant. The youngest and least mature LP at topping, 19-21, was initially the
lowest in FW, but increased in FW the most over time. The more mature LPs increased
the least in FW over time. The FW of the uppermost three LPs (or nine leaves), being
the least mature at topping, increased over time (Fig. 2-2a). However, the FW of the
lowermost four LPs (or 12 leaves) did not increase over time (Fig. 2-2b). This
observation quantified the suggestion by Wolf and Gross (1937) that more mature
leaves at topping would have fewer changes over time.

The cured weight (CW) of leaves harvested when they were mature was
influenced more by LP than was FW (Fig. 2-3). The highest two LPs, 16-18 and 19-
21, contributed 37.1% of the total cured weight of 4141 kg ha1, while the lowest two
LPs, 1-3 and 4-6, contributed only 19.9% of the total CW. Under good growing
conditions like those encountered in the present study, the upper leaves typically will

18

19

19-21
16-18
13-15
10-12

7-9

4-6

1-3
■1

ii;™;iW

4298 (16.3 %)

h

3897 (14.8 %)

h

-{

H

o

3623 : (13.8 ■%}

o
Q.

>»-

3728 (14,2 %}

;;■■: 3825 (14,5 %) '^10^2::;

3899 (14,8 %)

H

LSD
« 1 — 1

3047 (11.6
t — ■ — i — •- — i •—! 1 1 — ■ r

— ' 1 '

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000

Fresh Leaf Weight (kg/ha)

Fig. 2-1. Fresh weight of flue-cured tobacco as influenced by leaf position (LP) (LSD
0.05 = 193). Vertical line represents mean across all LPs. Numerical values
within bars are means (n=16) of each LP and (%) is that LP's contribution to
the total yield of 26 317 kg/ha.

20

E

cr

O)

£

f

£

CO

3

CD

500

400

o

LP 13-1 5 Means (n=36)
LP 16-18 Means (n=36)
LP 19-21 Means (n=36)

• LP 1 3-1 5 y = 272.3 + 1 .86x RA2 = 0.87
^-^— LP 16-18 y = 239.1 +3.55x RA2 = 0.94
---- LP 19-21 y = 148.5 + 12.2x - 0.14xA2 RA2:

0.96

21

- 1—
35

42

49

Fig. 2

0 7 14 21 28

Days After Topping (DAT)
2a. Fresh weight of flue-cured tobacco upper stalk leaf positions (LP) in
response to days after topping. LSDs (0.05) for comparison of LPs at 0, 7, 14,
21, 28, 35, and 42 DAT are 30, 16, 14, 14, 15, 10, and 15, respectively.

cr

2>

<D

360

340

320

2 300
CD

280

a-..

- ■ - • — LP 1 -3 Means (n=36)

♦ — LP 4-6 Means (n=36)

•-•■D-- LP 7-9 Means (n=36)

--♦-- LP 10-12 Means (n=36)

— I-

14

— T"

21

28

Days After Topping (DAT)
Fig. 2-2b. Fresh weight of flue-cured tobacco lower stalk leaf positions (LP) in

response to days after topping. LSDs (0.05) for comparison of LPs at 0, 7, 14,
and 21 DAT are 30, 16, 14, and 14, respectively.

21

o

CO

3

t — ' — i — « — i — ' — i — >— ^t — i — i — ■ — r
0 100 200 300 400 500 600 700 800 900 1000

Cured Leaf Weight (kg/ha)

Fig. 2-3. Cured weight of flue-cured tobacco as influenced by leaf position (LP) (LSD
0.05 = 40). Vertical line represents mean across all LPs. Numerical values
within bars are means (n=16) of each LP and (%) is that LP's contribution to
the total yield of 4141 kg/ha.

22

contribute the highest CW of all leaves (Brown and Terrill, 1972; Darkis et al., 1936,
1952). Over time after topping, the CW increases observed for individual LPs were a
result of the inherent differences in age of the leaves which comprised that LP (Fig. 2-
4a and 2-4b). The influence of leaf age on CW increases over time was similar to that
previously discussed for FW, except that the CW of LP 10-12 also increased with time
after topping (Fig. 2-4b). Only the lowest three LPs (or nine leaves) did not
significantly increase in CW over time.

Cured weight yield (CWY) is the percentage cured leaf that results from a given
amount of freshly harvested leaf after the curing process. Cured weight yield generally
increased from the lowest LPs to the highest LPs (Fig. 2-5). The CWY of other tobacco
crops was also shown to increase as LP increased (Suggs et al., 1987). It is desirable to
have a high CWY because the costs per unit of curing and handling are reduced due to the
higher return of salable product. The CWY for an individual LP over time was driven by
the differential in leaf age of the LPs at topping. The CWY response to time after topping
was similar to that observed with CW in that the upper four LPs (or 12 leaves)
increased in CWY over time (Fig. 2-6a), while the the lowest three LPs (or nine
leaves) did not (Fig. 2-6b). Handling costs per LP would be similar on a FW basis.
However, because CWY and CW increased progressively with higher LPs, the net returns
per LP likely would increase as LP advanced up the plant.

Leaf area was highest at the lower LPs and lowest at the highest LPs (Fig. 2-7).
This leaf area distribution is expected since the lowest leaves are formed prior to or
shortly after the seedlings are transplanted. The first leaves formed in the field after
transplanting are normally the largest with the upper leaves being smaller giving most
flue-cured tobacco cultivars their characteristic conical shape. Lower topping heights
than those used in this study can result in larger upper leaves, and some cultivars
produce large upper leaves. Turner and Incoll (1971) reported 80% of the leaf area of
a tobacco plant was contained in the 20 cm to 80 cm sections on the stalk. The stalk

23

60

"So

J3

.s?

'3

re

0)

-J

•o

u

1-
3

0

45-

40-

35-

30

o- — LP 1-3 means (n=36)

■*■ - LP 4-6 means (n=36)
-a LP 7-9 means (n=36)

-r
7

14

— i-
21

Fig. 2

Days After Topping (DAT)

4a. Cured weight of flue-cured tobacco lower stalk leaf positions (LP) in
response to days after topping. LSDs (0.05) for comparison of LPs at 0, 7, and
14 DAT are 3, 2, and 2, respectively.

a-

CO

O)

'5

T3

0)
w

o

85
75
65
55
45
35
25 H

15

•
O

LP 10-12 Means (n=36)
LP 13-15 Means (n=36)
LP 16-18 Means (n=36)
LP 19-21 Means (n=36)

LP 10-12 y = 44.8 + 0.50x RA2 = 0.86
LP 13-15 y = 40.9 + 0.60x RA2 = 0.79
LP 16-18 y = 33.1 +1.01X RA2 = 0.91
LP 1 9-21 y = 1 7.8 + 2.60x - 0.05xA2 RA2 = 0.97

- r-
14

21

— I-
35

Fig. 2-

0 7 14 21 28 35 42

Days After Topping (DAT)

4b. Cured weight of flue-cured tobacco upper stalk leaf positions (LP) in
response to days after topping. LSDs (0.05) for comparison of LPs 0, 7, 14,
21, 28, 35, and 42 DAT are 3, 3, 2, 3, 3, 3, and 4, respectively.

i

49

24

c
o

w
o

Q.

03
0

19-21

16-18

13-15

10-12

7-9

4-6

1-3

18.8

19.0

llllil

liii

15 1

12 6

!!■■ ■■■' ■■■'■■■■.■■■

11.3

H

h

-I

P.I.I U. 1. 1. ..1.1.1 ' I.- I -.1

H

H

H

H

H

LSD

-i — i — ■ — i — i — i — i — i — ■ — i — i — | — . — , — . — i — . — , — . — p
0 2 4 6 8 10 12 14 16 18 20

Cured Weight Yield (g cured leaf/100 g green leaf)

Fig. 2-5. Cured weight yield of flue-cured tobacco as influenced by leaf position (LP)
(LSD 0.05 = 0.7). Vertical line represents mean across all LPs. Numerical
values within bars are means (n=16) of each LP.

25

16

£- 15-

14 -L

13-

12-

■g

B

(l>

a>

0)

>-

O)

^-

x:

m

CJ>

Cl>

o

5

o

»*_

s>

a)

£

_i

-o

T>

©

0)

3

3

O

o

i-n

11

• ••• - LP 1 -3 means (n=36)
-• — LP 4-6 means (n=36)
-D-" LP 7-9 means (n=36)

-r-
14

- r-
21

0 7

Days After Topping

Fig. 2-6a. Cured weight yield of flue-cured tobacco lower stalk leaf positions (LP) in
response to days after topping. LSDs (0.05) for comparison of LPs at 0, 7, and
14 DAT are 1.0, 0.4, and 0.5, respectively.

•n

c

o

u

>

60

~*

60

60

0

O

o

' — I

Uh

*-^

*

-i

T)

T3

U

a

-

B

3

3

■ i

u

60

20-

18

16-

14 -A

12

A
♦
O

LP 10-12 Means (n=36)
LP 13-15 Means (n=36)
LP 16-18 Means (n=36)
LP 19-21 Means (n=36)

- r-

14

LP 10-12 y = 14.16 + 0.1 1x RA2 = 0.78
LP 13-15 y= 15.09 + 0.09x RA2 = 0.59
LP 16-18 y= 14.35 + 0.13x RA2 = 0.80
LP 19-21 y = 13.09 + 0.27X - 0.0002xA2 RA2 = 0.93

1

- r-
28

42

49

21 28 35

Days After Topping (DAT)

Fig. 2-6b. Cured weight yield of flue-cured tobacco upper stalk leaf positions (LP) in
response to days after topping. LSDs (0.05) for comparison of LPs at 0, 7, 14,
21, 28, 35, and 42 DAT are 1.0, 0.4, 0.5, 0.5, 0.8, 0.5 and 0.5, respectively.

26

19-21

16-18

c

o

•■E 13-15

w

O

10-12
7-9
4-6
1-3

5902

H

5946

.512

6657

5548

LSD

H

— i • 1 ■ 1 > 1 ' 1 ' r

1000 2000 3000 4000 5000 6000 7000

Leaf Area (sq. m/ha)
Fig. 2-7. Leaf area of flue-cured tobacco as influenced by leaf position (LP) (LSD 0.05
= 322). Vertical line represents mean across all LPs. Numerical values within
bars are means (n=16) of each LP.

27

heights for the plants used in the present study were about 100 cm. Each leaf should
occupy about 5 cm on the stalk. The middle five LPs, which contributed 74% of the total
leaf area, would fall in the 20 cm to 80 cm sections on the stalks of these plants. A true
measure of leaf area index (LAI) was not possible because the leaves were harvested as
they matured, however, the composite LAI was 4.32 for the data given here. Only LPs
1-3, 7-9, 13-15, and 19-21 were measured over time, but the leaf area development
was similar to the responses for the other parameters previously discussed. The leaf
areas for those LPs that were measured were influenced by leaf age and maturity over
time (Fig. 2-8).

Specific cured leaf weight (SCLW) is a measure of CW per unit of leaf area.
Specific cured leaf weight increased with each LP (Fig. 2-9), ranging from a low of
6.13 mg of CW cm2 leaf area at LP 1-3 to a high of 13.69 mg of CW cm2 leaf area at LP
19-21. The SCLW may be a useful measure for interpreting differences in CW between
LPs. Cured weight yield is simply a ratio of the CW from a given amount of FW. The
CWY is largely the difference in water concentration. However, SCLW measures the CW
per unit of leaf area thereby negating to some extent the influence of water concentration
between a group of leaves. At LP 19-21, the CW was 2.36 times higher than that at LP
1-3, while the SCLW at LP 19-21 was 2.23 times higher than that at LP 1-3. Based on
the SCLW measures observed in this study, there may be a higher proportion of
structural tissue at higher LPs. Specific cured leaf weight of the individual LPs
responded to time (Fig. 2-10) in a similar manner as did the parameters previously
discussed.

Value per kilogram (Fig. 2-11) increased as LP progressed from the lowest to
the highest leaves on the plant. Value per hectare (Fig. 2-12), being a function of CW
and value per kilogram, also increased at higher LPs. The uppermost LP (leaves 19-
21) contributed 19.9% of the total value ($15 315 ha1) of the tobacco crop, while the
lowest LP (leaves 1-3) contributed only 7.4% of the total value. Brown and Terrill

28

7000

6000

5000

-o —

o

cr
w

o>

E
o

CT

£ 4000 -

s

3000

si

A

-m— LP 1-3 Means (n=36)

"O LP 7-9 Means (n=36)

a LP 13-15 Means (n=36)

• LP 19-21 Means (n=36)

J-'

2000

^— LP 13-15 y
---- LP 19-21 y

= 5070+23x RA2 = 0.64
= 2988 + 148x- 1.9xA2 RA2 .

0.94

r

7

— J—
28

— T-
35

42

49

Fig. 2-

14 21

Days After Topping (DAT)
8. Leaf area of flue-cured tobacco leaf positions (LP) in response to days after
topping. LSDs (0.05) for comparison of LPs at 0, 7, 14, and 21 DAT are 503,
316, 253, and 218, respectively. DAT 28 and 35 are not significant.

29

c
o

CO

o

4-

nj

_i

19-21

i*.».

V,,. ;.,,,.... ..,,,.

H

16-18

12.08

H

13-15

10.26

H

H

LSD

10-12

9.18

H

7-9

8.67

4-6

7^7

x:S::::::::::SSS::::oS:::::'

H

1-3

6.13

' 1 ■ 1 r

H

— T •—

i

14

0 2 4 6 8 10 12

Specific Cured Leaf Weight (mg/sq. cm)
Fig. 2-9. Specific cured leaf weight of flue-cured tobacco as influenced by leaf position
(LP) (LSD 0.05 = 0.4). Vertical line represents mean across all LPs.
Numerical values within bars are means (n=16) of each LP.

f

E

ro

CD

1

O
u

16

14-

•5> 12

"cd

10-

■ LP 13-15 y = 8.02 + 0.08x RA2 = 0.83

---- LP 19-21 y = 6.61 + 0.28x - 0.003xA2 RA2 = 0.98

.--■*

^ *

7

" LP 1-3 Means (n=36)

O-" LP 7-9 Means (n=36)

a LP 13-15 Means (n=36)

• LP 19-21 Means (n=36)

i

35

— |—
42

i

49

Fig. 2-

21 28

Days After Topping (DAT)
10. Specific cured leaf weight of flue-cured tobacco leaf positions (LP) in
response to days after topping. LSDs (0.05) for comparison of LPs at 0, 7, 14,
21, 28, and 35 DAT are 0.48, 0.28, 0.34, 0.38, 0.56, and 0.47, respectively.

c
g
"+^
'w
o
0.

•*—

0
-I

19-21

3'77

X\:x:x:::::x:::::::::: ■

Mas

16-18

;■■:-. 3<79

;:xx;xv'xx'>x;x;x;

H

13-15

3.63

— 1

10-12

3-72

— |

7-9

3.67

4-6

111 3.5 8

— 1

H

LSD

1-3

3.30 |— |

i ■ 1

1

3.00

3.25

3.50

3.75

4.00

c
o

§

Q-

w—
CO

Dollars per Kilogram

Fig. 2-11. Value per kilogram of flue-cured tobacco as influenced by leaf position (LP)
(LSD 0.05 = 0.06). Vertical line represents mean across all LPs. Numerical
values within bars are means (n=16) of each LP.

19-21

3037 {19.9 %)

::x:x>>>>-':>':';:;:y'::x:x:x:::x':o:^:
■:■:■:■:■:■:■:■:■:■:■:::-:■:■:■:■: ■:•:■■■; :•:::: ::

—1
H

H

LSD

16-18

2763 (18.0 \;

13-15

2326 (15.2 %} |||

H

10-12

2214 (14,5 ro)

x:x

_

H

7-9

2103 (13.7 %)

-

A

4-6

1735 (11.3 %}

H

1-3

1135 [7»* % |— |

i ■ 1 ■ 1

' r-1

'

- 1 — '

l ' 1

0 500 1000 1500 2000 2500 3000 3500

Dollars per Hectare
Fig. 2-12. Value per hectare of flue-cured tobacco as influenced by leaf position (LP)
(LSD 0.05 = 152). Vertical line represents mean across all leaf positions.
Numerical values within bars are means (n=16) of each LP and (%) is that LP's
contribution to the total value of 15 315 $/ha.

30

31

(1972) found the middle and upper leaves of flue-cured tobacco contributed the most
value to the total value of the crop. The higher value of the upper LPs would support the
suggestion that management practices should strive to protect the upper leaves from
pests late in the harvesting season so as to derive the maximum yield and value from
those leaves.

The numerical grade index of flue-cured tobacco (Bowman et al., 1988) is based
on the USDA flue-cured tobacco grading system which considers several leaf
characteristics including position on the stalk, maturity, color and quality of the cured
leaf. Based on the grades received for the tobacco evaluated in this study, the lowest five
LPs were equal in grade index with the upper two LPs being lower in grade index (Fig.
2-13). The grade index values reported for the lower five LPs indicated ripe and
mature tobacco, while the upper leaf grade index values were indicative of unripe and/or
immature leaf. Suggs (1986) reported a high correlation of grade index to unit price of
tobacco crops. However, based on the data for grade index and value per kilogram by LP
reported in this study there was a poor relationship between price and grade index
across LPs. The grade indices typically reported are a weighted average across all LPs.
Higher quality tobacco, and subsequently higher value tobacco will have a higher grade
index. However, the prices paid per grade of tobacco from a given LP are determined by
market demand, and may not correlate as well with the grade indices from that LP.

Lamina N concentration (Fig. 2-14) generally increased as LP progressed up the
stalk. Brown and Terrill (1973), Nel et al. (1974), Neas et al. (1978), Darkis et al.
(1936, 1952) also found N concentration increased as LP advanced up the stalk. The age
of the leaves contained within a given LP influenced the N concentration of that LP over
time (Fig. 2-15). The least mature LPs at topping were the highest in N concentration,
but as those immature LPs increased in CW and leaf area, the N concentration declined
rapidly. Raper and McCants (1966) reported that flue-cured tobacco plants had

Leaf Chemical Characteristics

32

q

o
a.

0)

r
40 50 60

Grade Index (not weighted)
Fig. 2-13. Grade index of flue-cured tobacco as influenced by leaf position (LP) (LSD
0.05 = 7.7). Vertical line represents mean across all LPs. Numerical values
within bars are means (n=16) of each LP.

33

c
o

CO

O

o_
5

CD

19-21

£ »> . o

H

16-18

:-:;:;.,,:-:-.-:-,:::v:v. ■:::;■>:■:■>

19. S

— 1

13-15

17.6

i

I

10-12

Hi i8-1

1111

LSD

7-9

16.0

1

1
1

4-6

16 3

1

1-3

16.6

:

■ i ' — r

■ i ■ i ■> — i — ' — i — i — i — i — r

r"

"l — ■ — i — ■ — i — « — 1

Fig. 2

8 10 12 14 16 18 20 22 24 26

Lamina Nitrogen Concentration (g/kg)

14. Lamina N concentration of flue-cured tobacco as influenced by leaf position
(LP) (LSD 0.05 = 1.8). Vertical line represents mean across all LPs.
Numerical values within bars are means (n=16) of each LP.

50

o>

— 40 H

1

c

CD
O

c
o
O

V

LP 7-9 y = 23.95 - 0.77x + 0.023xA2 RA2 = 0.99

-^— LP 13-15 y = 33.10 - 1.10x + 0.019xA2 RA2 = 0.97
- - - - LP 1 9-21 y = 47.07 - 1 .32x + 0.01 7xA2 RA2 = 0.99

LP 1-3 Means (n=36)
LP 7-9 Means (n=36)
LP 13-15 Means (n=36)
LP 19-21 Means (n=36)

ft JL "*

14 21 28 35 42

Days After Topping (DAT)

Fig. 2-15. Lamina N concentration of flue-cured tobacco leaf positions (LP) in

response to days after topping. LSDs (0.05) for comparison of LPs at 0, 7, 14,
21, 28, and 35 DAT are 3.1, 2.6, 1.0, 1.7, 1.4, and 0.6, respectively.

49

34

accumulated 89.5% of the total N uptake 77 days after the seedlings were transplanted.
This period of time approximates the topping time in the present study. The total N
uptake was not measured in the present study. However, the rapid decline in N
concentration at the immature LPs may indicate that most of the N had been taken up by
the plants at topping and was diluted as the leaves expanded and accumulated dry matter.

Nicotine concentration (Fig. 2-16) was influenced by LP. Nicotine concentration
declined from the lowest LP to the middle LPs, then increased again to the upper LPs.
This nicotine concentration by LP pattern was similar to that reported by Walker
(1968) and Nel et al. (1974), however, other studies dealing with flue-cured tobacco
found nicotine concentration increased with higher LPs (Brown and Terrill, 1973; Neas
et al., 1978; and Darkis et al., 1936, 1952). Nicotine concentration increased with
leaf maturity (Fig. 2-17). Srivastava et al. (1984) reported that nicotine
accumulation of Dixie Shade Wrapper tobacco was only 18.4% of the total accumulation
70 days after seedlings were transplanted. Nicotine is synthesized in the roots (Dawson
and Solt, 1959), and the topping process is believed to stimulate root growth (Steinberg
and Jeffery, 1957). Nicotine concentration increase in the tobacco leaf is a most
important response to topping and leaf maturity (Steinberg and Jeffery, 1957; Moseley
et al., 1963; Walker, 1968; Elliot, 1975). Topping established a set leaf number per
plant and assuming root growth was stimulated, nicotine concentration should increase
as the leaves mature.

Total non-structural carbohydrates (TNC) are the energy reserves the plant has
accumulated which can be used for new plant growth (Smith, 1981). The concentration
of TNC in leaves changed over time after topping (Fig. 2-18). The rapid increases in
TNC concentration at LPs 13-15 and 19-21 were probably due to both topping and leaf
maturity. The decline in the TNC concentration at the LPs as the final harvest neared
was likely due to a reduction in the photosynthetic capacity of the ageing leaves in
combination with some respiration of the TNC fraction due to maturity, ripening, and

35

19-21

16-18

13-15

10-12

7-9

4-6

1-3

22,0

:■':■:■:■ :-:+yZ^^^^

H

16.9

H

c
g

CO

15.8

H

H

LSD

u

>•-

13.5

!H

H

_i

•2.5

H

14.0 J?f|

i

i

16.0

■ i ■ i i i t -| — i i ■ — r~

1

i -■< —

i '

i — ■ — r

■ « — i — '

0 2 4 6 8 10 12 14 16 18 20 22 24
Lamina Nicotine Concentration (g/kg)
Fig. 2-16. Lamina nicotine concentration of flue-cured tobacco as influenced by leaf
position (LP) (LSD 0.05 = 1.4). Vertical line represents mean across all LPs.
Numerical values within bars are means (n=16) of each LP.

S> 20-

S

c
o

2 15-

c

8

c
o
O

CD

8

CO

c

I
5

ID-

S'

■* —

LP 7-9 y = 9. 1 7 + 0.22x RA2 = 0.94
LP 13-15 y = 7.1 1 +0.26x RA2 = 0.97

LP 19-21 y = 4.00 + 0.60x - 0.006xA2 RA2 = 0.98

1

42

21 28

Days After Topping (DAT)

Fig. 2-17. Lamina nicotine concentration of flue-cured tobacco leaf positions (LP) in
response to days after topping. LSDs (0.05) for comparison of LPs at 0, 7, 14,
21, 28, and 35 DAT are 0.9, 0.7, 0.4, 0.5, 0.6, and 0.7, respectively.

T
49

36

CO

o

t

c
o

2 5

w

co
o

H

co

g

f

co

CD
O

o
O

O

.a

c

CO

O

600

500-

400

300-

200

14 21

Days After Topping (DAT)
Fig. 2-18. Lamina total non-structural carbohydrate concentration of flue-cured

tobacco leaf positions (LP) in response to days after topping. LSDs (0.05) for
comparison of LPs at 0, 7, 14, 21, 28, and 35 DAT are 70.3, 54.4, 49.8, 50.3,
37.5, and 24.3, respectively.

37

senescence of the leaves. The leaves taken for the final harvests in the present study
were judged to be mature to ripe. Kakie and Sugizaki (1970) and Kakie (1972)
reported that flue-cured tobacco leaves declined in total carbohydrate concentration as
the leaves progressed from maturity to over- maturity. The total carbohydrate decline
was associated with a decrease in starch concentration and an increase in the soluble
sugar fraction. But, there was some respiration of starch because the soluble sugar
increase was not equal to the starch decrease.

Reducing sugar concentration is important to the quality of flue-cured tobacco.
The reducing sugars are a product of starch (mostly TNC) metabolism induced during the
curing process (Askew and Blick, 1947). Kakie (1972) reported that total
carbohydrate concentration of mature green tobacco leaves ranged from 340 g kg1 to
416 g kg1 with a starch concentration ranging from 190 g kg1 to 370 g kg1. The ratio
of starch to total carbohydrates was 56% to 89%. The higher proportion of starch
occurred when the leaves were progressing from immaturity to maturity, while the
lower proportion of starch occurred as the leaves were progressing from maturity to
over-maturity. Reducing sugar concentration of flue-cured tobacco leaves will vary
greatly depending on the location, cultivar, and ultimately seasonal climatic conditions.
However, a concentration range generally from 150 g kg1 to 280 g kg1 has been
reported. The starch concentration of cured leaves is usually less than 30 g kg1 (Neas
et al., 1978; Nel et al., 1974) if mature leaves are harvested and cured properly.

Reducing sugar concentration was highest in the leaves from the middle LPs (Fig.
2-19). The middle leaves of flue-cured tobacco are nearly always the highest in
reducing sugar concentration (Brown and Terrill, 1973; Nel et al., 1974; Neas et al.,
1978; Darkis et al., 1936, 1952; Walker, 1968). Over time after topping, the
reducing sugar concentration (Fig. 2-20) followed a similar pattern to that of TNC
concentration. This result would be expected because the TNC is metabolized to reducing
sugars in the curing process. The reducing sugar concentrations at LPs 13-15 and 19-

38

c
o

"55
o
Q.

"5
©

19-21

148.1

H

16-18

170.0

H

13-15

...■:■:■/■■

218.6

In

10-12

■ 2 4 6,3 .

H

7-9

235 -3 ^'lli

Bill

H

4-6

:

;:::l::fflll

213.1

H

1-3

15 9.4 III

H

—1

LSD

i

i

i

50

100

150

200

250

300

Fig. 2-

Lamina Reducing Sugar Concentration (g/kg)
19. Lamina reducing sugar concentration of flue-cured tobacco as influenced by
leaf position (LP) (LSD 0.05 = 13.5). Vertical line represents mean across all
LPs. Numerical values within bars are means (n=16) of each LP.

3

300

.2 250

200-

150 -

CO

H

CD
O

c
o
o

Li

CO
O)

3

w

.e 100 H

o

i

a

CO

c
E

CO

50-

,<

LP 1 -3 Means (n=36)
• • — O— LP 7-9 Means (n=36)

a LP 13-15 Means (n=36)

• LP 19-21 Means (n=36)

— — LP13-15y = 132.3 + 7.5x-0.14xA2 RA2 = 0.88
---- LP 19-21 y = 37.6 + 9.6x- 0.1 6xA2 RA2 = 0.85

— f—
35

42

49

Fig. 2-

0 7 14 21 28

Days After Topping (DAT)
20 Lamina reducing sugar concentration of flue-cured tobacco leaf positions
(LP) in response to days after topping. LSDs (0.05) for comparison of LPs at 0,
7, 14, 21, 28, and 35 DAT are 33.3, 10.6, 10.4, 15.2, 11.3, and 6.0,
respectively.

39

21 changed proportionally with the TNC concentration of the same LPs (Fig. 2-21). A
poor relationship of reducing sugar to TNC concentration was found at LPs 1-3 and 7-9.
The N to nicotine (N:Nic) and reducing sugars to nicotine (Sug:Nic) concentration
ratios have been used to evaluate the potential smoking quality of flue-cured tobacco
(Moseley et al., 1963; Tso, 1972). The N:Nic (Fig. 2-22) was influenced by LP. The
lower N:Nic ratio values at LPs 1-3, 4-6, 13-15, 16-18, and 19-21 were within the
ranges found of other tobaccos for similar LPs (Brown and Terrill, 1973; Darkis et al.,
1952; Walker, 1968), however, the higher N:Nic values for LPs 7-9 and 10-12
exceeded published values for similar LPs. Tso (1972) determined that an N:Nic
approximating 1 :1 was the most desirable. The N:Nics of the LPs evaluated over time
after topping were different because of the differences in leaf age at topping (Fig. 2-
23). Maturation of tobacco leaves results in lower concentrations of N and higher
concentrations of nicotine (see Figs. 2-15 and 2-17). Moseley et al. (1963) reported
maturation of tobacco leaves resulted in lower N:Nic. The Sug:Nic ratio (Fig. 2-24) also
varied by LP. The Sug:Nic was highest at the middle LPs with lower Sug:Nic observed at
the upper and lower LPs. Brown and Terrill (1973) reported increasing Sug:Nic up to
the middle LPs, then a decline to the upper LPs, but their values for the middle LPs were
lower than the ones reported in the present study. Florida flue-cured tobacco is
typically higher in reducing sugar concentration and lower in nicotine than tobacco from
other states. Over time, each LP declined in the Sug:Nic (Fig. 2-25) indicating that
nicotine concentration was increasing proportionally higher than the reducing sugar
concentration. Moseley et al. (1963) found a reduction of the Sug:Nic was characteristic
of maturing tobacco leaves.

40

300

S 250-

c
.2

CO

£ 200 H

c

s

CD

o

1

150

100

50

Reducing Sugar Concentration = -137.2 + 0.658 (TNC)

RA2 = 0.820

• •>

1 1 1 1 1 1 1

200 250 300 350 400 450 500 550 600

Total Non-Structural Carbohydrate Concentration (g/kg)

Fig. 2-21. Relationship (p=0.001) between the total non-structural carbohydrate
(TNC) concentration of rapidly dried leaf lamina and the reducing sugar
concentration of cured leaf lamina from flue-cured tobacco leaf positions 13-15
and 19-21.

41

c

o

V-

(0

O

Q.

19-21

16-18

13-15

10-12

7-9

4-6

1-3

1 flfi

1

■ . ., I , V ■■■$ ■ ■ ■■,■ ■

1

1.15 f 1||

1

1

1

- ■ ^ : \ > 1 4

1

1.34

1

1

1.2 8

i

1

:1SIII 1 -- 1 6 •: '■ .

1

1

* ^"alE^' 1.0 4 7;I:-.

1

"I

'

LSD

I

i ■ 1-

- r

'

0.00

1.50

0.25 0.50 0.75 1.00 1.25

Nitrogen to Nicotine Concentration Ratio

Fig. 2-22. Lamina N to nicotine concentration ratio of flue-cured tobacco as influenced
by leaf position (LP) (LSD 0.05 = 0.13). Vertical line represents mean across
all LPs. Numerical values within bars are means (n=16) of each LP.

.2

DC
.2

I

a>
o
c
o
O

o
c

8

z
o

LP 7-9 y = 2.52 - 0.065x RA2 = 0.85

LP 1 3-1 5 y = 5. 1 4 - 0.29x + 0.0O5xA2 RA2 = 0.97

LP 1 9-21 y = 1 2.60 - 0.73x + 0.01 1 xA2 RA2 = 0.86

35

42

I

49

Days After Topping (DAT)
Fig. 2-23. Lamina N to nicotine concentration ratio of flue-cured tobacco leaf positions
(LP) in response to days after topping. LSDs (0.05) for comparison of LPs at 0,
7, 14, 21, 28, and 35 DAT are 2.35, 1.18, 0.18, 0.12, 0.08, and 0.07,
respectively.

42

19-21

16-18

13-15

10-12

7-9

4-6

1-3

6,7 \—\

— 1

10.1

c
o

mil 13*3 ' 'iiiii

-H

w
o

0_

llllll 16,2 ^Jllllllll

— 1

18.8

— \

15.2

— 1

It 1°° ■ \

i

-i

i

LSD

■ i ■ i ■ i * i

■ i "

1 • T

0 2 4 6 8 10 12 14 16 18 20 22

Reducing Sugar to Nicotine Concentration Ratio

Fig. 2-24. Lamina reducing sugar to nicotine concentration ratio of flue-cured tobacco
as influenced by leaf position (LP) (LSD 0.05 = 1.5). Vertical line represents
mean across all LPs. Numerical values within bars are means (n=16) of each
LP.

CO

cr

a;

c

8

co
en

CO

O)

c
o

3
"D

<D
DC

LP 1-3 Means (n=36)
LP 7-9 Means (n=36)
LP 13-15 Means (n=36)
LP 19-21 Means (n=36)

""" """"■""""- »«^

•"

MIIIIIIIIIHIII

LP 7-9 y = 22.07 - 0.25x RA2 = 0.98
— ^— LP 13-15 y = 22.30- 0.1 7x RA2 = 0.78
.... LP 19-21 y = 15.53 -0.1 7x RA2 = 0.49

I 1 1 1

35

- 1—
42

49

Fig. 2

0 7 14 21 28

Days After Topping (DAT)
25. Lamina reducing sugar to nicotine concentration ratio of flue-cured tobacco
leaf positions (LP) in response to days after topping. LSDs (0.05) for
comparison of LPs at 0, 7, 14, 21, 28, and 35 DAT are 3.6, 1.7, 1.4, 1.5, 1.3,
and 1.3, respectively.

43

Leaf Mineral Characteristic

Lamina Ca concentration (Fig. 2-26) was highest in the lowest LPs. This result
was expected because Ca is considered to be non-mobile in plants (Tisdale and Nelson,
1975). Calcium concentrations have been found to be highest in the lower leaves of
tobacco in previous studies as well (Darkis et al., 1936, 1952; Askew et al., 1947;
Walker, 1968; Neas et al.,1978). Calcium concentrations changed little over time after
topping for all LPs (Fig. 2-27). Raper and McCants (1966) found that flue-cured
tobacco plants had accumulated 81 .8% of the total Ca uptake 77 days after seedling
transplantation. One possible interpretation of these data is that Ca uptake continued at a
fairly constant rate after topping because for the leaves within the given LPs to maintain
the Ca concentration in response to CW increases a considerable amount of Ca must be
taken up by the roots and translocated to the leaves. Raper and McCants (1 966) based
their total uptake percentages on the composition of plants harvested 91 days after
seedlings were transplanted. Data collection for the present study continued until 130
days after the seedlings had been transplanted.

Lamina Mg concentration by LP (Fig. 2-28) followed an almost identical pattern
as that of Ca. A similar distribution of Mg concentration in leaves has been reported by
Askew et al. (1947), Darkis et al. (1952), and Walker (1968). The Mg concentration
by LP over time after topping was constant (Fig. 2-29), much like that observed for Ca.
Raper and McCants (1966) reported that 77 days after the seedlings were transplanted
tobacco plants had accumulated 90.0% of the total Mg that was accumulated after 91 days
in the field. Because Mg and Ca concentration patterns, not the actual concentrations,
were similar over time, the same argument previously made about Ca concentration over
time should be valid for Mg. It also could be argued, based on the observations in the
present study, that had Raper and McCants (1966) continued to take samples after 91
days after transplanting the total uptake of Mg and Ca may have been different. This
suggestion is supported by observations by Srivastava et al. (1984) who found that

44

c
o

w
o

Q.

CO
0

19-21

16-18

13-15

10-12

7-9

4-6

1-3

12-7

tlllll

H

liilil

H

tliiii

H

22 1

33 1

H

LSD

-> r

5

— r-
20

— r-
30

35

10 15 20 25

Lamina Calcium Concentration (g/kg)

Fig. 2-26. Lamina Ca concentration of flue-cured tobacco as influenced by leaf position
(LP) (LSD 0.05 = 1.4). Vertical line represents mean across all LPs.

Numerical values within bars are means (n=16) of each LP.

35

o>

OC

O)

30

c

o

CO

25

CD

o

c:

O

o

ag

20

o

co

c

E

03

15

-- ■-- LP 1-3 Means (n=36)

- - O- " LP 7-9 Means (n=36)

— D — LP 1 3- 1 5 Means (n=36)

• LP 19-21 Means (n=36)

.... LP 19-21 y = 11.43 =0.078x RA2 = 0.54

o

Days After Topping (DAT)
Fig. 2-27. Lamina Ca concentration of flue-cured tobacco leaf positions (LP) in

response to days after topping. LSDs (0.05) for comparison of LPs at 0, 7, 14,
21, 28, and 35 DAT are 2.5, 0.6, 0.8, 0.8, 0.5, and 0.7, respectively.

45

c
o

w
o
Q.

«»-
CO
(D

-I

19-21

::■:■::■■■■■■ ...■:.■.■:■:■:■:■:■:■:■■■■■■ y . .■ .
5.5' :;:.,■.

1

H

LSO

H

16-18

5.3

13-15

5.0

10-12

5.7

H

7-9

6.4

H

4-6

0,6

;:;:;:|:;S:i::S::y:-.y '.;..

H

1-3

14.9

I — -^ — r • i

-i-

■ , i

1 ■ 1

0 2 4 6 8 10 12 14 16

Lamina Magnesium Concentration (g/kg)
Fig. 2-28. Lamina Mg concentration of flue-cured tobacco as influenced by leaf position
(LP) (LSD 0.05 = 0.7). Vertical line represents mean across all LPs.
Numerical values within bars are means (n=16) of each LP.

16

O)

o

CO

h-

c
a>
o
c
O

o

03

c

I

14-

12-

10-

-■■-- LP 1-3 Means (n=36)

••O LP 7-9 Means (n=36)

Q LP 13-1 5 Means (n=36)

• LP 19-21 Means (n=36)

^^— LP 13-15 y = 6.04 - 0.07x + 0.0001 xA2 RA2 = 0.96
---- LP19-21 y = 6.08- 0.06x + 0.0001 xA2 R*2 = 0.48

— r~
35

42

I

49

Fig. 2-

14 21 28

Days After Topping (DAT)
29. Lamina Mg concentration of flue-cured tobacco leaf positions (LP) in
response to days after topping. LSDs (0.05) for comparison of LPs at 0, 7, 14,
21 , 28, and 35 DAT are 1 .3, 0.3, 0.3, 0.4, 0.2, and 0.2, respectively.

46

Dixie Shade Wrapper tobacco had taken up only 54.2% and 42.7% of the total Ca and Mg,
respectively, 80 days after seedling transplantation. They compared the percentage
uptake to final harvest values taken 120 days after transplanting.

Lamina K concentration (Fig. 2-30) was highest at the lower LPs and lowest at
the upper LPs. Potassium is generally considered to be a mobile element in plants
(Tisdale and Nelson, 1975). However, the fact that lower K concentrations in upper
leaves than lower leaves have been reported by Darkis et al. (1936, 1952), Askew et
al. (1947), Walker (1968), and Neas et al. (1978) may indicate that K is not as
mobile in the tobacco plant as in other plants. The change in K concentration over time
was influenced by the age of the leaves within an LP (Fig. 2-31). Raper and McCants
(1966) reported that flue-cured tobacco plants had accumulated 97.4% of all K 77 days
after transplanting. Srivastava et al. (1984) found Dixie Shade Wrapper tobacco had
taken up only 55.4% of all K 80 days after transplanting. Atkinson et al. (1977) found
Burley tobacco plants had accumulated 95.1% of all K 73 days after seedling
transplantation. The tobacco plants in the present study may have accumulated most of
the K at topping because the K concentrations at the least mature LPs declined after
topping, while K concentrations at the more mature LPs remained about the same.

Lamina P concentration (Fig. 2-32) differed little at LPs. Differences existed
between some LPs, but unlike other leaf mineral components previously discussed, these
P concentration data differed from other published reports. Askew et al. (1947),
Darkis et al. (1952), and Nel et al. (1974) found P concentrations to be higher at
higher LPs. Of all the leaf parameters evaluated over time, the most dynamic
relationship existed for P concentration by LP (Fig. 2-33). These differences between
LPs existed due to the inherent differences in leaf age at topping. The least mature LP at
topping, 19-21, had the highest P concentration and most likely had the highest
metabolic activity. The most interesting aspect of the P concentration changes over time
was that the P concentrations at LPs 7-9, 13-15, and 19-21 increased over the 21

47

19-21
16-18
13-15
10-12

7-9

4-6

1-3
0

... ■■■.■■:■■.■:■:■.■*...:. ... . . . . :.:. .. ;

1

03

2 1.0 ■

H

20.4

H

LSD

O
Q.

2 5.0'

wmmm:mmmmm iiipi^^»iiiii»i ; i l§

1

H

_i

- 25.0

IF

H

25.7

H

2 6.5

; aM,

H

i ■ i ■ 1 —

5 10 15

i r

20

i
25

3

Lamina Potassium Concentration (g/kg)

Fig. 2-30. Lamina K concentration of flue-cured tobacco as influenced by leaf position
(LP) (LSD 0.05 = 1.6). Vertical line represents mean across all LPs.
Numerical values within bars are means (n=16) of each LP.

O)

CD

o

c

O

o

(0

c

E
ro

32
30
28
26
24
22
20
18

LP 1-3 Means (n=36)

LP 7-9 Means (n=3G)

LP 13-15 Means (n=36)

LP 19-21 Means (n=36)

—^^ LP 13-15 y = 27.0- 0.1 9x R*2 = 0.86

- - - - LP 1 9-21 y = 30.97 - 0.45x + 0.005xA2 R"2 = 0.95

42

49

0 7 14 21 28 35

Days After Topping (DAT)

Fig. 2-31. Lamina K concentration of flue-cured tobacco leaf positions (LP) in

response to days after topping. LSDs (0.05) for comparison of LPs at 0, 7, 14,
21, 28, and 35 DAT are 3.1, 1.5, 1.5, 1.5, 0.8, and 1.3, respectively.

19-21

16-18

13-15

10-12

7-9

4-6

1-3

3.3

m i

i|

i

3.0

H

_o

3.1

LSD

o
0.

03

a
i

3.4

3.2

_|

\

n

3.4

•■.■:■:■■■:■■■:■■ ■ ■.:■..■■■■ ■ ■■:■.■:■:■:■: ■■■■■■ ■■■■ ■.■,■.■.■.-.■.■.■.■.■.■ ■.

2,9

•i

• — i ■ 1 ■ —

— r

— i — >—

0.0

4.0

0.5 1.0 1.5 2.0 2.5 3.0 3.5

Lamina Phosphorus Concentration (g/kg)

Fig. 2-32. Lamina P concentration of flue-cured tobacco as influenced by leaf position
(LP) (LSD 0.05 = 0.3). Vertical line represents mean across all LPs.
Numerical values within bars are means (n=16) of each LP.

5.0

3

c
o

i_

o
o
e
o
O

Q-

cc

E
5

4.5 -►

4.0

3.5-

- • " LP 1 -3 Means (n=3G)

O LP 7-9 Means (n=36)

D LP 13-15 Means (n=36)

• LP 19-21 Means (n=36)

X

■" LP 7-9 y = 2.75 + 0.029 x R*2 = 0.93

■— — LP 13-15 y = 3.09 - 0.05x + 0.001 xA2 RA2 = 0.92
■"■■ LP 19-21 y = 4.50 - 0.14x + 0.002xA2 R"2 = 0.98
-^

r
42

1
49

0 7 14 21 28 35

Days After Topping (DAT)

Fig. 2-33. Lamina P concentration of flue-cured tobacco leaf positions (LP) in

response to days after topping. LSDs (0.05) for comparison of LPs at 0, 7, 14,
21, 28, and 35 DAT are 0.4, 0.2, 0.2, 0.2, 0.2, and 0.2, respectively.

49

days prior to final harvest. Because the leaves comprising LP 1 9-21 were the most
recently formed and were on the plant for the longest period of time, the most
information was accumulated for this LP. However, when viewing the concentration
curves for LPs 7-9 and 13-15, it may be suggested that had these LPs been sampled
over the same stages of development as was LP 19-21, their respective relationships
would look similar. This theory may be supported by the lowest P concentration points,
which were about 2.6 g kg1, on the respective curves that were similar at all three LPs.
The final P concentrations also were nearly equal for each LP which agreed with the data
reported for the individual LPs in Fig. 2-32.

Conclusions

Flue-cured tobacco is harvested by LP as the leaves mature. Differences existed
for agronomic, chemical, and mineral characteristics based on the position or node on
the tobacco stalk at which leaves were formed. The highest yield and value were found at
the highest LPs. At topping, differences in the agronomic, chemical, and mineral
characteristics at LPs were a result of leaf age and previous development. The yield and
chemical and mineral concentrations of the lowest nine leaves did not change over time
after topping indicating that those leaves were essentially mature at topping. However,
the yield, chemical, and mineral characteristics of the upper 12 leaves (or 4 LPs) did
change over time, with the largest changes evident in the uppermost leaves. The
observation that characteristics of flue-cured tobacco leaves are different based on the
position or node at which the leaves are formed would support continuation of the
current practices by which leaves are harvested and marketed based on LP.

CHAPTER 3

LOWER LEAF HARVESTING EFFECTS ON AGRONOMIC

CHARACTERISTICS OF FLUE-CURED TOBACCO

Introduction

Federal programs dictate how much flue-cured tobacco (Nicotiana tabacum L)
can be marketed. A combination of area allotments and weight quotas is assigned to each
farm. New tobacco cultivars and improved cultural practices enable many tobacco
growers to exceed their weight quotas on less than the area allotted to produce the
tobacco. Consequently, some farmers choose not to plant their entire area allotment,
since they cannot sell the tobacco produced in excess of the weight quota. This
management decision is sound under good growing conditions, where yields can be
predicted with reasonable accuracy.

Lower leaf harvesting options are available that may allow farmers opportunities
to increase their net income from tobacco. If the upper leaves are substantially more
valuable in price than the lower leaves, the farmer may wish to produce his weight quota
with the upper leaves. Consequently, the lower leaves could be discarded.

Lower leaf pruning of flue-cured tobacco became an issue in the mid 1 970's
when an over-supply of lower stalk tobacco pushed prices downward causing receipts of
this type tobacco to be increased by the farmer-owned Flue-Cured Tobacco Cooperative
Stabilization Corporation (FCTCS) (Wernsman and Matzinger, 1 980). The FCTCS
purchases tobacco that does not receive bids of more than one cent above the designated
United States Department of Agriculture price support. Because of the large receipts of
this lower leaf tobacco, the federal tobacco program was amended in 1 978 to allow

50

51

farmers to plant 1 0% more acreage if they would prune or not harvest the lowest four
leaves of their tobacco crop. This program was known as the "four leaf program."

Studies dealing with lower leaf harvesting options have resulted in mixed
conclusions with respect to effects on yield. Currin and Pitner (1980) reported that
pruning and discarding the lowest four leaves did not lower yields or affect the leaf
chemical component balance of the remaining leaves, when compared to harvesting all
the leaves. Leaving the lowest four leaves on the stalk and not harvesting them, reduced
yield compared to the treatments involving either pruning and discarding the lowest four
leaves or harvesting all leaves. Stocks (1988) found that pruning and discarding the
lowest three or four leaves resulted in equal yields and an increase in the price per
kilogram when compared to harvesting all leaves. But, not removing and not harvesting
the same lower leaves reduced yields. Currin and Stanton (1989) and Stocks (1988)
reported that pruning more than four leaves had a negative impact on yield and value of
flue-cured tobacco.

Court and Hendel (1989) evaluated leaf number management by several topping
height and lower leaf pruning regimes. Eighteen leaves per plant was the control.
Reduction in leaf number harvested from 18 to 15 to 12 resulted in a reduction in yield
and value of the crop for each reduction in leaf number. Pruning the lower leaves or
topping down to the desired leaf number produced similar reductions in yield and value.
Suggs (1972) evaluated a wide array of leaf pruning treatments and concluded that yield
and value decreased with an increase in the number of leaves pruned. However, the
lowest three leaves could be pruned with little decrease in yield. Crop value declined as
the number of lower leaves pruned exceeded three. Wernsman and Matzinger (1980)
found that yield reductions due to lower leaf pruning of mammoth cultivars could be
compensated for by topping to a higher leaf number.

In the above-mentioned studies, there are discrepancies regarding the effects of
lower leaf pruning. Results from studies conducted in the Southeastern U.S. (Suggs,

52

1972; Currin and Pitner, 1980; Stocks, 1988; Currin and Stanton, 1989) suggested
that pruning the lowest three or four leaves of flue-cured tobacco did not reduce yield or
value appreciably. However, in a study conducted in Southern Canada, Court and Hendel
(1989) did find yield losses associated with lower leaf pruning. The present study
evaluated the influence of five lower leaf harvesting options on tobacco plants topped to
exactly 21 leaves. Because results from some previous work suggests that the tobacco
plant compensates in some manner for the cured weight lost due to lower leaf pruning,
the 21 leaves on each plant were partitioned into seven, 3-leaf stalk positions so that
yield by leaf position could be evaluated to determine where any "yield compensation"
may occur.

Materials and Methods

The location, cultivars, and management practices for the present study were
identical to those previously discussed in Chapter 2. Only methods used in the present
study that differ from those discussed in Chapter 2 are discussed below.

Five lower leaf harvesting options were evaluated in this study. These
treatments were as follows: 1) harvesting all 21 leaves (LPs 1-3 to 19-21)(control),
2) prune and discard the lowest three leaves on the stalk, harvest 18 leaves (LPs 4-6 to
19-21), 3) do not prune or harvest the lowest three leaves, harvest 18 leaves (LPs 4-
6 to 19-21), 4) prune and discard the lowest six leaves on the stalk, harvest 15 leaves
(LPs 7-9 to 19-21), and 5) do not prune or harvest the lowest six leaves, 15 leaves
harvested (LPs 7-9 to 19-21). Leaves were removed from plants of the pruning
treatments at topping when leaf number was established. Currin and Pitner (1980)
found pruning the lower leaves at early topping produced the highest yields. The topping
time used in the present study would be considered early topping. The pruned leaves
were cured in the normal manner to evaluate what their contributions to yield and value
would have been.

53

A split-plot arrangement of treatments was utilized in the field with cultivars
being main plots and lower leaf harvesting treatments being sub-plots. But, the addition
of the leaf position variable resulted in a split-split-plot design with leaf position being
the sub-sub-plot. Four replications of the cultivars and lower leaf harvesting
treatments were evaluated each year.

A split-split-split-plot design was used for statistical analysis with years being
main plots, cultivars being sub-plots, lower leaf harvesting options being sub-sub-
plots, and leaf positions being sub-sub-sub-plots. Analysis of variance and Fisher's
Least Significant Difference (LSD) were carried out by methods described by Gomez and
Gomez (1984). The factors of primary interest in this study were lower leaf
harvesting options and leaf positions, and their interaction. There were no significant
interactions between harvesting options and leaf position, year, or cultivar for the
agronomic variables, so the following discussion focuses on the effects of harvesting
options effects across years and cultivars. Total yields were computed by summing
yields of all leaf positions and analysis of variance was performed on all data to
determine significant effects due to harvesting options. A split-split-plot design with
years being main plots, cultivars being sub-plots, and lower leaf harvesting options
being sub-sub-plots was used for the analysis. A second analysis was also performed on
yield data which included weights of pruned leaves in order to evaluate the contributions
of the pruned leaves. The LSD values computed from the two statistical analyses were
very similar. Therefore, another analysis including the two treatments with the pruned
leaves added was carried out. No differences were found in how the harvesting options
were segregated by means comparison from the individual analyses. For simplification,
the LSD values given in the figures were computed from the combined analysis of
treatments, otherwise two LSD values of numerical value would have been necessary.

54

Results and Discussion

Lower leaf harvesting treatments did not influence the fresh weight, cured
weight, leaf area, or value at the LPs above those that were either pruned or were left on
the plant and not harvested (data not shown). Suggs (1972), Currin and Pitner
(1980), and Stocks (1988) found equivalent yields and economic values from
treatments involving pruning of the lower three or four leaves or harvesting all of the
leaves. Furthermore, Currin and Pitner (1980) and Stocks (1988) found that leaving
the lowest three or four leaves on the plant and not harvesting them reduced yields and
values when compared to pruning and discarding those leaves or harvesting them
normally. From those studies it may be inferred that pruning treatments increased
yield and economic value in the leaves above those pruned, while not pruning or
harvesting the lower leaves did not influence the yield or values at the higher LPs.

Fresh weight (FW) (Fig. 3-1), cured weight (CW) (Fig. 3-2), and leaf area
index (LAI) (Fig. 3-3) were reduced as a result of the lower leaf harvesting treatments.
Pruning or not pruning per se had no effect on these parameters; rather, the number of
harvested leaves per treatment was responsible for the observed results. Court and
Hendel (1989) also noted that reduced leaf number per plant reduced yield parameters,
either by lower leaf pruning or topping to a lower leaf number.

In the present study, the pruned leaves were saved and cured normally to
evaluate the effects of the early harvesting by pruning compared to normal harvesting of
the same leaves. When the FW, CW, and LA of the pruned leaves were added back to the
yields of the corresponding pruning treatments (Figs. 3-1, 3-2, 3-3), no differences
in FW, CW, or LAI were found between the pruning treatments (computed with 21 total
leaves) and the control treatment (21 leaves harvested). This observation supports the
view that at topping the lower leaves which were pruned had reached maturity. In
Chapter 2, it was also noted that the lowest nine leaves had reached maturity at topping.

55

No Prune Low 1

■

Actual Treatment Means []] Pruned Leaves Added

6 Leaves ■

| 19190

Prune Low [HI

25910

6 Leaves ■

| 19350

No Prune Low L

3 Leaves H

1 23600

Prune Low Ijjj j ■ 1 1 ' 1 1 1 1 1 ' | | ' 1 1 1 j ;

| 26304

3 Leaves H

123440

Harvest .AJI 1

Leaves H

| 26320
i i — i '

Fig

10000

15000

20000

25000

Fresh Weight (kg/ha)
3-1 . The effects of lower leaf harvesting on fresh weight of flue-cured tobacco
and the effects of the pruned leaves on the total yield of the pruning treatments.
LSD (0.05) = 1197 for all comparisons. Values outside bars are the treatment
means.

Fig

2000

No Prune Law

■

Actual Treatment Means O

3runed Leaves Added

6 Leaves

| 3350

Prune Low

"J1" 4180

6 Leaves

| 3360

No Prune Low

3 Leaves

3810

Prune Low

|| 4138

3 Leaves

3820

Harvest .All

Leaves

| 4150
i i i i i '

2500

3000

3500

4000

4500

Cured Weight (kg/ha)

3-2. The effects of lower leaf harvesting on cured weight of flue-cured tobacco
and the effects of the pruned leaves on the total yield of the pruning treatments.
LSD (0.05) = 148 for all comparisons. Values outside bars are the treatment
means.

56

No Prune Low 1

■

Actual Treatment Means CD

Pruned Leaves Added

6 Leaves 1

[ 3.11

Prune Law [^

]4 34

6 Leaves ■

H 3.13

No Prune -Low L

3 Leaves |

I3'88

Prune Low li

4.37

3 Leaves M

3.82

Harvest .All 1

Leaves 1

I432

— i 1 r

I I

2.0

2.5

3.0

3.5

4.0

4.5

5.0

Leaf Area Index (sq. m leaf/sq. m land area)

Fig. 3-3. The effects of lower leaf harvesting on the leaf area index of flue-cured

tobacco and the effects of the pruned leaves on the leaf area index of the pruning
treatments. LSD (0.05) = 0.17 for all comparisons. Values outside bars are the
treatment means.

57

No previous studies dealing with the effects of lower leaf removal evaluated the leaves
that were pruned.

Harvest index (HI) is a ratio of the weight of the economic portion of a crop to the
total shoot biomass of the above-ground portion of the crop. The HI is typically used
with grain crops to evaluate the grain yield efficiency of a cultivar. A reduction in the
number of leaves harvested resulted in a decline in HI (Fig. 3-4). However, a higher HI
was found when the lower six leaves were pruned compared to not pruning or harvesting
the same six leaves. This result was due to the lower stalk cured weight when six leaves
were pruned (Fig. 3-5) since CWs were equal for the two treatments (Fig 3-2). The
difference in stalk weight was unexpected. Literature relating tobacco stalk weight to
such treatments does not exist. Kollman et al. (1974) found reduced sink size of
soybeans (Glycine max L Merr.) increased stem and petiole weight. A maximum HI of
71 was found when no leaves were pruned and all leaves were harvested. As with other
agronomic parameters previously discussed, the addition of the CW of pruned leaves
resulted in His which were almost identical to the treatment where all leaves were
harvested (Fig. 3-4). A HI for tobacco by the definition given above has not been
reported, but Suggs (1984) found leaf weight to total leaf plus stalk weight ranged from
47% to 64%.

Cured weight yield (CWY) (Fig. 3-6) and specific cured leaf weight (SCLW)
(Fig. 3-7) increased as more lower leaves were pruned and discarded or were not
harvested. The average CWY and SCLW of the pruning treatments were not different
from the control when the corresponding CWY and SCLW of the pruned leaves were
included in the totals. In Chapter 2, the CWY and SCLW were found to be lowest in the
lowest LPs. Consequently, the average CWY and SCLW of the total crop would be expected
to increase as the number of lower leaves harvested decreased. Suggs et al.(1987) found
the CWY of the first harvest of a tobacco crop was the lowest of all harvests. This first
harvest also required one of the longest curing times. More importantly, the ratio of

58

No Prune Low
6 Leaves

Prune Law
6 Leaves

No Prune Low
3 Leaves

Prune Low
3 Leaves

Harvest All
Leaves ^_^^^^^^^

50 60 70

Harvest Index (g cured leaf/100 g stalk + leaves)

Fig. 3-4. The effects of lower leaf harvesting on the harvest index of flue-cured

tobacco and the effects of the pruned leaves on the harvest index of the pruning
treatments. LSD (0.05) = 1.0 for all comparisons. Values outside bars are the
treatment means.

No Prune 6 Low Leaves

Prune 6 Low Leaves

No Prune 3 Low Leaves

Prune 3 Low Leaves

Harvest all Leaves

1000

1200

t • r

1400 1600

1800

Stalk Cured Weight (kg/ha)

Fig. 3-5. The effects of lower leaf harvesting on the stalk weight of flue-cured

tobacco. LSD (0.05) = 88 for all comparisons. Values outside bars are the
treatment means.

59

No Prune Low
6 Leaves

Prune Law
6 Leaves

No Prune -Low
3 Leaves

Prune Low
3 Leaves

Harvest _AJI
Leaves ^^^^^^^_______^_

12 14 16

Cured Weight Yield (g cured leaf/100 g fresh leaf)
Fig. 3-6. The effects of lower leaf harvesting on the cured weight yield of flue-cured
tobacco and the effects of the pruned leaves on the cured weight yield of the
pruning treatments. LSD (0.05) = 0.5 for all comparisons. Values outside bars
are the treatment means.

No Prune Low

■

Actual Treatment Means

a

Pruned Leaved Added

6 Leaves

1 10-77

Prune Law

T[| 9.66

6 Leaves

| 10.76

No Prune -Low

3 Leaves

| 9.82

9.48

Prune Low

3 Leaves

| 9.99

Harvest .AJI

| 9.61

Leaves

1 1—

7.0 8.0 9.0 10.0 11.0

Specific Cured Leaf Weight (mg cured leaf/sq cm leaf)

Fig. 3-7. The effects of lower leaf harvesting on the specific cured leaf weight of flue-
cured tobacco and the effects of the pruned leaves on the specific cured leaf weight
of the pruning treatments. LSD (0.05) = 0.31 for all comparisons. Values
outside bars are the treatment means.

60

curing cost to CW was highest for the first harvest. Not harvesting the lower leaves may
result in more efficient handling and curing of the tobacco crop due to the higher CW per
unit of FW harvested and reduced curing cost per unit of CW.

Value per hectare of the tobacco crop declined as the total number of leaves
harvested decreased (Fig. 3-8). As with FW and CW, the values of the pruned LPs were
equal to the values of the those same LPs when normally harvested. Value per kilogram
improved when the lowest three or more leaves were not harvested (Fig. 3-9). An
increase in the average value per kilogram as a result of lower leaf pruning has been
observed in other studies (Suggs, 1972; Currin and Pitner, 1980; Stocks, 1988; Court
and Hendel, 1989; Currin and Stanton, 1989). The increase in average price resulted
because the lowest LPs were of the lowest value per kilogram (Table 3-1).

The potential benefits associated with not harvesting lower leaves include: 1) a
higher average price per unit of the crop, 2) higher returns of CW per unit of FW
handled, 3) a lower curing cost per unit of CW, and 4) a higher value returned to quota.
Although there was a statistically significant increase in value per kilogram in the
present study, there also was a significant reduction in yield and value per hectare when
the lower leaves were not harvested.

The critical value used to determine if a given lower leaf harvesting treatment
significantly influenced value per hectare was $627 ha-1 (Fig. 3-10). The difference
between the control and harvest 18 leaves treatments was $1060 ha1. The difference
between the critical value and the actual difference was $433 ha1 . For there to be no
statistical difference in the values of the treatments, the harvest 18 leaves treatments
must increase in value by at least $433 ha1. This difference can be made up by
increased yield of the remaining leaves as found by Currin and Pitner (1980), Stocks
(1988), and Currin and Stanton (1989). However, in the present study and that by
Court and Hendel (1989) yield and value were lowered by reducing the total number of

61

No Prune Low

■

Actual Treatment Means

m

Pruned Leaves Added

6 Leaves

| 12710

Prune Law

| 15616

6 Leaves

| 12740

No Prune Low

3 Leaves

| 14410

Prune Low

J 15459

3 Leaves

1 14430

Harvest .All

Leaves

1 15490

■ i

I

5000

7500

10000

12500

15000

Dollars per Hectare ($/ha)

Fig. 3-8. The effects of lower leaf harvesting on the value per hectare of flue-cured
tobacco and the effects of the pruned leaves on the value per hectare of the
pruning treatments. LSD (0.05) = 573 for all comparisons. Values outside bars
are the treatment means.

No Prune Low. I

■

Actual Treatment

means

m

Pruned leaves added

6 Leaves 1

| 3.79

Prune Low. Ii

{ | j j 1 1 i ; | 3.73

6 Leaves 1

13.79

Nn Prune | nw 1

3 Leaves 1

03.79

|3.78

Prune Low I

II i II 1 1 1 1 ! l] 3.73

3 Leaves 1

Harvest All 1

Leaves 1

| 3.73

■ i

T

I 1

r

3.50

3.55

3.60

3.65

3.70

3.75

3.80

Fig

Dollars per Kilograms ($/kg)

3-9. The effects of lower leaf harvesting on the value per kilogram of flue-cured
tobacco and the effects of the pruned leaves on the value per kilogram of the
pruning treatments. LSD (0.05) = 0.04 for all comparisons. Values outside
bars are the treatment means.

62

Table 3-1 . Value per kilogram by leaf position of the lower leaf harvesting treatments.

Lower Leaf

prune low

3 leaves

Harvesting

no prune
low 3 leaves

Treatments

prune low

6 leaves

Leaf

Position

harvest all
leaves

no prune
low 6 leaves

$ kg-1

19-21

3.77

3.76

3.73

3.75

3.73

16-18

3.79

3.79

3.81

3.74

3.74

13-15

3.82

3.82

3.84

3.84

3.86

10-12

3.71

3.72

3.77

3.74

3.75

7-9

3.67

3.69

3.69

3.70

3.70

4-6

3.57

3.63

3.61

3.49x

NHY

1 -3

3.29

3.41*

NHy

3.40x

NHY

Vindicates these leaves were pruned at topping.

y/indicates these leaves from these treatments were not harvested.

No Prune 6 Low Leaves

Prune 6 Low Leaves

No Prune 3 Low Leaves

Prune 3 Low Leaves

Harvest all Leaves

10000

12000

14000

16000

Dollars per Hectare ($/ha)

Fig. 3-10. The effects of lower leaf harvesting on the value per hectare of flue-cured
tobacco. LSD (0.05) = 627 for all comparisons. Values outside bars are the
treatment means.

63

leaves harvested. Consequently, in these cases the value differences must be
compensated for by either increasing the value per kilogram or planting more area.

The harvest 18 leaves treatments yielded 3815 kg ha1. Based on this yield and
the needed minimum value increase ($433 ha1 ) not to be different from the control,
value per kilogram would need to increase by $0.11 kg1 ($433 ha1/3815 kg ha1).
An increased value of $0.11 kg1 is not unrealistic, but the same value per kilogram to
make up the value loss for the harvest 15 leaves option was $0.64 kg1 ($2138 ha1
/3355 kg ha1). Pruning or otherwise not harvesting the lowest six leaves was not
feasible based on the results from the present study.

The other method of compensating for value lost by not harvesting lower leaves is
planting more area. The value per hectare when all 21 leaves were harvested was
$15,490 ha1. The average value per hectare when only 18 or 15 leaves were harvested
was $14,420 ha-1 or $12,730 ha1, respectively. The additional hectareage required to
compensate for the reduced value when harvesting 1 8 leaves was 1 .07, whereas 1 .22
additional ha would be required for the 15-leaf harvest. Pruning or otherwise not
harvesting the lowest three leaves appeared to be the more viable option since value per
kilogram was equal and yield and value per hectare were higher when compared to the
pruning or otherwise not harvesting the lower six leaves.

In the middle 1980's, lower leaf harvesting decisions were based on economics.
The average value per kilogram for the lower leaf (P group) grades of flue-cured
tobacco were well below all others. A comparison of leaf position grade groups for 1986
and 1990 revealed the dramatic changes that have occurred on the U.S. flue-cured
tobacco market floor (Table 3-2). Beginning in 1989, increased demand for lower leaf
U.S. flue-cured tobacco drove prices for that leaf to levels approaching that of middle
leaves. The lower leaf grades (P group) increased 22 to 31% in value depending on
maturity classification, while the middle and upper stalk grades (X, C, and B groups)
increased very little in value over the same period (Table 3-2). The concept of not

64

Table 3-2. Changes in the Georgia-Florida (Type 14) flue-cured tobacco market

average value per kilogram from 1986 to 1990 of all ripe and mature or unripe
and immature grades common to both years.

— Ripe

& Mature

Grades —

- Unripe

& Immature

Grades -

Leaf Position
Grade Group

.... y

1986

ear ----
1990

.... y

1986

ear —
1990

B Group

-- $
3.85

kg-i ----
3.97

Change
+ 3%

— - $
3.64

kg-1 ----
3.75

Change
+ 3%

C Group

3.62

3.66

+ 1%

3.53

3.62

+ 3%

X Group

3.44

3.51

+ 2%

3.18

3.42

+ 8%

P Group

2.78

3.51

+ 22%

2.51

3.29

+ 31%

Source: 1986 and 1990 Georgia-Florida (Type 14) tobacco market grade reports from
the Market News Reporter, Doug Hendrix.

65

harvesting the lowest leaves at the present price structure is not economically sound,
unless potential yield exceeds quota. Still, if the present price structure were similar
to that of 1986, not harvesting the lower leaves would be a realistic option.

Conclusions

Harvesting methods for lower leaves of tobacco did not affect yield parameters of
individual leaves. Pruning and discarding lower leaves was no more or less beneficial to
total yield and value than leaving the lower leaves on the stalk and not harvesting or
discarding them. Total yield and value was reduced as the total number of leaves
harvested was reduced by lower leaf harvesting treatments. Average value per kilogram
was increased by not harvesting three or more lower leaves because these leaves were
the lowest in value per kilogram and CW. At the time of pruning, the lower leaves had
reached their maximum yield and value because returning their yields and values to the
respective pruning treatments resulted in no differences between the total yield or value
of the control treatment, which involved normal harvesting of the same leaves that were
pruned.

If the potential yield of the tobacco crop is such that the yield lost by not
harvesting lower leaves can be tolerated, this practice is advantageous because the
average price per kilogram is enhanced. Total curing cost likely will be lower by not
having to handle the lowest yielding leaves. Yield and value loss must be tolerated, but
not harvesting lower leaves of flue-cured tobacco will likely result in a higher per
kilogram profit margin.

CHAPTER 4

LOWER LEAF HARVESTING: THE INFLUENCE OF TIME ON THE CHEMICAL AND MINERAL

CHARACTERISTICS OF FLUE-CURED TOBACCO LEAF POSITIONS.

Introduction

Lower leaf harvesting options of flue-cured tobacco (Nicotiana tabacum L) have
been recommended based on the total crop response to removal of lower leaves. Studies
by Suggs (1972), Currin and Pitner (1980), and Stocks (1988) found pruning and
discarding the lowest three or four leaves had no impact on the total yield or chemical
balance of tobacco leaves. Court and Hendel (1 989) reported yield reductions associated
with reduced leaf number harvested by either lower leaf pruning or topping to a lower
leaf number, but no effects on the leaf chemical components.

In tobacco production, the leaves to be harvested are in a constant state of flux as
they progress from young, very immature leaves to mature leaves which are ready for
harvest. Turgeon (1 989) stated that "leaves of dicotylendous plants stop importing and
begin to export photoassimilate when they are 30-60% fully expanded. Developing
leaves continue to import photoassimilate from source leaves for a period after they
have begun to export their own products of photosynthesis." Prior to the topping
process, a definitive source-sink relationship exists on the tobacco plant. There is an
apical meristem (sink) that may have terminated to an inflorescence, newly-unfolded
leaves (sink), leaves in a source-sink transition, and leaves that are mature or
maturing and are exclusively exporters of photosynthate. Hurng et al. (1 989)
concluded that removal of the reproductive sink (topping) caused the leaves of tobacco
plants to act as alternate sinks. Crafts-Brandner et al. ( 1 984) found that depodding (or
sink removal) of soybean (Glycine max L. Merr.) plants caused leaves and stems to act

66

67

as alternate sinks. After topping, based on changes in the area of the leaves at given LPs
over time (Chapter 2), only the leaves at the upper-most LP (19-21) probably would
be in the transition phase of source-sink development as described by Turgeon (1989).
All other leaves should be exclusive exporters of photoassimilate. After topping, the
leaves of a tobacco plant serve two purposes: 1) generation of substrates for dry matter
production via photosynthesis, and 2) storage organs for the products of photosynthesis
(starch) and other processes, i.e. nicotine synthesis of the roots.

Lower leaf harvesting options are essentially manipulations of the source and
sink leaves. If one chooses to not prune or harvest lower leaves, it is possible they may
act as sinks. If one chooses to prune the lower leaves, potential sinks are removed and
the remaining leaf area (sinks) remaining will be smaller. Normal harvesting of flue-
cured tobacco is essentially a leaf pruning procedure in that leaves are removed
methodically throughout the harvest season as they mature on the stalk.

Numerous studies have quantitified the effects of source-sink manipulations of
other plants. Removal of the grain sink of corn (Zea mays L.) caused increases in the
carbohydrate concentration of both upper and lower leaves (Allison and Weinmann,
1970). Soybean pod pruning increased leaf carbohydrate concentration (McAlister and
Krober, 1958; Kollmann et al., 1974; Ciha and Brun, 1978; Mondal et al., 1978;
Streeter and Jeffers, 1979; Crafts-Brandner et al., 1984), and also increased leaf N
and P concentrations (Kollman et al. 1974; Crafts-Brandner et al., 1984). Kollmann et
al. (1974) further reported that leaf Ca and K concentrations were decreased due to
depodding of soybean. Lawn and Brun (1974) found soybean depodding decreased net
photosynthesis, and that the photosynthetic decline was linked to an accumulation of
assimilates in the leaves that would have been translocated to the developing pods.
Depodding of soybean also delayed leaf senescence (Hicks and Pendleton, 1969; Mondal et
al., 1978; Crafts-Brandner et al., 1984). The effects of reproductive sink removal can
be summarized to include increased leaf carbohydrate levels with a subsequent decline in

68

net photosynthesis, increase in leaf N and P concentrations, decreases in leaf Ca and K
concentrations, and a delay in the onset of senescence.

Removal of more than 1 0% of the leaf area of wheat (Triticum aestivum L.) and
oat (Avena sativa L.) plants reduced grain yield (Womack and Thurman, 1962). Pauli
and Stickler (1961) found that increasing the percentage of leaves pruned from grain
sorghum (Sorghum bicolor L. Moench) plants decreased the total carbohydrate
concentration in the vegetative tissue and grain. Grain N concentration increased, but
vegetative tissue N concentration and the grain yield of sorghum were reduced as
defoliation increased (Stickler and Pauli, 1961). Weber (1955) and McAlister and
Krober (1958) found soybean seed yield and size decreased in response to increasing
defoliation. Grain yield reductions by defoliation were induced by a decline in the total
photosynthetic capacity of the plant caused by a reduction in leaf area.

Flue-cured tobacco is managed differently than most other agronomic crops in
that the leaves, and not the seed, are harvested. Also, leaves are removed as they mature
on the plant. Most source-sink manipulation studies have dealt with either the effects of
removal of the reproductive sink on leaf and seed characters or the influence of
defoliation on seed characters.

The objective of the present study was to evaluate the effects of pruning, not
pruning or harvesting, or harvesting normally, the lower three or six leaves on flue-
cured tobacco plants. The effects were evaluated on leaves harvested as they matured on
the stalk, or monitored over time to maturity. Because previous studies have not been
designed to examine effects relative to leaves at specific stalk positions, the present
study focused on changes by leaf position.

Materials and Methods

The location, cultivars, and management practices for the present study were
identical to those previously discussed in Chapter 2. The lower leaf harvesting
treatments used in the present study were the same as those previously described in

69

Chapter 3. Methods that differ from those discussed in Chapters 2 or 3 are described
below.

Two separate studies were included to evaluate the effects of lower leaf
harvesting options. A normal harvest study was conducted to evaluate the effects of
lower leaf harvesting options under typical management. A time after pruning and
topping study was designed to monitor temporal changes in leaves at a given LP to
determine when differences appeared.
Normal Harvest Study

Plots consisted of ten plants spaced 41 cm apart, planted in rows spaced 121 cm
apart. Four replications of lower leaf harvesting treatments and cultivars were
evaluated each year in a split-split-plot design. Cultivars were main plots, harvesting
options were sub-plots, and leaf positions were sub-sub-plots. A split-split-split-
plot design was used for statistical analysis with years being main plots, cultivars being
sub-plots, harvesting options being sub-sub-plots, and leaf positions being sub-sub-
sub-plots. Analysis of variance and single degree of freedom contrast procedures were
carried out by methods described by Gomez and Gomez (1984).

Eight cured leaves were subsampled for chemical or mineral analyses from
leaves at LPs 7-9, 13-15, and 19-21. These LPs were selected because they were
common to all treatments and inherently different in many characteristics. The midribs
were removed from the lamina. The lamina was ground using a Wiley mill with a 1 mm
screen. Total N, nicotine, and reducing sugar analyses were performed by R.J. Reynolds
Tobacco Company in Winston-Salem, NC, and Philip Morris Tobacco Company in
Richmond, VA. For Ca, Mg, K, and P analyses, samples were prepared by the ashing and
acid digestion method described by Walsh (1971). The resulting solutions were
analyzed by Inductively Coupled Argon Plasma (ICAP) in the University of Florida's
Institute of Food and Agricultural Science Extension Soil Testing Laboratory by methods
described by Hanlon and Devore (1989).

70

The leaf chemical and mineral data are reported for leaf lamina only. Midribs
were not evaluated, and previous work indicated that their chemical and mineral
constituents are different from those of the lamina (Darkis et al., 1952).
Time After Pruning Study

Plots consisted of two plants spaced 41 cm apart, planted in rows spaced 121 cm
apart (1 m2 of total area). Three replicates of cultivars and lower leaf harvesting
treatments were evaluated each year and were arranged in the field in a split-split-
split-plot design with cultivars being main plots, harvesting options being sub-plots,
leaf position being sub-sub-plots, and harvest dates being sub-sub-sub-plots. The 21
leaves were partitioned into seven, 3-leaf stalk positions for harvesting purposes.
Weekly harvests were taken of all 3-leaf stalk positions that remained on the stalk,
beginning one week after topping. A set of samples was taken at topping, when the
pruning treatments were imposed, to establish a baseline of the initial levels for the
components at all LPs. Because this study was designed to monitor LP changes over time,
LPs that were harvested in the normal harvest study were removed from all plants that
were to be used for future harvest date analysis. The progression of the LPs as they
were harvested is indicated in Table 4-1.

Because the lower leaf harvesting options resulted in reductions in the number of
leaves harvested either by pruning, or not pruning or harvesting of the lower leaves, all
LPs were not harvested for all treatments. When the lower three leaves were pruned
and discarded at topping or were otherwise not pruned or harvested, only LPs 4-6
through 19-21 were harvested. When the lower six leaves were pruned and discarded at
topping or were otherwise not pruned or harvested, only LPs 7-9 through 19-21 were
harvested. The control treatment (harvest all 21 leaves) resulted in harvesting of all
LPs. For the harvest dates from 21 to 49 days after pruning or topping, all treatments
had an equal number of LPs since LPs 7-9 through 19-21 were common to all
treatments.

71

Table 4-1 . The leaf positions removed per plant by harvest date in the days after
pruning and topping study.

g and topping
28 35

0

7

Udyb all

14

21

42

49

loaf

1 9-21

1 9-21

led 1

1 9-21

1 9-21

1 9-21 1 9-21

1 9-21

19-21x

16-18

16-18

16-18

16-18

16-18 16-18

1 6-1 8X

13-15

1 3-1 5

13-15

1 3-1 5

13-15 13-15x

10-12

10-12

10-12

10-12

1 0-1 2X

7 - 9

7 - 9

7 - 9

7-9x

4-6

4-6

4-6x

1 -3

1-3X

'Bold type indicates that leaf area, leaf mineral and chemical components, and
total non-structural carbohydrates (TNC) were measured on those leaf positions.
x Indicates leaf positions which were harvested normally on this date.

72

Each LP sample consisted of six leaves (2 plants X a 3-leaf position). All leaf
samples were cured in the normal flue-curing manner. After curing, the leaves were
rehydrated for handling purposes. The six leaves at each LP were used for leaf chemical
or mineral analyses. The midribs were removed and the lamina was ground to 1 mm
using a Wiley mill. Total N, nicotine, reducing sugar, Ca, Mg, K, and P analyses were
performed by the same methods described above.

Analysis of the entire data set was not possible due to lack of balance. With each
successive harvest date there was a loss of one LP that was harvested in the normal
harvest study (Table 4-1). As a result, each harvest date was analyzed individually.
Leaf position was an overwhelming factor across harvest dates. For analysis of the
influence of harvesting effects at LP over time, each LP was analyzed for each harvest
date. The statistical design used then was a split-split-plot design with years being
main plots, cultivars being sub-plots, and harvesting options being sub-sub-plots.
Analysis of variance and single degree of freedom contrasts procedures were carried out
by methods described by Gomez and Gomez (1984).
Lower Leaf Harvesting Options Statistical Comparisons

Single-degree of freedom contrasts were chosen to determine differences between
harvesting schemes. With contrasts the possible comparisons are limited to the number
of degrees of freedom for the effect analyzed. There were a total of five harvesting
treatments, so there were four possible contrasts. The comparisons chosen were derived
from a desire to determine combined and individual effects of the harvesting schemes. To
determine the effects of pruning lower leaves versus not pruning and not harvesting
lower leaves, a comparison was made between the combined effects of pruning the lower
three and six leaves and the combined effects of not pruning and not harvesting the lower
three and six leaves. This contrast was designated "prune vs no prune". There were few
effects associated with the lower three leaf harvesting options, but strong effects
associated with the lower six leaf harvesting options. Consequently, a comparison was

73

made between pruning of the lower six leaves and not pruning or harvesting the lower
six leaves. This contrast was designated "prune 6 vs no prune 6". The harvest all leaves
treatment was considered the control. To evaluate deviations from the norm of the lower
leaf harvesting regimes, comparisons were made between the control versus the
combined pruning treatments, designated "harv all vs prune", and the control versus the
combined not pruning and not harvesting lower leaves treatments, designated "harv all

vs no prune".

Results and Discussion

Leaf Chemical Characters

Nicotine concentration was lower in the leaves that comprised 13-15 due to not

pruning or harvesting the lower six leaves in the normal harvest study (Table 4-2).

Suggs (1972) found higher nicotine concentrations when nine lower leaves were

pruned, but no differences when six or less leaves were pruned. Currin and Pitner

(1980), Stocks (1988), and Court and Hendel (1989) reported no differences in

nicotine concentration due to lower leaf pruning. Over time, nicotine concentrations in

leaves at LPs 7-9, 13-15, and 19-21 were lower as a result of not pruning or

harvesting the lower leaves (Fig. 4-1 & Table 4-3, Fig. 4-2 & Table 4-4, Fig. 4-3 &

Table 4-5). Nicotine concentration for the control was not different from that of the

pruning treatments in the normal harvest study. This result was also observed over

time, however, over the first 14 days after pruning the nicotine concentrations at all

LPs were similar to those at the LPs in the no pruning treatments. Leaves were

discarded from the pruning treatments at topping. Normal harvesting is technically a

pruning process, but since only three leaves were removed per harvest, all lower six

leaves of the control treatment had not been harvested until 14 days after the pruning

treatments were imposed. Nicotine concentrations under normal harvesting were

similar to the no pruning treatments initially, but as more leaves were harvested from

the control treatment the nicotine concentration approached that observed in the pruning

74

Table 4-2. The effects of lower leaf harvesting options on nicotine concentration of
flue-cured tobacco by leaf position (normal harvest study).

Lower Leaf

leaf position
13 - 15

Harv. Options

7 - 9

19-21

concentration (g

kg-1)

Harv all 21 leaves

12.5

15.8

22.0

Prune low 3 leaves

12.7

15.6

20.8

No prune low 3 leaves

12.9

15.9

21.7

Prune low 6 leaves

12.6

15.4

20.5

No prune low 6 leaves

11.4

13.2

19.6

Prune Treats mean

12.7

15.5

20.7

No Prune Treats mean

12.1

14.6

20.7

COmRASTS

P > F

Prune vs No Prune

0.376

0.142

0.989

Prune 6 vs No Prune 6

0.125

0.019

0.473

Harv all vs Prune

0.858

0.641

0.226

Harv all vs No Prune

0.585

0.098

0.222

CV (%) (reps = 4)

17.3

16.9

16.5

75

15

B 14-

c
o

CO

E H
1

O

O
|

8

cc

c

E

CO

12-

11

10

..vC-nnn"""^

Harvest All Leaves

O — Prune Low 6 Leaves

- - - O" " No Prune Low 6 Leaves
— A * " Pruning Treatments Mean
— ^r- - No Paining Treatments Mean

1 1 I

7 14 21

Days After Pruning and Topping

Fig. 4-1. Influence of lower leaf harvesting options on the lamina nicotine

concentration of flue-cured tobacco leaf position 7-9. Appropriate contrasts are
given below.

Table 4-3. Single degree of freedom contrasts for the data presented in Fig. 4-1.

days

after
1 4

pruning

7

21

CONTRASTS

P

>

F

Prune vs No Prune

0.084

0.009

0.042

Prune 6 vs No Prune 6

0.187

0.034

0.012

Harv all vs Prune

0.711

0.002

0.244

Harv all vs No Prune

0.077

0.284

0.006

CV (%) (reps = 3)

17.3

13.6

13.2

76

D)

g

o

o
O

a)

c

o
o

03

c

E
ra

Days After Pruning and Topping

Fig. 4-2. Influence of lower leaf harvesting options on the lamina nicotine

concentration of flue-cured tobacco leaf position 13-15. Appropriate contrasts
are given below.

Table 4-4. Single degree of freedom contrasts for the data presented in Fig. 4-2.

days after pruning
14 21 28

35

CONTT-iASTS

Prune vs No Prune 0.191 0.001 0.006

Prune 6 vs No Prune 6 0.583 0.048 0.018

Harv all vs Prune 0.522 0.002 0.118

Harv all vs No Prune 0.092 0.926 0.001

CV (%) (reps = 3) 21.9 15.1 16.6

0.005

0.219

0.005

0.679

0.855

0.084

0.028

0.008

21.0

22.2

77

22.5-

I

S 20.0-

c
o

I 17.5-

| 150

2

8 125

CO

.E 10.0

E

3

7.5-

5.0

Harvest All Leaves
#■■•• Prune Low 6 Leaves

- - - O" ' No Prune Low 6 Leaves
-•-A'" Pruning Treatments Mean

- "A" " No Pruning Treatments Mean

—r
7

— r-
14

— t-
21

- r-
28

35 42

Days After Pruning and Topping

49

Fig. 4-3. Influence of lower leaf harvesting options on the lamina nicotine

concentration of flue-cured tobacco leaf position 19-21. Appropriate contrasts
are given below.

Table 4-5. Single degree of freedom contrasts for the data presented in Fig. 4-3.

days after pruning

14 21 28 35 42

49

CONTTRASTS

Prune vs No Prune 0.035 0.001 0.007 0.004 0.171 0.019 0.009

Prune 6 vs No Prune 6 0.199 0.031 0.013 0.002 0.496 0.009 0.004

Harv all vs Prune 0.710 0.020 0.461 0.856 0.241 0.345 0.197

Harv all vs No Prune 0.203 0.525 0.004 0.100 0.026 0.006 0.001

CV(%) Reps = 3 28.8 18.6 19.8 22.8 24.8 19.4 12.5

78

treatments. Nicotine is synthesized in the roots and translocated to the shoot where it
accumulates predominantly in the leaf (Wolf and Bates, 1964). Based on the nicotine
concentration data over time, it seems likely that the lower leaves that remained on the
plants acted as sinks for nicotine.

Nitrogen concentration was not affected by lower leaf harvesting. This response
was surprising since the concentration of nicotine, a N-containing compound, was
decreased by not removing lower leaves. Leaf N concentration was found to increase in
response to reproductive sink removal in soybean (Glycine max L Merr.) (Kollman et
al., 1974; Crafts-Brandner et al., 1984). The N concentration of composited leaf and
stem tissue decreased as a result of leaf removal of grain sorghum (Sorghum bicolor L.
Moench) (Pauli and Stickler, 1961). However, delayed topping of flue-cured tobacco
decreased the nicotine concentration in leaves with no affect on the N concentration
(Woltz, 1955; Marshall and Seltmann, 1964; Elliot, 1966).

In the normal harvest study, the N to nicotine concentration ratio (N:Nic) at LP
13-15 was higher as a result of not pruning the lowest six leaves (Table 4-6). The
N:Nic at LPs 13-15 and 19-21 were also higher for the no pruning treatments over
time (Fig. 4-4 & Table 4-7, Fig. 4-5 & Table 4-8). The responses for N:Nic largely
paralleled those observed for nicotine concentration. Since N concentration was not
affected by pruning or not pruning lower leaves, the changes in the N:Nic were due
primarily to changes in the nicotine concentration. Tso (1972) reported that an N:Nic
approximating 1 :1 was desirable for the best smoking quality of flue-cured tobacco
leaves. While small differences in N:Nic were found among treatments and the N:Nic was
always higher than 1:1, it is questionable whether the smoking quality would differ
significantly among any of the imposed treatments. Weybrew et al. (1984) found that
smoker preference, being a qualitative variable, and quantitative chemical measures
were not always closely correlated.

Table 4-6. Effects of lower leaf harvesting options on the N to nicotine concentration
ratio of flue-cured tobacco by leaf position (normal harvest study).

Lower Leaf leaf position

Harv. Options 7 - 9 13 - 15 19-21

N to nicotine concentration ratio ---

Harv all 21 leaves 1.29 1.14 1.10

Prune low 3 leaves 1.27 1.17 1.10

No prune low 3 leaves 1 .27 1.16 1-09

Prune low 6 leaves 1.25 1.16 1.10

No prune low 6 leaves 1.34 1.29 1.15

Prune Treats mean

1.26

1.17

1.10

No Prune Treats mean

1.31

1.23

1.12

CONTRASTS
Prune vs No Prune

0.246

P > F
0.120

0.555

Prune 6 vs No Prune 6

0.094

0.016

0.332

Harv all vs Prune

0.563

0.515

0.967

Harv all vs No Prune

0.708

0.057

0.659

CV (%) (reps = 4)

11.5

11.7

13.1

79

80

■B 3.00

CO

rr

o

|

c 2.50

8

c
o
O

CD

z

O

cc

c

3

1.50

1.00

— Q— Harvest All Leaves

— f .... Paine Low 6 Leaves

• - O" " No Prune Low 6 Leaves

• - A " " Pruning Treat ments Mean

■ -W - No Pruning Treatments Mean

14

— I-
21

28

35

Days After Pruning and Topping

Fig. 4-4. Influence of lower leaf harvesting options on lamina N to nicotine

concentration ratio of flue-cured tobacco leaf position 13-15. Appropriate
contrasts are given below.

Table 4-7. Single degree of freedom contrasts for the data presented in Fig. 4-4.

days after pruning
14 21 28

35

CONTRASTS

Prune vs No Prune 0.464

Prune 6 vs No Prune 6 0.802

Harv all vs Prune

0.983

Harv all vs No Prune 0.563

CV (%) (reps = 3) 27.7

0.007

0.045

0.001

0.148

0.097

0.132

0.006

0.524

0.065

0.589

0.547

0.138

0.652

0.256

0.029

0.015

16.9

15.4

10.8

9.7

81

o

03

cr

c
o

g

a;

m

c

o

E
5

6.0-

Days After Pruning and Topping

Fig. 4-5. Influence of lower leaf harvesting options on lamina N to nicotine

concentration ratio of flue-cured tobacco leaf position 19-21. Appropriate
contrasts are given below.

Table 4-8. Single degree of freedom contrasts for the data presented in Fig. 4-5.

days after pruning

14 21 28 35 42

49

CONTFIASTS

Prune vs No Prune 0.049 0.002 0.002 0.003 0.038 0.002 0.017

Prune 6 vs No Prune 6 0.543 0.039 0.030 0.003 0.891 0.001 0.023

Harv all vs Prune 0.045 0.061 0.962 0.463 0.507 0.816 0.913

Harv all vs No Prune 0.013 0.390 0.009 0.065 0.021 0.016 0.038

CV(%) Reps = 3 54.5 21.2 17.1 18.8 13.2 9.8 9.6

82

The reducing sugar concentration of leaves from LP 7-9 were higher when lower
leaves were not pruned or harvested, both over time and in the normal harvest study
(Table 4-9, Fig. 4-6 & Table 4-10). Higher leaf carbohydrate levels resulted when
reproductive sinks were removed from soybean and corn (McAlister and Krober, 1958;
Allison and Weinmann, 1970; Kollmann et al., 1974; Ciha and Brun, 1978; Mondal et
al., 1978; Streeter and Jeffers, 1979; Crafts-Brandner et al.,1984). Pauli and
Stickler (1961) reported lower plant tissue carbohydrate concentration in grain
sorghum resulted from defoliation. Total non-structural carbohydrate (TNC)
concentration at LP 7-9 was not affected by harvesting treatments. Intuitively, a higher
reducing sugar concentration should be the result of a higher TNC concentration. As
discussed in Chapter 2, the reducing sugar concentration changed proportionally with
the TNC concentration at LPs 13-15 and 19-21, however, reducing sugar concentration
did not change proportionally with TNC concentration at LP 7-9.

The reducing sugar to nicotine concentration ratio (Sug:Nic) was higher at LP 7-
9 and LP 13-15 from the normal harvest study in response to not pruning or discarding
lower leaves (Table 4-11). The Sug:Nic of the leaves from LP 7-9 was higher because
of a combination of higher sugar concentration and lower nicotine concentration when the
lower leaves were not pruned or harvested. However, a higher Sug:Nic at LP 13-15
solely resulted from a higher nicotine concentration. Over time, the Sug:Nic of leaves
within LPs 7-9, 13-15, and 19-21 varied due to the effects of either pruning, not
pruning or harvesting, or harvesting the lower leaves in the normal manner (Fig. 4-7
& Table 4-12, Fig. 4-8 & Table 4-13, Fig. 4-9 & Table 4-14).
Mineral Characteristics

Phosphorus was the only mineral whose concentration was responsive to the
harvesting treatments. In the normal harvest study, the P concentrations in leaves from
LPs 7-9 and 13-15 were lower as a result of not pruning or harvesting the lower

83

Table 4-9. Effects of lower leaf harvesting options on the reducing sugar concentration
of flue-cured tobacco by leaf position (normal harvest study).

f position
13 - 15

Harv. Options

7 - 9

19-21

Ding sugar

concentration

(9 kg1)

Harv all 21 leaves

234.5

210.6

148.3

Prune low 3 leaves
No prune low 3 leaves

232.3
241.8

217.8
214.0

143.9
147.7

Prune low 6 leaves

231.9

217.6

141.9

No prune low 6 leaves

255.0

224.0

151.3

Prune Treats mean

232.1

217.7

142.9

No Prune Treats mean

248.4

219.0

149.5

CONTTFiASTS

P

> F

Prune vs No Prune

0.006

0.791

0.206

Prune 6 vs No Prune 6

0.006

0.361

0.205

Harv all vs Prune

0.728

0.248

0.399

Harv all vs No Prune

0.052

0.172

0.847

CV (%) (reps = 4)

9.5

9.1

14.0

84

-. 250

o>

o

CO

fc-

c

<x>

o

c

o

o

CO

3

CO

o

3

0>

tr

CO

*E

CO

_l

240

230

220-

210-

200 -

190-

180

Harvest All Leaves
Paine Low 6 Leaves
No Prune Low 6 Leaves
-• -A " " Pruning Treatments Mean

A" ~ No Pruning Treatments Mean

1

14

— I-
21

Days After Pruning and Topping

Fig. 4-6. Influence of lower leaf harvesting options on reducing sugar concentration of
flue-cured tobacco leaf position 7-9. Appropriate contrasts are given below.

Table 4-10. Single degree of freedom contrasts for the data presented in Fig. 4-6.

days

after
14

pruning

7

21

rY^nTJAQTQ

p

>

p

L<*_fl\ I rwo io —

Prune vs No Prune

0.104

0.057

0.025

Prune 6 vs No Prune 6

0.259

0.234

0.032

Harv all vs Prune

0.543

0.274

0.225

Harv all vs No Prune

0.457

0.623

0.004

CV (%) (reps = 3)

19.4

17.9

14.4

85

Table 4-1 1 . Effects of lower leaf harvesting options on the reducing sugar to nicotine
concentration ratio of flue-cured tobacco by leaf position (normal harvest
study).

Lower Leaf leaf position

Harv. Options 7 - 9 13 - 15 19 - 21

reducing sugar to nicotine concentration ratio

Harv all 21 leaves 19.3 14.2 7.0

Prune low 3 leaves 19.0 14.8 7.3

No prune low 3 leaves 20.0 14.3 7.2

Prune low 6 leaves 19.8 15.0 7 1

No prune low 6 leaves 23.3 17.9 8.2

Prune Treats mean

19.4

14.9

7.2

No Prune Treats mean

21.7

16.1

7.7

CONTRASTS

P > F

Prune vs No Prune

0.060

0.138

0.342

Prune 6 vs No Prune 6

0.041

0.011

0.134

Harv all vs Prune

0.961

0.495

0.812

Harv all vs No Prune

0.111

0.061

0.311

CV (%) (reps = 4)

23.2

20.8

27.0

86

7 14 21

Days After Pruning and Topping

Fig. 4-7. Influence of lower leaf harvesting options on reducing sugar to nicotine
concentration ratio of flue-cured tobacco leaf position 7-9. Appropriate
contrasts are given below.

Table 4-12. Single degree of freedom contrasts for the data presented in Fig. 4-7.

days

after pruning
14

7

21

CONTRASTS

P

>

F

Prune vs No Prune

0.101

0.007

0.033

Prune 6 vs No Prune 6

0.208

0.055

0.016

Harv all vs Prune

0.517

0.040

0.081

Harv all vs No Prune

0.474

0.837

0.001

CV (%) (reps = 3)

31.4

26.4

24.5

87

26

CO

CC

c
g

CO

24 -

— O — Harvest All Leaves

•"■# — Prune Low 6 Leaves

• • O" ' No Prune Low 6 Leaves

• -A " " Pruning Treatments Mean

• -A- - No Prune Treatments Mean

14 21 28

Days After Pruning and Topping

35

Fig. 4-8. Influence of lower leaf harvesting options on reducing sugar to nicotine
concentration ratio of flue-cured tobacco leaf position 13-15. Appropriate
contrasts are given below.

Table 4-13. Single degree of freedom contrasts for the data presented in Fig. 4-8.

after
21

pri

7

14

28

35

CONTFIASTS

P >

F

Prune vs No Prune

0.187

0.009

0.001

0.007

0.067

Prune 6 vs No Prune 6

0.186

0.131

0.011

0.004

0.572

Harv all vs Prune

0.596

0.070

0.081

0.516

0.711

Harv all vs No Prune

0.575

0.692

0.001

0.103

0.064

CV (%) (reps = 3)

35.7

27.2

22.8

24.8

22.1

88

o

2 co

CO
O) c

3 O

fl

O CD

-2 9

CD o
OC O
JO Q,

SI

18

16-

14-

12-

10-

8-

6-

Harvesl All Leaves
Prune Low 6 Leaves
No Prune Low 6 Leaves
- ■ "A • " Pruning Treatments Mean
— A" ~ No Pruning Treatments Mean

+

0

— J-
14

— |-
21

28

35

— r-
42

— |—
49

Days After Pruning and Topping

Fig. 4-9. Influence of lower leaf harvesting options on reducing sugar to nicotine
concentration ratio of flue-cured tobacco leaf position 1 9-21 . Appropriate
contrasts are given below.

Table 4-14. Single degree of freedom contrasts for the data presented in Fig. 4-9.

days after pruning —

14 21 28 35 42

49

CONTT-1ASTS

Prune vs No Prune 0.032 0.038 0.010 0.021 0.124 0.004 0.001

Prune 6 vs No Prune 6 0.105 0.277 0.005 0.010 0.212 0.001 0.001

Harv all vs Prune 0.254 0.349 0.444 0.290 0.890 0.628 0.182

Harv all vs No Prune 0.655 0.420 0.005 0.374 0.259 0.005 0.001

CV(%) Reps = 3 54.0 38.3 32.2 33.7 28.7 26.4 18.8

89

leaves (Table 4-15). Differences in the P concentrations at LPs 7-9 and 13-15 due to
not removing lower leaves were also found over time (Fig. 4-10 & Table 4-16, Fig. 4-
11 & Table 4-17). Soybean pod pruning increased P concentration in the leaves
(Kollman et al., 1974; Crafts-Brandner et al., 1984). Whereas soybean depodding
involves removal of a strong sink for P, the P concentrations of leaves likely differed in
the present study because the lower leaves that were not pruned or harvested acted as a

sink for P.

Conclusions

The quality of the cured leaf is affected by the ratios of the chemical components
of the leaf. If the chemical characteristics of the control (harvest all leaves) treatment
were used as standards, some generalizations can be made about the effects of the lower
leaf harvesting. The leaf chemical balance of the lower leaf pruning treatments more
closely approximated that of the control. When lower leaves were left on the plant,
nicotine dilution in the remaining leaves was the most obvious response. The lower
nicotine concentration resulted in higher than normal N to nicotine and reducing sugar to
nicotine concentration ratios. Phosphorous concentration of leaves from LPs 7-9 and
13-15 were lowered in response to not pruning or harvesting the lower leaves. The
concentration of other minerals were not affected by lower leaf harvesting.

Interesting responses occurred as a result of pruning, not pruning, or normal
harvesting, of lower leaves over time. Over the first 14 days after pruning, the
chemical and mineral characteristics were similar for the leaves above those which
were either not pruned or were harvested normally. However, as normal harvesting of
lower leaves progressed, the chemical and mineral characteristics of leaves above those
normally harvested approached those observed for the same leaves when lower leaves
were pruned and discarded.

90

Table 4-15. Effects of lower leaf harvesting options on the P concentration of flue-
cured tobacco by leaf position (normal harvest study).

Lower Leaf leaf position

Harv. Options 7 - 9 13 - 15 19-21

P concentration (g kg1)

Harv all 21 leaves 3.23 3.05 3.32

Prune low 3 leaves 3.31 3.12 3.17

No prune low 3 leaves 3.28 2.96 3.18

Prune low 6 leaves 3.43 3.03 3.10

No prune low 6 leaves 3.05 2.81 3.42

Prune Treats mean 3.37 3.08 3.14

No Prune Treats mean 3.14 2.87 3.33

f"Y"MTn/LQTQ

P > F

V^CIN I rv\o I o —

Prune vs No Prune

0.009

0.011

0.203

Prune 6 vs No Prune 6

0.001

0.032

0.078

Harv all vs Prune

0.133

0.752

0.220

Harv all vs No Prune

0.482

0.070

0.852

CV (%) (reps = 4)

9.1

9.7

15.5

co

c

E

3.6

3.4-

3

e
o

| 3.2

5
o
c
o
O

3.0-

2.8-

2.6

— O"
--A-

Harvest All Leaves
Prune Low 6 Leaves
No Prune Low 6 Leaves
Pruning Treatments Mean
No Pruning Treatments Mean

7 14 21

Days After Pruning and Topping

Fig. 4-10. Influence of lower leaf harvesting options on the P concentration of flue-
cured tobacco leaf position 7-9. Appropriate contrasts are given below.

91

Table 4-16. Single degree of freedom contrasts for the data presented in Fig. 4-10.

days

after
14

pruning

7

21

COMTFIASTS

P

>

F

Prune vs No Prune

0.601

0.079

0.242

Prune 6 vs No Prune 6

0.293

0.289

0.589

Harv all vs Prune

0.999

0.552

0.162

Harv all vs No Prune

0.669

0.045

0.022

CV (%) (reps = 3)

13.4

18.7

12.4

3.2

2.4

o>

JC

O)

3.0-

c

•s

o

■•— •

■

CO

i=

^x"

c

CD

O

2.8-

O

o

Q.

■

A.

«

c

E

CO

2.6-

Or"

Harvest All Leaves
Prune Low 6 Leaves
No Prune Low 6 Leaves
Pruning Treatments Mean
No Pruning Treatments Mean

X?

-o-/..

/y -m

ff , i '"* /A

/-.-.+ —

r/

o.

-*;%

^

/:
//

*«.

/s

"6

14 21 28

Days After Pruning and Topping

35

Fig. 4-11. Influence of lower leaf harvesting options on the P concentration of flue-
cured tobacco leaf position 13-15. Appropriate contrasts are given below.

92

Table 4-17. Single degree of contrasts for the data presented in Fig. 4-11.

days after pruning
14 21 28

35

CONTRASTS

Prune vs No Prune 0.047 0.045 0.092

Prune 6 vs No Prune 6 0.009 0.284 0.104

Harv all vs Prune 0.999 0.130 0.357

Harv all vs No Prune 0.101 0.883 0.025

CV (%) (reps = 3) 10.7 11.9 13.5

0.005

0.278

0.024

0.743

0.890

0.403

0.014

0.090

12.7

14.7

CHAPTER 5
SUMMARY AND CONCLUSIONS

The effects of five lower leaf harvesting treatments involving the lowest three or
six leaves on flue-cured tobacco (Nicotiana tabacum L) plants were evaluated in 1 989
and 1 990. Previous work had suggested there were positive effects on yield and value
associated with pruning and discarding lower leaves and negative effects on yield when
the same lower leaves were not pruned or harvested. The lower leaf harvesting
treatments were evaluated in situ on plants having exactly 2 1 leaves. Inherent
differences in the yield, chemical, and mineral properties of tobacco leaves in relation to
the position or node on the stalk at which leaves are formed have been reported. The 21
leaves were partitioned into seven, 3-leaf positions (LP) for harvesting purposes.
Controlling leaf number per plant and acquiring a given number of leaves per harvest
enabled a strict evaluation of the effects that lower leaf harvesting methods had on the
leaves above those involved in the treatments.

The characteristics of the leaves comprising a given LP were monitored under
two harvesting regimes. One harvesting regime involved harvesting leaves at a single LP
as they matured on the plant. This regime was termed normal harvest because it was
similar to the farmer's production practices. The other harvesting regime involved
weekly harvests of all LPs remaining on plants coinciding with the treatments in the
normal harvest study. This regime was termed whole plant harvesting because the
leaves within a given LP were monitored over the duration that each LP remained on the
plant, i.e. up to full maturity and normal harvesting. The whole plant harvesting regime
allowed any treatment effects observed at a given LP under normal harvesting to be
monitored over time, i.e. as leaves at an LP developed.

93

94

Data are lacking that describe the agronomic, chemical, and mineral properties
of currently-grown flue-cured tobacco cultivars by LP. The control treatment and the
two treatments involving pruning or not harvesting the lowest three leaves did not
result in significant effects for any parameters examined. Consequently, data from those
three treatments were used to provide information on the agronomic, chemical, and
mineral characteristics of flue-cured tobacco leaves harvested when the leaves were
mature (normal harvesting) or over time after topping to monitor changes with leaf
development.
Characterization of Flue-Cured Tobacco Leaves

There were inherent differences in the agronomic, chemical, and mineral
characteristics of the tobacco leaves based on the position or nodes on the stalk at which
leaves were formed. Yield, value, and nicotine and N concentrations increased with
higher leaves. The reducing sugar concentration and the concentration ratios of N to
nicotine and reducing sugar to nicotine were highest in the middle leaves. The Ca, Mg,
and K concentrations were highest in the lowest leaves and generally decreased to the
highest leaves. Phosphorous concentration was similar for all leaves.

Tobacco companies depend on the differences in the characteristics of tobacco
leaves to manufacture their products. The fact that leaf chemical components were
different depending upon the position on the stalk at which leaves were formed would
discourage large harvests which mix different leaf groups.

At topping, there were distinct differences in the agronomic, chemical, and
mineral characteristics of leaves dependent upon the position on the stalk. These
differences were the result of leaf age. Over time after topping, the agronomic,
chemical, and mineral properties of the youngest leaves changed the most. The lowest
nine leaves were near maturity at topping and few changes in their agronomic, chemical,
or mineral characteristics occurred from topping to final harvest. The characteristics

95

of the upper 1 2 leaves changed signifcantly over time. The changes depended upon the
age of the leaves with more extreme changes with younger leaves.
Lower Leaf Harvesting

Pruning and discarding the lower three or six leaves was no more advantageous
than not pruning or harvesting the same leaves because yields and values for the
respective treatments were equal. In short, the remaining leaves in the present study
did not compensate for the loss of the dry matter by pruning. Yields and values were
lower for treatments that involved not harvesting lower leaves than those observed for
the control treatment. This yield and value loss was associated with a reduction in the
total number of leaves harvested from 21 to 1 8 to 1 5. However, not harvesting three or
more lower leaves increased the average value per kilogram, cured weight yield, and
specific cured leaf weight. More cured leaf resulted from less fresh weight coupled with
a higher average price. The implications of this result are that the tobacco crop may be
cheaper to handle and cure per unit, and would likely result in a higher profit per unit.

In the present study, the pruned lower leaves were handled as normal harvests to
evaluate what their potential contribution would have been to the respective treatments.
The addition of the yields and values of these pruned leaves to their respective
treatments resulted in there being no differences for any agronomic parameters between
the pruning treatments with 21 total leaves and the control treatment which also had 21
total leaves.

Nicotine and P concentrations were lower in the leaves above those that were not
pruned or harvested, however, N concentration was not affected by lower leaf
harvesting. Reducing sugar concentration was lower in the leaves comprising LP 7-9
only. The lower nicotine concentration associated with not removing lower leaves caused
differences in the N to nicotine and nicotine to reducing sugar concentration ratios.

For the first 1 4 days after pruning, the leaf chemical concentrations were
similar for treatments involving normal harvesting of lower leaves and not harvesting

96

lower leaves. However, as normal harvesting progressively removed lower leaves, the
chemical characteristics of leaves under normal harvesting were similar to leaves from
treatments that involved pruning of lower leaves. Leaves were pruned at topping, and
normal harvest of the lowest three leaves was not initiated until seven days after
topping. Consequently, the lowest six leaves were not completely removed from the
control plants until 14 days after topping. Pruning lower leaves allowed chemical
compounds to accumulate in less leaf area resulting in the higher chemical
concentrations initially. But, over time as leaves were harvested from control plants,
equal leaf numbers per plant were attained for both the pruning treatments and the
control resulting in the control treatment accumulating chemical compounds in less leaf
area as well. However, the no pruning treatments always had the lower leaves on the
plants and those leaves likely acted as sinks for nicotine and P.

In summary, lower leaf pruning did not result in equal yields to a control. Some
previous work on this subject indicated that pruning lower leaves was advantageous
because yields were not reduced. In those studies, leaf number per plant was not
explicitly controlled, i.e. leaf numbers were not actually counted. The assumption that
topping to an equivalent height will result in an equivalent leaf number can be
erroneous. (There are no published data on this claim, but from the author's experience
with this and other studies that involve topping to a given leaf number, plant heights at a
given leaf number vary greatly.) If topping height is used as a point of reference for
leaf number, and more leaves than planned remain, equivalent yields due to the
treatment could be inferred when actually leaf number was the compensating factor.

At topping, the lowest leaves that were pruned had reached maturity. Given that
the lowest leaves are mature at topping, pruning those leaves should not cause an
increase in the yield of the leaves above those pruned. In the present study, yield lost
due to pruning was not compensated for by increased weights of the remaining leaves.
Neither did not pruning or harvesting lower leaves affect yield of remaining leaves.

97

However, the average value per kilogram was enhanced by not harvesting three or more
lower leaves because these leaves were the lowest in value. The average cured weight
yield and specific cured leaf weight were improved by not harvesting lower leaves as
well because the lower leaves were the thinnest and likely had the highest water
percentage of any leaves.

The bottom line on not harvesting lower leaves is that yield will be lost unless
additional leaves are added by topping to a higher leaf number. Based on the yield data
from each LP, one extra leaf at the top of the plant would likely compensate for the yield
lost by pruning or otherwise not harvesting the lowest three leaves. If the potential
yield of the tobacco crop is such that the yield loss by not harvesting lower leaves can be
tolerated, this practice is advantageous because the average price per kilogram is
enhanced. Total curing cost likely would be lower by not having to handle the lowest
yielding leaves. Yield and value loss must be tolerated, but not harvesting lower leaves
of flue-cured tobacco will likely result in a higher per kilogram profit margin.
Suggestions for Further Study

The LP data re-enforced the suggestion that future studies with flue-cured
tobacco should report data by LP because of the inherent differences that existed between
leaf characteristics due to the position on the stalk of a given group of leaves.

Some leaf chemical and mineral parameters were influenced by lower leaf
harvesting options. Those differences were inferred to be a result of the lower leaves
being left on the plant and not harvested causing dilution of nicotine and P. However, the
lower leaves from the treatments that involved not pruning and not harvesting were not
actually sampled, consequently the dilution theory is only a suggestion. If those leaves
had been sampled over time, the suggestion that they were accumulating nicotine and P to
the detriment of higher leaves could have been confirmed. Not removing the lower leaves
revealed an interesting observation. When the lower leaves that were not pruned or
harvested were again exposed to full solar radiation by removing all the leaves above

them, they became greener and survived on the plant much longer than the same leaves
which were shaded by higher leaves.

Although treatment differences were not found for total non-structural
carbohydrate (TNC) concentration, this parameter proved to be a most interesting part
of this study. The extremely high levels of TNC found in tobacco leaves were
unprecedented in the literature for leaves of other crop species. The actual TNC for
tobacco leaves has been reported sparingly in other studies. The measurement of TNC
may prove to be a useful variable for describing many basic and applied phenomena in
tobacco research.

98

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BIOGRAPHICAL SKETCH

Glenn Ralph Stocks, born December 23, 1963, was the first of three children
for Guyland and Carolyn Stocks of Battleboro, North Carolina. His father was a farmer of
tobacco, peanuts, cotton, com, soybeans, and a small herd of beef cattle. His mother was
an elementary school teacher.

Being the eldest of the three siblings, Glenn was exposed to the real world of
farming at an early age. As a fourth grader, at the age of 9, Glenn was excused from
school to assist in the harvesting of the 200 acre peanut crop. As the years went by, the
responsibilities on the farm increased.

In 1 975, after a successful cotton crop, the Stocks's purchased a farm in Halifax
County, about 7 miles northwest of Enfield, North Carolina. Having been renters of farm
land previously, the family moved to their own farm in 1 977 and began a new life of
independent farming. Of course, land still had to be leased, but now they had a homestead.

At the previous farming location, peanuts and cotton were king. The leased farm
had been a 600 acre (cleared land) plantation owned by the great grandson of General
Matt W. Ransom of the Civil War era. However, at the new homestead, leaseable acreage
was hard to come by.

Because of the difficulty in renting acreage, a high value crop, tobacco, was
planted. The newly purchased farm had about five acres of tobacco quota so more tobacco
poundage had to be leased. In 1 978, 20 acres of tobacco were grown. Now 1 4 years old,
Glenn served as his father's right hand man in the farming operation. Having ridden a
tractor with his dad since the age of 2, farming was in the boy's blood.

During the years from 1 978 to 1 982, Glenn learned much about farming. Over
this period, his dad grew about 30 acres of tobacco, 40 acres of peanut, and 30 to 40

104

105

acres each of corn and soybeans each year. Also, during this period, Glenn attended
Enfield Academy for his high school education. At Enfield Academy, he was a varsity
athlete in baseball, football, and basketball.

After graduation from Enfield Academy in 1 982, Glenn enrolled in the agronomy
undergraduate program at North Carolina State University in Raleigh. The initial
intention was to get an education in agriculture and return to the farm; however, over
the four years of undergraduate study, it became all too clear that farming was not going
to be a viable option.

In 1 984, Glenn worked as an R.J. Reynolds research apprentice, under the
direction of Dr. D.T. Bowman, the director of the North Carolina Variety Testing program
for tobacco, corn, soybeans, and small grains. It was during this program that Glenn
developed a great appreciation for agricultural research and extension.

Prior to receipt of his bachelor's degree, Glenn accepted an offer to pursue a
Master of Science degree under the direction of Dr. E.B. Whitty at the University of
Florida in Gainesville. On May 1 0, 1 986, Glenn graduated from N.C. State. On May 1 2,
1 986, he moved to Florida, and on May 1 5 he was in the tobacco research field
preparing for his thesis work.

During his master's program, Glenn was undecided on what route he would take
upon completion of that degree. During the M.S. program, Glenn learned a great deal
about research and extension under Dr. Whitty' s direction. Nearing the end of his
master's program, Glenn realized that if he could not farm, the best way he could help
farmers was to get a doctorate degree and hopefully be involved in a research and/or
extension program helping to assist farmers with their problems.

In January, 1 988, Glenn initiated a Ph.D. program again under the direction of
Dr. E.B. Whitty. Glenn wanted to study whole plant physiology as his major focus.
Ideally, he would like to be a general agronomist, rather than focus on one aspect of plant
physiology. The supervisory committee chosen was broad based, further emphasizing

106

the desire for diversification. The research project chosen was ambitious, but it had to
be this way for the successful transition from master's student to capable Ph.D.

Now, as Glenn nears completion of the Doctor of Philosophy degree, he feels ready
and able to go out into the world of agriculture research and extension. He realized a few
years ago that he could not be directly involved in production agriculture; however, if
upon receipt of the Ph.D. degree he can be employed in a position where he is conducting
research or supporting farmers on methods in which they can maintain their livelihood,
he will realize the purpose he has been educated to pursue.

The University of Florida has been more than just an educational facility for
Glenn. Having spent five and a half years and acquiring two graduate degrees at UF, Glenn
has developed into an agricultural professional. The interaction with the fine faculty,
staff, and students at UF have greatly enhanced Glenn's professional, as well as
educational, development.

Not only does Glenn leave UF with two graduate degrees, but on November 9,
1 991 , Glenn was married to Kathleen Nadine Best, a graduate of UF from the College of
Journalism.

The University of Florida has been very, very good to and for Glenn, and he will
forever hold fond memories and high esteem for the "home of the Gators."

I certify that I have read this study and that in my opinion it conforms to
acceptable standards of scholarly presentation and is fully adequate, in scope and quality,
as a dissertation for the degree of Doctor of Philosophy.

■-~> />

M -A I

%

E. Ben Whitty, Chi
Professor of Agronomy

I certify that I have read this study and that in my opinion it conforms to
acceptable standards of scholarly presentation and is fully adequate, in scope and quality,
as a dissertation for the degree of Doctor of Philosophy.

i

n^jh{

l\

I_L

Jerry M. Bennett
Professor of Agronomy

I certify that I have read this study and that in my opinion it conforms to
acceptable standards of scholarly presentation and is fully adequate, in scope and quality,
as a dissertation for the degree of Doctor of Philosophy.

. n i,

u

/.

'.*^t!l!?->l. '■ x ■'&'.. > ■u-

Raymond N. Gallaher
Professor of Agronomy

I certify that I have read this study and that in my opinion it conforms to
acceptable standards of scholarly presentation and is fully adequate, in scope and quality,
as a dissertation for the degree of Doctor of Philosophy.

/

A

Donn G. Shilling

Associate Professor of Agronomy

I certify that I have read this study and that in my opinion it conforms to
acceptable standards of scholarly presentation and is fully adequate, in scope and quality,
as a dissertation for the degree of Doctor of Philosophy.

/

jCg~J<~-

Fred M. Rhoads
Professor of Soil Science

This dissertation was submitted to the Graduate Faculty of the College of
Agriculture and to the Graduate School and was accepted as partial fulfillment of the
requirements for the degree of Doctor of Philosophy.

Dean, College of Agriculture

Dean, Graduate School

UNIVERSITY OF FLORIDA

3 1262 08285 421 6