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IV. Plant Growth and Nutrient Uptake

IV. Plant Growth and Nutrient Uptake

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TOBACCO GROWTH AND NUTRITION



217



In the commercial production of each type, under favorable temperature conditions, growth is most noticeably affected by the supplies of

available water and nitrogen in the soil. When the amount and distribution of rainfall were considered optimal, one-half of the total growth

during a 63-day period was found to occur during the fifth to seventh

week after transplanting; with poor rainfall distribution conditions,

however, one-half of the total growth was made during the seventh

to ninth week after transplanting (Grizzard et al., 1942). Over a fiveyear period, the beginning of grand growth for Havana seed tobacco

was found to vary from 30 to 50 days after transplanting depending on

environmental conditions early in the season (Morgan and Street, 1935).

The total amount of dry matter produced was lowest in the year when

initiation of major growth was the latest and highest in the year when

grand growth started the earliest after time of transplanting.

When other factors are not limiting, there is an increase in the rate

of growth as the level of available nitrogen increases from deficient to

adequate, For example, growth rate as measured by increase in height

was slow under deficient conditions but was rapid at a moderate level

of nitrogen. The sigmoid growth curve was best developed when

conditions were most favorable for slow rather than rapid growth

(Garner et al., 1934).

Studies with oriental tobacco showed that not only the total mass

of material produced, but also the growth curves for stems and leaves

were sigmoid (Wolf, 1947). It was also observed that the duration of

the period of expansion of leaves was similar at all stalk positions and

that the time required for leaves to obtain their maximal area was

about 3 weeks from the time they were sufficiently large to be measured.

Wolf concluded from his experience that, for oriental tobacco, the

best commercial product is produced when growth rates are slow and

uniform from the time plants are established until the leaves are

harvested; consequently, the growth curve for this class of tobacco

should approximate a straight line. Contrary to the effects reported by

Wolf with oriental tobacco, Raper (1966) has shown that for flue-cured,

the number of days required for leaves to reach their maximal area

and weight differs among stalk positions.

Attempts to describe the growth of tobacco by mathematical expressions apparently have been limited. The Mitscherlich equation was

applied to yield data for leaf and stalk and for the two combined, but

unsatisfactory results were obtained in that the computed yields varied

drastically from the actual yields (Garner et al., 1934). The value of

0.122 which Mitscherlich assigned to the proportionality constant C for

fertilizer nitrogen, was much too low to fit the yields actually obtained



218



C. B. MCCANTS AND W. G. WOL'IZ



at various rates of fertilization. When the value of this constant was

increased tenfold, the calculated growth curve for leaf yield more

nearly approximated the yields actually obtained. Because the relative

yields of leaves and stalks are modified by the level of available nitrogen,

Garner concluded that no single formula will satisfactorily fit the data

for yields of leaves plus stalks.

The relationship between the area of a leaf and its length and width

was found to be best described by a linear regression of leaf area on

the product of the length and the width with the regression line passing

through the origin of the coordinates (Suggs et al., 1960). The proportionality constant (regression coefficient) averaged 0.7028 for very

small leaves and 0.6345 for medium and large leaves. Although there

were some variations among varieties, plant spacings, and irrigation

treatments, Suggs et nl. concluded that the differences were not

appreciable.

€3.



DRY MATTERACCUMULATION



The total yield of dry matter varies considerably among the various

classes of tobacco and is highest for the air-cured and lowest for the

oriental. Within a given class the yield also varies with variety, spacing,

fertilization, and other cultural and environmental factors. Likewise,

the weights of the various plant parts, e.g., leaves, suckers, inflorescence,

and stalks are influenced by cultural and environmental factors. The dry

weights of roots, stalks, leaves, and of inflorescence of untopped cigar

wrapper tobacco 70 days after transplanting was 900, 2380, 2190, and

400 pounds per acre, respectively (Morgan and Street, 1935). The

yield of dry matter in all above-ground parts of burley tobacco (an aircured class) in two consecutive years varied from 5063 to 5889 pounds

per acre (Bortner, C. E., personal communication). The highest yield

occurred in a season which was dry for the first 9 weeks then wet for

the remainder of the growth period. In the year of the lower yield,

rainfall was normal during the first 10 weeks but below normal for the

remainder of the season.

The data in Table I illustrate the differences among varieties and

the influence of rates of fertilizer nitrogen on the dry weight of the

various above-ground parts of flue-cured tobacco. Within each variety,

the leaf portion of the total dry weight decreased with increase in the

rate of nitrogen. The relative increase in weight with addition of nitrogen was about the same for the other parts. However, there were considerable differences between experiments in the proportionate weights

of stalks versus tops plus suckers to the total weight. In experiment TF

215 the proportionate weights of these parts were about the same and



219



TOBACCO GROWTH AND NUTRITION



TABLE I

Yield of Dry Matter in Various Plant Parts of Several Varieties of Flue-Cured

Tobacco Fertilized with Various Rates of Nitrogen

Yield of dry matter (lb./A.)a

Variety

Coker 187



Coker 139



Hicks



NC 95



Rate

of N

(lb./A.)



15

30

45

60

15

30

45

60

60

92

60

92



Leaves



+



Tops

suckers



Experiment TF 215

1383

713

1537

793

1546

819

1613

924

1639

688

1723

824

1816

913

1931

961

Experiment TV 123

2071

836

2184

1039

2034

657

2191

730



Stalk



Total



706

856

901

950

647

816

872

1019



2802

3186

3266

3457

2974

3363

3601

3911



1599

1763

1971

2191



4506

4986

4662

5112



All plant parts were dried at 65°C.



each was equivalent to approximately 25 percent of the total dry weight.

In experiment TV 123, however, the proportionate weight of tops plus

suckers in the Hicks variety was 20 percent of the total whereas that

in NC 95 was 14 percent, The proportionate weights of the stalks to

the total weight for Hicks and NC 95 were 35 and 43 percent,

respectively.



C. EFFECTS

OF GROWTH

RATE ON LEAFQUALITY

The influence of variations in the rate of growth at different stages

of development on quality characteristics of the cured leaf has been

discussed extensively but has been examined experimentally in limited

detail. A major reason for this paucity of evidence is that the appropriate experiments must be conducted in the field during the normal

growing season since efforts to grow in the greenhouse tobacco which

develops the commercially important characteristics have not been

successful. The large number of problems involved in controlling the

environment of field experiments makes it difficult to follow a prescribed

environmental regime or to obtain unconfounded data on the influence

of different environmental regimes on growth and development of the

plant.

The authors’ experience on the influence of different moisture



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C. B. MCCANTS AND W. G. WOLTZ



regimes on plant growth and leaf characteristics suggests that the

desirable quality characteristics are not generally obtained when

moisture conditions are such that the plant is in a state of rapid growth

from transplanting until harvest commences. Under these conditions

the cured leaves have neither the desired color, aromatic, nor textural

properties, Because plants produced under moisture deficiency conditions which result in severe reductions in growth also do not develop

the desired properties, a reasonable deduction seems to be that some

growth pattern between these extremes is optimal. It is hypothesized that,

at one or more stages in the development of the plant, a slight stress

in moisture supply will be advantageous in the formation of commercially desirable leaf properties. Such a stress conceivably could

result in a shift in the utilization of organic materials from the formation of cellular structures to the formation of differentiation products

which are important in the development of quality characteristics. The

stage or stages of growth in which a moisture stress would be most

effective is not clearly delineated but is hypothesized to be about midway

between transplanting and flower development and again after the seedhead has been removed.

D. EFFECTSOF TOPPING

AND SUCKERING

The practice of topping (removal of the terminal bud) and suckering (removal of axillary buds) was adopted in the early stages of

tobacco culture. This practice has significant effects on the subsequent

development of the plant which are frequently manifested through

changes in the physical and chemical characteristics of the leaves.

In a study on the effects of topping and suckering on the morphological properties of the leaves, Wolf and Gross (1937) compared

leaves among plants topped at nine leaves and suckered, topped at

eighteen leaves and suckered, and not topped. Using leaves from the

not-topped plants as a basis, topping to nine leaves and suckering

resulted in an average increase of 84 percent in leaf size, 24 percent

in thickness, and 138 percent in dry weight. Topping to eighteen

leaves and suckering, increased leaf size 29 percent, thickness by 8 percent, and dry weight by 48 percent. It was concluded that the changes

in leaf properties by topping were due not to the formation of new

cells but to an increase in size of the cells in different tissues. All leaves

were not similarly affected. The younger the leaf, the greater were the

effects of topping. Leaves that were mature, such as those on the lower

part of the stalk, were affected very little by topping.

Donev ( 1961) reported that topping, compared with not-topping

increased the thickness of leaves 15 to 20 percent, enlarged the root



TOBACCO GROWTH AND NUTRITION



221



system 10 percent, and increased yield 25 percent. Topped plants have

been observed to wilt less during moisture stress than untopped ones;

this is probably a manifestation of treatment effect on leaf thickness

and on the root system (Carr and Neas, 1951; Woltz, 1955).

Berthold (1931) also has reported that topping and suckering

resulted in a larger root system of tobacco. Additional evidence for

this type of response is provided by the relationship between topping

and nicotine content of the leaves. Gaines (1959) and Woltz ( 1955),

for example, have shown that topping compared with not-topping

resulted in an increase in the nicotine content of the leaves. Nicotine

is formed primarily in the roots of the plant (Dawson, 1960), and a

relationship between nicotine synthesis and root development has

been demonstrated (Wolf and Bates, 1964). Thus an increase in

nicotine formation from topping suggests that this practice caused an

increase in root development.

Marshall and Seltmann (1964) studied the effects of topping at

four stages of growth: button, early flower, full flower, and late flower.

The number of leaves left per plant was the same for all treatments.

Yield, value per acre, and quality as appraised by representatives of

tobacco companies were highest from plants topped at the button or

early flower stage and decreased as topping was delayed. In general,

the contents of sugar and nicotine in the cured tobacco decreased with

delay in the time of topping after the early flower stage. Similar results

have been reported by Elliot ( 19.33).

Woltz (1955) reported that topping flue-cured tobacco plants when

the first five to ten flowers were pink, and removing the suckers periodically, increased the yield and contents of nicotine and sugar in the

leaves above those of the not-topped plants. Topping, however, did

not influence the nitrogen or potassium concentration in the tissue or

the rate of bum. Failure to remove the suckers significantly decreased

the yield below that of the suckered plants. With respect to yield and

value indices, addition of extra nitrogen to untopped tobacco did not

overcome the adverse effects caused by the failure to top and sucker.



E. NUTRLENT

ACCUMULATION

The quantity of each nutrient absorbed by a field-grown crop of

tobacco varies considerably; it is dependent on the class of tobacco,

fertilization practices, residual level of nutrients in the soil, number

of plants per acre, rainfall, and other environmental factors. Therefore,

values reported in the literature reflect the local environmental conditions and management practices under which the crops were grown.

The values obtained by Garner (1939) and Grizzard et al. (1942),



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C. B. MCCANTS AND W. G. WOLTZ



are considerably lower than those obtained more recently and presented

in Fig. 1. The total yield of dry matter in this crop was 3828 pounds

per acre and the yield of cured leaf was 2250 pounds per acre. Over

a two-year period in which the total average yield of dry matter of

burley tobacco was 5476 pounds per acre, the contents of nitrogen,

phosphorus, potassium, calcium, and magnesium on a pounds-per-acre

basis were ,200, 15, 325, 120, and 15, respectively (Bortner, C. E., personal communication). The total amount of nitrogen in the aboveground parts of an acre of shade-grown tobacco has been reported to

be about 155 pounds (Morgan and Street, 1935).

V.



Nitrogen



Among the elements essential for the commercial production of

tobacco, none has as pronounced an effect nor requires the degree of

attention in fertility practices as nitrogen. From the seedling stage

through final harvest, the soil nitrogen regime affects the process of

plant development more than any other mineral element. With respect

to time of absorption, form in which absorbed, concentration in the

leaf at various stages of growth, and in numerous other aspects, the

role of nitrogen in the development and properties of the tobacco leaf

is of major importance. The influence of variations in nitrogen supply

on growth of the plant and properties of the cured leaf has been investigated more extensively than have the effects of any other essential

element.



SUPPLYON LEAFPROPERTIES

A. EFFECTOF NITROGEN

1. Green Leaves

Except at extremely deficient levels, the total number of leaves

produced by a plant is not appreciably influenced by the level of

available nitrogen (Garner et al., 1934). With adequate moisture, an

increase in the supply of nitrogen from deficiency to excessive results

in an increase in the area of the leaf but a decrease in the weight per

unit area, the latter effect being due primarily to a decrease in the

thickness of the leaf (Raper, M 6 ) . This effect of nitrogen on the size

and thickness of the leaf is of considerable practical importance in

relation to the fertilization practices for tobaccos for different commercial uses. Thus, a liberal supply of nitrogen is desirable when the

object is to produce a large, thin leaf such as required for cigar wrapper or binder, whereas a moderate supply is necessary for the development of the flue-cured class.



TOBACCO GROWTH AND NUTRITION



223



It is generally recognized that the maturity of all types of tobacco

is significantly influenced by the supply of available nitrogen in the

latter stages of development. For proper maturity it is essential that

the rate of nitrogen absorption decrease rather rapidly during the

latter portion of the growth period. By the time the plant has attained

its maximal leaf area, the readily available supply of nitrogen in the

soil should be essentially exhausted.

Although apparent nitrogen deficiency symptoms do not generally

occur when the concentration in a particular leaf is above 1.5 to 2.0

percent, nonapparent nitrogen stresses may occur which have physiological effects that are of practical importance. The growth of a

tobacco plant involves the successive development of 16 to 20 leaves.

Leaves at the basal portion of the plant are approaching maturity

when those at the top are still in a very active stage of growth, thus

each leaf on the plant is a different physiological age. Consequently,

when conditions of nitrogen availability result in a nitrogen stress

within the plant, the effects may be different on the various leaves.

Studies to determine such effects have been quite limited, and the

results obtained must be subjected to restricted interpretations.

In field experiments where a nitrogen availability regime was

created so that the plant was subjected to a nitrogen stress less than

required for acute deficiency, a slight yellow color indicated reduction

in chlorophyll content and length and width measurements showed a

reduction in leaf area (Raper, 1966). The reduction in area, however,

seldom was accompanied by a reduction in the total dry weight of the

leaves; instead there was a greater weight per unit area with the stress

than with the nonstress condition. In other studies, the stage of plant

growth at which nitrogen stresses were imposed appeared to have

only a slight effect on this relationship between leaf area and leaf

weight (Pearse, 1960a). Such responses suggest that within certain

limits, the photosynthetic capacity of the leaves is not necessarily

altered by nitrogen stresses which do not result in extreme variations

in the total leaf area.

Because moderate alterations in leaf area in field experiments were

not accompanied by changes in dry weight, the assumption has been

made that the cells of the leaves with the lesser total area have a

greater quantity of assimilated carbon. Evidence presented by Heyes

and Brown (1956) indicates that the dry weight of the cell is determined primarily by the content of cellulose and other cell wall materials.

It is suggested that the mass of the cell wall material relative to the

total mass of ths cell is increased by the nitrogen regime which reduces

leaf area.



224



C . B. MCCANTS AND W. G . WOLTZ



2. Physical Characteristics of Cured Leaves

The delay in maturity which results from excessive nitrogen,

prevents normal development of the leaves, and thus when they are

cured they lack the desired chemical and physical properties. The

characteristics of the leaves may vary somewhat, but generally they are

dark brown to black in color and dry and chaffy. A deficiency of nitrogen,

however, increases the probability of premature yellowing of leaves

in the field, Under these conditions the cured leaves are generally pale

in color and lack the desired textural properties associated with high

quality in tobacco.

An increase in the supply of available soil nitrogen from deficiency

to adequacy has been shown to decrease the fire-holding capacity of

tobacco (Garner et al., 1934). Since a thin leaf usually has better

burning qualities than a thick, close-textured one, and since high

concentrations of nitrogen in the leaf tend to produce the former

characteristic, the decrease in combustibility i s probably due to its

effects on the chemical composition of the leaf. It has been suggested

that proteins and related nitrogen compounds tend to adversely affect

burning properties of leaves due to the difficulty of combustion.

3. Chemical Properties of Cured Leaves



Tobacco with a high total nitrogen content produces a strong

pungent-tasting smoke whereas tobacco low in nitrogen has a flat

insipid-tasting smoke. Nitrogen is considered to be a dominant factor

which influences the level of strength in tobacco smoke. Whether the level

is too high or too low depends on the use that is made of the tobacco.

Nitrogen is an integral constituent of the nicotine molecule, and

thus nitrogen is an important factor in nicotine synthesis. The accumulation of nicotine in the plant is regulated more by the nitrogen supply

than any other plant nutrient. The data generally show that the

nicotine content of field-grown plants increases with increase in the

amount of available nitrogen up to the point where excesses result in

physiological breakdown of the leaves.

Whereas the concentration of nitrogen in the tissue is positively

correlated with nicotine it is negatively related to the sugar content of

the leaf (Woltz et al., 1948). One of the important quality characteristics of flue-cured tobacco for use in cigarettes is the relationship of

sugar and nicotine, frequently referred to as the sugar : nicotine ratio;

consequently, nitrogen assumes a critical role in the development of

this property. The sooner nitrogen deficiency occurs after transplanting,

the higher is the sugar : nicotine ratio (Pearse, 196Ob). Leaves at the



TOBACCO GROWTH AND NUTRITION



22.5



middle and top stalk positions may have a relatively high nicotine

level when nitrogen deficiency occurs late in the season whereas an

early deficiency results in a relatively low level of nicotine in leaves at

these stalk positions. Evidently nicotine synthesis is severely reduced

shortly after the roots are deprived of adequate quantities of external

nitrogen.

Data on the alkaloid, sugar, and nitrogen contents of selected

leaves indicate that the introduction of a nitrogen stress during a

segment of growth increases the reducing sugars and decreases the

alkaloids in leaves produced during this segment (Raper, 1966). A

relief of the stress restored the sugar : alkaloid balance in leaves

produced subsequently.

A severe nitrogen deficiency, even though temporary, has been

shown to result in a low quality leaf physically and chemically. A

slight nitrogen stress throughout the growing season has on occasion

given a lower quality leaf than when the same amount of nitrogen

was absorbed early. These types of response suggest that the most

acceptable performance of tobacco may be expected from nitrogen

fertilization practices in which a high percentage of the total available

nitrogen is present during early stages of plant growth and rapidly

diminishes during the later phase.



B. RESPONSE

TO AMMONIUM AND NITRATE FORMS

OF NITROGEN

Probably no other phase in the fertilization of tobacco has been

studied more extensively than the response to various sources of

nitrogen. Because the results obtained have not always been consistent,

the conclusion has frequently been drawn that the form included in

the fertilizer is not significant. However, the literature abounds with

evidence that the form of nitrogen absorbed by tobacco is a factor

influencing growth and development of the plant and that when soil

management and fertilization practices are conducive to the absorption

of a specific form, measurable and significant differences in response

have been obtained.

1. Generalized Experimental Procedures



In evaluating the relative response of tobacco to the ammonium

and nitrate forms, two basically different experimental procedures are

employed. In one, sand or solution cultures are used and the nitrogen

level is recharged frequently by the addition of a nutrient solution

containing the nitrogen in the desired form or ratio of forms. The

data obtained generally consist of total dry weight of the plant after

several weeks of growth and the percentages of nitrogen, mineral



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C. B. MCCANTS AND W. G . WOLTZ



elements and certain carbohydrates and nitrogen compounds in the

leaf. No attempts are made to harvest and cure the leaves in the normal

manner. This procedure provides evidence of the influence of a particular nitrogen regime on certain growth processes, mineral absorption,

and dry matter production, but the effects on commercial properties

of plants grown under normal production procedures can only be

deduced.

In the second procedure, the experiments are conducted in the field

and the nitrogen variable is usually applied by a single application of

the standard source or sources of fertilizer nitrogen. The leaves are

harvested and processed in the conventional manner, Data obtained

usually include yield and a quality index based on visual characteristics of leaves and prices paid for tobacco of similar appearance,

chemical properties, and a limited number of physical properties of the

leaves. These studies provide evidence on the effects from the application of different forms of nitrogen, but since oxidation of the ammonium

to the nitrate form may occur to varying degrees, precise information

on the regime on which the plant was grown is generally not available.

2. Factors Affecting Relative Absorption of Nitrogen Forms

Although tobacco has been shown to absorb and make some growth

on certain reduction products of nitrate-N in aseptic-cultures (Steinberg, 195313) and to absorb limited amounts of urea N through the

leaves (Volk and McAuliffe, 1954), under normal cultural practices

essentially all the nitrogen absorbed is in the ammonium and/or the

nitrate form. Nutrient uptake and nitrogen and carbohydrate metabolism, and growth of the plant are markedly different depending on the

dominant form absorbed.

The relative uptake of the two forms will vary considerably depending on the composition and acidity of the solution and the stage of

plant development. From experiments in which plants were supplied

ammonium nitrate enriched with I5N, Jackson and Volk (1966) found

that young tobacco seedlings (39 days from seeding) absorbed nitrogen

primarily as ammonium. Older plants (70 days after seeding), however,

absorbed more nitrate than ammonium.

Data from several sources indicate that the acidity of the solution

in which tobacco plants are grown influences the absorption and assimilation of ammonium and nitrate nitrogen. McEvoy (1957) reported

that nitrate nitrogen was utilized more effectively from an acid medium,

with an optimum at pH 5. When part (16%)of the nitrogen was supplied as ammonium, growth was maximal at pH 8. Although growth of

the plants provided with ammonium was improved by adjustment in



TOBACCO GROWTH AND NUTRITION



227



the p H of the solution, the maximum attained was less than that from

the nitrate solution.

Chouteau (1963) found with ammonium nutrition that increasing

the p H by the addition of bicarbonate to the nutrient media improved

the growth of tobacco and caused toxicity symptoms to disappear.

With nitrate nutrition, however, bicarbonate always had a depressing

effect on growth and high concentrations resulted in chlorosis. For both

ammonium and nitrate nutrition, the presence of bicarbonate in the

medium increased the content of cations and of organic acids, particularly citric acid, in the plant. He concluded that the improvement in

the growth of tobacco due to the additions of bicarbonate to the ammonium cultures was due not only to changes brought about by the

increase in pH, but also to absorption and metabolism of bicarbonate.

Studies by Takahashi and Yoshida (1958) also show that pH had

only a slight effect on growth, nutrient absorption, and yield of tobacco

when nitrate nitrogen was used. In ammonium cultures, however,

increasing acidity retarded growth and nutrient absorption and increased the contents of ammonium nitrogen and asparagine in the

tissue.



3. Growth Response in Sand and Solution Cultures

Evans and Weeks (1947) used a sand-culture technique to study

the influence of various ratios of nitrate and ammonium nitrogen on

the growth and composition of burley tobacco. They reported a sixfold

increase in growth of plants receiving all the nitrogen as nitrate compared to those which receive only ammonium. Hawkins (1956) found

that relative to an all-nitrate solution, the growth of tobacco was reduced one-third in solutions containing 50 percent of the nitrogen as

ammonium and 80 percent when all the nitrogen was supplied as

ammonium. Similar types of response have been reported by McEvoy

(1946) and Gilmore (1953).

The relative effects of ammonium and nitrate nutrition on the

growth of tobacco plants in controlled nutrient environment cultures

may be summarized by the results reported by Skogley and McCants

(1963a). Plants of a flue-cured tobacco variety were grown for 20 days

in an all-nitrate medium and then divided into two groups. One group

was continued on the all-nitrate solution while the other group was

provided a solution in which the nitrogen was in the ammonium form.

The plants grown with the ammonium form maintained a dry weight

yield similar to that of plants grown on the nitrate form for only 4 days.

After 21 days, the yield of dry matter of plants grown on the ammonium

form was only 33 percent of that of plants grown on the nitrate form.



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