COTTON FIBRE
GROWTH:
Iimprovements in cotton fiber properties for textiles depend on changes in
the growth and development of the fiber.
Manipulation of fiber perimeter has a potential to impact the length,
micronaire, and strength of cotton fibers. The perimeter of the fiber is
regulated by biological mechanisms that control the expansion characteristic
of the cell wall and establish cell diameter.
mprovements in fiber quality can take many different forms. Changes in
length, strength, uniformity, and fineness In one recent analysis, fiber
perimeter was shown to be the single quantitative trait of the fiber that
affects all other traits . Fiber perimeter is the variable that has the
greatest affect on fiber elongation and strength properties. While mature
dead fibers have an elliptical morphology, living fibers have a cylindrical
morphology during growth and development. Geometrically, perimeter is
directly determined by diameter (perimeter = diameter × p). Thus, fiber
diameter is the only variable that directly affects perimeter. For this
reason, understanding the biological mechanisms that regulate fiber diameter
is important for the long-term improvement of cotton.
A review of the literature indicates that many researchers believe diameter
is established at fiber initiation and is maintained throughout the duration
of fiber development . A few studies have examined, either directly or
indirectly, changes in fiber diameter during development. Some studies
indicate that diameter remains constant ; while others indicate that fiber
diameter increases as the fiber develops.
The first three stages occur while the fiber is alive and actively growing.
Fiber initiation involves the initial isodiametric expansion of the
epidermal cell above the surface of the ovule. This stage may last only a
day or so for each fiber. Because there are several waves of fiber
initiation across the surface of the ovule , one may find fiber initials at
any time during the first 5 or 6 d post anthesis. The elongation phase
encompasses the major expansion growth phase of the fiber. Depending on
genotype, this stage may last for several weeks post anthesis. During this
stage of development the fiber deposits a thin, expandable primary cell wall
composed of a variety of carbohydrate polymers . As the fiber approaches the
end of elongation, the major phase of secondary wall synthesis starts. In
cotton fiber, the secondary cell wall is composed almost exclusively of
cellulose. During this stage, which lasts until the boll opens (50 to 60 d
post anthesis), the cell wall becomes progressively thicker and the living
protoplast decreases in volume. There is a significant overlap in the timing
of the elongation and secondary wall synthesis stages. Thus, fibers are
simultaneously elongating and depositing secondary cell wall.
The establishment of fiber diameter is a complex process that is governed,
to a certain extent, by the overall mechanism by which fibers expand. The
expansion of fiber cells is governed by the same related mechanisms
occurring in other walled plant cells. Most cells exhibit diffuse cell
growth, in which new wall and membrane materials are added throughout the
surface area of the cell. Specialized, highly elongated cells, such as root
hairs and pollen tubes, expand via tip synthesis where new wall and membrane
materials are added only at a specific location that becomes the growing tip
of the cell. While the growth mechanisms for cotton fiber have not been
fully documented, recent evidence indicates that throughout the initiation
and early elongation phases of development, cotton fiber expands primarily
via diffuse growth . Later in fiber development, late in cell elongation,
and well into secondary cell wall synthesis (35 d post anthesis), the
organization of cellular organelles is consistent with continued diffuse
growth . Many cells that expand via diffuse growth exhibit increases in both
cell length and diameter; but cells that exhibit tip synthesis do not
exhibit increases in cell diameter . If cotton fiber expands by diffuse
growth, then it is reasonable to suggest that cell diameter might increase
during the cell elongation phase of development.
Cell expansion is also regulated by the extensibility of the cell wall. For
this reason, cell expansion most commonly occurs in cells that have only a
primary cell wall . Primary cell walls contain low levels of cellulose.
Production of the more rigid secondary cell wall usually signals the
cessation of cell expansion. Secondary cell wall formation is often
indicated by the development of wall birefringence.
Analyses of fiber diameter and cell wall birefringence show that fiber
diameter significantly increased as fibers grew and developed secondary cell
walls. Both cotton species and all the genotypes tested exhibited similar
increases in diameter; however, the specific rates of change differed.
Fibers continued to increase in diameter during the secondary wall synthesis
stage of development, indicating that the synthesis of secondary cell wall
does not coincide with the cessation of cell expansion.
GINNING
The generally recommended machinery sequence at gins for spindle-picked
cotton is rock and green-boll trap, feed control, tower drier, cylinder
cleaner, stick machine, tower drier, cylinder cleaner, extractor feeder, gin
stand, lint cleaner, lint cleaner, and press.
Cylinder cleaners use rotating spiked drums that open and clean the
seedcotton by scrubbing it across a grid-rod or wire mesh screen that allows
the trash to sift through. The stick machine utilizes the sling-off action
of channel-type saw cylinders to extract foreign matter from the seedcotton
by centrifugal force. In addition to feeding seedcotton to the gin stand,
the extractor feeder cleans the cotton using the stick machine's sling-off
principle.
In some cases the extractor-feeder is a combination of a cylinder cleaner
and an extractor. Sometimes an impact or revolving screen cleaner is used in
addition to the second cylinder cleaner. In the impact cleaner, seedcotton
is conveyed across a series of revolving, serrated disks instead of the
grid-rod or wire mesh screen.
Lint cleaners at gins are mostly of the controlled-batt, saw type. In this
cleaner a saw cylinder combs the fibers and extracts trash from the lint
cotton by a combination of centrifugal force, scrubbing action between saw
cylinder and grid bars, and gravity assisted by an air current
Seedcotton-type cleaners extract the large trash components from cotton.
However, they have only a small influence on the cotton's grade index,
visible liint foreign-matter content, and fiber length distribution when
compared with the lint cleaning effects. Also, the number of neps created by
the entire seedcotton cleaning process is about the same as the increase
caused by one saw-cylinder lint cleaner.
Most cotton gins today use one or two stages of saw-type lint cleaners. The
use of too many stages of lint cleaning can reduce the market value of the
bale, because the weight loss may offset any gain from grade improvement.
Increasing the number of saw lint cleaners at gins, in addition to
increasing the nep count and short-fiber content of the raw lint, causes
problems at the spinning mill. These show up as more neps in the card web
and reduced yarn strength and appearance .
Pima cotton, extra-long-staple cotton, is roller ginned to preserve its
length and to minimize neps. To maintain the highest possible quality bale
of pima cotton, mill-type lint cleaners were for a long time the predominant
cleaner used by the roller-ginning industry. Today, various combinations of
impacts, incline, and pneumatic cleaners are used in most roller-ginning
plants to increase lint-cleaning capacity.
COTTON FIBER QUALITY:
Two simple words, fiber quality, mean quite different things to cotton
growers and to cotton processors. No after-harvest mechanisms are available
to either growers or processors that can improve intrinsic fiber quality.
Most cotton production research by physiologists and agronomists has been
directed toward improving yields, so the few cultural-input strategies
suggested for improving fiber quality during the production season are of
limited validity. Thus, producers have limited alternatives in production
practices that might result in fibers of acceptable quality and yield
without increased production costs.
Fiber processors seek to acquire the highest quality cotton at the lowest
price, and attempt to meet processing requirements by blending bales with
different average fiber properties. Of course, bale averages for fiber
properties do not describe the fiber-quality ranges that can occur within
the bales or the resulting blends. Further, the natural variability among
cotton fibers unpredictably reduces the processing success for blends made
up of low-priced, lower-quality fibers and high-priced, higher-quality
fibers.
Blends that fail to meet processing specifications show marked increases in
processing disruptions and product defects that cut into the profits of the
yarn and textile manufacturers. Mill owners do not have sufficient knowledge
of the role classing-office fiber properties play in determining the outcome
of cotton spinning and dyeing processes.
Even when a processor is able to make the connection between yarn and fabric
defects and increased proportions of low-quality fibers, producers have no
way of explaining why the rejected bales failed to meet processing
specifications when the bale averages for important fiber properties fell
within the acceptable ranges.
If, on the other hand, the causes of a processing defect are unknown,
neither the producer nor the processor will be able to prevent or avoid that
defect in the future. Any future research that is designed to predict,
prevent, or avoid low-quality cotton fibers that cause processing defects in
yarn and fabric must address the interface between cotton production and
cotton processing.
Every bale of cotton produced in the USA crosses that interface via the
USDA-AMS classing offices, which report bale averages of quantified fiber
properties. Indeed, fiber-quality data reports from classing offices are
designed as a common quantitative language that can be interpreted and
understood by both producers and processors. But the meaning and utility of
classing-office reports can vary, depending on the instrument used to
evaluate.
Fiber maturity is a composite of factors, including inherent genetic
fineness compared with the perimeter or cross section achieved under
prevailing growing conditions and the relative fiber cell-wall thickness and
the primary -to- secondary fiber cell-wall ratio, and the time elapsed
between flowering and boll opening or harvest. While all the above traits
are important to varying degrees in determining processing success, none of
them appear in classing-office reports.
Micronaire, which is often treated as the fiber maturity measurement in
classing-office data, provides an empirical composite of fiber cross section
and relative wall thickening. But laydown blends that are based solely on
bale-average micronaire will vary greatly in processing properties and
outcomes.
Cotton physiologists who follow fiber development can discuss fiber
chronological maturity in terms of days after floral anthesis. But, they
must quantify the corresponding fiber physical maturity as micronaire
readings for samples pooled across several plants, because valid micronaire
determinations require at least 10 g of individualized fiber.
Some fiber properties, like length and single fiber strength, appear to be
simple and easily understood terms. But the bale average length reported by
the classing office does not describe the range or variability of fiber
lengths that must be handled by the spinning equipment processing each
individual fiber from the highly variable fiber population found in that
bale.
Even when a processing problem can be linked directly to a substandard fiber
property, surprisingly little is known about the causes of variability in
fiber shape and maturity. For example:
Spinners can see the results of excessive variability in fiber length or
strength when manifested as yarn breaks and production halts.Knitters and
weavers can see the knots and slubs or holes that reduce the value of
fabrics made from defective yarns that were spun from poor-quality fibre
Inspectors of dyed fabrics can see the unacceptable color streaks and specks
associated with variations in fiber maturity and the relative dye-uptake
success.
The grower, ginner, and buyer can see variations in color or trash content
of ginned and baled cotton.
But there are no inspectors or instruments that can see or predict any of
the above quality traits of fibers while they are developing in the boll.
There is no definitive reference source, model, or database to which a
producer can turn for information on how cultural inputs could be adapted to
the prevailing growth conditions of soil fertility, water availability, and
weather (temperature, for example) to produce higher quality fiber.
The scattered research publications that address fiber quality, usually in
conjunction with yield improvement, are confusing because their measurement
protocols are not standardized and results are not reported in terms that
are meaningful to either producers or processors. Thus, physiological and
agronomic studies of fiber quality frequently widen, rather than bridge, the
communication gap between cotton producers and processors.
This overview assembles and assesses current literature citations regarding
the quantitation of fiber quality and the manner in which irrigation, soil
fertility, weather, and cotton genetic potential interact to modulate fiber
quality. The ultimate goal is to provide access to the best answers
currently available to the question of what causes the annual and regional
fiber quality variations
From the physiologist's perspective, the fiber quality of a specific cotton
genotype is a composite of fiber shape and maturity properties that depend
on complex interactions among the genetics and physiology of the plants
producing the fibers and the growth environment prevailing during the cotton
production season.
Fiber shape properties, particularly length and diameter, are largely
dependent on genetics. Fiber maturity properties, which are dependent on
deposition of photosynthate in the fiber cell wall, are more sensitive to
changes in the growth environment. The effects of the growth environment on
the genetic potential of a genotype modulate both shape and maturity
properties to varying degrees.
Anatomically, a cotton fiber is a seed hair, a single hyperelongated cell
arising from the protodermal cells of the outer integument layer of the seed
coat. Like all living plant cells, developing cotton fibers respond
individually to fluctuations in the macro- and microenvironments. Thus, the
fibers on a single seed constitute continua of fiber length, shape,
cell-wall thickness, and physical maturity .
Environmental variations within the plant canopy, among the individual
plants, and within and among fields ensure that the fiber population in each
boll, indeed on each seed, encompasses a broad range of fiber properties and
that every bale of cotton contains a highly variable population of fibers.
Successful processing of cotton lint depends on appropriate management
during and after harvest of those highly variable fiber properties that have
been shown to affect finished-product quality and manufacturing efficiency .
If fiber-blending strategies and subsequent spinning and dyeing processes
are to be optimized for specific end-uses and profitability, production
managers in textile mills need accurate and effective descriptive and
predictive quantitative measures of both the means and the ranges of these
highly variable fiber properties .
In the USA, the components of cotton fiber quality are usually defined as
those properties reported for every bale by the classing offices of the
USDA-AMS, which currently include length, length uniformity index, strength,
micronaire, color as reflectance (Rd) and yellowness (+b), and trash
content, all quantified by the High Volume Instrument (HVI) line. The
classing offices also provide each bale with the more qualitative classers'
color and leaf grades and with estimates of preparation (degree of roughness
of ginned lint) and content of extraneous matter.
The naturally wide variations in fiber quality, in combination with
differences in end-use requirements, result in significant variability in
the value of the cotton lint to the processor. Therefore, a system of
premiums and discounts has been established to denote a specified base
quality. In general, cotton fiber value increases as the bulk-averaged
fibers increase in whiteness (+Rd), length, strength, and micronaire; and
discounts are made for both low mike (micronaire less than 3.5) and high
mike (micronaire more than 4.9).
Ideal fiber-quality specifications favored by processors traditionally have
been summarized thusly: "as white as snow, as long as wool, as strong as
steel, as fine as silk, and as cheap as hell." These specifications are
extremely difficult to incorporate into a breeding program or to set as
goals for cotton producers. Fiber-classing technologies in use and being
tested allow quantitation of fiber properties, improvement of standards for
end-product quality, and, perhaps most importantly, creation of a
fiber-quality language and system of fiber-quality measurements that can be
meaningful and useful to producers and processors alike.
GENE AND ENVIRONMENTAL VARIABILITY:
Improvements in textile processing, particularly advances in spinning
technology, have led to increased emphasis on breeding cotton for both
improved yield and improved fiber properties Studies of gene action suggest
that, within upland cotton genotypes there is little non-additive gene
action in fiber length, strength, and fineness ; that is, genes determine
those fiber properties. However, large interactions between combined annual
environmental factors (primarily weather) and fiber strength suggest that
environmental variability can prevent full realization of the fiber-quality
potential of a cotton genotype.
More recently, statistical comparisons of the relative genetic and
environmental influences upon fiber strength suggest that fiber strength is
determined by a few major genes, rather than by variations in the growth
environment . Indeed, spatial variations of single fertility factors in the
edaphic environment were found to be unrelated to fiber strength and only
weakly correlated with fiber length .
Genetic potential of a specific genotype is defined as the level of fiber
yield or quality that could be attained under optimal growing conditions.
The degree to which genetic potential is realized changes in response to
environmental fluctuations such as application of water or fertilizer and
the inevitable seasonal shifts such as temperature, day length, and
insolation.
In addition to environment-related modulations of fiber quality at the crop
and whole-plant levels, significant differences in fiber properties also can
be traced to variations among the shapes and maturities of fibers on a
single seed and, consequently, within a given boll.
EFFECT ON FIBER LENGTH:
Comparisons of the fiber-length arrays from different regions on a single
seed have revealed that markedly different patterns in fiber length can be
found in the micropylar, middle, and chalazal regions of a cotton seed - at
either end and around the middle . Mean fiber lengths were shortest at the
micropylar (upper, pointed end of the seed) . The most mature fibers and the
fibers having the largest perimeters also were found in the micropylar
region of the seed. After hand ginning, the percentage of short fibers less
than 0.5 inch or 12.7 mm long on a cotton seed was extremely low.
It has been reported that, in ginned and baled cotton, the short fibers with
small perimeters did not originate in the micropylar region of the seed .
MEasurements of fibers from micropylar and chalazal regions of seeds
revealed that the location of a seed within the boll was related to the
magnitude of the differences in the properties of fibers from the micropylar
and chalazal regions.
Significant variations in fiber maturity also can be related to the seed
position (apical, medial, or due to the variability inherent in cotton
fiber, there is no absolute value for fiber length within a genotype or
within a test sample . Even on a single seed, fiber lengths vary
significantly because the longer fibers occur at the chalazal (cup-shaped,
lower) end of the seed and the shorter fibers are found at the micropylar
(pointed) end. Coefficients of fiber-length variation, which also vary
significantly from sample to sample, are on the order of 40% for upland
cotton.
Variations in fiber length attributable to genotype and fiber location on
the seed are modulated by factors in the micro- and macroenvironment .
Environmental changes occurring around the time of floral anthesis may limit
fiber initiation or retard the onset of fiber elongation. Suboptimal
environmental conditions during the fiber elongation phase may decrease the
rate of elongation or shorten the elongation period so that the genotypic
potential for fiber length is not fully realized . Further, the results of
environmental stresses and the corresponding physiological responses to the
growth environment may become evident at a stage in fiber development that
is offset in time from the occurrence of the stressful conditions.
Fiber lengths on individual seeds can be determined while the fibers are
still attached to the seed , by hand stapling or by photoelectric
measurement after ginning. Traditionally, staple lengths have been measured
and reported to the nearest 32nd of an inch or to the nearest millimeter.
The four upland staple classes are: short (<21>34 mm). Additionally, short
fiber content is defined as the percentage of fiber less than 12.7 mm.
Cotton buyers and processors used the term staple length long before
development of quantitative methods for measuring fiber properties.
Consequently, staple length has never been formally defined in terms of a
statistically valid length distribution.
In Fibrograph testing, fibers are randomly caught on combs, and the beard
formed by the captured fibers is scanned photoelectrically from base to tip
. The amount of light passing through the beard is a measure of the number
of fibers that extend various distances from the combs. Data are recorded as
span length (the distance spanned by a specific percentage of fibers in the
test beard). Span lengths are usually reported as 2.5 and 50%. The 2.5% span
length is the basis for machine settings at various stages during fiber
processing.
The uniformity ratio is the ratio between the two span lengths expressed as
a percentage of the longer length. The Fibrograph provides a relatively fast
method for reproducibility in measuring the length and length uniformity of
fiber samples. Fibrograph test data are used in research studies, in
qualitative surveys such as those checking commercial staple-length
classifications, and in assembling cotton bales into uniform lots.
Since 1980, USDA-AMS classing offices have relied almost entirely on
high-volume instrumentation (HVI) for measuring fiber length and other fiber
properties (Moore, 1996). The HVI length analyzer determines length
parameters by photoelectrically scanning a test beard that is selected by a
specimen loader and prepared by a comber/brusher attachment
The fibers in the test beard are assumed to be uniform in cross-section, but
this is a false assumption because the cross section of each individual
fiber in the beard varies significantly from tip to tip. The HVI
fiber-length data are converted into the percentage of the total number of
fibers present at each length value and into other length parameters, such
as mean length, upper-half mean length, and length uniformity . This test
method for determining cotton fiber length is considered acceptable for
testing commercial shipments when the testing services use the same
reference standard cotton samples.
All fiber-length methods discussed above require a minimum of 5 g of ginned
fibers and were developed for rapid classing of relatively large, bulk fiber
samples. For analyses of small fiber samples , fiber property measurements
with an electron-optical particle-sizer, the Zellweger Uster AFIS-A2 have
been found to be acceptably sensitive, rapid, and reproducible. The AFIS-A2
Length and Diameter module generates values for mean fiber length by weight
and mean fiber length by number, fiber length histograms, and values for
upper quartile length, and for short-fiber contents by weight and by number
(the percentages of fibers shorter than 12.7 mm). The AFIS-A2 Length and
Diameter module also quantifies mean fiber diameter by number .
Although short-fiber content is not currently included in official USDA-AMS
classing office reports, short-fiber content is increasingly recognized as a
fiber property comparable in importance to fiber fineness, strength, and
length . The importance of short-fiber content in determining
fiber-processing success, yarn properties, and fabric performance has led
the post-harvest sector of the U.S. cotton industry to assign top priority
to minimizing short-fiber content, whatever the causes .
The perceived importance of short-fiber content to processors has led to
increased demands for development and approval of a standard short-fiber
content measurement that would be added to classing office HVI systems .
This accepted classing office-measurement would allow inclusion of
short-fiber content in the cotton valuation system. Documentation of
post-ginning short-fiber content at the bale level is expected to reduce the
cost of textile processing and to increase the value of the raw fiber .
However, modulation of short-fiber content before harvest cannot be
accomplished until the causes of increased short-fiber content are better
understood.
Fiber length is primarily a genetic trait, but short-fiber content is
dependent upon genotype, growing conditions, and harvesting, ginning, and
processing methods. Further, little is known about the levels or sources of
pre-harvest short-fiber content .
It is essential that geneticists and physiologists understand the underlying
concepts and the practical limitations of the methods for measuring fiber
length and short-fiber content so that the strong genetic component in fiber
length can be separated from environmental components introduced by
excessive temperatures and water or nutrient deficiencies. Genetic
improvement of fiber length is fruitless if the responses of the new
genotypes to the growth environment prevent full realization of the enhanced
genetic potential or if the fibers produced by the new genotypes break more
easily during harvesting or processing. The reported effects of several
environmental factors on fiber length and short-fiber content, which are
assumed to be primarily genotype-dependent, are discussed in the subsections
that follow.
FIBER LENGTH AND TEMPERATURE:
Maximum cotton fiber lengths were reached when night temperatures were
around 19 to 20 °C, depending on the genotype . Early-stage fiber elongation
was highly temperature dependent; late fiber elongation was temperature
independent . Fiber length (upper-half mean length) was negatively
correlated with the difference between maximum and minimum temperature.
Modifications of fiber length by growth temperatures also have been observed
in planting-date studies in which the later planting dates were associated
with small increases in 2.5 and 50% span lengths . If the growing season is
long enough and other inhibitory factors do not interfere with fiber
development, early-season delays in fiber initiation and elongation may be
counteracted by an extension of the elongation period .
Variations in fiber length and the elongation period also were associated
with relative heat-unit accumulations. Regression analyses showed that
genotypes that produced longer fibers were more responsive to heat-unit
accumulation levels than were genotypes that produced shorter fibers .
However, the earliness of the genotype was also a factor in the relationship
between fiber length (and short-fiber content by weight) and accumulated
heat units .
As temperature increased, the number of small motes per boll also increased.
Fertilization efficiency, which was negatively correlated with small-mote
frequency, also decreased. Although fiber length did not change
significantly with increasing temperature, the percentage of short-fibers
was lower when temperatures were higher. The apparent improvement in fiber
length uniformity may be related to increased assimilate availability to the
fibers because there were fewer seeds per boll.
FIBER LENGTH AND WATER:
Cotton water relationships and irrigation traditionally have been studied
with respect to yield . Fiber length was not affected unless the water
deficit was great enough to lower the yield to 700 kg ha-1. Fiber elongation
was inhibited when the midday water potential was -2.5 to -2.8 mPa.
Occurrence of moisture deficits during the early flowering period did not
alter fiber length. However, when drought occurred later in the flowering
period, fiber length was decreased .
Severe water deficits during the fiber elongation stage reduce fiber length
, apparently due simply to the direct mechanical and physiological processes
of cell expansion. However, water availability and the duration and timing
of flowering and boll set can result in complex physiological interactions
between water deficits and fiber properties including length.
FIBRE LENGTH AND LIGHT:
Changes in the growth environment also alter canopy structure and the photon
flux environment within the canopy. For example, loss of leaves and bolls
from unfavorable weather (wind, hail), disease, or herbivory and
compensatory regrowth can greatly affect both fiber yield and quality . The
amount of light within the crop canopy is an important determinant of
photosynthetic activity and, therefore, of the source-to-sink relationships
that allocate photoassimilate within the canopy . Eaton and Ergle (1954)
observed that reduced-light treatments increased fiber length. Shading
during the first 7 d after floral anthesis resulted in a 2% increase in the
2.5% span length .
Shading (or prolonged periods of cloudy weather) and seasonal shifts in day
length also modulate temperature, which modifies fiber properties, including
length.
Commercial cotton genotypes are considered to be day-length neutral with
respect to both flowering and fruiting . However, incorporation of
day-length data in upland and pima fiber-quality models, based on
accumulated heat units, increased the coefficients of determination for the
length predictors from 30 to 54% for the upland model and from 44 to 57% for
the pima model .
It was found that the light wavelengths reflected from red and green mulches
increased fiber length, even though plants grown under those mulches
received less reflected photosynthetic flux than did plants grown with white
mulches. The longest fiber was harvested from plants that received the
highest far red/red ratios.
FIBER LENGTH AND MINERAL NUTRITION:
Studies of the mineral nutrition of cotton and the related soil chemistry
usually have emphasized increased yield and fruiting efficiency . More
recently, the effects of nutrient stress on boll shedding have been examined
. Also, several mineral-nutrition studies have been extended to include
fiber quality .
Reports of fiber property trends following nutrient additions are often
contradictory due to the interactive effects of genotype, climate, and soil
conditions. Potassium added at the rate of 112 kg K ha-1yr-1 did not affect
the 2.5% span length , when genotype was a significant factor in determining
both 2.5 and 50% span lengths . Genotype was not a significant factor in
Acala fiber length, but an additional 480 kg K ha-1yr-1 increased the mean
fiber length . K ha-1yr-1 increased the length uniformity ratio and
increased 50%, but not 2.5% span length. Genotype and the interaction,
genotype-by-environment, determined the 2.5% span length.
As mentioned above, fiber length is assumed to be genotype-dependent, but
growth-environment fluctuations - both those resulting from seasonal and
annual variability in weather conditions and those induced by cultural
practices and inputs - modulate the range and mean of the fiber length
population at the test sample, bale, and crop levels.
Quantitation of fiber length is relatively straightforward and reproducible,
and fiber length (along with micronaire) is one of the most likely fiber
properties to be included when cotton production research is extended beyond
yield determinations. Other fiber properties are less readily quantified,
and the resulting data are not so easily understood or analyzed
statistically. This is particularly true of fiber-breaking strength, which
has become a crucial fiber property due to changes in spinning techniques.
FIBER STRENGTH:
The inherent breaking strength of individual cotton fibers is considered to
be the most important factor in determining the strength of the yarn spun
from those fibers . Recent developments in high-speed yarn spinning
technology, specifically open-end rotor spinning systems, have shifted the
fiber-quality requirements of the textile industry toward higher-strength
fibers that can compensate for the decrease in yarn strength associated with
open-end rotor spinning techniques.
Compared with conventional ring spinning, open-end rotor-spun yarn
production capacity is five times greater and, consequently, more
economical. Rotor-spun yarn is more even than the ring-spun, but is 15 to
20% weaker than ring-spun yarn of the same thickness. Thus, mills using
open-end rotor and friction spinning have given improved fiber strength
highest priority. Length and length uniformity, followed by fiber strength
and fineness, remain the most important fiber properties in determining
ring-spun yarn strength.
Historically, two instruments have been used to measure fiber tensile
strength, the Pressley apparatus and the Stelometer . In both of these
flat-bundle methods, a bundle of fibers is combed parallel and secured
between two clamps. A force to try to separate the clamps is applied and
gradually increased until the fiber bundle breaks. Fiber tensile strength is
calculated from the ratio of the breaking load to bundle mass. Due to the
natural lack of homogeneity within a population of cotton fibers, bundle
fiber selection, bundle construction and, therefore, bundle mass
measurements, are subject to considerable experimental error .
Fiber strength, that is, the force required to break a fiber, varies along
the length of the fiber, as does fiber fineness measured as perimeter,
diameter, or cross section Further, the inherent variability within and
among cotton fibers ensures that two fiber bundles of the same weight will
not contain the same number of fibers. Also, the within-sample variability
guarantees that the clamps of the strength testing apparatus will not grasp
the various fibers in the bundle at precisely equivalent positions along the
lengths. Thus, a normalizing length-weight factor is included in bundle
strength calculations.
In the textile literature, fiber strength is reported as breaking tenacity
or grams of breaking load per tex, where tex is the fiber linear density in
grams per kilometer . Both Pressley and stelometer breaking tenacities are
reported as 1/8 in. gauge tests, the 1/8 in. (or 3.2 mm) referring to the
distance between the two Pressley clamps. Flat-bundle measurements of fiber
strength are considered satisfactory for acceptance testing and for research
studies of the influence of genotype, environment, and processing on fiber
(bundle) strength and elongation.
The relationships between fiber strength and elongation and processing
success also have been examined using flat-bundle strength testing methods .
However cotton fiber testing today requires that procedures be rapid,
reproducible, automated, and without significant operator bias.
Consequently, the HVI systems used for length measurements in USDA-AMS
classing offices are also used to measure the breaking strength of the same
fiber bundles (beards) formed during length measurement.
Originally, HVI strength tests were calibrated against the 1/8-in. gauge
Pressley measurement, but the bundle-strengths of reference cottons are now
established by Stelometer tests that also provide bundle elongation-percent
data. Fiber bundle elongation is measured directly from the displacement of
the jaws during the bundle-breaking process, and the fiber bundle strength
and elongation data usually are reported together (ASTM, 1994, D 4604-86).
The HVI bundle-strength measurements are reported in grams-force tex-1 and
can range from 30 and above (very strong) to 20 or below (very weak). In
agronomic papers, fiber strengths are normally reported as kN m kg-1, where
one Newton equals 9.81 kg-force .
The HVI bundle-strength and elongation-percent testing methods are
satisfactory for acceptance testing and research studies when 3.0 to 3.3 g
of blended fibers are available and the relative humidity of the testing
room is adequately controlled. A 1% increase in relative humidity and the
accompanying increase in fiber moisture content will increase the strength
value by 0.2 to 0.3 g tex-1, depending on the fiber genotype and maturity.
Further, classing-office HVI measurements of fiber strength do not
adequately describe the variations of fiber strength along the length of the
individual fibers or within the test bundle. Thus, predictions of yarn
strength based on HVI bundle-strength data can be inadequate and misleading
. The problem of fiber-strength variability is being addressed by improved
HVI calibration methods and by computer simulations of bundle-break tests in
which the simulations are based on large single-fiber strength databases of
more than 20 000 single fiber long-elongation curves obtained with MANTIS .
Fiber Strength, Environment, and Genotype:
Reports of stelometer measurements of fiber bundle strength are relatively
rare in the refereed agronomic literature. Consequently, the interactions of
environment and genotype in determining fiber strength are not as well
documented as the corresponding interactions that modulate fiber length.
Growth environment, and genotype response to that environment, play a part
in determining fiber strength and strength variability .
Early studies showed fiber strength to be significantly and positively
correlated with maximum or mean growth temperature, maximum minus minimum
growth temperature, and potential insolation . Increased strength was
correlated with a decrease in precipitation. Minimum temperature did not
affect fiber strength. All environmental variables were interrelated, and a
close general association between fiber strength and environment was
interpreted as indicating that fiber strength is more responsive to the
growth environment than are fiber length and fineness. Other investigators
reported that fiber strength was correlated with genotype only.
Square removal did not affect either fiber elongation or fiber strength .
Shading, leaf-pruning, and partial fruit removal decreased fiber strength .
Selective square removal had no effect on fiber strength in bolls at the
first, second, or third position on a fruiting branch . Fiber strength was
slightly greater in bolls from the first 4 to 6 wk of flowering, compared
with fibers from bolls produced by flowers opening during the last 2 wk of
the flowering period .
In that study, fiber strength was positively correlated with heat unit
accumulation during boll development, but genotype, competition among bolls,
assimilatory capacity, and variations in light environment also helped
determine fiber strength. Early defoliation, at 20% open bolls, increased
fiber strength and length, but the yield loss due to earlier defoliation
offset any potential improvement in fiber quality .
FIBER MATURITY:
Of the fiber properties reported by USDA-AMS classing offices for use by the
textile industry, fiber maturity is probably the least well-defined and most
misunderstood. The term, fiber maturity, used in cotton marketing and
processing is not an estimate of the time elapsed between floral anthesis
and fiber harvest . However, such chronological maturity can be a useful
concept in studies that follow fiber development and maturation with time .
On the physiological and the physical bases, fiber maturity is generally
accepted to be the degree (amount) of fiber cell-wall thickening relative to
the diameter or fineness of the fiber .
Classically, a mature fiber is a fiber in which two times the cell wall
thickness equals or exceeds the diameter of the fiber cell lumen, the space
enclosed by the fiber cell walls . However, this simple definition of fiber
maturity is complicated by the fact that the cross section of a cotton fiber
is never a perfect circle; the fiber diameter is primarily a genetic
characteristic.
Further, both the fiber diameter and the cell-wall thickness vary
significantly along the length of the fiber. Thus, attempting to
differentiate, on the basis of wall thickness, between naturally thin-walled
or genetically fine fibers and truly immature fibers with thin walls greatly
complicates maturity comparisons among and within genotypes.
Within a single fiber sample examined by image analysis, cell-wall thickness
ranged from 3.4 to 4.9 µm when lumen diameters ranged from 2.4 to 5.2 µm .
Based on the cited definition of a mature fiber having a cell-wall thickness
two times the lumen diameter, 90% of the 40 fibers in that sample were
mature, assuming that here had been no fiber-selection bias in the
measurements.
Unfortunately, none of the available methods for quantifying cell-wall
thickness is sufficiently rapid and reproducible to be used by agronomists,
the classing offices, or fiber processors. Fiber diameter can be quantified,
but diameter data are of limited use in determining fiber maturity without
estimates of the relationship between lumen width and wall thickness.
Instead, processors have attempted to relate fiber fineness to processing
outcome.
Estimating Fiber Fineness:
Fiber fineness has long been recognized as an important factor in yarn
strength and uniformity, properties that depend largely on the average
number of fibers in the yarn cross section. Spinning larger numbers of finer
fibers together results in stronger, more uniform yarns than if they had
been made up of fewer, thicker fibers . However, direct determinations of
biological fineness in terms of fiber or lumen diameter and cell-wall
thickness are precluded by the high costs in both time and labor, the
noncircular cross sections of dry cotton fibers, and the high degree of
variation in fiber fineness.
Advances in image analysis have improved determinations of fiber biological
fineness and maturity , but fiber image analyses remain too slow and limited
with respect to sample size for inclusion in the HVI-based cotton-classing
process.
Originally, the textile industry adopted gravimetric fiber fineness or
linear density as an indicator of the fiber-spinning properties that depend
on fiber fineness and maturity combined . This gravimetric fineness testing
method was discontinued in 1989, but the textile linear density unit of tex
persists. Tex is measured as grams per kilometer of fiber or yarn, and fiber
fineness is usually expressed as millitex or micrograms per meter . Earlier,
direct measurements of fiber fineness (either biological or gravimetric)
subsequently were replaced by indirect fineness measurements based on the
resistance of a bundle of fibers to airflow.
The first indirect test method approved by ASTM for measurement of fiber
maturity, lineardensity, and maturity index was the causticaire method. In
that test, the resistance of a plug of cotton to airflow was measured before
and after a cell-wall swelling treatment with an 18% (4.5 M) solution of
NaOH (ASTM, 1991, D 2480-82). The ratio between the rate of airflow through
an untreated and then treated fiber plug was taken as indication of the
degree of fiber wall development. The airflow reading for the treated sample
was squared and corrected for maturity to serve as an indirect estimate of
linear density. Causticaire method results were found to be highly variable
among laboratories, and the method never was recommended for acceptance
testing before it was discontinued in 1992.
The arealometer was the first dual-compression airflow instrument for
estimating both fiber fineness and fiber maturity from airflow rates through
untreated raw cotton (ASTM, 1976, D 1449-58; Lord and Heap, 1988). The
arealometer provides an indirect measurement of the specific surface area of
loose cotton fibers, that is, the external area of fibers per unit volume
(approximately 200-mg samples in four to five replicates). Empirical
formulae were developed for calculating the approximate maturity ratio and
the average perimeter, wall thickness, and weight per inch from the specific
surface area data. The precision and accuracy of arealometer determinations
were sensitive to variations in sample preparation, to repeated sample
handling, and to previous mechanical treatment of the fibers, e.g.,
conditions during harvesting, blending, and opening. The arealometer was
never approved for acceptance testing, and the ASTM method was withdrawn in
1977 without replacement.
The variations in biological fineness and relative maturity of cotton fibers
that were described earlier cause the porous plugs used in air-compression
measurements to respond differently to compression and, consequently, to
airflow . The IIC-Shirley Fineness/Maturity Tester (Shirley FMT), a
dual-compression instrument, was developed to compensate for this
plug-variation effect (ASTM, 1994, D 3818-92). The Shirley FMT is considered
suitable for research, but is not used for acceptance testing due to low
precision and accuracy. Instead, micronaire has become the standard estimate
of both fineness and maturity in the USDA-AMS classing offices.
Fiber Maturity and Environment:
Whatever the direct or indirect method used for estimating fiber maturity,
the fiber property being as sayed remains the thickness of the cell wall.
The primary cell wall and cuticle (together »0.1 µm thick) make up about
2.4% of the total wall thickness ( »4.1 µm of the cotton fiber thickness at
harvest) . The rest of the fiber cell wall (»98%) is the cellulosic
secondary wall, which thickens significantly as polymerized photosynthate is
deposited during fiber maturation. Therefore, any environmental factor that
affects photosynthetic C fixation and cellulose synthesis will also modulate
cotton fiber wall thickening and, consequently, fiber physiological
maturation
Fiber Maturity and Temperature and Planting Date:
The dilution, on a weight basis, of the chemically complex primary cell wall
by secondary-wall cellulose has been followed with X-ray fluorescence
spectroscopy. This technique determines the decrease, with time, in the
relative weight ratio of the Ca associated with the pectin-rich primary wall
. Growth-environment differences between the two years of the studies cited
significantly altered maturation rates, which were quantified as rate of Ca
weight-dilution, of both upland and pima genotypes. The rates of secondary
wall deposition in both upland and pima genotypes were closely correlated
with growth temperature; that is, heat-unit accumulation .
Micronaire (micronAFIS) also was found to increase linearly with time for
upland and pima genotypes . The rates of micronaire increase were correlated
with heat-unit accumulations . Rates of increase in fiber cross-sectional
area were less linear than the corresponding micronaire-increase rates, and
rates of upland and pima fiber cell-wall thickening were linear and without
significant genotypic effect .
Environmental modulation of fiber maturity (micronaire) by temperature was
most often identified in planting- and flowering-date studies . The effects
of planting date on micronaire, Shirley FMT fiber maturity ratio, and fiber
fineness (in millitex) were highly significant in a South African study (Greef
and Human, 1983). Although genotypic differences were detected among the
three years of that study, delayed planting generally resulted in lower
micronaire. The effect on fiber maturity of late planting was repeated in
the Shirley FMT maturity ratio and fiber fineness data.
Planting date significantly modified degree of thickening, immature fiber
fraction, cross-sectional area, and micronaire (micronAFIS) of four upland
genotypes that also were grown in South Carolina . In general, micronaire
decreased with later planting, but early planting also reduced micronaire of
Deltapine 5490, a long-season genotype, in a year when temperatures were
suboptimal during the early part of the season.
Harvest dates in this study also were staggered so that the length of the
growing season was held constant within each year. Therefore, season-length
should not have been an important factor in the relationships found between
planting date and fiber maturity.
Fiber Maturity and Source-Sink Manipulation:
Variations in fiber maturity were linked with source-sink modulations
related to flowering date , and seed position within the bolls . However,
manipulation of source-sink relationships by early-season square (floral
bud) removal had no consistently significant effect on upland cotton
micronaire in one study . However, selective square removal at the first,
second, and third fruiting sites along the branches increased micronaire,
compared with controls from which no squares had been removed beyond natural
square shedding . The increases in micronaire after selective square
removals were associated with increased fiber wall thickness, but not with
increased strength of elongation percent. Early-season square removal did
not affect fiber perimeter or wall thickness (measured by arealometer) .
Partial defruiting increased micronaire and had no consistent effect on
upland fiber perimeter in bolls from August flowers.
Fiber Maturity and Water:
Generous water availability can delay fiber maturation (cellulose
deposition) by stimulating competition for assimilates between early-season
bolls and vegetative growth . Adequate water also can increase the maturity
of fibers from mid-season flowers by supporting photosynthetic C fixation.
In a year with insufficient rainfall, initiating irrigation when the
first-set bolls were 20-d old increased micronaire, but irrigation
initiation at first bloom had no effect on fiber maturity. Irrigation and
water-conservation effects on fiber fineness (millitex) were inconsistent
between years, but both added water and mulching tended to increase fiber
fineness. Aberrations in cell-wall synthesis that were correlated with
drought stress have been detected and characterized by glycoconjugate
analysis .
An adequate water supply during the growing season allowed maturation of
more bolls at upper and outer fruiting positions, but the mote counts tended
to be higher in those extra bolls and the fibers within those bolls tended
to be less mature . Rainfall and the associated reduction in insolation
levels during the blooming period resulted in reduced fiber maturity .
Irrigation method also modified micronaire levels and distributions among
fruiting sites.
Early-season drought resulted in fibers of greater maturity and higher
micronaire in bolls at branch positions 1 and 2 on the lower branches of
rainfed plants. However, reduced insolation and heavy rain reduced
micronaire and increased immature fiber fractions in bolls from flowers that
opened during the prolonged rain incident. Soil water deficit as well as
excess may reduce micronaire if the water stress is severe or prolonged .
Fiber Maturity and Genetic Improvement:
Micronaire or maturity data now appear in most cotton improvement reports .
In a five-parent half-diallel mating design, environment had no effect on
HVI micronaire . However, a significant genotypic effect was found to be
associated with differences between parents and the F1 generation and with
differences among the F1 generation. The micronaire means for the parents
were not significantly different, although HVI micronaire means were
significantly different for the F1 generation as a group. The HVI was judged
to be insufficiently sensitive for detection of the small difference in
fiber maturity resulting from the crosses.
In another study, F2 hybrids had finer fibers (lower micronaire) than did
the parents, but the improvements were deemed too small to be of commercial
value. Unlike the effects of environment on the genetic components of other
fiber properties, variance in micronaire due to the genotype-by-environment
interaction can reach levels expected for genetic variance in length and
strength . Significant interactions were found between genetic additive
variance and environmental variability for micronaire, strength, and span
length in a study of 64 F2 hybrids .
The strong environmental components in micronaire and fiber maturity limit
the usefulness of these fiber properties in studies of genotypic differences
in response to growth environment. Based on micronaire, fiber maturity,
cell-wall thickness, fiber perimeter, or fiber fineness data, row spacing
had either no or minimal effect on okra-leaf or normal-leaf genotypes .
Early planting reduced micronaire, wall-thickness, and fiber fineness of the
okra-leaf genotype in one year of that study. In another study of leaf
pubescence, nectaried vs. no nectaries, and leaf shape, interactions with
environment were significant but of much smaller magnitude than the
interactions among traits .
Micronaire means for Bt transgenic lines were higher than the micronaire
means of Coker 312 and MD51ne when those genotypes were grown in Arizona .
In two years out of three, micronaire means of all genotypes in this study,
including the controls, exceeded 4.9; in other words, were penalty grade.
This apparent undesirable environmental effect on micronaire may have been
caused by a change in fiber testing methods in the one year of the three for
which micronaire readings were below the upper penalty limit. Genotypic
differences in bulk micronaire may either be emphasized or minimized,
depending on the measurement method used .
GRADE:
In U.S. cotton classing, nonmandatory grade standards were first established
in 1909, but compulsory upland grade standards were not set until 1915 .
Official pima standards were first set in 1918. Grade is a composite
assessment of three factors - color, leaf, and preparation . Color and trash
(leaf and stem residues) can be quantified instrumentally, but traditional,
manual cotton grade classification is still provided by USDA-AMS in addition
to the instrumental HVI trash and color values. Thus, cotton grade reports
are still made in terms of traditional color and leaf grades; for example,
light spotted, tinged, strict low middling.
Preparation:
There is no approved instrumental measure of preparation - the degree of
roughness/smoothness of the ginned lint. Methods of harvesting, handling,
and ginning the cotton fibers produce differences in roughness that are
apparent during manual inspection; but no clear correlations have been found
between degree of preparation and spinning success. The frequency of tangled
knots or mats of fiber (neps) may be higher in high-prep lint, and both the
growth and processing environments can modulate nep frequency . However,
abnormal preparation occurs in less than 0.5% of the U.S. crop during
harvesting and ginning.
Trash or Leaf Grade:
Even under ideal field conditions, cotton lint becomes contaminated with
leaf residues and other trash . Although most foreign matter is removed by
cleaning processes during ginning, total trash extraction is impractical and
can lower the quality of ginned fiber. In HVI cotton classing, a video
scanner measures trash in raw cotton, and the trash data are reported in
terms of the total trash area and trash particle counts (ASTM, D 4604-86, D
4605-86). Trash content data may be used for acceptance testing. In 1993,
classer's grade was split into color grade and leaf grade . Other factors
being equal, cotton fibers mixed with the smallest amount of foreign matter
have the highest value. Therefore, recent research efforts have been
directed toward the development of a computer vision system that measures
detailed trash and color attributes of raw cotton .
The term leaf includes dried, broken plant foliage, bark, and stem particles
and can be divided into two general categories: large-leaf and pin or pepper
trash . Pepper trash significantly lowers the value of the cotton to the
manufacturer, and is more difficult and expensive to remove than the larger
pieces of trash.Other trash found in ginned cotton can include stems, burs,
bark, whole seeds, seed fragments, motes (underdeveloped seeds), grass,
sand, oil, and dust. The growth environment obviously affects the amount of
wind-borne contaminants trapped among the fibers. Environmental factors that
affect pollination and seed development determine the frequency of
undersized seeds and motes.
Reductions in the frequencies of motes and small-leaf trash also have been
correlated with semi-smooth and super-okra leaf traits . Environment (crop
year), harvest system, genotype, and second order interactions between those
factors all had significant effects on leaf grade . Delayed harvest resulted
in lower-grade fiber. The presence of trash particles also may affect
negatively the color grade.
Fiber Color:
Raw fiber stock color measurements are used in controlling the color of
manufactured gray, bleached, or dyed yarns and fabrics . Of the three
components of cotton grade, fiber color is most directly linked to growth
environment. Color measurements also are correlated with overall fiber
quality so that bright (reflective, high Rd), creamy-white fibers are more
mature and of higher quality than the dull, gray or yellowish fibers
associated with field weathering and generally lower fiber quality .
Although upland cotton fibers are naturally white to creamy-white,
pre-harvest exposure to weathering and microbial action can cause fibers to
darken and to lose brightness.
Premature termination of fiber maturation by applications of growth
regulators, frost, or drought characteristically increases the saturation of
the yellow (+b) fiber-color component. Other conditions, including insect
damage and foreign matter contamination, also modify fiber color.
The ultimate acceptance test for fiber color, as well as for finished yarns
and fabrics, is the human eye. Therefore, instrumental color measurements
must be correlated closely with visual judgment. In the HVI classing system,
color is quantified as the degrees of reflectance (Rd) and yellowness (+b),
two of the three tri-stimulus color scales of the Nickerson-Hunter
colorimeter.
Fiber maturity has been associated with dye-uptake variability in finished
yarn and fabric, but the color grades of raw fibers seldom have been linked
to environmental factors or agronomic practices during production.
Other Environmental Effects on Cotton Fiber Quality:
Although not yet included in the USDA-AMS cotton fiber classing system,
cotton stickiness is becoming an increasingly important problem . Two major
causes of cotton stickiness are insect honeydew from whiteflies and aphids
and abnormally high levels of natural plant sugars, which are often related
to premature crop termination by frost or drought. Insect honeydew
contamination is randomly deposited on the lint in heavy droplets and has a
devastating production-halting effect on fiber processing.
The cost of clearing and cleaning processing equipment halted by sticky
cotton is so high that buyers have included honeydew free clauses in
purchase contracts and have refused cotton from regions known to have
insect-control problems. Rapid methods for instrumental detection of
honeydew are under development for use in classing offices and mills .
FIBER QUALITY OR FIBER YIELD?
Like all agricultural commodities, the value of cotton lint responds to
fluctuations in the supply-and-demand forces of the marketplace. In
addition, pressure toward specific improvements in cotton fiber quality -
for example, the higher fiber strength needed for today's high-speed
spinning - has been intensified as a result of technological advances in
textile production and imposition of increasingly stringent quality
standards for finished cotton products.
Changes in fiber-quality requirements and increases in economic competition
on the domestic and international levels have resulted in fiber quality
becoming a value determinant equal to fiber yield . Indeed, it is the
quality, not the quantity, of fibers ginned from the cotton seeds that
decides the end use and economic value of a cotton crop and, consequently,
determines the profit returned to both the producers and processors.
Wide differences in cotton fiber quality and shifts in demand for particular
fiber properties, based on end-use processing requirements, have resulted in
the creation of a price schedule, specific to each crop year, that includes
premiums and discounts for grade, staple length, micronaire, and strength .
This price schedule is made possible by the development of rapid,
quantitative methods for measuring those fiber properties considered most
important for successful textile production . With the wide availability of
fiber-quality data from HVI, predictive models for ginning, bale-mix
selection, and fiber-processing success could be developed for textile mills
.
Price-analysis systems based on HVI fiber-quality data also became feasible
. Quantitation, predictive modeling, and statistical analyses of what had
been subjective and qualitative fiber properties are now both practical and
common in textile processing and marketing.
Field-production and breeding researchers, for various reasons, have failed
to take full advantage of the fiber-quality quantitation methods developed
for the textile industry. Most field and genetic improvement studies still
focus on yield improvement while devoting little attention to fiber quality
beyond obtaining bulk fiber length, strength, and micronaire averages for
each treatment . Indeed, cotton crop simulation and mapping models of the
effects of growth environment on cotton have been limited almost entirely to
yield prediction and cultural-input management.
Plant physiological studies and textile-processing models suggest that bulk
fiber-property averages at the bale, module, or crop level do not describe
fiber quality with sufficient precision for use in a vertical integration of
cotton production and processing. More importantly, bulk fiber-property
means do not adequately and quantitatively describe the variation in the
fiber populations or plant metabolic responses to environmental factors
during the growing season. Such pooled or averaged descriptors cannot
accurately predict how the highly variable fiber populations might perform
during processing.
Meaningful descriptors of the effects of environment on cotton fiber quality
await high-resolution examinations of the variabilities, induced and
natural, in fiber-quality averages. Only then can the genetic and
environmental sources of fiber-quality variability be quantified, predicted,
and modulated to produce the high-quality cotton lint demanded by today's
textile industry and, ultimately, the consumer.
Increased understanding of the physiological responses to the environment
that interactively determine cotton fiber quality is essential. Only with
such knowledge can real progress be made toward producing high yields of
cotton fibers that are white as snow, as strong as steel, as fine as silk,
and as uniform as genotypic responses to the environment will allow.
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