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CROP ECOLOGY, MANAGEMENT & QUALITY

Plant Density Modifies Within-Canopy Cotton Fiber Quality

^a University of Georgia, Coastal Plain Experiment Station, P.O. Box 748, Tifton, GA 31793
^b Cotton Incorporated, 6399 Weston Parkway, Cary, NC 27513
^c University of Georgia, Rural Development Center, P.O. Box 1209, Tifton, GA 31793

^* Corresponding author (cbednarz{at}uga.edu)

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS REFERENCES

 
Modifying fruit distribution through varying plant density may affect cotton fiber quality. This study was conducted to determine how fiber quality of cotton (Gossypium hirsutum L.) is manipulated through plant density and fruiting position. Two cotton cultivars were over seeded and hand thinned to 3.6, 9.0, 12.6, and 21.5 plants m^–2 at the University of Georgia in 2001 and 2002. Immediately before machine harvest, plants from 6 m of one center row were removed from each plot and hand harvested by fruiting position. After hand harvest, seed cotton from each fruiting position was ginned separately for fiber quality analysis. Much of the data collected in this investigation suggest two recurring patterns with respect to fiber quality and fruiting position. First, the superior fruiting positions in terms of overall fiber quality (i.e., longer, more uniform and mature fibers) occur at first sympodial positions generally in the midcanopy region (i.e., main stem nodes 10–17), also known as inner fruiting positions. The second recurring pattern in this investigation suggests lower plant densities resulted in more desirable fiber properties at these inner fruiting positions. These data suggest reducing the percentage of the total yield produced at inner fruiting positions through reduced plant densities increased the source-to-sink ratio during boll filling in this region of the canopy, resulting in improved fiber properties. If this is true, modifications in crop management may increase the source-to-sink ratio during boll filling of the remaining fruiting positions (i.e., outer fruiting positions), possibly resulting in greater improvements in fiber quality.

	INTRODUCTION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS REFERENCES

 
ADVANCES in yarn spinning and fabric manufacturing technologies have improved the fiber processing efficiency of the U.S. textile industry (Deussen, 1992). To operate at peak efficiency, however, these newer technologies must process cotton fibers of high quality (Faerber, 1995). Accordingly, the United States Department of Agriculture (USDA)/Commodity Credit Corporation (CCC) modified the Schedule of Premiums and Discounts for Upland and Extra Long Staple Cotton. The most notable changes to the schedule were the inclusion of fiber length uniformity (a measure of the degree of length uniformity of the fibers in a sample) and an increase in the base level for fiber strength (level of fiber strength at which no price premium or discount is received). Beginning with the 2000 crop, the CCC schedule applied price premiums or discounts to cotton that exceeded or failed to meet these newly established standards. Some textile manufacturers, however, have already adopted their own standards for fiber length uniformity and have even begun to discriminate against cottons produced in certain regions of the U.S. Cotton Belt simply because historical records from these regions indicate they generally do not meet the in-house standards. Thus, if U.S. cotton is to remain competitive on a global market, fiber quality must meet these new standards.

Unfortunately, between 1998 and 2002, the quality of U.S. cotton actually declined. Some have speculated this deterioration is due to the wide spread adoption of transgenic cotton cultivars that were inadequately tested for yield and fiber quality before their release. Others have conjectured the decline in fiber quality resulted from changes in crop management that arose from adoption of transgenic cotton cultivars. For instance, technology fees associated with transgenic cotton cultivars are an economic incentive for the grower to reduce seeding rates. Bednarz et al. (2000) illustrated that the fruiting habit of cotton may impart yield stability with reduced seeding rates or plant densities through the production of fruit on longer sympodial branches, additional main stem nodes, and additional monopodial branches. It is generally believed, however, that lint produced on monopodial branches, more apical main stem nodes, and more distal sympodial branch fruiting positions (i.e., exterior fruiting positions) is lower in quality (Bernhardt and Phillips, 1986; Knight, 1988; Crawley, 1999). As plant density is decreased, the percentage of the total yield produced at these exterior fruiting sites is increased (Bednarz et al., 2000). Thus, it seems reasonable that less desirable fiber quality may result from reduced plant densities. Therefore, the objectives of this investigation were to determine how fiber quality of cotton is affected by plant density.

	MATERIALS AND METHODS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS REFERENCES

 
Plot Establishment and Maintenance:
Experiments were conducted in 2001 at the Coastal Plain Experiment Station in Tifton, GA, on a Tifton loamy sand (Fine-loamy, kaolinitic, thermic Plinthic Kandiudults) and in 2001 and 2002 at the Southwest Branch Experiment Station in Plains, GA, on a Greenville sandy clay loam (Fine, kaolinitic, thermic Rhodic Kandiudults). In March of each year, 672 kg ha^–1 of 3–9-18 plus micronutrients (8% Ca, 2% Mg, 9% S, 0.13% B, 0.10% Fe, 1% Mn, and 0.35% Zn) was broadcast and harrow incorporated. Trifluralin (,,-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine; 1.12 kg a.i. ha^–1) was then broadcast and harrow incorporated immediately before ripping and bedding. While ripping and bedding, 32 kg a.i. ha^–1 of 1,3-dichloropropene was injected under the row for nematode control at Tifton. All other fertility, weed, and insect-pest control practices were in accordance with the University of Georgia Cooperative Extension Service Guidelines (Brown et al., 2001). Water stress was minimized with overhead sprinkler irrigation in all studies. Cotton (cvs. DPL 458 BR and FM 966) was over seeded on 10 and 14 May 2001 at Tifton and Plains, respectively, and 12 May 2002 at Plains and hand thinned to 3.6, 9.0, 12.6, and 21.5 plants m^–2 on stand establishment (i.e., approximately 3 wk after planting). Each plot was 4 rows (0.9-m centers) wide and 38 m long. The two cultivars chosen for this study were selected on the basis of fiber quality. One cultivar, DPL 458 BR, generally does not produce highly desirable fiber qualities while the other cultivar, FM 966, does. Since the focus of this study was fiber quality, both cultivars were managed as non-transgenic. Harvest aids were applied at approximately 70% open boll in each study and were a combination of tribufos (S,S,S-tributyl phosphorotrithioate; 0.321 kg a.i. ha^–1) plus thidiazuron (N-phenyl-N'-1,2,3-thiadiazol-5-ylurea; 0.093 kg a.i. ha^–1) plus ethephon [(2-chloroethyl)phosphonic acid; 1.103 kg a.i. ha^–1].

Data Collection
Immediately before machine harvest, plants in approximately 1 m of row were removed from each end of all plots with a 2.1 m-wide Bush Hog mower (Bush Hog, Incorporated, Selma, AL) to avoid inaccurate measures of plot yield and fiber quality due to the end-of-row effect (Holman and Bednarz, 2001). After all plots were machine harvested the seed cotton was shipped to the USDA/Agricultural Research Service/Cotton Ginning Research Unit in Stoneville, MS, for ginning. The focus of this portion of the study was lint yield and fiber quality differences at the field level and has been reported (Bednarz et al., 2005).

Also immediately before machine harvest, plants from 6 m of one of the center rows were removed from each plot and hand harvested by fruiting position. After hand harvest, seed cotton from each fruiting position was ginned separate with a table-top laboratory gin and delivered to Cotton Incorporated (Cary, NC) for fiber quality analysis. The focus of this portion of the study was fiber quality differences among the different fruiting positions within the canopy. Fiber quality was determined with an Uster Technologies (Charlotte, NC) Advanced Fiber Information System (AFIS) instrument. AFIS measures the properties of approximately 3000 individual fibers per sample by optical analysis. In the current study, the AFIS function that expresses the results on a weight basis (rather than by fiber number) is reported because textile mills manage their fiber stock by weight. AFIS measurements presented herein include (on a weight basis) length in cm, percentage variation in length, upper quartile length in cm (i.e., length of the longest 25% of the fibers), percentage short fiber content (i.e., percentage of fibers less than 1.27 cm in length), fineness in mg km^–1, and the immature fiber content.

While four plant densities were utilized in this investigation, for clarity only two plant densities are presented. The two plant densities presented (9.0 and 12.6 plants m^–2) are consistent with the greater majority of the U.S. cotton acreage. Also, the data not presented represent plant densities that would be less profitable for the producer and did not provide additional information for this investigation.

Statistical Analyses
First sympodial position data were analyzed as a split plot design where the factorial arrangement of treatments (cultivar x plant density) was the main plot and main stem nodes were the split plot factor for each environment. Replications (rep), rep x factorial treatments, and rep x main stem node were considered random effects in the mixed model analysis. Factorial effects, main stem node, and factorial effects x main stem node were considered fixed effects. The Satterthwaite method of determining the error degrees of freedom (df) was also specified.

Means for bolls at each sympodial branch position at each main stem node were computed for each plot within an environment. These data were analyzed for each environment by a split plot design, where the factorial arrangement of treatments was the main plot and sympodial branch position was the split plot. Replications (rep), rep x factorial treatments, and rep x sympodial branch position were considered random in the mixed model analysis. Factorial effects, sympodial branch position, and factorial effects x sympodial branch position were considered fixed effects. The Satterthwaite method of determining the error df was again used.

	RESULTS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS REFERENCES

 
Fiber Lengths (Weight Based)
At the field level (i.e., when plots were machine harvested, blending seed cotton across fruiting positions, and ginned together), AFIS mean fiber length did not differ among plant densities (Bednarz et al., 2005). At the canopy level (i.e., when plots were hand harvested, segregating seed cotton across fruiting positions, and ginned separately), plant density differences in AFIS mean fiber length were observed at Plains, GA, in 2002 (Table 1). Generally, the lower plant densities resulted in longer AFIS mean fiber lengths in this environment. Sympodial branch fruiting position differences were observed at Tifton, GA, in 2001 (Table 1). AFIS mean fiber length decreased with increasing sympodial branch fruiting position in this environment. These results are consistent with those of Knight (1988) and Crawley (1999). Plant density x sympodial branch fruiting position interactions were not observed in any environment (Table 1).

View larger version (20K): [in this window] [in a new window]   Fig. 1. First sympodial position Advanced Fiber Information System (AFIS) mean fiber length (weight based) in studies conducted at the University of Georgia in 2001 and 2002. Plains, GA 2001 P > F: Cultivar (C), <0.0001; Density (D), 0.1165; CxD, 0.0284; Node (N), <0.0001; CxN, <0.0001; DxN, 0.0056; CxDxN, 0.0702; LSD = 0.052. Tifton, GA 2001 P > F: Cultivar (C), 0.0003; Density (D), 0.7595; CxD, 0.7164; Node (N), 0.0063; CxN, 0.0341; DxN, 0.0073; CxDxN, 0.6080; LSD = 0.051. Plains, GA 2002 P > F: Cultivar (C), <0.0001; Density (D), 0.0039; CxD, 0.5752; Node (N), <0.0001; CxN, 0.0058; DxN, <0.0001; CxDxN, 0.0025; LSD = 0.053.

AFIS upper quartile length (average fiber length of the longest 25% of fibers; weight based) data were also recorded by fruiting position. These data closely mirrored the AFIS mean fiber length data and are not presented.

At the field level, AFIS fiber length coefficient of variation (a measure of the variability of fiber lengths in a sample, weight based) was reduced in the lower plant densities (Bednarz et al., 2005). At the canopy level, plant density differences in AFIS fiber length coefficient of variation were observed in all environments (Table 2). Generally, the lower plant densities resulted in reduced AFIS fiber length coefficient of variation. Sympodial branch fruiting position differences were observed at Plains and Tifton, GA, in 2001 (Table 2). Plant density x sympodial branch fruiting position interactions were observed in Plains, GA, 2001 (Table 2). In Tifton, GA, 2001, AFIS fiber length coefficient of variation increased with increasing sympodial branch fruiting position.

View larger version (19K): [in this window] [in a new window]   Fig. 2. First sympodial position Advanced Fiber Information System (AFIS) fiber length coefficient of variation (weight based) in studies conducted at the Univeristy of Georgia in 2001 and 2002. Plains, GA 2001 P > F: Cultivar (C), 0.0456; Density (D), 0.1642; CxD, 0.3028; Node (N), <0.0001; CxN, 0.0038; DxN, 0.0224; CxDxN, 0.1987; LSD = 1.197. Tifton, GA 2001 P > F: Cultivar (C), 0.1042; Density (D), 0.1712; CxD, 0.7434; Node (N), <0.0001; CxN, 0.0748; DxN, 0.0476; CxDxN, 0.0309; LSD = 1.093. Plains, GA 2002 P > F: Cultivar (C), 0.1289; Density (D), 0.0012; CxD, 0.3757; Node (N), <0.0001; CxN, 0.0295; DxN, 0.0005; CxDx N, 0.3624; LSD = 1.559.

AFIS short fiber content (fibers less than 1.27 cm in length) data were also recorded by fruiting position. These data closely mirrored the AFIS mean fiber length coefficient of variation data and are not presented. Generally, as fiber length coefficient of variation increased, short fiber content increased as well.

Fiber Fineness and Maturity
At the field level, AFIS fineness was reduced in the higher plant densities (Bednarz et al., 2005). At the canopy level, plant density differences in AFIS fineness were observed in all environments (Table 3) with the higher plant densities resulting in lower AFIS fineness. Sympodial branch fruiting position differences were observed in all environments (Table 3). Generally, the distal sympodial branch positions produced fibers with lower AFIS fineness. These results are also consistent with those of Knight (1988) and Crawley (1999). Plant density x sympodial branch fruiting position interactions were observed in Plains, and Tifton, GA 2001 (Table 3).

View larger version (20K): [in this window] [in a new window]   Fig. 3. First sympodial position Advanced Fiber Information System (AFIS) fineness in studies conducted at the University of Georgia in 2001 and 2002. Plains, GA 2001 P > F: Cultivar (C), <0.0001; Density (D), <0.0001; CxD, 0.6795; Node (N), <0.0001; CxN, <0.0001; DxN, 0.0006; CxDxN, 0.0933; LSD = 3.963. Tifton, GA 2001 P > F: Cultivar (C), <0.0001; Density (D), 0.0382; CxD, 0.3385; Node (N), <0.0001; CxN, 0.7449; DxN, 0.1081; CxDxN, 0.0314; LSD = 3.903. Plains, GA 2002 P > F: Cultivar (C), <0.0001; Density (D), 0.0003; CxD, 0.2029; Node (N), <0.0001; CxN, <0.0001; DxN, 0.0003; CxDxN, 0.8423; LSD = 4.312.

At the field level, AFIS fiber maturity was reduced in the higher plant densities (Bednarz et al., 2005). At the canopy level, plant density differences in AFIS immature fiber content were observed in all environments (Table 4) with the higher plant densities resulting in higher AFIS immature fiber contents. Sympodial branch fruiting position differences were observed at Tifton, GA, in 2001 and Plains, GA, in 2002 (Table 4). Generally, the distal sympodial branch positions produced fibers with greater AFIS immature fiber contents. These results are also consistent with those of Knight (1988) and Crawley (1999). Plant density x sympodial branch fruiting position interactions were observed only in Plains, GA, in 2001 (Table 4).

View larger version (19K): [in this window] [in a new window]   Fig. 4. First sympodial position Advanced Fiber Information System (AFIS) immature fiber content in studies conducted at the University of Georgia in 2001 and 2002. Plains, GA 2001 P > F: Cultivar (C), 0.1676; Density (D), 0.0133; CxD, 0.6203; Node (N), <0.0001; CxN, 0.0004; DxN, 0.0072; CxDxN, 0.0061; LSD = 0.674. Tifton, GA 2001 P > F: Cultivar (C), 0.4648; Density (D), 0.1468; CxD, 0.6605; Node (N), <0.0001; CxN, 0.2997; DxN, 0.0133; CxDxN, 0.4937; LSD = 0.662. Plains, GA 2002 P > F: Cultivar (C), 0.7209; Density (D), <0.0001; CxD, 0.4989; Node (N), <0.0001; CxN, 0.0042; DxN, 0.0004; CxDxN, 0.1099; LSD = 0.625.

	DISCUSSION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS REFERENCES

 
Much of the data collected in this investigation suggests two recurring patterns with respect to fiber quality and fruiting position. First, the superior fruiting positions in terms of overall fiber quality (i.e., longer, more uniform, and mature fibers) occur at first sympodial positions generally in the midcanopy region (i.e., main stem nodes 10–17) also known as inner fruiting positions. These results, however, have also been well documented by Knight (1988) and Crawley (1999). The second recurring pattern in this investigation suggests the lower plant density actually resulted in more desirable fiber properties at these inner fruiting positions. This second new discovery raises two questions. First, why were more desirable fibers produced at inner positions in the lower plant densities? Bednarz et al. (2000) indicated the percentage of the total yield arising at inner fruiting positions increases with increasing plant density. Therefore, the number of developing bolls in this region is greater in higher plant densities. Ashley (1972) demonstrated that long-distance translocation of carbohydrates in cotton is very limited. Thus, the source-to-sink ratio in this region of the canopy was likely reduced in the higher plant densities throughout boll development, resulting in less desirable fiber properties. Second, if lower plant densities resulted in more desirable fiber properties at the canopy level, why were these findings not observed at the field level (Bednarz et al., 2005)? While AFIS fiber properties were more desirable at inner positions in the lower plant densities, the percentage of the total yield arising from these fruiting positions was lower (Bednarz et al., 2000). In addition, a greater percentage of the total yield in the lower plant densities arose at fruiting positions at the bottom and top of the canopy (also known as outer positions), where fiber quality is generally lower. Thus, the net effect was little or no measurable gain in overall fiber quality among the plant densities.

	CONCLUSIONS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS REFERENCES

 
Interestingly, the region of a cotton canopy that produces the majority of the crop yield (i.e., the inner positions) is also the region that produces the most desirable fiber properties. While small gains in inner position fiber quality were made through reduced plant densities, it seems plausible the greatest gains in overall fiber quality would occur if outer position fiber quality were improved. Inner position fiber quality in this investigation was already highly desirable, regardless of plant density. Outer position fiber quality, however, was likely unacceptable in several instances. Previous studies (Bednarz et al., 2000) have indicated outer fruiting positions may contribute from 20 to 40% of the total crop yield. Thus, improved outer position fiber quality could likely result in improved field level fiber quality. The question arises, how can crop management be modified to improve outer position fiber quality?

Figure 4 indicates fruit produced at the bottom and the top of the canopy are less mature than inner position fruit. Ashley (1972) indicated long distance transport of carbohydrate is very limited in cotton. In addition, shading of lower canopy leaves likely results in reduced carbohydrate production in that region of the canopy. Thus, fruit produced at the bottom of the canopy receive less carbohydrate from potential source leaves regardless of leaf location in the canopy. Also, fruit produced at the top of the canopy likely receive less carbohydrate simply because they are initiated late in the growing season when daylengths and stored carbohydrates are reduced. It seems plausible that increased sunlight penetration to the lower canopy may improve fruit maturity in that region. In addition, reduced fruit initiation late in the growing season would represent a reduction in the number of carbohydrate sinks in the upper canopy. A reduction in the number of new sinks may result in increased carbohydrate availability for preexisting sinks, possibly resulting in improved fruit maturity in the upper canopy. Current investigations have been designed to modify canopy architecture such that sunlight penetration to the lower canopy is increased and late season fruit initiation is decreased.

	ACKNOWLEDGMENTS

 
The authors would like to thank Benjamin G. Mullinix, Jr. for assistance with the statistical analyses and T. Dudley Cook and Lola C. Sexton for the technical support. Appreciation is also extended to Dr. Mike D. Watson, Norma M. Keyes, and LaQuit D. Davis and the Cotton Incorporated Textile Services Laboratory staff for assistance with the fiber quality analyses and interpretation. The authors also thank the Georgia Agricultural Commodity Commission for Cotton and Cotton Incorporated for the financial support.

Received for publication August 25, 2005.

	REFERENCES

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS REFERENCES

 

• Ashley, D.A. 1972. 14C-Labelled photosynthate translocation and utilization in cotton plants. Crop Sci. 12:69–74.
• Bednarz, C.W., D.C. Bridges, and S.M. Brown. 2000. Analysis of cotton yield stability across population densities. Agron. J. 92:128–135.[Abstract/Free Full Text]
• Bednarz, C.W., W.D. Shurley, W.S. Anthony, and R.L. Nichols. 2005. Yield, quality, and profitability of cotton produced at varying plant densities. Agron. J. 97:235–240.[Abstract/Free Full Text]
• Bernhardt, J.L., and J.R. Phillips. 1986. Fruiting position influence on yield components of cotton bolls. I. Fiber properties. p. 113–115. In J. M. Brown and T. C. Nelson (ed.) Proc. Beltwide Cotton Prod. Res. Conf., Las Vegas, NV, National Cotton Council of America, Memphis, TN.
• Brown, S.M., S. Culpepper, G. Harris, P. Jost, B. Kemerait, P. Roberts, and D. Shurley. 2001. 2001 Georgia Cotton Production Guide, CSS 97–01, Univ. of Georgia, Coop. Ext. Serv., Tifton, GA.
• Crawley, S.R. 1999. Effects of fruiting site on fiber properties, yield, and yield components of two different maturity cotton cultivars. M.S. Thesis. Mississippi State University. Mississippi State.
• Deussen, H. 1992. Improved cotton fiber properties: The textile industry's key to success in global competition. p. 43–63. In C. R. Benedict and G. M. Jividen (ed.) Cotton Fiber Cellulose: Structure, Function and Utilization Conference, National Cotton Council of America, Memphis, TN.
• Faerber, C. 1995. Future demands on cotton fiber quality in the textile industry, technology-quality-cost. p. 1449–1454. In D. A. Richter and J. Armour (ed.) Proc. Beltwide Cotton Prod. Res. Conf., San Antonio, TX, National Cotton Council of America, Memphis, TN.
• Holman, E.M., and C.W. Bednarz. 2001. Alley effect on several cotton cultivars in small plot research. Commun. Soil Sci. Plant Anal. 32:119–126.[CrossRef]
• Knight, B.L. 1988. Effects of fruiting position on yield and fiber quality in cotton. M.S. Thesis. Mississippi State University. Mississippi State.
• Roberts, P.M., and C.W. Bednarz. 2005. The effect of stink bug damage on fiber quality. p. 173–181. In P. H. Jost et al. (ed.) 2004 Cotton research-extension report. UGA/CPES Research-Extension Publication No. 6. Univ. of Georgia, Tifton.

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This Article Abstract Figures Only Full Text (PDF) Free Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in ISI Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (2) Citing Articles via Google Scholar Google Scholar Articles by Bednarz, C. W. Articles by Brown, S. M. Search for Related Content PubMed Articles by Bednarz, C. W. Articles by Brown, S. M. Agricola Articles by Bednarz, C. W. Articles by Brown, S. M. Related Collections Crop Growth and Development Cotton Production Agriculture Crop Ecology