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a Univ. of Georgia, Coastal Plain Exp. Stn., P.O. Box 748, Tifton, GA 31793
b Univ. of Georgia, Rural Dev. Center, P.O. Box 1209, Tifton, GA 31793
c USDA-ARS Cotton Ginning Res. Unit, P.O. Box 256, Stoneville, MS 38776
* Corresponding author (cbednarz{at}tifton.cpes.peachnet.edu)
Received for publication November 2, 2001.
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Abbreviations: AFIS, advanced fiber information system • AGI, adjusted gross income • CV, coefficient of variation • DAP, days after planting • HVI, high volume instrument • NACB, nodes from the uppermost first sympodial position cracked boll to the uppermost harvestable boll • UHM, upper half mean fiber length
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Cotton fiber quality is determined primarily by genetics, but can also be influenced by environmental factors (Meredith, 1984) such as soil type, insect pressure, weather, growing season length, and harvest and ginning management. While many of the cotton cultivars grown in the USA are genetically similar, the environmental conditions in which they are grown and their impact on crop management are very diverse. For instance, due to poorly drained soils, late season insect pest pressure and inclement weather patterns during the fall months, producers in the Mid-South region of the U.S. Cotton Belt manage their crops such that harvest is completed by late October (Parvin, 1990). In other regions, more favorable fall weather conditions and well-drained soils allow crop maturity and harvest to be delayed if necessary. The Mid-South region, however, historically produces some of the highest quality cotton across the U.S. Cotton Belt. While there may exist several environmentally related explanations for these differences, it may also result from management for early crop maturity and a timely harvest. Thus, the lack of emphasis on a timely harvest in other regions could be a source of significant yield and quality losses.
Many studies have investigated the impact of early and late harvests on cotton lint yield and fiber quality (Barker et al., 1976; Brown and Hyer, 1956; Columbus et al., 1990; Ray and Minton, 1973; Snipes and Baskin, 1994; Williford, 1992; Williford et al., 1995, 1987). Few studies, however, have investigated the effects of systematic delayed harvest on yield and quality (Ray and Minton, 1973; Williford et al., 1995). Also, since fiber length uniformity has not been a determinant of price received by the grower before 2000, current information regarding the relationship between harvest timing and fiber length uniformity is insufficient. Therefore, the objectives of this study were to investigate the effects of systematic delayed harvest on cotton (i) fiber length uniformity and other fiber properties, (ii) lint yield, and (iii) profitability.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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,,-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. All other fertility, weed, and insect-pest control practices were in accordance with the University of Georgia Cooperative Extension Service Guidelines (Brown et al., 1998). Cotton was planted on 27 Apr. 1998 (cv. SureGrow 501), 10 May 1999 (cv. DeltaPine NuCOTN 33B), and 1 May 2000 (cv. DeltaPine NuCOTN 33B) at a rate of 11 seeds m-2. The original study area in 1999 was planted to SureGrow 501. As the crop matured, however, severe lodging was observed with this cultivar, which would have hampered harvest-aid application. Thus, the entire study was moved to another test site on the same farm that was planted to DeltaPine NuCOTN 33B. Other than cultivar selection, crop management between the two test sites was identical. At 90 days after planting (DAP) each year, plots were established within the test area by mowing a 7.6-m alley between each block with a tractor mounted, 2.1 m wide Bush Hog (Bush Hog, Inc., Selma, AL) mower. Alleys were not established until this time to avoid the inaccurate measures of plot yield and fiber quality due to the end-of-row effect (Holman and Bednarz, 2001). Each plot was 4 rows (0.9-m centers) wide and 15 m long. Water stress was minimized in all studies with overhead sprinkler irrigation systems. The experimental design was a randomized block design with four replications.
Treatment Establishment and Data Collection
Treatments were begun each year when the first open boll was observed in the test area. Thirteen treatments were randomly assigned to each block in the study. Harvest-aids were applied to each plot according to the week after first open boll designation assigned to it. For example, harvest aids applied to treatments during the fourth week after first open boll were considered Week 4 treatments. Harvest-aids were applied with a John Deere (Moline, IL) model 600 high clearance sprayer equipped with compressed air, TX-8 spray nozzles on 46-cm centers and a 3.6-m boom. The carrier volume for each application was 94 L ha-1. The harvest aids applied 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-yl-urea; 0.093 kg a.i. ha-1) plus ethephon ((2-chloroethyl)phosphonic acid; 1.103 kg a.i. ha-1). Immediately before each harvest aid application, the numbers of opened and unopened bolls were recorded along a 1-m section of row from one of the two center rows in each plot. Also, immediately before harvest aid application, the number of main stem nodes from the uppermost first sympodial position cracked boll to the uppermost main stem node with a harvestable boll (NACB) were recorded on 10 plants that were randomly selected from the center two rows in each plot. Approximately 2 wk after each harvest aid application, the center two rows of each plot were harvested with a spindle picker (International Harvester model 622; Case Corp., Racine, WI) equipped with a bagging attachment for small plot research. Mechanical difficulties with the plot picker at Week 12 in 1999 resulted in unreliable plot yield data. Therefore, lint yields and economic data are not reported for this week. All defoliation dates, harvest dates, and the mean percent open boll recorded for each week of the study are presented in Table 1.
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While ginning in 1998, one lint sample per plot was collected and delivered to the USDA–Agricultural Marketing Services (AMS)–Cotton Division, Cotton Classing Office in Macon, GA, for fiber quality analysis. Fiber quality at this office was determined using a Zellweger Uster (Charlotte, NC) model 900-A High Volume Instrument (HVI). In 1999 and 2000, a total of six lint samples were collected per plot. Three lint samples from each plot were again delivered to the Cotton Classing Office in Macon, GA, for fiber quality determination using the HVI line. The other three lint samples were delivered to Cotton Incorporated (Cary, NC) for additional fiber quality analyses using a Zellweger Uster (Charlotte, NC) Advanced Fiber Information System (AFIS) instrument. For each fiber sample, the AFIS instrument analyzed five subsamples of 3000 fibers each.
Economic Analysis
Net return was calculated each year for the 13 treatments (weeks after first open boll). Because all production practices, inputs, and costs were the same for each treatment, costs were not considered and it is only necessary to compare income per hectare. The measure of comparison used in this study is the adjusted gross income (AGI), which considers differences in yield and quality. The adjusted gross income was calculated as follows:
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The average 1 November and 1 February cash or spot price was 136¢ kg-1 in 1998, 117¢ kg-1 in 1999, and 129¢ kg-1 in 2000. Net ginning and warehousing charges were 13.2¢ kg-1 in 1998 and 1999 and 11¢ kg-1 in 2000.
High volume instrument leaf grades were not considered reliable in 1998 as the seed cotton was not ginned with lint cleaning. Therefore, leaf grades in 1998 were assumed to be the same as the color grade (i.e., 41 color grade = 4 leaf grade; 51 color grade = 5 leaf grade, etc). Leaf grades in 1999 and 2000 ranged from 3.0 to 3.4 and 2.0 to 2.2, respectively. Uniformity was not considered an official USDA–AMS quality factor for price premiums or discounts before 2000.
Statistical Analyses
The data for fiber quality in 1999 and 2000 were analyzed using PROC MIXED (SAS Inst., 2000) as a split-plot in space (stripped split-plot; Steel and Torrie, 1960, p. 242–250) where treatment (weeks after first open boll) was the main plot and lint sample was the subplot. While ginning in 1999 and 2000, the first lint sample was taken from the beginning of the gin run, the second sample from the middle of the same run, and the third sample from near the end of the same run. Thus, these three samples are considered stripped across the main plots (samples were ordered).
The data for fiber quality in 1998 and lint yield in 1998, 1999, and 2000 were analyzed as a randomized complete block design using PROC MIXED. The data were not combined across years because (i) cultivar and ginning technique differed between the first and last 2 yr of the study and (ii) the amount and distribution of rainfall during the harvest period differed in all years of the study.
The data for Fig. 1 were, however, combined across years and were analyzed as a randomized complete block design using PROC MIXED. A regression analysis was done to examine the impact of cultivar and year. The F test did not change whether cultivar or year were or were not included in the model. Therefore, we concluded that the slope presented is representative of all cultivars and years and no loss of information occurred through combining the data.
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RESULTS AND DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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In 1998, HVI fiber length uniformity, the ratio between the mean fiber length and the average length of the longest one-half of the fibers in a sample, ranged from 83.85 to 85.10% and did not differ (data not presented). In 1999 and 2000, however, differences were observed (Table 2). In 1999, length uniformity was greatest when harvest aids were applied at 64 and 79% open boll (Weeks 4 and 5), while in 2000 length uniformity was greatest when harvest aids were applied from 58 to 88% open boll (Weeks 3–6). Regression analyses indicated HVI fiber length uniformity and percent open bolls when harvest aids were applied were not related in 1998 and 1999 (Table 3). In 2000, however, HVI fiber length uniformity was greatest when harvest aids were applied at 61.2% open boll (Table 3). In addition, once the crop reached 100% open boll, HVI fiber length uniformity decreased 0.387 and 0.427% wk-1 in 1999 and 2000, respectively (Table 4).
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The fiber lengths in a sample are highly variable and can range from <0.5 to >5 cm. High volume instrument fiber length uniformity and the AFIS average fiber length by number coefficient of variation [L(n)CV] are both indicators of this variability. As indicated earlier, the AFIS instrument analyzed five subsamples of 3000 fibers each and computed a coefficient of variation (CV) for each sample. These CVs were statistically analyzed and the results are presented in Table 2. The AFIS L(n)CV was greatest in 1999 and 2000 when harvest aid applications were delayed until >90% open boll. Regression analyses indicated the AFIS L(n)CV was lowest when harvest aids were applied at 40.1 and 46.8% open boll in 1999 and 2000, respectively (Table 3).
Fiber elongation occurs for the first 16 to 19 d postanthesis (Berlin, 1986). As an indeterminate crop, cotton will produce fruit that vary in age by several weeks. Thus, application of harvest aids too early (i.e., before 
60% open boll) probably resulted in reduced fiber length uniformity because the process of fiber elongation was not fully complete in many fruit at this time.
Fiber length uniformity also began to decrease when harvest aids were applied after 90% open boll in 1999 and 2000. In both years, fiber length uniformity was lowest when harvest aid applications were delayed until >90% open boll. While the physiological stages of boll maturity may aid in the understanding of decreased fiber length uniformity before 60% open boll, they do not provide an explanation for decreased uniformity when harvest aid applications were delayed until >90% open boll. Examination of the fiber strength data, however, may provide some insight.
Fiber strength differed with timing of harvest aid application in all years (Table 2). In all years fiber strength was greatest during the initial harvest aid application timings and decreased thereafter (Table 3). Regression analysis revealed a relationship between fiber strength and fiber length uniformity after ginning in 1999 and 2000. The slopes of the relationships were found to be different between years and the data were not combined. Fiber strength and fiber length uniformity after ginning were positively related in 1999 [slope = 0.037, F(1,154) = 35.71, P < 0.01] and 2000 [slope = 0.013, F(1,154) = 5.27, P < 0.03]. These data indicate fiber strength and fiber length uniformity decreased concurrently in 1999 and 2000.
Several researchers have shown that the ginning setup will influence fiber properties (Anthony, 1990, 1992, 1996; Barker et al., 1976; Columbus et al., 1990; Mangialardi, 1993; Williford et al., 1987). In these studies, reductions in fiber length uniformity were documented when additional lint cleaners were included in the ginning sequence. Reduced fiber length uniformity has also been reported after ginning cotton cultivars of lower fiber strength (Anthony, 1990, 1996). Thus, the relationship between fiber strength and length uniformity in 1999 and 2000 could be the result of lint cleaning fibers of lower strength. This observation is further supported by the nonsignificant relationship between fiber strength and length uniformity in 1998, as lint cleaning was not included in the ginning setup during this year.
The USDA–AMS base for HVI fiber strength (1998, 1999, 2000) ranged from 230 to 250 kN m kg-1 in 1998 and 1999 and from 250 to 288 kN m kg-1 in 2000. In 1998 and 1999 price premiums were received throughout the study period for fiber strength. In 2000, however, price discounts were received from Week 5 to 12 for low fiber strength (Table 2). These discounts were primarily due to changes in the USDA–AMS schedule for 2000.
The HVI upper half mean fiber length (UHM), defined as the mean fiber length of the longest one half of the fibers in a sample, did not differ in 1998 and 1999 (Table 5). In 2000, the HVI-UHM was greatest when harvest aids were applied before 80% open boll (Table 5). Regression analyses (Table 3) indicated the HVI-UHM was greatest when harvest aids were applied at 47.9, 56.7, and 39.1% open bolls in 1998, 1999, and 2000, respectively. The USDA–AMS base for HVI-UHM (1998, 1999, 2000) is 2.70 cm. Thus, in 2000 price discounts were received for low UHM at several harvest timings (Table 5).
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In all years of this study, HVI micronaire and AFIS fineness, both measures of fiber fineness, and as AFIS maturity were lowest when harvest aids were applied from 0 to 2 wk after first open boll and increased thereafter (Table 6). Percent open boll at the time of harvest aid application was related to HVI micronaire and AFIS fineness and maturity (Table 3). In 1998 and 1999 HVI micronaire increased from first open boll to 100% open boll and in 2000 increased from first open boll to 99.3% open boll. The AFIS fineness and maturity increased from first open boll to 100% open boll in 1999 and 2000. After the fiber elongation phase, fiber filling occurs for the next 3 to 6 wk postanthesis (Berlin, 1986). Thus, the initial harvest-aid applications resulted in lower fiber microniare and maturity because fiber filling was not complete during these timings.
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A total of 20 rainfall events occurred during the 13 wk that cotton was harvested in this study in both 1998 and 1999 (Table 7). In 1998, however, the total amount of rainfall received was more than three times greater than in 1999. In 1998, most of the rainfall occurred from Week 3 to 7 and very little rainfall occurred thereafter. In 2000, a total of 24 rainfall events were recorded during the harvest period, which mostly occurred from Weeks 1 to 4 (Table 7).
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The maximum adjusted gross income in 1998 occurred when harvest aids were applied at 60.6% open boll (Table 3). Price discounts received for unacceptable HVI fiber color in 1998 were primarily responsible for the lower adjusted gross incomes at later dates when lint yields were greater (Table 9). Addition of lint cleaning to the ginning sequence has been shown to improve fiber color grades (Anthony, 1994). Recall, in 1998 lint cleaning was unavailable with the ginning equipment used for this study. Thus, price discounts received for reduced HVI fiber color may have been somewhat less or entirely omitted if the ginning setup had been consistent with commercial ginning operations for spindle-harvested cotton. In 1998 the adjusted gross income decreased by $35.82 ha-1 wk-1 once the crop reached 100% open boll (Table 4).
The maximum adjusted gross income in 1999 occurred when harvest aids were applied at 77.8% open boll (Table 3). Price discounts were not received for reduced fiber quality in 1999 (Table 9). Thus, the maximum adjusted gross income and lint yield occurred concurrently (Table 3). In 2000, the maximum adjusted gross income occurred when harvest aids were applied at 84.7% open boll. In 2000 the adjusted gross income decreased by $69.94 ha-1 wk-1 once the crop reached 100% open boll (Table 4).
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CONCLUSIONS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Under the current cotton marketing system, the penalty for reduced lint yield is much greater than the penalty for unacceptable fiber quality. Therefore, it may become less profitable for growers to manage for maximum fiber quality if lint yield is sacrificed in the process. Within the textile industry, however, profitability is highly dependant on fiber quality. Thus, a consensus over the value of raw cotton fiber would likely benefit both groups.
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ACKNOWLEDGMENTS |
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REFERENCES |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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K. S. Balkcom, D. W. Reeves, J. N. Shaw, C. H. Burmester, and L. M. Curtis Cotton Yield and Fiber Quality from Irrigated Tillage Systems in the Tennessee Valley Agron. J., April 11, 2006; 98(3): 596 - 602. [Abstract] [Full Text] [PDF]
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