Since the introduction of transgenic crops,

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1 The Journal of Cotton Science 9:89 98 () The Cotton Foundation 89 AGRONOMY AND SOILS Effects of Different Seeding Rates and Plant Growth Regulators on Earl-planted Cotton W.T. Pettigrew* and J.T. Johnson ABSTRACT W.T. Pettigrew and J. T. Johnson, USDA-ARS, Crop Genetics and Production Research Unit, P.O. Box, Stoneville, MS 8776 *Corresponding author Although the earl-planted cotton production sstem offers the potential of improved lint ield, production techniques need to be optimied to ensure consistent ield enhancement. The objectives of this stud were to determine how different seeding rates and application rates of mepiquattpe plant growth regulator compounds (PGR) affected cotton growth and production under earl planting conditions. A field stud was conducted under earl planting conditions from through using four cotton cultivars (PM 8BR, STV 69B, STV 89BR, and DPL BR) and four seeding rates (7, 9,, and plants m - ). Depending on the ear, half the plots were treated with either mepiquat chloride or mepiquat pentaborate (), while the remaining plots were untreated (). Dr matter partitioning, canop light interception, bloom counts, lint ield, ield components, and fiber qualit data were collected throughout the experiment. When PGR was not applied, leaf area index (LAI) increased as the seeding rate increased, but the LAI plateaued at plants m - when a PGR was applied. When a PGR was applied to the crop, plant height was reduced 9% and specific leaf weight was increased %. Plants treated with a PGR produced more flowers earl in the season, and the untreated control plants produced more blooms later in the season. The potential for earlier maturit of plants treated with a PGR was also reflected in the reduced nodes above white bloom (NAWB) data relative to the control plants. No ield response was observed from PGR application, but the lowest seeding rate (7 plants m - ) had % lower ield than an of the other seeding rates. Few fiber qualit differences were detected among PGR application rates or seeding rates. The longer growing season associated with the earl planting sstem allowed late season flowers on the control plants to develop into mature open bolls and resulted in equivalent ields between the control and plants treated with a PGR. Since the introduction of transgenic crops, producers have had to deal with the additional input costs associated with technolog fees. Fees for each transgenic trait are generall assessed on a cost per seed basis, which allows producers a measure of control over their expenses for the use of a transgenic trait. Reducing seeding rates, as a means to minimie this technolog fee, while still taking advantage of the transgenic trait and potentiall maximiing profit margins, is a temptation for man cotton producers. Numerous plant population densit studies have been conducted in cotton to determine the optimal plant densities for maximum ield (Buxton et al., 977; Smith et al., 979; Mohamad et al.,98; Kerb et al., 99a,b; Jadhao et al., 99; Sawan et al., 99; Bednar et al., ). Optimal plant densities across multiple row widths ranged from plants m - for normal-leaf cultivars to - plants m - for okra-leaf cultivars (Heitholt, 99). Final population densities in a production field are dependent on the seeding rate, germination, emergence, and survival of the planted seed. For producers hoping to reduce the technolog fee expense, the challenge is to optimie seeding rates with the germination rate of the given seed lot and the anticipated environmental conditions during planting and emergence (temperature; moisture; fungicide and insecticide applications; seedling disease, and insect pressure) that affect plant survival to achieve final population densities near the lower end of the optimum plant population range. Properl performed, this scenario would allow producers to minimie technolog fee assessments without overl compromising ield potential. The use of the new higher ield potential earl-planted cotton production sstem (Pettigrew, ) complicates this seeding rate decision, because obtaining an adequate stand is a ke to the success of the sstem,

2 Pettigrew and Johnson: Seeding Rates and Growth Regulators in Earl-Planted Cotton 9 and earl planted seed is placed in a potentiall more stressful planting environment. Another input decision for producers is whether to appl plant growth regulator compounds to the crop. The use of mepiquat chloride and the related compound mepiquat pentaborate to control excessive vegetative growth in cotton has become almost ubiquitous across the U.S. Cotton Belt, but the perceived benefits ma not justif the expense of this input. While a reduction in plant height is a relativel consistent response to the mepiquat compounds, the ield response is inconsistent at best (York, 98a,b; Kerb, 98; Cathe and Meredith, 988; Cook and Kenned, ; Biles and Cothren, ). Cathe and Meredith (988) reported that mepiquat chloride produced an increase in lint ield for late-planted (mid-ma) cotton but caused a ield decrease in earl-planted (mid-april) cotton. It was concluded that environmental conditions favoring excessive vegetative growth, such as late planting, would most likel provide a positive ield response to mepiquat chloride. The cooler temperature-induced reductions in earl season growth observed with earlier planted (April ) untreated cotton (Pettigrew, ) raises questions about the need for and response to these mepiquat compounds on earl-planted cotton plants. Increasing plant populations that would tend to promote excessive vegetative growth led to a greater response in lint ield to mepiquat chloride (York, 98b). Much of the ield increase was attributed to the earlier maturit of the plants treated with mepiquat chloride rather than to control of vegetative growth. None of the previous mepiquat chloride or plant densit studies were conducted under the ver earl-planted conditions used with the cotton earl planting production sstem (Pettigrew, ). Because of this, there is uncertaint about the response of earl-planted cotton to mepiquat chloride-tpe compounds and different seeding rates. In addition, the optimal seeding rate for earl-planted cotton, which will allow the producer to minimie technolog fee, remains uncertain. The objectives of this stud were to determine how earl-planted cotton responds to different levels of mepiquat compounds and to different seeding rates. MATERIALS AND METHODS Field studies were conducted on a Dubbs silt loam soil (fine-silt, mixed, active, thermic Tpic Hapludalfs) near Stoneville, MS during through, to determine the effects of mepiquat-tpe growth regulators and different seeding rates on earl-planted cotton. Mepiquat chloride (Pix; BASF Corp.; Research Triangle Park, NC) was applied at 9 g a.i. ha - () or not applied () in through. In, mepiquat pentaborate (Pentia; BASF Corp.) was substituted for mepiquat chloride and was applied at g a.i. ha - () or not applied (). Each ear, half of the plus PGR treatment was applied in earl June during the squaring stage, with the remaining half applied to wk later when the plants were in earl bloom. Two cotton genotpes were grown each ear. In and, Stoneville 69B (STV 69B; Stoneville Pedigreed Seed; Memphis, TN) and Pamaster 8 BR (PM 8BR; Delta Pine and Land Co.; Scott, MS) were grown. Deltapine BR (DPL BR; Delta Pine and Land Co.) was grown instead of PM 8BR in and. Although STV 69B was still grown in, Stoneville 89BR (STV 89BR; Stoneville Pedigreed Seed) was substituted for STV 69B in. Four seeding rates were used in this stud. The goal of the seeding rates was to achieve final plant densities of 7 plants m -, 9 plants m -, plants m -, and plants m -. Seeding rates were adjusted to achieve the desired final population densities b assuming survival of 7% of the planted seeds under the conditions encountered with earl planting. The sie of the individual experimental plots was rows spaced. m apart and 8. m in length. Plots were planted on April in, April in, March in, and March in. The experimental design was a randomied complete block with a split plot arrangement of treatments and six replications. Main plots consisted of the different rates of the plant growth regulators and subplots were the cotton genotpes and seeding rates. The subplots were arranged as a factorial. Dr matter harvests were taken between 6 and 9 d after planting (DAP) in ; from 8 thru 86 DAP in, and from 8 thru 8 DAP in. The earl harvest dates in and occurred approximatel during the earl blooming period, while the later harvest date in approximatel corresponded to a cut-out harvest date. Cut-out refers to a period of slowing vegetative growth and flowering due to a strong demand for assimilates b the existing boll load. On each harvest date, the above ground portions of plants from. m of row

3 JOURNAL OF COTTON SCIENCE, Volume 9, Issue, were harvested from one of the outside rows of each plot and separated into leaves, stems and petioles, squares, and blooms and bolls. Leaves were passed through a LI- leaf area meter (LI-COR, Lincoln, NE ) to determine leaf area index (LAI), and mainstem nodes were counted. Samples were dried for at least 8 h at 6 C, and dr weights were recorded. In addition to the LAI determined b the destructive dr matter partitioning harvests, LAI was also quantified b use of the LAI- plant canop analer (LI-COR; Lincoln, NE) between 9 and DAP in, and 9 DAP in, and and 7 DAP in. All readings were taken between 8 h to h (8: am and : am, CDT) using a view cap. Due to the heterogeneous nature of some of the plot canopies, a minimum of above-canop readings and 6 below-canop readings were taken per plot. Four transects were made with the orientation of the field of view changing between perpendicular and parallel to the row direction on alternate transects. During all readings, the sensor was shielded from direct sunlight using a.7-m diameter patio umbrella (Hicks and Lascano, 99). The number of white blooms (blooms at anthesis) per subplot was counted on a weekl basis to document the blooming rate throughout the growing season. These counts were taken on 6. m of row from one of the inner subplot rows and were initiated at first bloom and continued until production of blooms had virtuall ceased. The number of main-stem nodes above a smpodial branch that had a white bloom at the first branch fruiting position (NAWB) was also counted weekl on three plants per plot to document the progression of reproductive development up the stem, as well as crop maturit. Bloom counts and NAWB data were collected ever ear of the stud. The percentage of photosnthetic photon flux densit (PPFD) intercepted b the canopies of both experiments was determined with a LI 9SB point quantum sensor (LI-COR; Lincoln, NE) positioned above the canop and a -m-long LI 9SB line quantum sensor placed on the ground perpendicular to and centered on the row. Two measurements were taken per plot with the average of those two measurements used for statistical analsis. All measurements were taken between h and h (: pm and : pm, CDT) with all above canop reading 7 μmol m - s -. These PPFD interception data were collected on 7 and 98 d after planting (DAP) 9 in, 7 and DAP in, 8 and 6 DAP in, and DAP in. Cotton was defoliated using a mixture of tribufos and ethephon during earl-to-mid September each ear. Approximatel wk after defoliation, the two center rows of each subplot were harvested with a spindle picker and weighed. After defoliation, but prior to mechanical harvest, a -boll sample was collected from each subplot for use in determination of ield components. Boll mass was determined from these -boll samples b dividing the weight of seed cotton b the number of bolls harvested. These samples were then ginned and weighed to calculate lint percentage, which was used to calculate lint ield from the mechanicall-harvested seed cotton. The number of bolls produced per unit ground area was calculated from the boll mass and total seed cotton weights per subplot. Average seed mass was determined from non-delinted seeds per sample and reported as weight per individual seed. Lint samples from each subplot were sent to Starlab Inc. (Knoxville, TN) for fiber qualit determinations. Fiber strength (T) was determined with a stelometer. Span lengths were measured with a digital fibrograph. Fiber maturit, wall thickness, and perimeter were calculated from arealometer measurements. Statistical analses were performed using the PROC MIXED program of SAS (SAS Institute; Car, NC). For traits in which there was a significant interaction between ear and PGR rates or seeding rates, the results are presented b ear. When PGR rate or seeding rate effects were consistent across ears, then the PGR or seeding rate means were averaged across ears, and the interactions between ear and PGR rate or seeding rate were considered a random source of error. When the interactions were not significant, PGR rate and seeding rates were averaged across cotton genotpes. The use of different genotpes during different ears of the stud prevented averaging genotpe means across ears. Means were separated b a protected LSD at P.. RESULTS AND DISCUSSION Different climatic conditions following planting resulted in different final plant population densities for each ear (Table ). The desired survival of 7% of the planted seed in this earl planting scenario was achieved onl in. Lower population densities were attained in through, which indicated that the assumed survival percentage (7%) was too

4 Pettigrew and Johnson: Seeding Rates and Growth Regulators in Earl-Planted Cotton 9 high, and that higher seeding rates would have been more appropriate to achieve the population densit goals during those ears. Table. Actual cotton plant population densit for each of the desired seeding rates for through Seeding rate Plant Population (plant m - ) 7 plants m plants m plants m plants m LSD (P =.).... To achieved the desired seeding rate, actual seeding rates are adjusted assuming 7% survival of planted seed. Plant populations counted approximatel d after planting. No significant interactions were observed between seeding rate and PGR application rates for the dr matter partitioning components, so seeding rates were averaged across PGR rates and PGR rates were averaged across seeding rates. Except for specific leaf weights, there were few differences in the components of dr matter partitioning among the seeding rates (Table ). The two highest seeding rates ( and plants m - ) had approximatel % lower specific leaf weights than the two lowest seeding rates (7 and 9 plants m - ). The heterogeneous nature of the canopies and distribution of plants within the row for the lower seeding rates, coupled with the small sample sie of the dr matter harvest ma have been insufficient to detect potential differences among the seeding rates. B using a sampling strateg designed for heterogeneous canopies, the LAI- Plant Canop Analer can compensate for the increased variabilit associated with a heterogeneous canop structure. Utiliing this approach, a significant interaction was observed between seeding rates and PGR rates for the nondestructive leaf area index (LAI) measurements (Table ). When PGR was not applied to the plots, the LAI was significantl different among seeding rates, with the LAI becoming progressivel greater as the seeding rate increased. When the PGR was applied, the LAI increased with increasing seeding rate up to the plant m - seeding rate. Increasing the seeding rate to plants m - did not result in a further LAI increase. LAI did not differ between PGR rates for an of the seeding rates except for the plants m - seeding rate where the application of PGR caused an % reduction in LAI compared with the untreated control. In previous research, Heitholt et al. (996) were unable to detect LAI differences between plots treated with mepiquat chloride and untreated plots using the LAI- Plant Canop Analer. Table. The effect of seeding rates and plant growth regulator (PGR) application rates averaged across cotton genotpes and ears on cotton dr matter partitioning data Variable Seeding rate Height (cm) Nodes plant - Height:node Leaf area index Specific leaf weight (g m - ) Vegetative weight (g m - ) Reproductive weight (g m - ) Harvest index 7 plants m plants m plants m plants m LSD (P =.) ns ns ns ns.8 ns ns ns P > F PGR application No PGR Plus PGR LSD (P =.).. ns. ns ns. P > F To achieve the desired seeding rate, actual seeding rates are adjusted assuming 7% survival of planted seed. PGR was mepiquat chloride at 9 g a.i. ha - in through and mepiquat pentaborate at g a.i. ha - in.

5 JOURNAL OF COTTON SCIENCE, Volume 9, Issue, 9 Table. The effect of seeding rates and plant growth regulator (PGR) application rates averaged across cotton genotpes and the ears on cotton leaf area index measured nondestructivel using a LAI- Plant Canop Analer Seeding rate Cotton leaf area index No PGR Plus PGR Mean 7 plants m plants m plants m -... plants m LSD (P =.) PGR rates within seeding rates.9 Seeding rates within PGR rates. Seeding rate mean averaged across PGR rates. To achieve the desired seeding rate, actual seeding rates are adjusted assuming 7% survival of planted seed. PGR was mepiquat chloride at 9 g a.i. ha - in through and mepiquat pentaborate at g a.i. ha - in. PGR application altered the growth of the plants so that man of the dr matter partitioning components were affected (Table ). It has been reported that these compounds reduced the plant stature relative to the untreated control plants (York, 98a,b; Kerb, 98; Cathe and Meredith, 988; Cook and Kenned, ; Biles and Cothren, ). PGR application reduced plant height b 9% and reduced both the number of main stem nodes and the height to node ratio b %. Although no differences were detected in LAI among PGR application rates from the destructive sampling, the plants treated with PGR had % greater specific leaf weight than the untreated control. Overall vegetative and reproductive weights did not differ between the treated or untreated plants, but the harvest index (ratio of reproductive weight to total weight) was 8% greater in the PGR-treated plants. The canop PPFD interception response to different seeding rates or PGR application rates was inconsistent across sampling dates (Table ). Canop PPFD interception among seeding rates was different on one of the measurement dates, while it was Table. The effect of seeding rates and plant growth regulator (PGR) application rates averaged across cotton genotpes on cotton canop photosnthetic photon flux densit (PPFD) interception at various das after planting (DAP) PPFD interception (%) Variable 6 DAP 9 DAP 68 DAP 99 DAP 7 DAP 96 DAP 9 DAP Seeding rate 7 plants m plants m plants m plants m LSD (P =.).7 ns ns ns ns ns ns P > F PGR application No PGR LSD (P =.) ns ns ns.8 ns ns. P > F To achieve the desired seeding rate, actual seeding rates are adjusted assuming 7% survival of planted seed. PGR was mepiquat chloride at 9 g a.i. ha - in through and mepiquat pentaborate at g a.i. ha - in.

6 Pettigrew and Johnson: Seeding Rates and Growth Regulators in Earl-Planted Cotton 9 different between the PGR application rates on two of the seven measurement dates. When significant differences were detected, the canopies of the lowest seeding rate (7 plants m - ) intercepted less solar radiation than the other seeding rates, and the canopies of plants treated with a PGR intercepted less solar radiation relative to the untreated control canopies. Gwathme et al. (99) and Heitholt et al. (996) also reported that cotton canopies treated with mepiquat chloride intercepted less solar radiation than the canopies of untreated cotton plants. The flowering rate between PGR application rates was inconsistent among the ears (Fig. and ). The flowering rate between the two rates of PGR application in or was not different. While the PGR-treated plants produced more earl-season flowers in both and, the untreated control plants exhibited a higher late season flowering rate in both of those ears. This higher earl season flowering induced b mepiquat compounds has previousl been reported b Biles and Cothren (), but the did not observe the increased late season flowering in the untreated plants noted in this stud. In general, differences were not observed in the rate of flowering among the seeding rates (data not shown), but when differences were observed, the higher seeding rates produced more blooms earl in the season and the lower seeding rates produced more blooms late in the season. A similar pattern of flower production among divergent cotton population densities was also reported b Jones and Wells (997). In addition, Heitholt (99) reported no differences in total seasonal flower production among different plant densities ranging from to plants m - for normal-leaf cultivars. This earlier reproductive development in the plants treated with PGR was also reflected in a reduced NAWB number relative to the control plants on most of the measurement dates (Fig. and ). This reduced NAWB for the PGR-treated plants was consistent during each ear of the stud. As blooms form on higher main-stem nodes, the NAWB decreases Blooms m - Blooms m Das after planting Fig.. White blooms (blooms at anthesis) m - of ground area of cotton at various das after planting (DAP) throughout the and growing seasons in plots either treated on not treated with plant growth regulator compounds (PGR). PGR application rate means were averaged across cotton genotpes and seeding rates. Vertical bars denote LSD values at P =. and are present onl when the differences between soil moisture treatments are significant Das after planting Fig.. White blooms (blooms at anthesis) m - of ground area of cotton at various das after planting (DAP) throughout the and growing seasons in plots either treated on not treated with plant growth regulator compounds (PGR). PGR application rate means were averaged across cotton genotpes and seeding rates. Vertical bars denote LSD values at P =. and are present onl when the differences between soil moisture treatments are significant.

7 JOURNAL OF COTTON SCIENCE, Volume 9, Issue, as the maturit of the plant progresses. Because the NAWB difference between PGR treatments is generall less than one node on all measurement dates, this maturit difference equates to less than or d, assuming a vertical blooming interval of. to d (Bednar and Nichols, ). When the NAWB decreases to, the crop is considered to be at cut-out (Bourland et al., 99). Earlier maturit of PGR-treated plants has been reported b others (York, 98a; Kerb, 98). There was no interaction between seeding rates and PGR application rates for lint ield or an of the components of ield, so seeding rates were averaged across PGR rates, and PGR application rates were averaged across seeding rates. Because these results were consistent across ears, the seeding rate means and PGR means were also averaged across ears. The lowest seeding rate (7 plants m - ) averaged % lower lint ield than an of the other seeding rates (Table ). Lint ield among the other seeding rates Nodes above white bloom Das after planting Fig.. Number of main-stem nodes of cotton above a smpodial branch with a first-position white bloom (bloom at anthesis) at various das after planting (DAP) throughout the and growing seasons in plots either treated on not treated with plant growth regulator compounds (PGR). PGR application rate means were averaged across cotton genotpes and seeding rates. Vertical bars denote LSD values at P =. and are present onl when the differences between soil moisture treatments are significant. 9 was not different. Production of fewer bolls per unit ground area was the ield component responsible for the reduction in lint ield observed with the 7 plants m - seeding rate. None of the other ield components were different among the seeding rates. Although appling a PGR did not affect lint ield, man of the ield components were altered b a PGR application. Bolls for the PGR-treated plants had % greater boll mass than bolls from the control plants due primaril to the % more seed per boll and % larger seed mass. Similar increases in boll and seed mass in response to mepiquat chloride were reported b York (98a, 98b), Cathe and Meredith (988), and Biles and Cothren (). This larger boll mass for the PGR-treated plants was offset b the reduced lint percentage of the PGR-treated plants relative to the control plants, which explains the lack of ield response to the PGR application. York (98a, 98b), Cathe and Meredith (988), and Biles and Cothren () also found that mepiquat chloride reduced lint Nodes above white bloom Das after planting Figure. Number of main-stem nodes of cotton above a smpodial branch with a first-position white bloom (bloom at anthesis) at various das after planting (DAP) throughout the and growing seasons in plots either treated on not treated with plant growth regulator compounds (PGR). PGR application rate means were averaged across cotton genotpes and seeding rates. Vertical bars denote LSD values at P =. and are present onl when the differences between soil moisture treatments are significant.

8 Pettigrew and Johnson: Seeding Rates and Growth Regulators in Earl-Planted Cotton 96 percentage. Neither the number of bolls produced per unit ground area nor the lint index was different among the PGR application rates. There few differences in the fiber qualit traits among seeding rates (Table 6). Although the micronaire with the plants m - seeding rate was significantl lower than either the 9 plants m - or plants m - seeding rates, there was no discernable trend for a seeding rate effect on micronaire. Fiber perimeter, a component of micronaire, for the plants m - seeding rate was also significantl lower than the other seeding rates. The onl fiber traits affected b appling PGR were fiber elongation and the span lengths. A % reduction in fiber elongation Table. The effect of seeding rates and plant growth regulator (PGR) application rates averaged across cotton genotpes and the ears on cotton lint ield and ield components Variable Seeding rate Lint ield (kg ha - ) Boll number (bolls m - ) Boll mass (g) Seed number (boll - ) Seed mass (mg) Lint percentage (%) 7 plants m plants m plants m plants m Lint index (mg seed - ) LSD (P =.) 6 ns ns ns ns ns P > F PGR application Plus PGR LSD (P =.) ns ns..6. ns P > F To achieve the desired seeding rate, actual seeding rates are adjusted assuming 7% survival of planted seed. PGR was mepiquat chloride at 9 g a.i. ha - in through and mepiquat pentaborate at g a.i. ha - in. Table 6. The effect of seeding rates and plant growth regulator (PGR) application rates averaged across cotton genotpes and the ears on cotton fiber qualit traits Variable Seeding rate Fiber strength (kn m kg - ) Fiber elongation (%) Span length (cm). % % Length uniformit (%) x Micronaire Fiber maturit (%) Fiber perimeter (μm) 7 plants m plants m plants m plants m LSD (P =.) ns ns ns ns ns.7 ns.6 P > F PGR application LSD (P =.) ns... ns ns ns ns P > F x Length uniformit = ( % span length /. % span length) X. To achieve the desired seeding rate, actual seeding rates are adjusted assuming 7% survival of planted seed. PGR was mepiquat chloride at 9 g a.i. ha - in through and mepiquat pentaborate at g a.i. ha - in.

9 JOURNAL OF COTTON SCIENCE, Volume 9, Issue, occurred when a PGR was applied, but both the.% and % span lengths were increased in response to PGR application. Although these differences ma be statisticall significant, biologicall the ma be of little consequence because the are so small. Cathe and Meredith (988) also reported similar fiber elongation reductions and.% span length increases in response to mepiquat chloride application. A slight increase in the fiber length upper half mean caused b treatment with mepiquat chloride was reported b (York, 98a). No lint ield advantage was attained from appling the mepiquat compounds to the cotton crop under these earl planted conditions, although PGR application ma have slightl accelerated the crop maturit as demonstrated b the reduced NAWB numbers. Although the PGR-treated plants had enhanced flowering earl in the season, the longer growing season provided b the earl planting production sstem allowed the control plants to continue flowering and setting bolls later in the season. These flowering trends appear to have cancelled each other out, resulting in no ield differences between the PGR-treated and control plants. When production circumstances, such as late planting, planting a late maturing cultivar, or an earl frost, conspire separatel or in combination to curtail the time available for later boll set and maturation, a PGR application ma provide a ield boost over the untreated cotton b an acceleration of the reproductive growth. Cathe and Meredith (988) found mepiquat chloride produced a ield increase when the cotton was planted later in the growing season. Furthermore, York (98b) indicated that for the two lowest plant populations in his stud, no ield response to mepiquat chloride would have been observed if the growing season had been long enough for all the bolls set to mature and open. While Heitholt (99) identified plants m - as the optimal population densit for normal-leaf cotton, the final mean plant densit produced b the 7 plants m - seeding rate goal in this stud was essentiall equal to the plants m - densit (.8 plants m - ) and produced a ield reduction relative to the higher rates. This difference is probabl because the within row plant distribution with this stud contained more gaps and was less uniform than what occurred in the Heitholt (99) stud. Assuming that the plants m - densit is optimal, the seeding rate must be increased accordingl under earl planting conditions to achieve that final plant densit. Based on the data from this stud, for most ears one should 97 assume a survival rate lower than the 7% level used in this stud when adjusting seeding rates for earl planting conditions. In conclusion, although crop maturit ma have been slightl accelerated and some ield components were affected, the application of the mepiquat compounds did not significantl improve ield. This situation is partiall attributed to the longer growing season afforded b earl planting, which allowed the late flower production from the control plants to set bolls that opened in time for harvest. Yield responses from mepiquat compounds have been notoriousl inconsistent across man studies. It is questionable whether these plant growth regulating compounds are necessar in an earl planting situation. In addition, a higher seeding rate is needed with the earl planting production sstem to achieve optimal plant densities because of the lower level of seedling survival level, and the potential for a non-uniform distribution of plants within row. DISCLAIMER Trade names are necessar to report factuall on available data; however, the USDA neither guarantees nor warrants the standard of the product or service, and the use of the name b USDA implies no approval of the product or service to the exclusion of others that ma also be suitable. REFERENCES Bednar, C.W., and R.L. Nichols.. Phenological and morphological components of cotton crop maturit. Crop Sci. :97-. Bednar, C.W., W.D. Shurle, W.S. Athon, and R.L. Nichols.. Yield, qualit, and profitabilit of cotton produced at varing plant densities. Agron. J. 97:-. Biles, S.P., and J.T. Cothren.. Flowering and ield response of cotton to application of mepiquat chloride and PGR-IV. Crop Sci. :8-87. Bourland, F.M., D.M. Oosterhuuis, and N.P. Tugwell. 99. Concept for monitoring the growth and development of cotton plants using main stem counts. J. Prod. Agric. :-8. Buxton, D.R., R.E. Briggs, L.L. Patterson, and S.D. Watkins Canop characteristics of narrow-row cotton as influenced b plant densit. Agron. J. 69:99-9. Cathe, G.W, and W.R. Meredith, Jr Cotton response to planting date and mepiquat chloride. Agron. J. 8:6-66.

10 Pettigrew and Johnson: Seeding Rates and Growth Regulators in Earl-Planted Cotton 98 Cook, D.R., and C.W. Kenned.. Earl flower bud loss and mepiquat chloride effects on cotton ield distribution. Crop Sci. : Gwathme, C.O., O.M. Wassel, and C.E. Michaud. 99. Pix effects on canop light interception b contrasting cotton varieties. p. -. In Proc. Beltwide Cotton Conf., -7 Jan. 99, San Antonio, TX. Natl. Cotton Counc. Am., Memphis, TN. Smith, C.W., B. A. Waddle, and H.H. Rame Plant spacings with irrigated cotton. J. Agron. 7: York, A.C. 98a. Cotton cultivar response to mepiquat chloride. Agron. J. 7: York, A.C. 98b. Response of cotton to mepiquat chloride with varing N rates and plant populations. Agron. J. 7: Heitholt, J.J. 99. Canop characteristics associated with deficient and excessive cotton plant population densities. Crop Sci. :9-97. Heitholt, J.J. 99. Cotton flowering and boll retention in different planting configurations and leaf shapes. Agron. J. 87: Heitholt, J.J., W.R. Meredith, Jr., and J.R. Williford Comparison of cotton genotpes varing in canop characteristics in 76-cm vs. -cm rows. Crop Sci. 6:9-96. Hicks, S.K., and R.J. Lascano. 99. Estimation of leaf area index for cotton canopies using the LI-COR LAI- Plant Canop Analer. Agron. J. 87:8-6. Jadhao, J.K., A.M. Degaonkar, and W.N. Narkhede. 99. Performance of hbrid cotton cultivars at different plant densities and nitrogen levels under rainfed conditions. Ind. J. Agron. 8:-. Jones, M.A., and R.Wells Dr matter allocation and fruiting patterns of cotton grown at two divergent plant populations. Crop Sci. 7: Kerb, T.A. 98. Cotton response to mepiquat chloride. Agron. J. 77:-8. Kerb, T.A., K.G. Cassman, and M. Keele. 99a. Genotpes and plant densities for narrow-row cotton sstems. I. Height, nodes earliness, and location of ield. Crop Sci. :6-69. Kerb, T.A., K.G. Cassman, and M. Keele. 99b. Genotpes and plant densities for narrow-row cotton sstems. II. Leaf area and dr-matter partitioning. Crop Sci. :69-6. Mohamad, K.B., W.P. Sappenfield, and J.M. Poehlman. 98. Cotton cultivar response to plant population in a shortseason, narrow-row cultural sstem. Agron. J. 7:69-6. Pettigrew, W.T.. Improved ield potential with an earl planting cotton production sstem. Agron. J. 9:997-. Sawan, Z.M., A.E. Bason, W.L. McCuistion, and A.H.A. El Farra. 99. Effect of plant population densities and application of growth retardants on cottonseed ield and qualit. J. Am. Soc. Oil Chem. 7:-7.