NODES ABOVE WHITE FLOWER AND HEAT UNITS AS INDICATORS OF COTTON HARVEST AID TIMING. A Thesis JOSHUA BRIAN BYNUM

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1 NODES ABOVE WHITE FLOWER AND HEAT UNITS AS INDICATORS OF COTTON HARVEST AID TIMING A Thesis by JOSHUA BRIAN BYNUM Submitted to the Office of Graduate Studies of Texas A&M University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE May 2005 Major Subject: Agronomy

2 NODES ABOVE WHITE FLOWER AND HEAT UNITS AS INDICATORS OF COTTON HARVEST AID TIMING A Thesis by JOSHUA BRIAN BYNUM Submitted to the Office of Graduate Studies of Texas A&M University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Approved as to style and content by: J. Tom Cothren Robert G. Lemon (Chair of Committee) (Member) James R. Mahan (Member) David W. Reed (Member) Mark A. Hussey (Head of Department) May 2005 Major Subject: Agronomy

3 iii ABSTRACT Nodes Above White Flower and Heat Units as Indicators of Cotton Harvest Aid Timing. (May 2005) Joshua Brian Bynum, B.S., West Texas A&M University Chair of Advisory Committee: Dr. J. Tom Cothren The timing of harvest aid application on cotton (Gossypium hirsutum L.) is critical, and poses potential problems when mistimed. The consequences of premature harvest aid application could result in reduced profit to the grower through the need for additional applications, reduced lint yield, poor fiber quality, and/or delayed harvest. A delayed application of harvest aid materials may also reduce lint yield and fiber quality if late season inclement weather patterns are established. Currently, there are many methods utilized for determining application of harvest aid materials. One method utilizes accumulated heat units, or growing degree days (HU or DD60 s), following plant physiological maturity. Physiological maturity (cutout) is identified as nodes above white flower equals 5 (NAWF=5). This method triggers the application of harvest aid chemicals when 850 HU have been accumulated beyond cutout. Due to differing environmental and edaphic characteristics across the Cotton Belt, application of harvest aid chemicals at this time may be premature in terms of optimizing lint yield and fiber quality. A two-year study was established to determine the proper timing of harvest aid application for picker harvested cotton in south central Texas. The design utilized a split-plot with four replications. The main plots consisted of three nodal positions

4 iv (NAWF=3, 4, and 5), and the subplots were five HU accumulations (650, 750, 850, 950, and 1050) that corresponded to each of the nodal positions. In both years, lint yields increased with an increase in HU accumulation. Greater yields were achieved when HU accumulation was initiated after NAWF = 4. This two-year study indicates that harvest aid applications made at NAWF = 4 plus 1050 HU would optimize yield potential for picker harvested cotton in south central Texas.

5 v DEDICATION This thesis is dedicated to my beautiful wife and best friend, Katie, whose love, support, and friendship made it possible for me to complete this degree.

6 vi ACKNOWLEDGEMENTS I would first like to thank God, through whom all things are made possible, for blessing me with such a rich life and the ability to complete this task. I would like to recognize and extend appreciation to the following members of my graduate committee for their support and mentorship: Dr. Tom Cothren, committee chair; Dr. Robert Lemon, member; Dr. James Mahan, member; and Dr. David Reed, member. Their assistance, encouragement, and support are greatly appreciated. Recognition is given to my co-workers and peers: Cy McGuire, Shane Halfmann, and Anthony Gola. I would also like to thank the following student workers for countless hours spent providing help with this project: Brett Niccum, Ellen Batchelder, and Quentin Shieldknight. I would like to extend gratitude to Danny Fromme, Ty Witten, and Ramon Mery for their advice and friendship throughout this endeavor. Special appreciation is given to my committee chair, advisor, and mentor, Dr. Tom Cothren, for his advice, example, support, and generosity. Thanks is also extended to my beautiful wife Katie, and loving family Kevin, Ronda, and Tim, for their unconditional and continuous support, encouragement, and love. Difficult tasks in life can be made much easier by the people around you who offer their friendship, love, support, advice, and encouragement. To those mentioned on this page, thanks, and I am forever grateful.

7 vii TABLE OF CONTENTS Page ABSTRACT.. DEDICATION... ACKNOWLEDGEMENTS.. TABLE OF CONTENTS... LIST OF FIGURES.. LIST OF TABLES... iii v vi vii ix x CHAPTER I INTRODUCTION... 1 Literature Review... 2 Growing Degree-Day Units... 2 Monitoring NAWF.. 3 Harvest Aid Timing. 5 Objectives II MATERIALS AND METHODS. 7 III RESULTS AND DISCUSSION.. 10 Harvest Aid Timing. 10 Plant Height, Total Nodes, and Total Bolls. 15 Percent Open Boll 18 Nodes Above Cracked Boll. 22 Lint Yield. 23 Fiber Quality 28 Loan Value IV CONCLUSIONS. 45 REFERENCES APPENDIX A.. 50

8 viii Page APPENDIX B.. 55 APPENDIX C.. 61 APPENDIX D.. 63 VITA 65

9 ix LIST OF FIGURES FIGURE Page 1 Historical weather averaged over nine years, maximum and minimum temperatures throughout the growing season and the corresponding accumulated heat units, Historical weather averaged over nine years, maximum and minimum temperatures throughout the growing season and the corresponding accumulated heat units, Relationship of percent open boll, at defoliation, to accumulated heat units beyond cutout, designated as NAWF = 3, 4, and 5, Relationship of percent open bolls, at defoliation, to accumulated heat units beyond cutout, designated as NAWF = 3, 4, and 5, Relationship of nodes above cracked boll to accumulated heat units beyond cutout, designated as NAWF 3, 4, and 5, Relationship of nodes above cracked boll to accumulated heat units beyond cutout, designated as NAWF 3, 4, and 5, Correlation between lint yield and accumulated heat units beyond cutout, designated as NAWF = 3, 4, and 5, Correlation between lint yield and accumulated heat units beyond cutout, designated as NAWF = 4, and 5, Relationship of fiber strength to accumulated heat units beyond cutout, designated as NAWF = 3, 4, and 5, Relationship of fiber yellowness to accumulated heat units beyond cutout, designated as NAWF = 3, 4, and 5, Relationship of fiber micronaire to accumulated heat units beyond cutout, designated as NAWF = 3, 4, and 5,

10 x LIST OF TABLES TABLE Page 1 Date of harvest aid application and accumulated heat units from each corresponding nodal position, Date of harvest aid application and accumulated heat units from each corresponding nodal position, Total nodes per plant, plant heights, and height to nodes ratios at harvest, Total bolls per plant and the percent of bolls above designated NAWF at harvest, The percent of open bolls at defoliation and harvest, The number of nodes above cracked boll at defoliation and harvest, Lint yield as affected by harvest aid treatment relative to NAWF and HU values, Lint yield as affected by harvest aid treatment relative to NAWF and HU values, Interactive means for lint yield relative to current COTMAN guideline, designated as 850 HU beyond NAWF = 5, Interactive means for lint yield relative to current COTMAN guideline, designated as 850 HU beyond NAWF = 5, Micronaire values, fiber uniformity, and fiber elongation, Fiber strength, length, leaf grade, reflectance, and yellowness, Loan value as affected by harvest aid treatment relative to NAWF and HU values, Loan value as affected by harvest aid treatment relative to NAWF and HU values,

11 xi TABLE Page 15 Monetary returns by harvest aid treatment relative to current COTMAN guideline, designated as 850 HU beyond NAWF = 5, Monetary returns by harvest aid treatment relative to current COTMAN guideline, designated as 850 HU beyond NAWF = 5,

12 1 CHAPTER I INTRODUCTION Fine-tuning current management practices is a viable option for the sustainability of agriculture. In cotton production, the use of harvest aids constitutes a sizeable monetary input. Application timing of harvest aids to cotton (Gossypium hirsutum L.) is critical, and poses potential problems when mistimed. The consequences of premature harvest aid application can result in reduced profit to the grower through the need for additional applications, reduced lint yield, poor fiber quality, and/or delayed harvest. A delayed application of harvest aid materials may also reduce lint yield and fiber quality if late season inclement weather patterns are established. Nearly all of the 5.5 million acres of cotton harvested in Texas, in 2004, utilized harvest aid materials prior to harvest. Harvest aid chemicals hasten the opening of green, maturing bolls to allow producers to harvest their crop earlier than if bolls opened naturally. The ability to harvest earlier is highly desired by producers, because it reduces the risk of their crop being subjected to inclement weather. Harvest aid chemicals also improve fiber quality by reducing the exposure time of the lint to weathering. However, premature application of harvest aid chemicals can decrease lint yield and fiber quality, by reducing the overall lint obtained as well as fiber maturity. Currently, there are many methods utilized for determining application of harvest aid materials. Many of these methods are labor intensive or require a significant amount of time. Presently, no method is distinctly better than any other, and they all have This thesis follows the style and format of Crop Science.

13 2 limitations. One method utilizes accumulated heat units, or growing degree days (HU or DD60 s) following plant physiological maturity, which is also known as cutout. Physiological maturity exists when there are five nodes above the uppermost first position white flower (NAWF). At cutout, subsequent HU accumulation is calculated by subtracting a base temperature of 60 F from the average daily temperature. According to COTMAN TM guidelines, this method triggers the application of harvest aid chemicals when 850 HU have been accumulated after reaching cutout. In some growing regions, application of harvest aid chemicals at this time could be premature in terms of optimizing lint yield and fiber quality. LITERATURE REVIEW Growing Degree-Day Units Historically, growth stages of cotton have been expressed as the number of days after planting. Silvertooth (1995) reports that plant growth is directly related to the temperature and environmental conditions to which they are exposed, and not necessarily to the number of calendar days. Cotton, a native of tropical regions, requires warm days and relatively warm nights for optimum growth and development (Gibson and Joham, 1968). Cotton growth proceeds from vegetative to reproductive stages, with a linear increase in heat unit accumulation (Fry, 1983). Because plant growth rates are highly correlated with temperature (Wanjura and Supak, 1985), the number of days from squaring to flowering, as well as the days from flowering to boll opening are impacted by temperature (Hesketh and Low, 1968). Previous work indicated that an average of 950 HU were required for a white flower to develop into an open boll (Young et al.

14 3 1980). Post anthesis, individual bolls require approximately 600 HU to reach maturity (Silvertooth et al., 1999). The developmental period for individual bolls, the time needed for the setting of the total boll crop, and fiber quality, are all highly temperature dependent (Wanjura and Supak, 1985). Even the diurnal ring formations within the fiber are related to the rise and fall of daily temperature and not associated with periods of light and darkness (Grant et al., 1966). Degree-days for cotton are defined as the amount of heat that is accumulated during a 24-hour time period when the average ambient temperature is above the base threshold temperature, which for cotton is 15.5ºC (60ºF) (Hake et al., 1996). Increased HU accumulation after cutout to defoliation has been shown to increase lint yield (Witten and Cothren, 2003), and also serves as an effective means of defining crop maturity (Benson et al., 2000). When harvest aid application was initiated at 850 HU beyond cutout, defoliation timing, in terms of different heat unit accumulations, directly influenced yield (Benson et al., 2000). In work by Witten and Cothren (2002), lint yield significantly increased as heat unit accumulation increased up to 1050 HU beyond cutout. Monitoring NAWF Monitoring NAWF allows for better precision and confidence in making end-ofseason management decisions (Bourland et al., 1992). A NAWF value gives an insightful measurement of the growth status of the crop from mid- to late-season (Oosterhuis, et al., 1992). The NAWF value is related to variation in canopy

15 4 photosynthesis, which implies that growth activity of the crop can be assessed by monitoring nodes above white flower (Bourland et al., 1992). Lint yield, which is highly correlated to total boll production, is significantly influenced by the flowering rate and boll retention (Grimes et al., 1969). In cotton development, decreasing NAWF values are indicative of a reduced photosynthetic rate and increased fruit load (Bourland et al., 1992). Properly managed cotton plants should contain a minimum of eight sympodia (fruiting branches) at first bloom (Bourland et al., 1992). White flowers located in the first position on sympodia, grow progressively closer to the plant apex (Oosterhuis et al., 1992). The appearance of white flowers in the apex is indicative of flower cessation and is precluded by termination of nodal extension; this event is known as cutout (Guinn, 1979). Cutout has also been defined as the time when a marked decrease in growth, flowering, and boll retention occurs (Patterson et al., 1978). Another way of expressing cutout is that it is the point at which the demand for photosynthate exceeds the crop s ability to meet this supply for both the vegetative and reproductive demands (Guinn, 1984). During flowering, subsequent first-position flowers on sympodia open at three-day intervals (Oosterhuis, 1991). The uppermost first position white flower is often used to describe the balance between fruit set and rate of terminal growth (Oosterhuis et al., 1992). When a NAWF value exists that is less than five, undesirable boll retention and boll size is often present for the designated nodal positions (Bourland et al., 1992). As NAWF approaches five, the economic value of these flowers decrease (Bourland et al., 1992). Therefore, the last effective flower population is set at NAWF=5 (Bourland et al., 1992). However, Witten and Cothren

16 5 (2003) reported that NAWF=5 may not be indicative of cutout in all growing environments. Harvest Aid Timing Defoliation timing has significant effects on yield and percent first harvest (Benson et al., 2000). Various methods are currently used to determine the proper timing of harvest aid chemicals. These methods include percent open boll, nodes above cracked boll, and boll slicing methods, all of which require a subjective identification of the last effective boll population (Benson et al., 2000). Tharp (1960) reported that maximum boll size could be determined at 18 days post-anthesis. However, bolls that are set later in the season may require a different amount of heat units to mature than bolls set earlier in the season (Morris, 1964). These two statements imply that boll size is an inaccurate measure of boll maturity. Because the application of harvest aid materials is based upon boll maturity (Witten and Cothren, 2002), any means to more reliably predict maturation should optimize harvest aid timing. The desire to harvest as early as possible must be balanced with yield (Mauney, 1986). By harvesting cotton early, the risk of exposing open bolls to inclement weather is reduced. However, premature harvest aid application can cause other problems such as the need for additional harvest aid applications, reduced lint yield and fiber quality, and delayed harvest (Witten and Cothren, 2002). When cotton harvest is delayed until inclement weather patterns are established, both yield and fiber quality reductions (McConnell et al., 1995). The subsequent weathering of bolls, due to the delayed harvest, decreases the quality and weight of the lint (Waddle, 1984). Monetary losses

17 6 resulting from mistimed defoliation can be significant (Witten and Cothren, 2002). If defoliation is based on the last effective boll population, as suggested by Benson et al., 2000, timely management decisions, such as monitoring NAWF, can be very beneficial (Oosterhuis et al., 1992). Work in Arkansas has shown that the optimum time for defoliation is 850 HU beyond NAWF=5 (Benson et al., 2000). However, the accumulation of 850 HU beyond NAWF=5 may not be indicative of the proper application timing of harvest aid chemicals in all growing environments (Witten and Cothren, 2002). OBJECTIVES The primary objective of this study was to determine the proper timing for harvest aid application in terms of optimizing lint yield and fiber quality through calculating accumulated heat units beyond cutout. Furthermore, this study was designed to determine if the current guideline of 850 accumulated HU beyond NAWF=5 is indicative of proper harvest aid timing. This study will help determine the appropriate timing of harvest aid chemicals for picker harvested cotton is south central Texas, in order to optimize lint yield and fiber quality. Results from this study should aid in broadening the understanding of the last effective boll population in cotton and HU accumulation relative to boll maturity.

18 7 CHAPTER II METHODS AND MATERIALS A two-year study was conducted in 2003 and 2004, to determine the proper timing of harvest aid application for picker harvested cotton in south central Texas. In both years, field plots were located at the Texas Agricultural Experiment Station (TAES) Research Farm in Burleson County near College Station, TX. The experimental site is on a Weswood silt loam soil (fine-silty, mixed, superactive, thermic, Udifluventic Halpustepts), having a ph of 8.2. Plots were disked before being bedded on 1.11-m centers. Fertilization consisted of 135 kg ha -1 of urea ammonium nitrate (UAN) applied in furrow. In both years, cv. Delta and Pine Land 451 B/RR was seeded at 128,440 plants ha -1, using a John Deere 1700 MaxEmerge Plus Vacuum planter. In 2003, plots were planted on May 12, while in 2004, plots were planted on April 8. Plots were four 1.11-m rows that were m in length. Furrow irrigation was applied as needed at approximately 7.5 cm of water at each irrigation. The crop was managed by recommendations made for local production to prevent disease, control insects, and manage weed populations. In both years, plots were arranged as a split-plot design with four replications. The main plots consisted of three nodal positions (NAWF=3, 4, and 5); subplots consisted of five HU accumulations (650, 750, 850, 950, and 1050) beyond each corresponding nodal position. Of the four rows, data was only obtained from row one or four, and rows two and three were machine-harvested using a two-row spindle picker, to determine lint yield.

19 8 Weather data was obtained from a nearby USDA weather station. The ambient daily high and low temperatures were used to calculate heat units. The heat unit calculations utilized DD60 s and were not converted into DD15.5 s, as all referenced literature uses DD60 s. A tank-mix of thidiazuron (Dropp ) (0.11 kg ha -1 ), tribufos (Def /Folex ) (1.16 L ha -1 ), and ethephon (Prep ) (1.53 L ha -1 ) was applied to each plot when the designated heat unit accumulation was reached following the corresponding nodal position. Harvest aid chemicals were applied with L ha -1 of water using a compressed air small plot sprayer with Tee Jet (Spraying Systems Inc.) TX-VS 10 hollow cone nozzles at 51-cm nozzle spacings. Prior to harvest aid application, ten plants per plot were removed and plant mapped to determine percent open boll, total bolls per plant, plant height, total nodes, and first fruiting node. Height measurements were taken from the cotyledonary node to the terminal of the plant. Total and first fruiting nodes were determined from the cotyledonary node to the terminal of the plant, with the cotyledonary node considered as node zero. In addition, nodes above cracked boll were assessed on ten representative plants per plot. Prior to harvest, 14 days after treatment (DAT), these procedures were repeated to assess the effect of harvest aid application. In both years, the two middle rows were machine picked 14 DAT. Seed cotton yields were determined, and 150 g sub-samples were collected from each plot for ginning to determine percent turnout and lint yield. Each sample was ginned using a ten-saw, hand-fed, portable gin. After ginning, 50 g fiber samples from each plot were

20 9 subjected to High Volume Instrument (HVI) classing, at the International Textile Center in Lubbock, Texas. Results from HVI classing were utilized to calculate the Commodity Credit Corporation (CCC) loan value for each treatment. These monetary values were retained in standard units. Statistical analysis was conducted on all appropriate data presented in this document. The SAS statistical software was used for all data analysis (SAS Institute, ). Data was subjected to the Mixed Models Procedure with degrees of freedom estimated using the Satterthwaite approximation (Satterthwaite, 1946). Means were separated using the Tukey-Kramer procedure to determine statistical differences at the 5% significance level. Linear regression analysis was conducted using the Regression Procedure at the 5% level. Data for 2003 and 2004 were combined over years in the absence of year x treatment interaction.

21 10 CHAPTER III RESULTS AND DISCUSSION Harvest Aid Timing Cotton, a native of tropical regions, requires warm days and relatively warm nights for optimum growth and development (Gibson and Joham, 1968). In both 2003 and 2004, relatively mild temperatures were experienced throughout the growing season. Accumulation of daily HU began to decline approximately 110 days after planting (DAP) in 2003 (Figure 1). Daily HU accumulation in 2004 started low but began to plateau approximately 50 DAP, and remained fairly constant for the remainder of the growing season (Figure 2). Calendar dates, number of days following planting and HU accumulations corresponding to the three designated nodal positions are listed in Tables 1 and 2. Beginning at first bloom, plots were assessed weekly for NAWF, to properly determine when plots reached NAWF values of 5, 4, and 3. Under optimal conditions, cotton plants should possess a minimum of eight sympodia at first bloom (Bourland et al., 1992). In both years of the study, the average NAWF value at first bloom was approximately nine. Nodes above white flower values 5, 4, and 3 were reached 74, 78, and 82 DAP, respectively, in In 2004, NAWF values of 5, 4, and 3, were reached 102, 108, and 113 DAP, respectively. Although HU accumulation from planting to NAWF values was similar between years, the large discrepancy in DAP between the two years can be attributed to a difference in planting dates. Planting in 2003 was delayed due to persistent dry weather. When designated NAWF values were reached, HU accumulation was initiated.

22 Temperature F Max Min DD60's Avg Max Avg Min Days After Planting Figure 1. Historical weather averaged over nine years, maximum and minimum temperatures throughout the growing season and the corresponding accumulated heat units, 2003.

23 Temperature F Max Min DD60's Avg Max Avg Min Days After Planting Figure 2. Historical weather averaged over nine years, maximum and minimum temperatures throughout the growing season and the corresponding accumulated heat units, 2004.

24 Table 1. Date of harvest aid application and accumulated heat units from each corresponding nodal position, Nodal Position HU NAWF = 5 NAWF = 4 NAWF = 3 Date DAP HU Date DAP DD60 s Date DAP HU Aug Aug Aug Aug Aug Sept Aug Sept Sept Sept Sept Sept Sept Sept Sept NAWF = 5 represents five sympodia above the uppermost first position white flower. DAP corresponds to days after planting. HU refer to accumulated heat units beyond reaching cutout, designated as NAWF = 3, 4, or 5. 13

25 Table 2. Date of harvest aid application and accumulated heat units from each corresponding nodal position, Nodal Position HU NAWF = 5 NAWF = 4 NAWF = 3 date DAP DD60 s Date DAP DD60 s Date DAP DD60 s Aug Aug Aug Aug Aug Sept Aug Sept Sept Sept Sept Sept Sept Sept Sept NAWF = 5 represents five sympodia above the uppermost first position white flower. DAP corresponds to days after planting. HU refers to accumulated heat units beyond reaching cutout, designated as NAWF 3, 4, or 5. 14

26 15 Plant Height, Total Nodes, and Total Bolls Final plant heights, total nodes, height to node ratios, and total bolls plant -1 were determined by end-of-season plant mapping (Tables 3 and 4). Plant heights, in 2003, averaged 80-cm and 81-cm across NAWF and HU treatments, respectively. Nodes above white flower and HU treatments averaged 23 and 22 total nodes, respectively in Height to node ratios averaged 3.58-cm across NAWF and HU treatments in 2003, and were not statistically different. Total bolls plant -1 ranged from 9.03 to across HU treatments; however, no differences between treatment means were noted for NAWF or HU treatments in Plant heights in 2004 were approximately 24 cm taller than in 2003 with an average of 104 cm across all NAWF and HU treatments. Total nodes plant -1 in 2004 was approximately 22 across all NAWF and HU treatments. In 2004, height to node ratios were approximately 1.12 cm more than 2003, and ranged from 4.66-cm to 4.97-cm for HU treatments. The 650 and 750 HU treatments were significantly lower than the 850, 950, or 1050 HU treatments. The NAWF = 5 treatment was significantly higher than NAWF = 3 or 4 for height to node ratios in Total bolls plant -1, in 2004, averaged 12.1 across NAWF and HU treatments. No statistical differences were observed between treatments for total bolls plant -1. Nodes representing the location of each NAWF treatment were identified and utilized to determine the percent of bolls located above the nodal position. The node number was determined from the cotyledonary node to the node containing the first position white flower, with the cotyledonary node considered as node zero. In both years, the average node containing the white bloom was 17, 18, and 19 for NAWF=5, 4,

27 Table 3. Total nodes per plant, plant heights, and height to nodes ratios at harvest, Harvest HU total nodes plant -1 height (cm) plant -1 height:node ratio (cm) d a b b b cd a b b b c a b a a b a b a a a a a a a Pr > f NAWF a a a a b b a a a b c b a a a Pr > f NAWF*HU HU and NAWF values within a single column followed by the same letter are not different at a 5% probability level. Probability of the ANOVA. 16

28 Table 4. Total bolls per plant and the percent of bolls above designated NAWF at harvest, Harvest HU total bolls plant -1 % bolls above designated NAWF a a 7.00 a 8.58 b a a 5.00 ab 8.33 b a a 5.00 ab a a a 5.67 a b a a 3.00 b 8.17 b Pr > f NAWF a a 4.00 b 4.85 c a a 4.65 b 9.10 b a a 6.75 a a Pr > f NAWF*HU HU and NAWF values within a single column followed by the same letter are not different at a 5% probability level. Probability of the ANOVA. 17

29 18 and 3, respectively. In 2003, the percent of bolls located above the designated nodal position was 6.75, 4.65, and 4.0 for NAWF 5, 4, and 3, respectively. The HU treatments ranged from 3 to 7 percent for percent of bolls located above the designated nodal position. In 2004, the percentage of bolls located above the designated nodal positions was considerably higher than in 2003, which ranged from 4.85 for NAWF = 3 to percent for NAWF = 5. The HU treatments ranged from 8.17 to percent of the bolls located above NAWF = 3 to NAWF = 5. Percent Open Boll The percent of open bolls (POB) was assessed via plant mapping immediately prior to harvest aid application. The effect of harvest aid materials and HU accumulation was determined by an additional plant mapping prior to harvest. Significant year x treatment interaction existed for POB at defoliation and harvest; therefore, data is presented separately by year. For each of the nodal positions 3, 4, and 5, POB was strongly correlated with HU accumulation in both years (Figures 3 and 4). Significant yield loss occurred when harvest aids were applied to cotton with fewer than 60% open bolls (Snipes and Baskin, 1994). In 2003, 950 HU were required for NAWF = 3 and 4 to correspond with 60% open bolls whereas NAWF = 5 required 1050 HU to reach 60% open bolls. In 2004, approximately 750, 850, and 1050 HU were required for NAWF = 3, 4, and 5, respectively, to satisfy 60% open bolls. Percent open bolls differed at defoliation in both years for NAWF and HU treatments (Table 5). In 2003, NAWF = 5 had a significantly lower percentage of open bolls than NAWF = 3 or 4 at defoliation. Heat unit treatment means ranged from 11 to

30 y = x R 2 = % open boll y = x R 2 = 0.94 NAWF=5 NAWF=4 NAWF=3 30 y = x R 2 = Accumulated DD60's Figure 3. Relationship of percent open boll, at defoliation, to accumulated heat units beyond cutout, designated as NAWF = 3, 4, and 5, Each data point represents the mean of four replications.

31 y = x R 2 = 0.88 % open boll y = x R 2 = 0.99 y = x R 2 = 0.98 NAWF=5 NAWF=4 NAWF= Accumulated DD60's Figure 4. Relationship of percent open boll, at defoliation, to accumulated heat units beyond cutout, designated as NAWF = 3, 4, and 5, Each data point represents the mean of four replications.

32 Table 5. The percent of open bolls at defoliation and harvest, Defoliation Harvest HU percent open bolls plant d e d b d d d a c c c a b b b a a a a a Pr > f NAWF a a a a a b b a b c c a Pr > f NAWF*HU HU and NAWF values within a single column followed by the same letter are not different at a 5% probability level. Probability of the ANOVA. 21

33 22 72 POB, with the 1050 HU treatment being significantly higher than all other treatments in Full separation of treatment means was observed between NAWF treatments and also HU treatments in In this separation of means, NAWF = 5 presented the lowest POB, and NAWF = 3 the greatest POB. Heat unit treatment means ranged from 38 to 79 POB at defoliation with the 1050 HU treatments being statistically greater than all other treatments. The overall POB at harvest was higher in 2004 than in 2003, with averages of 97 and 74, respectively (Table 5). This overall difference in POB is due to the higher ambient temperature at the time of harvest aid application in 2004, which was more conducive for successful defoliation. In 2003, full separation among NAWF treatments existed with NAWF = 3 having the highest POB, and NAWF = 5 having the lowest. In 2003, the 1050 HU treatment exhibited a significantly higher POB than all other HU treatments. In 2004, the 650 HU treatment was significantly lower POB than all other HU treatments at 89; while HU treatments 750, 850, 950, and 1050 were near 100% open. Nodes Above Cracked Boll Nodes above cracked boll (NACB) values were determined by subtracting the node number containing the uppermost first position cracked boll from the node number containing the uppermost harvestable boll. Two NACB measurements were taken. The first measurement was taken immediately prior to defoliation, and the second measurement was taken prior to harvest. Significant year x treatment interactions

34 23 existed for NACB; therefore, data was analyzed and reported separately by year. In both years, strong correlations existed between NACB values and HU accumulation (Figures 5 and 6). Kerby et al. (1992) reports that harvest aid materials should be applied at NACB = 4. In 2003, correlations between NACB and HU accumulation indicated that the NAWF = 3, 4, and 5 treatments reached NACB = 4 at approximately 750, 850 and 1050 accumulated HU, respectively. In 2004, the NAWF = 3 treatment reached NACB = 4 prior to 650 accumulated HU. The NAWF = 4 and 5 treatments reached NACB = 4 at approximately 650 and 850 accumulated HU. Correlations in 2004 were stronger than in 2003 due to more variability among NACB in In 2003, NAWF treatment means exhibited full separation, with NAWF = 5 having the highest NACB value and NAWF = 3 having the lowest (Table 6). These results imply that maturity is greater with decreasing NAWF values. Heat unit treatments followed a similar pattern with the 650 HU treatment exhibiting a higher NACB value than all other treatments and the 1050 HU treatment having the lowest value. In 2004, NAWF and HU treatments exhibited full separation with trends similar to those observed in Lint Yield Significant year x treatment interaction was observed for lint yield due to considerably greater yields observed in In both years, interaction occurred between the two main effects; therefore analysis could not be pooled over main effects. In 2003, HU treatments exhibited full separation for NAWF=3 and 5, with the 1050 HU treatment having the greatest yield (Table 7). The 950 and 1050 HU treatments were

35 y = x R 2 = 0.58 NACB y = x R 2 = 0.69 y = x R 2 = 0.54 NAWF=5 NAWF=4 NAWF= Accumulated DD60's Figure 5. Relationship of nodes above cracked boll (NACB) to accumulated heat units beyond cutout, designated as NAWF = 3, 4, and 5, Each data point represents the mean of four replications.

36 y = x R 2 = 0.96 NACB y = x R 2 = 0.93 NAWF=5 NAWF=4 NAWF=3 2 1 y = x R 2 = Accumulated DD60's Figure 6. Relationship of nodes above cracked boll (NACB) to accumulated heat units beyond cutout, designated as NAWF = 3, 4, and 5, Each data point represents the mean of four replications.

37 Table 6. The number of nodes above cracked boll at defoliation and harvest, Defoliation Harvest HU nodes above cracked boll plant a 5.00 a 1.62 a 1.54 a b 3.68 b 1.57 a 0.94 b bc 2.87 c 1.05 b 0.57 c bc 1.80 d 0.73 bc 0.39 c c 1.10 e 0.39 c 0.06 d Pr > f NAWF c 1.47 c 1.14 a 0.20 c b 2.65 b 0.93 a 0.75 b a 4.54 a 1.15 a 1.15 a Pr > f NAWF*HU HU and NAWF values within a single column followed by the same letter are not different at a 5% probability level. Probability of the ANOVA. 26

38 Table 7. Lint yield as affected by harvest aid treatment relative to NAWF and HU values, lint yield kg ha -1 HU NAWF = 3 NAWF = 4 NAWF = e 1093 d 1074 e d 1200 c 1096 d c 1229 b 1109 c b 1309 a 1217 b a 1312 a 1304 a Pr > f HU values within a single column followed by the same letter are not different at a 5% probability level. Probability of the ANOVA. 27

39 28 significantly greater than all other HU treatments for NAWF=4. In 2004, differences were observed within each nodal position (Table 8). For NAWF=3 and 4, the 650 HU treatment was statistically lower than all other HU treatments, while the 1050 HU treatment was numerically the greatest. The 1050 HU treatment was significantly greater than all other HU treatments for NAWF=5. Lint yields were analyzed relative to the current COTMAN guideline of 850 HU beyond NAWF=5 (Tables 9 and 10). In 2003 and 2004, the 1050 HU beyond NAWF=4 treatment resulted in the greatest amount of lint obtained above the current guideline with 203 and 527 kg, respectively. Lower lint yields were obtained from all treatments that occurred prior to 850 HU beyond NAWF=5 in both years. Positive correlations existed between lint yield and accumulated HU for all nodal positions in 2003 (Figure 7). The slope for yield of NAWF = 3 was different than NAWF = 4 or 5. No differences existed between slopes for NAWF = 4 or 5 for either year. In 2004, the NAWF = 3 treatment fit a 3 rd order polynomial regression better than linear regression and therefore is not reported (Figure 8). The NAWF = 4 and 5 treatments exhibited no difference of slope; however, for both years, intercepts differed between NAWF = 4 and 5 with NAWF = 4 being greater in both years. This difference indicates a greater yield potential when HU accumulation is initiated at NAWF = 4. Fiber Quality Significant year x treatment interaction was observed for micronaire values, fiber uniformity, and fiber elongation (Table 11). In 2003, no differences were observed between nodal positions for micronaire. However, the 750 HU treatment had a

40 Table 8. Lint yield as affected by harvest aid treatment relative to NAWF and HU values, lint yield kg ha -1 HU NAWF = 3 NAWF = 4 NAWF = b 1630 d 1443 d a 1878 c 1648 c a 2008 bc 1659 bc a 2146 ab 1838 b a 2186 a 2028 a Pr > f HU values within a single column followed by the same letter are not different at a 5% probability level. Probability of the ANOVA. 29

41 Table 9. Interactive means for lint yield relative to current COTMAN guideline, designated as 850 HU beyond NAWF = 5, kg ha -1 from NAWF = 5 and 850 HU HU NAWF = 3 NAWF = 4 NAWF = 5 Pr > f = e d c b a Pr > f = b a c HU and NAWF values within a single column followed by the same letter are not different at a 5% probability level. Probability of the ANOVA. 30

42 Table 10. Interactive means for lint yield relative to current COTMAN guideline, designated as 850 HU beyond NAWF = 5, kg ha -1 from NAWF = 5 and 850 HU NAWF = 3 NAWF = 4 NAWF = 5 Pr > f = d c bc b a Pr > f = a a b HU and NAWF values within a single column followed by the same letter are not different at a 5% probability level. Probability of the ANOVA. 31

43 y = 0.345x R 2 = kg ha y = 0.547x R 2 = 0.92 y = 0.581x R 2 = 0.89 NAWF=5 NAWF=4 NAWF= Accumulated DD60's Figure 7. Correlation between lint yield and accumulated heat units beyond cutout, designated as NAWF = 3, 4, and 5, Each data point represents the mean of four replications.

44 y = 1.196x R 2 = kg ha y = 1.36x R 2 = NAWF=5 NAWF= Accumulated DD60's Figure 8. Correlation between lint yield and heat units beyond cutout, designated as NAWF = 4 and 5, Each data point represents the mean of four replications.

45 Table 11. Micronaire values, fiber uniformity, and fiber elongation, High Volume Instrument Testing Micronaire Uniformity Elongation HU value percent percent a 4.14 a a ab 6.78 b 5.75 abc b 4.30 a a a 7.53 a 5.98 a a 4.24 a a a 7.21 ab 5.88 ab a 4.05 a a c 7.46 a 5.74 bc a 4.15 a a bc 7.58 a 5.65 c Pr > f NAWF a 4.22 a a a 7.40 a 5.76 a a 4.21 a a a 7.43 a 5.74 a a 4.10 a a a 7.10 a 5.91 a Pr > f NAWF*HU HU and NAWF values within a single column followed by the same letter are not different at a 5% probability level. Probability of the ANOVA. 34

46 35 significantly lower micronaire value than all other HU treatments. In 2004, no statistical differences were observed between NAWF or HU treatments for micronaire. No differences were observed between NAWF or HU treatments for fiber uniformity in Although no significant differences were detected between NAWF treatment means for fiber uniformity in 2004, differences were observed by HU treatments for fiber uniformity. These differences however were not correlated to increasing or decreasing HU accumulations. No differences were observed between NAWF treatments for fiber elongation in 2003 or There were differences in fiber elongation between HU treatments for both years; however the response was not consistent. In 2003 the 1050 HU treatment had the highest percent elongation but the lowest in No year x treatment interaction existed for fiber strength, length, leaf grade, reflectance, or yellowness (Table 12). The NAWF = 5 treatment exhibited the greatest fiber strength. Differences were also observed between HU treatments for fiber strength with the 1050 HU treatment having the lowest strength of all the HU treatments. This difference could be due to weathering of the fiber the longer the plants were left in the field before harvest aids were applied. No differences were noted between NAWF treatments for fiber length. No differences were observed between NAWF or HU treatments for leaf grade or reflectance. The NAWF = 5 treatment had a statistically higher percent of yellowness than NAWF 3 or 4. The HU treatments were significantly different with the 650 HU treatment displaying the lowest percent of fiber yellowness and the 1050 HU treatment having the highest percent of yellowness. Strong

47 Table 12. Fiber strength, length, leaf grade, reflectance, and yellowness, High Volume Instrument Testing Strength Length Leaf Reflectance Yellowness HU g tex ths of an inch percent percent value a a 4.96 a a 8.28 a a c 4.63 a a 8.18 a a ab 4.75 a a 7.86 b a bc 4.67 a a 7.65 bc b bc 4.87 a a 7.42 c Pr > f NAWF b a 4.78 a a 7.70 b b a 4.78 a a 7.85 b a a 4.77 a a 8.08 a Pr > f NAWF*HU HU and NAWF values within a single column followed by the same letter are not different at a 5% probability level. Probability of the ANOVA. 36

48 37 correlations were noted for fiber strength and percent yellowness against HU accumulation in both years (Figures 9 and 10). Micronaire values, in 2003, were also highly correlated to HU accumulation (Figure 11). Loan Value No significant differences were observed for loan values between treatments in either year (Tables 13 and 14). The previous statement implies that fiber quality was not impacted by treatment. Monetary returns were calculated and analyzed relative to the current COTMAN guideline (Tables 15 and 16). In both years, monetary returns were the greatest for treatments that were defoliated following the current COTMAN guideline. The 1050 HU beyond NAWF=4 treatment resulted in the greatest return above the current COTMAN guideline in both years.

49 g tex y = x R 2 = 0.65 y = x R 2 = 0.90 NAWF=5 NAWF=4 NAWF= y = x R 2 = Accumulated DD60's Figure 9. Relationship of fiber strength to accumulated heat units beyond cutout, designated as NAWF = 3, 4, and 5, Each data point represents mean of four replications and two years.

50 y = x R 2 = b value y = x R 2 = 0.91 y = x R 2 = 0.96 NAWF=5 NAWF=4 NAWF= Accumulated DD60's Figure 10. Relationship of fiber yellowness to accumulated heat units beyond cutout, designated as NAWF = 3, 4, and 5, Each data point represents a mean of four replications and two years.

51 micronaire value y = x R 2 = 0.88 y = x R 2 = 0.78 y = x R 2 = 0.88 NAWF=5 NAWF=4 NAWF= Accumulated DD60's Figure 11. Relationship of fiber micronaire to accumulated heat units beyond cutout, designated as NAWF = 3, 4, and 5, Each data point represents a mean of four replications and two years.

52 Table 13. Loan value as affected by harvest aid treatment relative to NAWF and HU values, dollars lbs -1 HU NAWF = 3 NAWF = 4 NAWF = 5 Pr > f = a a a a a Pr > f = a a a HU and NAWF values within a single column followed by the same letter are not different at a 5% probability level. Probability of the ANOVA. 41

53 Table 14. Loan value as affected by harvest aid treatment relative to NAWF and HU values, dollars lbs -1 HU NAWF = 3 NAWF = 4 NAWF = 5 Pr > f = a a a a a Pr > f = a a a HU and NAWF values within a single column followed by the same letter are not different at a 5% probability level. Probability of the ANOVA. 42

54 Table 15. Monetary returns by harvest aid treatment relative to current COTMAN guideline, designated as 850 HU beyond NAWF = 5, dollars acre -1 HU NAWF = 3 NAWF = 4 NAWF = Statistical analysis was not conducted on monetary values. 43

55 Table 16. Monetary returns by harvest aid treatment relative to current COTMAN guideline, designated as 850 HU beyond NAWF = 5, dollars acre -1 HU NAWF = 3 NAWF = 4 NAWF = Statistical analysis was not conducted on monetary values. 44

56 45 CHAPTER IV CONCLUSIONS According to data generated in these studies, NAWF = 5 and 850 HU proved to be premature for the application of harvest aids using the POB and NACB methods, in terms of optimizing lint yields. In 2003, NAWF = 5 accumulated 1050 HU before reaching 60% open boll. The NAWF = 5 treatment required 1000 HU to satisfy 60% open boll in In comparison, the NACB = 4 method was satisfied by 850 HU after NAWF = 5 in 2004; however, in 2003, 1050 HU were needed to reach NACB = 4. In both years, lint yield continued to increase with an increase in HU accumulation. Previous research had established cutout as NAWF = 5, because 95% of all first position fruit are established at this growth stage and yield produced beyond this growth stage contributes less than 5% to overall yield (Oosterhuis et al., 1992). Data reported in this document suggest that a greater percentage of total lint yield can be attributed to nodes greater than NAWF = 5. In 2003 and 2004, 6.75 and 15.45% of the total fruit was located above NAWF = 5, respectively. The large discrepancy between the two years can be attributed to rainfall patterns and overall plant vigor during the bloom period. Nodes above white flower equals 4 in 2003, and NAWF= 3, in 2004, most closely coincided with 5% of the total fruit being located above the corresponding nodal position. The above statement would indicate that physiological cutout would occur later than NAWF = 5 in this region. Results from both years concur that greater lint yields are achieved when HU accumulation is initiated at NAWF = 4 in our production region. Furthermore, lint