Defining Optimal Defoliation and Harvest Timing for Various Fruiting Patterns of Cotton in North Carolina

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Title: Defining Optimal Defoliation and Harvest Timing for Various Fruiting Patterns of Cotton in North Carolina
Author: Collins, Guy David
Advisors: Keith Edmisten, Committee Chair
David Jordan, Committee Member
Randy Wells, Committee Member
Abstract: Upland Cotton (Gossypium hirsutum L.) is a perennial plant produced as an annual crop in North Carolina. Due to high variability in net returns, and narrow profit margins, growers must focus attention not only on lint yield but also on lint quality. Implementing sound agronomic practices, such as proper defoliation timing and harvest timing, may help maximize lint yield and fiber quality. Cotton is normally defoliated when 60 percent of the total harvestable bolls are open. It is hypothesized that defoliation could be initiated before 60 OBPD (% open bolls) if fruiting is compact, and in contrast, defoliation could be delayed beyond 60 OBPD if fruiting is extended. Two experiments were conducted in 2004 and 2005 at Upper Coastal Plains Research Station near Rocky Mount, North Carolina, to observe the effects of defoliation and harvest timings on crops of various levels of maturity or fruiting habits. One study involved plant growth regulator strategies to mimic compact, normal, and extended fruiting habits, respectively. The other study included three variety maturity groups to accomplish the various fruiting habits. The targeted defoliation timings in each study were 50, 70 and 90 OBPD and the targeted harvest timings were 14 days after defoliation and 28 days after defoliation. According to lint yield data in 2005 from the study involving plant growth regulator strategies, a crop with compact fruiting could be defoliated earlier than 60 OBPD without sacrificing yields. Delaying harvest for a crop defoliated early may help maximize yield and fiber length, whereas an early harvest may be more appropriate for a crop defoliated late, especially if significant amounts of rainfall are experienced. In 2005, micronaire values decreased 4% by delaying harvest, regardless of defoliation timing. Data also suggests that NACB (nodes above cracked boll) ~ 3 corresponded to maximum yields, especially in cases where mepiquat chloride was used. Data from the study involving various cultivars suggests that cultivar differences may be largely responsible for quality variations in micronaire, fiber length, length uniformity, and fiber strength. Defoliation before 60 OBPD was proven to be acceptable in some cases, however, harvest may need to be delayed to achieve maximum yields. In contrast, optimal yields were reached when a crop defoliated beyond 60 OBPD was harvested early. These effects were largely a result of variations in the amount of rainfall occurring during the harvest period. Data also suggests that defoliation initiated at NACB ~ 3 corresponded to maximum yields and fiber quality. Data indicated that delaying defoliation may increase yields, regardless of varieties. Plant mapping data suggests that fruiting habits were different, however, all three cultivars seemed to possess an extended fruiting habit, therefore assumptions regarding fruiting compactness can not made based on a particular cultivar maturity group.
Date: 2006-05-26
Degree: MS
Discipline: Crop Science

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