Maintaining Cotton Fiber Quality Through Harvest

Figure 1

Figure 1. Cotton field during harvest.

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Understanding how to manage cotton fiber quality characteristics can help maintain cotton fiber quality. Harvest aid application timing is an important management tool to help preserve yield potential and reduce possible regrowth that can lower cotton fiber quality.

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Fiber Quality Characteristics

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Length. To help maximize fiber length, proper management and ideal growing conditions must be available during the elongation phase of fiber development. Fiber elongation takes place in the first 16 to 25 days of boll development.1 During this time, high temperatures, water stress, and potassium deficiency can result in shorter fibers. Fiber length can also be affected by the ginning process. If cotton moisture is low during ginning, fiber length can be compromised due to breakage. The ideal ginning moisture range is 6 to 8%.2 When lint moisture is below 5%, each percentage lower is equivalent to 1/100th of an inch reduction in length.

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Strength. Fiber strength is primarily determined by the variety; however, the environment can have a small effect on strength. Certain cultural practices can increase or decrease the lint strength. Severe potassium deficiency can decrease lint strength and extreme weather conditions may cause physical or microbial damage to fiber, resulting in reduced strength.

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Micronaire—Fiber with micronaire values that are too high or too low can affect cotton quality by limiting how the fiber can be used within the textile industry. Fibers with low micronaire are typically caused by inadequate carbohydrates and can easily form neps during the ginning process.1 High micronaire is a result of excessive carbohydrates during development, which forms a more coarse fiber that limits their textile use. While varietal differences can contribute to micronaire level, growing environment is a strong factor in determining micronaire.

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In certain situations, management decisions may help producers avoid too low or too high micronaire fiber. Early termination of fiber development during the growing season can result in immature fiber with low micronaire, making it important to select varieties with appropriate maturities and to avoid applying plant growth regulators too early. Similar to strength, a potassium deficiency can cause low micronaire since deficient plants will still set bolls normally, but supply an insufficient amount of carbohydrates, resulting in reduced micronaire. Excessive irrigation, fertilizer, and high plant populations can also contribute to a low micronaire value. High micronaire can occur when extremely warm weather conditions cause severe boll shed. When only a few bolls are retained on the plant, high amounts of carbohydrates are available, which causes high micronaire. Moderate weather conditions may cause too much boll production and retention, limiting the carbohydrates available for each boll, resulting in lower micronaire.

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When to Apply Harvest Aids

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Timing of harvest aid applications and harvest can affect cotton quality. Applying harvest aids prematurely can stall the maturation of green bolls, reducing fiber quality.3 Delaying harvest aid applications can increase the potential for poor late-season weather, which may also reduce cotton quality.

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There are several methods to help decide when to apply a harvest aid, and they include the following:

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  • Percent open boll. This is an estimation of how many harvestable bolls are on the plant. Applications are recommended at 50 to 70% open boll, but boll distribution on the plant can vary, making ideal timing range from 42 to 81% open boll.3
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  • Sharp knife technique. Cross section the uppermost harvestable boll. Mature bolls will be difficult to cut open and will have seeds with dark seed coats.
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  • Nodes above cracked boll (NACB). Count the number of main stem nodes from the uppermost harvestable boll. Research has shown that no lint weight loss occurs when harvest aids are applied at three NACB. Yield loss can occur at NACB greater than four.3
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Harvest aid applications should be made when conditions are warm and sunny, with good soil moisture. It is important to have full plant coverage during application. Spray volume should be a minimum of 15 gallons per acre for ground applications and 5 gallons per acre for aerial applications.3

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Cotton Storage

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Once cotton is harvested and stored either in modules built by the cotton picker or modules built by a module builder, it will remain in the field until transported to a ginning facility. To maintain fiber quality during storage, cotton must be properly defoliated prior to harvest. Vegetative material or green trash left in the cotton module can result in excess moisture content, high trash count, and stained cotton lint.

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Figure 2

Figure 2. Cotton bales protected with plastic wrap.

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To help protect cotton during storage, rectangular modules should be covered with a high-quality tarp. Tarps should be checked for any tears or pin holes before use. Round modules are wrapped with plastic that covers the circumference of the bale and a few inches on the ends (Figure 2). Any excess moisture in the cotton can cause condensation, so modules should be monitored. When elevated moisture levels occur, temperatures increase within the module compromising lint grade and seed germination. Extreme cases can result in spontaneous combustion. Cotton module or bale temperature should be monitored for the first five to seven days. Ideally, cotton harvested at correct moisture levels should only increase 10 to 15 °F in the first five to seven days of module storage, then level off or decrease in temperature. A 15 to 20 °F temperature increase during the first five to seven days indicates a high moisture problem and the module should be ginned as soon as possible.2 After the initial daily temperature check, modules should continue to be checked every three to four days. If a module reaches a temperature of 120 °F at any time during storage, the cotton should be ginned immediately.

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A study performed in 2009 was conducted to determine if the three different cotton module types, traditional large modules, half-sized modules, and round modules cause any problems in ginning or fiber quality.4 Data was collected at seven gins located in Texas, Tennessee, Missouri, and Mississippi. While cotton degradation was observed when cotton modules were placed too close together than recommended by the manufacturer, the ginning and fiber quality observations between the three module types were too small to conclude that any of the differences were based on the module type and not other factors.